Defect reduction in MOCVD grown Si/GaAs

This paper reports a study of the effectiveness of thermal annealing and strained layer superlattices (SLS's) in defect reduction in Si/GaAs structures. The GaAs layers were grown on (100) Si substrates by low pressure MOCVD. They were evaluated by TEM, HREM, EBIC and PL. As-grown layers contained dislocation densities in the 108--109 cm-2 range, depending on the layer thickness. Post-growth and in situ annealing were performed on a wide variety of these structures. TEM examination shows that in situ annealing was more effective as it resulted in confining a large portion of the threading dislocations to the interface region. Furthermore, the interaction of threading dislocations to form closed loops was evident. Additionally, the effect of GaAs/GaInAs and GaInAs/GaAsP SLS's on dislocation bending was investigated. The former SLS, although not lattice matched to GaAs, proved more effective. Capacitance transient spectroscopy has been applied to identify deep levels associated with heteroepitaxial GaAs grown on silicon. Results from p+n diode test structures reveal creation of the electron trap EL2 and a high density of hole states in the bandgap. This is the first reported observation of hole traps in MBE GaAs on Si. The activation behavior of the electron and hole signal peaks fits the signature of two different charge states associated with EL2, a native point defect complex seen in MOCVD, VPE, and bulk-grown GaAs, but not usually observed in MBE grown GaAs. The spectra seen show many similarities with earlier deep level transient spectroscopy (DLTS) observations on plastically deformed GaAs