IEEE TRANSACTIONS ON FL.b.CTKON DEVIChS, VOL 15, NO 2 , FbBRUARY IYXX I39

Charge Control, DC, and RF Performance of a 0.35- pm Pseudomorphic AIGaAsLnGaAs Modulation-

Doped Field-Effect Transistor LO1 D. NGUYEN, STUDENT MEMBER, IEEE, WILLIAM J. SCHAFF, PAUL J. TASKER,

ALLEN N. LEPORE, STUDENT MEMBER, IEEE, LAUREN F. PALMATEER, MARK C. FOISY, A N D

LESTER F. EASTMAN, FELLOW, IEEE

Abstract-This paper describes the first study of charge control in conjunction with dc and rf performance of 0.35-pm gate-length pseu- domorphic AlGaAs/InGaAs MODFET's. Using C-V measurements, we estimate that a two-dimensional electron gas (2DEG) density as high as 1.0 x 10'' cm-' can be accumulated in the InGaAs channel at 77 K before the gate begins to modulate parasitic charges in the AIGaAs. This improvement in charge control, about 10-30 percent over a typ- ical AIGaAs/GaAs MODFET, may partially be responsible for the su- perior dc and rf performance of the AIGaAs/InCaAs MODFET. At room temperature, the 0.35pm gate-length devices reported here give a maximum dc voltage gain g,,,/g,,, of 32 and a current gain cutoff frequency fT of 46 GHz. These results are state of the art for MOD- FET's of similar gate length.

I. INTRODUCTION VER THE PAST several years, the MODFET has 0 attracted much attention in high-speed digital and mi-

crowave device applications. Lattice-matched Al- GaAs /GaAs MODFET's have demonstrated a switching speed of 5.8 ps/gate at 77 K [I] and a room temperature noise figure of 2.7 dB with an associated gain of 3.8 dB at 62 GHz [2]. In spite of these impressive results, there are problems associated with the AlGaAs/GaAs system. n-type AlGaAs with an A1 mole fraction greater than about 22 percent tends to have deep levels that are cited to be the cause of the persistent photoconductivity effect [3] and I-V collapse in AIGaAs/GaAs MODFET's at low tem- peratures [4].

More recently, GaAs/InGaAs [5] and then Al- GaAs/InGaAs [6] systems have been introduced. The InGaAs, which is lattice mismatched to GaAs substrates, is kept thin enough so that the mismatch is accommodated entirely as elastic strain resulting in an essentially dislo- cation-free pseudomorphic material [5], [7]. In compar- ing to the AlGaAs/GaAs system, the use of pseudo-

Manuscript received March 6, 1987; revised September 16, 1987. L. D. Nguyen was supported under a Fellowship from Honeywell. This work was supported in part by the Joint Services Electronics Program, the Army Research Office, IBM E. Fishkill, and the GE Electronics Laboratory, Syr- acuse, NY, and was performed in part at the National Nanofabrication Fa- cility, which is partially supported by the National Science Foundation un- der Grant ECS-8200312.

The authors are with the School of Electrical Engineering, and the Na- tional Nanofabrication Facility, Cornell University, Ithaca, NY 14853.

IEEE Log Number 8718172.

morphic InGaAs channels allows either a similar conduction band discontinuity between the AlGaAs layer and the channel with a lower A1 mole fraction or a larger discontinuity for the same A1 mole fraction. Furthermore, the InGaAs channel should lead to better device perfor- mance due to the superior transport properties of In- GaAs[8]. A higher output resistance, 520 fl * mm for 1- pm devices [9], and a lower noise figure, 2.4 dB with an associated gain of 4.4 dB at 62 GHz [lo], have been dem- onstrated in the AlGaAs /InGaAs material system.

In the following sections, we will demonstrate that the AlGaAs /InGaAs MODFET offers better charge control, smaller output conductance, and higher current gain cut- off frequency than previously published AlGaAs/GaAs MODFET's of similar gate lengths.

11. DEVICE STRUCTURE AND FABRICATIONS The AlGaAs/InGaAs MODFET layers used for this

study were grown by molecular-beam epitaxy. A typical structure is shown in Fig. l(a). First, a 1-pm unintention- ally doped GaAs buffer was grown at 580°C on an un- dope! low-pressure LEC GaAs substrate followed by a 170-A undoped Ino 15Gao s5As channel grown at 520°C. The substrate temperatye was then ramped to 710°C dur- ing growth ,Of the 25-A undoped Alo 15G%85A~ spacer. Next, 375-A n+ Alo 15G% 8 s A ~ was gr2wn followed by graded-composition AlGaAs over 100 A to GaAs for a total of 333-A n' cap. The conduction band diagram of this structure is shown in Fig. l(b). The conduction band discontinuity -0.23 eV at the AIo 15Gaos5As/ Ino 15Gao8sA~ interface is taken to be the sum of the discontinuities in the Al, lsG% s5As/GaAs and GaAs/Ino 15Gaos5As systems. We use 0.11 eV for the former [ 1 11 and 0.12 eV for the latter[7]. For comparison, a discontinuity of 0.23 eV is achieved in the Al- GaAs/GaAs system with twice the A1 mole fraction [ l l ] .

FATFET geometries (96 X 96 pm) and submicrometer FET's (0.35 x 300 pm) were fabricated on the same layer using a hybrid optical/electron-beam lithography process. Mesa isolFtion wasofollowed by Ni/AuGe/Ag/Au ( 100 A /900 A /lo00 A /lo00 A ) ohmic contact metalliza- tion. The ohmic metal was alloyed at a peak temperature

0018-9383/88/0200-0139$01.00 O 1988 IEEE

IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 35, NO. 2, FEBRUARY 1988

I 3758, JX10'' crn-' A1.1sGa.&s I 1708, In.rsGa.& channel

1 urn undoped GaAs buffer

Semi-insulating GaAs substrate

(a)

\ GATE BIAS = -0.3 VOLTS

0 100 200 300 400 500 600 700 800 900 1000 DISTANCE REIATNE TO THE GATE LOCATION (A)

(b) Fig. 1 . (a) A typical structure of a pseudomorphic AlGaAs/InGaAs

MODFET and (b) the associated conduction band diagram.

of 57OoC, resulting in a contact resistance of about 0.4 s2 * mm. Nominally 0.35-pm gates were defined at the cen- ter of a 3-pm source-drain spacing by electron-beam di- rect write. A mixture of NH40H : H 2 0 2 : H 2 0 adjusted to a p h 7.1 was used to recess the gate region below the GaAs cap layer immediately before gate ev!poration. The gate met!l consists of 400- A Ti and 3500- A Au. Finally, a 3500-A Au overlay metallization was deposited to fa- cilitate bonding.

111. CHARGE CONTROL Fig. 2 shows the C-Vprofile of a 96 X 96 pm FATFET

measured at 77 K in the dark. Also shown for comparison is the C-V of a typical AlGaAs /GaAs MODFET (A1 per- cent = 0.3). To characterize the charge control of differ- ent MODFET structures, we follow the procedure in [ 121 to estimate the 2DEG density at the onset of parasitic charge modulation in the AlGaAs, denoted by nsm, and use it as a figure of merit. n,, is computed by integrating the C-V curve from the threshold voltage V,, to the volt- age at which the capacitance sharply rises above its nom- inal value. A high value of nsm does not only allow a large current swing, but also tends to yield better device per- formance [12], [13]. In general, high doping in the Al- GaAs, a small spacer layer, and a large effective conduc- tion band discontinuity (the difference between the donor level in the AlGaAs and the conduction band of the In- GaAs or GaAs channel) lead to high values of n,, [12], [13]-all of which can be readily achieved in the pseu-

s

-0.1 0.1 0.3 0.5 0.7 0.9 1.1 1.3

GATE-SOURCE VOLTAGE MINUS THRESHOLD VOLTAGE (Volts)

Fig. 2 . Capacitance profiles of 96 x 96 pm FATFET's at 77 K .

- Modeled Result Experimental Data

-1.4 -1.2 -1.0 -0.8 -0.6 -0.4 -0 .2 0.0 0.2 0.4

GATE TO SOURCE VOLTAGE (Volts)

Fig. 3 . Simulated C-V profile versus experimental data at 77 K.

domorphic AlGaAs/InGaAs MODFET. In this work, an nsm value of 1.0 x 10I2 cmp2 has been obtained at 77 K in the Alo.lsGao.8sAs /Ino. IsGao.8sAs structure compared to that of 0.7 X 10l2 cm-2 in the Alo.30G~.70As/GaAs struc- ture. The increase in nsm, we believe, is largely due to the shallower donor in the 0.15 A1 mole fraction AlGaAs, which results in an increase in the effective conduction band discontinuity. n,y,,, values as high as 1.5 X 10l2 cm-* at 77 K and 1.1 x IO'* cm-2 at 300 K for Al- GaAs/InGaAs structures with higher A1 mole fractions (0.20 I x 5 0.35) have been reported by our laboratory

To complement our experimental data, we have modi- fied a classical (Fermi-Dirac statistic) I-D charge control model for the AlGaAs/GaAs system [I51 to allow the modeling of the InGaAs channel [ 141. Fig. 3 shows a typ- ical simulated C-V profile versus experimental data at 77 K. The agreement is generally good except near and after the onset of parasitic charge modulation in the AlGaAs. Currently, we are investigating this discrepancy and de- tails of our study will be reported at a later date.

~ 4 1 .

IV. DC PERFORMANCE The I-Vand transfer characteristics of a typical 0.35 X

300 pm device are shown in Figs. 4 and 5 , respectively. The maximum extrinsic transconductance g,, is 250

NGUYEN P I (11 CHARGE CONTROL. DC. A N D RF PERFORMANCE OF 0 7 5 pm MODFET 141

250 1

2.5 VD (volts) 0 . 0

Fig. 4 . Current-voltage characteristic of a typical 0.35 X 300 pm Al- GaAs/InGaAs MODFET. The top curve corresponds to V,, = 0 . 8 V and V,, = -0 .2 V/step.

i /

0 . 0 2Bo.o ID hAh) 0 . 0

Fig. 5 . Extrinsic transconductance versus drain current. The maximum 8,- is 250 mS/mm.

mS/mm, which is somewhat low for a 0.35-pm Al- GaAs/InGaAs MODFET due to a high source resistance of 1.7 D . mm (measured by the end resistance method). The dc output conductance gd is extremely small for a 0.35-pm device, about 2.3 mS or 7.7 mS/mm. We at- tribute this desirable characteristic to the improved con- finement of electrons in the InGaAs quantum well (see Fig. 1 (b)). Of more importance is the ratio of g,,,/g, of a device (the maximum dc voltage gain). Here it is about 3 2 , the highest reported yet for a MODFET of similar gate length. For comparison, values of 10-15 are more typical for 0.25-pm AlGaAs /GaAs MODFET’s and GaAs MESFET’s [161, 1171.

V. RF PERFORMANCE The S-parameters were measured from 2 to 18 GHz at

room temperature. Shown in Fig. 6 and Table I are an equivalent circuit model and its circuit element values when biased to give maximumfT. As can be seen in Fig. 7, excellent agreement is achieved between the measured S-parameters and modeled results. Fig. 8 shows the cur- rent gain 1 h z l \ * versus frequency. An extrapolation of the experimental data at a rate of -6 dB/octave gives an fT

of 46 GHz. This result is state of the art for MODFET’s of similar gate length. A plot offT as a function of drain bias current is given in Fig. 9.

Using the above equivalent circuit model, we estimate a unity power gain cutoff frequency (A,,;,,) of 70 GHz. This low value nfi,,,, is mainly due to the large size of our devices ( W = 300 p m ) and, to a lesser extent, high source resistance ( R , = 5.8 Q ) . Appropriate device scal-

0 I 0

Source Source

Fig. 6. Equivalent circuit model of MODFET.

90

-j50

0

Fig. 7 . S-parameters and modelled results ( Vo,, = 2.0 V , Vx3 = 0.2 V , I , / , = 34 mA) . The experimental data and modeled results are shown as black dots and triangles, respectively.

TABLE 1 EQUIVALENT CIRCUIT PARAMETERS OF A N AIGaAs/InGaAs MODEFET

(V, ,$ = 2 V. V,, = 0.2 V , I d , = 34 m A . )

~~ Pararnerer Value

9,” 132 mS

2 3 piec

cv 0 394 pF

0 0 3 1 pF

Cd, 0041 pF

0 0 9 2 pF

c o g

CY 8 8 7 mS

5 2 4 n

3 0 0 n

4 4 2 n

5 7 9 n

0 172 nH

0 112 nH

L, 0025 nH

ings and further reduction in the source resistance should result in significant improvements in fmax ( indeed, an f,,, of 135 GHz has been recently reported by us with 0.3 X 75 pm devices) [14]. We would also like to point out that the RF output conductance in our equivalent circuit model is significantly higher (by a factor of - 3 . 5 ) than

IEEE TRANSACTIONS ON ELECTRON DEVICES. VOI. 3 s . N O 2 . FF.RKUARY 19x8 142

30

2 5

- 2 0 m v

5 1 5

z w LL

3 u 1 0

5

0

1

\, EXPERIMENTAL DATA

- MODELLED RESULT

MODELLED RESULT WITH lNOUCTORS REMOVED

- E W O L A T E D AT -6 OB/ OCTAVE

\

\

\

\ \ FT = 46 GHZ

1 I I , , l \ I , I , . J

5 1 0 5 0 1 0 0

FREOUENCY (GHZ)

Fig. 8. Current gain versus frequency ( V,,, = 2 . 0 V , = 0.2 V. /t,s = 34 mA ) .

J

0 10 20 30 40 50 60 70 80 D W N CURREM (mA)

Fig. 9. Extrapolatedf; versus drain bias current ( V<,< = 2.0 V )

its dc value, which further reduces thef,,,. Currently, we do not yet have a full explanation for this discrepancy.

VI. AlGaAs /InGaAs VERSUS AlGaAs /GaAs Recent controversies concerning the extrapolation pro-

cedure to obtain the fr value [18]-[20] cause difficulties in evaluating the intrinsic performance of the Al- GaAs/InGaAs and AlGaAs/GaAs MODFET’s. As we pointed out in [ 181, an arbitrary extrapolation of the 1 h2 , 1 to unity tends to give an artifically high f r value due to the presence of bond wire inductances. For example, while it is widely accepted that state-of-the-art i-pm gate- length AlGaAs/GaAs MODFET’s have anfr - 80 GHz [21], a closer look at the published data in [21] reveals that the 80-GHz value is obtained by incorrectly extrap- olating the experimental data (the extrapolated curve does not have the required - 6-dB/octave slope) [20]. Our best estimate for thefTof the device in [21] is -45 GHz, which is in close agreement with the ratio g,,/27r C,,7 = 5 1 GHz from its equivalent circuit model.

While we do not attempt to resolve these controversies in this paper, we feel there is a necessity to reanalyze the published fr data of state-of-the-art devices to establish a

1 0 0 90 80

70

60

50 - N

6- 40

t 0 30 z - E -

20

1 0

AIGaAs/lnGaAs MODFEls

MODFETs

I I I i 1 I I I I

0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 1

GATE LENGTH (UM) 2

Fig. 10. Calculated f, versu\ gate length of btate-of-the-art MODFET’\.

TABLE 11 E Q ~ I \ 41 F\T CiRCL I T PARAMFTI R\ O t SI 2 I t - 0 1 - 1 H I -AKr MODFbT’\

- 1 ,Ga,,Ar/ln ,Ga,,Ar AlGa ASiGaAS

MODFET, MODFETr

-~

ILL86 lLUGe86 ThirWork ILL84 NEC86 TOS85 GE85

1221

1 0 0

290

0 580

0 033

77 9

21 5

21

I101

0 2 5

150

0 186

0 0 2 1

82 6

7 1

1231

0 35 1 00

300 290

0 394 0 377

0 0 3 1 0 0 2 6

132 40 6

46 18

53 17

1241 I251

0 5 0 0 2 5

200 200

0 2 4 0 0 180

0 0 1 0 0 0 2 0

4 4 0 5 2 0

45 46

3 1 47

1211

0 25

150

0 270

0 0 1 5

85 7

80

51

meaningful comparison. To this end we have chosen to use the fT obtained by taking the ratio of g,,,(,/2a Cy, from the equivalent circuit model as a figure of merit. This ap- proach benefits from the widely available data in the lit- erature and avoids the misinterpretation of the experimen- tal data due to the presence of bond wire inductances. Generally, the f r calculated by this method, though not exact, tends to agree with the fr value obtained by cor- rectly extrapolating the I h 2 , \ at a rate of -6 dB/octave. In Table I1 we summarize the published equivalent circuit model element values of state-of-the art MODFET’s. Also shown are the calculatedfT = g,,,,/27r CR, for each device. A plot offr versus gate length for these devices is given in Fig. 10. From this plot, it is clear that Al- GaAs/InGaAs MODFET’s have higher fT than Al- GaAs/GaAs MODFET’s of similar gate lengths.

VII. CONCLUSION The AlGaAs /InGaAs MODFET has better charge eon-

trol, smaller output conductance, and higher current gain cutoff frequency than the AlGaAs/GaAs MODFET. We

NGUYEN el al CHARGE CONTROL, DC. AND RF PERFORMANCE OF 0 3 S - p n MODFET 143

attribute these improvements to the larger effective con- duction band discontinuity, the improved confinement of electrons in the InGaAs channel, and the better transport properties in the AlGaAs/InGaAs system. The 0.35-pm gate-length MODFET’s reported here give a maximum dc voltage gain of 32 and current gain cutoff frequency of 46 GHz. These results are state of the art for MODFET’s of similar gate length. Our analysis clearly shows that thef, of the AlGaAs/InGaAs MODFET is higher than that of the AlGaAs/GaAs MODFET at all gate lengths, which helps explaining the superior RF performance of the for- mer.

ACKNOWLEDGMENT The authors gratefully acknowledge helpful discussions

with S. Anderson, and D. Radulescu, and technical as- sistance from J . Berry, D. Shire, G. W. Wang, and D. Barker. We would like to thank E. Weaver for her prep- aration of the manuscript. We would also like to thank B. Ford of Harris Corp. for his donation of the GaAs sub- strates used in this work.

REFERENCES N. J . Shah, S.-S. Pei, C. W. Tu, and R. C. Tiberio, “Gate-length dependence of the speed of SSI circuits using submicrometer selec- tively doped heterostructure transistor technology,” IEEE Trans. Electron Devices, vol. ED-33, pp. 543-547, May 1986. K. H. G. Duh, P. C. Chao, P. M. Smith, L. F. Lester, and B. R. Lee, “60 GHz low-noise high-electron mobility transistors,” Elec- tron. Lett., vol. 22 , pp, 647-649, June 5 , 1986. T. J. Drummond, W. Kopp, R . Fischer, H. Morkog, R . E. Thorne, and A. Y. Cho, “Photoconductivity effect in extremely high mobility modulation doped (Al,Ga)As/GaAs heterostructures,” J . Appl. Phys., vol. 53, p. 1238, Feb. 1982. R. Fischer, T . J. Drummond, J. Klem, W. Kopp, T. S. Henderson, D. Perrachione, and H . Morkop, “On the collapse of drain I -V char- acteristics in modulation doped FET’s at cryogenic temperatures.” IEEE Truns. Elecrron Devices, vol. ED-31, p. 1028, Aug. 1984. J . J. Rosenberg, M. Benlamri. P. D. Kirchner, J . M. Woodall, and G. D. Pettit, “An In, ,,Ga,,,As/GaAs pseudomorphic single quan- tum well HEMT,” IEEE Electron Device Lett., vol. EDL-6, no. I O , Oct. 1985. A. Ketterson, M. Moloney, W. T. Masselink, C. K. Peng. J. Klem, R. Fischer, W. Kopp, and H. Morkof, “High transconductance InGaAs /AlGaAs pseudomorphic modulation-doped field effect tran- sistors,” IEEE Electron Device Lett., vol. EDL-6, pp. 628-630, Dec. 1985. W. J. Schaff, L. F. Eastman, K. L. Kavanagh, P. D. Kirchner. G. D. Pettit, and J. M. Woodall, “Capacitance characterization of GaInAs grown on GaAs by MBE,” presented at the 1986 Electron. Materials Conf., Univ. of Mass., Amherst, MA, June 25-27, 1986. A. Cappy, B. Carnez, R. Fauquembergues, G. Salmer, and E. Con- stant, “Comparative potential performance of Si, GaAs, GaInAs, InAs submicrometer-gate FET’s,” IEEE Trans. Electron Devices, vol. ED- 27, Nov. 1980. L. F. Palmateer, W. J . Schatf, P. J . Tasker, and L. F. Eastman, “Improved output resistance graded channel in AI,, l sCq arAs/Gal~,In., As/GaAs MODFETs,” private communica- tion. T. Henderson, M. I. Aksun, C. K. Peng, H. Morkog, P. C. Chao, P. M. Smith. K.-H. G. Duh, and L. F. Lester, “Microwave perfor- mance of a quarter-micrometer gate low-noise pseudomorphic In- GaAs /AlGaAs modulation-doped field eft‘ect transistor,’’ IEEE Elec- tron Device Lett., vol. EDL-7, pp. 649-651, Dec. 1986. J . Batey and S. L. Wright, “Energy band alignment in GaAs: (A1,Ga)As heterostructures: The dependence of alloy composition,” J . Appl. Phys., vol. 59, Jan. 1, 1986. L. H. Camnitz, P. J . Tasker, P. A . Maki, H . Lee, J . Huang, and L. F. Eastman, “The role of charge control on drift mobility in Al-

GaAs/GaAs MODFET’s,” in Proc. IEEEICornell Con$ Advanced Concepts in High Speed Semiconductor Devices and Circuits, pp. 199- 208, 1985.

[13] L. H. Camnitz, Ph.D. dissertation Cornell Univ., Ithaca, NY, 1985. [14] L. D. Nguyen, M.C. Foisy, P. J . Tasker, W. J. Schaff, A. N. Lepore,

and L. F. Eastman, “Carrier deconfinement limited velocity in pseu- domorphic AlGaAs /InGaAs modulation-doped field-effect transistors (MODFETs),” presented at the 1987 IEEEiCornell Conf. on Ad- vanced Concepts in High Speed Semiconductor Devices and Circuit, Cornell Univ., Ithaca, NY, Aug. 10-12, 1987.

[I51 M. C. Foisy, J . C. Huang, P. J . Tasker, and L. F. Eastman, “Mod- ulation efficiency limited high frequency performance of the MOD- FET,” presented at the 2nd Topical Meeting on Picosecond Elec- tronics and Optoelectronics, Hyatt Lake Tahoe, NV, Jan. 14-16, 1987.

1161 L. H. Camnitz, P. J . Tasker, H. Lee, D. van der Merwe, and L. F. Eastman, “Microwave characterization of very high transconduc- tance MODFET,” in IEDM Tech. Dig., pp. 360-363, 1984.

1171 P. C. Chao, P. M. Smith, S . Wanuga, W. H. Perkins, and E. D. Wolf, “Channel-length effects in quarter-micrometer gate-length GaAs MESFET’s,” IEEE Electron Device Lett., vol. EDL-4. Sept. 1983.

[I81 L. D. Nguyeu, P. 1. Tasker, and W. J.Schaff, “Comment on ‘A new low-noise AIGaAs/GaAs ZDEG FET with a surface undoped layer,”’ IEEE Trans. Electron Devices, vol. ED-34, p. 1187. May 1987.

[I91 H. Hida, K. Ohata, Y. Suzuki, and H.Toyoshima, “Reply to ’Com- ments on “A new low-noise AIGaAs/GaAs ZDEG FET with a sur- face undoped layer,”’” IEEE Trans. Electron Devices, vol. ED-34, p. 1187, May 1987.

[20] P. J . Tasker and L. F. Eastman, “The correct determination of in- trinsic f T of FET devices from measured microwave data,” presented at the 1 lth Workshop on Compound Semiconductor Devices and In- tegrated Circuits, Grainau, W. Germany, May 4-6, 1987.

[21] P. C. Chao, S. C. Palmateer, P. M. Smith, U.K. Mishra, K.-H. G. Duh, and J. C. M. Hwang, “Millimeter-wave low-noise high elec- tron mobility transistors,” IEEE Electron Device Lett., vol. EDL-6, Oct. 1985.

[22] A. A. Ketterson, W. T. Masselink, J . S . Gedymin, J. Klem, C.-K. Peng, W. F. Kopp, H. MorkoG, and K. R . Gleason, “Characteriza- tion of InGaAs/AIGaAs pseudomorphic modulation-doped field ef- fect transistors,” IEEE Trans. Electron Devices, vol. ED-33, May 1986.

1231 D. J . Arnold, R. Fischer, W. F . Kopp, T. S. Henderson, and H. Morkoq, “Microwave characterization of (Al,Ga)As/GaAs modula- tion-doped FET’s: Bias dependence of small-signal parameters,” IEEE Truns. Electron Devices, vol. ED-31, Oct. 1984.

1241 H. Hida, K. Ohata, Y . Suzuki, and H. Toyoshima, “A new low-noise AIGaAs/GaAs 2DEG FET with a surface undoped layer,” IEEE Truns. Electron Devices, vol. ED-33, May 1986.

12.51 K. Kamei, H. Kawasaki, S . Hori, K . Shibata, M. Higashiura, M. 0. Watanabe, and Y . Ashizawa, “Extremely low-noise 0.25 wm-gate HEMTs,” presented at the Int. Symp. GaAs and Related Compounds, Karuizawa, Japan, 1985.

Lei D. Nguyen (S’83) was born i n Saigon, Viet- nam, in 1959. He received the A S degree (with high Honors) in engineering science from Broome Community College, Binghamton, NY, in 1982 and the B.S. degree (with high distinction) in electrical engineering from Cornell University, Ithaca, NY, in 1984 He is currently working to- ward the Ph.D degree m electrical engineering at Cornell Univer\ity His research involves the de- sign, fabrication, and characterization of pseudo- morphic AIGaAs/InGaAs modulation-doped

field-effect transi\tor\ (MODFET’s) for millimeter-wave applications He was a recipient of a RCA Graduate Fellowship in 1984 and a Honeywell Graduate Fellowship in 1985, 1986, and 1987

During the sumiiiers of 1985. 1986, and 1987, he was with the GaAs millimeter-wave section of the Honeywell Physical Sciences Center in Bloommgton, MN, a\ a Summer Intern. His work at Honeywell concerned the fabrication and characterization of AlGaAs /GaAs and Al- GaAs/InGaAs MODFET’s.

Mr. Nguyen is a member of the Tau Beta Pi

144 IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 35, NO. 2, FEBRUARY 1988

William J. Schaff was born in Buffalo, NY. He received the B.S. degree in electrical engineering, from Cornell in 1978.

During 1978 and 1979, he was an Engineer with the Hams Corporation, RF Communications Division, in Rochester, NY, performing systems design work. In September 1979, he resumed graduate research at Cornell. During this time, he has been retained as a consultant by the General Electric Company, Discrete Semiconductor De- vice Center, in Syracuse, NY, and Raytheon,

Lauren F. Palmateer received the B.S. degree in electrical engineering from Monmouth College, West Long Branch, NJ, in 1983. She is currently working toward the M.S./Ph.D. degrees at the School of Electrical Engineering, Cornell Univer- sity, Ithaca, NY.

While at Monmouth College from 1979 to 1983 she was also employed at Bell Laboratories, Crawford Hill, NJ, where she was technical assis- tant to Dr. Arno Penzias. There she was involved in radio astronomy using the millimeter-wave an-

Special Microwave Device Operation, Northborough, MA, in the area of deep-level transient spectroscopy. Upon completion of graduate thesis re- search in January 1984, he remained at Cornell on the research staff and continues to serve as an industrial consultant.

tenna at Crawford Hill. After graduating, she joined the GaAs Materials and Devices Group at the IBM Thomas J. Watson Research Center, York- town Heights, NY. She is currently on educational leave of absence from IBM. Her primary research efforts are in the design, fabrication, and char- acterization of AIInAs/GaInAs on InP substrate MODFET’s.

* *

Paul J. Tasker was born in Douglas, Isle of Man, in 1958. He received the B.Sc degree (First Class Honours) in physics and electronics in 1976 and the Ph.D. degree from the Department of Electri- cal and Electronic Engineering in 1983, both from Leeds University. His Ph.D. research was in the area of numencal modeling, 111-V semiconductor device processing, ion implantation, and dc and microwave charactenzation.

Upon completion of his Ph.D. degree he joined the Electrical Engineering Department of Cornell

Mark C. Foisy received the Sc.B. degree (with Honors) from Brown University, Providence, RI, in 1981. He is currently working toward the Ph.D. degree in electrical engineering at Cornell Uni- versity. His research is in computer modeling of the MODFET.

He has worked for IBM, Poughkeepsie, and AT&T Bell Laboratories, Murray Hill, NJ.

Mr. Foisy is a member of the Electron Devices Society, Tau Beta Pi, and Sigma XI.

University, Ithaca, NY, as a Research Associate. His main technical in- terests and experience are in the areas of microwave characterization and the modeling of semiconductor devices. As a Research Associate at Cor- nell, he is involved in research and overseeing graduate student education in the fields of microwave measurements, microwave circuit design, and 111-V semiconductor device modeling.

* Lester F. Eastman (A’53-M’SS-SM’SS-F’69) was born in Utica, NY, and received the B.S., M.S., and Ph.D. degrees from Cornell University in 1953, 1955, and 1957, respectively.

He joined the faculty of electrical engineering at Cornell University in 1957. He spent the 1978- 1979 year on leave at MIT’s Lincoln Laboratory. Since 1964, he has been involved pnmarily in graduate education and research in compound semiconductor materials and microwave devices. He has consulted for several laboratones and is

the Director of Cornell’s Joint Service Electronics Program. He was named the John LaPorte Given Foundation Chair Professor of

Engineering at Cornell in January 1985. Dr. Eastman has been a Fellow of the IEEE since 1969, and was the

IEEE Electron Device Society National Lecturer during 1983. In 1982, he was General Chairman of the International Symposium on Gallium Arsen- ide and Related Compounds. He is presently serving on the U.S. Govern- ment Advisory Group on Electron Devices.

*

Allen N. Lepore (S’87) was born in Hartford, CT, on July 31, 1961. He received the B.S. degree in engineering/physics in 1983 from Trinity Col- lege, Hartford, CT. He is currently working to- ward the Ph.D. degree in electncal engineering at Cornell University, Ithaca, NY His primary work is on the design, fabrication, and testing of self- aligned-gate digital AIGaAs/GaAs MODFET’s and associated electron-beam lithography.

Mr. Lepore is a member of the APS and Phi Beta Kappa.