We report electroluminescence originating from L-valley transitions in n-type Ge/Si0.15Ge0.85 quantum cascade structures centred at 3.4 and 4.9 THz. . Different strain-compensated heterostructures, grown on a Si substrate by ultrahigh vacuum chemical vapor deposition, have been investigated. The design employs a vertical optical transition and the observed spectral features are well described by non-equilibrium Green’s function calculations. We observe two emission peaks that are due to a non-selective injection in the upper state of the radiative transition. Comparison with similar III-V emitters is used to deduce radiative efficiencies. We will present new results from 4 quantum well Ge/SiGe emitters based on diagonal transitions in real space.
A terahertz intersubband emitter based on silicon is presented. The emission originates from n-type Ge/SiGe quantum cascade structures. We designed a strain-compensated single quantum active region based on a vertical optical transition and tensile-strained Si0.15Ge0.85 barriers. The 51 quantum cascade periods (corresponding to 4.2 μm) were grown on a Si1-xGex reverse graded virtual substrate on Ge/Si(001) substrates. Deeply etched diffraction gratings were processed and the surface emitting devices were characterized at 5 K with a Fourier transform infrared spectrometer. We observed two distinct peaks at 3.4 and 4.9 THz with a line broadening of 20%. This is an important step towards the realization of an Ge/SiGe THz quantum cascade laser.
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