The physical principles of terahertz silicon lasers based on intracenter transitions



The first silicon laser was reported in the year 2000. It is based on impurity transitions of the hydrogen-like phosphorus donor in monocrystalline silicon. Several lasers based on other group-V donors in silicon have been demonstrated since then. These lasers operate at low lattice temperatures under optical pumping by a midinfrared laser and emit light at discrete wavelengths in the range from 50 to 230 µm (between 1.2 and 6.9 THz). Dipole-allowed optical transitions between particular excited states of group-V substitutional donors are utilized for donor-type terahertz (THz) silicon lasers. Population inversion is achieved due to specific electron–phonon interactions of the impurity atom. This results in long-living and short-living excited states of the donor centers. Another type of THz laser utilizes stimulated resonant Raman-type scattering of photons by a Raman-active intracenter electronic transition. By varying the pump-laser frequency, the frequency of the Raman intracenter silicon laser can be continuously changed between at least 4.5 and 6.4 THz. The gain of the donor and Raman-type THz silicon lasers is of the order of 0.5 to 10 cm−1, which is similar to the net gain realized in THz quantum cascade lasers and infrared Raman silicon lasers. In addition, fundamental aspects of the laser process provide new information about the peculiarities of electronic capture by shallow impurity centers in silicon, lifetimes of nonequilibrium carriers in excited impurity states, and electron–phonon interaction.