Band gap and band parameters of InN and GaN from quasiparticle energy calculations based on exact-exchange density-functional theory

We have studied the electronic structure of InN and GaN employing G0W0 calculations based on exact-exchange density-functional theory. For InN our approach predicts a gap of 0.7 eV. Taking the Burnstein-Moss effect into account, the increase of the apparent quasiparticle gap with increasing electron concentration is in good agreement with the observed blue shift of the experimental optical absorption edge. Moreover, the concentration dependence of the effective mass, which results from the non-parabolicity of the conduction band, agrees well with recent experimental findings. Based on the quasiparticle band structure the parameter set for a 4x4 kp Hamiltonian has been derived.Comment: 3 pages including 3 figures; related publications can be found at http://www.fhi-berlin.mpg.de/th/th.htm

Exciting prospects for solids: Exact-exchange based functionals meet quasiparticle energy calculations

Focussing on spectroscopic aspects of semiconductors and insulators we will illustrate how quasiparticle energy calculations in the G0W0 approximation can be successfully combined with density-functional theory calculations in the exact-exchange optimised e ective potential approach (OEPx) to achieve a first principles description of the electronic structure that overcomes the limitations of local or gradiant corrected DFT functionals (LDA and GGA)

Role of semicore states in the electronic structure of group-III nitrides: An exact exchange study

The bandstructure of the zinc-blende phase of AlN, GaN, InN is calculated employing the exact-exchange (EXX) Kohn-Sham density-functional theory and a pseudopotential plane-wave approach. The cation semicore d electrons are treated both as valence and as core states. The EXX bandgaps of AlN and GaN (obtained with the Ga 3d electrons included as core states) are in excellent agreement with previous EXX results, GW calculations and experiment. Inclusion of the semicore d electrons as valence states leads to a large reduction in the EXX bandgaps of GaN and InN. Contrary to common belief, the removal of the self-interaction, by the EXX approach, does not account for the large disagreement for the position of the semicore d electrons between the LDA results and experiment.Comment: 10 pages including 3 figures; related publications can be found at http://www.fhi-berlin.mpg.de/th/th.htm

Strain effects and band parameters in MgO, ZnO, and CdO

We have derived consistent sets of band parameters (bandgaps, crystal-field splittings, effective masses, Luttinger, and EP parameters) and strain deformation potentials for MgO, ZnO, and CdO in the wurtzite phase. To overcome the limitations of density-functional theory in the local-density and generalized gradient approximations, we employ a hybrid functional as well as exact-exchange-based quasiparticle energy calculations in the G0W0 approach. We demonstrate that the band and strain parameters derived in this fashion are in very good agreement with the available experimental data and provide predictions for all parameters that have not been determined experimentally so far. VC 2012 American Institute of Physics

Strain Relaxation Mechanisms and Local Structural Changes in Si_{1-x}$Ge_{x} Alloys

In this work, we address issues pertinent to the understanding of the structural and electronic properties of Si_{1-x} Ge_{x}alloys, namely, (i) how does the lattice constant mismatch between bulk Si and bulk Ge manifests itself in the alloy system? and (ii) what are the relevant strain release mechanisms? To provide answers to these questions, we have carried out an in-depth study of the changes in the local geometric and electronic structures arising from the strain relaxation in Si_{1-x} Ge_{x} alloys using an ab initio molecular dynamics scheme. The optimized lattice constant, while exhibiting a general trend of linear dependence on the composition (Vegard's law), shows a negative deviation from Vegard's law in the vicinity of x=0.5. We delineate the mechanisms responsible for each one of the above features. We show that the radial-strain relaxation through bond stretching is responsible for the overall trend of linear dependence of the lattice constant on the composition. On the other hand, the negative deviation from Vegard's law is shown to arise from the angular-strain relaxation.Comment: 21 pages, 7 figure

Quantum well state of self-forming 3C-SiC inclusions in 4H SiC determined by ballistic electron emission microscopy

High-temperature-processing-induced double-stacking-fault 3C-SiC inclusions in 4H SiC were studied with ballistic electron emission microscopy in ultrahigh vacuum. Distinctive quantum well structures corresponding to individual inclusions were found and the quantum well two-dimensional conduction band minimum was determined to be approximately 0.53 ?? 0.06 eV below the conduction band minimum of bulk 4H SiC. Macroscopic diode I-V measurements indicate no significant evidence of metal/semiconductor interface state variation across the inclusions.open292

AB-initio calculation of the phase-diagram and microscopic structure of semiconductor binary alloys

We show how the thermodynamic properties, in particular the low temperature phase-diagram, of binary semiconductor alloys can be calculated from ab-initio total energy calculations performed for few ordered structures. Application has been made to SixGe1-x alloys. These calculations allow us to study also the stability of the bulk ordered structures, bond ionicity and its dependence on the chemical environment, and the variation of the lattice parameter and bond lengths with composition x