CONTINUOUS-WAVE, MICROWAVE-MODULATED, AND THERMAL-MODULATED PHOTOLUMINESCENCE STUDIES OF THE BII3 LAYERED SEMICONDUCTOR

This paper reports the extensive investigation of the luminescence pro perties of the bismuth triiodide, BiI3, layered semiconductor. The lum inescence spectrum is comprised of relatively narrow stacking fault ex citons (R, S, and T) in addition to broader bands at lower energies. T he present work emphasizes the investigation of the broader bands. Res earch of the BiI3 involved utilization of continuous-wave photolumines cence (PL) and PL excitation (PLE), together with two modulated techni ques: thermal-modulated PL (TMPL) and microwave-modulated PL (MMPL). T he TMPL and the MMPL of the stacking fault excitons served to confirm the previously suggested interaction among the R, S, and T states. Exp erimental evidence indicates that the broader emission lines may be di vided into several subgroups, some of which are associated with band e dge to deep state transitions. The deep state within the band gap may be attributed to stoichiometric or strain defects. Results showed that the latter transitions correlated to band edge properties. One Subgro up, however, displayed independent behavior, due mainly to an absence of coupling to the band edge. This subgroup is associated with a trans ition between relatively localized donor and acceptor states.