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Seoul, South Korea

Oh D.K.,Hanyang University | Bang S.Y.,Hanyang University | Choi B.G.,Hanyang University | Maneeratanasarn P.,Hanyang University | And 4 more authors.
Journal of Crystal Growth | Year: 2012

Boule of GaN crystal was grown with 50 mm diameter and 3 mm thickness by hydride vapor phase epitaxy and cut using a wire saw to produce freestanding wafers. These were, mechanically polished with diamond slurry and followed with chemical mechanical polishing for final surface preparation. Surface morphology was examined by non-contact mode atomic force microscopy before and after thermal annealing process performed at 700, 800, 900, and 1000 °C for 1 h, in air. Wafers with optimum surface quality submitted to thermal annealing treatment at 900 °C were characterized by reduced scratched density and residual stress, and surface roughness of 0.096 nm. Surface quality improvement was confirmed by relatively large recovery of the room temperature near band edge luminescence intensity. © 2012 Elsevier B.V.

Freitas Jr. J.A.,U.S. Navy | Mastro M.A.,U.S. Navy | Glaser E.R.,U.S. Navy | Garces N.Y.,Global Strategies Group | And 4 more authors.
Journal of Crystal Growth | Year: 2012

Thick freestanding films or bulk GaN substrates with very low background impurity levels (≤1×10 15/cm 3) and high crystalline quality are required for a number of electronic device applications. Low pressure chemical vapor and molecular beam epitaxy techniques can systematically deposit films with low residual impurity concentrations. However, their typical slow growth rate prevents their utilization for substrate growth. The hydride vapor phase epitaxy deposition technique can achieve hundreds of microns per hour growth rate, but these films have typically high free carrier concentration (≥3×10 17/cm 3). It is crucial to verify if this method can reproducibly deliver thick freestanding GaN films of high crystalline quality with exceptionally low free carrier concentration. Low temperature photoluminescence and room temperature Raman scattering experiments carried out on a number of samples indicate that they have high crystalline quality and uncommonly low donor background levels. Reduced concentration of uncompensated shallow donors verified by low temperature electron paramagnetic resonance was confirmed by detailed high sensitive SIMS analyses. In addition, it was verified by X-ray diffraction analysis that relatively low dislocation densities can be achieved.

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