HIGH-FIELD CYCLOTRON-RESONANCE AND VALENCE-BAND STRUCTURE IN SEMICONDUCTING DIAMOND

The cyclotron resonance of thermally excited free holes has been obser ved in synthetic semiconducting diamond at ultrahigh magnetic fields u p to 150 T generated by the single-turn-coil technique with pulsed far -infrared laser radiations of 28, 36, and 119 mum. Three absorption pe aks were observed at and above room temperature for the magnetic field s parallel to the [100), [111], and [110) crystallographic directions. The typical value of omega(c)tau was as small as 2 at 40-degrees-C ev en in ultrahigh fields. One of the three peaks was observed in the cyc lotron-resonance inactive circular polarization for holes, while the o ther two lines were observed in cyclotron-resonance active circular po larization for holes. Assuming that these resonance absorption lines a re due to three holes of the valence bands at the GAMMA point, i.e., l ight-hole, heavy-hole, amd split-off-hole, we can conclude that the ba nd dispersion curve for one of the three bands has a negative (electro nlike) curvature in some directions.