Development of Homoepitaxially Grown GaN Thin Film Layers on Freestanding Bulk m-plane Substrates by Metalorganic Chemic
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1040-Q01-08
Development of Homoepitaxially Grown GaN Thin Film Layers on Freestanding Bulk m-plane Substrates by Metalorganic Chemical Vapor Deposition (MOCVD) Vibhu Jindal1, James Grandusky1, Neeraj Tripathi1, Mihir Tungare1, Fatemeh Shahedipour-Sandvik1, Peter Sandvik2, and Vinayak Tilak2 1 College of Nanoscale Science and Engineering, University at Albany, 255 Fuller Road, Albany, NY, 12203 2 Global Research Centre, General Electric, Niskayuna, NY, 12309 ABSTRACT High quality homoepitaxial growth of m-plane GaN films on freestanding m-plane HVPE GaN substrates has been performed using metalorganic chemical vapor deposition. A large growth space was studied. Large areas of no-nucleation along with high densities of defects were observed when layers were grown under growth conditions for c-plane GaN. It is believed that these structural defects were in large part due to the low lateral growth rates as well as unequal lateral growth rates in a- and ccrystallographic directions. To achieve high quality, fully coalesced epitaxial layers, growth conditions were optimized with respect to growth temperature, V/III ratios and reactor pressure. Higher growth temperatures led to smoother surfaces due to increased surface diffusion of adatoms. Overall, growth at higher temperature and lower V/III ratios decreased the surface roughness and resulted in better optical properties as observed by photoluminescence. Although these improvements resulted in smoother layers, some macroscopic defects were still observed on the epi-surface as a result of contamination and subsurface damage remaining on bulk substrates. The addition of a step involving the annealing of the bulk substrate under a hydrogen and nitrogen environment, prior to growth, drastically reduced such macroscopic defects. INTRODUCTION Group III-nitride materials have attracted much attention in the past decade due to their potential for optoelectronic systems such as laser diodes, light emitting diodes and detecting devices for chemical and biological sensors [1-3]. III-nitrides are inherently piezoelectric and pyroelectric materials due to their wurtzite structure. Since the polar axis in the wurtzite lattice is the direction, large polarization fields can arise in heterostructures grown along this orientation. At present, all relevant devices in IIInitrides are grown along the polar axis due to which the optoelectronic properties of corresponding strained heterostructures are affected by the presence of polarization fields [4-6]. On the other hand, the realization of III-nitride heterostructures along nonpolar directions offers the possibility of eliminating these polarization effects as demonstrated for devices grown on (1-100) m-plane and (11-20) a-plane [7-8]. Similar to c-plane GaN, m-plane and a-plane GaN are also grown on foreign substrates such as LiAlO2 and r-plane sapphire or 4H-SiC, respectively, which can give rise to high defect densities. The reported defect density for typical a-plane GaN on r-plane sapphire reaches 109-1010 cm-2, with the surfaces ge
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