Thermal processing of semiconductor alloy core glass fibers

Abstract

Semiconductor core glass-clad fibers are of great interest as optical and optoelectronic platforms for their high transparency in infrared and the potential control of their electrical properties by doping or strain engineering. Various devices like infrared optical fibers, solar cells, light detectors, and an optical modulator have been demonstrated using semiconductor core glass fibers. To date, semiconductor core glass fiber has been focused on elemental material systems such as silicon or germanium. In this study, the complexity of material systems for semiconductor core fibers was increased to incorporate eutectic alloy systems. In this thesis, semiconductor alloy core glass fibers were fabricated using molten core drawing (MCD) technique. Eutectic alloy systems such as silicon-gold (Si0.9Au0.1) and silicon-gallium antimonide (Si0.94GaSb0.06) were chosen for the fiber core materials. Purification and recrystallization of Si were achieved in the alloy core fibers using thermal processing. Furthermore, we have shown possibilities of controlling structures of segregated GaSb and Au in the alloy core fibers using laser-driven thermal processing. During the laser-driven thermal processing on inhomogeneous alloy core fibers, liquid droplet flows through solid along a temperature gradient were observed. In silicon-gold alloy core glass fiber, migration rates of silicon-gold liquid droplets were increased over 300 µm/s under a temperature gradient of 5·103K/cm near the melting temperature of silicon. We successfully explained such high migration rates of liquid alloy using a diffusion control model that has previously only been validated with temperature gradients below 120 K/cm. Thermal processing of eutectic alloy systems opens up the possibility of scalable single recrystallization of fiber core materials and of adding greater functionality to semiconductor core glass fiber for optoelectronic applications. The study on the rapid liquid migration through solid can also be helpful to predict the engineering condition for the thermal processing of alloy materials. The laser-driven thermal processing we performed for the fibers can be extended to two-dimensional materials, which are the core of modern semiconductor fabrication technology.