S. Fung

Bio: S. Fung is an academic researcher. The author has contributed to research in topics: Positron Lifetime Spectroscopy & Acceptor. The author has an hindex of 1, co-authored 1 publications receiving 33 citations.

Nature of the acceptor responsible for p-type conduction in liquid encapsulated Czochralski-grown undoped gallium antimonide

Abstract: Acceptors in liquid encapsulated Czochralski-grown undoped gallium antimonide (GaSb) were studied by temperature dependent Hall measurement and positron lifetime spectroscopy (PLS). Because of its high concentration and low ionization energy, a level at EV+34meV is found to be the important acceptor responsible for the p-type conduction of the samples. Two different kinds of VGa-related defects (lifetimes of 280ps and 315ps, respectively) having different microstructures were characterized by PLS. By comparing their annealing behaviors and charge state occupancies, the EV+34meV level could not be related to the two VGa-related defects.

Native point defects in GaSb

Abstract: We have applied positron annihilation spectroscopy to study native point defects in Te-doped n-type and nominally undoped p-type GaSb single crystals. The results show that the dominant vacancy defect trapping positrons in bulk GaSb is the gallium monovacancy. The temperature dependence of the average positron lifetime in both p- and n-type GaSb indicates that negative ion type defects with no associated open volume compete with the Ga vacancies. Based on comparison with theoretical predictions, these negative ions are identified as Ga antisites. The concentrations of these negatively charged defects exceed the Ga vacancy concentrations nearly by an order of magnitude. We conclude that the Ga antisite is the native defect responsible for p-type conductivity in GaSb single crystals.

Temperature-dependent terahertz spectroscopy of inverted-band three-layer InAs/GaSb/InAs quantum well

Abstract: We report on temperature-dependent terahertz spectroscopy of a three-layer InAs/GaSb/InAs quantum well (QW) with inverted-band structure. The interband optical transitions, measured up to 16 T at different temperatures by Landau-level magnetospectroscopy, demonstrate the inverted-band structure of the QW. The terahertz photoluminescence at different temperatures allows us to directly extract the optical gap in the vicinity of the Γ point of the Brillouin zone. Our results experimentally demonstrate that the gap in the three-layer QWs is temperature independent and exceeds by four times the maximum band gap available in the inverted InAs/GaSb bilayers.

Optical and Electric Properties of Aligned-Growing Ta2O5 Nanorods

Abstract: These vertically aligned Ta 2 O 5 nanorods were deposited on Si (100) substrates by thermal deposition in a vacuum of the order of 10 -2 Tonal about 600°C. When excited by 514 nm Ar + laser, they showed a strong photoluminescence at ∼622 nm, which was attributed to the oxygen vacancies. In addition, their dielectric constant is ∼20 in the frequency range from 1 kHz to 10 MHz, far larger than that of SiO 2 and Si 3 N 4 . Due to this cone-shaped morphology, the Ta 2 O 5 nanorods exhibited a threshold field of ∼8.5 V /μm in field emission and a field enhancement factor of 764 that are sufficiently high for field emission application.

Intrinsic point defects and the n - and p -type dopability of the narrow gap semiconductors GaSb and InSb

Abstract: The presence of defects in the narrow gap semiconductors GaSb and InSb affects their dopability and hence applicability for a range of optoelectronic applications. Here, we report hybrid density functional theory (DFT)-based calculations of the properties of intrinsic point defects in the two systems, including spin-orbit coupling effects, which influence strongly their band structures. With the hybrid DFT approach adopted, we obtain excellent agreement between our calculated band dispersions and structural, elastic, and vibrational properties and available measurements. We compute point defect formation energies in both systems, finding that antisite disorder tends to dominate, apart from in GaSb under certain conditions, where cation vacancies can form in significant concentrations. Calculated self-consistent Fermi energies and equilibrium carrier and defect concentrations confirm the intrinsic n- and p-type behavior of both materials under anion-rich and anion-poor conditions. Moreover, by computing the compensating defect concentrations due to the presence of ionized donors and acceptors, we explain the observed dopability of GaSb and InSb.

Hole density and acceptor-type defects in MBE-grown GaSb1-x Bix

Abstract: We study acceptor-type defects in GaSb1−xBix grown by molecular beam epitaxy. The hole density of the GaSb1−xBix layers, from capacitance-voltage measurements of Schottky diodes, is higher than that of the binary alloys and increases linearly up to 1019 − cm 3 with the Bi content. Positron annihilation spectroscopy and ab initio calculations show that both Ga vacancies and Ga antisites contribute to the hole density and that the proportion of the two acceptor-type defects vary in the layers. The modification of the band gap due to Bi incorporation as well as the growth parameters are suggested to affect the concentrations of acceptor-type defects.