Publications by April S. Brown.

Papers Published

  1. Kang, S. and Doolittle, W.A. and Lee, K.K. and Dai, Z.R. and Wang, Z.L. and Stock, S.R. and Brown, A.S., Characterization of AlGaN/GaN structures on various substrates grown by radio frequency-plasma assisted molecular beam epitaxy, Journal of Electronic Materials, vol. 30 no. 3 (2001), pp. 156 - 161 .
    (last updated on 2007/04/14)

    Abstract:
    The structural properties and surface morphology of AlGaN/GaN structures grown on LiGaO2 (LGO), sapphire, and hydride vapor phase epitaxy (HVPE)-grown GaN templates are compared. AlGaN grown on LGO substrates shows the narrowest x-ray full width at half maximum (FWHM) for both symmetric less than or equal 00.4> and asymmetric less than or equal 10.5> reflections. Atomic force microscopy (AFM) analysis on AlGaN surfaces on LGO substrates also show the smoothest morphology as determined by grain size and rms roughness. The small lattice mismatch of LGO to nitrides and easily achievable Ga-polarity of the grown films are the primary reasons for the smoother surface of AlGaN/GaN structure on this alternative substrate. Optimizations of growth conditions and substrate preparation results in step flow growth for an AlGaN/GaN structure with 300 A thick Al0.25Ga0.75N on 2.4 μm thick GaN. A high III/V flux ratio during growth and recently improved polishing of LGO substrates aids in promoting two dimensional step flow growth. The GaN nucleation layer directly on the LGO substrates showed no evidence of mixed phase cubic and hexagonal structure that is typically observed in the nucleation buffer on sapphire substrates. Cross-sectional high-resolution transmission electron microscopy (HRTEM) was performed on an AlGaN/GaN hetero-structure grown on LGO. The atomic arrangement at the AlGaN/GaN interface was sharp and regular, with locally observed monolayer and bilayer steps.

    Keywords:
    Heterojunctions;Semiconducting aluminum compounds;Gallium nitride;Semiconductor growth;Molecular beam epitaxy;Surface properties;Morphology;Atomic force microscopy;Grain size and shape;Surface roughness;Transmission electron microscopy;Interfaces (materials);