Undoped gallium antimonide studied by positron annihilation spectroscopy
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Undoped gallium antimonide studied by positron annihilation spectroscopy S. K. Ma1, C. C. Ling1*, H. M. Weng2 and D. S. Hang3 1
Department of Physics, The University of Hong Kong, Pokfulam Road, Hong Kong, China Department of Modern Physics, University of Science and Technology of China, Hefei, China 3 Department of Physics, Nanjing University, Nanjing, China 2
* e-mail correspondence: [email protected] ABSTRACT Positron lifetime spectroscopy has been used to study the vacancy type defects in undoped gallium antimonide. Temperature dependent positron trapping into the VGarelated defect having a characteristic lifetime of 310ps was observed in the as-grown sample. The lifetime data were well described by a model involving the thermal ionization (0/-) of the VGa-related defect and its ionization energy was found to be E(0/)=83meV. For the electron irradiated sample, the VGa-related defect with lifetime of 310ps that was found in the non-irradiated samples was also identified. Moreover, another lifetime component (280ps) was only observed in the electron irradiated sample but not in the non-irradiated sample. It was also attributed to the VGa-related defect. The two identified VGa-related defects should have different microstructures because of their difference in characteristic lifetimes. The 280ps component remains thermally stable after the 500oC annealing while the 310ps component anneals at 300oC. I.
INTRODUCTION
Gallium antimonide (GaSb) is a III-V semiconductor having a narrow direct band gap (~0.75eV at 300K) that can be used in fabricating high frequency and long wavelength optoelectronic devices. Undoped GaSb is usually p-type having a hole concentration of ~10161017cm-3. The residual acceptor responsible for the p-type conduction was reported to be doubly ionized, to be related to Ga in excess and has been attributed to GaSb, VGa or VGaGaSb related defects [1-5]. Detailed reviews of this material can be found in references [1] and [2]. Positron annihilation spectroscopy (PAS) is a nondestructive probe selectively sensitive to neutral or negatively charged open volume defects in semiconductors [6]. Open volume defects, like vacancy, are positron trapping centers as they present as a potential well to the positron in the solid. The positron in the solid will thus finally annihilate with an electron either in the delocalized bulk state or in the localized defect state. The principle of PAS is that the outgoing annihilation gamma photons carry the information of the electronic environment at which the positron annihilates. Although extensive PAS studies have been performed on III-V semiconductors, little work has been carried out on the GaSb material [7-11]. In our previous studies [10,11], a 315ps positron lifetime component was identified in heavily Zn-doped and undoped GaSb materials
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and it was attributed to the VGa-related defect. This defect annealed at the temperature of ~300oC. Furthermore, we have also observed the correlation between the annealing of the 777meV PL signal (band A) and
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