ORCID

https://orcid.org/0009-0003-5253-4266

Date of Award

Fall 2025

Language

English

Embargo Period

10-29-2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

College/School/Department

Department of Nanoscale Science and Engineering

Program

Nanoscale Engineering

First Advisor

Serge Oktyabrsky

Committee Members

Serge Oktyabrsky, Vincent LaBella, Alain Diebold, Mengbing Huang,Vladimir Mitin

Keywords

Asymmetrically Doped, Schrodinger Poisson Solver, Dual Band IR sensor, IR Sensor, Scintillator, Waveguide

Subject Categories

Engineering Physics | Nuclear Engineering | Quantum Physics | Semiconductor and Optical Materials

Abstract

This dissertation discloses the physics, fabrication, characterization, and analysis of two novel types of group III-V semiconductor detectors relying on quantum confinement of carriers, namely voltage-tunable quantum well infrared photodetectors (QWIP) and a high-yield ultrafast quantum dot scintillation detector (QDSD). Both QWIP and QDSD heterostructures presented here were grown on 3” GaAs (001) substrates using molecular beam epitaxy (MBE).

A major part of the dissertation focuses on development of the voltage-tunable QWIPs targeting detection in the mid-wave infrared region (MWIR) (3μm -5μm) and long-wave infrared region (LWIR) (8μm -12μm) with control of sensitivity by the applied bias. The QWIPs utilize the design consisting of asymmetrically doped double QWs, where the external electric field alters the electron population in the wells and hence the spectral responsivity of the device. The design rules are obtained by calculating the electronic transition energies for symmetric and antisymmetric double-QW states using a 1D Schrödinger–Poisson solver. The MBE-grown semiconductor heterostructure contains 25 periods of coupled double GaAs QWs and AlxGa1-xAs barriers. One of the QWs in the pair is modulation-doped to provide asymmetry in potential between the two QWs. Standard fabrication techniques, containing UV lithography, contact metallization, and wet chemical etching are followed to build mesa structures of 2 different sizes. The QWIPs are characterized with blackbody radiation to evaluate the responsivity, detectivity, and with FTIR down to 77 K to evaluate the detection wavelength and its control with applied external voltage. From the ratio of the responsivities of the two prominent detection bands, voltage tunability of the detectors were evaluated. Depending on the growth parameters (QW width, Barrier width, Al concentration) of the detector, a QWIP with voltage-tunable detection band between MWIR (~5 μm) and LWIR (~8 μm) with an order of magnitude sensitivity control is demonstrated.

Voltage tunable QWIPs with detection in LWIR (8 -11 μm) show a sensitivity control of 2x with applied bias of +/- 4V, which is further optimized to gain a sensitivity control of 10x. Due to the voltage tunable IR detection capability, these QWIPs become a promising candidate for various applications such as Military and defense, environmental monitoring and AI-based object recognition.

The last chapter of this dissertation discusses the development of a novel InAs/GaAs quantum dot (QD) scintillation detector exhibiting high light-yield and high energy resolution. High speed and efficiency of this semiconductor QD scintillator makes it a promising alternative for medical imaging, nuclear security and other high-energy physics applications. The MBE-grown epitaxial semiconductor heterostructure contains self-assembled InAs QDs serving as artificial luminescent centers, converting the kinetic energy of incoming charged particles into photons, which are then collected by a monolithically integrated InGaAs p-i-n photodiode through waveguiding. These novel devices often suffered from poor energy resolution and light yield, exhibiting high variance responses to monoenergetic sources which significantly reduces detectors accuracy and precision. To mitigate this issue, we developed a 26-micron-thick scintillator demonstrating a yield about 35 electrons/keV (~15% of the achievable maximum), with an energy resolution of 4.4% using 5.5MeV alpha particle. The intrinsic resolution of the scintillating material is evaluated to be 1.9%. The collection of charges from different regions of the scintillator is studied using the multimodal response observed from flood exposure to 4.4 MeV alpha particle. The detectors response to gamma photons is presented using Ba-133 source. A hybrid response due to ionizing track share between scintillator and photodetector (PD) is observed with maximum yield of 45 electrons/keV. Noise-limited time resolution of 59ps is demonstrated by this high-yield detector which can be further improved with cleaner fabrication and better readout electronics.

License

This work is licensed under the University at Albany Standard Author Agreement.

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