Impurities In ZnSe Research Articles

Self-compensation in nitrogen-doped ZnSe

The structural and electronic properties of column V acceptor impurities in ZnSe are reviewed with special emphasis on N. The results of our calculations indicate that As and P acceptors possess two atomic configurations: a metastable effective-mass state with a small lattice relaxation and a stable deep state with a large lattice relaxation. Substitutional N gives rise to shallow acceptor states in either configuration. The low 20–30% doping efficiency is proposed to be caused by N bonding at interstitial sites. Various interstitial bonding configurations are found to give both shallow donor and shallow acceptor states leading to self-compensation. Post growth in diffusion of N is proposed to be useful in increasing the concentration of shallow acceptor states.

Theory of defects, impurities, and doping in ZnSe

The formation of native defects and incorporation of dopant impurities in ZnSe are addressed from a first-principles point of view. Our calculations of the atomic and electronic structure yield explicit microscopic information about atomic positions, relaxation and bonding. Hyperfine parameters are computed, which can be directly compared with experimental data. Our formalism also produces concentrations of the various defects and impurities. One of our major findings is that native defects are not responsible for the doping difficulties in ZnSe. Investigations of Li, a potential p-type dopant, indicate that the achievable hole concentration is restricted in this case by the limited stability and solubility of Li on the substitutional acceptor site.

Self-compensation through a large lattice relaxation in p-type ZnSe

The energetics of self-compensation through atomic relaxation around acceptor impurities in ZnSe were examined via first principles total energy calculations. We find large charge state and impurity-dependent lattice relaxations for As and P acceptors which can account for the experimentally observed difficulties in obtaining low-resistivity p-type ZnSe from these dopants. A much smaller relaxation is found for Li.

Alkali atoms as acceptor impurities in ZnSe

The electronic structure of Li, Na, and K substitutional impurities in ZnSe are calculated within the framework of the self-consistent-field multiple-scattering molecular cluster model. The Li and Na impurities induce an a 1 resonance in the valence band and a t 2 state in the band gap. According to our results, the Li and Na acceptor states originate from the t 2 orbital in the gap. The degree of localization of the gap state increases with atomic number, as a result from core repulsion effects and from the orthogonality between the impurity states. We suggest that the latter mechanism could be applied to Li and Na acceptors in other II–VI compounds.

The effect of precipitates on electrical properties of ZnSe:Ga

The self-compensation of donor impurities in ZnSe is briefly reviewed from the defect chemistry viewpoint. It is shown that a fairly good fit to the experimental data for ZnSe:Ga is attained by means of the impurity segregation model, ISM, developed in this paper. The ISM makes use of Ga transfer from Ga Zn positions into GaSe precipitates. The formation of the precipitates takes place at the concentration of Ga incorporated higher than some critical value, [Ga] c, which is a function of the temperature of the equilibration process. The ISM shows that binary compounds, such as ZnSe, can be effectively doped up to a limited impurity concentration only.

Effects of the Crystal Field in the Spectra of Iron Group Impurities in ZnSe

AbstractThe many‐electron crystal field term states are calculated with account of the symmetry dependent deformation of the 3d orbitals and of the dependence of one‐electron energies on the spin orientations. It is shown that the one‐electron 3d orbitals of symmetry t2 are extended with respect to orbitals of symmetry e by 1 to 4%. The relative deformation depends on the ratio of a σ‐type resonant integral to a π‐type resonant integral.

Extended x-ray absorption fine structure studies of diffused copper impurities in ZnSe

We have performed the first extended x-ray absorption fine structure investigation of the local environment around dilute copper impurities diffused into the II-VI semiconductor ZnSe. An average first nearest neighbor distance of 2.32±0.06 Å is obtained. Our results indicate a rather large distortion of the local environment surrounding the copper impurities and/or displacement of these impurity atoms from simple substitutional sites (CuZn) and high symmetry interstitial sites (CuI).

Impact ionization of deep impurities in zinc selenide

Multiplication measurements, in which the photocurrent in a Schottky diode is measured as a function of electric field, have been used to obtain information on impact processes at deep impurities in ZnSe. For ZnSe:Mn one sees multiplication governed by impact transfer of electrons from the impurity to the conduction band. At higher fields, band-to-band impact ionization occurs. For ZnSe:Cu, the impurity concentration is not high enough for one to see a contribution to the multiplication from impact ionization. A theory of the multiplication as a function of field is presented and shown to be in agreement with the ZnSe:Mn data.

Autoionization of the 3T1 (3P) state of Ti impurities in ZnSe

Autoionization of the ³T₁ (³P) state of Ti impurities in ZnSe

Electron-Paramagnetic-Resonance Investigation of the Superhyperfine Structure of Iron-Group Impurities in II-VI Compounds

The electron-paramagnetic-resonance spectra of several iron-group impurities in ZnSe, ZnTe, and CdTe are shown to have resolved superhyperfine structure (SHFS) resulting from an interaction with one or two shells of Se or Te nuclei surrounding the impurity. We have observed interaction with the two nearest chalcogenide shells for ZnSe: ${\mathrm{Cr}}^{+}$, ZnSe: ${\mathrm{Mn}}^{2+}$, ZnTe: ${\mathrm{Cr}}^{+}$, ZnTe: ${\mathrm{Mn}}^{2+}$, and ZnTe: ${\mathrm{Fe}}^{+}$, and an interaction with only the nearest chalcogenide shell for ZnSe: ${\mathrm{Fe}}^{3+}$, ZnSe: ${\mathrm{Cr}}^{2+}$, and CdTe: ${\mathrm{Mn}}^{2+}$. Hensel's data on ${\mathrm{Fe}}^{3+}$ in ZnTe were analyzed for the first-shell Te SHFS. None of these data exhibit ${\mathrm{Zn}}^{67}$ SHFS, although the Cd chalcogenides show Cd SHFS. Several other impurities in II-VI compounds were studied to obtain additional information on SHFS. The SHFS results are compared for different impurities and crystals and discussed in relation to the delocalization expected from covalent bonding. The small observed delocalization is surprising in view of the fairly large covalent character of the crystals.