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HL: Fachverband Halbleiterphysik
HL 22: Focused Session: Semi- and nonpolar group III nitrides II
HL 22.2: Topical Talk
Dienstag, 24. März 2009, 14:30–15:00, BEY 118
Growth on nonpolar and semipolar GaN: The substrate dilemma — •T. Wernicke1, M. Weyers1, and M. Kneissl1, 2 — 1Ferdinand-Braun-Institute, Berlin, Germany — 2Institute of Solid State Physics, TU Berlin, Germany
Growth of nonpolar and semipolar GaN is very promising for achieving green laser diodes (LDs). However, the choice of the substrate is a difficult one: Heteroepitaxial growth on sapphire, SiC, LiAlO2 yields GaN films with a poor surface quality and high defect densities. On the other hand non- and semipolar bulk GaN substrates provide excellent crystal quality, but are so far only available in very small sizes. In this paper hetero- and homoepitaxial growth will be compared. For all heteroepitaxially grown semi- and nonpolar GaN layers threading dislocations (TD) and basal plane stacking faults (BSF) can be found. There are four possible mechanisms for the generation of BSF: Growth of the N-polar basal plane, formation during nucleation at substrate steps, formation at the coalescence front of differently stacked nucleation islands, and generation at planar defects occurring in m-plane GaN on LiAlO2. BSF induce surface roughening and are associated with partial dislocations causing nonradiative recombination. Thus they affect the performance of devices. We will show that BSFs and TDs can be reduced by epitaxial lateral overgrowth resulting in several micrometer wide defect free areas. However, for LEDs larger defect-free areas are required. GaN layers grown on bulk GaN substrates exhibit a high crystal quality, but show in many cases long-range surface structures with a height of ≈ 1 µ m.