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'~~1~f~q$ e t.&" P8TJ"A new air-stable electronic surface passivation for GaAs and other III-V comp u semiconductors that employs sulfur and a suitable metal ion, e.g., Zn, and that is ro ust towards plasma dielectric deposition has been developed. Initial improvements in photoluminescence are twice that of S-only treatments and have been preserved for >11 months with SiOXNYdielectric encapsulation. Photoluminescence and X-ray photoelectron spectroscopes indicate that the passivation consists of two major components with one being stable for >2 years in air. This process improves heterojunction bipolar transistor current gain for both large and small area devices.. High surface recombination velocities andiorFermi-level pinning due to a high density of mid-gap surface states (> 10'2/cm2) have diminished the performance of heterojunction bipolar transistors (HBTs) and delayed the realization of metal-insulatorsemiconductor (MIS) devices in III-V compound semiconductors.Reaction of the GaAs surface with sulfur or its compounds (1-11) produces a dramatic decrease in the interface states responsible for surface recombination and Fermi-level pinning. However, most sulfur-treated surfaces rapidly reoxidlze, returning to their original high density of mid-gap states. Previously reported air-stable S-based pa.ssivation techniques include a glow discharge in sulfur vapor with GaAs heated to 400°C (10) and immersion in S,CIJCC1, (1 1). Despite their air-stability, these processes are limited for actual device applications by either the high temperatures employed (10) or the over-etching of GaAs by S,Cl,, which necessitates in-situ measurement of current gain to terminate the process at maximum device performance (1 1). We have developed a new method whereby a high-quality semiconductor surface is preserved against air oxidation by sulfidation followed by reaction with a suitable metal ion in aqueous solution at room temperature. This process has been applied to prefabricated HBTs to drastically reduce the current gain dependence on surface area. It is also robust against silicon oxynitride encapsulation in a high-density plasma deposition system, making it suitable for fabrication of practical devices.Ĩ n this new process, the semiconductor surfaces were first sulfided using the S vapor and UV light as previously described (5,6). Samples were then immersed in an aqueous solution of a suitable metal salt for several seconds, rinsed with DI water, and blown dry with N2. Performing these steps in a N2 atmosphere prevents degradation of photosulfided surfaces by 0, prior to immersion and drying. After treatment with the metal salt, samples were exposed to atmosphere. The compositions of GaAs (100) surfaces before and after sulfur passivation were determined using X-ray photoelectron spectroscopy (XPS) (5). Photoluminescence (PL) intensity was employed as a relative measure of the depth of the surface depletion region, assuming negligible PL emission from the depleted depth , d = NJNa,, where N, is the surface state density an...

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