This symposium focused on recent developments in GaN, InN, AlN and their alloys that are now finding application in short wavelength lasers (~400 nm, cw at room temperature) and high power electronics (2.8 W/mm at 8 GHz). The symposium was kicked off by S. P. DenBaars from UCSB who reported on advances in AlGaN/GaN transistors with frequency performance metrics of 50 GHz for ft and 92 GHz for fmax for a 0.2 micron gate length. W. Weeks of Cree Research gave an update about their work on GaN grown on SiC and presented some of the first public discussion of their conductive AlGaN buffer that will allow vertical light emitting diode and laser structures. M. Shur summarized work on visible blind detectors with work now focusing on improving the device speed. F. Ponce presented his latest understanding of the microstructure of heterostructures in AlGaN/InGaN/GaN structures with evidence of nonotubes extending through the quantum well regions. This ties in with reports that In-composition modulations in the quantum well gives rise to quantum dots that may enhance stimulated light emission in lasers. The topic of In-segregation and quantum dot formation came up though out the meeting and is an area of controversy. This topic was also addressed by J. Rosner of HP who showed convincing cathodoluminescence images from the edge of InGaN quantum well structures demonstrating inhomogeneous emission. On the last morning, R. Molnar of Lincoln Laboratories presented his progress in growing pseudo-bulk GaN layers by high growth rate vapor phase epitaxy with state-of-the-art material properties.
While much of the symposium reported on advances in material preparation and understanding of detect issues, similar advances in material processing were reported. S. J. Pearton of Un. of Florida gave an excellent overview of the state of processing and future challenges with a particular emphasis on the technologies that will be required for realizing high power devices in the group-III-nitrides. R. J. Shul of Sandia National Laboratories presented recent results for dry etching these materials in high density plasmas with etch rates and facet morphologies that should be applicable to laser formation. Q. Z. Liu of UCSD reported on thermally stable PtSi and NiSi Schottky contacts to GaN that appeared attractive for high temperature electronics. Advances in ion implantation doping of GaN were also reported using annealing temperatures up to 1400 C to achieve n-type doping levels up to ~3e20 cm-3.
Additional areas of interest was the high luminescence reported for epitaxial Er-doping of GaN with emission at 1.54 microns (J. D. MacKenzie, Un. of Florida). The emission remained high even at room temperature and was higher than that seen for Er-doping in other semiconductors. S. Tanaka of RIKEN Semiconductor Laboratories presented exciting possibilities for the use of GaN quantum dots in laser structures to reduce the threshold current.
Some noted theoretical results were given by W. Chow of Sandia National Laboratories on the gain in laser structures. He suggested the re-absorption in nonhomogeneous InGaN quantum well layers (e. g. quantum dots) may cause an increase in the laser threshold currents. Significant discussion was generated by T. Yamanoto of Osaka University with his theoretical model for enhancing p-type doping in GaN by using oxygen co-doping with Be or Mg. Increasing the p-type conductivity is a critical issue to reducing laser thresholds in this material.
Dr. John C. Zolper MS 0603/ Dept 1314 Sandia National Laboratories Albuquerque, NM 87185-0603 email: jczolpe@sandia.gov