Si/SiGe quantum cascade structures emitting in the 10 μm range

In this paper, we report on the successful deposition of Si/SiGe quantum cascade (QC) structures by molecular beam epitaxy (MBE). The structures are pseudomorphically grown on Si in the metastable regime, thus low temperature (T=350 °C) deposition is required. Structural characterization has been performed using transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray reflectivity (XRR). The data indicate an interface roughness of about 2 monolayers and an excellent correlation of the layer periodicity within the stacks of cascades. Electroluminescence (EL) has been observed for several different p-type Si/SiGe QC structures. The observed energy agrees with the energy calculated for the HH2 to HH1 intersubband transition in the active well of the cascade structure and shows the expected confinement shift in dependence of the Ge concentration and the well width. The EL is strongly p-polarized. The results clearly indicate that the observed EL originates from the desired intersubband transition. The EL persists up to temperatures exceeding 180 K. The non-radiative lifetime of the HH2 state reaches values of about 0.5 ps, which is comparable to those of III/V QC structures.