Light trapping in horizontally aligned silicon microwire solar cells

Localised structuring of metal-semiconductor cores in silica clad fibres using laser-driven thermal gradients

The molten core drawing method allows scalable fabrication of novel core fibres with kilometre lengths. With metal and semiconducting components combined in a glass-clad fibre, CO2 laser irradiation was used to write localised structures in the core materials. Thermal gradients in axial and transverse directions allowed the controlled introduction, segregation and chemical reaction of metal components within an initially pure silicon core, and restructuring of heterogeneous material. Gold and tin longitudinal electrode fabrication, segregation of GaSb and Si into parallel layers, and Al doping of a GaSb core were demonstrated. Gold was introduced into Si fibres to purify the core or weld an exposed fibre core to a Si wafer. Ga and Sb introduced from opposite ends of a silicon fibre reacted to form III-V GaSb within the Group IV Si host, as confirmed by structural and chemical analysis and room temperature photoluminescence.

Semiconductor core fibres: materials science in a bottle

Novel core fibers have a wide range of applications in optics, as sources, detectors and nonlinear response media. Optoelectronic, and even electronic device applications are now possible, due to the introduction of methods for drawing fibres with a semiconductor core. This review examines progress in the development of glass-clad, crystalline core fibres, with an emphasis on semiconducting cores. The underlying materials science and the importance of post-processing techniques for recrystallization and purification are examined, with achievements and future prospects tied to the phase diagrams of the core materials.

The application space for optical fibers is growing, enabled by fibers built using special materials and processes. In this Review, the authors discuss the materials science behind producing crystalline core fibers for diverse applications and progress in the field.

Light Trapping in Single Elliptical Silicon Nanowires

Light trapping in single nanowires (NWs) is of vital importance for photovoltaic applications. However, circular NWs (CNWs) can limit their light-trapping ability due to high geometrical symmetry. In this work, we present a detailed study of light trapping in single silicon NWs with an elliptical cross-section (ENWs). We demonstrate that the ENWs exhibit significantly enhanced light trapping compared with the CNWs, which can be ascribed to the symmetry-broken structure that can orthogonalize the direction of light illumination and the leaky mode resonances (LMRs). That is, the elliptical cross-section can simultaneously increase the light path length by increasing the vertical axis and reshape the LMR modes by decreasing the horizontal axis. We found that the light absorption can be engineered via tuning the horizontal and vertical axes, the photocurrent is significantly enhanced by 374.0% (150.3%, 74.1%) or 146.1% (61.0%, 35.3%) in comparison with that of the CNWs with the same diameter as the horizontal axis of 100 (200, 400) nm or the vertical axis of 1000 nm, respectively. This work advances our understanding of how to improve light trapping based on the symmetry breaking from the CNWs to ENWs and provides a rational way for designing high-efficiency single NW photovoltaic devices.

Laser restructuring and photoluminescence of glass-clad GaSb/Si-core optical fibres

Semiconductor-core optical fibres have potential applications in photonics and optoelectronics due to large nonlinear optical coefficients and an extended transparency window. Laser processing can impose large temperature gradients, an ability that has been used to improve the uniformity of unary fibre cores, and to inscribe compositional variations in alloy systems. Interest in an integrated light-emitting element suggests a move from Group IV to III-V materials, or a core that contains both. This paper describes the fabrication of GaSb/Si core fibres, and a subsequent CO₂ laser treatment that aggregates large regions of GaSb without suppressing room temperature photoluminescence. The ability to isolate a large III-V crystalline region within the Si core is an important step towards embedding semiconductor light sources within infrared light-transmitting silicon optical fibre.

Semiconductor-core optical fibres are of interest for their non-linear optical and electro-optical properties. Here, GaSb/Si composite-core optical fibres were fabricated and a CO₂ laser was used to facilitate controlled GaSb segregation within the silicon. This has implications for embedding light sources in IR-transmitting fibers

Laser recrystallization and inscription of compositional microstructures in crystalline SiGe-core fibres

Glass fibres with silicon cores have emerged as a versatile platform for all-optical processing, sensing and microscale optoelectronic devices. Using SiGe in the core extends the accessible wavelength range and potential optical functionality because the bandgap and optical properties can be tuned by changing the composition. However, silicon and germanium segregate unevenly during non-equilibrium solidification, presenting new fabrication challenges, and requiring detailed studies of the alloy crystallization dynamics in the fibre geometry. We report the fabrication of SiGe-core optical fibres, and the use of CO₂ laser irradiation to heat the glass cladding and recrystallize the core, improving optical transmission. We observe the ramifications of the classic models of solidification at the microscale, and demonstrate suppression of constitutional undercooling at high solidification velocities. Tailoring the recrystallization conditions allows formation of long single crystals with uniform composition, as well as fabrication of compositional microstructures, such as gratings, within the fibre core.

Using SiGe in the core of optical fibres extends the wavelength range and potential optical functionality, but fabrication challenges exist. Here, Coucheron et al. report the fabrication and tailoring of SiGe-core optical fibres using CO₂ laser irradiation to heat the glass cladding and recrystallize the core.