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A novel GaN HEMT with double recessed barrier layer for high efficiency-energy applications
Accepted Manuscript A novel GaN HEMT with double recessed barrier layer for high efficiency-energy applications
Hujun Jia, Qiuyuan Wu, Yehui Luo, Yintang Yang PII:
S0749-6036(17)31309-5
DOI:
10.1016/j.spmi.2017.07.047
Reference:
YSPMI 5157
To appear in:
Superlattices and Microstructures
Received Date:
28 May 2017
Revised Date:
20 July 2017
Accepted Date:
20 July 2017
Please cite this article as: Hujun Jia, Qiuyuan Wu, Yehui Luo, Yintang Yang, A novel GaN HEMT with double recessed barrier layer for high efficiency-energy applications, Superlattices and Microstructures (2017), doi: 10.1016/j.spmi.2017.07.047
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ACCEPTED MANUSCRIPT
A novel GaN HEMT with double recessed barrier layer for high efficiency-energy applications Hujun Jia*, Qiuyuan Wu, Yehui Luo,Yintang Yang (School of Microelectronics, Xidian University, Xi’an 710071, China)
Abstract In this paper, a novel GaN HEMT with high efficiency-energy characteristic is proposed. Different from the conventional structure, the proposed structure contains double recessed barriers layer (DRBL) beside the gate. The key idea in this work is to improve the microwave output characteristics. The simulated results show that the drain saturation current and peak transconductance of DRBL GaN HEMT is slightly decreased, the transconductance saturation flatness is increased by 0.5V and the breakdown voltage is also enhanced too. Due to the both recessed barrier layer, the gate-drain/gate-source capacitance is decreased by 6.3% and 11.3%, respectively. The RF simulated results show that the maximum oscillation frequency for DRBL GaN HEMT is increased from 57GHz to 64GHz and the saturation power density is 8.7W/mm at 600MHz, 6.9W/mm at 1200MHz with the higher power added efficiency (PAE). Further investigation show that DRBL GaN HEMT can achieve to 6.4W/mm and the maximum PAE 83.8% at 2400MHz. Both are higher than the 5.0W/mm and 80.3% for the conventional structure. When the operating frequency increases to X band, the DRBL GaN HEMT still exhibits the superior output performances. All the results show that the advantages and the potential capacities of DRBL GaN HEMT at high efficiency-energy are greater than the conventional GaN HEMT.
Keywords: GaN HEMT; Recessed barrier layer; Power added efficiency; Saturation power density *: Corresponding Author: Hujun Jia. Tel: (86)13772126387 E-mail: [email protected] Addr: School of Microelectronics, Xidian University, 710071, Xi’an, China.
ACCEPTED MANUSCRIPT 1. Introduction Recently, AlGaN/GaN high electron mobility transistor (HEMT) has attracted much attention in high frequency and high power applications due to its superior material properties, such as wide band gap, large electron saturated velocity, extremely high critical breakdown field and high radiation tolerance [1-3]. Simultaneously, the high-density two-dimensional electron gas at the AlGaN/GaN interface makes the AlGaN/GaN heterostructure devices superior to the conventional GaAs-based and InP-based devices [4-5]. These properties in combination with a greater advantage of the power quality factor for GaN material, making the AlGaN/GaN HEMT possess a broader development prospect for microwave high power applications. In recent years, tremendous progress has been made in the DC and RF performance of GaN HEMT. The devices with field modulating plates limit the risks of the current collapse and improve the breakdown voltage [6-7]. The maximum output power density has been successfully demonstrated with 32.2W/mm at 120V, 4GHz [8]. Attributing to the improving process technology, highly uniform AlGaN/GaN HEMT films are achieved for the ultra-high frequency band [9-10], the maximum oscillation frequency for GaN HEMT has been to 582GHz [11]. As the development of GaN devices, microwave power amplifiers (PA) based on GaN HEMT have been applied to the wireless communication system, phased array radar, aerospace fields and so on. Although, mostly ways in achieving the high efficiency output target are based on the control of external circuit to the tube and the use of compensation [12-14]. As the core of the PA, the characteristics of GaN HEMT are also important to the whole performances. With the more and more high request to the PA, it is necessary to find and design a novel GaN HEMT for the high power output with high power added efficiency (PAE). The high efficiency-energy GaN HEMT well has a great potential in uprating the performance of the amplifier and reducing the power consumption. Based on the above idea, a novel GaN HEMT with double recessed barrier layer
ACCEPTED MANUSCRIPT (DRBL) was proposed and analyzed for high efficiency-energy applications. Comparing with the conventional (Con) structure, the proposed structure contains double recessed barriers layer (DRBL) beside the gate, which are used to support two high resistance area to slow the increasement of the drain saturation current for exchanging the broader peak transconductance region. Using the 2D simulator ISE_TCAD, the simulated results show that the DRBL GaN HEMT takes full advantages of the elimination of gate depletion layer extending to source and drain resulting from the double recessed barrier region, which reflects well on the performance of breakdown voltage (Vb), gate-source capacitance (Cgs) and gate-drain capacitance (Cgd). The RF simulated results are verified by ADS simulation, it exhibits that the DRBL GaN HEMT has superior microwave output characteristics than the conventional GaN HEMT device. In the proposed DRBL GaN HEMT, the redistribution of the electric field can decrease the high electric field peak at the edge of the gate electrode. The electron injection effect of the gate electrode would be reduced and the current collapse effect would be mitigated. Thereby, the impact of the surface state on the device performance is improved. Under the existing process equipment conditions, the negative effects on the device performance caused by the etching-induced damage is slightly.
2. Device structure The schematic cross-sections of the conventional GaN HEMT and DRBL GaN HEMT structure used in this simulation are presented in Fig.1. Compared with the Con structure, there are two recessed AlGaN barrier layer region in the DRBL structure. The fabrication processes of DRBL GaN HEMT are the same as the convention one except for the formation of the recessed region. The source/drain electrode was formed by a Ti/Al/Ni/Au stack annealing at 850℃ for 30sec in N2 ambient. A Ni/Au stack was used to form the gate electrode by the e-beam evaporation. The recessed AlGaN barrier layer area can be produced through an
ACCEPTED MANUSCRIPT additional HBr/Ar plasma dry etching technology in the inductively coupled plasma (ICP) system. The height (H1) and length (L1) for the recessed gate-source region in the DRBL GaN HEMT are 5nm, 0.5μm. It is the same as the size of the recessed gatedrain region, H2=5nm, L2=0.5μm. All semiconductor layers were not intentionally doped except the GaN buffer layer. In order to simulate the influence of the carrier scattering in the GaN buffer layer, the GaN layer is n type doped with doping concentration of 1×1015cm-3 in the simulation. The nominal Al composition of AlGaN was chosen to be 0.25. The gate Schottky contact with a barrier height of 1.0eV and the gate width (Wg) is by default 1mm. It is worth noting that DRBL structure has the same device parameters with Con structure to have a meaningful comparison. The other common simulation parameters of both structures are given in the Table.1.
Table.1 Device structure parameters for both structures Device parameters
Value
Gate Length (Lg)
1μm
Gate-source spacing length (Lgs)
1μm
Gate-drain spacing length (Lgd)
2.5μm
Thickness of AlGaN barrier layer
25nm
Thickness of GaN buffer layer
3μm
Thickness of AlN nucleating layer
40nm
Doping of GaN buffer layer
1×1015cm-3
Doping of n-type cap layer
1×1020cm-3
The 2D simulator, ISE_TCAD is used to simulate the device characteristics with GaN, AlGaN and AlN material parameters for both structures [15]. In order to achieve realistic results, many important and necessary models are activated. The basic Poisson and drift-diffusion equations, Schrödinger-Poisson coupled equations, Shockley read hall (SRH) and Auger for generation and recombination, Doping Dep, Enormal and High Fieldsat for mobility, Incomplete for incomplete ionization of dopants and Avalance for impact ionization. A temperature of 300 K is employed by default in simulations.
ACCEPTED MANUSCRIPT
SourceLgs=1μm Gate Lg=1μm
a
N+
25nm
Lgd=2.5μm
Drain N+
Al0.25Ga0.75N 2DEG
3μm
GaN AlN
40nm
Substrate
SourceLgs=1μm Gate Lg=1μm
b
N+
Lgd=2.5μm H2
H1
25nm
Drain
L1
N+
L2
Al0.25Ga0.75N 2DEG
3μm 40nm
GaN AlN Substrate
Fig.1 Schematic cross-sections of the (a) Con GaN HEMT, (b) DRBL GaN HEMT
3. Results and discussions 3.1 DC characteristics The simulated data of DC drain current (Ids) versus the drain-source voltage (Vds) for both DRBL and Con structures are depicted in Fig.2. The gate bias voltage (Vgs) varies from -1 to 0V with a step of 1V. It can be seen that the Ids of the DRBL structure is slightly decreased at various Vgs compared with the Con structure. The drain saturation current for DRBL and Con GaN HEMT are 571mA/mm and 609mA/mm, respectively. Due to the existence of the double recessed barrier layer in the DRBL structure, the thickness of the AlGaN layer beside the gate is reduced, which resulting in the decrease of the density of the two dimension electron gas (n2D)
ACCEPTED MANUSCRIPT at the corresponding position. From the channel current equation showed below: I ds q Wg s n2 D
(1)
Where Wg is the gate width, υs is the saturated electron velocity. It is clearly that the Ids could be proportional to the n2D. So, when the n2D of the GaN HEMT decrease, the Ids of the GaN HEMT will decrease too. Fig.3 shows the simulated current density distribution under the conditions of Vgs=0V, Vds=20V for DRBL and Con GaN HEMT. It can been seen that the current density focus primarily on the AlGaN/GaN interface and the maximum current density (5.7e7 A/cm2) in the DRBL structure is smaller than that (6.2e7 A/cm2) in the Con GaN HEMT. Therefore, the drain saturation current of the DRBL GaN HEMT is decreased. But the differences are not very big.
800
Con GaN HEMT DRBL GaN HEMT
700
Vgs=0V
Ids(mA/mm)
600 500
Vgs=-1V
400 300 200 100 0
0
2
4
6
8
10 12 14 16 18 20 22
Vds(V) Fig.2 Simulated drain current versus the drain source voltage at gate bias voltage of -1V, 0V
ACCEPTED MANUSCRIPT
Fig.3 Simulated current density distributions of both structures (a) Con, (b) DRBL
The DC transfer characteristics at drain voltage of 20V are shown in Fig.4. For the depleted GaN HEMT, When n2D is 0, that is, when the channel is exhausted completely, the gate bias voltage at this time is the threshold voltage. It can be seen that both of the GaN HEMT structures have the similar threshold voltage (Vt). It could be attributed to the same thickness of AlGaN barrier layer under the gate. Due to the similar high concentration n2D in the drain-source channel for Con and DRBL structure, the Negative voltage applied on the gate to deplete the n2D is also similar for both structures. From the Fig.4, the Vt for the Con and DRBL GaN HEMT are -3.5V and -3.4V, respectively. The results of the first derivative curve of the transfer characteristics are shown in Fig.5, called the transconductance of the device. It is clearly that the Con GaN HEMT is equipped with the higher peak transconductance, 263mS/mm. Because the Con structure can output even bigger drain current under the same control of the gate voltage compared to the DRBL GaN HETM. It means in the Con structure, the gate has a better control to the channel which results in the bigger peak transconductance. Although, the peak transconductance of the DRBL GaN HETM, 241mS/mm, is decreased due to the double recessed barrier layer, it is worth noting that the flat site of peak transconductance is expanded. Vgo and Vco in the Fig.5 means the gate-source voltage where transconductance near to the maximum and to compression. Further reseach indicates that the power added efficiency increases with decreasing peak transconductance. Therefore, for the proposed DRBL GaN HEMT, the appropriate reduction for transconductance would be beneficial to the greater efficiency output characteristics.
ACCEPTED MANUSCRIPT In the DRBL structure, the recessed region plays a role in increasing the channel resistance, which restricts the growth rate of the drain current. Besides, the double recessed areas beside the gate reduce depletion layer extension to source/drain effectively. So, the depletion layer is mainly centered below the gate. The channel carriers flowing below the gate depletion are concentrated on a certain area. After the transconductance achieves to the saturation region, as the gate-source voltage continues to increase, the extent of the transconductance increases will slow down. And that, it will not present a rapid rise and fall likes that in the Con GaN HEMT. Compared with the Con structure, the double recessed barrier layer makes the DRBL GaN HEMT possesses a wider flat area of the transconductance which could be benefit for the high linearity and high efficiency output characteristics. The flat area of the transconductance for the two structures can be calculated by Vco-Vgo, and the results of Con and DRBL structures are 1.4V and 1.9V, respectively.
Ids(mA/mm)
800
Con GaN HEMT DRBL GaN HEMT
600
Vds=20V
400 200
0 -4.0 -3.5 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5
Vgs(V) Fig.4 Drain current versus gate voltage under drain-source voltage of 20V for both structures
ACCEPTED MANUSCRIPT 300
Con GaN HEMT DRBL GaN HEMT
gm(mS/mm)
250 200 150 100 50 0 -6
Vco
Vgo
-5
-4
-3
-2
-1
0
1
2
Vgs(V) Fig.5 Transconductance versus gate voltage under drain-source voltage of 20V for both structures
The simulated three-terminal breakdown characteristics for both structures are presented in Fig.6. The simulated results show that the breakdown voltages (Vb) are 195V, 212V for the Con and DRBL GaN HEMT. Fig.7 shows the distributions of electrostatic potential of both structures. It is well known that, the gate field emission induces a breakdown of the device. By the employment of the gate-drain recessed structure, the electrostatic potential distributions of the DRBL structure become more uniform. Simultaneously, the mitigation of the electric field crowding at the gate corner decreases the probability of the electron injection effect to the surface and reduces the surface leakage current [16]. With the help of recessed barrier layer, the current collapse effect would be also mitigated. So, the DRBL GaN HEMT could withstand greater drain breakdown voltage.
ACCEPTED MANUSCRIPT 0.4 Con GaN HEMT DRBL GaN HEMT
Ids(mA/mm)
0.3
Vb=212V
0.2
Vb=195V
0.1
0.0
0
50
100
150
200
250
Vds(V) Fig.6 Simulated three-terminal breakdown characteristics of both structures
Fig.7 Distributions of electrostatic potential of both structures (a) Con, (b) DRBL
3.2 RF characteristics Fig.8 and Fig.9 show the simulated gate-source capacitance (Cgs) and gate-drain capacitance (Cgd) for both structures. The DC bias conditions are Vgs=0V and Vds=20V. It can be seen that the Cgs and Cgd of the DRBL structure are 2.59pF/mm
ACCEPTED MANUSCRIPT and 58.5fF/mm, respectively. It is reduced by 11.3% and 6.3% compared with that of the Con GaN HEMT. The reason for this is that the recessed gate-drain and gatesource region reduces depletion layer extension to the source/drain effectively [1718]. The depletion region is promoted to spread in the vertical direction. It means the distance from the gate electrode to the lower surface of the depletion layer increased. The gate depletion layer distribution in the proposed structure has been further modulated, so, the smaller Cgs and Cgd can be obtained.
3.5
Con GaN HEMT DRBL GaN HEMT
3.0
Cgs(pF/mm)
2.5 2.0 1.5 1.0 0.5 0.0 1E+08
1E+09
1E+10
1E+11
1E+12
Frequency(Hz) Fig.8 Simulated gate-source capacitance versus frequency
70
Con GaN HEMT DRBL GaN HEMT
65
Cgd(fF/mm)
60 55 50 45 40 35 1E+08
1E+09
1E+10
1E+11
1E+12
Frequency(Hz) Fig.9 Simulated gate-drain capacitance versus frequency
ACCEPTED MANUSCRIPT The ac transconductance (gmac) of Con and DRBL structures are also simulated and the results are shown in Fig.10. Compared to the results in the Fig.5, the peak transconductance for both structures are increased about 8-9mS/mm at the frequency conditions. The gmac of Con structure is 271 mS/mm and the gmac of DRBL structure is 250 mS/mm.
300
gmac(mS/mm)
250 200
Con GaN HEMT DRBL GaN HEMT
150 100 50 0 1E+06
1E+07
1E+08
1E+09
1E+10
1E+11
Frequency(Hz) Fig.10 Simulated ac transconductance versus frequency
Fig.11 shows the simulated small-signal current gain (h21), maximum available gain (MAG) and unilateral power gain (U) for the both structures as a function of the frequency at Vgs=0 V and Vds=40 V. The results show that the cut-off frequency (ft) of the DRBL structure is 14.2GHz and it is similar to the result of the Con structure. But the maximum frequency (fmax) of DRBL GaN HEMT is 64GHz, which is increased by about 12.3% compared with that of the Con GaN HEMT. The expressions for the ft and fmax are as followings:
ft
gm 2π(Cgs Cgd )
(2)
ft Rds 2 Rg
(3)
f max
Where Rds is the drain-source resistance and Rg is the gate resistance. Based on the above equation of ft, it could be inferred that because the positive effects by the
ACCEPTED MANUSCRIPT decreased Cgs and Cgd is offset by the decline of the gm, the ft for the DRBL GaN HEMT is almost not changed. The enhanced of the fmax is due to the smaller gate resistance. From the Fig.11, it can be also seen that the U and MAG of the DRBL GaN HEMT are increased 1.2dB and 0.8dB compared to the Con structure at the same frequency. It means that the DRBL GaN HEMT has the greater power conversion ability and possesses the higher output efficiency.
50 Con-h21 DRBL-h21 Con-U DRBL-U Con-MAG DRBL-MAG
Gain (dB)
40 30 20
Vgs=0V Vds=20V
10 0 1E8
1E9
1E10
1E11
Frequency (Hz) Fig.11 Simulated small-signal high frequency characteristics of Con and DRBL structures
3.3 High efficiency-energy verification In order to compare the large-signal performance between the DRBL GaN HEMT and Con GaN HEMT, the corresponding DC and RF simulated results are extracted into the EE_HEMT1 model to simulate the power output characteristics by ADS software [19]. The large-signal simulated result at 600MHz is presented in Fig.12. It is worth noted that the PAE of DRBL GaN HEMT is always larger than that of Con GaN HEMT. The DRBL GaN HEMT biased at Vds=20V exhibit an output power (Pout) of 42.2dBm, power density of 8.3W/mm and a maximum PAE of 90.2% at 600MHz. With the increase of the input power (Pin), the difference of the Pout between the DRBL and Con GaN HEMT is gradually reduced. When the Pin gets to 30dBm, DRBL GaN HEMT has the same Pout as the Con
ACCEPTED MANUSCRIPT GaN HEMT. At that moment, the bigger PAE for the DRBL GaN HEMT attributes to the smaller DC consumption. As the Pin continuously increasing, the DC consumption of DRBL GaN HEMT is almost to the Con GaN HEMT, then, both PAEs are closed to each other. By means of analysis to the Ids-Vds characteristic above, the drain current output capability of Con structure is a bit better than DRBL GaN HEMT. In addition, the advantages of smaller gate-source/gate-drain capacitance for DRBL GaN HEMT don’t play out at the lower frequency band. So, the DRBL GaN HEMT has the similar saturation output power as the Con GaN HEMT.
50
Vgs=-4V
90
46 f0=600MHz
80
44
70
42
60
40
Con-Pout DBRL-Pout Con-PAE DBRL-PAE
38 36
50
PAE (%)
Pout (dBm)
48 Vds=20V
40 30
34 14 16 18 20 22 24 26 28 30 32 34 36
Pin (dBm) Fig.12 Large-signal performance for both structures at 600MHz with Vgs= -4V, Vds=20V
When the operating frequency increased to 1200MHz, the simulated large-signal performance is shown in Fig.13. It can be seen that the PAE of the DRBL GaN HEMT is still higher than the Con GaN HEMT with the same saturated output power.
ACCEPTED MANUSCRIPT 50
Vgs=-4V
90
46 f0=1200MHz
80
44
70
42
60
40
50 Con-Pout DBRL-Pout 40 Con-PAE DBRL-PAE 30
38 36
PAE (%)
Pout (dBm)
48 Vds=20V
34 14 16 18 20 22 24 26 28 30 32 34 36
Pin (dBm) Fig.13 Large-signal performance for both structures at 1200MHz with Vgs=-4V, Vds=20V
48
Vgs=-4V Vds=20V
46
f0=2400MHz
90 80
44
70
42
60
40
50 Con-Pout DBRL-Pout 40 Con-PAE DBRL-PAE 30
38 36
PAE (%)
Pout (dBm)
50
34 14 16 18 20 22 24 26 28 30 32 34 36
Pin (dBm) Fig.14 Large-signal performance for both structures at 2400MHz with Vgs=-4V, Vds=20V
However, as the operating frequency enlarging to the S band 2400MHz, obvious changes have taken place to the DRBL GaN HEMT. The corresponding results are presented in Fig.14. In the whole region, the PAE and the Pout of the DRBL structure are always higher compared to the Con GaN HEMT. With the operating frequency increased to S band, the advantages of smaller gate-source/gate-drain capacitance for DRBL GaN HEMT began to gradually prominent. When the Pin=26dBm, the DRBL GaN HEMT could get the maximum PAE of 83.8%, the Pout of 40.8dBm. Both are higher than the 80.3% and 39.8dBm for the Con GaN HEMT.
ACCEPTED MANUSCRIPT In order to exhibit a visualized comparison of output characteristics between the two structures, corresponding results are extracted into the Table.2. It is clearly seen that the DRBL GaN HEMT possesses the superior RF characteristics and has the greater efficiency output capability which is benefit for the high efficiency-energy applications.
Table.2 The comparison of output characteristics between the DRBL and Con GaN HEMT at different frequency Frequency Parameters
DRBL GaN HEMT
Con GaN HEMT
600MHz
1200MHz
2400MHz
600MHz
1200MHz
2400MHz
Power density
8.7W/mm
6.9W/mm
6.4W/mm
8.7W/mm
6.7W/mm
5.0W/mm
Gain
10.4dB
9.4dB
9.1dB
10.4dB
9.3dB
8.0dB
PAE at saturation
87.3%
84.5%
81%
84.5%
82.5%
78.5%
The maximum PAE
90.2%
88%
83.8%
88%
84.7%
80.3%
Further investigation show that when the operating frequency increases to X band 10GHz, the DRBL GaN HEMT still possesses the high efficiency and large saturation power output characteristics compared to the conventional structure. The simulated results are presented in Fig.15. As the Pin enlarging to 34dBm, the PAE of the DRBL GaN HEMT achieves the peak value. The maximum PAE of the DRBL GaN HEMT is 59% and the corresponding power density achieves to 4.1W/mm. So, in the high frequency band, the DRBL GaN HEMT still shows the excellent performance. It is verified that the DRBL GaN HEMT has a greater advantages and potential capacities at high efficiency-energy applications.
ACCEPTED MANUSCRIPT
48
Vgs=-3.8V Vds=20V
46
f0=10GHz
80 Con-Pout DBRL-Pout 70 Con-PAE DBRL-PAE 60
44 42
50
40
40
38 30
36 34 24
PAE (%)
Pout (dBm)
50
26
28
30
32
34
36
38
20 40
Pin (dBm) Fig.15 Large-signal performance for both structures at 10GHz with Vgs= -3.8V, Vds=20V
4. Conclusions In summary, a novel GaN HEMT with double recessed barrier layer is proposed in this paper for high efficiency-energy applications. The proposed structure has two recessed AlGaN region beside the gate which slightly decreases the drain saturation current but expands the flat region of the transconductance. By ISE simulation, the transconductance saturation region of DRBL GaN HEMT is increased by 0.5V, the breakdown voltage is increased by 8.7%, and the gate-source/gate-darin capacitance is decreased by 11.3% and 6.3%, respectively. The simulated small-signal high frequency characteristics of DRBL GaN HEMT show that the RF characteristics are improved. The maximum oscillation frequency for DRBL GaN HEMT is increased from 57GHz to 64GHz and the power gain is increased by 1dB. The superior characteristics with DRBL GaN HEMT make it having the greater output potential at high power high efficiency. The simulated large-signal performances validate that the DRBL GaN HEMT possesses the higher output power and the higher power added efficiency. So, the DRBL GaN HEMT has a greater advantages and potential capacities at high efficiency-energy applications.
ACCEPTED MANUSCRIPT 5. Acknowledgments This work was supported in part by the National Natural Science Foundation of China (NSFC) under Grant No. 61671343,and in part by the National Key Basic Research Program of China (973 Program) under grant No. 2014CB339900.
ACCEPTED MANUSCRIPT References [1] Pengelly R S, Wood S M, Milligan J W, et al. A Review of GaN on SiC High Electron-Mobility Power Transistors and MMICs [J]. IEEE Transactions on Microwave Theory & Techniques, 2012, 60(6):1764-1783. [2] Jiang Q, Liu C, Lu Y, et al. 1.4-kV AlGaN/GaN HEMTs on a GaN-on-SOI platform[J]. IEEE Electron Device Letters, 2013, 34(3): 357-359. [3] Wang X L, Cheng T S, Ma Z Y, et al. 1-mm gate periphery AlGaN/AlN/GaN HEMTs on SiC with output power of 9.39 W at 8GHz [J]. Solid-state electronics, 2007, 51(3): 428-432. [4] Köhler K, Müller S, Aidam R, et al. Influence of the surface potential on electrical properties of AlxGa1-xN/GaN heterostructures with different Alcontent: effect of growth method [J]. Journal of Applied Physics, 2010, 107(5): 053711. [5] Ambacher O, Foutz B, Smart J, et al. Two dimensional electron gases induced by spontaneous and piezoelectric polarization in undoped and doped AlGaN/GaN heterostructures [J]. Journal of applied physics, 2000, 87(1): 334344. [6] Hoshi S, Itoh M, Marui T, et al. 12.88 W/mm GaN high electron mobility transistor on silicon substrate for high voltage operation[J]. Applied Physics Express, 2009, 2(6): 061001. [7] Dumka D C, Saunier P. GaN on Si HEMT with 65% power added efficiency at 10 GHz [J]. Electronics Letters, 2010, 46(13): 946-947. [8] Wu Y F, Saxler A, Moore M, et al. 30-W/mm GaN HEMTs by field plate optimization [J]. IEEE Electron Device Letters, 2004, 25(3): 117-119. [9] Higashiwaki M, Mimura T, Matsui T. AlGaN/GaN heterostructure field-effect transistors on 4H-SiC substrates with current-gain cutoff frequency of 190 GHz[J]. Applied physics express, 2008, 1(2): 021103. [10] Chung J W, Hoke W E, Chumbes E M, et al. AlGaN/GaN HEMT with 300-GHz [J]. IEEE Electron Device Letters, 2010, 31(3): 195-197. [11] Shinohara K, Regan D C, Tang Y, et al. Scaling of GaN HEMTs and Schottky diodes for submillimeter-wave MMIC applications[J]. IEEE Transactions on Electron Devices, 2013, 60(10): 2982-2996. [12] Kizilbey O, Palamutçuogullari O, Yarman S B. 3.5-3.8 GHz class-E balanced GaN HEMT power amplifier with 20W Pout and 80% PAE [J]. IEICE Electronics Express, 2013, 10(5): 20130104-20130104. [13] Chéron J, Campovecchio M, Barataud D, et al. Wideband harmonically matched packaged GaN HEMTs with high PAE performances at S-band frequencies [J]. International journal of microwave and wireless technologies, 2013, 5(04): 437-
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[15] [16]
[17]
[18]
[19]
445. Yamanaka K, Tuyama Y, Ohtsuka H, et al. Internally-matched GaN HEMT high efficiency power amplifier for space solar power stations [C]. Asia-Pacific Microwave Conference, IEEE, 2010: 119-122. Integrated Systems Engineering, manual for DESSIS, ISE TCAD Release 10.0[A]. Zurich Switzerland, 2004. Yuan S, Duan B, Yuan X, et al. New Al 0.25 Ga 0.75 N/GaN high electron mobility transistor with partial etched AlGaN layer[J]. Superlattices and Microstructures, 2016, 93: 303-307. H. Jia, Y. Luo, H. Zhang, et al. A novel 4H-SiC MESFET with serpentine channel for high power and high frequency applications [J]. Superlattices and Microstructures, 2017, 101:315-322. H. Jia, H. Zhang, Y. Luo, et al. Improved multi-recessed 4H–SiC MESFETs with double-recessed p-buffer layer [J]. Materials Science in Semiconductor Processing, 2015, 40:650-654. Angilent Technologies, "ADS Documentation, user manuals," Version ADS2010.
ACCEPTED MANUSCRIPT
A novel GaN HEMT with double recessed barrier layer for high efficiencyenergy applications is proposed.
The proposed structure has a broader saturated transconductance region compared to the conventional structure.
The gate-drain and gate-source capacitance are decreased by 6.3% and 11.3%, respectively.
The new structure has the advantages of RF characteristic that the fmax is increased from 57GHz to 64GHz.
The proposed structure has the greater abilities of outputting higher power and higher power added efficiency at higher operating frequency.
Hujun Jia, Qiuyuan Wu, Yehui Luo, Yintang Yang PII:
S0749-6036(17)31309-5
DOI:
10.1016/j.spmi.2017.07.047
Reference:
YSPMI 5157
To appear in:
Superlattices and Microstructures
Received Date:
28 May 2017
Revised Date:
20 July 2017
Accepted Date:
20 July 2017
Please cite this article as: Hujun Jia, Qiuyuan Wu, Yehui Luo, Yintang Yang, A novel GaN HEMT with double recessed barrier layer for high efficiency-energy applications, Superlattices and Microstructures (2017), doi: 10.1016/j.spmi.2017.07.047
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ACCEPTED MANUSCRIPT
A novel GaN HEMT with double recessed barrier layer for high efficiency-energy applications Hujun Jia*, Qiuyuan Wu, Yehui Luo,Yintang Yang (School of Microelectronics, Xidian University, Xi’an 710071, China)
Abstract In this paper, a novel GaN HEMT with high efficiency-energy characteristic is proposed. Different from the conventional structure, the proposed structure contains double recessed barriers layer (DRBL) beside the gate. The key idea in this work is to improve the microwave output characteristics. The simulated results show that the drain saturation current and peak transconductance of DRBL GaN HEMT is slightly decreased, the transconductance saturation flatness is increased by 0.5V and the breakdown voltage is also enhanced too. Due to the both recessed barrier layer, the gate-drain/gate-source capacitance is decreased by 6.3% and 11.3%, respectively. The RF simulated results show that the maximum oscillation frequency for DRBL GaN HEMT is increased from 57GHz to 64GHz and the saturation power density is 8.7W/mm at 600MHz, 6.9W/mm at 1200MHz with the higher power added efficiency (PAE). Further investigation show that DRBL GaN HEMT can achieve to 6.4W/mm and the maximum PAE 83.8% at 2400MHz. Both are higher than the 5.0W/mm and 80.3% for the conventional structure. When the operating frequency increases to X band, the DRBL GaN HEMT still exhibits the superior output performances. All the results show that the advantages and the potential capacities of DRBL GaN HEMT at high efficiency-energy are greater than the conventional GaN HEMT.
Keywords: GaN HEMT; Recessed barrier layer; Power added efficiency; Saturation power density *: Corresponding Author: Hujun Jia. Tel: (86)13772126387 E-mail: [email protected] Addr: School of Microelectronics, Xidian University, 710071, Xi’an, China.
ACCEPTED MANUSCRIPT 1. Introduction Recently, AlGaN/GaN high electron mobility transistor (HEMT) has attracted much attention in high frequency and high power applications due to its superior material properties, such as wide band gap, large electron saturated velocity, extremely high critical breakdown field and high radiation tolerance [1-3]. Simultaneously, the high-density two-dimensional electron gas at the AlGaN/GaN interface makes the AlGaN/GaN heterostructure devices superior to the conventional GaAs-based and InP-based devices [4-5]. These properties in combination with a greater advantage of the power quality factor for GaN material, making the AlGaN/GaN HEMT possess a broader development prospect for microwave high power applications. In recent years, tremendous progress has been made in the DC and RF performance of GaN HEMT. The devices with field modulating plates limit the risks of the current collapse and improve the breakdown voltage [6-7]. The maximum output power density has been successfully demonstrated with 32.2W/mm at 120V, 4GHz [8]. Attributing to the improving process technology, highly uniform AlGaN/GaN HEMT films are achieved for the ultra-high frequency band [9-10], the maximum oscillation frequency for GaN HEMT has been to 582GHz [11]. As the development of GaN devices, microwave power amplifiers (PA) based on GaN HEMT have been applied to the wireless communication system, phased array radar, aerospace fields and so on. Although, mostly ways in achieving the high efficiency output target are based on the control of external circuit to the tube and the use of compensation [12-14]. As the core of the PA, the characteristics of GaN HEMT are also important to the whole performances. With the more and more high request to the PA, it is necessary to find and design a novel GaN HEMT for the high power output with high power added efficiency (PAE). The high efficiency-energy GaN HEMT well has a great potential in uprating the performance of the amplifier and reducing the power consumption. Based on the above idea, a novel GaN HEMT with double recessed barrier layer
ACCEPTED MANUSCRIPT (DRBL) was proposed and analyzed for high efficiency-energy applications. Comparing with the conventional (Con) structure, the proposed structure contains double recessed barriers layer (DRBL) beside the gate, which are used to support two high resistance area to slow the increasement of the drain saturation current for exchanging the broader peak transconductance region. Using the 2D simulator ISE_TCAD, the simulated results show that the DRBL GaN HEMT takes full advantages of the elimination of gate depletion layer extending to source and drain resulting from the double recessed barrier region, which reflects well on the performance of breakdown voltage (Vb), gate-source capacitance (Cgs) and gate-drain capacitance (Cgd). The RF simulated results are verified by ADS simulation, it exhibits that the DRBL GaN HEMT has superior microwave output characteristics than the conventional GaN HEMT device. In the proposed DRBL GaN HEMT, the redistribution of the electric field can decrease the high electric field peak at the edge of the gate electrode. The electron injection effect of the gate electrode would be reduced and the current collapse effect would be mitigated. Thereby, the impact of the surface state on the device performance is improved. Under the existing process equipment conditions, the negative effects on the device performance caused by the etching-induced damage is slightly.
2. Device structure The schematic cross-sections of the conventional GaN HEMT and DRBL GaN HEMT structure used in this simulation are presented in Fig.1. Compared with the Con structure, there are two recessed AlGaN barrier layer region in the DRBL structure. The fabrication processes of DRBL GaN HEMT are the same as the convention one except for the formation of the recessed region. The source/drain electrode was formed by a Ti/Al/Ni/Au stack annealing at 850℃ for 30sec in N2 ambient. A Ni/Au stack was used to form the gate electrode by the e-beam evaporation. The recessed AlGaN barrier layer area can be produced through an
ACCEPTED MANUSCRIPT additional HBr/Ar plasma dry etching technology in the inductively coupled plasma (ICP) system. The height (H1) and length (L1) for the recessed gate-source region in the DRBL GaN HEMT are 5nm, 0.5μm. It is the same as the size of the recessed gatedrain region, H2=5nm, L2=0.5μm. All semiconductor layers were not intentionally doped except the GaN buffer layer. In order to simulate the influence of the carrier scattering in the GaN buffer layer, the GaN layer is n type doped with doping concentration of 1×1015cm-3 in the simulation. The nominal Al composition of AlGaN was chosen to be 0.25. The gate Schottky contact with a barrier height of 1.0eV and the gate width (Wg) is by default 1mm. It is worth noting that DRBL structure has the same device parameters with Con structure to have a meaningful comparison. The other common simulation parameters of both structures are given in the Table.1.
Table.1 Device structure parameters for both structures Device parameters
Value
Gate Length (Lg)
1μm
Gate-source spacing length (Lgs)
1μm
Gate-drain spacing length (Lgd)
2.5μm
Thickness of AlGaN barrier layer
25nm
Thickness of GaN buffer layer
3μm
Thickness of AlN nucleating layer
40nm
Doping of GaN buffer layer
1×1015cm-3
Doping of n-type cap layer
1×1020cm-3
The 2D simulator, ISE_TCAD is used to simulate the device characteristics with GaN, AlGaN and AlN material parameters for both structures [15]. In order to achieve realistic results, many important and necessary models are activated. The basic Poisson and drift-diffusion equations, Schrödinger-Poisson coupled equations, Shockley read hall (SRH) and Auger for generation and recombination, Doping Dep, Enormal and High Fieldsat for mobility, Incomplete for incomplete ionization of dopants and Avalance for impact ionization. A temperature of 300 K is employed by default in simulations.
ACCEPTED MANUSCRIPT
SourceLgs=1μm Gate Lg=1μm
a
N+
25nm
Lgd=2.5μm
Drain N+
Al0.25Ga0.75N 2DEG
3μm
GaN AlN
40nm
Substrate
SourceLgs=1μm Gate Lg=1μm
b
N+
Lgd=2.5μm H2
H1
25nm
Drain
L1
N+
L2
Al0.25Ga0.75N 2DEG
3μm 40nm
GaN AlN Substrate
Fig.1 Schematic cross-sections of the (a) Con GaN HEMT, (b) DRBL GaN HEMT
3. Results and discussions 3.1 DC characteristics The simulated data of DC drain current (Ids) versus the drain-source voltage (Vds) for both DRBL and Con structures are depicted in Fig.2. The gate bias voltage (Vgs) varies from -1 to 0V with a step of 1V. It can be seen that the Ids of the DRBL structure is slightly decreased at various Vgs compared with the Con structure. The drain saturation current for DRBL and Con GaN HEMT are 571mA/mm and 609mA/mm, respectively. Due to the existence of the double recessed barrier layer in the DRBL structure, the thickness of the AlGaN layer beside the gate is reduced, which resulting in the decrease of the density of the two dimension electron gas (n2D)
ACCEPTED MANUSCRIPT at the corresponding position. From the channel current equation showed below: I ds q Wg s n2 D
(1)
Where Wg is the gate width, υs is the saturated electron velocity. It is clearly that the Ids could be proportional to the n2D. So, when the n2D of the GaN HEMT decrease, the Ids of the GaN HEMT will decrease too. Fig.3 shows the simulated current density distribution under the conditions of Vgs=0V, Vds=20V for DRBL and Con GaN HEMT. It can been seen that the current density focus primarily on the AlGaN/GaN interface and the maximum current density (5.7e7 A/cm2) in the DRBL structure is smaller than that (6.2e7 A/cm2) in the Con GaN HEMT. Therefore, the drain saturation current of the DRBL GaN HEMT is decreased. But the differences are not very big.
800
Con GaN HEMT DRBL GaN HEMT
700
Vgs=0V
Ids(mA/mm)
600 500
Vgs=-1V
400 300 200 100 0
0
2
4
6
8
10 12 14 16 18 20 22
Vds(V) Fig.2 Simulated drain current versus the drain source voltage at gate bias voltage of -1V, 0V
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Fig.3 Simulated current density distributions of both structures (a) Con, (b) DRBL
The DC transfer characteristics at drain voltage of 20V are shown in Fig.4. For the depleted GaN HEMT, When n2D is 0, that is, when the channel is exhausted completely, the gate bias voltage at this time is the threshold voltage. It can be seen that both of the GaN HEMT structures have the similar threshold voltage (Vt). It could be attributed to the same thickness of AlGaN barrier layer under the gate. Due to the similar high concentration n2D in the drain-source channel for Con and DRBL structure, the Negative voltage applied on the gate to deplete the n2D is also similar for both structures. From the Fig.4, the Vt for the Con and DRBL GaN HEMT are -3.5V and -3.4V, respectively. The results of the first derivative curve of the transfer characteristics are shown in Fig.5, called the transconductance of the device. It is clearly that the Con GaN HEMT is equipped with the higher peak transconductance, 263mS/mm. Because the Con structure can output even bigger drain current under the same control of the gate voltage compared to the DRBL GaN HETM. It means in the Con structure, the gate has a better control to the channel which results in the bigger peak transconductance. Although, the peak transconductance of the DRBL GaN HETM, 241mS/mm, is decreased due to the double recessed barrier layer, it is worth noting that the flat site of peak transconductance is expanded. Vgo and Vco in the Fig.5 means the gate-source voltage where transconductance near to the maximum and to compression. Further reseach indicates that the power added efficiency increases with decreasing peak transconductance. Therefore, for the proposed DRBL GaN HEMT, the appropriate reduction for transconductance would be beneficial to the greater efficiency output characteristics.
ACCEPTED MANUSCRIPT In the DRBL structure, the recessed region plays a role in increasing the channel resistance, which restricts the growth rate of the drain current. Besides, the double recessed areas beside the gate reduce depletion layer extension to source/drain effectively. So, the depletion layer is mainly centered below the gate. The channel carriers flowing below the gate depletion are concentrated on a certain area. After the transconductance achieves to the saturation region, as the gate-source voltage continues to increase, the extent of the transconductance increases will slow down. And that, it will not present a rapid rise and fall likes that in the Con GaN HEMT. Compared with the Con structure, the double recessed barrier layer makes the DRBL GaN HEMT possesses a wider flat area of the transconductance which could be benefit for the high linearity and high efficiency output characteristics. The flat area of the transconductance for the two structures can be calculated by Vco-Vgo, and the results of Con and DRBL structures are 1.4V and 1.9V, respectively.
Ids(mA/mm)
800
Con GaN HEMT DRBL GaN HEMT
600
Vds=20V
400 200
0 -4.0 -3.5 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5
Vgs(V) Fig.4 Drain current versus gate voltage under drain-source voltage of 20V for both structures
ACCEPTED MANUSCRIPT 300
Con GaN HEMT DRBL GaN HEMT
gm(mS/mm)
250 200 150 100 50 0 -6
Vco
Vgo
-5
-4
-3
-2
-1
0
1
2
Vgs(V) Fig.5 Transconductance versus gate voltage under drain-source voltage of 20V for both structures
The simulated three-terminal breakdown characteristics for both structures are presented in Fig.6. The simulated results show that the breakdown voltages (Vb) are 195V, 212V for the Con and DRBL GaN HEMT. Fig.7 shows the distributions of electrostatic potential of both structures. It is well known that, the gate field emission induces a breakdown of the device. By the employment of the gate-drain recessed structure, the electrostatic potential distributions of the DRBL structure become more uniform. Simultaneously, the mitigation of the electric field crowding at the gate corner decreases the probability of the electron injection effect to the surface and reduces the surface leakage current [16]. With the help of recessed barrier layer, the current collapse effect would be also mitigated. So, the DRBL GaN HEMT could withstand greater drain breakdown voltage.
ACCEPTED MANUSCRIPT 0.4 Con GaN HEMT DRBL GaN HEMT
Ids(mA/mm)
0.3
Vb=212V
0.2
Vb=195V
0.1
0.0
0
50
100
150
200
250
Vds(V) Fig.6 Simulated three-terminal breakdown characteristics of both structures
Fig.7 Distributions of electrostatic potential of both structures (a) Con, (b) DRBL
3.2 RF characteristics Fig.8 and Fig.9 show the simulated gate-source capacitance (Cgs) and gate-drain capacitance (Cgd) for both structures. The DC bias conditions are Vgs=0V and Vds=20V. It can be seen that the Cgs and Cgd of the DRBL structure are 2.59pF/mm
ACCEPTED MANUSCRIPT and 58.5fF/mm, respectively. It is reduced by 11.3% and 6.3% compared with that of the Con GaN HEMT. The reason for this is that the recessed gate-drain and gatesource region reduces depletion layer extension to the source/drain effectively [1718]. The depletion region is promoted to spread in the vertical direction. It means the distance from the gate electrode to the lower surface of the depletion layer increased. The gate depletion layer distribution in the proposed structure has been further modulated, so, the smaller Cgs and Cgd can be obtained.
3.5
Con GaN HEMT DRBL GaN HEMT
3.0
Cgs(pF/mm)
2.5 2.0 1.5 1.0 0.5 0.0 1E+08
1E+09
1E+10
1E+11
1E+12
Frequency(Hz) Fig.8 Simulated gate-source capacitance versus frequency
70
Con GaN HEMT DRBL GaN HEMT
65
Cgd(fF/mm)
60 55 50 45 40 35 1E+08
1E+09
1E+10
1E+11
1E+12
Frequency(Hz) Fig.9 Simulated gate-drain capacitance versus frequency
ACCEPTED MANUSCRIPT The ac transconductance (gmac) of Con and DRBL structures are also simulated and the results are shown in Fig.10. Compared to the results in the Fig.5, the peak transconductance for both structures are increased about 8-9mS/mm at the frequency conditions. The gmac of Con structure is 271 mS/mm and the gmac of DRBL structure is 250 mS/mm.
300
gmac(mS/mm)
250 200
Con GaN HEMT DRBL GaN HEMT
150 100 50 0 1E+06
1E+07
1E+08
1E+09
1E+10
1E+11
Frequency(Hz) Fig.10 Simulated ac transconductance versus frequency
Fig.11 shows the simulated small-signal current gain (h21), maximum available gain (MAG) and unilateral power gain (U) for the both structures as a function of the frequency at Vgs=0 V and Vds=40 V. The results show that the cut-off frequency (ft) of the DRBL structure is 14.2GHz and it is similar to the result of the Con structure. But the maximum frequency (fmax) of DRBL GaN HEMT is 64GHz, which is increased by about 12.3% compared with that of the Con GaN HEMT. The expressions for the ft and fmax are as followings:
ft
gm 2π(Cgs Cgd )
(2)
ft Rds 2 Rg
(3)
f max
Where Rds is the drain-source resistance and Rg is the gate resistance. Based on the above equation of ft, it could be inferred that because the positive effects by the
ACCEPTED MANUSCRIPT decreased Cgs and Cgd is offset by the decline of the gm, the ft for the DRBL GaN HEMT is almost not changed. The enhanced of the fmax is due to the smaller gate resistance. From the Fig.11, it can be also seen that the U and MAG of the DRBL GaN HEMT are increased 1.2dB and 0.8dB compared to the Con structure at the same frequency. It means that the DRBL GaN HEMT has the greater power conversion ability and possesses the higher output efficiency.
50 Con-h21 DRBL-h21 Con-U DRBL-U Con-MAG DRBL-MAG
Gain (dB)
40 30 20
Vgs=0V Vds=20V
10 0 1E8
1E9
1E10
1E11
Frequency (Hz) Fig.11 Simulated small-signal high frequency characteristics of Con and DRBL structures
3.3 High efficiency-energy verification In order to compare the large-signal performance between the DRBL GaN HEMT and Con GaN HEMT, the corresponding DC and RF simulated results are extracted into the EE_HEMT1 model to simulate the power output characteristics by ADS software [19]. The large-signal simulated result at 600MHz is presented in Fig.12. It is worth noted that the PAE of DRBL GaN HEMT is always larger than that of Con GaN HEMT. The DRBL GaN HEMT biased at Vds=20V exhibit an output power (Pout) of 42.2dBm, power density of 8.3W/mm and a maximum PAE of 90.2% at 600MHz. With the increase of the input power (Pin), the difference of the Pout between the DRBL and Con GaN HEMT is gradually reduced. When the Pin gets to 30dBm, DRBL GaN HEMT has the same Pout as the Con
ACCEPTED MANUSCRIPT GaN HEMT. At that moment, the bigger PAE for the DRBL GaN HEMT attributes to the smaller DC consumption. As the Pin continuously increasing, the DC consumption of DRBL GaN HEMT is almost to the Con GaN HEMT, then, both PAEs are closed to each other. By means of analysis to the Ids-Vds characteristic above, the drain current output capability of Con structure is a bit better than DRBL GaN HEMT. In addition, the advantages of smaller gate-source/gate-drain capacitance for DRBL GaN HEMT don’t play out at the lower frequency band. So, the DRBL GaN HEMT has the similar saturation output power as the Con GaN HEMT.
50
Vgs=-4V
90
46 f0=600MHz
80
44
70
42
60
40
Con-Pout DBRL-Pout Con-PAE DBRL-PAE
38 36
50
PAE (%)
Pout (dBm)
48 Vds=20V
40 30
34 14 16 18 20 22 24 26 28 30 32 34 36
Pin (dBm) Fig.12 Large-signal performance for both structures at 600MHz with Vgs= -4V, Vds=20V
When the operating frequency increased to 1200MHz, the simulated large-signal performance is shown in Fig.13. It can be seen that the PAE of the DRBL GaN HEMT is still higher than the Con GaN HEMT with the same saturated output power.
ACCEPTED MANUSCRIPT 50
Vgs=-4V
90
46 f0=1200MHz
80
44
70
42
60
40
50 Con-Pout DBRL-Pout 40 Con-PAE DBRL-PAE 30
38 36
PAE (%)
Pout (dBm)
48 Vds=20V
34 14 16 18 20 22 24 26 28 30 32 34 36
Pin (dBm) Fig.13 Large-signal performance for both structures at 1200MHz with Vgs=-4V, Vds=20V
48
Vgs=-4V Vds=20V
46
f0=2400MHz
90 80
44
70
42
60
40
50 Con-Pout DBRL-Pout 40 Con-PAE DBRL-PAE 30
38 36
PAE (%)
Pout (dBm)
50
34 14 16 18 20 22 24 26 28 30 32 34 36
Pin (dBm) Fig.14 Large-signal performance for both structures at 2400MHz with Vgs=-4V, Vds=20V
However, as the operating frequency enlarging to the S band 2400MHz, obvious changes have taken place to the DRBL GaN HEMT. The corresponding results are presented in Fig.14. In the whole region, the PAE and the Pout of the DRBL structure are always higher compared to the Con GaN HEMT. With the operating frequency increased to S band, the advantages of smaller gate-source/gate-drain capacitance for DRBL GaN HEMT began to gradually prominent. When the Pin=26dBm, the DRBL GaN HEMT could get the maximum PAE of 83.8%, the Pout of 40.8dBm. Both are higher than the 80.3% and 39.8dBm for the Con GaN HEMT.
ACCEPTED MANUSCRIPT In order to exhibit a visualized comparison of output characteristics between the two structures, corresponding results are extracted into the Table.2. It is clearly seen that the DRBL GaN HEMT possesses the superior RF characteristics and has the greater efficiency output capability which is benefit for the high efficiency-energy applications.
Table.2 The comparison of output characteristics between the DRBL and Con GaN HEMT at different frequency Frequency Parameters
DRBL GaN HEMT
Con GaN HEMT
600MHz
1200MHz
2400MHz
600MHz
1200MHz
2400MHz
Power density
8.7W/mm
6.9W/mm
6.4W/mm
8.7W/mm
6.7W/mm
5.0W/mm
Gain
10.4dB
9.4dB
9.1dB
10.4dB
9.3dB
8.0dB
PAE at saturation
87.3%
84.5%
81%
84.5%
82.5%
78.5%
The maximum PAE
90.2%
88%
83.8%
88%
84.7%
80.3%
Further investigation show that when the operating frequency increases to X band 10GHz, the DRBL GaN HEMT still possesses the high efficiency and large saturation power output characteristics compared to the conventional structure. The simulated results are presented in Fig.15. As the Pin enlarging to 34dBm, the PAE of the DRBL GaN HEMT achieves the peak value. The maximum PAE of the DRBL GaN HEMT is 59% and the corresponding power density achieves to 4.1W/mm. So, in the high frequency band, the DRBL GaN HEMT still shows the excellent performance. It is verified that the DRBL GaN HEMT has a greater advantages and potential capacities at high efficiency-energy applications.
ACCEPTED MANUSCRIPT
48
Vgs=-3.8V Vds=20V
46
f0=10GHz
80 Con-Pout DBRL-Pout 70 Con-PAE DBRL-PAE 60
44 42
50
40
40
38 30
36 34 24
PAE (%)
Pout (dBm)
50
26
28
30
32
34
36
38
20 40
Pin (dBm) Fig.15 Large-signal performance for both structures at 10GHz with Vgs= -3.8V, Vds=20V
4. Conclusions In summary, a novel GaN HEMT with double recessed barrier layer is proposed in this paper for high efficiency-energy applications. The proposed structure has two recessed AlGaN region beside the gate which slightly decreases the drain saturation current but expands the flat region of the transconductance. By ISE simulation, the transconductance saturation region of DRBL GaN HEMT is increased by 0.5V, the breakdown voltage is increased by 8.7%, and the gate-source/gate-darin capacitance is decreased by 11.3% and 6.3%, respectively. The simulated small-signal high frequency characteristics of DRBL GaN HEMT show that the RF characteristics are improved. The maximum oscillation frequency for DRBL GaN HEMT is increased from 57GHz to 64GHz and the power gain is increased by 1dB. The superior characteristics with DRBL GaN HEMT make it having the greater output potential at high power high efficiency. The simulated large-signal performances validate that the DRBL GaN HEMT possesses the higher output power and the higher power added efficiency. So, the DRBL GaN HEMT has a greater advantages and potential capacities at high efficiency-energy applications.
ACCEPTED MANUSCRIPT 5. Acknowledgments This work was supported in part by the National Natural Science Foundation of China (NSFC) under Grant No. 61671343,and in part by the National Key Basic Research Program of China (973 Program) under grant No. 2014CB339900.
ACCEPTED MANUSCRIPT References [1] Pengelly R S, Wood S M, Milligan J W, et al. A Review of GaN on SiC High Electron-Mobility Power Transistors and MMICs [J]. IEEE Transactions on Microwave Theory & Techniques, 2012, 60(6):1764-1783. [2] Jiang Q, Liu C, Lu Y, et al. 1.4-kV AlGaN/GaN HEMTs on a GaN-on-SOI platform[J]. IEEE Electron Device Letters, 2013, 34(3): 357-359. [3] Wang X L, Cheng T S, Ma Z Y, et al. 1-mm gate periphery AlGaN/AlN/GaN HEMTs on SiC with output power of 9.39 W at 8GHz [J]. Solid-state electronics, 2007, 51(3): 428-432. [4] Köhler K, Müller S, Aidam R, et al. Influence of the surface potential on electrical properties of AlxGa1-xN/GaN heterostructures with different Alcontent: effect of growth method [J]. Journal of Applied Physics, 2010, 107(5): 053711. [5] Ambacher O, Foutz B, Smart J, et al. Two dimensional electron gases induced by spontaneous and piezoelectric polarization in undoped and doped AlGaN/GaN heterostructures [J]. Journal of applied physics, 2000, 87(1): 334344. [6] Hoshi S, Itoh M, Marui T, et al. 12.88 W/mm GaN high electron mobility transistor on silicon substrate for high voltage operation[J]. Applied Physics Express, 2009, 2(6): 061001. [7] Dumka D C, Saunier P. GaN on Si HEMT with 65% power added efficiency at 10 GHz [J]. Electronics Letters, 2010, 46(13): 946-947. [8] Wu Y F, Saxler A, Moore M, et al. 30-W/mm GaN HEMTs by field plate optimization [J]. IEEE Electron Device Letters, 2004, 25(3): 117-119. [9] Higashiwaki M, Mimura T, Matsui T. AlGaN/GaN heterostructure field-effect transistors on 4H-SiC substrates with current-gain cutoff frequency of 190 GHz[J]. Applied physics express, 2008, 1(2): 021103. [10] Chung J W, Hoke W E, Chumbes E M, et al. AlGaN/GaN HEMT with 300-GHz [J]. IEEE Electron Device Letters, 2010, 31(3): 195-197. [11] Shinohara K, Regan D C, Tang Y, et al. Scaling of GaN HEMTs and Schottky diodes for submillimeter-wave MMIC applications[J]. IEEE Transactions on Electron Devices, 2013, 60(10): 2982-2996. [12] Kizilbey O, Palamutçuogullari O, Yarman S B. 3.5-3.8 GHz class-E balanced GaN HEMT power amplifier with 20W Pout and 80% PAE [J]. IEICE Electronics Express, 2013, 10(5): 20130104-20130104. [13] Chéron J, Campovecchio M, Barataud D, et al. Wideband harmonically matched packaged GaN HEMTs with high PAE performances at S-band frequencies [J]. International journal of microwave and wireless technologies, 2013, 5(04): 437-
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[14]
[15] [16]
[17]
[18]
[19]
445. Yamanaka K, Tuyama Y, Ohtsuka H, et al. Internally-matched GaN HEMT high efficiency power amplifier for space solar power stations [C]. Asia-Pacific Microwave Conference, IEEE, 2010: 119-122. Integrated Systems Engineering, manual for DESSIS, ISE TCAD Release 10.0[A]. Zurich Switzerland, 2004. Yuan S, Duan B, Yuan X, et al. New Al 0.25 Ga 0.75 N/GaN high electron mobility transistor with partial etched AlGaN layer[J]. Superlattices and Microstructures, 2016, 93: 303-307. H. Jia, Y. Luo, H. Zhang, et al. A novel 4H-SiC MESFET with serpentine channel for high power and high frequency applications [J]. Superlattices and Microstructures, 2017, 101:315-322. H. Jia, H. Zhang, Y. Luo, et al. Improved multi-recessed 4H–SiC MESFETs with double-recessed p-buffer layer [J]. Materials Science in Semiconductor Processing, 2015, 40:650-654. Angilent Technologies, "ADS Documentation, user manuals," Version ADS2010.
ACCEPTED MANUSCRIPT
A novel GaN HEMT with double recessed barrier layer for high efficiencyenergy applications is proposed.
The proposed structure has a broader saturated transconductance region compared to the conventional structure.
The gate-drain and gate-source capacitance are decreased by 6.3% and 11.3%, respectively.
The new structure has the advantages of RF characteristic that the fmax is increased from 57GHz to 64GHz.
The proposed structure has the greater abilities of outputting higher power and higher power added efficiency at higher operating frequency.