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Abstract: The temperature dependent electrical transport behavior of n–n InGaN/Si heterostructures grown by plasma-assisted MBE was studied. Structural characteristics of the as-grown InGaN epilayers were evaluated high resolution X-ray diffraction and composition of InGaN was estimated from photoluminescence spectra using standard Vegard''s law. Current density–voltage plots (J–V–T) revealed that the ideality factor (η) and Schottky barrier height (SBH) (Φ b) are temperature dependent and the incorrect values of the Richardson''s constant (A ∗∗) produced, suggests an inhomogeneous barrier at the heterostructure interface. The higher value of the ideality factor compared to the ideal value and its temperature dependence suggest that the current transport is mainly dominated by thermionic field emission. [Copyright &y& Elsevier]

Abstract: We present an extensive study on the structural, electrical and optical properties of InN thin films grown on c-Al2O3, GaN(130nm)/Al2O3, GaN(200nm)/Al2O3 and GaN(4μm)/Al2O3 by using plasma-assisted molecular beam epitaxy. The high resolution X-ray diffraction study reveals better crystalline quality for the film grown on GaN(4μm)/Al2O3 as compared to others. The electronic and optical properties seem to be greatly influenced by the structural quality of the films, as can be evidenced from Hall measurement and optical absorption spectroscopy. Kane''s k.p model was used to describe the dependence of optical absorption edge of InN films on carrier concentration by considering the non-parabolic dispersion relation for carrier in the conduction band. Room temperature Raman spectra for the InN films grown on GaN show the signature of residual tensile stress in contrast to the compressive stress observed for the films grown directly on c-Al2O3. [Copyright &y& Elsevier]

Abstract: Ultra thin films of pure β-Si3N4 (0001) were grown on Si (111) surface by exposing the surface to radio- frequency nitrogen plasma with a high content of nitrogen atoms. Using β-Si3N4 layer as a buffer layer, GaN epilayers were grown on Si (111) substrate by plasma-assisted molecular beam epitaxy. The valence band offset (VBO) of GaN/β-Si3N4/Si heterojunctions is determined by X-ray photoemission spectroscopy. The VBO at the β-Si3N4 / Si interface was determined by valence-band photoelectron spectra to be 1.84eV. The valence band of GaN is found to be 0.41±0.05eV below that of β-Si3N4 and a type-II heterojunction. The conduction band offset was deduced to be ~2.36eV, and a change of the interface dipole of 1.29eV was observed for GaN/β-Si3N4 interface formation. [Copyright &y& Elsevier]

Abstract: In the present work, we report the growth of wurtzite InN epilayers on GaN/Si (111) substrate by plasma-assisted molecular beam epitaxy (PAMBE). The growth parameters such as indium flux, substrate temperature and RF power affect the crystallographic and morphological properties of InN layers, which were evaluated using high resolution X-ray diffraction (HRXRD) analysis and atomic force microscopy (AFM). It is found that excess indium (In) concentrations and surface roughness were increased with increase in In flux and growth temperature. The intensity of HRXRD (0002) peak, corresponding to c-axis orientation has been increased and full width at half maxima (FWHM) has decreased with increase in RF power. It was found that highly c-axis oriented InN epilayers can be grown at 450°C growth temperature, 450W RF power and 1.30×10−7 mbar In beam equivalent pressure (BEP). The energy gap of InN layers grown by optimizing growth conditions was determined by photoluminescence and optical absorption measurement. [Copyright &y& Elsevier]

Abstract: Photoluminescence (PL) of high quality GaN epitaxial layer grown on β-Si3N4/Si (111) substrate using nitridation–annealing–nitridation method by plasma-assisted molecular beam epitaxy (PA-MBE) was investigated in the range of 5–300K. Crystallinity of GaN epilayers was evaluated by high resolution X-ray diffraction (HRXRD) and surface morphology by Atomic Force Microscopy (AFM) and high resolution scanning electron microscopy (HRSEM). The temperature-dependent photoluminescence spectra showed an anomalous behaviour with an ‘S-like’ shape of free exciton (FX) emission peaks. Distant shallow donor–acceptor pair (DAP) line peak at approximately 3.285eV was also observed at 5K, followed by LO replica sidebands separated by 91meV. The activation energy of the free exciton for GaN epilayers was also evaluated to be ∼27.8±0.7meV from the temperature-dependent PL studies. Low carrier concentrations were observed ∼4.5±2×1017 cm−3 by measurements and it indicates the silicon nitride layer, which not only acts as a growth buffer layer, but also effectively prevents Si diffusion from the substrate to GaN epilayers. The absence of yellow band emission at around 2.2eV signifies the high quality of film. The tensile stress in GaN film calculated by the thermal stress model agrees very well with that derived from Raman spectroscopy. [Copyright &y& Elsevier]

Abstract: InN layers were directly grown on Ge substrate by plasma-assisted molecular beam epitaxy (PAMBE). The valence band offset (VBO) of wurtzite InN/Ge heterojunction is determined by X-ray photoemission spectroscopy (XPS). The valence band of Ge is found to be 0.18±0.04eV above that of InN and a type-II heterojunction with a conduction band offset (CBO) of ~0.16eV is found. The accurate determination of the VBO and CBO is important for the design of InN/Ge based electronic devices. [Copyright &y& Elsevier]