Interaction of Optically Excited Carriers with Intraicosahedral Phonons

Abstract

The transport of electrons in boron-rich solids is strongly impeded by capture processes in intrinsic traps. Forβ-rhombohedral boron it was shown that these traps are generated by the interaction between electrons and specific intraicosahedral phonons. The phonons involved are quenched, when the traps are occupied by doping with suitable metals leading ton-type. To prove this phonon quenching, inβ-rhombohedral boron and boron carbide electron–hole pairs have been generated by optical interband excitation. For optical steady-state excitation the existence of band-type carriers is proved by a Drude-type free-carrier absorption. Difference spectra of optically excited and unexited samples confirm that the phonons, which interact with electrons to generate the traps, are quenched at a measurable degree. A misinterpretion caused by the temperature raised by the irradiation can definitely be excluded, because this effect would be opposite to the one measured.