THz amplification based on impurity-band transitions in Si/GeSi heterostructures

Terahertz stimulated emission based on impurity-band optical transitions of phosphor donor centers embedded in Si/GeSi heterostructures is reported. THz emission was measured from selectively doped Si/GeSi structures excited by CO₂ laser radiation. Amplification of 8-9 THz emission with the coefficient of 2-3 cm^-1 is obtained for structures with gently strained selectively doped Si layers (N_d ap 10¹⁷ cm^-3) under pump density of 200 kW/cm². Corresponding net gain taking into account small overlapping of active layer with THz mode is estimated to be ~ 200-300 cm^-1. Experimental data demonstrate the possibility to use impurity-band transitions for THz laser action. The capability of Si/GeSi quantum cascade scheme which can support inverted population on donor-continuum transitions of Si conduction band is also analyzed.