We have established a method for time-resolved cyclotron resonance measurements using an electron spin resonance cavity with a temporal resolution 15 ns under photo-excitation in an undoped semiconductor, cuprous oxide. The observed photo-carriers are generated via long-lived 1s-excitons excited at the phonon assisted absorption edge below the yellow gap. This work focuses on the fast response that is within 80 ns after photo-excitation of high-density excitons. A shift of the photo-carriers from a magnetoplasma resonance to a cyclotron resonance, previously known as a steady resonance in highly doped semiconductors, is observed for the first time in the temporal domain. We successfully explain the real and imaginary parts of the transient microwave absorption using spectral simulations, taking account of the depolarization factors in two different sample shapes and configurations in the cavity.
Topical issue: Excitonic Processes in Condensed Matter, Nanostructured and Molecular