Surface leakage current control with heterojunction-type passivation in semi-insulating CdZnTe material

摘要

Inter-pixel resistance in the planar structure X-ray or gamma-ray detector has severe effects on signal cross-talk and the signal integration time. Generally, Br-MeOH etching in Cd-based compounds leaves a Te-rich or Cd-rich surface resulting from selective etching. The etching then converts the Te-rich or Cd-rich surface in air into TeO_2 or CdO oxides, which exhibit low resistance. To reduce the surface recombination, we adopted (NH_4)_2S for surface passivation in the polycrystalline CdZnTe:Cl grown by thermal evaporation method. The optimization of passivation was confirmed by I-V measurement and X-ray photoemission spectroscopy (XPS) analysis. From the I-V curve, we confirmed that the surface resistance was considerably increased after passivation with (NH_4)_2S. XPS data showed that (NH_4)_2S passivation removed conductive TeO_2 layers and induced formation of insulating CdTeO_3 and CdS layers. A heterojunction by the thin CdS layer and CdZnTe was formed.