Donor-like Deep Level Defects in GaN Characterized by Double-correlation Deep Level Transient Spectroscopy
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Donor-like Deep Level Defects in GaN Characterized by Double-correlation Deep Level Transient Spectroscopy M. Ahoujja, 1 M. Hogsed, 2 Y.K. Yeo, 2 and R. L. Hengehold2 1 2
Department of Physics, University of Dayton, Dayton, OH, USA Air Force Institute of Technology, Wright-Patterson AFB, OH, USA
ABSTRACT Si doped GaN grown by molecular beam epitaxy on sapphire substrates were characterized by capacitance transient spectroscopy. Conventional deep level transient spectroscopy (DLTS) measurements displayed six deep level defects, labeled A1, A, B, C1, C, and D, with activation energy ranging from 0.20 to 0.82 eV below the conduction band. Based on the logarithmic dependence of the DLTS spectral peaks on the filling pulse width, it is deduced that the defects A, B, C, and D are concentrated in the vicinity of line dislocations. Double-correlation DLTS (DDLTS) measurements, on the other hand, showed that only defects A (0.82 eV) and D (0.22 eV) exhibited deep donor-like characteristics. Following a 1.0 MeV electron irradiation of the GaN sample, one radiation-induced peak, E, with activation energy less than 0.20 eV was observed in the DLTS spectrum. However, after annealing at 350 oC, this DLTS peak intensity was found to diminish significantly. INTRODUCTION GaN and its related Group III-nitrides are of interest in the fabrication of hightemperature and high-frequency electronic devices as well as blue to UV light emitting and detecting devices [1-3]. Defects and impurities, which are either intentionally or unintentionally introduced, often control the properties of these materials and are responsible for degradation of device performance [4,5]. Therefore, an understanding of the role of the extended, and point defects in GaN, and the mechanisms for their formation is essential for the realization of high performance devices. In this study, deep defects in as grown silicon doped GaN and silicon doped GaN irradiated with 1.0 MeV electron at a dose of 2x1016 cm-2 are investigated using conventional DLTS and doublecorrelation DLTS measurements. EXPERIMENT 1 µm thick GaN layers doped with silicon were grown by radio-frequency plasma assisted molecular beam epitaxy (MBE) on the c-plane of a sapphire substrate. Prior to metal deposition, the GaN wafers were cut into small pieces of 5x5 mm2 each, degreased using standard chemical solvents, and followed by a dip in a boiling aqua regia (HCL / HNO3 : 3/1) solution for 30 s and a rinse in de-ionized water. For Ohmic contacts, a Ti(300Å)/Al(800Å)/Ti(1200Å)/Au(500Å) metallization was deposited by electron beam evaporation and annealed under a nitrogen atmosphere at 900 °C for 45 s in a rapid thermal anneal system. For Schottky contacts, a Ni(350 Å)/Au(4000 Å) metallization
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was used. DLTS measurements were made from 70 to 450 K using a fast capacitance meter with a 100 mV test signal at 1 MHz. Measurements of 800 capacitance transients were made at each temperature and then averaged together to significantly improve the signal. The rate window me
