Variations in mechanisms of selective area growth of GaN on nano-patterned substrates by MOVPE

The growth behaviour of GaN selective area growth (SAG) by MOVPE on two types of nano-patterned GaN substrates has been investigated. Samples were characterized by SEM, AFM and TEM. Results indicate that well formed nano-pyramids with base size of ˜150 nm, and sharp tips are readily grown through mask patterns defined by electron beam lithography (EBL). A growth rate of nearly zero on the {101¯1} nano-facets, effectively self-limiting growth (SLG), has been observed under a wide range of growth conditions using a conventional growth mode. In contrast, pulsed growth is able to change the SLG behaviour, and thereby control the size of pyramids, even to coalesce the pyramids to form flat, smooth GaN films. SLG-like behaviour of GaN SAG on patterns defined by nano-imprint lithography (NIL) is also observed and enabled nano-pyramids to form. However, GaN SAG on NIL patterns shows accelerated growth in some pores at the early stage of the growth. This accelerated growth is attributed to the possible presence of screw-type dislocations in the pore.