V. Haxha

Tunability of the piezoelectric fields in strained III-V semiconductors

In this work we show that tetragonal strain can be used to create a sign reversal of the piezoelectric field in InAs/GaAs semiconductor heterostructures. The strain dependence of the internal displacement of the cation-anion pairs and of the bond polarity are taken into account, beyond the linear model, within an ab initio scheme. The reported tunability of the piezoelectric field is a concept that can be exploited in optoelectronic devices.

Non-linear piezoelectricity in zinc blende GaAs and InAs semiconductors

We investigate the strain dependence of piezoelectric effect, both linear and non linear, in zincblende GaAs and InAs semiconductors. We expanded the polarization in terms of the ionic and dipole charges, internal displacement and the exploited the ab-initio Density Functional Theory (DFT) to evaluate the dependence of all quantities on the strain tensor. By this detailed study of the non linear piezoelectric effect, we report that even third order effects are significant.

Control of strain in GaSbAs/InAs/GaAs quantum dots

We discuss strain simulations of quantum dot structures covered with a GaSbAs strain reducing capping layer in the presence of Sb segregation. Cross Sectional Scanning Tunneling Microscopy shows strong Sb and In segregation in the material surrounding the quantum dot. Using the three layer model originally proposed for the SiGe system by D. J. Godbey, M. G. Ancona, J. Vac. Sci. Technol. A 15, 976 (1997) we accurately calculate the segregation profile and include a non uniform composition to our models. Using atomistic modeling, we present strain maps of the quantum dot structures that show the propagation of the strain into the GaAs region is strongly affected by the shape and composition of the strain reduction layer.

Empirical bond order potential calculations of the elastic properties of epitaxial InGaSbAs layers

In this paper, we show the use of an optimally parameterized empirical potential of the Abell-Tersoff type and demonstrate that we can obtain a deep level of insight into the properties of the epitaxially grown quaternary alloy InGaAsSb. We find that the strain energy as a function of composition does not follow intuitive averages between the binary constituents and that the theoretical behaviour appears to be substantiated by experimental evidence of growth of InAs self-assembled quantum dots capped by GaSbAs.

The use of Abel-Tersoff potentials in atomistic simulations of InGaAsSb/GaAs

In this paper we show the use of an optimally parameterized empirical potential of the Abell-Tersoff type for atomistic simulations of the elastic properties of the epitaxially grown quaternary alloy InGaAsSb. We find that the strain energy as a function of composition does not follow intuitive averages between the binary constituents. Furthermore we will provide an explanation for the often observed decomposition into ternary components. The predictions of our model appear to be substantiated by experimental evidence of growth of InAs self assembled quantum dots capped by GaSbAs.

Non linear piezoelectricity in zincblende GaAs and InAs semiconductors

We investigate the strain dependence of piezoelectric effect, both linear and non linear, in zincblende GaAs and InAs semiconductors. We expanded the polarization in terms of the ionic and dipole charges, internal displacement and the exploited the ab-initio Density Functional Theory (DFT) to evaluate the dependence of all quantities on the strain tensor. By this detailed study of the non linear piezoelectric effect, we report that even third order effects are significant.

Strain dependence of internal displacement and effective charge in wurtzite III-N semiconductors

The elastic and dielectric properties of binary III-N wurtzite semiconductors have been investigated as a function of strain. Using an ab initio density functional theory (DFT), we concentrate on the internal displacement (u) and Born effective charge (Z*) and show that our model provides a unique non linear dependence of the III-N material properties as a function of strain.

Erratum: Second-order piezoelectricity in wurtzite III-N semiconductors [Phys. Rev. B 84, 085211 (2011)]

We note two typographical errors in our recent paper. First, in Table III, the Lw/Lb ratio in the first row should be 3/5, not 3/50. Second, we gave an incorrect sign for some of the parameters listed in Table IV. The parameters of e311, e333, and e133 in Table IV should read as given here. Because the correct signs were used to calculate the fields in the original work, these corrections do not affect our conclusions.

Second-order piezoelectricity in wurtzite III-N semiconductors (vol 84, 085211, 2011)

We note two typographical errors in our recent paper. First, in Table III, the Lw/Lb ratio in the first row should be 3/5, not 3/50. Second, we gave an incorrect sign for some of the parameters listed in Table IV. The parameters of e311, e333, and e133 in Table IV should read as given here. Because the correct signs were used to calculate the fields in the original work, these corrections do not affect our conclusions.

Calculating strain using atomistic simulations: A review

We present a short review of methods of evaluating of strain from atomistic models in the context of linear elasticity.