Electrical Study of Schottky Barriers on Cleaved InP and GaAs (110) Surfaces
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Kendplewicz and W.E. Spicer Stanford University, Stanford,
Ca.
EXTENDED ABSTRACT ** We have performed a systematic study of the electrical properties of a large number of metal/n-GaAs and metal/n-InP diodes. Diodes were fabricated on clean cleaved InP and GaAs (110) surfaces in ultra-high vacuum with in-situ metal deposition of Cr, Mn, Sn, Ni, Al, Pd, Cu, Ag and Au. Using current-voltage (I-V) and capacitance-voltage (C-V) measuring techniques, we were able to obtain very reliable and consistent determinations of the barrier height, */b and ideality factor, n. All of the metal6 3 semiconductor systems formed on lightly doped (< 5x101 /cm ) substrates were characterized by near-unity (1.05) ideality factors. The effects of doping on the electrical characteristics of the n-GaAs diodes were investigated. A decrease in the effective I-V barrier height, an increase in the ideality factor in forward bias and a strong voltage dependence on the thermionic emission currents in reverse bias were found for diodes formed on the more heavily doped samples. These changes are essentially metal-independent, but depend strongly on the doping of the substrate. The characterization (and elimination in some cases) of peripheral leakage currents from the thermionic emission current for the n-GaAs systems was found to be essential in obtaining consistent results in our work and in reinterpreting some of the prior work in the literature. The dominant leakage current in the GaAs diodes flows through a small area, low barrier at the periphery of the device and can be eliminated by mesa etching. The influence of surface contamination on the electrical characteristics of Schottky diodes formed on n-InP was also investigated. The previously reported large differences between the electrical characteristics of diodes prepared on clean InP(110) surfaces and those prepared on air exposed InP(110) surfaces were not found. In fact, essentially identical barrier heights were found for diodes formed on air-exposed and clean InP (110) surfaces for almost all of the systems studied. The consistent and reproducible barrier height determinations reported in this study, when combined with the results of recent surface sensitive studies, are a particularly critical test of models of Schottky barrier formation. Because the thick metal film diodes formed on the clean cleaved (110) surfaces have been produced under the same conditions and evaporation rates during the initial stages of Schottky barrier formations as in the photoemission spectroscopy studies, we can confidently compare the results of measuring techniques which are macroscopic in nature (electrical device measurements) with the results of measuring techniques which are microscopic in nature (photoemission spectroscopy). As can be seen in Figures 1 and 2, the barrier heights measured from the electrical characteristics of thick metal film diodes were found to be consistent with those reported during the initial stages (sub to several monolayers of metal) of Schottky barrier formation by photoem
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