Gallium vacancy in GaSb studied by positron lifetime spectroscopy and photoluminescence
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Gallium vacancy in GaSb studied by positron lifetime spectroscopy and photoluminescence W. K. Mui, M. K. Lui, C.C. Ling, C. D. Beling, S. Fung Department of Physics, The University of Hong Kong, Pokfulam Road, Hong Kong, P. R. China K. W. Cheah, K. F. Li Department of Physics, Hong Kong Baptist University, Hong Kong, P. R. China Y. W. Zhao P.O. Box 912, Material Science centre, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, P. R. China E-mail correspondence: [email protected]
ABSTRACT Positron lifetime technique and photoluminescence (PL) were employed to study the vacancy type defects in p-type Zn-doped and undoped GaSb samples. In the positron lifetime study, Ga vacancy related defect was identified in these materials and it was found to anneal out at temperature of about 350oC. For the PL measurement on the as-grown undoped sample performed at 10K, a transition peak having a photon energy of about 777meV was observed. This transition peak was observed to disappear after a 400oC annealing. Our results is consistent with the general belief that the 777meV transition is related to the VGaGaSb defect, which is the proposed residual acceptor of GaSb.
INTRODUCTION Gallium Antimonide is a III-V semiconductor having a narrow band gap, a small effective electron mass and a high electron mobility. It is the basic material for a variety of lattice-matched materials having band gap ranging from 0.8 to 4.3µm. It is the potential material for fabricating optoelectronic, photovoltalic and high frequency devices. Undoped GaSb is ptype and has a hole concentration of 1016-1017cm-3 [1,2]. The residual acceptor was known to be doubly ionized [3] and related to a deficiency of Sb or an excess of Ga [4-6]. Annealing the undoped GaSb for several hours converted its p-type conducting nature to n-type. It was explained by the creation of VSb upon the annealing, for which VSb was a donor compensating the residual acceptor. However, if the sample was annealed for several tens of hours, it would convert back to p-type with an even larger hole concentration as compared to the original asgrown value [7]. The residual acceptor has long time been attributed to the VGaGaSb defect [7-9]. The increase of hole concentration upon prolonged annealing can be understood by the formation of VGaGaSb resulting from the reaction between the VSb defect and its neighboring Ga atom. The VGaGaSb defect was also related to a luminescence signal called band A (located at about H9.5.1
777meV) which was commonly found in the photoluminescence and cathodoluminecense spectra of a variety of GaSb materials [7,10-15]. However, these correlations between the residual acceptor, the VGaGaSb and the 777meV luminescence signal have not yet been directly confirmed by experimental observation. Positron lifetime technique is a non-destructive defect probe which is selectively sensitive towards open volume defects [16, 17]. Positrons implanted into a solid will be rapidly thermalized and then undergo diffusion. An open volume defect in the lat
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