Physical mechanisms of intersubband-absorption linewidth broadening in s -Ge/SiGe quantum wells

We analyze the linewidth of intersubband absorption features observed in n-type s-Ge/Ge0.82Si0.18 multiquantum wells grown on Si(001) substrates. Supported by a thorough theoretical modeling, we discuss the role on the line broadening of electron scattering due to interface roughness, spatial distribution and density of ionized donors, phonons, alloy disorder, and extended defects. To this aim, the absorption spectra of a set of samples featuring different well widths and doping profiles are measured obtaining a very good agreement with the theoretical results. We demonstrate values of the half width at half maximum of the E0->E1 absorption peak as small as 2 meV. Our analysis suggests that the coherence time of electron wave functions in n-doped Ge/SiGe quantum wells is not yet limited by intrinsic scattering mechanisms up to room temperature, opening new perspectives for the quantum design of silicon-based light emitting devices.