Third order elastic constants of III-Nitride alloys
M. Petrov, L. Lymperakis, P. Dluzewski[*], and J. Neugebauer
Semiconductor based nanostructures, like Quantum Dots (QDs), are of great interest both from the fundamental point of view as well as for their potential optoelectronic applications: The zero-dimensional nature of Quantum Dots (QD) provides a more efficient carrier localization and results in superior characteristics with respect to their optical properties.
- Ab-initio calculated pressure dependence of GaN elastic constants.
In group III-nitrides, due to the large lattice mismatch and the stiffness of the material, the quantum dots embedded in the semiconductor matrix are highly strained and the inclusion of nonlinear elastic effects is crucial. However, so far experimental and/or theoretical data on the composition and stress dependence of the elastic constants of AlGaN alloys are still lacking.
In this work we combine ab-initio with Finite Elements Method (FEM) calculations in order to study the strain, electric, and polarization fields in a system of a GaN QD embedded in AlN matrix. The second and third order elastic constants of AlGaN alloys are derived by first principles calculations. In a second step these constants are used as input for FEM calculations of the electro-mechanically coupled non-linear boundary problem of the strain and polarization constitutive equations.
- The electric potential distributions for a GaN QD embedded in AlN matrix.
Our calculations reveal that there is is a large difference of the electric potential between the bottom and the top of the QD of the order of ~1.4 V with interesting consequences for the carriers localization: Holes are expected to be attracted towards the negative values of the potential, namely towards the bottom of the QD, while on the other hand electrons are expected to be trapped towards the upper part of the QD.
Moreover, our results show that the inclusion of third order elastic constants in our FEM calculation does not qualitatively change the potential distribution associated with the QD system. However, inclusion of non-linear effects result in up to 5% larger absolute electric potential values. It is under question if this change may significantly influence the energy states and the spatial localization of the carriers.
[*] P. Dluzwewski, Polish Academy of Sciences, Institute of Fundamental Technological Research
