ANGLE-RESOLVED X-RAY PHOTOEMISSION-STUDY OF GAAS(001) SURFACES

Angle-resolved X-ray photoelectron spectroscopy (XPS) has been used to characterise chemically etched GaAs(001) versus epitaxially grown sur faces. The measured amplitude of X-ray photoelectron diffraction (XPD) modulation is then an excellent probe of the local structural environ ment around the emitter atom in the near-surface substrate. The observ ed modulations are here compared to the results of single- and double- scattering cluster calculations with a fine agreement, Moreover, becau se of our choice of the emission plane and taking into account the sim ilarity in the scattering factors of Ga and As atoms, XPD effects can be almost eliminated from the angular variation of the fractional peak ratio I(As)/(I(As) + I(Ga)) which is then easily related to the arsen ic concentration profile C(As)(z). A best-fitting procedure is used to select the experimental concentration depth profile which characteris es the surface under study. Samples exposed to different technological treatments, like ion implantation, chemical etching and annealing hav e been studied and compared. The concentrations of As atoms at the sur face for As-capped, MBE-grown (001) samples after annealing around 350 -degrees-C and for chemically etched GaAs(001) wafers indicate the sam e type of surface (As-terminated) as far as composition and structure are concerned.