Characterisation of Semiconductor Nanowires for Use in Semiconductor Lasers

Abstract

A monolithically integrated III-V light emitting device on silicon-on-insulator (SOI) substrate would considerably simplify photonic integration with Complementary Metal-Oxide-Semiconductor (CMOS) technology. This thesis presents an approach for designing an edge-emitting device with a combined III-V/Si waveguide. High-quality InGaAs nanowires (NWs) can be grown directly on the SOI wafers, free from defects and dislocations. By using these nanowires on an SOI wafer, a hybrid waveguide with a high optical mode overlap between the III-V gain material and the silicon waveguide is designed. The as-grown InGaAs nanowires on SOI substrate are assessed by several techniques, including photoluminescence (PL), Raman, scanning electron microscope (SEM), and energy-dispersive x-ray spectroscopy (EDX) characterisation. Different nanowires with different diameters and periods are examined in this study. These studies reveal that the indium composition in the nanowire arrays is not uniform. Two different indium compositions exist in a single nanowire. A lower indium composition is at the base of the nanowires in the horizontal direction, and a higher indium composition is above the core layer in the vertical direction. Moreover, the density of the nanowire arrays affects the uniformity of the indium composition. Denser arrays show that the indium composition decreased significantly from the edges of the arrays towards the centre of the arrays. These two different indium compositions are responsible for the appearance of the two distinct peaks in the PL and Raman spectra. Additionally, the optical performance of the fabricated waveguide is examined by optical pumping. PL imaging is used to measure the intensity and extract the power efficiency from the waveguide. The study demonstrates a steady-state intensity saturation with a reduction in the power efficiency as the pumping power increases when the measurements are taken from the vertical direction. This behaviour indicates that lasing occurs in the in-plane direction. Furthermore, PL images showing a higher concentration of light near the edges of the nanowire arrays support this conclusion, as the in-plane guided light is strongly reflected at the waveguide boundaries.