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