Halide ion transport-resistant barrier layers for enhanced stability in halide-containing semiconductor radiation detectors

Abstract

Radiation detectors and methods of detecting incident radiation using the radiation detectors are provided. The radiation detectors are based on halide-containing semiconductor photoactive layers. In the radiation detectors, a halide ion transport-resistant barrier layer is disposed between the halide-containing semiconductor and a metal electrode to suppress the migration of halide ions from the halide-containing semiconductor into a neighboring metal electrode.

Description

Atty. Dkt. No. 00100-0398-PCTHALIDE ION TRANSPORT-RESISTANT BARRIER LAYERS FOR ENHANCED STABILITY IN HALIDE-CONTAINING SEMICONDUCTOR RADIATION DETECTORS CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority to U.S. provisional patent application number 63 / 680,992 that was filed August 8, 2024, the entire contents of which are incorporated herein by reference.REFERENCE TO GOVERNMENT RIGHTS

[0002] This invention was made with government support under HDTRA- 12-02-0002 awarded by the Defense Threat Reduction Agency. The government has certain rights in the invention.BACKGROUND

[0003] Cesium lead bromide (CsPbBn) is a promising metal halide perovskite semiconductor for practical applications such as photodetectors, radiation imaging, gammaray detection, and X-ray detection. CsPbBn has several advantages over other semiconductors that are used in these applications, including ease of purification, ease of crystal growth, high defect tolerance, high yield efficiency, and ease of handling.

[0004] Even though new records in the performance of CsPbBn-based devices are consistently set, instability is a big obstacle to the commercialization of crystalline halide perovskite devices. This is due to the reactivity of these halide compounds with metal electrodes. Halide ions migrate to the anode of the device under biased conditions where they interact with most metals, creating a detrimental metal halide interlayer. They also create defects in the bulk crystal, gradually deteriorating the device's performance.SUMMARY

[0005] Radiation detectors and methods of detecting incident radiation using the radiation detectors are provided. The radiation detectors use areduction / oxidation (redox)-resistant barrier layer between a halide-containing semiconductor active layer and a metal electrode toAtty. Dkt. No. 00100-0398-PCTsuppress reactivity-related challenges of the halide-containing semiconductor compounds without compromising the performance of detectors.

[0006] Radiation detectors, methods of detecting incident radiation using the radiation detectors, and methods of making the radiation detectors are provided.

[0007] One example of a radiation detector includes: a metal electrode; a continuous halide ion transport-resistant barrier layer comprising or consisting of a non-particulate, amorphous, inorganic, non-metallic. halide ion transport-resistant material on and in direct contact with the metal electrode; a photoactive layer comprising or consisting of a crystalline halide-containing semiconductor on and in direct contact with the continuous halide ion transport-resistant barrier layer, opposite the metal electrode, wherein metal electrode and the photoactive layer are characterized in that a Schottky barrier forms between the metal electrode and the crystalline halide-containing semiconductor under a bias; a second electrode in electrical communication with the photoactive layer, wherein the metal electrode and the second electrode are configured to apply an electric field across the photoactive layer; and a signal detector configured to measure a photocurrent generated in the crystalline halide-containing semiconductor photoactive layer when the crystalline halide-containing semiconductor photoactive layer is exposed to incident radiation.

[0008] One example of a method for detecting incident radiation, such as gamma radiation or X-rays, using a radiation detector of a type disclosed herein includes the steps of: exposing the crystalline halide-containing semiconductor to incident radiation, wherein the crystalline halide-containing semiconductor absorbs the incident gamma radiation and generates a photocurrent; and detecting the photocurrent with the signal detector.

[0009] One example of a method of making a radiation detector of a type disclosed herein includes the steps of: depositing a continuous layer of the non-particulate, amorphous, inorganic, non-metallic, halide ion transport-resistant barrier material on a surface of the crystalline halide-containing semiconductor; depositing the metal electrode on the continuous layer of the non-particulate, amorphous, inorganic, non-metallic, halide ion transport-resistant barrier material; and disposing the second electrode in electrical communications with the crystalline halide-containing semiconductor.

[0010] Other principal features and advantages of the invention will become apparent to those skilled in the art upon review of the following drawings, the detailed description, and the appended claims.Atty. Dkt. No. 00100-0398-PCTBRIEF DESCRIPTION OF THE DRAWINGS

[0011] Illustrative embodiments of the invention will hereafter be described with reference to the accompanying drawings, wherein like numerals denote like elements.

[0012] FIG. 1 A: Schematic diagram of a radiation detector having a halide ion transportresistant barrier layer between a metal anode and a photoactive metal halide semiconductor. FIG. IB: Schematic diagram of a radiation detector having a first halide ion transportresistant barrier layer between a metal anode and a photoactive metal halide semiconductor and a second halide ion transport-resistant barrier layer between a metal anode and the photoactive metal halide semiconductor.

[0013] FIGS. 2A-2D: (FIG. 2A) Dark current of Device 1 of the Example as a function of voltage, (FIG. 2B) channel number, (FIG. 2C) energy resolution, and (FIG. 2D) photopeak counting rate as a function of time.

[0014] FIGS. 3A-3D: (FIG. 3A) Pulse height spectrum of241Am source measured by Device 2 of the Example using an analog device acquisition (DAQ) system, (FIG. 3B) channel number, (FIG. 3C) energy resolution, and (FIG. 3D) photopeak counting rate as a function of time.

[0015] FIGS. 4A-4D: (FIG. 4A) Pulse height spectrum of241Am source measured by Device 2A of the Example using a digital DAQ system. (FIG. 4B) channel number, (FIG. 4C) energy resolution, and (FIG. 4D) photopeak counting rate as a function of time.

[0016] FIG. 5 A. The spectra of241Am for Device 2B of the Example. (FIG. 5B) Channel number, (FIG. 5C) energy resolution, and (FIG. 5D) number of counts at photo peaks at functions of time for the device.

[0017] FIG. 6A. The spectra of241Am for Device 2C of the Example. (FIG. 6B) Gamma spectrum of combined data, (FIG. 6C) channel number and energy resolution, and (FIG. 6D) counting rate and energy resolution as functions of time.

[0018] FIGS. 7A-7B: Stability test results (Channel number, ER and Count Rate vs run time) for Device 3 of the Example (FIG. 7A). The device was tested under continuous mode testing using a241Am excitation source. Applied conditions were high voltage 300 V and shaping time 3 ps. Long term stability test results for Device 3 (FIG. 7B). The gain was x80.Atty. Dkt. No. 00100-0398-PCTMeasurement conditions for the device were as follows: high voltage = 300 V, shaping = 3 ps, collection time = 600 s.

[0019] FIGS. 8A-8B: Stability test results (Channel number, ER and Count Rate vs run time) for Device 4 of the Example (FIG. 8A). The device was tested under continuous mode testing using a241Am excitation source. Applied conditions were up to Day 31 and 400 V from Day 31 to Day 36 and shaping time was 3 ps. Long term stability test results for Device 4 (FIG. 8B). The gain was x80. Measurement conditions for the device were as follows: high voltage = 300 V, shaping = 3 ps, collection time = 600 s.

[0020] FIG. 9A. The spectra of241Am for Device 5 of the Example. (FIG. 9B) Gamma spectrum of combined data, (FIG. 9C) channel number and energy resolution, and (FIG. 9D) counting rate and energy resolution as functions of time.DETAILED DESCRIPTION

[0021] Radiation detectors and methods of detecting incident radiation using the radiation detectors are provided. The radiation detectors, which use metal halide perovskite semiconductors, such as cesium lead bromide (CsPbBn), or other metal halide semiconductors, as a photoactive material, have improved stability and performance due to reduced halide diffusion from the photoactive material to the electrodes.

[0022] In the radiation detectors, a halide ion transport-resistant barrier layer is disposed between the metal halide semiconductor and a metal electrode. The halide ion transportresistant barrier layer suppresses the migration of halide ions from the perovskite into the metal anode, which is a primary cause of device performance degradation due to the reaction of the halide ions with the metal. This degradation is caused by the formation of metal halide interlayers at the metal halide semiconductor / electrode interface and vacancies in the metal halide semiconductor, which diminishes detector performance over time.

[0023] By preventing direct contact between the metal electrode and the metal halide semiconductor, the barrier layer significantly reduces the dark current and noise levels of the detector, enhancing the detector's sensitivity and operational longevity without compromising on the detector’s ability to accurately measure incident radiation. As a result, the radiation detectors are well suited for use in the detection of radiation, including gamma radiation and X-rays.Atty. Dkt. No. 00100-0398-PCT

[0024] The halide ion transport-resistant barrier layers can be used to improve the performance of a wide range of radiation detectors that would otherw ise be prone to instability due to the high mobility of halide ions in their photoactive material. Radiation detectors incorporating the halide ion transport-resistant barrier layers are useful in a range of applications, including radiation imaging (e.g., single-photon emission computed tomography (SPECT) in medical imaging), solar energy harvesting, photon-counting, and high-flux synchrotron experiments.

[0025] One example of a radiation detector is shown schematically in FIG. 1A. In this radiation detector, a metal with a relatively low work function (o) is utilized as an anode, while a metal with a relatively high work function serves as the cathode. A halide ion transport-resistant barrier layer in direct contact with the metal anode and the metal halide semiconductor separates those two layers. The halide ion transport-resistant barrier layer can be deposited directly on the metal halide semiconductor (e.g., a CsPbBn crystal), followed by the deposition of the metal anode directly on the halide ion transport-resistant barrier layer. Suitable deposition techniques for halide ion transport-resistant materials and metals include, but are not limited to, sputtering, including magnetron sputtering and plasma sputtering, thermal evaporation, atomic layer deposition, electron beam evaporation, and solution processing.

[0026] The second electrode (the cathode in the device of FIG. 1A) can be in direct contact with the halide-containing semiconductor layer or may be separated from the halide-containing semiconductor layer through one or more functional layers through which carriers (e.g., electrons and / or holes) can pass. In either case, the second electrode is considered to be “in electrical communication with” the halide-containing semiconductor layer. For example, a hole transport layer and / or a hole injection layer can be disposed betw een a cathode and the halide-containing semiconductor. Poly[bis(4-phenyl)(2.5.6-trimethylphenyl)amine (PTAA) is one non-limiting example of a hole transport material. A coating of a passivating material, such as an Inconel 625 alloy can be applied over the air-exposed surfaces to prevent air oxidation, further enhancing the operational stability of the radiation detector.

[0027] A signal detector is configured to measure a signal generated by electron-hole pairs that are formed when the halide-containing semiconductor is exposed to incident radiation, such as gamma rays or X-rays. When the radiation detector is biased, a large Schottky barrier for both holes and electrons forms between the metal anode and the halide-Atty. Dkt. No. 00100-0398-PCTcontaining semiconductor. While the electrodes are configured in a planar orientation in FIG.1 A, the radiation detectors are not limited to planar-type detectors.

[0028] The radiation detectors detect incident radiation by exposing the halide-containing semiconductor to said incident radiation, wherein the halide-containing semiconductor absorbs the incident radiation, thereby generating electron-hole pairs. A signal detector can then be used to measure at least one of the energy or intensity of the absorbed incident radiation by detecting the generated electrons and / or holes. During the operation of the radiation detector of FIG. 1A, an electrical voltage is applied to the cathode, which collects the signal, and the anode is grounded. Alternatively, the electrical voltage may be applied to the anode, which collects the signal, and the cathode is grounded. The radiation detectors include Schottky diode detectors designed to operate under a high reverse bias voltage with enhanced stability and low dark current and enhanced signal clarity7, facilitated by the halide ion transport-resistant barrier layer that reduces degradation from halide ion migration. These advantages can be achieved even during long-term measurements (e.g.. measurements having durations of more than one day, more than one week, or more than one month under continuous non-stop operation).

[0029] In some embodiments of the radiation detectors, a Schottky barrier is formed between the halide-containing semiconductor and both the metal anode and a metal cathode. As shown in FIG. IB, in these embodiments, a halide ion transport-resistant barrier layer can be included between each electrode and the halide-containing semiconductor. The first and second halide ion transport-resistant layers can be composed of the same halide ion transportresistant material or different halide ion transport-resistant materials.

[0030] Halide-Containing Semiconductors:

[0031] The halide-containing semiconductors are single-crystal photoactive semiconductors that absorb incident radiation, such as incident gamma radiation, and generate a photocurrent. The halide-containing semiconductors are semiconducting compounds that comprise at least one halide element. Metal halides and chalcohalides are examples of semiconductors that include halides. Examples of metal halide semiconductors include metal halide perovskites. The metal halide perovskites may be all-inorganic perovskites or organic-inorganic hybrid perovskites. For example, the metal halide semiconductor can be a metal halide perovskite having the formula AMX3, where A is an alkali metal cation (Group I cation) or an organic ion, such as a monovalent alkylammoniumAtty. Dkt. No. 00100-0398-PCTcation (for example, methylammonium, formamidinium, or a combination thereof), X is a halide ion, and M is an octahedrally coordinated bivalent metal atom. Examples of allinorganic perovskites include compounds such as CsPbBn, CsPbCh, RbPbBrs. and RbPbCh. Examples of hybrid organic-inorganic perovskites include compounds such as APbBn and APbh, wherein A is methylammonium and / or formamidinium.

[0032] Other suitable metal halide perovskites have the formula amAMXs. where am is an alkyl diamine cation, an aromatic diamine cation, an aromatic azole cation, or a cyclic alkyl diamine cation; A is a monovalent alkylammonium cation or an alkali metal cation (Group I cation); X is a halide ion; and M is an octahedrally coordinated bivalent metal atom. Am can also represent a hydrazinediium cation.

[0033] Other suitable metal halide semiconductors have the formula AB2X5, where A represents T1 or In. B represents Sn or Pb. and X represents Br or I. The formula AB2X5 covers solid solutions that include both A elements, both B elements, and / or both X elements, as well as the end members of the formula.

[0034] Still other metal halide semiconductors have the formula Hg3Q2X2, where Q represents a chalcogen atom or a combination of chalcogen atoms (e.g., a combination of S, Se, and Te), and X is a halide ion or a combination of halide ions. Still other metal halide semiconductors include chalcohalides. For example, chalcogenides having the chemical formula AeBX4, wherein A is a metal, B is sulfur or selenium, and X is a halide ion. Still other metal halide semiconductors include copper halide chalcogenides, such as Cu2hSe6 and its solid solutions, which include other halogens and / or other chalcogens.

[0035] A description of photoactive metal halide semiconductor crystals and methods of making them can be found in U.S. Patent No. 8.519,347 and PCT patent application publication number No. WO2017030624.

[0036] Electrodes:

[0037] In the radiation detectors, it is advantageous to form Schottky barrier contacts rather than Ohmic contacts between the electrodes and halide-containing semiconductor because Schottky barrier contacts significantly improve charge collection efficiency by reducing dark current and enabling higher operating bias, leading to enhanced energy resolution and detection efficiency. Some embodiments of the detectors are asymmetric Schottky radiation detectors in which the two electrodes are made from two different metalsAtty. Dkt. No. 00100-0398-PCTand form Schotky junctions with different barrier heights with the halide-containing semiconductor. In an asymmetric Schotky radiation detector, one electrode (e.g., the anode) has a low work function and the other electrode (e.g., the cathode) has a high work function.

[0038] Metal Anodes:

[0039] In a Schottky7radiation detector, the work function of the metal anode is lower than that of the halide-containing semiconductor and the work function difference between the metal anode and the photoactive halide-containing semiconductor is large and results in the formation of a Schotky barrier to minimize dark current and noise under operational conditions. Examples of metals having a lower work function than many halide-containing semiconductors, including many metal halide perovskites, such as CsPbBn, include bismuth (Bi), indium (In), tin (Sn), lead (Pb). antimony (Sb), gallium (Ga), chromium (Cr), titanium (Ti), aluminum (Al), and alloys thereof, including indium-gallium alloys.

[0040] Cathodes:

[0041] The work function of the cathode material in a Schotky radiation detector is higher than that of the halide-containing semiconductor. Examples of metals having a higher work function than many metal halide semiconductors, including many metal halide perovskites, such as CsPbBn, include gold (Au), platinum (Pt), nickel (Ni), osmium (Os), and palladium (Pd). Indium tin oxide (ITO) is an example of a high work function electrically conductive oxide.

[0042] Halide Ion Transport-Resistant Barrier Layers:

[0043] The halide ion transport-resistant barrier layer, which is positioned to prevent direct contact between the halide-containing semiconductor and its neighboring anode and / or in some cases its neighboring cathode, prevents or reduces the extent of halide ion diffusion from the metal halide-containing semiconductor of the active layer to a metal electrode, without significantly impeding electronic transport. The halide ion transport-resistant layer is desirably also chemically inert to reduction and oxidation processes in the radiation detector. Thus, the halide ion transport-resistant layer may also be redox-resistant. The halide ion transport-resistant barrier layer is continuous, non-particulate, inorganic film with a uniform composition that is non-porous on the scale of halide ions, such that it acts as a barrier to halide ion diffusion. This layer prevents or hinders halide ions from the halide-containing semiconductor from migrating to and reacting with the metal electrode. As such, the halideAtty. Dkt. No. 00100-0398-PCTion transport-resistant barrier layers maintain the integrity of the Schottky junction formed between the metal electrode (e.g., anode) and the halide-containing semiconductor, without interfering with the operation of the detector.

[0044] The halide ion transport-resistant barrier material is an inorganic material, meaning that it is not composed of organic molecules, such as organic polymers.Additionally, the inorganic material is not a metal or metal alloy. Thus, the halide ion transport-resistant barrier layer is distinguishable from the metal electrodes.

[0045] The halide ion transport-resistant barrier layer is desirably an amorphous layer. Examples of suitable materials for a halide ion transport-resistant barrier layer include the following materials, including the amorphous forms thereof: carbon, transition metal carbides, such as titanium carbide (TiC), inorganic oxides, such as metal oxides (e.g., titanium dioxide, tin oxide, and aluminum oxide) and non-metal or metalloid oxides (e.g., silicon oxides), boron, boron nitride, and refractory metal compounds (e g., tungsten (W) compounds, rhenium (Re) compounds, tantalum (Ta) compounds, molybdenum (Mo) compounds, and niobium (Nb) compounds). Refractory metal compounds include refractory metal carbides, refractory metal silicides, refractory metal nitrides, and combinations of two or more of these materials.

[0046] Amorphous carbon includes "graphite-like” carbon having mainly sp2bonding but lacking long-range order. Amorphous forms of carbon may also comprise oxygen and hydrogen atoms. Examples of graphite-like carbon include hydrogenated amorphous carbon, glassy carbon, and amorphous pyrolytic carbon. However, particulate films - that is, films comprising or consisting of discrete particles, including nanoparticles or microparticles - are not effective at preventing of hindering halide ion diffusion due to their inherent porosity. Therefore, films of carbon nanoparticles, such as fullerene (C60), carbon nanotubes, and the like are not suitable materials for a halide ion transport-resistant barrier layer.

[0047] Optimal thickness of the halide ion transport-resistant barrier layers will depend on the performance requirements of the radiation detector and the particular barrier layer being used. The maximum thickness of a halide ion transport-resistant barrier layer is primarily determined by whether charge transport can still occur across the layer. If the barrier layer is too thick, it not only blocks halide ion migration, which is desirable, but also begins to impede or completely block electronic conduction. In such a case, even if theAtty. Dkt. No. 00100-0398-PCTbarrier prevents degradation, the device will not operate because charge carriers cannot reach the contact.

[0048] Therefore, the optimal thickness of the halide ion transport-resistant barrier layer will depend on the electronic properties of the halide ion transport-resistant barrier material. Conductive or semi conductive barriers can tolerate greater thicknesses, including up to -100 nm, without disrupting device function. In contrast, more insulating materials may have a much lower maximum usable thickness, often below 20-30 nm, before electronic transport is compromised. The tradeoff between degradation resistance and impeding charge transport can be evaluated for each barrier, and an optimal thickness can be identified based on factors such as conductivity, band alignment, and interaction with the electrode and the semiconductor.

[0049] By way of illustration only, halide ion transport-resistant barrier layers having a layer thickness of at least 10 nm, at least 15 nm, at least 20 nm, at least 30 nm, or at least 50 nm can be used. This includes, for example, embodiments of the radiation detectors in which the halide ion transport-resistant barrier layer has a thickness in the range from 10 nm to 100 nm, and further includes embodiments of the radiation detectors in which the halide ion transport-resistant barrier layer has a thickness in the range from 20 nm to 50 nm.EXAMPLES

[0050] Low dark current, asymmetric Schottky diode radiation detector devices have been fabricated and operated under reverse biasing. High work function materials, such as Au, Pt, C, and ITO, were used as cathodes to form a Schottky barrier between these cathodes and a CsPbB crystal. On the other side, lower work function materials, such as Bi, Ga-In alloys, Ti, Cr, In. Sb. Sn. and Pb, were deposited on the CsPbBn crystals as anodes. The performance and stability of these devices were studied by measuring the gamma spectrum of241Am sources. Although these electrodes worked well, allowing the detector to produce a good gamma spectrum, the devices quickly became noisy, and the anode electrodes reacted starting from their edges. It was found that chemical reactions between the metallic electrodes and the CsPbBn semiconductor material under high bias voltage occurred, degrading the lifetime of the detectors within a short time.

[0051] To address the negative impacts of reactions between halide-containmg semiconductors and metal anodes, halide ion transport-resistant barrier layers were insertedAtty. Dkt. No. 00100-0398-PCTbetween the metal anodes of CsPbBr -based Schottky diode radiation detectors, and their effect on detector stability was tested.

[0052] Two devices (Device 1 and Device 2A) were fabricated with thin layers of amorphous carbon as halide ion transport-resistant barrier layers between CsPbBrs cry stals (the photoactive layers of the detectors) and bismuth or lead anodes. One device was fabricated with a thin layer of TiC as a halide ion transport-resistant barrier layer between a CsPbBrs crystal and a bismuth anode (Device 4). A comparative device (Device 3) having the same construction as Device 4, but without the thin layer of TiC between the CsPbBrs crystal and the bismuth anode, was also fabricated. The fabrication and testing of the radiation detectors are described below.

[0053] Detector fabrication:

[0054] Device 1: CsPbBrs ingots were cut into desired thicknesses, polished mechanically with fine polishing 12000 grit sandpaper, and washed with toluene to prepare the surface for metal deposition. The nominal size of the CsPbBrs crystal was 6.4x6xl.4 mm3. After this, a carbon layer (thickness > 10 nm) was deposited by using a MA0600 DC sputter. The power applied for sputtering was 18 W, and sputtering time was 300 s. On top of the carbon layer, a bismuth (Bi) (thickness ~ 350 nm) anode was deposited by using MNT sputter under vacuum with a pressure of 9E-2 torr and current of 2 mA. Opposite the Bi anode, a platinum (Pt) (thickness ~ 150 nm) cathode was deposited by using a MA0600 sputter using the power of 10 W, and sputtering was done for 15 min on 3 cycles in the interval of 300 s each. The electrode was connected to the collection circuit using copper wire, and a low-melting alloy made the contact. The detector was not protected from the outer environment, but the detector was held on the glass slide using paraffin wax on the edges. The device had the configuration of Bi / C / CsPbBrs / Pt.

[0055] Device 2A: A second device was fabricated with Au and Pb as cathode and anode, respectively. The dimensions of the CsPbBrs cry stal were 5.2x6.3x1.8 mm3. An approximately 10 nm-thick layer of amorphous carbon was deposited on the surface of the CsPbBrs crystal, followed by the deposition of a Pb anode (>100 nm thick) on the carbon. To avoid Pb air-oxidation of the side exposed to the environment, approximately 20 nm of Inconel 625 alloy was sputtered on the Pb to protect it. Thus, the fabricated device had the configuration of: Inconel / Pb / C / CsPbBrs / Au. The electrodes were deposited on the CsPbBrsAtty. Dkt. No. 00100-0398-PCTcrystal under vacuum of less than 5 mTorr using the MA0600 DC sputter. The parameters for sputtering the Au, Pb, C, and Inconel 625 alloy are listed in Table 1.

[0056] Table 1. The set parameters on the MA0600 sputterSputterTime Number of Expected thickness Target power(s) cycles (nm)(Watt)C 15 300 1 10Pb 10 150 10 250Inconel 625 15 300 2 30Au 10 300 2 150

[0057] Device 2B (Comparative):

[0058] A detector with an Au / CsPbBn / Pb configuration was fabricated for comparison with Device 2A. Au and Pb were deposited directly on the polished CsPbBn crystal using the same methods and conditions as those used for Device 2A.

[0059] Device 2C (Comparative):

[0060] Another detector with an Au / CsPbBrs / In configuration was fabricated for comparison with Device 2A. Au was deposited directly on the polished CsPbBrs crystal using the same methods and conditions as those used for Device 2A. In was deposited directly on the polished CsPbBn crystal, opposite the Au, to a thickness of 300 nm via thermal evaporation.

[0061] Device 3 (Comparative) and Device 4:

[0062] Device 3 - A detector with a Bi / CsPbBn / Pt configuration was fabricated by depositing 350-nm bismuth and 150-nm platinum layers onto a 2-mm-thick device.

[0063] Device 4 - To increase the longevity of Device 3, it was refabricated using a passivation layer of titanium carbide (TiC) in between the Bi and the CsPbBn, resulting in a Bi / TiC / CsPbBn / Pt configuration. The TiC layer exhibited a uniform and continuous film over the CsPbBn surface.

[0064] Device 5:

[0065] Device 5 was fabricated with a configuration of Au / TiCh / CsPbBn / TiCh / Bi, where the TiCh functioned as halide ion transport-resistant barrier layers between both metal electrodes and the CsPbBn crystal. 10 nm T1O2 layers of TiCh were deposited on the crystalAtty. Dkt. No. 00100-0398-PCTusing atomic layer deposition (ALD), followed by the deposition of a 150 nm-thick Au electrode using DC sputtering, and a 250 nm-thick Bi electrode using thermal evaporation.

[0066] Crystal growth and sample preparation

[0067] CsPbBn crystals were grown in a silica tube (vacuum-sealed under -10‘4torr) using a four-zone Bridgeman technique. A temperature gradient of 17° C / cm was maintained in a growth region, and crystals were grown at the rate of 1 mm / h. This controlled environment facilitated the controlled crystallization of the CsPbBn material and allowed for the formation of high-quality crystals. All the purification steps for binary compounds (CsBr and PbBn) and detailed growth steps are described in Chung, D.Y. et al., Cryst. Growth. Des.2024, 25: 9590.

[0068] Following crystal grow th, the ingot was sliced into small samples using a diamond wire saw (Diamond WireTec), employing a 0.25 mm thick stainless-steel wire coated with diamonds. Subsequently, the cut samples were polished by using P4000. P8000. and P 12000 grade sandpaper with WD-40 oil as a lubricant. Then, the polished samples were cleaned with toluene to remove the excess oil from the surface (-10 min) and dried in air. Prior to the metal deposition, the sample w as treated with (Jelight Model 30, UVO cleaner ) ozone to remove the oxygen layer from the surface.

[0069] Metal deposition

[0070] The deposition conditions and instruments w ere different for different electrodes. Bismuth (Bi) was deposited at the rate of 1.2-1.4 kA / s by using an LC Technology thermal evaporator. Platinum (Pt) was deposited by using a Leica EM ACE600 sputter at the rate of 10 A / s.

[0071] TiC deposition (Device 4)

[0072] A thin layer of titanium carbide (~40-nm-thick) was deposited using electron beam evaporation. The deposition rate was 0.02-0.05 nm / s. High power and a long period of time w ere used for the deposition (120 mA current, -90 min). A 300 nm layer of bismuth w as deposited on top of the titanium carbide, and 150 nm of platinum was deposited on the other side. The detector’s width was 2 mm.

[0073] Detector fabricationAtty. Dkt. No. 00100-0398-PCT

[0074] The electrodes were connected to the collection circuit by using copper wire (200 micron thick), and contact was carried out by a commercial silver paint from Ted Pella. Copper strips were used to fix wires on glass slides. The thickness of the metal electrodes was not experimentally determined aside from what was indicated by the crystal thickness monitor employed by the deposition equipment. To minimize the dark current, the electrodes were fabricated in a guard ring structure in which the center cathode electrode was surrounded by a guard ring cathode electrode, while the opposite side anode electrode covered the whole area of the crystal surface. During normal operation, the center and guard electrodes were kept at the same potential, and the signal was collected from the central electrode. After testing each time, all the devices were stored inside the drawer in the dark environment.

[0075] Electrical properties and detector performance measurements:

[0076] Devices 1 and 2A-2C:

[0077] The I-V characteristic curves for the radiation detectors were measured under dark conditions using a Keithley 6571B electrometer. To check the detector performance, a 1 pCi241Am source was used. The energy resolution of a characteristic peak was calculated using the following formula: FWHM / (peak channel number) x 100%. During the measurement, the devices were placed in a sample assembly box and connected to a 5093-R2 preamplifier (eV Products Inc.). A positive bias voltage was applied to the Bi or Pb electrode. The signal from the preamplifier was amplified by an ORTEC572A amplifier (Amptek Inc.) with a gain of x80 and different shaping times ranging from 1 to 10 ps. The pulse height was digitized by a dual 16000 input multichannel analyzer (Model ASPEC-927), and the spectral data were recorded using MAESTRO-32 software every 10 minutes.

[0078] Due to limited analog channels for the stability study, the second half of the data for the second device were recorded using a PX5 digital pulse processor from Amptek Ltd, which can digitize preamp signals directly.

[0079] A Python code was written to analyze the data, and the channel number, energy resolution, and the photopeak’s counting rate were monitored as a function of time. The channel number (representing the energy’ of the X-ray and gamma-ray detected) and energy resolution were two essential parameters indicating the stability of the fabricated devices. A decline in the counting rate typically occurred as the anode gradually corroded through itsAtty. Dkt. No. 00100-0398-PCTreaction with the crystal semiconductor. Hence, the fluctuation in the counting rate served as an additional reliable quantitative measure of the devices' long-term stability.

[0080] Devices 3 and 4:

[0081] The electrical properties (TV) were measured with a Keithley 6517B under dark conditions.

[0082] An241Am (59.5 keV) y-ray source was used. The formula to determine the energy resolution of a characteristic peak was FWHM / (peak channel number) x 100%. No adjustments were made to the experimental data during the energy resolution calculation. During the gamma measurement, the device was placed in a sample assembly box and connected to a 5093-R2 preamplifier (eV Products Inc ). A positive bias voltage was applied for data collection. The signal from the preamplifier was amplified by an ORTEC572A amplifier (Amptek Inc.) with a gain ofz80 and different shaping times ranging from 1 to 10 ps. The electronic signals were analyzed by a dual 16000 input multichannel analyzer (Model ASPEC-927), and the spectral data was recorded using MAESTRO-32 software.

[0083] Scanning Electron Microscopy (SEM) and Energy-Dispersive X-Ray Spectroscopy (EDS) measurements

[0084] The morphology of the electrodes and underlying surface for the freshly deposited electrode and the electrode after device failure was examined with scanning electron microscopy (JEOL JSM-7900FLV). The elemental composition of the deposited electrode after device failure was also studied with an Aztec system connected with the same SEM device. The voltage applied for this measurement was lOkV and in the regular vacuum mode.

[0085] Results:

[0086] Devices 1 and 2A-2C'. The radiation detectors that incorporated amorphous carbon as the halide ion transport-resistant barrier layer produced a very low dark current that was not sensitive to the thickness of the carbon layer. The lifetimes of the radiation detectors operating stably under strong voltage bias for up to at least several weeks (continuous nonstop operation) was increased by orders of magnitude by the halide ion transport-resistant barrier layers.

[0087] Device 1Atty. Dkt. No. 00100-0398-PCT

[0088] For high performance, low dark current is essential because an excessively high noise level will obscure the signal from single particle occurrences. A small and stable dark current of 5.6 nA was achieved under the electric field of 2142 V / cm, which is shown in FIG.2A. For the long stability' gamma measurement, the conditions applied were: high voltage 1428V / cm (1.4 mm thick device); gain 80; shaping time 3 microseconds; and collection time 600 s. The device continuously worked for over 27.25 days under the applied field of 1428 V / cm. The detector exhibited stability during the first week after several hours, maintaining the energy resolution of 8.84% (FIG. 2C) with constant count rate (FIG. 2D) and channel number at 607.4 (FIG. 2B). In the second week, the detector experienced intermittent hiccups, which resulted in a slight increase in the energy resolution of 8.95%, with a decrease in channel number, which remained constant at 606.3. Almost the same condition remained in the third week, but after that, the performance of the device gradually decreased as a result of an increase in the noise floor, and the performance degraded. This was attributed to the fact that the layer of carbon used was thinner than optimal (~10 nm). When a thicker layer of amorphous carbon is used, the performance of the detector can be extended significantly.

[0089] Devices 2A - 2C

[0090] Two data sets were recorded for Device 2A using analog and digital DAQ systems. The first measurement using the analog system was taken for seven days, as shown in FIGS. 3A-3D. The device was operated under constant electrical field of 1670 V / cm. The preamp signal was amplified with the gain of 80 and shaped to Gaussian distribution with the shaping time of 6 ps. The pulse height spectra were reconstructed from day 4 to day 7, in which the energy resolution was stable, as shown in FIG. 3A. The energy resolution (ER) was estimated to be 7.5% (FIG. 3 A). To calculate the channel number, energy’ resolution, and counting rate as a function of time, the pulse height spectra were reconstructed for every 12 hours of data. The channel number was very stable for days (FIG. 3B). The energy resolution was relatively stable except for fluctuations between the second and third day (FIG. 3C), which resulted in fluctuations in the counting rate. The counting rate dropped on the fourth day because the241Am source was accidentally moved out of the center of the device. Other than that, the counting rate was stable for over seven days when the test was stopped (FIG.3D).

[0091] Next, the stability’ of Device 2A was monitored by the digital system for 11 days (FIGS. 4A-4D). Before starting the long-term stability' test, the241Am spectrum wasAtty. Dkt. No. 00100-0398-PCTmeasured at the applied electrical field of 2500 V / m in an optimized condition. An excellent energy resolution of 4.9% at 59.5 keV was obtained without energy' correction, as shown in FIG. 4A. Then, the applied electrical field was maintained constant at 1670 V / m for the longterm stability test. For that applied voltage, the trapezoidal shaping parameters were optimized to be 8 ps and 1.2 ps for peaking time and flat top, respectively. A better energy resolution was obtained to be 6.8%, which was constant for 8 days before it became noisy, as shown in FIG. 3C. The channel number was stable for more than 9 days before slightly decreasing (FIG. 4B). The counting rate was also stable for 8 days, as shown in FIG. 4D. Although the device became unstable for a different reason than electrode reactivity, the counting rate did not decrease, indicating that no loss of anode electrode was observed, and that the barrier layer was functioning properly.

[0092] The performance of Device 2B was characterized using the methods described above for Device 2A, but biased at 700 V to evaluate its stability under a high electric field of 3500 V / cm. After 6 hours, Device 2B became noisy with a noising edge extending over the photopeak as shown in FIG. 5A. The energy resolution became worse, and channel numbers started going down as shown in FIGS. 5B and 5C. Subsequently, the measurement was stopped. These demonstrate that, in the absence of a halide ion transport-resistant barrier layer, a high electrical field has strong negative impact on the stability of the radiation detector.

[0093] The performance of Device 2C was characterized using the methods described above for Device 2A but biased at 280V (-1500 V / cm) during the stability test. Gamma spectra of a241Am source were measured by Device 2C every' 10 minutes as shown in FIG.6A. FIG. 6B show s the gamma spectrum of combined data when it worked w ell. The channel number was steadily improved for 8 and a half days as shown in FIG. 6C. The data indicate that the bulk was improved during biasing. The energy resolution reached its lowest value after tw o days, and then it gradually increased because of electrode degradation. The degradation of the energy resolution accelerated from day 10 to day 12, reaching an unresolvable peak on day 12, while the counting rate began to decrease from day 11 onward as shown in FIG. 6D.

[0094] Devices 1 and 2A, which included halide ion transport-resistant barrier layers, worked very well, with excellent energy resolution over time periods that were several orders of magnitude longer than the radiation detectors that lacked the barrier layers. Using halideAtty. Dkt. No. 00100-0398-PCTion transport-resistant carbon as the barrier layer, channel number, energy resolution, and counting rate were stable for long periods of time (e.g., >2 months) under continuous nonstop operation and (e.g., > 11) months under intermittent operation.

[0095] Devices 3 and 4

[0096] Comparative Device 3

[0097] Under an electric field of 300 V, a small and stable dark current of 2 nA was achieved. I-V measurements showed Schottky behavior in the forward-bias configuration.

[0098] The conditions for long stability y-ray measurement were as follows: a gain of x80, shaping time of 3 ps, collection time of 600 s, and high voltage of 300 V (2-mm-thick device). The device was operated for 16 days under an applied field of 300 V (FIG. 7 A). The channel number, energy resolution, and photopeak counting rate were monitored as functions of time. On Day 1, the device exhibited a good response to241Am, with ER of 9.3%. In the first four days, the detector was stable and operated well; however, after that, the device became noisier, and the measurement was stopped for a week. The device was stored in the dark for one week and measured under the same conditions. The device was improved because of the bias; as a result, the channel number and counting rate increased, as shown in FIG. 7A. The channel number was 612, and the ER was 10% (FIG. 7A), and simultaneously, a steady count rate was observed. However, after 16 days, the device again became noisier and did not resume operation, presumably because of the formation of BiBn at the interface of the crystal surface owing to the applied electric field. It could be seen that the anode electrode from a failed device had begun to corrode from the edges. The spectroscopic responses of the device on Days 1, 8, and 16 are depicted in FIG. 7B, which shows that the response until Day 16 was good.

[0099] Device 4

[0100] Radiation detector Device 4 exhibited Schottky7behavior with an extremely low7dark current of 4 nA under an electric field of 300 V, as shown in FIG. 8B. A long-term stability test was conducted under a241Am source using an electric field of 300 V, a shaping time of 3 ps, and a gain of *80. On Day 1 , an impressive response with an ER of 10.5% was detected. This device w as operated for up to 36 days (FIG. 8A). The channel number and energy resolution remained stable until Day 31; the counting rate increased until Day 15 and then slowly began to decrease (FIG. 8 A). After Day 31. the electric field was increased toAtty. Dkt. No. 00100-0398-PCT400 V. Consequently, the channel number increased and the resolution improved, but the counting rate decreased rapidly (FIG. 8A). As the counting rate decreased rapidly, measurements were stopped after 36 days. However, until Day 31, the spectroscopic response of this device was good (FIG. 8B), for Day 1 vs. Day 15 vs. Day 31.

[0101] Device 3 operated continuously for 16 days under an electric field of 1500 V / cm, and Device 4, made by incorporating thin ~40 nm of TiC as a halide ion transport-resistant barrier, operated continuously for 36 days with a constant energy resolution and channel number under the electric field of 1500 V / cm. Additionally, when stored under ambient conditions and tested periodically, they remained functional and stable for up to 327 days.

[0102] To better understand the long-term stability of metal contacts, SEM and EDS analyses were conducted to examine surface morphology and elemental composition at the electrode / sermconductor interface. These measurements were performed under two conditions: (1) immediately after metal deposition (“fresh” state) and (2) after device failure (“degraded” state). The goal was to identify chemical and structural changes, such as bromide migration, oxidation, or void formation, which may correlate with device degradation and instability.

[0103] Upon aging, distinct surface changes w ere observed at the TiC / CsPbBra interface for Device 4. including the formation of large particulates on top of the TiC. EDS mapping revealed a significant change in bromine distribution: while the fresh device showed a sharp boundary' between the Br-rich perovskite and the TiC contact, the aged device exhibited a nearly uniform Br signal across the TiC and polished surface interface, suggesting extensive halide migration from the CsPbBrs. Quantitative EDS analysis of mapped regions confirmed a significant increase in bromine content, with the Cs:Pb:Br ratio shifting from 1.00:1.00:2.97 in the pristine device to 1.06:1.00:3.31 after degradation. These results indicate halide migration to the TiC interface.

[0104] Among all electrodes studied, Bi w as the most chemically stable and least reactive with halides under bias. The TiC barrier interlay er proved effective in further isolating the Bi contact from direct chemical interaction with the perovskite. These results demonstrate that the Bi / TiC / CLB / Pt configuration can enable high-stability perovskite detectors in medical, security, high-flux synchrotron, and other applications.

[0105] Device 5:Atty. Dkt. No. 00100-0398-PCT

[0106] For the stability tests. Device 5 was biased continuously at 300V (-1500 V / cm). The channel number was very stable for 90 days without noticeable degradation. The energy resolution was a bit unstable for the first 44 days and then it was stable at around 8% at 59.5 keV gamma from a241Am source. (FIGS. 9A - 9D) The channel number was also quite stable with minimal reduction after 90 days. The thin TiCh layer allowed electrons to tunnel from the CsPbBn crystal to the Bi electrode, while mitigating the diffusion of Br ions to the electrode. Therefore, the stability performance of Device 5 was exceptional compared to bare analogous devices having Bi, In and Pb electrodes, but lacking the halide ion transportresistant barriers.

[0107] The word "illustrative" is used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as "illustrative" is not necessarily to be construed as preferred or advantageous over other aspects or designs. Further, for the purposes of this disclosure and unless otherwise specified, "a" or "an" means "one or more.”

[0108] The foregoing description of illustrative embodiments of the invention has been presented for purposes of illustration and of description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. The embodiments were chosen and described in order to explain the principles of the invention and as practical applications of the invention to enable one skilled in the art to utilize the invention in various embodiments and with various modifications as suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.

Claims

Atty. Dkt. No. 00100-0398-PCTWHAT IS CLAIMED IS:

1. A radiation detector comprising:a metal electrode;a continuous halide ion transport-resistant barrier layer comprising a non-particulate, amorphous, inorganic, non-metallic, halide ion transport-resistant material on and in direct contact with the metal electrode;a photoactive layer comprising a crystalline halide-containing semiconductor on and in direct contact with the continuous halide ion transport-resistant barrier layer opposite the metal electrode, wherein metal electrode and the photoactive layer are characterized in that a Schottky barrier forms between the metal electrode and the crystalline halide-containing semiconductor under a bias;a second electrode in electrical communication with the photoactive layer, wherein the metal electrode and the second electrode are configured to apply an electric field across the photoactive layer; anda signal detector configured to measure a photocurrent generated in the crystalline halide-containing semiconductor photoactive layer when the crystalline halide-containing semiconductor photoactive layer is exposed to incident radiation.

2. The radiation detector of claim 1, further comprising a second continuous halide ion transport-resistant barrier layer comprising a non-particulate, amorphous, inorganic, non-metallic, halide ion transport-resistant barrier material between and in direct contact with the crystalline halide-containing semiconductor and the second electrode.

3. The radiation detector of claim 1, wherein the non-particulate. amorphous, inorganic, non-metallic, halide ion transport-resistant barrier material is carbon.

4. The radiation detector of claim 1, wherein the non-particulate, amorphous, inorganic, non-metallic, halide ion transport-resistant barrier material is titanium carbide.

5. The radiation detector of claim 1, wherein the non-particulate, amorphous, inorganic, non-metallic, halide ion transport-resistant barrier material is titanium dioxide or tin oxide.Atty. Dkt. No. 00100-0398-PCT6. The radiation detector of claim 1, wherein the non-particulate. amorphous, inorganic, non-metallic, halide ion transport-resistant barrier material is boron nitride.

7. The radiation detector of claim 1, wherein the non-particulate, amorphous, inorganic, non-metallic, halide ion transport-resistant barrier layer is a refractory metal oxide, a refractory metal nitride, or a refractory metal silicide.

8. The radiation detector of claim 1, wherein the halide-containing semiconductor of the photoactive layer is a metal halide perovskite.

9. The radiation detector of claim 1 , wherein the metal electrode is a bismuth (Bi) anode.

10. The radiation detector of claim 1, wherein the metal electrode is a lead (Pb) anode.

11. The radiation detector of claim 1 , wherein the metal electrode is an indium (In) anode, a tin (Sn) anode, an antimony (Sb) anode, a gallium (Ga) anode, a chromium (Cr) anode, a titanium (Ti) anode, or an indium-gallium alloy anode.

12. The radiation detector of claim 1, wherein the second electrode is a gold (Au) cathode, a platinum (Pt) cathode, a nickel (Ni) cathode, an osmium (Os) cathode, a palladium (Pd) cathode, or an indium tin oxide (ITO) cathode.

13. The radiation detector of claim 8, wherein the metal halide perovskite is CsPbBrs. the non-particulate, amorphous, inorganic, non-metallic, halide ion transportresistant material is carbon, and the metal electrode is a lead (Pb) anode, a bismuth (Bi) anode, an indium (In) anode, a tin (Sn) anode, an antimony (Sb) anode, a gallium (Ga) anode , a chromium (Cr) anode, a titanium (Ti) anode, an aluminum (Al) anode, or an indiumgallium alloy anode.

14. The radiation detector of claim 8, wherein the metal halide perovskite is CsPbB . the non-particulate, amorphous, inorganic, non-metallic, halide ion transport-Atty. Dkt. No. 00100-0398-PCTresistant material is carbon, titanium carbide, or titanium dioxide, and the metal electrode is a lead (Pb) anode or a bismuth (Bi) anode.

15. The radiation detector of claim 14. wherein the second electrode is a gold (Au) cathode or a platinum (Pt) cathode.

16. The radiation detector of claim 14, wherein the non-particulate, amorphous, inorganic, non-metallic, halide ion transport-resistant barrier material is carbon and the metal electrode is the bismuth (Bi) anode.

17. The radiation detector of claim 14, wherein the non-particulate, amorphous, inorganic, non-metallic, halide ion transport-resistant barrier material is carbon and the metal electrode is the lead (Pb) anode.

18. The radiation detector of claim 14, wherein the non-particulate, amorphous, inorganic, non-metallic, halide ion transport-resistant barrier is titanium carbide and the metal electrode is the bismuth (Bi) anode.

19. A method for detecting incident radiation using the radiation detector of claim 1, the method comprising:exposing the crystalline halide-containing semiconductor to incident radiation, wherein the crystalline halide-containing semiconductor absorbs the incident gamma radiation and generates a photocurrent; anddetecting the photocurrent with the signal detector.

20. The method of claim 19, wherein the incident radiation comprises gamma radiation.

21. A method of making the radiation detector of claim 1. the method comprising: depositing a continuous layer of the non-particulate, amorphous, inorganic, non-metallic, halide ion transport-resistant barrier material on a surface of the crystalline halide-containing semiconductor;depositing the metal electrode on the continuous layer of the non-particulate, amorphous, inorganic, non-metallic, halide ion transport-resistant barrier material; andAtty. Dkt. No. 00100-0398-PCTdisposing the second electrode in electrical communications with the crystalline halide-containing semiconductor.

22. The method of claim 21, wherein the continuous layer of the non-particulate, amorphous, inorganic, non-metallic, halide ion transport-resistant barrier layer is deposited on a surface of the cry stalline halide-containing semiconductor using a technique selected from: atomic layer deposition; electron beam deposition; sputtering; thermal evaporation; and solution processing.

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