Magneto-Spectroscopy of Two-Electron Transitions in Homoepitaxial GaN.
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Magneto-Spectroscopy of Two-Electron Transitions in Homoepitaxial GaN. M.Wojdak1, J.M.Baranowski1$:\VPRáHN1,3 .3DNXáD156W I.Grzegory2 and S.Porowski2 1 2
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Warsaw, Poland 3 Grenoble High Magnetic Field Laboratory, MPI/FKF-CNRS, BP166X, F-38042 Grenoble Cedex 9, France ABSTRACT Two-electron transition occurs when the exciton bound to a neutral donor (DBE) recombines and leaves the donor in an excited state. The two-electron energy is therefore lower than that of the DBE peak by the difference in ground and excited state of the neutral donor. In a magnetic field the two-electron satellite splits into several components. These intra-donor excitations have been studied in homoepitaxial GaN up to magnetic fields reaching 23T. For Faraday (B c) configuration the two-electron transition splits mainly into 2s, 2p0, 2p+ and 2pcomponents. The total splitting between 2p+ and 2p- is equal to Landau energy. For Voigt (B⊥c) configuration in addition to transition to 2s, 2p0, 2p- and 2p+ there are additional lines which origin is discussed. It has been found that for two configurations of magnetic field the separation between 2p+ and 2p- is not exactly equal, what indicates the anisotropy of the electron effective mass. It has been found that m||* = 0.205m0 and m⊥* = 0.225m0. INTRODUCTION Homoepitaxial GaN layers are characterised by very good optical quality [1,2]. In this work the investigation of two-electron photoluminescence in a high magnetic fields is presented. Recombination of exciton combined with excitation of donor has been observed for the first time in CdS [3]. The two-electron transition in GaN have been reported previously [1,4]. The identification of the two-electron line was confirmed by magnetooptical measurements with magnetic fields up to 14T [5]. This transition has been detected in heteroepitaxial layers grown on Al2O3 [4] and in homoepitaxial layers grown on GaN single crystals [1,6]. The nature of the donor involved in two-electron transitions has not been identified. In this work we undertook study of two-electron transition in homoepitaxial GaN layers in magnetic fields reaching 23 T. The investigation of two-electron spectra in homoepitaxial layers has advantage connected with presence of relatively narrow emission lines. This property connected with high magnetic fields allows obtaining precise experimental data and therefore more deep interpretation of experimental results. EXPERIMENTAL RESULTS AND DISCUSSION The homoepitaxial layers have been deposited on GaN single crystals. The GaN crystals have been grown from gallium solution in a high nitrogen pressure of about 15 kbar and I8.10.1
temperature of about 1600C. The epitaxy was performed in MOCVD reactor using TMG and NH3 and H2 as a carrier gas. The magnetooptical measurements have been done in resistive magnet at liquid helium temperature
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