A deep level with the activation energy around O.45-O.6eV has persistently appeared in GaN samples grown by hydride vapor-phase epitaxy, organometallic vapor-phase epitaxy and molecular beam epitaxy. However, the origin of this deep level still remains unclear. In this study, we investigated this deep level trap E2 of GaN films by using deep level transient spectroscopy. The GaN films were grown by a conventional low pressure organometallic vapor-phase epitaxy technique with different V/Ill

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... os. Frequency-dependent capacitance measurement was performed to determine the most proper frequency for capacitance measurements Capacitance-voltage measurements were then applied to obtain the canier concentrations. The carrier concentration became higher as the flow rate of NH3 got lower. The deep level E2 is found in GaN samples grown with higher V/Ill ratios. The trap concentration of level E2 increased with increasing NH3 flow rate. Compared with the theoretical prediction ofthe nitrogen antisite level in GaN, the level E2 was believed to be related to nitrogen antisites. Keyword GaN, deep level, organometallic vapor-phase epitaxy, V/Ill ratios, frequency capacitance, antisite defect, DLTS INTROI)UCTION Group 111-V mtrides have wide bandgaps varied from 1.9eV, of InN, to 6.3eV, of A1N, and been promising materials for blue and ultraviolet optoelectronic devices1, high temperature, and high power transisors23, and solar-blind ultraviolet detectors.4 However, the progress of GaN technology has often been limited by material quality, such as high defect densities. Therefore, it is important to investigate the deep level traps in GaN. Deep-level transient spectroscopy (DLTS) and transient capacitance methods have been used to characterize the deep level traps in GaN grown by hydride vapor-phase epitaxy (HyPE), organometallic vapor-phase epitaxy (OMVPE) and molecular beam epitaxy (MBE). Several deep level centers in n-GaN with activation energies ranging from 0.14-1 .63eV have been reported5". Among them, a deep level with the activation energy around O.45-O.598eV has been observed in samples grown by different techniques5'6'7'9"°. The origin of this deep level still remains unclear. In the present study, we characterized deep level traps of two sets of GaN films by using deeplevel transient spectroscopy (DLTS) and transient capacitance method. EXPERIMENT Two sets of n-type GaN film were discussed in this study. The set I, fabricated by AXTRON planetary reactor, contained about 4 im thick Si-doped GaN layer (labeled Ri). The set II were prepared by a conventional low pressure OMVPE, and the thickness ofundoped GaN film was about 2gm. The detail growth procedure had been described elsewhere.'2 The Set II, in brief, was grown by a conventonal low pressure OMVPE reactor with trimethylgallium (TMG) as the column III precursor, and NH3 as the column V precursor, respectively. A thin (500A) GaN buffer layer was deposited on c-plane sapphire substrate at 525 using TMG and NH3, and GaN film was then grown at 1050 . The GaN films, set II, was grown with different V/Ill ratios. The flow rate of NH3 were 2500 sccm 2000 sccm 1500 sccm,