Nonstoichiometry, Band STRUCTURE and Origin of Surface States on (100) GaAs Surface Studied by Aes, Pys and Sps

The preparation and characterization of the atomically clean and crystalline (<100>) GaAs surface is of both fundamental and practical importance. Apart from ion beam etching combined wlth UHV annealing, an atomically clean (<100>) GaAs surface can also be prepared by accurate chemical treatment combined with subsequent thermal cleaning by electron bombardment heating in UHV around 800 K. This chapter presents the results of the preliminary investigation of the n-type (<100>) GaAs surface, which is thermally cleaned at 800 Kin UHV of 10^-7pa by means of Auger electron spectroscopy (AES), photoemission yield spectroscopy (PYS) and surface photovoltage spectroscopy (SPS). From the low energy part of the photoemission yield spectrum of the investigated surface, the work function is determined whereas from the high energy part of this spectrum the ionization energy is obtained. The intrinsic surface state band on the atomically clean n-type (<100>) GaAs surface has been independently confirmed by the low energy part of the SPS spectrum of this surface since the only transitions that can produce the SPS signal for the n-type (<100>) GaAs surface are those from filled surface states localized in the band gap to the conduction band.