Group V acceptors in CdTe:Ab initiocalculation of lattice relaxation and the electric-field gradient

Lattice Relaxation around Arsenic and Selenium in CdTe

“…The latter was used to investigate the size dependence of the super-cells constructed around one substitutional As atom in CdTe. The calculations yielded good agreement with our EXAFS experiment (see Table1) so that the determined relaxations can be used as a solid basis for further interpretations of derived parameters such as hyperfine interaction parameters of defect complexes (for further details see [1,8]). …”

“…1 we compare our measured bond length with the results obtained from the pseudopotential calculations as well as the LAPW values according to ref. [1]. The agreement is very good.…”

“…The experimental challenge lies in the necessary compromise between a concentration high enough for an EXAFS detection, but low enough to avoid compensation and clustering of the dopants in the semiconductors. In the case of As in CdTe, the aim was to experimentally verify the lattice relaxation around the impurity atom as determined theoretically with the LAPW method used to calculate the electric field gradient in comparison with the measured value in a PAC experiment [1]. In order to understand the driving force for the lattice relaxation we also determined the relaxation around Se, the neighbouring element to As and isovalent to Te, for which no doping effects in CdTe are known.…”

Experimental Verification of Calculated Lattice Relaxations Around Impurities in CdTE

“…In the case of As and Br in CdTe acting as acceptor and donor, resp., when incorporated substitionally on the Te sublattice, information on lattice relaxation around the impurity atom has already been obtained by hyperfine interaction studies. Making use of the donor-acceptor-pair formation between In-As and Ag-Br the electric field gradient (EFG) was determined for the non-cubic configuration with the resulting pairs of 111 Cd-As [1] and 111 Cd-Br [2] after the decay of 111 In or 111 Ag, resp., employing the perturbed angular correlation (PAC) technique. In ab initio calculations using density functional theory (DFT) as implemented in the WIEN97 program the EFGs were reproduced when the lattice distances around the impurity atom were first allowed to relax to minimize the forces within the super-cell [1,3].…”

“…Making use of the donor-acceptor-pair formation between In-As and Ag-Br the electric field gradient (EFG) was determined for the non-cubic configuration with the resulting pairs of 111 Cd-As [1] and 111 Cd-Br [2] after the decay of 111 In or 111 Ag, resp., employing the perturbed angular correlation (PAC) technique. In ab initio calculations using density functional theory (DFT) as implemented in the WIEN97 program the EFGs were reproduced when the lattice distances around the impurity atom were first allowed to relax to minimize the forces within the super-cell [1,3]. Since the EFG has a high sensitivity to the actual size of atomic relaxations around the probing atom, it is most desirable to experimentally strengthen this approach by determining the bond lengths around the impurity atom directly, which can be achieved with fluorescence detected X-ray Absorption Fine Structure (XAFS with X-ray Absorption Near-Edge Spectroscopy XANES and Extended X-ray Absorption Fine Structure EXAFS).…”