The growth of homoepitaxial GaN, AlGaN layers, and GaN/AlGaN multiple quantum wells (MQWs) on Ga- and N-faces of bulk GaN single crystal substrates prepared by pressure-controlled solution growth (PC-SG) has been performed by radio-frequency molecular-beam epitaxy (RF-MBE). It was determined that homoepitaxial GaN layers grown on both Ga- and N-faces had good crystallinity with narrow full-width at half maximum (FWHM) of 150 and 94 arcsec for the (0002) plane and 119 and 106 arcsec for the (10-12) plane in x-ray rocking curve measurements, respectively. Crack-free AlGaN epilayers with Al mole fraction up to 30% were obtained on both faces. AlGaN epilayers on Ga-faces with higher Al mole fraction than those on N-faces under the same Al flux condition were obtained. Furthermore, phase separation existed only in the AlGaN epilayers grown on N-faces. The 5 K photoluminescence spectra for the GaN/AlGaN MQW structures grown on Ga-faces at peak energy of 3.419 to 3.686 eV can be obtained by varying the well thickness from 18 to 2 ML.
We have attempted the grown of GaN by RF-MBE which crystalline quality is a match for the by MOCVD, performing homoepitaxial growth using MOCVD-GaN as a substrate. We confirmed that homoepitaxial GaN had Ga polarity by (1 x 1) RHEED streaky pattern after coolingd own. 10 min-BHF-etching was the most effective for cleaning the surface of GaN substrate, and as the result crystalline quality of homoepitaxial GaN was improved. Thermal annealing of GaN substrate was also affect for the improvement of crystalline quality of homoepitaxial. From XRD measurement, FWHM of diffraction spectrum from homoepitaxial GaN almost equaled to that from GaN substrate. So, the crystalline quality of homoepitaxial GaN was not inferior to that of GaN substrate. Large compression strain in c plane of homoepitaxial GaN indicated that homoepitaxy prevented 3D growth and/or formation of defects. From PL measurement, we observed radiative recombination of free excitons clearly from homoepitaxial GaN.
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