Improvement of Electrical Properties of Hg_1-xZn_xSe upon Doping with Fe

Abstract

Results of measurements of electron concentration and mobility in mixed crystals of Hg1-xZnxSe (0 < x < 0.07) doped with resonant Fe donors (0 < nFe < 5 x 10 19 cm-3 ) at liquid helium temperatures are presented.The data show that there is a considerable improvement of the electrical properties of the material when Fe impurities are present. The analysis of the mobility in terms of the scattering from ionized centers (accounting for possible spatial correlation of impurity charges) and the alloy scattering is in agreement with the measured data.PACS numbers: 72.80. Ey, 72.20.Fr, 71.55.Fr Mixed crystals of II-VI semiconduction containing Zn have attracted recently a great deal of interest. This is related to the fact that the presence of Zn in, say, HgTe improves considerably mechanical [1] and electrical [2] properties compared to the case of, e.g., Cd containing compounds. Therefore, we have studied mixed crystals of Hg1-xZnxSe doped with resonant Fe hoping that the improvement related to the stabilizing effect of Zn observed by Cobb et al. [2] will combine with a similar effect related to the presence of Fe [3] and result in a particularly attractive semiconducting material from the point of view of possible applications. Furthermore, doping with iron is known to lead to an increased mobility, as evidenced by the study of the case of HgSe:Fe in the mixed valence regime [4]. The existence of similar enhancement in Hg1-x Zn x Se:Fe was confirmed in the course of our study.The highest molar fraction x attained in the crystals grown by the modified Bridgman method was 0.072. The Zn fraction in the studied samples was determined by energy dispersive X-ray analysis. The concentration of intentional Fe donors ranged from nFe = 0 (undoped samples), through intermediate Fe concentrations (corresponding to completely ionized system of donors at low temperatures), up to Fe = 5 x 10 19 cm-3 , when only a fraction of Fe donors were ionized (mixed valence regime).Electron conductivity and the Hall effect at liquid helium temperatures were measured and from those values the concentration of conduction electrons as well as their mobility were determined. As in HgSe:Fe, there is an increase in the electron concentration together with the amount of Fe impurities present in the (681) 682 W. Dobrowolski, E. Grodzicka, J. Kossut, B. Witkowska crystals, followed by a saturation (at high Fe doping levels) whose value depends on Zn molar fraction. The latter dependence shows that there is a relative shift of the resonant Fe level and the bottom of the conduction band induced by alloying with Zn. The observed mobility values, particularly in the samples with high concentrations of Fe, are quite high -indicating good quality of the crystals studied here. There are clear indications that the mechanism of the mobility enhancement, seen previously in HgSe:Fe [4], is also active in the present case of Hg 1 -xΖnx Se:Fe.To analyze the data quantitatively we have to incorporate in the appropriate model of the band structure the varia...