Dresden 2017 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 59: Nitrides: Preparation and Characterization II
HL 59.8: Talk
Wednesday, March 22, 2017, 17:00–17:15, POT 251
Polarity Control of GaN Nanowires — •Max Kraut, Martin Hetzl, Theresa Hoffmann, and Martin Stutzmann — Walter Schottky Institut and Physics Department, Technische Universität München, Garching, Germany
Heteroepitaxial GaN nanowires (NWs) have gained much interest in current research. However, the nucleation process of the GaN crystals, and in particular the orientation of the polar axis of the wurtzite crystal is not fully understood yet. Inconsistent results have been reported whether N, Ga or mixed polarity is the dominant feature. This indicates a complex interplay of growth mode, substrate type and growth parameters. We have systematically investigated the polarity distribution of GaN NWs grown by molecular beam epitaxy via selective area growth (SAG). Thanks to its high chemical and physical stability, diamond (111) has been used as a model substrate to elucidate the influence of the growth parameters, namely III/V flux ratio and substrate temperature Tsub. The polarity of individual NWs has been identified by Kelvin Probe Force Microscopy (KPFM) which allows a statistical investigation of large NW arrays. We find that Tsub is the driving force for the polarity distribution of GaN NWs on diamond whereas the III/V flux ratio plays a minor role. In particular, a variation of the fraction of Ga-polar SAG GaN NWs ranging from 45% up to 90% has been achieved by adjusting Tsub. In the case of self-assembled NWs and a comparably elevated temperature, N polarity is found to be the dominant crystal orientation. The findings obtained on diamond are in agreement with GaN NW growth on other substrates.