S. Pöykkö

Silicon vacancy in SiC: A high-spin state defect

We report results from spin-polarized ab initio local spin-density calculations for the silicon vacancy (VSi) in 3C– and 2H–SiC in all its possible charge states. The calculated electronic structure for SiC reveals the presence of a stable spin-aligned electron-state t2 near the midgap. The neutral and doubly negative charge states of VSi in 3C–SiC are stabilized in a high-spin configuration with S=1 giving rise to a ground state, which is a many-electron orbital singlet 3T1. For the singly negative VSi, we find a high-spin ground-state 4A2 with S=3/2. In the high-spin configuration, VSi preserves the Td symmetry. These results indicate that in neutral, singly, and doubly negative charge states a strong exchange coupling, which prefers parallel electron spins, overcomes the Jahn–Teller energy. In other charge states, the ground state of VSi has a low-spin configuration.

Possible n-type dopants in diamond and amorphous carbon

Abstract It has been extremely difficult to produce n-type conducting diamond, whereas it seems that n-type conducting tetrahedrally bonded amorphous carbon (ta-C) can be obtained using phosphorous or nitrogen as dopant. In this work we have studied substitutional group V–VII impurities (N, O and Cl) in diamond and ta-C using first-principles electronic structure methods. Electronic structure calculations reveal the differences between ta-C and diamond in the microscopic level and ease, therefore, the experimental search for producing n-type conducting diamond-like materials.

Nitrogen doping in ZnSe

Abstract The origin of the p-type doping problem in ZnSe is still controversial in spite of the numerous models presented. We have studied the electronic and structural properties of various nitrogen-related defects in ZnSe using the pseudopotential total-energy methods. The role of the defect complexes formed by nitrogen impurities and native defects in acceptor compensation is discussed.

Computational modelling of atomic-scale defect phenomena in compound semiconductors

This article summarizes recent work of first-principles simulation of atomic-scale defects in compound semiconductors. The calculations are based on the pseudopotential-plane wave techniques for density-functional theory. We discuss the structural and electronic properties of various point defects and their complexes. In particular, we focus on defect-induced metastabilities and compensation mechanisms due to defect-dopant pairing. The materials discussed in detail are GaAs, GaN, A1N and ZnSe.