Microstructural evolution of nonpolar (11-20) GaN grown on (1-102) sapphire using a 3D-2D method

Abstract

The microstructure of nonpolar, a-plane (11-20) GaN grown on r-plane (1-102) sapphire, using a three dimensional (3D)-two dimensional (2D) growth transition, has been studied at different stages of metal organic vapor phase epitaxy. The microstructure and morphology of GaN islands formed at the initial stages of growth, as well as the fully coalesced film, were characterized using transmission electron microscopy (TEM) and atomic force microscopy (AFM). The growth of GaN islands (bounded by {10-11} and (000-1) facets) was established under reactor conditions of relatively high pressure and high V/III ratio, whereas the island coalescence was achieved at lower pressure and low V/III ratio, leading to pit-free films with shallow striations along ⟨0001⟩. Cross-sectional TEM studies, in combination with the AFM studies of the uncoalesced films, showed that there was a correlation between the point at which partial dislocation line direction changed and the point at which growth conditions changed from the 3D to 2D mode. Lengthening the 3D growth stage obviously increased the size of the GaN islands and was also found to increase the basal plane stacking fault (BSF) length and decrease the density of partial dislocations in the coalesced films: It is suggested that BSFs in adjacent islands merge when islands are sufficiently large to impinge before the 2D growth step. Their merging necessitates the annihilation of some of the partial dislocations, and this causes the decrease in dislocation density.

Solid-State Lighting Based on Light Emitting Diode Technology

“…However, it was found that the defect density is currently much higher in GaN structures grown in such directions [35], unless expensive freestanding non-polar or semi-polar GaN substrates are used [36]. Furthermore, the indium incorporation in the InGaN MQWs grown along non-polar direction is 2-3…”

Defect reduction in overgrown semi-polar (11-22) GaN on a regularly arrayed micro-rod array template

“…During the second coalescence process, some BSFs are terminated by a formation of either PDs or PSFs, leading to a further reduction in BSF density. 24 Consequently, this forms one area with a low BSF density (i.e., L region) and another area with a high BSF density (i.e., H region), appearing in a periodic form along the m-direction.…”

“…TEM measurements have been performed using a Philips EM430 TEM operating at 200 kV. Based on an invisibility criterion, [20][21][22][23][24] dislocations are out of contrast when the product of a diffraction vector g and a dislocation displacement vector R equals zero, namely, g · R=0 (It would still be possible to observe a weak contrast of dislocations for a very thin specimen in the case of the dislocation unparalleled to its burger vector. This does not apply in our case.…”

Quantification of unintentional doping in non‐polar GaN using scanning capacitance microscopy

“…Transmission electron microscopy studies on the samples studied here have found that dislocation density decreases with increasing 3D growth time, and the prismatic stacking faults (PSFs) extend through the films at 60° from the GaN/sapphire interface [10]. Hence, the unintentionally-doped features inclined at 60° to the GaN/sapphire interface observed in SCM could be due to enhanced impurity incorporation around PSFs.…”