Cathodoluminescence measurement of high bandgap CdTe-based devices

High band-gap CdTe-based devices are being developed as top films to be used in tandem solar cells. CdTe can be alloyed with Mg and Zn to form Cd_xMg_1-xTe (CMT) or Cd_xZn_1-xTe (CZT) to increase the band gap; however, doping and passivation of these films continue to be a fundamental challenge. Films exhibiting better recombination lifetimes have been demonstrated by incorporating Se in CMT and CZT to from quaternary alloys. A fundamental understanding of the film properties are needed for all these films to realize their potential as photovoltaic absorbers. Optical characterization is one method to understand and aid in the development of high band-gap CdTe films. Scanning electron mapping of the luminescence of these film gives insight into film composition, homogeneity, and crystal quality. Herein we present our study of the optical properties of these materials using cathodoluminescence(CL). Additionally, electron beam-induced current (EBIC) is measured and correlated to the optical response. Unexpected peak shift and secondary peak presence indicate potential phase segregation or trap state formation.