The operating principles and experimental results concerning far-IR lasers based on the intersubband hot holes optical transitions in crossed electric and magnetic fields as well as on the optically excited intracenter shallow impurity states are reviewed and discussed. The analysis of the state of the art and the possible directions of the development of p-Ge hot hole intersubband transitions laser and the result of the recent theoretical and experimental investigations of new THz media based on impurity transitions in Si doped by phosphorus are presented.
The observation of spontaneous emission from phosphorus doped Si with a doping concentration of 0.9 X 1015 cm-3 and 2 X 1015 cm-3 is reported. Population inversion between the 2p0 state and the 1s(T) and 1s(E) states was achieved by optically pumping with a CO2 laser. The spontaneous emission increased with pump power. Electrons could be excited from the 1p0 state into the conduction band due to the absorption of background radiation or radiation from a far-IR probe laser. The frequency dependence of the absorption is in agreement with the cross section for photon ionization of a transition from the 2p0 state into the conduction band.
Theoretical proposals concerning submillimeter and far-infrared activity based on shallow acceptors states optical transitions in p-Ge and p-Si semiconductors are discussed. Preliminary experimental investigations will be presented.