Development of electrical and optical devices for next generation high-speed optical interconnects

Rapid advances in AI, LLMs, and IoT are pushing data traffic toward >1.6 Tb/s optical links with much lower energy per bit. VCSEL based multichannel transceivers are one of the most cost- and power-efficient choice for short-reach interconnects, but further scaling is limited by modal dispersion in multimode VCSELs and bandwidth/power ceilings in both VCSELs and silicon driver/control ICs as per-lane rates exceed 200 Gb/s. Accordingly, overcoming optical limitations requires both aggressive aperture scale-down and targeted process advancements in VCSEL fabrication. The electrical limits motivate using higher-speed electronic devices such as InP based Type-II DHBTs. Meanwhile, cryogenic and quantum computing demand ultra-efficient links bridging cryogenic processors to room-temperature peripheral electronics; Cryo-VCSELs offer ~100 GHz bandwidth at few milliampere bias range and enable >448-Gb/s PAM-4 operation but require tighter process control and microcavity-scaling insight. This thesis advances two fronts: first, a wafer-scale, OpenCV-based automated oxide-aperture measurement method that replaces manual ImageJ, enabling full-wafer oxidation maps at high throughput and exposing critical nonuniformities for <3-µm apertures; and, second, a quantitative study of emitter-ledge effects in sub-micron InP/GaAsSb Type-II DHBTs, showing a 160-nm ledge can more than double DC current gain β by suppressing surface recombination, but with trade-offs in ideality factor, yield, base resistance, and fT/fmax. Together, these results provide the process capability and device understanding needed to co-optimize Cryo-VCSEL sources and InP-DHBT electronics for fJ/bit-class, long-reach optical interconnects in hybrid-temperature computing systems.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Electrical & Computer Engr

Grantor

University of Illinois Urbana-Champaign

Year dc:date

2025

Author dc:creator

• Liu, Zetai

Contributors dc:contributor

• Feng, Milton

• High Speed Data Com, VCSEL, HBT, Fabrication, Testing

Statement dc:rights

• Copyright 2025 Zetai Liu

Language dc:language

en

Handle dc:identifier

https://hdl.handle.net/2142/132812

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/132812