Simulated effect of epitaxial growth variations on THz emission of SiGe/Ge quantum cascade structures

We report on the effects of growth variations on the computed electroluminescence of Ge/SiGe chirped superlattice quantum cascade structures. The chirped structures investigated comprise 50 periods, each of which has a sequence of 5-7 Ge quantum wells and SiGe barriers. We used an extended density matrix carrier transport model to calculate the electron population of each subband in a QW structure via solution of the Liouville equation. Our modelling results have shown that a 5% increase of all layers of designed structures implies 10% decrease of the electroluminescence intensity and a 15% increase implies a 40% reduction in electroluminescence. Structures with 25% increase of layer thickness lose up to 60% of their electroluminescence intensity.