Extended defects in MBE‐grown CdTe‐based solar cells

Abstract

AbstractExtended defects in the p ‐ZnTe/n ‐CdTe heterojunctions grown by the molecular‐beam epitaxy technique on two different substrates, GaAs and CdTe, have been investigated by deep‐level transient spectroscopy (DLTS) and transmission electron microscopy (TEM). Four hole traps, called H1 to H4, and one electron trap, called E3, have been revealed in the DLTS spectra measured for the heterojunctions grown on the GaAs substrates. The H1, H3, H4 and E3 traps have been attributed to the electronic states of dislocations on the ground of their logarithmic capture kinetics. The DLTS peaks associated with the H1 and E3 traps were not observed in the DLTS spectra measured for the heterojunction grown on the CdTe substrate. They are most likely associated with threading dislocations generated at the mismatched interface with the GaAs substrate. Cross‐sectional TEM images point out that they are dislocations of the 60°‐type. In both the types of heterojunctions the H4 trap was observed only under forward‐bias filling pulse, suggesting that this trap is associated with the CdTe/ZnTe interface. In addition, TEM images revealed also the presence of intrinsic and extrinsic stacking faults in the CdTe layers, which may considerably affect their electronic properties. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)