INFLUENCE OF LOW-TEMPERATURE ANNEALING IN VACUUM ON PHYSICAL PROPERTIES OF SINGLE CRYSTAL p-CdxHg1-xTe (x≈0,28)

Abstract

This research directed on the subsequent study of thermodynamics stability problem of Cd_xHg_1‑xTe (x=0,19÷0,3) and is continuation of experiments on the low-temperature annealing of this alloy system. The Cd_xHg_1-xTe crystals were grown from the basic components of 6N or 7N cleanness classes. With the result p-type conductivity material [N_A-N_D » (2÷4)·10¹⁵ см^‑3] was obtained. The p-Cd_xHg_1-xTe samples used in this investigation had a composition x»0,28. Samples were made in classical Hall configuration and annealed in a vacuum (10^-3 torr) at Т=373 К. Influence of low temperature annealing in a vacuum on physical properties of p-Cd_xHg_1‑xTe (x≈0,28) was studied on the basis of the Hall coefficient  measurements and conductivity measurements versus temperature, have performed on an automated dc system (standard KAMAK) in the temperature range of 80÷273 К. Quantitative analysis of changes of electrophysical parameters have performed on the basis of model for the р-Cd_xHg_1‑xTe. Already after the first stage of annealing, which lasted 4 hours, the electrophysical parameters of the p-Cd_xHg_1‑xTe (x≈0,28) have changed significantly. The reason for such changes is a significant increase in the concentration of mercury vacancies which is a defect of the acceptor type. In particular, after the first stage of annealing, the concentration of mercury vacancies increased by almost an order of magnitude and reached the value of [V_Hg] ≈ 2,4×10¹⁶ см^-3. However, the analysis of changes in the electrophysical parameters of the p-Cd_xHg_1‑xTe (x≈0,28) caused by the second stage of annealing allowed us to make an assumption about the possible existence of an upper limit of the concentration of mercury vacancies that can be achieved at this annealing temperature. The simulation results give all the grounds to conclude that this value will not exceed [V_Hg] ≈ 10¹⁷ см^-3. In view of this, we can confidently assert that the electrophysical parameters of single crystal Cd_xHg_1-xTe (x=0,19÷0,3) in which the concentration of donors N_D (n-type conductivity) or the concentration of acceptors N_A (p- type conductivity) in the initial state <(2÷3)×10¹⁵ см^-3, undergo significant changes in the presence of a sample in an environment with a temperature of 353÷373 K for several hours. Therefore, the conclusion that the passivation of the surface of this material is necessary to maintain the stability of the physical parameters of single crystal Cd_xHg_1-xTe (x=0,19÷0,3) with high mobility of charge carriers is valid not only for the material of the n-type conductivity, but also for the material of the p-type.

Key words: narrow gap semiconductors, Hall effect, conductivity, low-temperature annealing.