Modifications of electronic and chemical properties of gallium antimonide surface for device applications

Gallium antimonide (GaSb) is an important III-V compound semiconductor for optoelectronic devices operating in the infrared and near-infrared region. However the as-received GaSb surface is characterized by a thick layer of native oxide and a high density of mid-gap surface states, which reduces the minority carrier life-time and the device efficiency. Reduction in the surface defect concentration by control over the electronic and chemical properties of the GaSb surface is important in improving GaSb-based devices. In this work, the chemical processes for surface oxide reduction and electronic passivation of the GaSb (001) surface were developed and optimized. The surface chemical and electronic properties were investigated by X-ray photoelectron spectroscopy and photoluminescence.; In obtaining a smooth and clean GaSb substrate, non-aqueous processing is necessary, and the etching reagent with a low reaction rate with GaSb surface is desirable. Preparation of the GaSb surface by dipping into concentrated HCl followed by a 2-propanol rinse results in an atomic flat surface with a thin oxide overlayer. Elemental antimony, generated during the thermal oxidation of GaSb, is mainly responsible for the high density of mid-gap surface states. To electronically passivate the GaSb surface, a non-aqueous Na2S passivation regime was developed using inert solvent-benzene. This regime requires the addition of a chelating agent (15-crown-5) to solubilize Na 2S, and an organic oxidizing agent (anthraquinone, etc.) to act as an electron acceptor. The non-aqueous passivation process results in higher sulfide coverage, and lower content of the residual oxide and elemental Sb than that produced by aqueous-based passivation. Adsorption of group VI elements on the GaSb surface can effectively reduce the gap-region surface state density. Non-aqueous chalcogenide treatments using Na2S, Na2Se and Na2Te in benzene-based solutions result in a consistent enhancement in the photoluminescence yield. Sulfidization provides a higher concentration of Ga(Sb)-chalcogen bonds than does the use of Na2Se or Na2Te. The adsorption of selenium on the GaSb surface proceeds initially rapidly, followed by a much reduced adsorption rate as the selenide coverage increases. The adsorption process was analyzed based on a single precursor-mediated chemisorption, and the kinetics were derived using Langmuir-based adsorption and the coverage-dependent adsorption models.