Epitaxial Quantum Dot Scintillators with Monolithic Photodetector Integration: Physics, Fabrication and Characterization of Materials and Devices

Author

Allan Oreave Minns, University at Albany, State University of New YorkFollow

ORCID

0000-0003-2963-8027

Date of Award

Spring 2025

Language

English

Embargo Period

4-21-2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

College/School/Department

Department of Nanoscale Science and Engineering

Program

Nanoscale Sciences

First Advisor

Serge Oktyabrsky

Committee Members

Prof. Alain Diebold, Prof. Iulian Gherasoiu, Prof. Vincent LaBella, Dr. Pavel Murat

Keywords

Quantum dot, scintillator, optoelectronics, nanotechnology

Subject Categories

Electronic Devices and Semiconductor Manufacturing | Nanoscience and Nanotechnology | Nanotechnology Fabrication | Semiconductor and Optical Materials

Abstract

This dissertation discloses the physics, fabrication, and characterization of high-performance scintillator detectors based on epitaxial InAs quantum dots (QDs) in GaAs. The detector crystals grown include monolithically integrated In_0.35GaAs photodetectors with Al_0.92-0.6In_0.03-0.35Ga_0.05As metamorphic buffer layers (MBL). A device fabrication process was developed for the lithographic patterning, chemical etching, contact metallization and readout integration of materials grown by means of molecular beam epitaxy (MBE) on 3-inch GaAs (001) wafers. Low capacitance integration with readout electronics was achieved through wire bonds to custom printed circuit boards (PCBs) with commercial components.

The relationship between device geometry and response was explored through exposure to alpha particles from Americium-241, 510 nm laser scans and Monte Carlo (MC) simulations. The detector response was found to be described within a ray-optics framework which includes material characteristics and device dimensions. An accurate analytical device model was obtained through incorporation of solid and plane angle-based approaches to estimating light detection, absorption and escape.

To investigate the ability of the scintillation material to support picosecond scale timing resolution through high and fast light yield, the photodetector response to the scintillation emission was read out with low noise operational amplifier-based circuits. A simulation program with integrated circuit emphasis (SPICE) was used to evaluate readout circuit designs which were ultimately validated experimentally. The effects of modulation doping on scintillation photon yield corroborate previous measurements made with photoluminescence. Light yields exceeding 40,000 photons/MeV were observed at an overall efficiency of ~17%. Devices with ~1 GHz of bandwidth were used to achieve estimated timing resolutions as low as 30 ps. Linearity was studied via 5 calorimetry of air-attenuated alpha particles. The device model was validated and used in experimental design to minimize the contribution of internal collection efficiency gradients and discern a σ/μ upper limit of 2.6% for the intrinsic energy resolution of the scintillator.

License

This work is licensed under a Creative Commons Attribution 4.0 International License.

Recommended Citation

Minns, Allan Oreave, "Epitaxial Quantum Dot Scintillators with Monolithic Photodetector Integration: Physics, Fabrication and Characterization of Materials and Devices" (2025). Electronic Theses & Dissertations (2024 - present). 132.
https://scholarsarchive.library.albany.edu/etd/132