Mott—Schottky analyses on n- and p-GaAs/room temperature chloroaluminate molten-salt interfaces
✍ Scribed by R. Thapar; K. Rajeshwar
- Publisher
- Elsevier Science
- Year
- 1983
- Tongue
- English
- Weight
- 407 KB
- Volume
- 28
- Category
- Article
- ISSN
- 0013-4686
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✦ Synopsis
Mott-Schottky analyses were performed on n-and p_GaAs electrodes in room temperature molten-salt electrolytes comprising mixtures of AICI, and n-butyl pyridinium chloride (BPC) in approx. the 2:Lmolar ratio. These analyses revealed that the two interfaces, n-GaAs/AICI,-BPC and p-GaAs/AlCI,-BPC, conformed with the behavior expected from the simple depletion layer model after suitable etching of the electrode surfaces. The flat-hand potentials (k$J thus determined for interfaces were: -0.20 + 0.03 V (us Al 'IX') for n-GaAs and + 1.22 + 0.01 V (us AI"" ) for p-GaAs, respectively. The doping densities obtained from the slope of the Mott-Schottky plots, however, were 2-3 times higher than those predicted from the Hall data supplied by the manufacturer. Possible reasons for these discrepancies are discussed. The difference between the VI, values for the n-and p-type GaAs correspond to the energy bandgap of the semiconductor-a bchavior consistent with the absence of significant band-edge unpinning effects in the two cases. Alternatively, the data were seen to be consistent with a behavior such that the band-edges are fixed at the surface for n-and p-GaAs electrodes and all or most of the applied voltage drops across the depletion layer in the semiconductor. The present data arc compared with results from cyclic voltammetry obtained in a previous study. In this study, photocurrents were sustained on n-GaAs at potentials significantly positive of the valence band-edge in the presence of certain eleclroative species in the AICl,-BPC electrolyte. This behaviat may be understood in terms of charge accumulation at the interface such that the semiconductor band-edges no longer remain fixed, unlike in the situation above in the absence of redox species. The mechanisms underlying charge accumulation could involve the presence of either a high density of surface states or an inverted g-tvoe surface region caused by hole injection from highly oxidizing redox species as discussed by previous abthors.