Optical absorption edge and photoluminescence spectra in amorphous and crystalline boron-rich solids

Abstract

Optical absorption spectra for amorphous B, B 4 C and B 13 P 2 films are fitted by α h ω = A(h ω − E 0 ) n where n is not 2 but 3. Temperature dependence of the spectrum shows that the origin of n=3 may be linear densities of states at both band edges. Photoluminescence (PL) spectrum for β -rhombohedral boron has a peak at 1.14 eV and temperature independent broad width. This corresponds to recombination between a hole in the intrinsic acceptor level and an electron in the conduction band bottom or in the trapping level. Thermal quenching of the PL intensity is analyzed by two activation process, activation energies of which are 0.12 and 0.004 eV. The former may be escape process of hole or electron from the acceptor or the trapping level.