Quantum cascade laser design based on impurity–band transitions of donors in Si/GeSi(111) heterostructures

Abstract

The possibility of amplification of terahertz radiation due to optical transitions between a two- dimensional state continuum (2D) and shallow-level donor states in Si/GeSi(111) superlattices with selectively delta-doped quantum wells is analyzed theoretically. The mechanism of population inversion is based on fast ionization of donor centers by phonon-assisted tunneling into continuum of a lower subband in the neighboring quantum well. The fast tunneling is caused by hybridization of the impurity ground state and a 2D state continuum in the neighboring quantum well. It is shown that for the donor concentration of 5x10^11 cm^2 per period the terahertz gain can be as high as 10 cm^-1 in the wavelength range of 29–45 µm (6.5–10.2 THz).