Electroluminescence study on electron hole plasma in strained SiGe epitaxial layers

The electroluminescence (EL) of thick fully strained SiGe layers is investigated in order to clarify the recombination mechanisms. In the investigated temperature range of 20–80 K and for SiGe thickness of 70–450 nm an electron–hole plasma (EHP) is observed even at low current densities of 1 Acm⁻². In SiGe-based quantum devices the EHP condition is expected to be attained at even lower injection levels. We used the band filling model for EHP to extract the renormalized gap of SiGe in dependence on the plasma density by performing a line shape analysis of EL spectra. The results were compared with the theoretical prediction. Based on this analysis as well as on measurements and modelling of the spectral photocurrent and the external quantum efficiency, we were able to evaluate parameters of recombination transitions for EHP in SiGe. Above 200 K there is an important contribution to EL from the silicon regions. For a better evaluation of the SiGe contribution, we compared EL of SiGe diodes with EL of pure silicon diodes.