Stimulated far-infrared emission from boron acceptor centers in silicon

We report observation of far-infrared stimulated emission from intracenter transitions of boron doped silicon under mid-infrared optical pumping at low lattice temperature. While terahertz lasing has been demonstrated for all group-V hydrogen-like donors in silicon under photoionization and intracenter excitation of donors, formation of populated inversion between excited states of shallow acceptors suffered from relatively lower energy gaps between particular excited states permitting dipole optical intracenter transitions. Resonant intracenter excitation from the ground state into excited (7-0), (6-0) and (5-0) of boron acceptors in silicon, as shown, enable four-level lasing mechanism at moderate optical pump powers. Si:B laser operates at (7-0)-(8+1) and (6-0)-(8+1) transitions under the p3/2 valence band, the corresponding emission wavelengths are 172.3 µm and 171.6 µm. Contradictory to most of n-type silicon lasers, the population inversion mechanism in Si:B utilizes as an upper laser level the state which has not the longest lifetime, but favourites from four-level lasing scheme. Determination of binding energy of excited (8+1) state from Si:B laser emission spectra proves the experimental values previously obtained by indirect spectroscopic techniques.