Abstract
Taking advantage of electron diffraction based measurements, in a scanning electron microscope, can deliver non-destructive and quantitative information on extended defects in semiconductor thin films. In this work, we have studied a (11-22) semi-polar GaN thin film overgrown on regularly arrayed GaN micro-rod array templates grown by metal organic vapour phase epitaxy. We were able to optimise the diffraction conditions to image and quantify basal plane stacking faults (BSFs) and threading dislocations (TDs) using electron channelling contrast imaging (ECCI). Clusters of BSFs and TDs were observed with the same periodicity as the underlying micro-rod array template. The average BSF and TD densities were estimated to be ≈4 × 104 cm−1 and ≈5 × 108 cm−2, respectively. The contrast seen for BSFs in ECCI is similar to that observed for plan-view transmission electron microscopy images, with the only difference being the former acquiring the backscattered electrons and the latter collecting the transmitted electrons. Our present work shows the capability of ECCI for quantifying extended defects in semi-polar nitrides and represents a real step forward for optimising the growth conditions in these materials.
Highlights
Basal plane stacking faults (BSFs) can be created at the coalescence boundaries for compensating the translations between the neighbouring islands during the initial stage of the growth (Volmer Weber growth mode).8,9 In the case of the non-polar orientation, the displacement vector has a component parallel to the translation between the neighbouring islands, i.e., basal plane stacking faults (BSFs) are perpendicular to the growth surface
We demonstrate the application of electron channelling contrast imaging (ECCI) to image BSFs in semi-polar (11-22) GaN and determine the conditions to maximise the channelling contrast to reveal the BSFs and threading dislocations (TDs) in different scattering geometries
We will focus on the total density of TDs reaching the surface without identifying their types, and we assume that the imaged BSFs are of the I1 type due to their lowest formation energy
Summary
Basal plane stacking faults (BSFs) can be created at the coalescence boundaries for compensating the translations between the neighbouring islands during the initial stage of the growth (Volmer Weber growth mode). In the case of the non-polar orientation, the displacement vector has a component parallel to the translation between the neighbouring islands, i.e., BSFs are perpendicular to the growth surface (parallel to the coalescence boundaries). In the case of the non-polar orientation, the displacement vector has a component parallel to the translation between the neighbouring islands, i.e., BSFs are perpendicular to the growth surface (parallel to the coalescence boundaries). For the polar orientations, BSFs are parallel to the growth surface (perpendicular to the coalescence boundaries) and are not accepted to compensate the in-plane translation. The abovementioned techniques are either time consuming or destructive and do not provide statistically reliable spatial distribution of BSFs. Electron channelling contrast imaging (ECCI) in a SEM is one of the emerging techniques for characterising extended defects in a wide range of semiconductors, in particular, nitrides.. We demonstrate the application of ECCI to image BSFs in semi-polar (11-22) GaN and determine the conditions to maximise the channelling contrast to reveal the BSFs and TDs in different scattering geometries. We have validated our results by comparing them with a plan-view TEM image
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