2019年5月28日星期二

Defect properties of as-grown and electron-irradiated Te-doped GaSb studied by positron annihilation

Defects in as-grown undoped and tellurium-doped gallium antimonide were studied using positron lifetime and coincidence Doppler broadening measurements. The grown-in defects in these samples were supposed to be Ga vacancy (VGa)-related defects. More VGa-related defects were introduced into undoped and lightly Te-doped GaSb after electron irradiation at the doses of 1.0 × 1017 cm−2 and 1.0 × 1018 cm−2; however, in the heavily Te-doped GaSb, electron irradiation led to partial recovery of VGa. The role of Te content in the defect evolution is also discussed.


Source:IOPscience

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2019年5月23日星期四

Structural and optical characterization of GaSb on Si (001) grown by Molecular Beam Epitaxy

GaSb epilayers were grown on Si (001) using molecular beam epitaxy via AlSb quantum dots as an interfacial misfit (IMF) array between the Si substrates and GaSb epilayers. The effect of IMF array thickness, growth temperature and post annealing on the surface morphology, structural and optical properties of the GaSb on Si were investigated. Among five different IMF array thicknesses (5, 10, 20, 40 and 80 ML) that were used in this study, the best result was obtained from the sample with a 20 ML AlSb IMF array. Additionally, it was found that although the full width at half maximum (FWHM) and threading dislocation (TD) densities obtained from high resolution x-ray diffraction curves can be improved by increasing the growth temperature, a decrease in the photoluminescence (PL) signal and an increase in the surface roughness (RMS) emerged. On the other hand, the results indicate that by applying post annealing the GaSb epilayer crystal quality can be improved in terms of FWHM, TD density, PL signal or RMS depending on the post annealing temperature. By applying post annealing at 570 °C for 30 min we achieve a FWHM value of 260 arcsec for a 1 μm thick GaSb epilayer on Si (001) and improve the PL signal intensity without worsening the RMS value.


Source:IOPscience

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2019年5月9日星期四

Origin of a localized vibrational mode in a GaSb substrate with a MBE-grown ZnTe epilayer

A localized vibrational mode (LVM) with a remarkable fine structure is observed in the infrared transmission spectrum of a ZnTe epilayer grown with molecular beam epitaxy (MBE) on a GaSb substrate. On the basis of the Zn and Te deposited on the GaSb substrate during the MBE growth of ZnTe, and assuming diffusion of Zn and Te into GaSb, the LVM is attributed to Zn, substitutionally replacing either the cation, Ga (ZnGa), or the anion, Sb (ZnSb). The frequency of the LVM and its fine structure can then be interpreted in terms of the infrared active modes of 64Zn substituting for Sb as an anti-site impurity and treating the centre as an XY4 quasimolecule. With X64Zn and Y69Ga and 71Ga, occupying the nearest-neighbour sites reflecting all the possible combinations and permutations as well as the natural isotopic abundance of Ga, the fine structure of the LVM can be accounted for quantitatively.


Source:IOPscience

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