Microstructural characterization of α-GaN films grown on sapphire by organometallic vapor phase epitaxy

Abstract

Microstructure of α-GaN films grown by organometallic vapor phase epitaxy on sapphire substrates using low temperature AlN (or GaN) buffer layers has been studied by transmission electron microscopy. The defects which penetrate the GaN films are predominantly perfect edge dislocations with Burgers vectors of the 1/3〈112̄0〉 type, lying along the [0001] growth direction. The main sources of threading dislocations are the low angle grain boundaries, formed during coalescence of islands at the initial stages of GaN growth. The grain sizes range from 50 to 500 nm, with in-plane misorientations of less than 3°. The nature of these threading dislocations suggests that the defect density would not likely decrease appreciably at increasing film thickness, and the suppression of these dislocations could be more difficult.

The Composition Pulling Effect in MOVPE Grown InGaN on GaN and AlGaN and its TEM Characterization

“…The distribution of the pits corresponds to that of the dislocations penetrating the GaN layer. The pit pattern is similar to the dislocation pattern which has been observed by plan-view TEM of GaN on a LT buffer layer [9]. From the results of Ref.…”

“…Although crystalline quality of the GaN epitaxial layer is quite good, there is a high density of threading dislocations penetrating the GaN layer along the c-axis from the AlN buffer layer to the InGaN/GaN interface. These dislocations are predominantly perfect edge dislocation with burgers vectors of the 1/3<11-20> type [9]. The pit has a hexagonal inverted pyramid-like structure.…”

“…[9], it is suggested that the lines of pits are due to threading dislocations forming at grain boundaries in the GaN film. The calculated pit density is of the order of 10 9 cm -2 , which is in good agreement with the reported value of the dislocation density [9]. Thus it is found that the pits originate from edge dislocations penetrating the GaN layer.…”

High-quality GaN on intentionally roughened c-sapphire

“…Also seen are arrays of depressions which most probably consist of edge TDs (Fig. 1d), in agreement with TEM studies reporting TDs with predominantly mixed character with b = 1/3 1123 , pure edge character with b = 1/3 1120 , and very few of pure screw character with b = 0001 in as-grown device quality MOCVD GaN [8][9][10][11]. It is important to note that although grown on substrate surfaces of increasing roughness, the images in Figures 1c and 1d are very similar, both indicative of high-quality, fully coalesced GaN sur- faces that are not different from surfaces observed on GaN grown on undamaged sapphire [12].…”

Investigation of defects and surface polarity in GaN using hot wet etching together with microscopy and diffraction techniques

“…The poor match in both lattice parameter and thermal expansion coefficient results in a high density of threading dislocations (TD) (10 8 -10 10 cm -2 ) [1,2,3,4,5] that have been demonstrated to affect both electrical and optical properties of the material [6,7]. Mostly, the characterization of dislocations is carried out using TEM, a process that requires extensive sample preparation.…”