Amplified terahertz radiation (1.5 – 4.2 THz, 70 – 200 micron) in p-Ge is generated on transitions between light- and heavy-hole sub-bands in crossed electric and magnetic fields. Population inversion builds for certain E/B ratios, when light holes accumulate on closed trajectories below the optical phonon energy, while heavy holes scatter on optical phonons. Traditional p-Ge lasers output up to 10 W for cm3 active volume and microsecond pulse duration. The saturation intensity within the active crystal can reach kW/cm2, but such is unachievable at the output because of low gain. This is caused in part by the inhomogeneous doping of the melt-grown germanium traditionally used. The resulting deviation of E- and B-fields from orthogonality, by even 1 deg, remarkably reduces gain. Calculations for operating conditions, where current is saturated due to optical phonon scattering, show that 1 deg deviations occur for doping non-uniformity exceeding a few percent. Variations in acceptor concentration can be much higher in melt-grown germanium that has the required low doping level.
© 2003 Optical Society of AmericaPDF Article