Photoluminescence and Steady-State Interband Photoconductivity of High-Purity beta-Rhombohedral Boron

Photoluminescence and interband photoconductivity of high-purity beta-rhombohedral boron were measured at different temperatures up to steady-state conditions. To consistently describe the results in relation to one another and with respect to previous results, the energy band scheme was improved. An essential improvement is the replacement of the previously called "upper valence band" by two closely neighbored levels S1 and S2 with localized states. According to the proved correlation between structural defects and electronic properties they are attributed to vacancies in the structure, probably preferably in B(13) sites. The photoluminescence yields the energy positions of the unoccupied gap states, and those are the prerequisites for the interpretation of nonradiating cascade-like recombination of electrons via the series of intrinsic trapping levels. Depending on temperature this recombination path is in competition with the radiating recombination related to the transition of electrons into the defect levels near the valence band edge. The luminescence intensity decreases with increasing time and only partly recovers even in long dark periods