Semipolar (10-11) GaN growth on silicon-on-insulator substrates: Defect reduction and meltback etching suppression

摘要

We demonstrate the growth of almost strain-free (10-11) semipolar GaN on silicon-on-insulator (SOI) substrates, with no melt back etching and with a defect density strongly reduced compared to semipolar templates grown on patterned silicon substrates. This is carried out using SIM substrates with a very thin (similar to 150 nm) 6 degrees off (001) Si top layer. By resorting to very small nucleation (111) facets, revealed through chemical etching of the topmost thin Si layer, we are able to diminish significantly the overall dislocation density. Cathodoluminescence and scanning electron microscopy images at different stages of the growth illustrate how the defect density reduction operates and confirm the complete suppression of meltback etching over the whole 2 in. wafer. Low temperature photoluminescence and optical reflectivity indicate that complete strain relaxation is closely achieved ((DX)-X-0 at 3.473 +/- 0.001 eV), compared to semipolar epilayers grown onto "bulk" silicon ((DX)-X-0 at 3.460 eV). Thanks to this efficient strain relaxation, very thick layers, up to 9 mu m, could be obtained crack-free.