Despite decades of detailed study, the surface physics of III-V semiconductors remains a source of fascinating unsolved puzzles. One such is the occurrence of charge accumulation layers on the cleaned surfaces of InAs, but not on those of other III-V semiconductors, even those of very similar materials such as InSb, InP and GaAs. Even for InAs, the experimental results are often conflicting, leaving several puzzles to be solved.
We present here the first full explanation of charge accumulation on InAs and the lack of it on InSb, InP and GaAs. We show that there are two complimentary mechanisms for surface charge accumulation, both of which can be active on InAs, but not on the other materials. The interplay between them explains the contradicting experimental results. One mechanism involves only native defects, so is a truly intrinsic, but it is largely suppressed when clean surfaces are obtained by cleaving. In this case we propose that the charge accumulation on InAs is caused by the adsorption of residual hydrogen within the experimental chamber. Further, we find that the universal alignment of the hydrogen levels found for bulk semiconductors [C.G. Van de Walle and J. Neugebauer, Nat. 423, (2003) 626] does not work in the same way on the surface, since the bonds between hydrogen and host occur differently. Instead we show how the position of the level relates to the host structure, and hence explain why hydrogen only induces an accumulation layer on InAs.
Finally, we demonstrate that, in STM and AFM, adsorbed hydrogen can be indistinguishable from surface vacancies, both on InAs and on other III-V surfaces. We show that adsorbed H may plausibly even provide a better explanation for the debated symmetric vacancy images in STM of InP and GaAs, and help resolve some other disagreements between experiment and theory for those materials.
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