Topic: GaN on Silicon Substrates for Solid State Lighting: Strain Compensation
Speaker: Martin Albrecht, Research scientist at Leibniz-Institut für Kristallzüchtung.
Time: 2:00pm,June 7, 2013.
Location: Conference Room D111,SINANO
Growth of GaN-based light emitting diodes on silicon substrates is an attractive alternative to the technology based on sapphire or SiC. Several groups have already demonstrated that high quality GaN on Si can be grown by MOVPE on 100, 150 and also 150 mm diameter substrates and that growth is easier than on large diameter sapphire. Major challenge in the growth of thick GaN layers on silicon is the difference in thermal expansion coefficients between layer and substrate that causes tensile thermal stress during cooldown and may lead to cracking of the layer. In the last decade a number of concepts have been developed to overcome the cracking problem by growing graded AlGaN buffers, AlN interlayers and SiN interlayers. While thick, crackfree GaN-layers on silicon were demonstrated, the mechanism that induce compressive strain during growth are far from clear.
In Martin Albrecht's talk a detailed study on dislocation processes and relaxation mechanisms in the growth of GaN on silicon will be presented. Focus will be on (i) growth and relaxation of high temperature and low temperature AlN interlayers and their role in the strain management, (ii) dislocation glide and critical thickness issues, (ii) structure and formation of the “SiN mask” and their role in dislocation density reduction. Based on the detailed understanding of the dislocation processes GaN layers on silicon substrates can be obtained, that have dislocation densities in the range of 2x108cm-2, which is comparable to state of the art in GaN on sapphire. LEDs fabricated based on improved buffers have external quantum efficiencies higher then 60%.
12/1996–3/2000 Assistant Professor at the University of Erlangen
3/2004–now Research scientist at Leibniz-Institut für Kristallzüchtung
1981 Graduation from High School (Heinrich-Hertz-School Hamburg)
1989 Diploma in Physics, University of Hamburg
1996 Ph.D. in Physics, University of Hamburg
04/1990–12/1996 PhD student at the University of Erlangen,
Thesis: Surface energy and strain relaxation in heteroepitaxial growth- an analysis ofsolution grown GeSi
Field of research:
Mechanisms of crystal growth, selforganised growth, defects, dislocations mechanisms, optical electrical and structural properties of defects, Nitrides, analytical and high resolution transmission electron microscopy .
Papers in peer reviewed Journals: >150, Invited talks at international conferences: >30