Date of Award

Spring 2026

Document Type

Open Access Dissertation

Department

Electrical Engineering

First Advisor

Krishna C. Mandal

Abstract

This work investigates the device engineering and defect characterization of next-generation wide-bandgap semiconductor radiation detectors, specifically focusing on cadmium zinc telluride selenide (CdZnTeSe or CZTS) single crystal, 4H-silicon carbide (4H-SiC) epitaxial layer, and metal-oxide-semiconductor (MOS) 4H-SiC architectures. The research addresses the critical need for high-performance detectors capable of operating in harsh environments (i.e, in high radiation background and at high temperature) and at room temperature with superior energy resolution and low noise.

In the study of CZTS gamma-ray detectors, single crystals were grown using the vertical Bridgman method (VBM) and the vertical gradient freeze (VGF) method. Material characterization using EDX, XPS, and XRD confirmed high crystallinity and radial homogeneity, while infrared (IR) imaging showed the presence of Te-inclusions. Electrical measurements revealed high bulk resistivity (∼1.6×1010 Ω-cm) and low leakage current. Radiation detection results showed that VGF-grown detectors exhibited superior electron transport properties, achieving a mobility-lifetime (μτ) product of 3×10−3 cm2/V and nearly 100% charge collection efficiency (CCE) for alpha particles. Defect investigation via photo-induced current transient spectroscopy (PICTS) revealed the performance improvement to a lower concentration of deep-level traps in VGF grown than to VBM-grown crystals.

The investigation of 4H-SiC detectors focused on optimizing Schottky barrier diodes (SBDs) using various high-work-function metals (Cr, Mo, Pd, Ni). While all fabricated SBDs demonstrated alpha-particle detection, Pd-based detectors achieved the best energy resolution (~ 0.5% FWHM at 5.486 MeV) in optimized as well as self-biased (0 V) condition. Capacitance-mode deep-level transient spectroscopy (DLTS) was employed to identify several electrically active defects, including the dominant carbon-vacancy-related Z1/2 centers and EH5 traps, highlighting the decisive role of bulk defect density in defining detectors’ energy resolution.

Furthermore, the research explored advanced MOS/4H-SiC architectures using high-k dielectrics such as Y2O3, Al2O3, and Ga2O3. These oxide layers effectively passivated the epilayer surface and suppressed leakage currents to the picoampere range at high bias. MOS structures demonstrated for the first time enhanced hole transport and achieved sub-0.5% FWHM energy resolution for 5.486 MeV alpha particles. These devices also exhibited robust self-biased (0 V) detection capabilities, making them highly suitable for low-power aerospace, deep space, and nuclear core reactor applications. Collectively, this work provides comprehensive insights into the materials, device engineering, and defect dynamics required to advance state-of-the-art wide-bandgap semiconductor radiation spectroscopy.

Rights

©2026, Ritwik Nag

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