Development of electronic materials for infra-red detector systems.

Indium antimonide (InSb) and gallium antimonide (GaSb) are technologically important III-V semiconductor materials used in infrared detector systems. Yet, the application of these materials is to a certain extent limited, in that the techniques currently used for their growth are both expensive and problematic. Semiconductor electrochemical deposition, which has been successfully applied to the generation of II-VI semiconductor materials, may offer the prospect of overcoming such limitations. This work presents results that represent a significant contribution to the development of electrochemical methods for both InSb and GaSb thin film growth.The direct electrochemical co-deposition of InSb was achieved via the potentiostatic electrolysis of aqueous halide/citric acid electrolyte solutions, and for the first time, non-aqueous (ethylene glycol) electrolyte solutions containing the halides and tetraethylammonium chloride. This choice of solvents allowed the compound's deposition to be studied over a wide range of temperatures (RT to 185 °C). A first report was also made of the direct potentiostatic co-deposition of GaSb from an aqueous solution containing Ga[2](SO[4])[3] and SbCl[3].An extensive study was carried out on the relationship between the technique's fundamental growth parameters (temperature, deposition potential, solution composition etc.) and the film's compositional, crystallographic and morphological properties. The material's characterisation showed that there was tendency for the films to be non-stoichiometric. X-Ray diffraction patterns obtained from InSb films deposited from aqueous electrolyte solutions showed them to generally consist of two phases, the compound and, depending mostly on deposition potential, one of the elements. Films containing three phases, the compound and both elements, were deposited on Ti substrates from aqueous solutions and on to ITO substrates from non-aqueous solutions. These results were interpreted from both thermodynamic and kinetic viewpoints. This led to the conclusion that kinetic barriers to the formation of InSb still existed, even at the highest temperature used (~185 °C). In respect of GaSb, the compound's formation was complicated by a side reaction involving the evolution of H[2].New studies involving Scanning Electron Microscopy of the electrodeposited materials showed that they exhibited a nodular morphology, which can be explained in terms of the film's limiting current growth conditions. Energy Dispersive X-Ray Analysis (EDX) and Glow Discharge Optical Emission Spectroscopy (GDOES) identified indium chloride as a major impurity in the InSb films, especially those deposited from non-aqueous solutions. A mechanism for the incorporation of indium chloride was proposed, based on the physical entrapment of a precipitate of the compound.