Photoluminescence study of Si1−xGex/Si heterostructures grown by molecular beam epitaxy and ultrahigh vacuum chemical vapor deposition

Abstract

Photoluminescence (PL) of Si1−xGex/Si heterostructures grown by conventional molecular beam epitaxy (MBE), gas-source MBE (GSMBE), and ultrahigh vacuum chemical vapor deposition (UHV-CVD) has been investigated in the wavelength region of 1000–1800 nm. Single and multiple quantum wells (SQW and MQW, respectively) and uncapped Si1−xGex alloy epitaxial (EPI) layers on Si substrates have been studied. In the case of GSMBE and UHV-CVD, sharp band-edge PL of Si1−xGex appears and deep-level PL is very weak. PL lines due to bound excitons can be observed up to about 50 K for SQWs and MQWs but they disappear above 12 K for EPI layers. Broadening of the PL lines with an increase in excitation intensity due to bound multiple exciton complexes has been observed for the EPI layers while it can hardly be observed for SQWs and MQWs. In the case of conventional MBE, intense broad emission bands dominate the PL spectrum below the band gap of Si1−xGex for the SQWs and MQWs. Similar broad emission bands sometimes appear also in the PL spectra of the EPI layers grown by conventional MBE, in which dislocation-related D lines are dominant in most cases. From the dependence on the excitation power density, the annealing effects, and the difference between the growth methods, the broad emission bands are considered to be related to defects in the Si1−xGex layer or the interface which are characteristic of conventional MBE.