P-type Ge cyclotron-resonance laser: Theory and experiment.

Abstract

p-type germanium in crossed magnetic and electric fields is used as a continuously tunable laser source in the far infrared. To describe magneto-optical transitions responsible for the laser action, we use the complete version of the Pidgeon and Brown model, which accounts for the nonparabolicity and nonsphericity of the ${\mathrm{\ensuremath{\Gamma}}}_{8}$ valence bands in Ge. It is demonstrated that both features are of importance in the correct assignment of the transitions. Also, the heating effects in the light-hole Landau levels are estimated theoretically. The calculations are performed for magnetic fields B\ensuremath{\parallel}[110] and B\ensuremath{\parallel}[111]. We compare our theoretical results to experimental work in which we are able to achieve laser action in a tuning range from 28 to 76 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ by varying the magnetic field between 1.4 and 3.7 T. The laser output consists of a single line having a width of 0.25 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ and a maximum power of about 300 mW for a pulsewidth of 1 \ensuremath{\mu}sec. Hall measurements are performed on p-type Ge samples with the same configuration as that of the laser crystals in order to determine the effective electric fields involved in the laser action. It is shown that the effective fields differ considerably from the applied fields. We conclude that the laser action, for B\ensuremath{\parallel}[110], at low magnetic fields (B2.7 T) is governed by the 2-3 transition in the b set of light holes, while the action at high fields (B>2.8 T) is governed by the light-hole transition 0-1 in the same set. This agrees with estimations of the population inversion determined by other authors.