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GaAs MIS-like heterostructure FET employing two-dimensional hole gas
Surface
378
Science 174 (1986) 378-381 North-Holland. Amsterdam
A p-CHANNEL AlGaAs/ GaAs MIS-LIKE HET’EROSTRUCT’URE EMPLOYING TWO-DIMENSIONAL HOLE GAS K. OE, M. HIRANO,
FET
K. ABA1 and F. YANAGAWA
NTT Atsugi Electrical Communication Atsugi-shi, Kanagawa 243-01, Japan
Luhoratorres.
3-I. Morinosato
Wakamrva,
K. TSUBAKI NTT Murashino Electrical Tokyo 180, Japan Received
2 August
Communication
1985; accepted
Lrrboratones.
for publication
3-Y-l I, Mldoricho.
15 September
Musashrno-yhr.
1985
A p-channel AlGaAs/GaAs heterostructure FET which operates has been investigated for implementation in a complementary logic transconductances of 100 mS/mm at 77 K and 50 mS/mm at 300 device with 1 pm gate length. The improvement at 77 K is attributed the two-dimensional hole gas which was confirmed by Shubnikovvde
in MIS-transistor like mode circuit. Maximum values of K have been achieved in a to an increased mobility of Haas oscillations at 4.2 K.
1. Introduction There has been much interest shown of late in p-channel modulation doped heterostructure FETs (HFETs) based on p-AlGaAs/i-GaAs two-dimensional hole gas (2DHG) structure [l-3]. The achieved performances in these devices demonstrate the attractiveness of p-channel modulation doped HFET for use in a GaAs-based complementary integrated circuit. The realization of such circuits, however, requires a complicated layer structure that integrates two-dimensional electron gas (2DEG) and 2DHG. Very recently, a new type p-channel AlGaAs/GaAs 2DHG HFET which operates in the MIS-transistor like mode has been reported by the authors [4]. The p-channel device, which was fabricated on undoped AlGaAs/GaAs heterostructure. is simple and compatible with an integrated circuit technology, and it is considered that a complementary circuit scheme using a p-channel 2DHG HFET of this type will be most promising in future. But the reported performance of the devices is not yet comparable with those of the n-channel 2DEG HFETs. In this paper we report on trial to enhance the performance of the p-MIS HFET. which results in achievement of higher transconductances as grn = 100 mS/mm at 77 K and 50 mS/mm at room temperature. 0039-6028/86/$03.50 Physics Publishing
0 Elsevier Science Publishers B.V. (North-Holland Division) and Yamada Science Foundation
K. Oe et al. /A
p-channel AIGaAs/GaAs
MIS-like
heterostructure
FET
379
LANT GaAs( 50b AlGaAs( dt) GaAs (0.6um)
Fig. 1. Schematic cross section of the p-channel AlGaAs layer, d,, is 450 or 150 A.
2DHG
HFET.
The thickness
of the undoped
2. Device fabrication
A schematic cross section of the device is shown in fig. wafers were grown by molecular beam epitaxy (MBE) on semi-insulating GaAs substrates. An undoped 0.6 pm GaAs grown and was followed by undoped Al,,Ga,,As and a 50 A layer. The thickness of the second undoped Al,,Ga,, As layer, 150 A. The devices were fabricated using a self-aligned WB, that used to fabricate conventional, self-aligned gate GaAs reported in ref. [4].
1. The sample (100) oriented layer was first undoped GaAs d,, was 450 or gate similar to MESFETs as
3. Device performance It is well known that the extrinsic transconductances g, of FETs are much influenced by source resistance R, which consists of sheet resistance R,, and contact resistance R,.It is, therefore, essential to reduce R, to improve device performance. As R,, is inversely proportional to the implanted Be dose, more implanted Be is preferable from the point of the R,. Implanted Be causes Schottky characteristics of the HFETs to become inferior. As a result, two kinds of Be dose levels of 2 X lOi cm-* and 6 X lOi cm-* were applied in the device fabrication. It is found that R, is much influenced by the Ohmic metal material and is reduced to 0.6 s2 mm when AuZnNi and TiAu metal structure is used. Fig. 2 shows the g, dependence of the p-HFET on R,.The undoped AlGaAs layer of the device is 450 A thick, and the gate length is 1 pm. It is seen that g, was enhanced by as much as a factor of two by reducing R, and that g, values as high as 80 mS/mm at 77 K and 40 mS/mm at 300 K were obtained. The dramatic improvement in transconductance can be attributed to an increase in hole mobility. The two dimensionality of the holes in the device is confirmed by angular-dependent Shubnikov-de Haas measurements by means of applied gate bias at 4.2 K. In the current-voltage characteristic of the device, it is confirmed that the drain saturation current Z,, obeys the square law of gate voltage (VP - V,,) [4].
380
K. Oe et al. / A p-channel AIGaAs/GaAs
MIS-like
heterostructure
FET
vg-vth=-o.5v 77 K
Lg=l
urn
2100. E z E 0-lE5
‘\
0 ‘\
‘.
‘.
0.
‘.
..
‘-._
300
‘._
-- 0_
K
”
20.
cn
lo-
77 K 0
‘@._
loo‘ii‘ E 503;
5-
-- --__ 0
2-
_-- ‘._
005
0.5 R,
1
(n.mm)
Fig. 2. Transconductance Fig. 3. Transconductance circles (0) show intrinsic
g,
2
5
10
20
Lg (urn) dependence
of the p-HFET
on the source
g, (0) dependence of the p-HFET transconductance gm,,.
resistance
on the gate length
K,. at 77 K. Solid
Room-temperature field effect mobility, pFt, = 340 cm’,? s, can be obtained from the gradient of this (Id,)‘/’ versus (I$ - V,,) curve. It is worth noting that this field mobility which is obtained in the 1 pm gate length device nearly
Fig. 4. Current-voltage d,=150A.
characteristic
of the 2DHG
HFET
with a 1 pm gate structure
at 77 K;
K. Oe et al. / A p-channel AI&As/
GaAs MIS-like
heterostructure
FET
381
corresponds to a Hall mobility of the 2DHG at room temperature. This might suggest that the device performance is mainly governed by the hole mobility at room temperature. We can expect to enhance further the device performance by thinning the undoOped AlGaAs layer. Fig. 3 shows the g, dependence of the devices with 150 A AlGaAs layer on the gate length at 77 K. Transconductance g, as high as 100 mS/mm was obtained in the 1 pm gate device whose FET characteristic is shown in fig. 4. Taking account of the R,,intrinsic transconductance g,, which is shown by solid circles in the figure can be calculated by the usual equation. It should be noted that g,, increases gradually by decreasing the gate length even when the gate becomes as short as 1 pm. So, we can expect higher performance of the device by reducing gate length to less than 1 pm. Values of 50 mS/mm g, obtained in the device at 300 K also demonstrate the feasibility of the implementation of complementary logic using 2DEG- and 2DHG-HFETs at even room temperature.
4. Summary Transconductances g, as high as 100 mS/mm at 77 K and 50 mS/mm at 300 K were obtainedOin p-channel AlGaAs/GaAs MIS-like HFETs with 1 pm gate length and 150 A undoped AlGaAs layers. The improvement in transconductance at 77 K is attributed to an increased mobility of the 2DHG which was confirmed by SdH oscillations at 4.2 K. These results demonstrate the feasibility of the implementation of complementary logic using 2DEG- and 2DHG-HFETs at both 77 K and 300 K.
Acknowledgements The authors are indebted to Y. Imamura for valuable discussions relating to MBE growth and T. Mizutani for helpful discussions on FET characteristics. They also thank K. Maezawa for lamp annealing.
References [1] H.L. Stormer, K. Baldwin, A.C. Gossard and W. Wiegmann, Appl. Phys. Letters 44 (1984) 1062. [2] S. Tiwari and W.I. Wang, IEEE Electron Device Letters EDL-5 (1984) 333. [3] M. Hirano, K. Oe and F. Yanagawa, Japan. J. Appl. Phys. 23 (1984) L868. [4] K. Oe, M. Hirano, K. Arai and F. Yanagawa, Japan. J. Appl. Phys. 24 (1985) L335.
378
Science 174 (1986) 378-381 North-Holland. Amsterdam
A p-CHANNEL AlGaAs/ GaAs MIS-LIKE HET’EROSTRUCT’URE EMPLOYING TWO-DIMENSIONAL HOLE GAS K. OE, M. HIRANO,
FET
K. ABA1 and F. YANAGAWA
NTT Atsugi Electrical Communication Atsugi-shi, Kanagawa 243-01, Japan
Luhoratorres.
3-I. Morinosato
Wakamrva,
K. TSUBAKI NTT Murashino Electrical Tokyo 180, Japan Received
2 August
Communication
1985; accepted
Lrrboratones.
for publication
3-Y-l I, Mldoricho.
15 September
Musashrno-yhr.
1985
A p-channel AlGaAs/GaAs heterostructure FET which operates has been investigated for implementation in a complementary logic transconductances of 100 mS/mm at 77 K and 50 mS/mm at 300 device with 1 pm gate length. The improvement at 77 K is attributed the two-dimensional hole gas which was confirmed by Shubnikovvde
in MIS-transistor like mode circuit. Maximum values of K have been achieved in a to an increased mobility of Haas oscillations at 4.2 K.
1. Introduction There has been much interest shown of late in p-channel modulation doped heterostructure FETs (HFETs) based on p-AlGaAs/i-GaAs two-dimensional hole gas (2DHG) structure [l-3]. The achieved performances in these devices demonstrate the attractiveness of p-channel modulation doped HFET for use in a GaAs-based complementary integrated circuit. The realization of such circuits, however, requires a complicated layer structure that integrates two-dimensional electron gas (2DEG) and 2DHG. Very recently, a new type p-channel AlGaAs/GaAs 2DHG HFET which operates in the MIS-transistor like mode has been reported by the authors [4]. The p-channel device, which was fabricated on undoped AlGaAs/GaAs heterostructure. is simple and compatible with an integrated circuit technology, and it is considered that a complementary circuit scheme using a p-channel 2DHG HFET of this type will be most promising in future. But the reported performance of the devices is not yet comparable with those of the n-channel 2DEG HFETs. In this paper we report on trial to enhance the performance of the p-MIS HFET. which results in achievement of higher transconductances as grn = 100 mS/mm at 77 K and 50 mS/mm at room temperature. 0039-6028/86/$03.50 Physics Publishing
0 Elsevier Science Publishers B.V. (North-Holland Division) and Yamada Science Foundation
K. Oe et al. /A
p-channel AIGaAs/GaAs
MIS-like
heterostructure
FET
379
LANT GaAs( 50b AlGaAs( dt) GaAs (0.6um)
Fig. 1. Schematic cross section of the p-channel AlGaAs layer, d,, is 450 or 150 A.
2DHG
HFET.
The thickness
of the undoped
2. Device fabrication
A schematic cross section of the device is shown in fig. wafers were grown by molecular beam epitaxy (MBE) on semi-insulating GaAs substrates. An undoped 0.6 pm GaAs grown and was followed by undoped Al,,Ga,,As and a 50 A layer. The thickness of the second undoped Al,,Ga,, As layer, 150 A. The devices were fabricated using a self-aligned WB, that used to fabricate conventional, self-aligned gate GaAs reported in ref. [4].
1. The sample (100) oriented layer was first undoped GaAs d,, was 450 or gate similar to MESFETs as
3. Device performance It is well known that the extrinsic transconductances g, of FETs are much influenced by source resistance R, which consists of sheet resistance R,, and contact resistance R,.It is, therefore, essential to reduce R, to improve device performance. As R,, is inversely proportional to the implanted Be dose, more implanted Be is preferable from the point of the R,. Implanted Be causes Schottky characteristics of the HFETs to become inferior. As a result, two kinds of Be dose levels of 2 X lOi cm-* and 6 X lOi cm-* were applied in the device fabrication. It is found that R, is much influenced by the Ohmic metal material and is reduced to 0.6 s2 mm when AuZnNi and TiAu metal structure is used. Fig. 2 shows the g, dependence of the p-HFET on R,.The undoped AlGaAs layer of the device is 450 A thick, and the gate length is 1 pm. It is seen that g, was enhanced by as much as a factor of two by reducing R, and that g, values as high as 80 mS/mm at 77 K and 40 mS/mm at 300 K were obtained. The dramatic improvement in transconductance can be attributed to an increase in hole mobility. The two dimensionality of the holes in the device is confirmed by angular-dependent Shubnikov-de Haas measurements by means of applied gate bias at 4.2 K. In the current-voltage characteristic of the device, it is confirmed that the drain saturation current Z,, obeys the square law of gate voltage (VP - V,,) [4].
380
K. Oe et al. / A p-channel AIGaAs/GaAs
MIS-like
heterostructure
FET
vg-vth=-o.5v 77 K
Lg=l
urn
2100. E z E 0-lE5
‘\
0 ‘\
‘.
‘.
0.
‘.
..
‘-._
300
‘._
-- 0_
K
”
20.
cn
lo-
77 K 0
‘@._
loo‘ii‘ E 503;
5-
-- --__ 0
2-
_-- ‘._
005
0.5 R,
1
(n.mm)
Fig. 2. Transconductance Fig. 3. Transconductance circles (0) show intrinsic
g,
2
5
10
20
Lg (urn) dependence
of the p-HFET
on the source
g, (0) dependence of the p-HFET transconductance gm,,.
resistance
on the gate length
K,. at 77 K. Solid
Room-temperature field effect mobility, pFt, = 340 cm’,? s, can be obtained from the gradient of this (Id,)‘/’ versus (I$ - V,,) curve. It is worth noting that this field mobility which is obtained in the 1 pm gate length device nearly
Fig. 4. Current-voltage d,=150A.
characteristic
of the 2DHG
HFET
with a 1 pm gate structure
at 77 K;
K. Oe et al. / A p-channel AI&As/
GaAs MIS-like
heterostructure
FET
381
corresponds to a Hall mobility of the 2DHG at room temperature. This might suggest that the device performance is mainly governed by the hole mobility at room temperature. We can expect to enhance further the device performance by thinning the undoOped AlGaAs layer. Fig. 3 shows the g, dependence of the devices with 150 A AlGaAs layer on the gate length at 77 K. Transconductance g, as high as 100 mS/mm was obtained in the 1 pm gate device whose FET characteristic is shown in fig. 4. Taking account of the R,,intrinsic transconductance g,, which is shown by solid circles in the figure can be calculated by the usual equation. It should be noted that g,, increases gradually by decreasing the gate length even when the gate becomes as short as 1 pm. So, we can expect higher performance of the device by reducing gate length to less than 1 pm. Values of 50 mS/mm g, obtained in the device at 300 K also demonstrate the feasibility of the implementation of complementary logic using 2DEG- and 2DHG-HFETs at even room temperature.
4. Summary Transconductances g, as high as 100 mS/mm at 77 K and 50 mS/mm at 300 K were obtainedOin p-channel AlGaAs/GaAs MIS-like HFETs with 1 pm gate length and 150 A undoped AlGaAs layers. The improvement in transconductance at 77 K is attributed to an increased mobility of the 2DHG which was confirmed by SdH oscillations at 4.2 K. These results demonstrate the feasibility of the implementation of complementary logic using 2DEG- and 2DHG-HFETs at both 77 K and 300 K.
Acknowledgements The authors are indebted to Y. Imamura for valuable discussions relating to MBE growth and T. Mizutani for helpful discussions on FET characteristics. They also thank K. Maezawa for lamp annealing.
References [1] H.L. Stormer, K. Baldwin, A.C. Gossard and W. Wiegmann, Appl. Phys. Letters 44 (1984) 1062. [2] S. Tiwari and W.I. Wang, IEEE Electron Device Letters EDL-5 (1984) 333. [3] M. Hirano, K. Oe and F. Yanagawa, Japan. J. Appl. Phys. 23 (1984) L868. [4] K. Oe, M. Hirano, K. Arai and F. Yanagawa, Japan. J. Appl. Phys. 24 (1985) L335.