Development of III-nitride nanostructures by metal-organic chemical vapor deposition

III-nitride nanostructures have generated considerable interest in both basic research field and commercial applications because of their important electronic, optical, magnetic, and biological properties. III-nitride semiconductors with their ternary and quaternary alloys can cover an energy bandgap range of 0.7 eV to 6.2 eV. A flurry of interest in low dimensional III-nitride nanostructures is in part associated with the desire to develop new optoelectronic devices with improved quality and wider applications. Critical breakthroughs have been achieved by bottom up approach but suffer from large size and shape fluctuation in addition to phase separation into multiple components. Template-confined selective area growth (SAG) technique is one of the promising ways to fabricate nanostructures with precise control over size, shape, position and distribution for realization of nanostructure based devices.;III-nitride nanostructures were formed of different dimensions by SAG. The grown nanostructures were exhaustively studied in the current research, experimentally and theoretically, and lasing action was demonstrated in the UV region. Emitters in deep UV and deep green regions, of great technological importance, were also addressed by developing AlGaN and InGaN nanostructures by the same method.;Hexagonal pyramids, trapezoidal features, nanowires and nanodots have been obtained by SAG of GaN with better crystalline quality due to blocking, bending and/or annihilation of dislocations and with strong optical confinement. GaN pyramidal nanostructures show high quality resonant cavity and a signature of thresholding for lasing was also observed when optically pumped. The SAG of GaN nanostructures on different templates shows difference in shapes of nanostructure. The shapes were also seen to be different when nanostructures were grown in different orientations such as c-plane, m-plane and a-plane.;Potential of SAG grown nano-AlGaN pyramids as high finesse optical cavity for emitters with wavelength in UV and deep UV region was demonstrated. AlGaN pyramidal nanostructures were grown on GaN/sapphire and AlN/sapphire templates with incorporated Al% of up to 20%. It was shown that increase in Al content of gas phase adversely affects the growth rates of AlGaN nanostructures. Introduction of Indium as surfactant resulted in highly improved growth rates and higher incorporation of Al into the growing nanostructures. Optical modeling of the AlGaN nanostructures helped to determine the spectral response and spatial properties of the light emission, and preferred geometry for the optimum design of electron-pumped UV source. In the same way, AlGaN nanostructures also show visible differences in their growth when grown on different templates. The effect of interfacial strain is apparent in affecting the growth rate of nanostructures as well as in the differences in the alloy composition of AlGaN nanostructures when grown on different templates. AlGaN structures grown on AlN template layer were found to have higher growth rate and Al% incorporated than those grown on GaN templates. The effect of substrate orientation was once again visible when we observed difference in shapes of nanostructures grown in different crystallographic directions.;High density a-plane and c-plane InGaN nanostructures have been developed by SAG using pulsed MOCVD technique. SiO2 was used as a mask with nanopatterning through an anodic aluminum oxide template. The lateral dimensions of the pattern were controlled and varied from 30 nm to 180 nm by changing the anodization voltage and the electrolyte used. Different substrates such as a-plane GaN, r-plane sapphire and c-plane sapphire were used as templates to develop InGaN nanostructures in a- and c-crystallographic directions. Under identical growth conditions, different templates once again revealed different shapes of the nanostructures with differences in emission wavelength.;Finally, realization of different crystal shapes for III-nitride nanostructures was extensively investigated by Density Functional Theory (DFT) calculations and kinetic modeling. Different crystal surfaces such as c-plane, m-plane and a-plane were studied by employing DFT to better understand the energetics and kinetics of epitaxial growth on respective surfaces. The results of this work has not only helped in a deeper understanding of the stability of different surfaces in varying growth conditions but sheds light on very important surface interactions and surface properties such as adsorption, desorption and diffusion of adsorbed atoms during growth. In addition, the effect of strain in the lattice was studied to see its effect on the surface stability and diffusion barriers. Facet stabilization was described by kinetic modeling to explain the shapes of nanostructures in different growth regimes. This was achieved by proposing a model based on growth velocities to predict the shape of nanostructures in given growth conditions.