Epitaxial design, fabrication development, and characterization of transistor-injected quantum cascade laser structures

Mid-wave infrared (MWIR) and long-wave infrared (LWIR) coherent optical sources are garnering attention for their role in facilitating compact solutions to a range of important fields, such as spectroscopy, remote chemical sensing, and free-space optical communication systems. While the quantum cascade laser (QCL) presents one appealing solution for these infrared sources, inherent limitations related to its unipolar nature dictate the optical power (controlled by the current) and emission wavelength (controlled by active region bias) are inherently linked. The transistor-injected quantum cascade laser (TI-QCL) presents a novel three-terminal QCL design that seeks to address these limitations in order to provide a more controllable and efficient solution to the MWIR and LWIR problem space. By placing the cascaded active region within the base-collector space charge region of a heterojunction bipolar transistor (HBT), independent control of injection current and active-region bias is achievable. To progress the TI-QCL device concept closer to demonstration, efforts are taken in three domains: epitaxial design, fabrication process optimization, and sample characterization. In this work, the overall fabrication process for QCL and TI-QCL devices is presented along with the development efforts used to improve device performance including, among other efforts, ridge guide formation, lateral carrier isolation methods, and high-reflective facet coatings. These fabrication processes are used to create samples from two different epitaxial designs: the 3rd and 4th generation TI-QCL structures, both on InP substrates. The 3rd generation TI-QCL design targets an 8.3 μm emission whereas the 4th generation design targets 4.7 μm. Novel characterization results for the 3rd generation TI-QCL are demonstrated at 77 K, including negative differential collector current, self-oscillations in collector current, 1.58 μm short-wave infrared (SWIR) spontaneous emission, SWIIR lasing, and the first detected MWIR emission from a transistor-injected quantum cascade structure. Extended modeling capabilities are developed to better understand the quantum states in the active region, the carrier transport at the interface, and the performance of the optical mode. In addition, a depletion-approximation model is made for the TI-QCL to understand the field distribution at different bias and current conditions in the base-collector junction. These new insights are utilized to optimize the design of the 4th generation epitaxial material which includes a doped active region variant, an unintentionally-doped active region variant, and a standard QCL variant. Promising early electroluminescence and room-temperature electrical characterization results for this material are presented and analyzed using the depletion model. Future targets for optical characterization of the new material and potential future applications for a working TI-QCL device are discussed.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Electrical & Computer Engr

Grantor

University of Illinois Urbana-Champaign

Year dc:date

2025

Author dc:creator

• Kaufman, Robert Bruce

Contributors dc:contributor

• Dallesasse, John M
• Lee, Minjoo
• Bayram, Can
• Nahrstedt, Klara

• quantum cascade laser
• transistor laser
• midwave infrared

Statement dc:rights

• Copyright 2025 Robert Bruce Kaufman

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/129761

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F129761