Dependence of the stress–temperature coefficient on dislocation density in epitaxial GaN grown on α-Al2O3 and 6H–SiC substrates

We report measurements of stress in GaN epitaxial layers grown on 6H–SiC and α-Al2O3 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 measuremen...

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Bibliographic Details
Published in:Journal of applied physics 2004-02, Vol.95 (4), p.1692-1697
Main Authors: Ahmad, I., Holtz, M., Faleev, N. N., Temkin, H.
Format: Article
Language:English
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Summary:We report measurements of stress in GaN epitaxial layers grown on 6H–SiC and α-Al2O3 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 E22 phonon gives a Raman-stress factor of −3.4±0.3 cm−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.
ISSN:0021-8979
1089-7550
DOI:10.1063/1.1637707