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

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 TeO2 or CdO oxides, which exhibit low resistance. To reduce the surface recombination, we adopted (NH4)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 (NH4)2S. XPS data showed that (NH4)2S passivation removed conductive TeO2 layers and induced formation of insulating CdTeO3 and CdS layers. A heterojunction by the thin CdS layer and CdZnTe was formed.