Core properties and the role of screw dislocations in the bulk n-type conductivity in InN.

First principles calculations, based on density functional theory, have been carried out to investigate the role of screw dislocations in the bulk n-type conductivity which is usually observed in indium nitride. Energetics, atomic and electronic structures of different core configurations of dislocations, running along the [0001] polar or along the [112[combining macron]0] non-polar direction, have been determined and compared. This enabled inspection of the modifications in the properties of screw dislocations when the growth direction is changed. For the c-type screw dislocation, the configuration with a double 6-atom ring, involving wrong bonds was revealed as a ground state configuration, and for the a-type screw dislocation, the shuffle configuration was found to be energetically favoured over glide ones. Unlike core configurations of the a-type screw dislocation, those of the c-type screw dislocation have their Fermi levels pinned in the conduction band and thus act as a source of non-intentional n-type conductivity. This demonstrates that eliminating the contribution of screw dislocations to the n-type conductivity can be achieved by growing wurtzite InN along the non-polar direction.

Impact of screw and edge dislocations on the thermal conductivity of individual nanowires and bulk GaN: a molecular dynamics study.

We report the thermal transport properties of wurtzite GaN in the presence of dislocations using molecular dynamics simulations. A variety of isolated dislocations in a nanowire configuration are analyzed and found to considerably reduce the thermal conductivity while impacting its temperature dependence in a different manner. Isolated screw dislocations reduce the thermal conductivity by a factor of two, while the influence of edge dislocations is less pronounced. The relative reduction of thermal conductivity is correlated with the strain energy of each of the five studied types of dislocations and the nature of the bonds around the dislocation core. The temperature dependence of the thermal conductivity follows a physical law described by a T-1 variation in combination with an exponent factor that depends on the material's nature, type and the structural characteristics of the dislocation core. Furthermore, the impact of the dislocation density on the thermal conductivity of bulk GaN is examined. The variation and absolute values of the total thermal conductivity as a function of the dislocation density are similar for defected systems with both screw and edge dislocations. Nevertheless, we reveal that the thermal conductivity tensors along the parallel and perpendicular directions to the dislocation lines are different. The discrepancy of the anisotropy of the thermal conductivity grows with increasing density of dislocations and it is more pronounced for the systems with edge dislocations. Besides the fundamental insights of the presented results, these could also be used for the identification of the type of dislocations when one experimentally obtains the evolution of thermal conductivity with temperature since each type of dislocation has a different signature, or one could extract the density of dislocations with a simple measurement of thermal anisotropy.