Nanosecond cyclotron resonance in ultrapure diamond

We have investigated temporal properties of photo-excited carriers in ultrapure diamond by the nanosecond cyclotron resonance (CR) method. The ramp time and the amplitude of the CR signals are found to be dependent on the incident laser pulse energy as well as on the photon energy for excitation. The dependences are discussed based on the photoabsorption process due to the indirect excitons in diamond, which is assisted by absorption of the transverse-acoustic phonons. Similarities to the free-carrier generation via two-body excitonic collisions in a dipole-forbidden direct gap semiconductor, Cu2O, are pointed out.