Optical Study of GaN Doped with Mn Grown by Metal Organic Vapor Phase Epitaxy
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OPTICAL STUDY OF GaN DOPED WITH Mn GROWN BY METAL ORGANIC VAPOR PHASE EPITAXY R. Y. Korotkov, J. M. Gregie and B. W. Wessels Northwestern University Department of Materials Science and Engineering and Materials Research Center Evanston, IL 60208
ABSTRACT The optical properties of Mn-doped GaN were investigated. The films were grown by metalorganic vapor phase epitaxy using tricarbonyl (methylcyclopentadienyl) manganese as the dopant source. Two characteristic bands were observed in the absorption spectra of Mn-doped epilayers. The low energy band had a threshold at 1.4 ± 0.05 eV with a maximum at 1.5 ± 0.02 eV, with a full width half maximum of 245 ± 10 meV at 296 K. A second higher energy band was observed as a shoulder to the band edge absorption with a threshold energy of 2.06 eV at room temperature. Using photoluminescence spectroscopy, a new broad band was observed in the infrared spectra of GaN:Mn at 1.27 ± 0.02 eV with a full width half maximum of 0.26 ± 0.01 eV at 20K. From analysis of optical absorption and emission spectra Mn forms a deep acceptor level with optical transitions at 1.4 and 2.06 eV. The deep level nature of Mn indicates that it is a potential dopant for semi-insulating GaN.
INTRODUCTION While the optical properties of shallow impurities in GaN have been widely studied, the behavior of deep level defects in these materials are not well established. This is particularly the case for transition metals. These impurities can potentially limit the efficiency of opto-electronic devices, since they form multiple charge states that can act as efficient recombination centers. The open d-shell configuration of the transition metals usually results in several localized deep levels in the band gap, that are characteristic of the impurity [1-2]. Since these metals introduce deep levels, they are often used as dopants to obtain semi-insulating material [2]. Thus, the identification of transition metals that form deep levels in GaN is of importance. However, little is known about defect formation in GaN deliberately doped with a transition metal [3-4]. Nevertheless, transition metals as unintentional dopants have been studied in GaN [1,3,5]. Electron paramagnetic resonance (EPR) studies of residual impurities in GaN bulk crystals unambiguously identified the presence of Mn2+ ion by measuring its hyperfine structure due to interactions of 55Mn (I = 5/2) nuclei [1]. Co2+ has been observed in the infra-red photoluminescence (PL) spectra of GaN. The 1.047 eV band has been attributed to an internal electronic transition (4T2(F)→ 4A2(F)) of a transition metal with a 3d7 electronic configuration [5]. Trace impurities of Fe3+Ga (3d5) and Cr4+Ga (3d2) have also been tentatively correlated with the PL zero phonon lines (ZPLs) at 1.3 and 1.19 eV, respectively [3]. In this paper the optical properties of deliberately Mn-doped GaN are reported. The introduction of Mn in GaN leads to formation of deep levels that result in semi-insulating material in as-grown as well as annealed layers. From absorption and emission spe
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