Electron Irradiation Induced Trap in N-Type GaN
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Physics Department, Wright State University, Dayton, OH 45435 University Research Center, Wright State University, Dayton, OH 45435
Electrical and Computer Engineering and Materials Department, University of California, Santa Barbara, CA 93106 Massachusetts Institute of Technology, Lincoln Laboratory, Lexington, MA 02173
ABSTRACT A 1-MeV-electron-irradiation (EI) induced trap at Ec-0. 18 eV is found in n-type GaN by deep level transient spectroscopy (DLTS) measurements on Schottky barrier diodes, fabricated on both metal-organic-chemical-vapor-deposition and hydride-vapor-phase-epitaxy material grown on sapphire. The 300-K carrier concentrations of the two materials are 2.3 x 1016 cm-3 and 1.3 x 1017 cm"3 , respectively. Up to an irradiation dose of 1 x 1015 cm2 , the electron concentrations and pre-existing traps in the GaN layers are not significantly affected, while the EI-induced trap is produced at a rate of at least 0.2 cm1. The DLTS peaks in the two materials are shifted slightly, possibly due to electric-field effects. Comparison with theory suggests that the defect is most likely associated with the N vacancy or Ga interstitial. INTRODUCTION Rapid progress in the development of blue light-emitting diodes, UV detectors, and hightemperature transistors in the III-V nitride system (GaN, AlGaN, and InGaN) has led to great activity in the growth and characterization of these materials [1,2]. In the early days of GaN growth, the electrical conductivity was nearly always strongly n-type, and it was thought that the donor was a native defect, the N vacancy (VN) [3,4]. Later studies suggested that 0 [5] and Si [6] were the prime candidates for residual donors. Recently, in samples of n-GaN grown by metalorganic chemical vapor deposition (MOCVD) and hydride vapor-phase epitaxy (HyPE), several electron traps located at 0.25 eV, 0.60 eV, 0.67 eV, and 0.88 eV, below the conduction band, with concentrations in the range 1013 to 1015 cm"3, have been revealed by deep level transient spectroscopy (DLTS) [7-9]. Based on the effects of 270-keV N21 implantation and annealing, two deep centers, with activation energies of 0.60 eV and 0.67 eV, are believed to be N antisite and N interstitial, respectively [9]. Although vacancy defects in Si [10] and GaAs [11-13] induced by high-energy electron irradiation (EI) have been extensively studied in the past, only two, recent studies have been conducted in GaN [14,15], to our knowledge. In the first of these, Linde et al. [14] used optically detected magnetic resonance of a photoluminescence band at 0.93 eV, produced by 2.5-MeV-electron irradiation, to obtain a tentative identification of a Gainterstitial complex. In the second, Look et al. [15] used temperature-dependent Hall-effect (TDH) measurements to identify N-vacancy/N-interstitial (Frenkel) pairs produced by 1-MeVelectron irradiation. In this paper, we present, for the first time, a DLTS study of 1-MeVelectron-irradiated, n-type GaN. An El induced trap, located at Ec-0. 18 eV, is produced at a rate of at least 0.2 cm 1
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