Very high resolution photoelectron spectra of NEA-GaAs

The energy distribution of photoelectrons emitted from NEA-GaAs has been measured with a very high energy resolution (ΔE ≈ 5 meV). The sample consists of epitaxially grown p-type GaAs (hole concentration 1 × 10¹⁹ cm^-3) with a (100) surface. After cleaning the surface by heating in UHV (7 × 10^{-11 Torr}), Cs and O₂ were coadsorbed to obtain a NEA surface. A pulsed GaAlAs laser (λ = 820 nm, pulse width = 60 ps) was used for the light source, and the photoelectron energy distribution was measured by a high resolution time-of-flight electron spectrometer. A series of peaks with an approximately regular energy interval of 50 meV was observed in the spectra. Theoretical considerations reveal that the origin of the regular structure are the two-dimensional subbands of electrons at the X-point in the band-bending region near the surface.