STUDY OF SURFACE FIELD IN N-TYPE GAAS BEFORE AND AFTER SURFACE DOPING WITH H2

We have measured room-temperature (RT) electrolyte electroreflectance (EER) in moderately doped (approximately 10(16) cm-3) LEC n-GaAs, before and after hydrogenation, in the vicinity of the E0 critical point. The EER results are compared with 77 K internal photoemission (IPE) data obtained from Pd Schottky barrier structures grown on the GaAs. The EER spectra display weak but sharp features below E0 not seen by IPE. Before hydrogenation, two such features are seen, one ascribed to Si donors and the other to Si acceptors. After hydrogenation the feature ascribed to Si donors persists, although with greatly reduced intensity, but the feature ascribed to Si acceptors is replaced by a different feature somewhat closer to E0. Furthermore, a new transition is clearly evident above E0 after hydrogenation. After Schottky barrier formation on the same GaAs material, two additional thresholds were observed well below E0 in the 77 K IPE spectra. One is ascribed to Pd-induced empty states approximately 1.1 eV above the valence band; the second arises from transitions to states 0.14 eV below the conduction band, which are emptied by the band bending. Both of these signals are strongly increased by hydrogenation. A further feature is induced by hydrogenation slightly below E0 in the IPE spectra; this feature may be related to the EER feature induced by hydrogenation slightly below E0.