Selective Area Growth of Ga- and N-polar GaN Nanowire Arrays on Non-Polar Si (111) Substrates

Published

September 7, 2014

Author(s)

Matthew D. Brubaker, Shannon M. Duff, Todd E. Harvey, Paul T. Blanchard, Alexana Roshko, Aric W. Sanders, Norman A. Sanford

Abstract

This study presents a technique for obtaining Ga- and N-polar Gallium Nitride nanowire (GaN NW) arrays on non-polar Si (111) substrates by use of polarity-controlled AlN/GaN buffer layers. AlN films are demonstrated to adopt Al-/N-polarity for N-/Al-rich growth conditions, as characterized by a combination of piezoresponse force microscopy measurements (Fig. 1) and polarity-sensitive etch tests. Subsequently grown GaN layers propagate the AlN polarity, producing polarity-dependent surface reconstructions observed in the RHEED patterns after buffer layer growth (Fig. 2a,b). These RHEED measurements provide a means for convenient in-situ assessment of the buffer layer polarity, prior to deposition and patterning of the silicon nitride growth mask. After cleaning and reintroduction into the MBE system, GaN NW arrays were grown on the polarity- controlled growth templates at temperatures sufficiently high to inhibit growth on the silicon nitride mask (Fig. 2c,d). N-polar templates produced fast-growing structures with vertical sidewalls and irregular (but largely flat) top surfaces. In contrast, Ga-polar templates resulted in slow-growing pyramidal structures bounded by (1-102) planes. Longer NWs protruding from some of the pyramidal structures, likely to be fast-growing N-polar NWs, might nucleate on inversion domains in the Ga-polar buffer layer or from Ga droplets. The Ga-polar growth rate at selective growth temperatures is limited by decomposition, as determined by separate studies on planar GaN layers (Fig. 3). These results suggest that the process window, bounded by non-selective and no- growth conditions, is stringent for Ga-polar NW arrays, but may be somewhat more relaxed for fast- growing N-polar NW arrays.

Proceedings Title

Journal of Crystal Growth

Conference Dates

September 7-12, 2014

Conference Location

Flagstaff, AZ

Conference Title

18th International Conference on Molecular Beam Epitaxy

Pub Type

Conferences

Keywords

gallium nitride, nanowires, molecular beam epitaxy, crystallographic polarity

Citation

Brubaker, M. , Duff, S. , Harvey, T. , Blanchard, P. , Roshko, A. , Sanders, A. and Sanford, N. (2014), Selective Area Growth of Ga- and N-polar GaN Nanowire Arrays on Non-Polar Si (111) Substrates, Journal of Crystal Growth, Flagstaff, AZ (Accessed December 5, 2024)