The workshop opened with a session on LEDs lead off by an invited paper by Prof. Schneider from Fraunhofer-Freiburg. He discussed the use of Nitride LEDs encapsulated in various phosphors to make luminescent conversion (LUCO) LEDs. Data from LEDS fabricated by Siemens using Cree dies were presented. Also, the use of polymers in LEDs was discussed. Also in this session, T. Suski suggested that sub-bandgap emission from InGaN quantum wells in LEDs might be due to cubic InGaN inclusions. M. Schauler from Univ. of Ulm presented his group's work on LED fabrication.
The second session that afternoon covered bulk crystal growth and primarily consisted of papers from the High Pressure Research Center in Warsaw, Poland and the Ioffe Physical-Technical Institute in St. Petersburg, Russia. Another by J. Nause of CERMET, Inc. from the United States described his results in the bulk growth of AlN. The talks of the Polish group discussed properties of their crystals as well as new data were presented on crystals doped with Mg which resulted in high resistivity bulk GaN. Y. Melnik from Ioffe showed results from HVPE on SiC with free standing GaN crystals removed from the SiC as large as 7x6mm.
The final session of day discussed MBE growth. The session was opened by an invited talk from H. Morkoc from the Univ. of Illinois. Other papers in the session discussed topics such as RF nitrogen sources, use of beta-SiC and Si as substrates. The first day concluded with a cocktail reception followed by dinner.
B. Gil of Univ. of Montpellier opened the second day of the workshop with an invited talk on stain effects in GaN on different substrates. In his discussion, the relationship of exciton energies with strain was presented as well as other fundamental parameters such as deformation potentials. Other papers in the session involved various studies of GaN material with photoluminescence. Several presenters (T. Eustis, R. Seitz) discussed yellow band luminescence. The second session of the morning was opened by A. Hangleiter of the Univ. of Stuttgart with his invited paper on optical gain in GaN-based laser structures. He discussed experiment using both PL and PLE techniques as well as the effective mass of heavy holes in GaN. Also, an estimation for lowest possible lasing threshold in GaN based lasers was presented based on band calculations. Other papers in this session discussed various aspects of InGaN quantum wells.
The first session of the afternoon focused on native defects in GaN. This session included both talks by theoreticians and experimentalists. Talks by I. Gorczyca and V. Fiorentini presented their respective work involving calculations related to native defects. Prof. Stutzmann from the Technical Univ. of Munich. discussed the characterization of GaN grown using nitrogen-15. Other work presented included implantation damage (Dalmer), surface diffusion (Zywietz), ODMR of yellow luminescence (Michael) and Ga vacancies (Hautojarvi).
The second session of the afternoon focused on extended defects. In addition to papers discussing the use of transmission electron microscopy (TEM) (Albrecht, Speck, Arlery, Ruthena), Prof. Trager-Cowan of the Univ. of Strathclyde discussed the relationships between surface structure and luminescence. Prof. Hersee of the Univ. of New Mexico proposed that the boundaries in GaN on sapphire leads to a conduction band discontinuity that affect electrical conduction. Two late news papers were also presented. One paper by Prof. Eastman on "universal substrate' work done at Cornell Univ. and another by F. Ponce at Xerox PARC on correlation of TEM and luminescence in InGaN. The second day of the workshop closed with a third session on characterization. Papers presented included such topics as meltback etching (Novikov), Schottky contacts on GaN (Sporken), electron mobility (Orton) and photoconductive GaN (Monroy). Following the last session, a reception was held, followed by dinner.
The final day of the workshop opened with two sessions on AlGaN and related alloys. Papers on the growth and properties of MOCVD (Cros, Clur) and MBE (Korakakis, Ambacher) growth of AlGaN were presented while M. Bremser presented work on Si and Mg doping AlGaN. Other researchers presented results on GaNAs growth (Thordson) and InGaN deposition on glass. Prof. Eastman of Cornell Univ. presented details on AlGaN/GaN MODFETs. F. Bernardini presented calculations of polarization at AlN/GaN interfaces.
The third session of the morning involved p-doping of GaN. In addition to papers on growth (Haffouz, Cheng) and characterization (Sanchez) of Mg doped GaN, T. Strite of IBM Zurich presented work on high pressure annealing to optically activate Zn-implanted GaN. V. Torres presented calculations of hydrogen passivation of Mg in GaN.
The workshop closed with a session of MOVPE. Papers presented included GaN growth of SiC (Chi), reactor modeling (Karpov, Makarov), reactor performance for production (R. Niebuhr) and impurity analysis of InGaN grown by MOVPE (E. Piner), as well as a late newspaper in which J. Pankove of Astralux Corp. explained the need to eliminate dislocations in GaN to realize low threshold lasers.
In summary, in addition to the great food and beautiful weather, everyone came away with new knowledge and a great deal of enthusiasm.
The next European Workshop (EGW-3) will be held in Warsaw, Poland, and the organizers have promised that dancing will be encouraged in the evenings.
Michael D. Bremser, Ph.D. North Carolina State University Materials Science and Engineering Box 7907 ; 229 Riddick Hall Raleigh, NC 27695-7907