Development of Solid State Radiation Detectors Comprised of Halide and Oxide Perovskites
Open Access
- Author:
- Reiss, Justin
- Graduate Program:
- Materials Science and Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- December 10, 2024
- Committee Members:
- John Mauro, Program Head/Chair
Suzanne Mohney, Major Field Member
Saptarshi Das, Outside Unit & Field Member
Joan Redwing, Major Field Member
Timothy Eden, Chair & Dissertation Advisor - Keywords:
- Radiation Detection
Single Crystal Growth
Ceramics Processing
Metal-Halide Perovskites - Abstract:
- Solid-state γ-ray detectors are used throughout the medical industry, space exploration, and nuclear security efforts. There is an urgent need, particularly for homeland security and threat reduction, to develop large area, high energy resolution solid-state detectors that operate at room temperature. High purity germanium (HPGe) offers the highest energy resolution of any commercially available detector; however, cryogenic cooling requirements make field deployment impractical. For decades, researchers have been investigating various semiconductors which can operate at room temperature to replace HPGe; of these, cadmium zinc telluride (CZT) has shown the most commercial progress. Wide spread implementation of CZT detectors has been limited, as defects formed during the single crystal growth process make yields low, driving up detector costs and limit detector size. In recent years, metal-halide perovskites (MHPs) have shown significant promise for use as a room temperature solid state detector, with recent reports of performance rivaling that of CZT. Several challenges still remain for improving perovskite based detectors prior to field deployment, including reducing ion drift to stabilize charge transport, improving manufacturability and detector size, and identifying environmentally stable compositions. This work focused on addressing these challenges through various material fabrication processes, surface and contact engineering, development of polycrystalline based devices, and identification and fabrication of novel oxide semiconductor detectors. All of these materials and devices were characterized for their structure and material properties using a variety of analytical materials characterization techniques, followed by performance evaluation via X-ray sensitivity, α-particle pulses, and γ-ray spectroscopy. Single crystal CsPbBr3 and FAPbBr3 were both grown from solution based processes, with additional CsPbBr3 crystals sourced from the melt-based Bridgman technique. Each of these growth methods were analyzed for crystallographic defects, highlighting secondary domain formation from both seed boundaries and twinning. Rectifying junctions were engineered based upon TiN contacts deposited onto CsPbBr3, which demonstrated the desired dark current behavior with 100 nA/cm2 at -500 V/cm field strength. Various polishing methods were developed for both FAPbBr3 and CsPbBr3, both of which obtained <10 nm surface roughness. Passivation was identified as a critical factor to limit ion drift along the crystal surface. Depositing a thin layer (1-10 nm) of SiO2 via plasma enhanced atomic layer deposition (PE-ALD) significantly lowered current instability over time compared to other passivation techniques. Increasing SiO2 layer thickness to 10 nm on CsPbBr3 further increased current stability, with devices able to withstand -1000V without breakdown. These results highlight the importance of surface and bulk ion drift in MHPs, which can be mitigated through passivation and optimized crystal growth, respectively. While single crystal MHPs comprise the highest performing devices in literature, challenges remain with regards to their manufacturability, particularly at larger areas. As such, this work investigated bulk polycrystalline MHPs in an effort to increase manufacturability while maintaining reasonable device performance. The underlying hypothesis of these devices is that photo-generated electrons and holes will recombine at grain boundaries and other large defects; therefore, the microstructure of the polycrystalline device should be tailored to increase grain size and reduce porosity, thus decreasing overall defect density in the sintered compact. Investigations began with sintering studies on FAPbBr3 utilizing conventional sintering techniques. It was found that while grain growth and densification could be manipulated, further improvements were limited due to a lack of thermal energy. Devices fabricated from FAPbBr3 polycrystalline compacts demonstrated X-ray sensitivities of 169 µC / Gy cm2, which is 6-9x higher than commercially available solid-state X-ray detectors. Investigations pivoted to focus on consolidating CsPbBr3 via field assisted sintering technology (FAST). FAST applied to MHPs offers several benefits for densifying and inducing grain growth without applying excess thermal energy. Modifications of the FAST process to increase current flow through CsPbBr3 during processing resulted in substantial increases in density and grain size. Detectors fabricated from FAST manufactured CsPbBr3 showed promising α-particle pulses, with sharp spectra extracted from devices biased at -100V. γ-ray spectra was successfully obtained from FAST CsPbBr3, with energy resolutions of 4% at 662 keV, representing the first demonstration of spectroscopic γ-ray detection from a polycrystalline MHP. New oxide semiconductors were then investigated in an effort to improve the environmental stability compared to MHPs. A computational framework was utilized to down select materials based upon crystal structure, density, and band gap yielding KTaO3 and NaTaO3 as potential materials of interest. FAST was again applied to sinter KTaO3, which suffered phase instability challenges associated with volatile K+. Excess K2CO3 precursor was added to the powder feedstock, which effective reduced phase stability challenges, and acted as a sintering aid for improving density and microstructure. Devices fabricated from KTaO3 successfully detect α-particles, though resolution remains low mostly due to electrical instabilities. NaTaO3 was densified utilizing pressureless sintering followed by hot isostatic pressing. These ceramics proved to be dense (>99%) with grain sizes of 18.22 ± 1.95 µm. Devices fabricated from NaTaO3 were extremely stable under high biases, with no breakdown observed at 60 kV/cm field strengths. α-particle pulses from NaTaO3 devices had the highest pulse amplitudes of any material measured to date, with the amplitude varying as a function of bias, indicating that the carrier velocity and/or depletion width can be increased. Distinct γ-ray spectra under a 133Ba source was obtained, representing the first demonstration of γ-ray spectroscopy from a sintered oxide utilizing solid-state detection mechanisms.