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UBC Theses and Dissertations

Surface reconstructions during growth of GaAs₁-xBix alloys Masnadi Shirazi Nejad, Mostafa


GaAs₁-xBix is an exciting new semiconductor alloy with numerous promising applications. Incorporation of Bi into GaAs allows for a large reduction of the GaAs bandgap per percent incorporation (7x greater than In, with modest increase in lattice size) and shows strong photoluminescence (PL) and low material degradation associated with Bi. This will allow for longer wavelength devices to be grown on GaAs substrates, than is currently possible with pseudomorphic InGaAs on GaAs. Since Bi has a strong tendency for surface segregation, the molecular beam epitaxy (MBE) growth of GaAs₁-xBix is challenging. To achieve Bi incorporation, this alloy requires unconventional MBE growth conditions such as a low substrate temperature and low As overpressure. The low As:Ga flux ratio also makes Ga and Bi droplet formation a problem. Therefore careful control of growth parameters, especially the As:Ga flux ratio is necessary. In this regard reflection high-energy electron diffraction (RHEED) is used as a crucial tool in locating the optimum growth conditions. The surface reconstruction phase map of GaAs₁-xBix is explored in this study as a function of growth temperature and As:Ga ratio. For comparison, the phase map of GaAs, at low temperatures is also obtained. It is observed that the (1×3), (2×3), (2×4) surface phases are common between GaAs and GaAs₁-xBix but due to the presence of Bi, a new (2×1) reconstruction appears in the case of GaAs₁-xBix. This new reconstruction is observed for various Bi fluxes, showing the evolution of this phase with substrate temperature and As:Ga flux ratio. In addition, the emissivity of the (2×1) surface was found to be lower than for the other As-rich reconstructed surfaces (e.g. (1×3) and (2×3) surfaces) which suggests that the (2×1) surface phase is metallic. Throughout this work, several GaAs₁-xBix films were grown with (1×3) and (2×1) reconstructions at different substrate temperatures. Each film is characterized using high-resolution x-ray diffraction (XRD), photoluminescence spectra (PL) and atomic force microscopy (AFM). Superior crystal quality, higher Bi incorporation and higher intensity PL was observed for GaAs₁-xBix samples grown on (2×1) surfaces, relative to samples grown on (1×3) surfaces.

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