Search

Abstract: Gallium nitride (GaN) epitaxial layers were grown with different V/III ratios by varying the ammonia (NH3) flow rate, keeping the flow rate of the other precursor, trimethylgallium (TMG), constant, in an MOCVD system. X-ray rocking curve widths of a (102) reflection increase with an increase in V/III ratio while the (002) rocking curve widths decrease. The dislocation density was found to increase with an increase in ammonia flow rate, as determined by hot-wet chemical etching and atomic force microscopy. 77K photoluminescence studies show near band emission at 3.49eV and yellow luminescence peaking at 2.2eV. The yellow luminescence (YL) intensity decreases with an increase in V/III ratio. Positron annihilation spectroscopy studies show that the concentration of Ga-like vacancies increases with an increase in ammonia flow rate. This study confirms that the yellow luminescence in the GaN arises due to deep levels formed by gallium vacancies decorated with oxygen atoms. [ABSTRACT FROM AUTHOR]

AlN layers of thickness of about 2 μm have been grown with AlN nucleation layers (NLs) on (001) sapphire substrates using metal organic chemical vapor deposition. Increasing the AlN-NL deposition temperature from 850 to 1250 °C has been found to have significant effect on the surface morphology and the structural quality of the AlN layers. The surface morphology of the AlN-NLs and the AlN layers has been assessed using atomic force microscopy (AFM). The AFM images of the AlN-NLs reveal the coalescence pattern of NLs. AFM images of the AlN layers and the in-situ reflectance measurement disclose the surface morphology and the growth pattern of the AlN layers, respectively. Smooth surface with macro-steps and terrace features has been achieved for the AlN layer grown on the NL deposited at 950 °C. The structural quality of AlN layers has been studied by high resolution X-ray diffraction and Raman spectroscopy. The screw dislocation density from (002) reflection and the average edge dislocation density from (102), (302) and (100) reflections of the AlN layer on NL deposited at 950 °C are estimated to be 9×10 7 cm −2 and 4.4×10 9 cm −2 , respectively. Lateral correlation length ( L ) is calculated from the (114) reciprocal space mapping of the AlN layers and correlated with the edge dislocation density of the AlN layers. Raman E 2 (high) phonon mode indicates compressive strain in the AlN layers grown on the NLs deposited at various temperatures. From this work, it has been inferred that the uniform coalescence of the nucleation islands and the complete coverage of AlN-NL determine the surface morphology and the structural quality of the subsequently grown AlN layers. [ABSTRACT FROM AUTHOR]