Characterization of Si1−xGex/Si (100) heterostructures by photoluminescence and admittance spectroscopy

The authors report a complete and systematic study based on photoluminescence (PL) and deep-level transient spectroscopy (DLTS) measurements performed on fully strained or relaxed SiGe/Si single heterostructures (SH) and fully strained double heterostructures (DH) grown by rapid thermal chemical vapor deposition (RTCVD). First of all, the well-resolved free excitonic PL transition, clearly observed in high-quality pseudomorphic SiGe single layers grown by RTCVD, is used to acceed to the structural and interfacial characteristics of thin strained SiGe layers in the DH. The main results show the striking efficiency of a Si epitaxial capping layer in reducing drastically the SiGe surface recombination and the influence of the alloy disorder. In fact, this disorder must be taken into account to explain the broadening of the excitonic line. Moreover, the measurement of the no-phonon line full width at half-maximum is reported to be useful to control and analyze when the layer starts to relax or when some interfacial roughness occurs due to growth conditions. In a second hand, strong deep level behavior have been detected and analyzed in the relaxed layers by PL and DLTS. Sharp lines similar to the dislocation related D lines in Si, are attributed to the influence of the misfit dislocations at the SiGe/Si heterointerface and are associated with an Ev+0.51 eV interface state trap observed by DLTS. PL broad bands are assigned to originate from the 60° dislocations located in the SiGe layer and are connected with a Ev+0.38 eV deep level trap. Finally, this study has been conducted to characterize SiGe/Si heterostructures in order to acceed to the quality of the heterointerface, a crucial parameter for the future development of Si-advanced devices.