Weng Hui-Min

Bio: Weng Hui-Min is an academic researcher from University of Science and Technology of China. The author has contributed to research in topics: Positron & Beam (structure). The author has an hindex of 5, co-authored 18 publications receiving 69 citations.

Defect study of Zn-doped p-type gallium antimonide using positron lifetime spectroscopy

Abstract: Defects in p-type Zn-doped liquid-encapsulated Czochralski\char21{}grown GaSb were studied by the positron lifetime technique. The lifetime measurements were performed on the as-grown sample at temperature varying from 15 K to 297 K. A positron trapping center having a characteristic lifetime of 317 ps was identified as the neutral ${V}_{\mathrm{Ga}}$-related defect. Its concentration in the as-grown sample was found to be in the range of ${10}^{17}\char21{}{10}^{18} {\mathrm{cm}}^{\ensuremath{-}3}.$ At an annealing temperature of $300\ifmmode^\circ\else\textdegree\fi{}\mathrm{C},$ the ${V}_{\mathrm{Ga}}$-related defect began annealing out and a new defect capable of trapping positrons was formed. This newly formed defect, having a lifetime value of 379 ps, is attributed to a vacancy\char21{}Zn-defect complex. This defect started annealing out at a temperature of $580\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}.$ A positron shallow trap having binding energy and concentration of 75 meV and ${10}^{18} {\mathrm{cm}}^{\ensuremath{-}3},$ respectively, was also observed in the as-grown sample. This shallow trap is attributed to positrons forming hydrogenlike Rydberg states with the ionized dopant acceptor Zn.

Evolution of native point defects in ZnO bulk probed by positron annihilation spectroscopy

Abstract: This paper studies the evolution of native point defects with temperature in ZnO single crystals by positron lifetime and coincidence Doppler broadening (CDB) spectroscopy, combined with the calculated results of positron lifetime and electron momentum distribution. The calculated and experimental results of the positron lifetime in ZnO bulk ensure the presence of zinc monovacancy, and zinc monovacancy concentration begins to decrease above 600 °C annealing treatment. CDB is an effective method to distinguish the elemental species, here we combine this technique with calculated electron momentum distribution to determine the oxygen vacancies, which do not trap positrons due to their positive charge. The CDB spectra show that oxygen vacancies do not appear until 600 °C annealing treatment, and increase with the increase of annealing temperature. This study supports the idea that green luminescence has a close relation with oxygen vacancies.

Dependence of intrinsic defects in ZnO films on oxygen fraction studied by positron annihilation

Abstract: Defects in ZnO films grown by radio-frequency reactive magnetron sputtering under variable ratios between oxygen and argon gas have been investigated by using the monoenergetic positron beam technique. The dominate intrinsic defects in these ZnO samples are O vacancies (V-O) and Zn interstitials (Zn-i) when the oxygen fraction in the O-2/Ar feed gas does not exceed 70% in the processing chamber. On the other hand, zinc vacancies are preponderant in the ZnO Elms fabricated in richer oxygen environment. The concentration of zinc vacancies increases with the increasing (2) fraction. For the oxygen fraction 85%, the number of zinc vacancies that could trap positrons will be smaller. It is speculated that some unknown defects could shield zinc vacancies. The concentration of zinc vacancies in the ZnO films varies with the oxygen fraction in the growth chamber, which is in agreement with the results of photoluminescence spectra.

Experiments of producing slow positron beam

Abstract: In this article, we describe an apparatus for producing a slow-positron beam by moderating the decay positrons from a radioactive source using a W-vane moderator. The integral energy spectrum of the slow-positrons was measured with a retarding field analyser. The results are compared with that obtained using a Ni + MgO moderator at the same apparatus.

Positron lifetime studies on 8 MeV electron-irradiated n-type 6H silicon carbide

Abstract: The positron lifetime technique was employed to study vacancy-type defects in 8 MeV electron-irradiated n-type 6H silicon carbide. A long-lifetime component having a characteristic lifetime of 223–232 ps was observed in the irradiated sample and was attributed to the VCVSi divacancy. Other positron traps, which dominated at low temperatures, were observed to compete with the VCVSi for trapping positrons. A positron trapping model involving a positron shallow trap, a negatively charged monovacancy and the VCVSi divacancy was found to give a good description of the temperature-dependent positron lifetime data of the 1200 ◦ C annealed sample. The identity of the monovacancy could not be unambiguously determined, but its lifetime was found to be in the range 160–172 ps.

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.