Heteroepitaxial growth of GaN on vertical Si{110} sidewalls formed on trench-etched Si(001) substrates

A maskless Si trench structure was developed to integrate crystallographically non-polar GaN microstructures with semi-polar facets on Si(001). GaN “fins” were preferentially grown by MOCVD on Si{110} trench sidewalls formed by deep reactive ion etching (DRIE) of Si(001) such that GaN(0001)//Si{110} and GaN(10-10)//Si(001), resulting in a non-polar crystal structure with respect to the Si(001) substrate surface. No masking layer was required to prevent GaN growth on the Si(001) top surface of the trenches, instead, it was found that GaN nucleated preferentially on the Si{110} trench sidewalls. GaN was also observed to nucleate at the top corner of the trenches due to Si etching and exposure of high-index Si facets during the pre-growth H2 anneal. This undesired GaN nucleation was successfully suppressed by reducing the H2 anneal time and/or increasing the growth temperature and decreasing the precursor V/III to enhance Ga-adatom diffusion. Cross-sectional TEM studies confirmed that the GaN fins were crystallographically non-polar with respect to the Si(001) substrate surface and were bounded by semi-polar and non-polar facets. The reported Si fabrication and GaN growth process shows promise for the integration of non-polar and semi-polar GaN microstructures on industry standard Si(001) substrates.