Recent Progress in Implantation and Annealing of GaN and AlGaN
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'High Pressure Research Center, Polish Academy of Sciences, Warsaw, Poland d University of Florida, Department of Materials Science and Engineering, Gainesville, FL 32611, ABSTRACT Heterostructure modulation doped transistors (MODFETs) based on AlGaN/GaN structures have demonstrated impressive DC and microwave performance often despite high transistor access resistance. One approach to reducing the access resistance is to use selective area Si-implantation. While several reports exist on Si-implantation in GaN, little work has been done on implantation in AlGaN. In addition, more information on the annealing of implantation damage in GaN is needed to optimize its use in FETs and thyristors. We report the electrical and structural properties of Si-implanted Al0. 15Ga0 85N based on Hall measurements and Rutherford Backscattering (RBS) spectra, respectively. Al 0.15Ga0 85N shows less damage accumulation than GaN for a room temperature Si-implant dose of 5x10 15 cmn2 based on the minimum channeling yield (26% for AlGaN as compared to 34% for GaN), however, as with GaN, this damage is difficult to remove by thermal annealing at -1100 °C. We also report on high pressure (up to 15 kbar) and high temperature (up to 1500 °C) annealing for Si-implanted GaN. At 1250 'C -50% electrical activation is achieved which increases to -90% at 1500 °C. The photoluminescence of these samples is also restored, or even enhanced, by the high temperature treatments. Furthermore, RBS demonstrates that complete removal of the implantation induced damage is achieved for the 1500 0 C anneal. INTRODUCTION With the development of GaN-based electronics for high-power and high-temperature operation the reduction of the transistor access resistance becomes a more critical issue (1-4). The two approaches taken to reduce this resistance in other III-V semiconductor transistors are recessed gate designs and self-aligned implanted structures (5). Structures based on selective area implantation may be the preferred approach for GaN-based transistors due to the present difficulty in controllable wet etching of GaN (6). Although implantation doping of GaN has already been demonstrated, more work is needed to optimize the implant activation annealing process (7-9). In addition little work has been reported on the implantation doping and annealing of AlGaN. AlGaN layers will be employed in heterostructure transistors to realize a two dimensional electron gas (2-DEG) and to increase the transistor breakdown voltage. One would anticipate that the addition of Al to the GaN matrix will increase the damage threshold as is the case for AlGaAs as compared to GaAs (10), but this has not been studied prior to this work. In addition, it was recently reported that annealing implantation induced damage in GaN starts to occur between 1100 and 1300 'C, however, significant sample decomposition can also occur in this temperature range (11). Therefore, to study the fundamental limitation on implantation damage removal 979
Mat. Res. Soc. Symp. Proc. Vol. 482 © 1998 Material
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