- Email: [email protected]
InGaAsGaAs pseudomorphic heterostructure transistors prepared by MOVPE
,. . . . . . . .
ELSEVIER
CRYSTAL GROWTH
Journal of Crystal Growth 170 (1997) 438 441
InGaAs-GaAs pseudomorphic heterostructure transistors prepared by MOVPE Wen-Chau Liu *, Lih-Wen Lath, Jung-Hui Tsai, Kun-Wei Lin, Chin-Chuan Cheng Department q[ Electrical Engineering, National Cheng-Kun;, UniversiO', 1 Unirersitv Road, Taimn. Taiwan. ROC
Abstract
In this paper, we will demonstrate two new I n G a A s - G a A s pseudomorphic heterostructure transistors prepared by MOVPE technology, i.e. InGaAs GaAs graded-concentration doping-channel MIS-like field effect transistors (FET) and heterostructure-emitter and heterostructure-base ( I n G a A s - G a A s ) transistors (HEHBT). For the doping-channel MIS-like FET, the graded lno.]sGao.ssAs doping-channel structure is employed as the active channel. For a 0.8 × 100 /,tin: gate device, a breakdown voltage of 15 V, a maximum transconductance of 200 m S / m m , and a maximum drain saturation current of 735 m A / m m are obtained. For the HEHBT, the confinement effect for holes is enhanced owing to the presence of G a A s / I n G a A s / G a A s quantum wells. Thus, the emitter injection efficiency is increased and a high current gain can be obtained. Also, due to the lower surface recombination velocity of InGaAs base layers, the potential spike of the emitter base ( E - B ) junction can be reduced significantly. This can provide a lower collector-emitter offset voltage. For an emitter area of 4.9 × 10 5 cm 2, the common emitter current gain of 120 and the collector-emitter offset voltage of t00 mV are obtained.
1. I n t r o d u c t i o n
Heterojunction transistors have attracted considerable attention for microwave power and digital applications due to their high speed and high current handling capability [1-3]. Over the past years, the pseudomorphic InGaAs-GaAs heterostructure has been extensively studied because the strained-layer heterostructure allows the use of lattice-mismatched materials without generating misfit dislocations [4,5]. Liu et al. [6] have demonstrated a doping-channel MIS-like field-effect transistor (FET) by using n - -
Corresponding author. Fax: + 886 6 234 5482.
G a A s / n - - I n 0 : G a 0 . sAs two-layer pseudomorphic structures. An n--GaAs and n--In0:Ga0.sAs layer are employed as gate Schottky contact and active channel, respectively. Due to the enhancement of electron mobility and velocity in the InGaAs channel and the presence of the conduct-band discontinuity A E c between the GaAs and InGaAs, a lower transit time, high current linearity, and current handling capability are obtained, On the other hand, the confinement effect is a significant factor for heterojunction bipolar transistors (HBTs) [7,8]. The valenceband discontinuity AEv may determine the emitter injection efficiency and current gain. Typically, the offset voltage AVe, E of A1GaAs/GaAs HBT is large partially due to the higher GaAs-base surface recombination velocity. It will increase the power con-
0022 0248/97/$17.00 Copyright © 1997 Elsevier Science B.V. All rights reserved PII S 0 0 2 2 - 0 2 4 8 ( 9 6 ) 0 0 5 0 2 - 7
Wen-Chau Liu et al. / Journal o/' Crystal Growth 170 (1997) 438-441
sumption for the circuit applications. Thus, using an I n G a A s - G a A s heterostructure-base to replace the conventional GaAs base may overcome the above disadvantages of A1GaAs/GaAs HBT. In this paper, the performances of two new heterostructure transistors based on the l n G a A s / G a A s pseudomorphic structure, i.e. I n G a A s - G a A s graded-concentration doping-channel MIS-like FET and I n G a A s - G a A s heterostructure-emitter and heterostructure-base transistors (HEHBT) will be fabricated and demonstrated. In Sections 2 and 3, the device fabrication and experimental results are presented and discussed.
2. Experimental procedure The studied structures were grown by metalorganic vapor phase epitaxy (MOVPE). The low pressure growth (80 Tort) was carried out in a horizontal quartz reactor. The gas flow rates, the substrate temperature, the reactor pressure, and the values are all computer-controlled. The growth temperature was kept at 650°C. Triethylgallium (TEG), trimethylimdium (TMI), arsine (ASH3), and trimethylalumimum (TMA) were used as the Ga, In, As, and AI sources, respectively. Silane (Sill 4) and diethylzinc (DEZ) were used as the n-type and p-type dopant. The graded-concentration doping-channel MIS-like FET was grown on a (100)-oriented semi-insulating GaAs substrate. The layer structures consist of a 0.5 /xm undoped GaAs buffer layer, a 100 ~, n = 5 × 1017 c m 3, 100 A n + = 1 × 10 Is c m - ' ~ , and 50 n + = 4 × 10 Is cm 3 tri-step In0.isGa0ssAs gradeddoping channel, a 300 A AI 03Ga0.7 As undoped layer, and a 300 A n - = 3 × 10 Is c m 3 GaAs cap layer. For the HEHBT, it was grown on a (100)-oriented n+-GaAs substrate. The layer structure includes a 0.2 /,m n + = 3 × l0 ts cm 3 GaAs buffer layer, a 0.5 /xm n = 5 × 10 ~6 cm 3 GaAs collector layer, a 0.1/xm p + = 5 × l0 ts cm 3 GaAsbase, a 100 p + = 5 × 10 Is cm 3 in0=Ga0.sAs base layer, a 700 n=5× 10 ~7 cm 3 GaAs emitter layer, a 0.1 # m n = 5 × 10 ~r cm 3 Al0.~GaoTA s confinement layer, and a 2 0 0 , ~ n + = 3 × 10 Is cm 3 GaAs cap layer. After the epitaxial growth, wet chemical etching, vacuum evaporation, and lift-off techniques were used to fabricate the devices.
439
3. Results and discussions
3.1. Pelformances of hzo.15Gao.a5As-GaAs gradedconcentration doping-channel MIS-like FET Fig. 1 shows the output current-voltage ( I - V ) characteristics of the studied MIS-like FET. The maximum applied gate voltage is + 1.5 V, and the threshold voltage Vr is about - 3 . 7 V. A maximum transconductance gm about of 200 m S / m m and a very broad range of gate voltage larger than 3.5 V with the gm higher than 150 m S / m m is achieved. It also can be found that the drain saturation current los s has a maximum value of 735 m A / m m and shows a good current linear performance. This good performance is a result of the excellent properties of the graded-doping InGaAs layers. Because of the existence of the conduction band discontinuity A Ec, high-mobility electrons are confined at the A 1 G a A s - I n G a A s - G a A s region, even under the application of a high gate voltage. The gate voltage of up to 1.5 V can significantly increase the logic swing and noise margin for logic circuit application. Fig. 2 illustrates the gate-drain I - V characteristics. A gate-drain reverse breakdown voltage is measured to be about 15 V at 1~; = 10 /xA. This value is good, and suitable for high-power system application. Significantly, the high breakdown voltage is attributed
80 E
70
p... 7.
6O
,..,..
'%;s=I.SV
50 40
z,
3o
~,
20
.< ~
I0 I
0 0
0.5
I
I 1.5
I 2
DRAIN-SOITR(TE Fig.
1. T h e o u t p u t
studied MIS-likc
current-voltage
FET.
I 2.5
-J 3
VOI.TA(;E (/
I
l
3.5
4
4.5
VDs(V)
V) characteristics
of the
Wen-Chau Liu et al. / Journal of Co, stal Growth 170 (1997) 438-441
440
/
100 ~,~
60
~,
20
,.¢
-20 .<
-60 -IO0
,f i
-18
I
,< $ t!
l
-15
IB=0.1 mA/step
I
-12
I
i
-9
i
I
I
i
-6
i
GATE-SOUIICE VOI;I'AGE
VcE=I V/div
i
-3
3
0 Vc;s(V)
Fig. 2. The drain-gate current-voltage characteristics studied MIS-like FET.
of the
to the presence of an i-A1GaAs Schottky contact layer. Thus, the device can exhibit a good potential for circuit applications.
3.2. Performances of heterostructure-emitter and heterostructure-base transistors (HEHBT) Fig. 3 shows the energy band diagram under forward operation mode of the studied HEHBT. For the studied structure, the valence band discontinuity AEv is the summation of A Evl (A 10.45G a 0.55 A s / G a A s) and A Ev2 (GaAs/In02Ga0.8As). Thus, the emitter injection efficiency and the current gain could be enhanced. Also, it is worthy to note that the heterostructure emitter not only greatly reduces the collector-emitter offset voltage AVcE [9,10], but also prevents holes from injecting into the emitter region. Fig. 4 illustrates the experimental common-emitter I - V characteristics. The emitter size is 4.9 × 10 -5 cm -2 for the studied device. The common-emitter current gain of
E
_
_
B
C
......
t
_
jc..-
~...~
Fig. 4. The experimental common-emitter current-voltage characteristics of the studied HEHBT.
120 and a small collector-emitter offset voltage of 100 mV are obtained. Generally, the large AVcE of conventional HBTs is partially due to the large surface recombination velocity of the exposed GaAs base. In our device, the base metal was deposited on the lower surface recombination velocity layer (InGaAs layer). Therefore, the AVcE value can be reduced and the current gain is enhanced because the base current is suppressed significantly. Therefore, due to the presence of InGaAs-GaAs pseudomorphic heterostructures, our studied HEHBT could elevate the A E v value and decrease the base surface recombination current.
4. Conclusions In summary, two different InGaAs-GaAs pseudomorphic heterostructure transistors have been successfully fabricated and demonstrated. Due to the excellent properties of InGaAs layers, the gradedconcentration doping-channel MIS-like FET exhibits the advantages including the high gate breakdown voltage, high voltage-independent transconductance, and high drain saturation current. For the HEHBT, the pseudomorphic base structure provides high valence band discontinuity and improves the transistor performances, e.g. low offset voltage and high current gain.
<
_t
Fig. 3. The energy band diagram of the studied HEHBT under normal operation mode.
Acknowledgements Part of this work was supported by the National Science Council of China under Contract No. NSC
85-2215-E-006-023.
Wen-Chau Liu et al. / Journal of Co'stal Growth 170 (1997) 438-441
References [l] K. Morizuka, R. Katoh, M. Asska and N. Izuka, IEEE Electron Dev. Lett. EDL-9 (1988) 585. [2] H. Hida, A. Okamoto, H. Toyoshima and K. Ohata, 1EEE Electron Dev. Lett. EDL-7 (1986) 625. [3] Y.F. Yang, C.C. Hsu and E.S. Yang, IEEE Trans. Electron Dev. ED-41 (1994) 643. [4] J.W. Matthews and A.E. Blakeslee, J. Crystal Growth 27 (1974) 118. [5] K. Ploog, J. Crystal Growth 81 (1987) 304.
441
[6] W.C. Liu, W.C. Hsu, L.W. Laih and J.H. Tsai, Appl. Phys. Lett. 66 (1995) 1524. [7] H.R. Chen, C.Y. Chang, C.P. Lee, C.H. Huang, J.S. Tsang and K.L. Tsai, IEEE Electron Dev. Lett. EDL-15 (1994) 336. [8] S.S. Lu and C.C. Wu, IEEE Electron Dev. Lett. EDL-13 (1992) 468. [9] S.C. Lee, J.N. Kau and H.H. Lin, Appl. Phys. Lett. 45 (1984) 1114. [10] W.C. Liu and W.S. Lout, Solid-State Electron. 34 (1991) 717.
ELSEVIER
CRYSTAL GROWTH
Journal of Crystal Growth 170 (1997) 438 441
InGaAs-GaAs pseudomorphic heterostructure transistors prepared by MOVPE Wen-Chau Liu *, Lih-Wen Lath, Jung-Hui Tsai, Kun-Wei Lin, Chin-Chuan Cheng Department q[ Electrical Engineering, National Cheng-Kun;, UniversiO', 1 Unirersitv Road, Taimn. Taiwan. ROC
Abstract
In this paper, we will demonstrate two new I n G a A s - G a A s pseudomorphic heterostructure transistors prepared by MOVPE technology, i.e. InGaAs GaAs graded-concentration doping-channel MIS-like field effect transistors (FET) and heterostructure-emitter and heterostructure-base ( I n G a A s - G a A s ) transistors (HEHBT). For the doping-channel MIS-like FET, the graded lno.]sGao.ssAs doping-channel structure is employed as the active channel. For a 0.8 × 100 /,tin: gate device, a breakdown voltage of 15 V, a maximum transconductance of 200 m S / m m , and a maximum drain saturation current of 735 m A / m m are obtained. For the HEHBT, the confinement effect for holes is enhanced owing to the presence of G a A s / I n G a A s / G a A s quantum wells. Thus, the emitter injection efficiency is increased and a high current gain can be obtained. Also, due to the lower surface recombination velocity of InGaAs base layers, the potential spike of the emitter base ( E - B ) junction can be reduced significantly. This can provide a lower collector-emitter offset voltage. For an emitter area of 4.9 × 10 5 cm 2, the common emitter current gain of 120 and the collector-emitter offset voltage of t00 mV are obtained.
1. I n t r o d u c t i o n
Heterojunction transistors have attracted considerable attention for microwave power and digital applications due to their high speed and high current handling capability [1-3]. Over the past years, the pseudomorphic InGaAs-GaAs heterostructure has been extensively studied because the strained-layer heterostructure allows the use of lattice-mismatched materials without generating misfit dislocations [4,5]. Liu et al. [6] have demonstrated a doping-channel MIS-like field-effect transistor (FET) by using n - -
Corresponding author. Fax: + 886 6 234 5482.
G a A s / n - - I n 0 : G a 0 . sAs two-layer pseudomorphic structures. An n--GaAs and n--In0:Ga0.sAs layer are employed as gate Schottky contact and active channel, respectively. Due to the enhancement of electron mobility and velocity in the InGaAs channel and the presence of the conduct-band discontinuity A E c between the GaAs and InGaAs, a lower transit time, high current linearity, and current handling capability are obtained, On the other hand, the confinement effect is a significant factor for heterojunction bipolar transistors (HBTs) [7,8]. The valenceband discontinuity AEv may determine the emitter injection efficiency and current gain. Typically, the offset voltage AVe, E of A1GaAs/GaAs HBT is large partially due to the higher GaAs-base surface recombination velocity. It will increase the power con-
0022 0248/97/$17.00 Copyright © 1997 Elsevier Science B.V. All rights reserved PII S 0 0 2 2 - 0 2 4 8 ( 9 6 ) 0 0 5 0 2 - 7
Wen-Chau Liu et al. / Journal o/' Crystal Growth 170 (1997) 438-441
sumption for the circuit applications. Thus, using an I n G a A s - G a A s heterostructure-base to replace the conventional GaAs base may overcome the above disadvantages of A1GaAs/GaAs HBT. In this paper, the performances of two new heterostructure transistors based on the l n G a A s / G a A s pseudomorphic structure, i.e. I n G a A s - G a A s graded-concentration doping-channel MIS-like FET and I n G a A s - G a A s heterostructure-emitter and heterostructure-base transistors (HEHBT) will be fabricated and demonstrated. In Sections 2 and 3, the device fabrication and experimental results are presented and discussed.
2. Experimental procedure The studied structures were grown by metalorganic vapor phase epitaxy (MOVPE). The low pressure growth (80 Tort) was carried out in a horizontal quartz reactor. The gas flow rates, the substrate temperature, the reactor pressure, and the values are all computer-controlled. The growth temperature was kept at 650°C. Triethylgallium (TEG), trimethylimdium (TMI), arsine (ASH3), and trimethylalumimum (TMA) were used as the Ga, In, As, and AI sources, respectively. Silane (Sill 4) and diethylzinc (DEZ) were used as the n-type and p-type dopant. The graded-concentration doping-channel MIS-like FET was grown on a (100)-oriented semi-insulating GaAs substrate. The layer structures consist of a 0.5 /xm undoped GaAs buffer layer, a 100 ~, n = 5 × 1017 c m 3, 100 A n + = 1 × 10 Is c m - ' ~ , and 50 n + = 4 × 10 Is cm 3 tri-step In0.isGa0ssAs gradeddoping channel, a 300 A AI 03Ga0.7 As undoped layer, and a 300 A n - = 3 × 10 Is c m 3 GaAs cap layer. For the HEHBT, it was grown on a (100)-oriented n+-GaAs substrate. The layer structure includes a 0.2 /,m n + = 3 × l0 ts cm 3 GaAs buffer layer, a 0.5 /xm n = 5 × 10 ~6 cm 3 GaAs collector layer, a 0.1/xm p + = 5 × l0 ts cm 3 GaAsbase, a 100 p + = 5 × 10 Is cm 3 in0=Ga0.sAs base layer, a 700 n=5× 10 ~7 cm 3 GaAs emitter layer, a 0.1 # m n = 5 × 10 ~r cm 3 Al0.~GaoTA s confinement layer, and a 2 0 0 , ~ n + = 3 × 10 Is cm 3 GaAs cap layer. After the epitaxial growth, wet chemical etching, vacuum evaporation, and lift-off techniques were used to fabricate the devices.
439
3. Results and discussions
3.1. Pelformances of hzo.15Gao.a5As-GaAs gradedconcentration doping-channel MIS-like FET Fig. 1 shows the output current-voltage ( I - V ) characteristics of the studied MIS-like FET. The maximum applied gate voltage is + 1.5 V, and the threshold voltage Vr is about - 3 . 7 V. A maximum transconductance gm about of 200 m S / m m and a very broad range of gate voltage larger than 3.5 V with the gm higher than 150 m S / m m is achieved. It also can be found that the drain saturation current los s has a maximum value of 735 m A / m m and shows a good current linear performance. This good performance is a result of the excellent properties of the graded-doping InGaAs layers. Because of the existence of the conduction band discontinuity A Ec, high-mobility electrons are confined at the A 1 G a A s - I n G a A s - G a A s region, even under the application of a high gate voltage. The gate voltage of up to 1.5 V can significantly increase the logic swing and noise margin for logic circuit application. Fig. 2 illustrates the gate-drain I - V characteristics. A gate-drain reverse breakdown voltage is measured to be about 15 V at 1~; = 10 /xA. This value is good, and suitable for high-power system application. Significantly, the high breakdown voltage is attributed
80 E
70
p... 7.
6O
,..,..
'%;s=I.SV
50 40
z,
3o
~,
20
.< ~
I0 I
0 0
0.5
I
I 1.5
I 2
DRAIN-SOITR(TE Fig.
1. T h e o u t p u t
studied MIS-likc
current-voltage
FET.
I 2.5
-J 3
VOI.TA(;E (/
I
l
3.5
4
4.5
VDs(V)
V) characteristics
of the
Wen-Chau Liu et al. / Journal of Co, stal Growth 170 (1997) 438-441
440
/
100 ~,~
60
~,
20
,.¢
-20 .<
-60 -IO0
,f i
-18
I
,< $ t!
l
-15
IB=0.1 mA/step
I
-12
I
i
-9
i
I
I
i
-6
i
GATE-SOUIICE VOI;I'AGE
VcE=I V/div
i
-3
3
0 Vc;s(V)
Fig. 2. The drain-gate current-voltage characteristics studied MIS-like FET.
of the
to the presence of an i-A1GaAs Schottky contact layer. Thus, the device can exhibit a good potential for circuit applications.
3.2. Performances of heterostructure-emitter and heterostructure-base transistors (HEHBT) Fig. 3 shows the energy band diagram under forward operation mode of the studied HEHBT. For the studied structure, the valence band discontinuity AEv is the summation of A Evl (A 10.45G a 0.55 A s / G a A s) and A Ev2 (GaAs/In02Ga0.8As). Thus, the emitter injection efficiency and the current gain could be enhanced. Also, it is worthy to note that the heterostructure emitter not only greatly reduces the collector-emitter offset voltage AVcE [9,10], but also prevents holes from injecting into the emitter region. Fig. 4 illustrates the experimental common-emitter I - V characteristics. The emitter size is 4.9 × 10 -5 cm -2 for the studied device. The common-emitter current gain of
E
_
_
B
C
......
t
_
jc..-
~...~
Fig. 4. The experimental common-emitter current-voltage characteristics of the studied HEHBT.
120 and a small collector-emitter offset voltage of 100 mV are obtained. Generally, the large AVcE of conventional HBTs is partially due to the large surface recombination velocity of the exposed GaAs base. In our device, the base metal was deposited on the lower surface recombination velocity layer (InGaAs layer). Therefore, the AVcE value can be reduced and the current gain is enhanced because the base current is suppressed significantly. Therefore, due to the presence of InGaAs-GaAs pseudomorphic heterostructures, our studied HEHBT could elevate the A E v value and decrease the base surface recombination current.
4. Conclusions In summary, two different InGaAs-GaAs pseudomorphic heterostructure transistors have been successfully fabricated and demonstrated. Due to the excellent properties of InGaAs layers, the gradedconcentration doping-channel MIS-like FET exhibits the advantages including the high gate breakdown voltage, high voltage-independent transconductance, and high drain saturation current. For the HEHBT, the pseudomorphic base structure provides high valence band discontinuity and improves the transistor performances, e.g. low offset voltage and high current gain.
<
_t
Fig. 3. The energy band diagram of the studied HEHBT under normal operation mode.
Acknowledgements Part of this work was supported by the National Science Council of China under Contract No. NSC
85-2215-E-006-023.
Wen-Chau Liu et al. / Journal of Co'stal Growth 170 (1997) 438-441
References [l] K. Morizuka, R. Katoh, M. Asska and N. Izuka, IEEE Electron Dev. Lett. EDL-9 (1988) 585. [2] H. Hida, A. Okamoto, H. Toyoshima and K. Ohata, 1EEE Electron Dev. Lett. EDL-7 (1986) 625. [3] Y.F. Yang, C.C. Hsu and E.S. Yang, IEEE Trans. Electron Dev. ED-41 (1994) 643. [4] J.W. Matthews and A.E. Blakeslee, J. Crystal Growth 27 (1974) 118. [5] K. Ploog, J. Crystal Growth 81 (1987) 304.
441
[6] W.C. Liu, W.C. Hsu, L.W. Laih and J.H. Tsai, Appl. Phys. Lett. 66 (1995) 1524. [7] H.R. Chen, C.Y. Chang, C.P. Lee, C.H. Huang, J.S. Tsang and K.L. Tsai, IEEE Electron Dev. Lett. EDL-15 (1994) 336. [8] S.S. Lu and C.C. Wu, IEEE Electron Dev. Lett. EDL-13 (1992) 468. [9] S.C. Lee, J.N. Kau and H.H. Lin, Appl. Phys. Lett. 45 (1984) 1114. [10] W.C. Liu and W.S. Lout, Solid-State Electron. 34 (1991) 717.