Protoluminescence study of ultra-high vacuum cleaved germanium

We have studied the photoluminescence of Ge samples cleaved in ultra-high vacuum to better understand the role of intrinsic surface states in radiative and non-radiative recombination. We find that the surface states associated with the as-cleaved surface (2 × 1 reconstructed 〈111〉) are very efficient in quenching the band-to-band recombination at T ∼ 90 K. The transitions through surface states are predominantly non-radiative. The adsorption of oxygen, up to a half monolayer, markedly reduces this quenching effect by removing the surface state bands. Some preliminary experimental results on the question of radiative transitions involving the surface states is presented. No luminescence unambiguously attributable to surface state transitions is observed for wavelengths shorter than 5 μm. © 1978.