Terahertz Emission from Phosphor Centers in SiGe and SiGe/Si Semiconductors

Terahertz-range photoluminescence from silicon-germanium crystals and superlattices doped by phosphor has been studied under optical excitation by radiation from a mid-infrared CO2 laser at low temperature. SiGe crystals with a Ge content between 0.9 and 6.5 %, doped by phosphor with a concentration optimal for silicon laser operation, do not exhibit terahertz gain. On the contrary, terahertz-range gain of ~ 2.3 - 3.2 1/cm has been observed for donor-related optical transitions in Si/SiGe strained superlattices at pump intensities above 100 kW/cm2

THz amplification based on impurity-and 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 1/cm is obtained for structures with gently strained selectively doped Si layers (Nd ≈ 10^17 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 1/cm. 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