On the behavior of Bi in a CdTe lattice and the compensation effect in CdTe:Bi

Abstract

CdTe crystals of two types have been grown by the vertical Bridgman method: (i) crystals doped with Bi to ∼1018 cm−3 and (ii) double-doped (Bi + Cl) crystals with a Bi concentration of ∼1018 cm−3 and a Cl concentration of ∼1017 cm−3. The temperature dependences of the resistivity, photoconductivity, and low-temperature photoluminescence are investigated for the crystals grown. Analysis has shown that doping with Bi (crystals of the first type) leads to compensation of the material. The resistivity of the CdTe:Bi samples at room temperature, depending on the doping level, is varied in the range of 105–109 Ω cm. The hole concentration is determined by the acceptor level at Ev + 0.4 eV in lightly doped CdTe:Bi samples and by the deep center at Ev + 0.72 eV in heavily doped CdTe:Bi samples. Double doping leads to inversion of the conductivity type and reduces the resistivity to ∼1 Ω cm. Heavily doped CdTe:Bi crystals and double-doped crystals exhibit the presence of acceptors with an ionization energy of 36 meV, which is atypical of CdTe.