Abstract

Light management is essential to improve the performance of optoelectronic devices as they depend on the interaction between photons and device design. This research demonstrates novel approaches to enhance the light absorption in thin-film III-V photovoltaics (PV) and light emission from micrometer-scale light-emitting diodes (μLED). The high power conversion efficiency (PCE) realized in III-V PV makes them attractive power generation sources, especially for off-the-grid space-related missions. Thin-film PV (< 1 μm) offer great tolerance towards the inevitable radiation damage in the space environment as carrier collection is maintained compared to their optically thick counterparts (3-5 μm). To combat transmission loss of photons traveling through the thinned device, this work develops textured back surface reflectors (BSR) to increase the optical path length (OPL) of unabsorbed photons to generate electron-hole pairs. The textures are created via etching techniques and epitaxial regrowth and are characterized by surface imaging and reflectance (R) measurements. The textured BSR with high diffuse R increase the OPL, and the best-known design demonstrates over a four-fold increase in the OPL, which is two times greater than the planar BSR. This research delivers new analyses useful to the PV community, including the lifetime enhancement factor and free-carrier absorption modeling, which aim to improve the PCE in thin-film PV. Modern display technology is constantly integrated into daily use to convey information and connect people worldwide. The next generation of wearable devices requires small-featured displays to achieve high resolution. The μLED delivers value to near-eye displays through low power consumption, long lifetime, high contrast, and increased resolution. As these devices reduce in size, surface states limit the light output power (LOP) at the roughened sidewalls, and the perimeter-to-area ratio must be considered. This research focuses on developing a fabrication process that improves LOP through sidewall treatments. The dry etch process is optimized to reduce surface roughness, and sidewall treatments via wet-chemical etching, in situ etching, and regrowth aim to improve the sidewall quality. Scanning electron microscopy on the LED sidewalls supports the optimized fabrication process. Luminescence characterization reveals that combinations of etching and regrowth suppress non-radiative recombination events. These techniques render pathways to enhance LOP in LEDs smaller than 25 μm x 25 μm.

Publication Date

5-3-2022

Document Type

Dissertation

Student Type

Graduate

Degree Name

Microsystems Engineering (Ph.D.)

Department, Program, or Center

Microsystems Engineering (KGCOE)

Advisor

Seth Hubbard

Advisor/Committee Member

Mustafa A.G. Abushagur

Advisor/Committee Member

Parsian Mohseni

Campus

RIT – Main Campus

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