THz silicon lasers based on donor center transitions

Summary form only given. Results of experimental and theoretical study of terahertz frequency (1.3-7 THz, wavelength range 230-42 μm) stimulated emission based on the intracenter optical transitions of group-V shallow donor centers (phosphor P, antimony Sb, arsenic As, bismuth Bi) in silicon crystal are reviewed and discussed. The population inversion of bound Coulomb center states and appropriate light amplification is formed due to low-temperature (T<30K) phonon-assisted intracenter relaxation under optical excitation e.g. using CO₂ laser radiation. The lifetimes of principle impurity states, small signal gain and laser threshold intensity are considered in the framework of simplified multi-valley theoretical model of donor center states. Laser performances differed for different donor centers are summarized and compared with theoretical calculations. Special attention is paid to the effect of Si crystal lattice deformation under applied uniaxial stress (P<2kbar) on the phonon-assisted scattering which results in the essential enhancement of laser gain and the appropriate decrease of the laser threshold intensity (Si:P,Si:Sb) and can generate the shift of impurity transitions responsible for stimulated emission (Si:As).