Allocation and Properties of Iron States in Cd_1-xFe_xTe in Forbidden Gap Energy Range

Abstract

The use of different experimental methods (reflectivity, absorption, photoconductivity and cathodoluminescence) allowed us to confirm the existence of the deep donor-like state of iron and present allocation and properties of the iron states in Cd1-yFexTe (0 < x < 0.05) at 300 K and 77 K in the forbidden gap energy range. It was concluded that the increase in width of the forbidden gap with the change of temperature from 300 K to 77 K leads mainly to the rise of the energy distance between the donor-like iron state 5 E and the bottom of the conduction band. PACS numbers: 78.20. Ci, 78.20.Jq, 78.60.Hk The semiconducting compound Cd1-xFexTe belongs to the family of diluted magnetic semiconductors [1,2]. The optical properties of this compound have been studied using absorption [3,4], reflectivity [5,6], and photo-EPR measurements [7]. On the basis of the results of these measurements there has been recognized a state of iron, identified as the so-called deep donor and its ionization energy related to the transition Fe2+(d6 ) → Fe3+(d5 ) has been calculated to be 1.45 eV with respect to the bottom of the conduction band minimum (CBM). The existence of the donor-like state and its ionization energy value has been confirmed [6,8].Our reflectivity (RE), transmission and photoconductivity (PC) measurements procedure and experimental apparatus were described earlier [9]. The PC measurements were taken using modulated beam light (modulation frequency equal to 11 Hz) in the constant collecting electric field. In the cathodoluminescence (CL) measurements the employed electron beam energy was 10 keV. Using the calibrated dependence of the lattice constant versus chemical composition presented in paper [6], the iron concentrations x were determined.Reviews of the E0 maxima energy positions obtained from the RE measurements and Epc PC signal as a function of iron concentration x at 300 K (RT) and