The piezoelectric effect in polar semiconductor has seen increased interest in recent years because of the prospect of exploiting semiconducting behavior and piezoelectric response, i.e. generating electric fields in response to pressure, in novel optoelectronic devices with applications as pressure sensors and energy harvesting. In this paper we review the basic concepts and recent findings related to the novel concept of non-linear piezoelectricity, which can be exploited in composite nanostructured materials to increase the piezoelectric response compared to bulk materials. Applications to light emitting diodes and nanowires will also be discussed. We will show how the non-linear theory of piezoelectricity can in some cases lead to opposite predictions compared to the classic linear theory.

This work explores the strain dependence of the piezoelectric effect in GaAs and InAs zinc blende crystals. We write the polarization in terms of the internal anion-cation displacement and the ionic and dipole charges. We then use ab initio density functional theory to evaluate the dependence of all quantities on the strain tensor. We investigate which aspects of the elastic and dielectric response of zinc blende crystals are sources of non-linearities in the piezoelectric effect. We observe that the main source of non-linearities is the response to elastic deformation and, in particular, the internal sublattice displacement of the interpenetrating cation and anion sublattices. We show that the internal sublattice displacement dependence on the diagonal stress components is neither symmetric nor antisymmetric in the strain. Therefore, non-linear coefficients of order higher than quadratic are needed to correctly describe non-linear effects. Using a fitting procedure of the ab initio data, we also determine all non-linear piezoelectric coefficients up to the third power in the diagonal components of the strain tensor. We can report that non-linear effects up to third order can be significant in precisely determining the magnitude of the piezoelectric polarization if compressive or tensile strains larger than 10% are present. We notice however that, in nanostructures such as quantum dots, the optical properties are less sensitive to the third order non-linear piezoelectric effect and that third order coefficients can therefore be neglected.

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.

Based on ab initio calculations, we have investigated the atomic geometry, electronic properties and magnetic properties of Mn incorporation in GaAs. The inclusion of the Hubbard potential U in the calculation (namely with the σGGA+U scheme) results in the optimized geometry being contracted by approximately 2% relative to the relaxed geometry obtained by the (σGGA) method. Within both the σGGA and σGGA+U schemes the Mn impurity in bulk GaAs behaves like a d-hole with the majority spin state lying at 0.25 eV above the Fermi level. Theoretically simulated STM images for Mn/GaAs(110) indicate round protrusions at As sites and Ga sites, the latter being dependent on the Mn adsorption site (i.e. in different atomic layers). These results are supportive of a previous experimental STM image obtained with a very low Mn concentration.

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.

Atomistic Molecular Dynamics and Molecular Statics simulations are nowadays capable of accessing highly sophisticated high performance computer architectures. Therefore it is becoming natural to push these methods towards realistic experimental sizes in order to design simulations with predictive power. In order to simulate elastic strain in semiconductor nanostructures and their immediate environment one needs to typically include at least I million atoms. Such sizes require ad hoc methods that in spite of their empirical nature can still prove accurate compared to ab initio methods, at least in the subset of the physical properties that one is simulating. We will show how the Abell-Tersoff empirical potential can be convincingly used to simulate the elastic behavior of even epitaxial quantum dots comprising 3 million atoms and made of complex quaternary semiconductor alloys.

We address the issue of strain dependence of piezoelectric effect in semiconductor materials, which is manifested by the appearance of an electric field in response to crystal deformation. For III–V materials such as GaAs and InAs we find that strain considerably modifies the value of the piezoelectric coefficients. For the case of InAs pseudomorphically grown on GaAs substrate, our model predicts a sign reversal of the piezoelectric coefficients e14, e25 and e36 from negative to positive for strains of around 7%. This might explain several discrepancies between the theoretical and experimental observations made on nanostructures such as III–V quantum dots.

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.

In this paper we show the use of an optimally parameterized empirical potential of the Abell–Tersoff type to study the strain energy of the quaternary alloy InGaAsSb. We use our results to compute modified segregation energies in an improved kinetic model of segregation for the combined effects of group III and V exchange processes during epitaxial growth and compare with experimental data from Scanning Tunnelling Microscopy.

Modelling of III-V semiconductor materials and nanostructures has been a very active field in the last 15 years. The rapid development in the material synthesis of low dimensional structures for optical applications has triggered a world wide interest for modelling methods capable of accurately describing systems comprising millions of atoms. With the development of empirical or semiempirical methods, together with the ever increasing computational power available to scientists, it is now possible to model e.g. quantum dots inside simulation boxes comprising 3 million atoms. In this talk we will review the most recent developments in the field of empirical atomistic methods, particularly the bond order potentials, and discuss its links and reliance on ab initio calculations. The links between these methods and modeling of segregation effect will also be discussed.