INFLUENCE OF LOW-TEMPERATURE ANNEALING IN VACUUM ON PHYSICAL PROPERTIES OF SINGLE CRYSTAL n-CdxHg1-xTe (x ≈ 0,19)

Abstract

One of the outstanding problems, which arises up at Cd_xHg_1-xTe crystal growth and making of devices on his basis, there is the thermodynamics stability problem of fairly pure single-crystal n-Cd_xHg_1‑xTe (x ~ 0,19–0,21). Our research directed on the subsequent study of thermodynamics stability problem of n-Cd_xHg_1‑xTe 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 and were additionally doped by an indium from melt. With the result that lightly doped n-type material [N_D-N_A ~ (1–4)·10¹⁴ см^‑3] was obtained. The Cd_xHg_1-xTe samples used in this investigation had a composition x ~ 0,19. Samples made in classical Hall configuration were annealed in a vacuum (10^-3 torr) at Т = 373 К. Influence of low temperature annealing in a vacuum on physical properties of n-Cd_xHg_1‑xTe was studied on the basis of the Hall coefficient R_H and conductivity s measurements versus temperature have performed with an automated dc system (standard KAMAK) in the temperature range of 80–273 К. Already after the first stage of annealing during 4 hours the clear inversion of conduction type (n-type to p-type) in Cd_xHg_1-xTe sample (x ~ 0,19) was attained. And after a next stage of annealing (annealing time - 4 hours) we recorded the clear change of sign of the Hall coefficient in the temperature dependence R_H(1/T). Theoretical analysis obtained experimental data was executed on the basis of models for n- and р-Cd_xHg_1‑xTe. This allowed us to estimate of concentration of acceptors N_A and donors N_D, electron/hole mobility ratio, b = m_e/m_h, acceptor binding energy e_A. The simulation results showed that in the case of annealing in vacuum, the reason for inversion of the conductivity type is the thermal generation of defects of the acceptor type (vacancies Hg). The conclusion that the passivation of the surface of this material with a high mobility of charge carriers is necessary to maintain the stability of physical parameters was fully confirmed.

Key words: narrow gap semiconductors, Hall effect, conductivity, inversion of the conductivity type, low-temperature annealing