Modeling of Threading Dislocation Reduction in Growing GaN Layers

Abstract

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.

Extended defects and polarity of hydride vapor phase epitaxy GaN

“…Mathis et al 23 extended the model proposed by Speck et al 37 for cubic semiconductors into the case of wurzite GaN. According to this model efficiency and kinetics of dislocation reduction strongly depends on the initial dislocation distribution between different types of Burgers vectors.…”

“…However, these two papers seem to be somewhat contradictory. Mathis et al 23 concluded that there is an efficient reduction of threading dislocation density in films with a high fraction of mixed character dislocations since only such dislocations tend to be inclined. On the other hand, films with a high fraction of edge dislocations should not have significant dislocation reduction.…”

“…We observe a strong dislocation reduction (by almost four orders of magnitude in films of a thickness of a few hundreds micrometers) and the investigated films had a large fraction of mixed character dislocations. On the other hand, there are still some discrepancies between our experimental data and predictions of the theoretical model presented by Mathies et al 23 For example, this model predicts that dislocation density would saturate for large layer thickness and there is no such saturation observed in our data (see Fig. 5).…”

“…This fit was obtained for a value of 308 ± 35 Å for the K parameter. Mathis et al 23 applied a similar approach to analyze experimental data reported by Golan et al 39 obtained on HVPE GaN using plan-view TEM and X-ray diffraction measurements. They obtained a value of 275 Å for K, which agrees well with our value of 308 ± 35 Å for this parameter.…”

“…22 On the contrary, Mathis et al presented a theoretical model which leads to the conclusions that films with a high fraction of edge dislocations do not have significant dislocation reduction and mixed character dislocations promote the reduction reactions. 23 It seems than, that there is still some controversy about the dislocation density reduction mechanism and some additional experimental or/and theoretical studies are necessary. We believe that results of systematic studies presented in this paper can be an important experimental contribution to the discussion about the mechanism of dislocation reduction in HVPE GaN layers.…”