Contacts for High-Resistivity (Cd,Mn)Te Crystals

Semi-insulating (Cd,Mn)Te crystals offer a material that may compete well with the commonly used (Cd,Zn)Te crystals for manufacturing large-area X- and gamma-ray detectors . The Bridgman growth method yields good quality, high-resistivity (10⁹-10¹⁰ Ω·cm) crystals of (Cd,Mn)Te:V. Doping the as-grown crystals with the compensating agent vanadium ( ≈ 10¹⁶ cm^-3) ensures their high resistivity; thereafter, annealing them in cadmium vapors reduces the number of cadmium vacancies. Applying the crystals as detectors necessitates having satisfactory electrical contacts. Accordingly, we explored various techniques of ensuring good electrical contacts to these semi-insulating (Cd,Mn)Te crystals, assessing metallic layers, monocrystalline semiconductor layers, and amorphous (or nanocrystalline) semiconductor layers. We found that ZnTe heavily doped ( ≈ 10¹⁸ cm^-3) with Sb, and CdTe heavily doped ( ≈ 10¹⁷/cm^-3) with In, proved satisfactory semiconductor contact layers. They subsequently enabled us to establish good contacts (with only narrow tunneling barriers) to the Au layer that usually constitutes the most external contact layer. We outline our technology of applying electrical contacts to semi-insulating (Cd,Mn)Te, and describe some important properties.