Photoluminescence decay of direct and indirect transitions in Ge/SiGe multiple quantum wells

We report on the observation of room temperature direct band gap photoluminescence in compressively strained-Ge multiple quantum wells with Ge-rich SiGe barriers. A detailed experimental study of the temperature dependence of the photoluminescence is carried out from 5 K up to room temperature. We find that the direct gap photoluminescence at room temperature is due to the thermal excitation of carriers from L-type to Gamma-type confined states. Room temperature photoluminescence shows that Ge/SiGe multiple quantum wells are promising candidates for efficient light emitting devices monolithically integrated on Si.