Dependence of the stress–temperature coefficient on dislocation density in epitaxial GaN grown on α-Al[sub 2]O[sub 3] and 6H–SiC substrates.

Autor:	Ahmad, I., Holtz, M., Faleev, N. N., Temkin, H.
Předmět:	EPITAXY RAMAN effect X-ray diffraction PHONONS TEMPERATURE THIN films DISLOCATIONS in crystals
Zdroj:	Journal of Applied Physics; 2/15/2004, Vol. 95 Issue 4, p1692-1697, 6p, 2 Charts, 7 Graphs
Abstrakt:	We report measurements of stress in GaN epitaxial layers grown on 6H–SiC and α-Al[sub 2]O[sub 3] substrates. Biaxial stresses span +1.0 GPa (tensile) to -1.2 GPa (compressive). Stress determined from curvature measurements, obtained using phase-shift interferometry (PSI) microscopy, compare well with measurements using accepted techniques of x-ray diffraction (XRD) and Raman spectroscopy. Correlation between XRD and Raman measurements of the E[sub 2][sup 2] phonon gives a Raman-stress factor of -3.4±0.3 cm[sup -1]/GPa. We apply PSI microscopy for temperature dependent stress measurements of the GaN films. Variations found in the stress–temperature coefficient correlate well with threading dislocation densities. We develop a phenomenological model which describes the thermal stress of the epitaxial GaN as a superposition of that for ideal GaN and the free volume existing in the layers due to the threading dislocations. The model describes well the observed dependence. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]
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