Many of the papers presented at EMRS-97 were devoted to the indium phase separation and the formation of so-called quantum dots (QDs) in InGaN solid solutions. Kawakami, Sota and Deguchi showed the importance of QDs in the Nichia diode structure, the Strathclyde group reiterated their suggestion that fluctuations in the strained induced piezoelectric field are a major contributor to the broadening of the optical linewidths in the present InGaN-based LEDs. The group of CEA at Grenoble (Daudin, Feuillet) also described the possibility of controlled growth of GaN dots by MBE. The strong optical confinement they observed make these structures interesting for the development of future devices.
Numerous papers were given concerning the physics of the low temperature buffer layers, with a notable one given by Speck. Several TEM studies (Rouviere, Cherns, Ponce, Ruterana, Albrecht), and spatial fluorescence examinations (Trager-Cowan, Hoffmann, Bertram) were presented which showed the current progress being made concerning the physics of extended structural defects such as cubic phase inclusions or inversion domains, to cite a few examples. Advances in understanding the physics of growth have lead to an improvement of sample quality, as illustrated by the layer characteristics presented by researchers of Emcore Ltd and Aixtron Gmbh. Both industrial groups reported for instance an uniformity better than 2-3 nm for the InGaN photoluminescence wavelength. The growth of AlGaN (Clur, Stutzmann) is now rapidly progressing with interesting applications to Surface Acoustic Wave technology.
A plethora of fundamental properties were also studied and shown. Four wave mixing (Rühle) allowed the measurement of the coherence time of excitons, polariton effects were clearly addressed by Monemar, Look reviewed state of the art of transport properties, and Duboz reported measurement of the diffusion lengths of carriers by various methods. Even more fundamentals were beautifully described by S. Koch with the conclusion that the same gain can be expected in GaN materials and in II-VIs. Some interesting debate was initiated by O'Donnell, concerning the origin of the red shift observed between the gain peak and absorption edge. From the point of view of theoretical modeling, exciton binding energies and dispersion relations in GaN-AlGaN quantum wells were addressed (Bigenwald) and the comparison between wurtzite and cubic GaN for high frequency operating devices was made (Fauquembergue).
In addition to these material improvements, technological breakthroughs were also achieved. As an example, Binet beautifully demonstrated the fabrication of etched laser facets. Finally, the achievement of p doping and the fabrication of heterostructures by many groups allows us to advance with real optimism.
Dr. Bernard GIL Centre National de la Recherche Scientifique Universite de Montpellier II Groupe d'Etude des Semiconducteurs Case courrier 074 34095 Montpellier Cedex 5 France email: gil@ges.univ-montp2.fr
last updated Monday, June 23, 1997 3:04:11 PM.
© 1997 The Materials Research Society
