Radiation Damage Characterization in Ar + Implanted GaN
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R9.41.1
Radiation Damage Characterization in Ar+ Implanted GaN I. Usov 1 , A. Kvit 2 , Z. Reitmeier 2 , R. Davis 2 1 2
Los Alamos National Laboratory, MST-STC, Los Alamos, NM 87545, USA North Carolina State University, Department of Materials Science and Engineering, Raleigh, NC 27695, USA
ABSTRACT Damage microstructure evolution in GaN films implanted with argon ions (Ar+) as a function of implantation temperature was studied by cross-sectional transmission electron microscopy (TEM). After irradiation at room temperature, the implanted layer contained mostly isolated point defects. Implantation at elevated temperatures significantly reduced the number of isolated point defects. Numerous dislocations and regions exhibiting strain-contrast were observed after implantation at 300 oC. Bombardment at 600 oC resulted in formation of a new type of defect. Along with the partial dislocations and the strained regions, precipitates composed of carbon and nitrogen were identified by electron energy loss spectroscopy. These precipitates were formed in the vicinity of the Ar+ projected range where the amount of radiation damage was maximal. The high concentration of defects facilitated redistribution of carbon atoms introduced during the GaN film growth and resulted in the formation of precipitates. No precipitates were observed after implantation at 1000 oC. Consideration of the TEM results in conjunction with ion channeling data showed that presence of the precipitates correlated with a reverse annealing damage accumulation mode, which manifests itself as an increase of backscattering yield with increasing implantation temperature. The results of our study indicated that the carbon impurity in as-grown GaN films enhances the radiation damage accumulation rate and consequently has to be taken into account when ion implantation doping of GaN is performed. INTRODUCTION Development of GaN doping by ion implantation will significantly expand its application in microelectronics. A principle obstacle to obtain good quality implanted GaN layers is the difficulty in recovery of the crystalline lattice damaged by energetic particles. The crystalline lattice recovery can be achieved by performing ion implantation at elevated temperatures and/or by subsequent annealing. Previous studies have shown that defects produced by high dose ion implantation conducted at room temperature (RT) cannot be completely removed by annealing [1-5]. Annealing of GaN bombarded with Ar+ at elevated temperatures revealed that the recovery was worse than for the samples implanted at RT [5]. Moreover, it has been observed that there is an implantation temperature (Timp) range where the amount of disorder measured by channeling Rutherford backscattering spectroscopy (C/RBS) increased with the increase of the implantation temperature [6,7]. Such behavior is called “reverse annealing”. Similar effect, but at lower temperatures, has also been noticed during high-temperature implantation of silicon [8,9]. It was attributed to formation of secondary defects such a
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