Si1−xGex/Si multiquantum well (MQW) structures grown by molecular-beam epitaxy exhibit a broad, intense photoluminescence (PL) peak ∼120 meV below the band gap energy and/or phonon-resolved, near-band gap PL, depending on the MQW strain and the growth conditions.The origins of these two PL types have been identified. For MQWs with thin alloy layers (≤40–100 Å), the SiGe PL at 2 K is dominated by boron bound–exciton annihilation, which yields phonon-resolved transitions. For thicker layers, the PL is dominated by a broad, intense peak due to exciton recombination at small (≤∼15 Å) interstitial-type platelets that occur in densities up to ∼109 cm−2/QW. Etching experiments revealed that within a given MQW the platelet density is lowest in the first grown well and progressively increases in subsequent wells with increasing strain energy density, indicating that platelet formation is strictly a morphological phenomenon.
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures Processing, Measurement and Phenomena11, no. May 3 (1993): 899–901.