Optimization of MoRe contacts to InGaAs Quantum Wells

Abstract

This thesis presents the design, fabrication, and characterization of molybdenum–rhenium (MoRe) based MOSFET on InAlAs and InGaAs heterostructures, aiming to integrate superconducting contacts with III–V semiconductors for hybrid quantum compatible devices. The study addresses interfacial challenges that limit contact transparency and investigates different surface preparation and passivation techniques to improve MoRe semiconductor interfaces. Three pre treatments using hydrochloric acid HCl, ammonium sulfide NH4S2, and buffered oxide etchant (BOE) were systematically compared through fabrication and electrical characterization of test devices.
Comprehensive 2-probe and 4-probe measurements were performed to extract key device parameters including transconductance, threshold voltage, subthreshold swing, contact resistance, and carrier mobility. Among the tested processes, BOE treated samples exhibited the highest extracted electron mobility and lowest contact resistance, meanwhile during the processing, sulfur passivation might partially etch the MoRe layer. These results highlight the critical role of interface chemistry in maintaining contact integrity and device reproducibility.
Overall, the work establishes a fabrication route for MoRe/InGaAs hybrid MOSFETs and provides insight into the feasibility of incorporating superconducting contacts in III–V semiconductor platforms. The findings serve as a foundation for developing high mobility cryogenic transistors and future hybrid superconductor–semiconductor devices for quantum signal amplification and low noise applications. Future work like applying annealing and studying the superconducting current of the cryogenic devices could be investigated.

Popular Abstract

In the quest for faster and more energy-efficient electronics, scientists are exploring materials that combine semiconductors that can conduct electrons quickly and superconductors that can carry electric current without resistance. This research focuses on a special combination: a superconducting metal alloy made of MoRe joined with a semiconductor structure called an indium gallium arsenide InGaAs quantum well.
Quantum wells are ultra thin layers that trap electrons in a flat, two-dimensional sheet, allowing them to move freely with minimal scattering which is an essential feature for high speed transistors and quantum devices. When a superconductor like MoRe is connected to such a quantum well, it can induce “superconducting behavior” in the semiconductor through a phenomenon known as the proximity effect. This opens the door to building hybrid electronic components that could one day form the backbone of quantum computers.
However, making these two materials work together is not easy. The surfaces of semiconductors tend to oxidize, creating barriers that disrupt smooth electron flow. This thesis explores different chemical treatments to clean and prepare the surface before adding MoRe contacts. The results show that with the right surface preparation and careful control of fabrication steps, it’s possible to create cleaner interfaces and better electrical performance. This work brings us a step closer to integrating superconductors with high-mobility semiconductors, enabling more powerful and efficient quantum electronic technologies.

• author: Zhang, Chi
• supervisor: Louise Olausson
• organization: Department of Electrical and Information Technology
• course: EITM02 20251
• year: 2025
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: MOSFET Superconductivity Molybdenum–Rhenium
• report number: LU/LTH-EIT 2025-1105
• language: English
• id: 9216183
• date added to LUP: 2025-12-22 14:05:09
• date last changed: 2025-12-22 14:05:09