The Effect of Deposition Stoichiometry and Post-deposition Treatments on Deep Defects in CdTe

Polycrystalline Cadmium Telluride (CdTe) with different gas phase stoichiometry was deposited by the Elemental Vapor Transport (EVT) technique. CdTe solar cells were fabricated with different post deposition processing, such as CdCl
₂
heat treatment (HT) and Cu doping. The devices were characterized by standard Current-Voltage (JV) and Capacitance-Voltage (CV) measurements. Deep defect distribution was investigated with Deep Level Transient Spectroscopy (DLTS). Majority carrier traps with an activation energy of 0.4 eV were identified in devices at all deposition stoichiometry, and could be related to cadmium vacancy (VCd). Cl treated samples exhibited a deep minority carrier electron trap (~0.5 eV). Deep majority carrier traps were identified in various samples, possibly responsible for limiting the minority carrier lifetime. Samples with Cl and Cu showed a relatively shallower (~0.24 eV) electron trap with concentration up to 10
¹⁴
cm
^-3
; this defect could be responsible for dopant compensation in CdTe.