1864 IEEE IRANSACTIONS ON ELECTRON DEVICES, VOL. ED-33, NO. 11, NOVEMBER 1986

layer of the p-i-n-photodiode, grown on a semi-insulating InJ’ : Fe substrate, as a buffer layer beneath the FET. On top of this ayer the thin FET channel layer, n = 6-8 X l o i6 ~ m - ~ , is depo!,ii.ed; both are grown by LPE at a low temperature to minimize dc pant redistribution. The p-region of the p-i-n-diode and the gate re: gion of the FET are formed by a single selective diffusion step thn’lugh a sputtered Si3N4 mask, performed in a closed ampoule at tibout 540°C. The effective FET gatelength is L, = 4.5 pm and th: di- ameter of the planar p-i-n-diode is 80 pm.

An excellent transconductance of g,, = 150 mS/mm has x e n obtained which is the highest value for InGaAs-p-n-JFET’s of comparable gate length known to the authors. This corresponlis to a saturated electron drift velocity of at least 2.4 X IO7 cmis. These results are discussed in terms of FET design and processing. ’The planar pin diodes show low dark currents of Id 5 20 nA at - 5 V. With an external p-i-n-diode bias resistance of 100-kD photocu ‘rent gains of about 4000 have been measured on integrated p-i-n- FET devices. This value is consistent with the transconductances d ?[er- mined for single FET’s on the same wafer.

VIA-7 Sputter Ni-P as an Ohmic Contact to n-InP, p-InCi aAs and as a Diffusion Barrier-A. Appelbaum, M. Robbins, and F. Schrey, AT&T Bell Laboratories, Murray Hill, NJ 07974.

A new approach for making ohmic contacts to 111-V semi :on- ductors using a nonalloyed contact is reported. Ni2P is sputtel de- posited on high-doped 111-V semiconductors replacing the Au-k’ased alloy contact currently in use [I]-[4]. The contacts’ electrical (.klar- acteristic is similar to Au-based alloy contacts although no dopant is needed, Metallurgically, only very limited interaction OCCIY Y at the Ni,P-substrate interface unlike the extensive interaction w ~ i c h takes place at the AuiSubstrate interface during alloying [5]. Bs- sentially, this type of stable compound as an ohmic contact ca.2 be used in 111-V integrated circuits in a manner similar to the use of silicides in VLSI technology.

Ni2P is a metallic conductor with a bulk resistivity of 32 b’cn . cm. Films of Ni2P can be sputter deposited in both the amorpilous and crystalline forms by varying the sputtering parameters. The amorphous to crystalline transition has been found to take plal. P: at about 250°C and sufficient grain growth to exhibit X-ray reflecl ions takes place by 400°C. In both forms films of Ni2P have been fc und to form ohmic contacts to n-InP and p-InGaAs 3 X and 2 X IO-’ D . cm2 respectively. This low sheet resistance and spe:ific contact resistance makes this contact useful for most 111-V de vice applications. It was found that up to 300°C, amorphous (as s8put- tered) films on NizP as efficient diffusion barrier, between an outer Au layer and the 111-V substrate. It is possible, therefore, for a] lor- phous (as sputtered) films of NizP to functicn simultaneously Imth as a metallization layer and diffusion barrier.

[l] C. Camlibel, A. K. Chin, F. Ermanis, M. A. DiGiuseppe, J . A. I[ our- enco and W. A. Bonner, J . Electrochem. Soc., vol. 129, p. 2585, 1982.

[2] L. P. Erickson, A . Wasseern, and G. Y . Robinson, Thin Solid Falins, vol. 64, p. 421, 1979.

[3] A. Pioatrowska, A . Guivarih and G. Pelaus, Solid-state Electron., 1’01. 26, p. 179, 1983.

[4] V. G. Keramidas, H. Temkin, S. Mahajan, in Proc. 8th Znt. S;,rQp. GaAs and Related Compounds, H. W. Thin, Ed., p . 293, 1980.

[5] J . M. Vandenberg, H. Temkin, R. H. Haman, and M. A . DiGiuse Jpe, J. Appl. Phys., vol. 53, p. 7385, 1982.

VIA-I Transverse Junction Stripe Laser with a Lateral IXet- erobarrier by Diffusion-Enhanced Disordering-R. M. Kol )as, J . Y. Yang, Y. C. Lo, G. S . Lee, and K. Y. Hsieh, Departrll-nt of Electrical and Computer Engineering, North Carolina State I Jni- versity, Raleigh, ‘NC 27695-791 1.

We report the first continuous-wave room-temperature mulliple quantum well transverse junction stripe laser (MQW-TJS) ( I , , = 27 mA, X = 8140 A ) with an alloy disordered heterobarrier. The

addition of a lateral heterobarrier by zinc diffusion enhanced alloy disordering reduces the laser threshold by a factor of three com- pared to standard TJS lasers processed simultaneously. The reduc- tion in threshold and excellent single-mode performance of the MQW-TJS are attributed to the improved carrier confinement of a single heterobarrier compared to the traditional homojunction TJS.

This work differs from previous work on alloy disordered laser structures in that the diffused junction plays an active (not passive) roll in the current injection process and that the transition region between complete disorder and no disorder forms the active region of the laser. We will present laser performance data which is con- sistent with lateral, (parallel to the quantum wells) electron current injection across the n-p-p+ junction. The laser performance con- firms that high quality lateral p-n junctions and alloy disorderd het- erobarriers can be fabricated.

Given that commercially available TJS lasers have thresholds as low as 10-20 mA an optimized MQW-TJS could have thresholds as low as 2-5 mA. These lasers would be highly desirable as op- tical emitters on GaAs integrated optoelectronic circuits for high- speed optical interconnects.

VIB-1 Millimeter-Band Oscillations in a Resonant-Tunneling Device-Elliott R. Brown, T . C. L. G. Sollner, W. D. Goodhue, B. J . Clifton and P. E. Tannenwald, M. I. T. Lincoln Laboratory.

We report here the achievement of self-oscillations up to 43 GHz in a two-terminal resonant-tunneling device at room temperature. The device consists of a 4.5-nm layer of GaAs sandwiched between two 3.0-nm layers of A10,3Gao,,As. Outside of each AlGaAs layer is a 300-nm-thick region of 2 X l O I 7 c r K 3 n-Ga-As which serves to buffer the double-barrier region from substrate and contact re- gions. The basis for oscillation is the negative dynamic resistance displayed by the device when the electrons that tunnel through the AlGaAs barriers have energy slightly greater than the energy of the quasi-stationary state of the well. Until now the highest reported oscillation frequency of a resonant tunneling device was 18 GHz V I .

Oscillation was obtained with the device mounted in reduced- height rectangular waveguide and tuning was performed with a sliding backshort. The observed frequencies and powers of oscil- lation were 29 to 31 GHz with 1 to 3 pW in B-band, and 42 to 43 GHz with 0.5 to 1 .O pW in I/-band waveguide. Crucial to the per- formance of this oscillator is that the device capacitance be close to the value required to resonate with the whisker inductance (= 0.4 nH) in the 40-GHz region, and that the minimum value of negative resistance be comparable to the waveguide characteristic imped- ance.

The high-frequency capability of this particular resonant tunnel- ing device is attributed in large part to its buffer layer doping den- sity. A sample having similar barrier geometry but much greater buffer layer doping (2 X 1OI8 ~ m - ~ ) failed to oscillate in the above frequency bands, while several samples having far less doping (2 X 10l6 ~ m - ~ ) did not even display room-temperature negative re- sistance. The present device is superior to the sample with greater doping because it has a thicker depletion layer in the buffer region and thus a lower capacitance at bias voltages required for negative resistance. Separate measurements of the present device yielded a specific capacitance of C = 1.2 X lo5 pF/cm2, a specific negative resistance of R = 5 X lo-’ il . cm’ and a contact plus undepleted GaAs specific series resistance of R, = 2 X 0 cm2. Assum- ing that the tunnel diode model describes the present device per- formance, these values yield a resistive cutoff frequency (i.e., maximum oscillation frequency) of fc = ~ / [ ~ T C ( R R , ) ~ ’ ~ ] = 135 GHz. We are currently attempting to obtain oscillations in the 100- GHz region and are exploring new resonant tunneling structures to oscillate at even higher frequencies.

NASA. This work was supported by the U.S. Army Research Office and by

[l] T. C. L. G. Sollner, P. E. Tannenwald, D. D. Peck, and W. D. Good- hue, Appl. Phys. Lett . , vol. 45, p. 1319, 1984.