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High quality Ohmic contacts having specific transfer resistances in the range 0.06≲ ρt≲0.2 Ω mm have been fabricated using Au/Ge/Ni/Ag based metallizations on AlGaAs/GaAs and AlInAs/GaInAs heterostructures. For AlGaAs/GaAs the metallization consisting of 100 Å Ni/800 Å 80 at. % Au–20 at. % Ge/1000 Å Ag/800 Å Au accomplishes this at alloy cycles with maximum sample temperatures 540≤Tmax≤600 °C. The corresponding results for Al0.48In0.52As/Ga0.47In0.53As were achieved with 100 Å Ni/450 Å Ge/800 Å Au/200 Å Ag/800 Å Au, and with alloy cycles having 430 °C≤Tmax≤490 °C. The two semiconductor systems have been studied electrically using the transmission line model and analytically with the help of sputter Auger depth analysis, optical and scanning electron microscopy, and energy dispersive x-ray analysis. In this paper we shall discuss the differences in temperature dependence of metallurgical interactions between the two systems and the corresponding electrical behavior.

We have fabricated a metal-semiconductor-metal Schottky photodetector on a semi-insulating InP substrate using a nominally lattice-matched In0.52Al0.48As/In0.53(GaxAl1−x)0.47As (graded)/In0.53Ga0.47As structure grown by molecular beam epitaxy. On average the graded quaternary layer enhanced the responsivity by about 35% compared to an identical device without the graded region, reaching a maximum of 0.45 A/W at 10 V applied bias. The associated dark current was 95 nA; the dark capacitance was 90 fF. High-speed measurements with a gain-switched 1.3 μm laser diode demonstrated an instrumentation-limited impulse response of 50 ps.

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