Temperature-dependent carrier injection routes under optical excitation in high-purity diamond crystals

We have investigated carrier injection routes in high-purity diamond crystals in a wide temperature range using the time-resolved cyclotron resonance method. By analysing the excitation spectra, we find that carriers are injected under optical excitation above the energy threshold for exciton generation with emission of a transverse acoustic phonon at 10 K and 80 K, whereas with absorption of a transverse optical phonon at 300 K. The excitation power dependence clearly shows that the carriers are generated by thermal dissociation of excitons at 300 K.