Stress effects induced in SiGe strained layers by low-temperature ultraviolet-assisted oxidation

Low-temperature (550 °C) ultraviolet-assisted oxidation of epitaxially grown Si_0.8Ge_0.2 strained layers on (100) Si substrates leads to the formation of nanocrystalline Ge (nc-Ge) particles embedded in a SiO₂ layer which exhibit visible photoluminescence with an emission maximum situated at around 2.18 eV. Grazing incidence x-ray diffraction investigations of the remaining SiGe layer which was continually rejected by the advancing oxide layer have shown the presence of the (311) diffraction peak. This implies that the unoxidized SiGe layer has been fractured in many regions misoriented with respect to the initial layer. The displacement of the SiGe (311) peak position recorded for samples which had their grown oxide layer stripped away when compared with as-grown samples indicates the presence of a significant stress in these low-temperature grown oxide layers. This stress is believed to explain both the survival of the nc-Ge particles during prolonged oxidation and the fracturing of the buried SiGe layer. © 1998 American Institute of Physics.