Terahertz lasers based on intracentre transitions of group V donors in uniaxially deformed silicon

This paper presents a brief overview of available experimental data on the characteristics of stimulated terahertz emission (4.9 – 6.4 THz) from optically excited neutral group V donors (phosphorus, antimony, arsenic and bismuth) in crystalline silicon subjected to uniaxial compressive strain along the [100] axis. Strain is shown to have a significant effect on the characteristics in question. Optimal strain depends on the dopant and may reduce the threshold pump intensity and improve lasing efficiency. We discuss possible mechanisms behind this effect and estimate the limiting output emission parameters

Relaxation of Coulomb States in semiconductors probed by FEL radiation

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Optimizing the operation of terahertz silicon lasers

A thorough characterization of terahertz silicon lasers with respect to doping concentration and operation temperature has been carried out. Several factors limiting the laser operation, such as heating of the laser crystal and absorption by photoinduced free carriers are discussed. The optimal doping concentration has been determined. The influence of the pump geometry on the laser efficiency has been investigated. It was found that an external uniaxial force applied to the laser crystal lowers the pump threshold and increases the output power

Spin-orbit interaction and group-V donor lasing from silicon

In this report we focus on the spin-orbit interaction which lifts the degeneracy of the 1s(T2) multiplet of bismuth (Bi) and antimony (Sb) donors in silicon. As experimentally shown it influences on THz laser spectrum of pointed impurity centers under their optical CO2 laser excitation. Note here that in unstressed silicon crystal stimulated emission is based on the 2p(+/-) -1s(T2) intracenter transitions in Bi donor and the 2p0-1s(T2) transitions in Sb. Special attention is paid to the influence of the axial compression stress applied along [100] and [110] crystallographic axes on the laser states and laser frequencies. As shown the axial stress in Si:Bi and Si:Sb shifts the laser lines that has not been observed for Si:P and Si:As where the spin-orbit effect is negligible. In addition in Si:Bi the [100] stress higher than 2kbar switches the upper laser state to the 2p0. Moreover spectrum measurements demonstrate that Bi donors in stressed silicon lase on the states bounded to the upper 4-delta valleys of the conduction band. The experimental data are discussed and the laser frequencies compared with theoretical calculations of donor energy levels