C. Rödl

Branch-point energies and band discontinuities of III-nitrides and III-/II-oxides from quasiparticle band-structure calculations

Using quasiparticle band structures based on modern electronic-structure theory, we calculate the branch-point energies for zinc blende (GaN, InN), rocksalt (MgO, CdO), wurtzite (AlN, GaN, InN, ZnO), and rhombohedral crystals (In2O3). For InN, CdO, ZnO, and also In2O3 the branch-point energies are located within the lowest conduction band. These predictions are in agreement with observations of surface electron accumulation (InN, CdO) or conducting behavior of the oxides (ZnO, In2O3). The results are used to predict natural band offsets for the materials investigated.

Electronic and optical properties of MgxZn1−xO and CdxZn1−xO from ab initio calculations

Isostructural and heterostructural pseudobinary MgxZn1−xO and CdxZn1−xO alloys are studied by combining the wurtzite and the rocksalt polymorphs within a cluster expansion. The computationally demanding calculation of the quasiparticle electronic structure has been achieved for all cluster cells of the expansion using the recently developed HSE03+G0W0 scheme. These results are used to compute the configurational averages for the fundamental band gaps and the densities of states. A strongly nonlinear behavior of the band gaps is observed and it is quantified by means of the corresponding bowing parameters for both material systems. In order to calculate the macroscopic dielectric functions, including excitonic and local-field effects for iso- and heterostructural MgxZn1−xO alloys as well as wurtzite (wz) CdxZn1−xO, the Bethe–Salpeter equation has been solved for each of the corresponding clusters. The respective configurational averages indicate that the composition-dependent variation in the exciton peaks allows conclusions on the alloy composition and preparation conditions.

Band lineup between silicon and transparent conducting oxides

methods which require no knowledge of the structural details of the interfaces. The conduction- and valence-band discontinuities Ec and Ev between the oxides and crystalline silicon are calculated using two different band alignment methods employing the branch-point energies or the vacuum levels. In the case of In2O3 we study the rhombohedral rh and the body centered cubic bcc bixbyite geometries. ZnO crystallizes in wurtzite wz structure while for SnO2 the most important rutile rt geometry is investigated. The atomic geometries of the oxides and silicon are computed in the framework of density functional theory DFT using the local density approximation LDA for exchange and correlation XC. All computations are performed with the

Strain influence on valence-band ordering and excitons in ZnO: An ab initio study

Modern parameter-free methods to treat single- and two-particle electronic excitations are applied to compute the band structure and the lowest optical transitions of wurtzite ZnO under biaxial strain. The calculations are based on density functional theory with a spatially nonlocal exchange and correlation functional and include spin-orbit interaction. Quasiparticle shifts and excitonic effects are computed. In addition to the band parameters, also their dependence on biaxial strain and the ordering of the A, B, and C excitons are investigated. While the crystal-field splitting is very sensitive to strain, the spin-orbit splittings and the exciton binding energies remain unaffected.