Terahertz intersubband emission from silicon-germanium quantum cascades

Terahertz electroluminescence due to light hole-heavy hole intersubband transitions in p-type Si/SiGe quantum cascade structures has been observed in both surface-normal and edge emission geometries. THz output powers of up to 50 nW have been observed for surface emission from 100 period Si/sub 0.76/Ge/sub 0.24//Si heterostructures grown on a Si/sub 0.8/Ge/sub 0.2/ relaxed buffer or 'virtual substrate'.