UNPINNED BEHAVIOR OF THE ELECTRONIC-PROPERTIES OF A P-GAAS(CS,O) SURFACE AT ROOM-TEMPERATURE

The evolution of the surface band bending, photovoltage, and recombination rate is experimentally studied in situ by means of photoreflectance and photoluminescence techniques under deposition of cesium and oxygen on the surface of epitaxial p- and n-type GaAs layers at room temperature. The evolution of the band bending is explained in terms of Fermi level pinning by initial and adatom-induced donor-like and acceptor-like surface states. For the surface of p-type GaAs multiple reversible variations of the electronic properties are observed under alternate Cs and O-2 deposition. This unpinned behavior proves that adatom-induced surface states dominate over defect-induced states. Hysteresis in the dependences of photovoltage and photoluminescence intensity on the band bending shows that variations of the concentrations or cross sections of surface capture and recombination centers take place at the first cycles of Cs and O-2 deposition.