High temperature electrical conductivity in donor‐doped II–VI compounds

Abstract

PACS 61.72.Vv, 72.80.Ey Dopants of group III and group VII elements act as donors (D) in II -VI materials. Here we report the results of our investigations of donors in some II -VI donor-doped compounds (CdSe : Al, CdSe : Ga, CdSe : In, ZnSe : In, ZnS : Al, ZnS : Ga and ZnS : In) using the method of high temperature electrical conductivity (HTEC). Our interests lie in the activation energies determined from HTEC isobars and slopes of HTEC isotherms in the temperature region from 600 to 1200 °C where the donor action of dopant appears. We assumed the existence of near-zero activation energies of free carrier concentrations determined from HTEC isobars Arrhenius plots for the donor action regions. In some cases, this is realized as the result of formation of compensation through electroneutrality condition n = [D • ]. In this region, the best results to obtain high n-type conductivity in frozen-in crystals can be achieved. Unexpected negative HTEC activation energies with non-zero slopes of HTEC isotherms were obtained for the systems ZnSe : In, ZnS : Al and ZnS : Ga in the donor action region. The appearance of negative activation energies of HTEC and the models for high temperature defect equilibrium of these systems are analyzed.Introduction Knowledge of the high temperature defect equilibrium (HTDE) is needed to predict the properties of II -VI materials made under different preparation conditions. Trivalent metal atoms (Al, Ga, In) are important impurities in II -VI compounds. They act in II -VI compounds as donors. Doping with these dopants gives rise to large concentrations of donors, but often the electron concentration is a small fraction of the donor concentration as a result of self-compensation with formation of complex. It has been found that there are differences in doping mechanisms in II-VI compounds. At high level dopant concentrations, the mechanisms of doping are related to the solubility of dopants. The largest electron concentration has been found after annealing under metal component vapor pressure (p Me : p Cd or p Zn ). The best way to describe HTDE is to calculate defect concentrations [1] using experimentally determined high temperature electrical conductivity (HTEC) isotherms and isobars data. HTEC measurements of donor-doped II -VI compounds are interpreted in the literature differently and no single model has emerged providing basis for explanation of all the observations on concrete II -VI compound. In this investigation, we compare the activation energies (∆E) of HTEC isobars of donor-doped CdSe, ZnSe and ZnS and attempt to characterize defect structure of these donor doped II -VI compounds to compare the donor-action (DA) temperature regions. HTEC and the high temperature Hall effect experimental data in donor doped CdSe crystals have been reported in Ref. [2]. However, publications on HTEC and high temperature Hall effect measurement in ZnSe [3,4] are rare and no publications on ZnS have appeared. This work is our first attempt to systematize the HTEC experiments in donor doped II -...

High temperature electrical conductivity in ZnSe:In and in CdSe:In under selenium vapor pressure

“…2b can be compared with the value ∆E = 1.5 eV of isobar of undoped CdSe [14]. Earlier [16] we investigated the dependence of HTEC isotherm of ZnSe:In under p Zn as σ ~ Zn p γ , where γ ≈ 0.5. The electroneutrality condition (ENC) and mass balance (MB) approximations in ZnSe:In were…”

“…The vapour pressure was maintained by controlling the temperature of a component reservoir. The ampoule for the HTEC experiments had four sealed graphite electrodes, and the four-probe method was used High temperature Hall effect was measured by the Van der Pauw method in CdSe:In [16]. For determination of the time to reach defect equilibrium we used our investigations of chemical diffusion [17].…”

(Invited) Impact of Indiumand Gallium Doping on the Photovoltaic Performance of CdSe Quantum Dot Hybrid Solar Cells

“…These dopants have been reported in the literature to increase the electrical conductivity of bulk CdSe. 38,39 Literature suggests that CdSe can be doped to increase the concentration of the electron carriers (n-type), however, recent reports by Norris et al also show that CdSe QDs can be made p-type as well. 40 Here the purpose of doping CdSe QDs to increase the n-type of carrier in hybrid CdSe/P3HT solar cell to achieve increased performance.…”

Review on the Materials Properties and Photoelctrochemical (PEC) Solar Cells of CdSe, Cd_1-xZn_xSe, Cd_1-xIn_xSe, Thin Films

“…The Cddoping increased the density of trapping states that changed the position of the dark Fermi level leading to the deviation from linearity in the dependence of I ph on F at low illumination intensities. Dopants of group III and VII elements acted as donors (D) in II-VI materials as revealed investigated by K. Lott [128] and also in some II-VI donor-doped compounds (CdSe:Al, CdSe:Ga, CdSe: In, ZnSe: In, ZnS:Al, ZnS:Ga and ZnS: In) using the method of high temperature electrical heating. The activation energies calculated from HTEC isobars and slopes of HTEC isotherms in the temperature region from 600 to 1200 °C, exhibited the donor action of dopants.…”