Oxygen related shallow acceptor in GaN
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E5.10.1
Oxygen related shallow acceptor in GaN B. Monemar1, P. P. Paskov1, F. Tuomisto2, K. Saarinen2, M. Iwaya3, S. Kamiyama3, H. Amano3, I. Akasaki3, and S. Kimura4 1
Department of Physics and Measurement Technology, Linköping University, S-581 83 Linköping, Sweden 2 Laboratory of Physics, Helsinki University of Technology, P. O. Box 1100, HUT 02015, Finland 3 Department of Electrical and Electronic Engineering, Meijo University, 1-501 Shiogamaguchi, Tempaku-ku, Nagoya 468, Japan 4 Sumitomo Seika Chemicals Co Ltd, J5-33, 4-Chome Kitahama, Chuo-ku, Osaka 541-0041, Japan ABSTRACT We report on deliberate O doping of GaN epitaxial layers during MOCVD growth, using H2O and CO2 as precursors. The photoluminescence spectra show a dominant 3.27 eV emission at 2 K known to be a donor-acceptor pair (DAP) transition. In our samples the intensity of this DAP spectrum correlates with the commonly observed 3.466 eV acceptor bound exciton (ABE) peak, suggesting these spectra are related to the same acceptor. The general correlation of these acceptor spectra with O concentration (as established with SIMS data) suggest that the acceptor is O-related, most likely a VGa-O complex. The concentration was measured with positron annihilation spectroscopy and found to be in the 1016 cm-3 -1017 cm-3 range in different samples. Considering previous results the identity of this residual acceptor is suggested to be a VGa-O-H complex. Previous suggestions that this acceptor is related to Mg, Si or C are discussed and found to be less likely. INTRODUCTION The optical signatures of the shallow acceptors in GaN as obtained from photoluminescence (PL) spectra at low temperature are still not established. This is true for the bound exciton (BE) spectra as well as the lower energy donor-acceptor pair (DAP) emissions. A very commonly occurring and often strong DAP emission with a zero-phonon peak at about 3.27 eV [1, 2] is related to a residual acceptor with a binding energy about 0.225 eV that is so far not identified. In fact it is so commonly occurring and also dominant in doping with different acceptors, that in early work on HVPE GaN the idea was put forward that all substitutional acceptors in GaN had about the same binding energy [3, 4]. In recent years it has been suggested that the 3.27 eV DAP is related to the Mg acceptor, the only acceptor useful for p-doping of GaN [5, 6]. Mg introduces a broad PL band peaking at about 3.1 eV at moderate Mg doping, however, typically coexisting with the 3.27 eV DAP [7]. Various other suggestions have been made for the 0.225 eV acceptor, such as substitutional C [8] or Si [9] on N site. No convincing correlation of these suggested acceptors with corresponding doping experiments have been provided, however. In this work we demonstrate a positive correlation between the PL intensity of the 3.27 eV DAP emission as well as the 3.466 eV acceptor BE (ABE) emission line with O doping, in MOCVD grown layers.
E5.10.2
EXPERIMENTAL DETAILS A number of O-doped GaN layers of thickness of 1-2 µm layers were grown
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