Suppression of phase separation in InGaN due to elastic strain
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Suppression of phase separation in InGaN due to elastic strain S. Yu. Karpov MRS Internet Journal of Nitride Semiconductor Research / Volume 3 / January 1998 DOI: 10.1557/S1092578300000880, Published online: 13 June 2014
Link to this article: http://journals.cambridge.org/abstract_S1092578300000880 How to cite this article: S. Yu. Karpov (1998). Suppression of phase separation in InGaN due to elastic strain . MRS Internet Journal of Nitride Semiconductor Research, 3, pp e16 doi:10.1557/ S1092578300000880 Request Permissions : Click here
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MRS
Internet Journal Nitride Semiconductor Research
Suppression of phase separation in InGaN due to elastic strain S. Yu. Karpov1 1Advanced Technology
Center,
(Received Thursday, June 18, 1998; accepted Thursday, September 10, 1998)
The effect of elastic strain in epitaxial InGaN layers coherently grown on GaN wafers on spinodal decomposition of the ternary compound is examined. The effect results in considerable suppression of phase separation in the strained InGaN layers. To predict correctly the position of the miscibility gap in the T-x diagram it is important to take into account the compositional dependence of the elastic constants of the ternary compound. The contribution of the elastic strain to the Gibbs free energy of InGaN is calculated assuming uniform compression of the epitaxial layer with respect to the underlying GaN wafer. The interaction of binary constituents in the solid phase is accounted for on the base of regular solution model. The enthalpy of mixing is estimated using the Valence Force Field approximation. The strain effect becomes stronger with increasing In content in the InGaN. As a result the miscibility gap shifts remarkably into the area of higher InN concentration and becomes of asymmetrical shape. Various growth surface orientations and the type of crystalline structure (wurtzite or sphalerite) provide different effects of the elastic strain on phase separation in ternary compounds.
1
Introduction
One of the specific features of group-III nitrides is that various binary compounds have crystalline lattice constants differing significantly from each other. For example, the lattice constant mismatch between GaN and AlN is 2.5% and 4.1% for a and c constants respectively; the mismatch between GaN and InN is much greater − 10.7% and 15.0% ; for the pair InN and AlN the lattice constant mismatch approaches 13.6% and 19.7% for a and c constants [1]. The latter values are even comparable to the mismatch between the lattice constants of GaN and sapphire commonly used as the substrate for growth of group-III nitride epilayers. Such a large difference in the lattice constants results in two main effects. First, due to very different bond lengths, a considerable internal strain arises in ternary nitr
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