Photoelectron surface escape probability of (Ga,In)As : Cs–O in the 0.9 to [inverted lazy s] 1.6 μm range

Abstract

Ga1−xInxAs alloys in the composition range 0≤x≥0.52 and band-gap (Eg) range of 1.38 to 0.74 eV were activated with Cs and O2. Samples of different carrier concentrations were investigated. For band gaps down to about 0.8 eV, the photothreshold was equal to the band gap. The longest wavelength threshold determined was 1.58 μm. To the best of our knowledge, this represents the longest wavelength response yet achieved for photoemission into vacuum from a III-V compound. The surface escape probability, B, was derived from the quantum yield data for each sample. The B-vs-Eg data were analyzed according to a surface escape model which includes the effects of (i) a finite-width initial energy distribution of photoexcited carriers, (ii) the bent-band region and (iii) various types of surface potential barriers. Surface escape probability data pertaining to a single doping density could be explained by a model that includes only a work-function barrier or simple step potential. However, in order to explain the data for the several doping concentrations in a consistent manner, it was necessary to include an electron-semitransparent energy barrier above the vacuum level. A barrier width of 8 Å gives good agreement with the experimental data. This dimension is consistent with the thickness of the Cs–O activation layer which was experimentally determined to be on the order of a monolayer. These results are interpreted in terms of a surface double-dipole model.

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