Conventional and Pendeo-Epitaxial Growth of Non-Polar GaN(11-20) Thin Films on AlN/4H-SiC(11-20) Substrates and Their Characterization and Reduction in Defect Density

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Title: Conventional and Pendeo-Epitaxial Growth of Non-Polar GaN(11-20) Thin Films on AlN/4H-SiC(11-20) Substrates and Their Characterization and Reduction in Defect Density
Author: Wagner, Brian P.
Advisors: Dr. Robert F. Davis, Committee Chair
Abstract: Non-polar GaN(11-20) thin films were deposited on AlN/4H-SiC(11-20) substrates via metalorganic vapor phase epitaxy. Atomic force microscopy images revealed that the microstructure of the AlN buffer layer and the subsequently deposited GaN contained a highly oriented growth structure where parallel growth features were aligned in the [1-100] direction. Scanning electron microscopy showed that the interfaces between the substrate, buffer layer, and epi-layer were continuous. Cracking was observed in GaN films having a thickness greater than 800 nm. Planview transmission electron microscopy analysis revealed stacking faults and threading dislocations with densities of ~1.6x10ˆ6cmˆ-1 and ~ 3.3x10ˆ10cmˆ-1, respectively. X-ray diffraction confirmed that the GaN was deposited epitaxially in the same orientation as the substrate. The average on- and off-axis x-ray full-width half-maxima of the (11-20) and the (10-10) reflections were 948 arcsec and 5448 arcsec, respectively. Coalesced, non-polar GaN(11-20) ( films having volumes of material with reduced densities of dislocations and stacking faults has been achieved from etched stripes via the statistical and experimental determination of the effect of temperature and V/III ratio on the lateral and vertical growth rates of the GaN{0001} faces combined with pendeo-epitaxy. AFM of the uncoalesced GaN(0001) and GaN(000-1) faces revealed growth steps with some steps terminating at dislocations on the former and a pitted surface without growth steps, indicative of decomposition, on the latter. Coalescence was achieved via (a) a two-step route and the parameters of (1) T=1100°C and V/III=1323 for 1.5hrs and (2) 1020°C and V/III= 1323 for 1.5hrs and (b) a one-step route that employed T = 1020°C and a V/III ratio = 660 for six hours. The densities of dislocations in the GaN grown vertically over and laterally from the (11-20) stripes were ~4x10ˆ10 cmˆ-2 and ~2x10ˆ8 cmˆ-2, respectively; the densities of stacking fault in these volumes were ~1x10ˆ6 cmˆ-1 and ~2x10ˆ4cmˆ-1, respectively. Plan view AFM also revealed different microstructures and a reduction in the RMS roughness values from 1.2nm to 0.95nm in these respective regions.
Date: 2005-11-09
Degree: MS
Discipline: Materials Science and Engineering
URI: http://www.lib.ncsu.edu/resolver/1840.16/2719


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