Silicon donor and Stokes terahertz lasers

Abstract

Two types of lasers based on hydrogen-like impurity-related transitions in bulk silicon operate at frequencies between 1 and 7 THz (wavelength range of 50–230 μm). These lasers operate under mid-infrared optical pumping of n-doped silicon crystals at low temperatures (less than 30 K). Dipole-allowed optical transitions between particular excited states of group-V substitutional donors are utilized in the first type of terahertz silicon lasers. These lasers have a gain about 1–3 cm^-1 above the laser thresholds (more than 1 kW/cm²) and provide 10ps – 1μs pulses with a few mW output power on discrete lines. Raman-type Stokes stimulated emission in the range 4.6–5.8 THz has been observed from silicon crystals doped by antimony and phosphorus donors when optically excited by radiation from a tunable infrared free electron laser. The scattering occurs on the 1s(E)→1s(A₁) donor electronic transition accompanied by an emission of the intervalley transverse acoustic g-phonon. The Stokes lasing has a peak power of a few tenths of a mW and a pulse width of a few ns. The Raman optical gain is about 7.4 cm/GW and the optical threshold intensity is about 100 kW/cm².