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Articles you may be interested inDislocation reduction in sulfur-and germanium-doped indium phosphide single crystals grown by the vertical gradient freeze process: A transient finite-element study J. Appl. Phys. 97, 043520 (2005); 10.1063/1.1848190Reduction of threading dislocation density in SiGe layers on Si (001) using a two-step strain-relaxation procedure Appl.In this article, we have developed models for threading dislocation ͑TD͒ reduction due to the introduction of an intentionally strained layer. Three different types of dislocations have been considered in this model: misfit dislocations ͑MDs͒, mobile TDs, and TDs whose glide motion has been blocked by a MD crossing the glide path of the TD ͑immobile TDs͒. The models are based on MD formation by the process of lateral TD motion. The strain-induced TD motion leads to possible annihilation reactions of mobile TDs with either other mobile TDs or blocked TDs, or reactions in which a mobile TD is converted to an immobile TD by a blocking reaction with a MD. The evolution of the density of mobile and blocked TDs and the MD density is represented by three coupled nonlinear first order differential equations. When blocking of TDs by MDs is not considered, the equations have an analytical solution that shows that the final TD density should decrease exponentially where the argument of the exponent is proportional to the product of the reaction radius between TDs ͑the annihilation radius r A ͒ and the nominal misfit strain ⑀ m . The no-blocking limit represents the maximum possible TD reduction through the introduction of a strained layer, regardless whether this layer has a discrete step in strain, step-grade, or continuous strain grading. When only blocking reactions are considered ͑no annihilation͒, again analytic solutions to the equations are obtained which show the maximum possible plastic strain relaxation for a discretely strained layer. Several examples of numerical solutions to the three coupled differential equations are described for cases that include both blocking and annihilation reactions.

In this work, a model is developed to treat threading dislocation (TD) reduction in (0001) wurtzite epitaxial GaN thin films. The model is based on an approach originally proposed for (001) f.c.c. thin film growth and uses the concepts of mutual TD motion and reactions. We show that the experimentally observed slow TD reduction in GaN can be explained by low TD reaction probabilities due to TD line directions practically normal to the film surface. The behavior of screw dislocations in III-nitride films is considered and is found to strongly impact TD reduction. Dislocation reduction data in hydride vapor phase epitaxy (HVPE) grown GaN is well-described by this model. The model provides an explanation for the non-saturating TD density in thick GaN films.

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In these studies, we have investigated the role of low-temperature growth in the reduction of threading dislocation ͑TD͒ densities in large mismatch heteroepitaxy. Low-and high-temperature ͑LT͒ and ͑HT͒ GaAs growths on highly mismatched substrates were used to find the mechanism of enhanced TD reduction in LT grown ͑250°C͒ GaAs. LT templates have symmetric ͑equal͒ TD subdensities on the ͕111͖A and ͕111͖B planes, whereas HT templates have asymmetric TD subdensities. A model based on TD reactions was applied to the experimental results and confirmed the beneficial role of symmetric TD subdensities in LT GaAs TD reduction. A ductile-to-brittle transition in dislocation behavior was observed at ϳ400°C.