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

Abstract

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 {10$ \bar 1 $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. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Cathodoluminescence studies of GaN coalesced from nanopyramids selectively grown by MOVPE

“…Figure 5 Integrated intensity (nm x counts) corresponding to 1-3 periods (450 nm) of the growth mask pattern. These can be related to strain variations and/or unintentional doping in and between neighbouring GaN nanopyramids [12]. However, data shown below indicate that the contribution to the lateral variation in GaN NBE emission energy due to doping variations is relatively small.…”

“…This compressive strain blueshifts the NBE energy compared to the value for bulk GaN, and this shift is expected to increase with depth in a GaN-on-sapphire sample. The network of dislocations usually exists in the first few nm of the coalesced epilayer [12]. Whilst the dislocations help to relieve the compressive stress in the lower level of the coalesced layer, there is evidence that the epitaxy grown between the nanopyramids in the early stage of coalescence can be under compressive strain [21].…”

“…More details on sample growth are given in Ref. [12]. The light emitting properties of the samples were studied by room temperature CL hyperspectral imaging using two different set ups: a field emission SEM using an angled sample [11] and an electron probe micro-analyser [14] respectively.…”

Facet recovery and light emission from GaN/InGaN/GaN core-shell structures grown by metal organic vapour phase epitaxy on etched GaN nanorod arrays

“…For the 20, 60, and 300 s duration etches, re growth occurred along the full length of the nanorods to reveal {1-100} m-plane facets on the sidewalls and {10-11} facets on the nanorod tops to form nanopyramids. 32 The passivation has a striking impact on the geometry of the re-grown GaN. At the bottom of the nanorods of the 60-s-and 300-s-etched samples, the verticality inherent to m-plane growth is lost.…”

Effect of coalescence layer thickness on the properties of thin‐chip InGaN/GaN light emitting diodes with embedded photonic quasi‐crystal structures

“…Fully coalesced GaN epitaxial layers were overgrown using a pulsed MOVPE technique 14. Figure 2 compares the measured and simulated optical reflectance of one of the embedded PQCs formed by this process.…”