High-temperature electrical properties of undoped Cd1-xMnxTe (x = 0.05-0.55) crystals under cadmium vapor pressure

Abstract

For the first time, the results of a study of the high-temperature electrical characteristics of undoped Cd1-xMnxTe single crystals in a wide composition range x = 0.05-0.55 are described. For this purpose, a study of Hall effect was made at the temperatures of 723–1073 K and isothermal and temperature dependences of electrical parameters were constructed. At 300 K, all the samples studied had a p-type conductivity, and Cd1-xMnxTe crystals with x = 0.02 and 0.15 had a low resistivity (102-103 Ohm×cm) while with x = 0.3 and 0.55 they had a relatively high ρ~ 107 Ohm×cm, which is due to an increase in the band gap with an increase in the MnTe content. The sample with the lowest Mn content (x = 0.02) showed the instability of the impurity-defect system during the first heating-cooling cycles: the conductivity type changed from p- to n- above 750 K and the mobility gradually increased as a result of the introduction of Cd atoms from the gas phase to the interstitial positions of the lattice. In this sample, during the first heating, the influence of donor impurities is noticeable, since the experimental line lg[e-] is significantly (~ 1-1.4 orders of magnitude) higher than that for model (undoped) CdTe, probably due to the donor behavior of Mn atoms. The crystal with the highest MnTe content (Cd0.45Mn0.55Te) also demonstrated the instability of the impurity-defect system, which was reflected in the decrease in the electrical conductivity after heat treatment at 773-873 K by almost one order of magnitude, which can be explained by a superposition of the results of the interaction of donor Cd atoms introduced from the gas phase with its native acceptor point defects (compensation) and the interaction of impurities between the matrix and Te inclusions. It has been established that a peculiarity of Cd1-xMnxTe crystals with a high content MnTe (x = 0.15, 0.55, and partially 0.3) is the inverse dependence of the carrier concentration on the cadmium vapor pressure caused by the onset of mixed conductivity of these crystals at high temperatures (T> 873 K). Accordingly, for these crystals, the value 1/RH at the moment of the onset of mixed conductivity characterizes the conditional rather than real mobility of the charge carriers. On the pressure dependences of the charge carrier concentration, the corresponding dependences are lower than the undoped CdTe (especially at low temperatures) for samples with x≥0.15 indicating that the introduction of a significant amount of MnTe (x≥0.15) leads to a decrease in the charge carrier concentration by 0.5-0.8 orders of magnitude (at ~ 773 K). This is due to the influence of Mn atoms, which form a stronger bond with Te than Cd, and therefore the generation of electrons requires more energy than in pure CdTe.