Microstructures of Cubic and Hexagonal GaN Grown on (0001) Sapphire by ECR-MBE with Various Electric Biases

Mechanism of stabilization of zincblende GaN on hexagonal substrates: Insight gained from growth on ZrB2 (0 0 0 1)

“…A factor which has often been discussed in the literature as a requirement for the stabilization of ZB-GaN on hexagonal substrates is a high Ga/N ratio during growth [7][8][9]12]. In the present work it was shown that ZB-GaN (1 1 1) of high phase purity could be obtained for a Ga/N ratio close to one; the growth surface was Ga-terminated, but there were no excess Ga adatoms contributing to surface reconstructions or droplet formation upon cooling.…”

“…In other words, these samples can be considered pure ZB (1 1 1) layers, at least within the resolution of the PL technique. This result is in contrast to previous studies of ZB-GaN (1 1 1), where data supporting the phase purity were either not given or else showed worse purity compared to our samples [5][6][7][8][9]. The introduction of a small fraction of WZ inclusions for more Ga-rich growth conditions could be attributed to GaN growth from metallic Ga droplets by a vapor-iquid-solid (VLS) related mechanism [22].…”

“…In growth situations with larger average island size, some WZ islands may be nucleated leading to reduced phase purity of predominately ZB-GaN films. This could explain why it is more difficult to obtain ZB-GaN (1 1 1) films of high phase purity on c-plane sapphire [7][8][9] compared to ZrB 2 .…”

“…Intentional growth of zincblende (ZB) GaN on the (0 0 1) face using cubic substrates has been widely studied [4], and in a few cases layers of predominantly (1 1 1)-oriented ZB GaN have also been obtained on substrates of hexagonal surface symmetry [5][6][7][8][9]. In the former case the reason for nucleation of the ZB phase is clear (reduction of the layer/substrate interfacial energy), but it is not well understood for the latter case.…”

Structural Control of Cubic and Hexagonal GaN by Changing the Electric Bias during ECR-MBE Growth

“…Yang et al [4] attempted an intriguing sequential growth method for h-GaN and c-GaN on GaAs (111) substrates by varying the substrate temperature during growth. In our previous study, cGaN was obtained by changing the electric bias voltages applied to the sapphire (0001) substrates during GaN growth by electron-cyclotron-resonance plasma-excited molecular beam epitaxy (ECR-MBE) [5,6]. The bias voltage-mediated method should have an advantage over the temperature-mediated method because the former is much quicker and simpler than the latter; hence, the bias voltage method has the potential to grow sharp hexagonal and cubic interfaces and superlattice structures.…”