Jahn-Teller Levels of Defects in A ^IV B ^VI Semiconductors Doped by High Dose Ion Implantation

Abstract

Investigation of heavily doped semiconductors is a vast field, which remains actual in the physics of semiconductors. A ^IV B ^VI semiconductors are widely known and used in IR-detectors, long-wavelength lasers and thermoelectric converters. Owing to the high dielectric constant and the low value of effective mass of the carriers, the wave functions of shallow Coulomb centers must overlap and merge into allowed band even at relatively small impurity concentration. III-group impurities (In, Ga, Tl) lead to appearance of unique properties of these materials upon doping such as pining of the Fermi level persistent photoconductivity, negative magnetoresistance. These properties can be explained by the existence of localized and resonance states in these materials, which can lie in the forbidden, conduction and valence band depending on the compound composition and type of impurity. The model is connected with Jahn-Teller instability of the crystalline environment of point defects in A ^IV B ^VI semiconductors. We have tried to observe these states (levels) by producing high concentration of native defects For this goal ion implantation process with doses up to 10¹⁸ ions/cm² was used. In addition to doping this process produces the vacancies (mainly tellurium vacancies) with the concentration of two orders of magnitude greater than the concentration of the implanted ions. It was shown (irrespective of type of ions) the existence of resonance level, which stabilizes the Fermi level in PbTe crystals at 80 K by 0.05 eV above the bottom of the conduction band.