Photoelectric Emission from InAs: Surface Properties and Interband Transitions

Photoelectric yield spectra and energy distributions at photon energies between 2.8 and 6.2 eV have been measured for the (110) surface of InAs cleaved in high vacuum and covered with various amounts of cesium. Cleavage produces an inversion layer on the $n$-type crystal investigated ($N_D=2.5\mathrm{}\times {10}^{15}$ ${\mathrm{cm}}^{-3\mathrm{}}$); on a clean surface the Fermi level coincides with the top of the valence band. The electron affinity and work function of the clean (110) surface are $\chi =4.55\mathrm{}\pm 0.05$ eV and $\varphi =4.90\mathrm{}\pm 0.05$ eV, respectively. Deposition of 1/20 monolayer of cesium results in a degenerate $n$-type surface, which indicates a low density of surface states in the energy gap. Our measurements confirm several important interband transitions in InAs, namely, the ${\Gamma }_{15v}-{\Gamma }_{15c}$ transition at $h\nu =4.30\mathrm{}$ eV, an $L_{3v}-L_{3c}$ transition near $h\nu =6\mathrm{}$ eV with a new position of $L_{3v}$ at 1.3 and 1.6 eV below ${\Gamma }_{15v}$, and an $X_{5v}-X_{1c}$ transition at 4.50 eV. We also report two transitions not observed previously. Whatever information can be gained about conservation of the $\mathbf{k}$ vector points to a strong predominance of direct transitions.