Acceptors in undoped gallium antimonide
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Acceptors in undoped gallium antimonide M. K. Lui, C. C. Ling, X. D. Chen Department of Physics, The University of Hong Kong, Hong Kong, China K. W. Cheah, K. F. Li Department of Physics, Hong Kong Baptist University, Hong Kong, China E-mail correspondence: [email protected] ABSTRACT Undoped GaSb materials were studied by temperature dependent Hall (TDH) measurements and photoluminescence (PL). The TDH data reveals four acceptor levels (having ionization energies of 7meV, 32meV, 89meV and 123meV) in the as-grown undoped GaSb samples. The 32meV and the 89meV levels were attributed to the GaSb defect and the VGa-related defect. The GaSb defect was found to be the important acceptor responsible for the p-type nature of the present undoped GaSb samples because of its abundance and its low ionization energy. This defect was thermally stable after the 500oC annealing. Similar to the non-irradiated samples, the 777meV and the 800meV PL signals were also observed in the electron irradiated undoped GaSb samples. The decrease of the two peaks’ intensities with respect to the electron irradiation dosage reveals the introduction of a non-radiative defect during the electron irradiation process, which competes with the transition responsible for the 777meV and the 800meV PL peaks. INTRODUCTION Gallium antimonide is a narrow band gap III-V semiconductor having a high electron mobility and a small effective electron mass. It is suitable for fabricating high frequency electronic and long wavelength photonic devices. Moreover, GaSb is also the basic material having the lattice parameter which well matches various ternary and quaternary III-V compounds with bandgap varying from 0.3eV to 1.58eV [1,2]. Undoped Gallium antimonide is p-type in nature having the hole concentration of 1016-1017cm-3 [1,2]. The residual acceptor is usually believed to be doubly ionizable [3], contain the structure of a vacancy and be related to Ga in excess. It has been attributed to have structures of VGa, GaSb and VGaGaSb. [1-5]. The residual acceptor was also thought to be involved in the transition resulting in the band A PL signal (~777meV), which was commonly found in photoluminescence and cathodoluminescence experiments [5-11]. We have studied the residual acceptor and the Ga vacancy in undoped GaSb with the use of positron lifetime technique and Hall measurement [12]. A 315ps lifetime component was identified in the as-grown and it was attributed to the VGa-related defect [12,13]. Correlation between the annealing of the VGa-related defect and the 777meV PL signal was also observed, for which they both anneal at 300oC [12]. However, it was also noticed that the hole
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concentration is independent of the annealing temperature up to 500oC. This implies the VGarelated defect identified in the lifetime measurement would not be the residual acceptor as it has already been annealed out at 300oC. In the present study, we have studied the non-irradiated and the electron irradiated undoped GaSb samples with the use of TDH measurement and PL. We
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