Dependence Of Crystalline Quality Research Articles

Achievement of polarity reversion from Al(Ga)-polar to N-polar for AlGaN film on AlN seeding layer grown by a novel flow‐modulation technology

N-polar AlGaN epi-layer was realized on AlN seeding layer grown with a novel flow-modulation method. The polarity reversion from Al(Ga)-polar to N-polar for AlGaN/AlN films was confirmed by KOH etching and subsequent observation with optical microscope as well as high-resolution X-ray diffraction (HR-XRD) measurement. In particular, the dependence of crystalline quality and defect size in the N-polar AlGaN epi-layers on the V/III ratio was investigated with HR-XRD and scanning electron microscopy (SEM). It was found that as the full width at half maximum (FWHM) value of the X-ray rocking curve (XRC) varied with the V/III ratio in a fluctuating mode for the N–polar AlGaN epi-layers, and a FWHM value as small as 450 arcsec was achieved for the sample grown with a V/III ratio of 988. Moreover, it was revealed by the SEM measurement that the maximum diagonal length of hexagonal cone on the surface of the N-polar AlGaN epi-layers decreased sharply when a V/III ratio of 1236 was used although the crystalline quality and the surface morphology of the N-polar AlGaN epi-layers were not improved simultaneously. The peculiar migration of the group-III atoms on the surface of the N-polar AlGaN epi-layer associated with the molar ratio of TMA/(TMA + TMG) was considered to be responsible for this result.

Polarity dependence of In‐rich InGaN ternary alloys grown by RF‐MBE

AbstractIn‐rich (XIn > 0.5) InGaN ternary alloys were grown on N‐ and Ga‐polarity GaN templates by radio‐frequency plasma assisted molecular beam epitaxy (RF‐MBE) and their polarity dependence was investigated. In‐rich InGaN alloys with In‐content ranging from 0.5 to 1.0 could be grown without phase separation and sharp single diffraction peak was observed for these samples in X‐ray diffraction (XRD) 2θ–ω scan. Compared to N‐polarity samples, In‐polarity InGaN showed better crystalline quality in spite of about 100 °C lower growth temperature. Moreover, the dependence of crystalline quality on V/III ratio was investigated for In‐polarity samples. It was found that the phase separation in the InGaN tends to occur under metal‐rich condition but this can be prevented in N‐rich and around unity stoichiometry conditions as well. Precise control of V/III ratio to around unity stoichiometry was realized by using a shutter control method, which resulted in improvement of crystalline quality and surface morphology of In‐rich InGaN films. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of nitridation on crystallinity of GaN grown on GaAs by MBE

GaN films are grown on [0 0 1] GaAs substrates by plasma-assisted molecular beam epitaxy using a three-step process that consists of a substrate nitridation, deposition of a low-temperature buffer layer, and a high-temperature overgrowth. Films are evaluated by X-ray diffraction and the dependence of crystalline quality on the nitridation temperature is studied. It is demonstrated that nitridation has to be performed at low-temperature to achieve c-oriented α-GaN. Higher nitridation temperature promotes formation of mis-oriented domains and β-GaN inclusions