Band Alignment at CdS/wide-band-gap Cu(In,Ga)Se2Hetero-junction by using PES/IPES

Abstract

Direct characterization of band alignment at chemical bath deposition <TEX>$(CBD)-CdS/Cu_{0.93}(In_{1-x}Ga_x)Se_2$</TEX> has been carried out by photoemission spectroscopy (PES) and inverse photoemission spectroscopy (IPES). Ar ion beam etching at the condition of the low ion kinetic energy of 400 eV yields a removal of surface contamination as well as successful development of intrinsic feature of each layer and the interfaces. Especially interior regions of the wide gap CIGS layers with a band gap of <TEX>$1.4\~1.6\;eV$</TEX> were successfully exposed. IPES spectra revealed that conduction band offset (CBO) at the interface region over the wide gap CIGS of x = 0.60 and 0.75 was negative, where the conduction band minimum of CdS was lower than that of CIGS. It was also observed that an energy spacing between conduction band minimum (CBM) of CdS layer and valance band maximum (VBM) of <TEX>$Cu_{0.93}(In_{0.25}Ga_{0.75})Se_2$</TEX> layer at interface region was no wider than that of the interface over the <TEX>$Cu_{0.93}(In_{0.60}Ga_{0.40})Se_2$</TEX> layer.