| Research Abstract |
(1) A novel photoluminescence (PL)-based measurement method (PL Surface State Spectroscopy : PLS^3) for semiconductor surface state density, N_<ss>, was newly developed. It consists of detailed measurement of the band-edge photoluminescence efficiency as a function of the excitation intensity, and its rigorous analysis by computer. By this method, N_<ss> distribution as well as the value of surface recombination velocity, S, can be determined in a contactless and nondestructive fashion. (2) The proposed PLS^3 technique was successfully applied for the first time for in-situ determination of the N_<ss> distribution on variously processed free surface of GaAs, InP, InGaAs and Si. Chemically etched, anodized and passivated surfaces, as well as the original as-received surface, give rise to U-shaped surface state density distributions with characteristic charge neutrality energy levels, E_<HO>, which is consistent with the disorder induced gap state (DIGS) model. The usefulness of the present method for the assessment of ultrahigh-vacuum-based processes, such as MBE growth and photo-CVD, was also confirmed. (3) Combined use of a developed C-V simulation technique and PLS^3 technique revealed the existence of continuous U-shaped states at growth interrupted interfaces of MBE GaAs, and lattice matched and pseudmorphic heterointerfaces. The previously observed carrier profile anomaly around the interface can be explained by these continuous states. (4) Schottky barrier height of Al/GaAs(100) can be precisely controlled over a wide range of about 400 meV by the insertion of an ultrathin MBE Si interface control layer (Si ICL) with suitable doping. The result is consistent with a proposed model for Schottky barrier formation. Moreover, HF treatment of GaAs surface before PCVD-SiO_2 deposition is highly effective in suppressing the interface reactions during rapid thermal annealing.
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