Ge photodetectors for Si microphotonics

Abstract

This thesis demonstrates the integration of pure Ge near-infrared photodetectors on Si. Ge epilayers were grown directly on Si by a two-step ultra-high-vacuum/chemical-vapor-deposition (UHV/CVD) process. This work conclusively proves that threading-dislocation densities in the Ge epilayers, measured both by plan-view transmission electron microscopy and etch-pit-density (EPD) counting, were reduced by cyclic thermal annealing. Additionally, Ge mesas with no threading dislocations as measured by EPD were also demonstrated. The removal of threading-dislocations can be attributed to the thermal stress induced dislocation glide and reactions. Using the annealed Ge epilayers grown on Si, p-i-n Ge photodetectors with maximum responsivities of 770 mA/W at 1.3 μm were fabricated. Finally, to allow the integration of Ge epilayers in Si microelectronic processing, the protection and passivation of Ge was investigated. The passivation was provided by the oxidation of Si epilayers grown on Ge. Capacitance-voltage characteristics of metal-oxide-semiconductor devices demonstrated the high quality of the passivation with the measured interface state density of 4 x 1011 cm-2eV- 1.