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

Abstract

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 HH 2 to HH 1 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 HH 2 state reaches values of about 0.5 ps, which is comparable to those of III/V QC structures.