Optimisation of seed and mask surfaces in epitaxial lateral overgrowth of indium phosphide on silicon for silicon photonics

The effect of chemical mechanical polishing (CMP) on epitaxial lateral overgrowth (ELOG) of InP is investigated. To this end, silicon wafers with a seed layer of InP has been treated in two ways; by depositing SiO₂ mask and polishing it prior to performing ELOG, and by growing additional InP directly on the InP/Si wafer and then polishing the InP layer prior to depositing and patterning SiO₂ followed by subsequent ELOG. For InP seed, a two step process with Chemlox™ slurry and sodium hypochlorite mixed with citric acid-based slurry has been used whereas for SiO₂ surface polishing, only one slurry was employed. Analysis of the ELOG layers has been carried out with atomic force microscope (AFM) and panchromatic cathodoluminescence (PC-CL) in-situ a scanning electron microscope (SEM). The results show that polishing the InP/Si layer has not only a beneficial effect on surface morphology of the ELOG layer but also on reduction of its defect density as a consequence of improved conditions for near-ideal coalescence.