Date of Award

1987

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Abstract

Prospects of electrochemically forming layers of the III-V semiconductor GaAs from room temperature chloroaluminate melts (AlCl$\sb3$:1-butylpyridinium chloride (BPC) or AlCl$\sb3$:1-methyl-3-ethylimidazolium chloride (MEIC)) are investigated. Prior to codeposition experiments, electrochemical behaviors of gallium and arsenic species were investigated by voltammetry, potentiometry and coulometry, and the complexation discussed in acid-base terms. At room temperature, deposition of Ga(O) was possible from acidic but not basic melts, whereas deposition of As(O) was achieved from acidic, basic and neutral melts. Potentiometry of Ga(I) species as a function of melt acidity indicates that GaCl$\sb2\sp-$ may be the predominant lower valence gallium species in the basic regime. Little dependence of Ga(I) was found on melt acidity in acidic chloroaluminate melt compositions. Fast atom bombardment (FAB) mass spectrometric analyses of chloroaluminate melts, with and without added GaCl$\sb3$ or AsCl$\sb3$, are reported. Anions such as AlCl$\sb4\sp-$, Al$\sb2$Cl$\sb7\sp-$, GaCl$\sb4\sp-$ and Ga$\sb2$Cl$\sb7\sp-$ were detected along with subvalent species. In addition, various oxychloro and hydroxychloro species such as Al$\sb2$OCl$\sb5\sp-$, AlCl$\sb3$OH$\sp-$, Al$\sb2$Cl$\sb6$OH$\sp-$ and Al$\sb3$Cl$\sb8$O$\sp-$, along with the corresponding Ga species were detected. Results obtained reflect the chemistry in the condensed phase as well as gas phase reaction products. Potentiostatically controlled reduction of mixtures of Ga(III) and As(III) in acidic AlCl$\sb3$:BPC and neutral AlCl$\sb3$:MEIC melts lead to films containing both gallium and arsenic. When both Ga(III) and As(III) are present in acidic AlCl$\sb3$:BPC melts, with Ga(III) in excess, electrodeposits are obtained which contain crystalline GaAs. Electrodeposited films were analyzed by X-ray Fluorescence, Electron Dispersive Scattering, Inductively Coupled Plasma and X-ray Diffraction. Mixtures of GaCl$\sb3$ and BPC or MEIC were found to constitute a novel room temperature melt system. Differential Scanning Calorimetry, Electrochemical, FAB Mass Spectrometric and Raman studies were performed to characterize these melts. The suitability of these melts for thin film fabrication of GaAs is discussed briefly.

Pages

271

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