Achieving Low-Dose Rate X-Ray Imaging Based on 2D/3D-Mixed Perovskite Films.

X-ray detection and imaging are widely used in medical diagnosis, product inspection, security monitoring, etc. Large-scale polycrystalline perovskite thick films possess high potential for direct X-ray imaging. However, the notorious problems of baseline drift and high detection limit caused by ions migration are still remained. Here, ion migration is reduced by incorporating 2D perovskite into 3D perovskite, thereby increasing the ion activation energy. This approach hinders ion migration within the perovskite film, consequently suppressing baseline drift and reducing the lowest detection limit(LOD) of the device. As a result, the baseline drifting declines by 20 times and the LOD reduces to 21.1 nGy s-1, while the device maintains a satisfactory sensitivity of 5.6 × 103 µC Gy-1 cm-2. This work provides a new strategy to achieve low ion migration in large-scale X-ray detectors and may provide new thoughts for the application of mixed-dimension perovskite.

Effects of the Process Parameters on the Properties of Sputter-Deposited Tin Oxide Thin Films.

This study examined the effects of the oxygen partial pressure on the properties of tin oxide (SnOx) thin films deposited by radio frequency magnetron sputtering using a SnO target. The properties of the samples were characterized by Hall Effect measurements, dynamic-secondary ion mass spectrometry, X-ray photoelectron spectroscopy (XPS), X-ray diffraction, and atomic force microscopy. All the samples exhibited dominant Sn2+ XPS peaks, indicating that SnO with p-type conductivity was the main composition regardless of the oxygen partial pressure. The samples deposited with an oxygen partial pressure of 12% showed the best p-type characteristics, which included a maximum hole mobility of 1.94 cm²/Vs, carrier concentration of 3.83×1017/cm³, Sn2+ peak area percentage of 91.34%, Sn4+ peak area percentage of 2.35%, and Sn0 peak area percentage of 6.31%. As the oxygen partial pressure was increased to more than 12%, the Sn2+ peak area percentage decreased while the Sn4+ peak area percentage increased. This was attributed to the reduction of the SnO phase and the growth of the SnO2 phase in the samples due to the incorporation of more oxygen. These results are expected to contribute to the development of p-type SnO-based TFTs with good performance.

Using N-I-N Photodiodes Made of Perovskite Single Crystals for Low Noise Gamma-Ray Spectroscopy.

Solution-processed lead halide perovskite single crystals (LHPSCs) are believed to have great potential in gamma-ray spectroscopy. However, obtaining low-defect LHPSCs from a solution at low temperatures is difficult compared to obtaining Bridgman single crystals such as CdTe and Si. Herein, noise from the intrinsic defects of LHPSCs is considered as the main problem hindering their gamma-ray detection performance. By isolating the defect-induced holes in LHPSCs via energy barriers, we show that NIN photodiodes based on three types of LHPSCs, i.e., MAPbBr3 (MA = CH3NH3), MAPbBr2.5Cl0.5, and cascade LHPSCs, have demonstrated good energy resolution in the range of 6.7-10.3% for 662 keV 137Cs gamma-ray photons. The noise for >10 mm3 devices is low, in the order of 340-860 electrons, and the electron collection efficiency reaches 23-43%. These results pave the way for obtaining low-cost, large, high energy-resolution gamma-ray detectors at room temperature (300 K).

Integrated Water-Level Sensor Using Thin-Film Transistor Technology.

A low-cost water-level sensor was developed utilizing a capacitive sensor design with only one thin-film transistor (TFT). The integration of the a-IGZO TFT process facilitated the complete integration of the water-level sensor on a substrate, including essential components, such as the transistor, capacitor, wires, and sensing electrode. This integration eliminates the need for a separate mounting process, resulting in a robust sensor assembly. To comprehensively assess the performance of the developed water-level sensor, rigorous evaluations were conducted using both MOSFET and TFT integration. In the case of the water-level sensor featuring a-IGZO TFT integration, a voltage output of 4.2 V was measured when the tank was empty, while a voltage output of 0.9 V was measured when the tank was full. Notably, the integrated sensor system demonstrated a higher output voltage compared with the MOSFET sensor, primarily due to the significantly reduced parasitic capacitance of the TFT. The use of a-IGZO TFT in the integrated sensor system contributes to enhanced sensitivity and accuracy. The lower parasitic capacitance inherent in TFT technology allows for improved voltage measurement precision, resulting in more reliable and precise water-level sensing capability. The development of this integrated water-level sensor holds immense potential for a wide range of applications that require a combination of cost-effectiveness, accurate monitoring, and flexibility in form factor. With its affordability, the sensor is accessible for various industries and applications.

Fast Response, High Spectral Rejection Ratio, Self-Filtered Ultranarrowband Photodetectors Based on Perovskite Single-Crystal Heterojunctions.

Narrowband photodetectors have wide application potential in high-resolution imaging and encrypted communication, due to their high-precision spectral resolution capability. In this work, we report a fast response, high spectral rejection ratio, and self-filtered ultranarrowband photodetector with a new mechanism, which introduces bulk recombination by doping Bi3+ and cooperates with surface recombination for further quenching photogenerated charges generated by short-wavelength-light excitation in perovskite single-crystal. A perovskite film focused on collecting charges is fabricated on the single crystal by a lattice-matched solution-processed epitaxial growth method. Due to the formation of PN heterojunctions, a narrowband photodetector in this mechanism has remarkable spectral selectivity and detection performance with an ultranarrow full width at half-maximum (FWHM) of 7.7 nm and a high spectral rejection ratio of 790, as well as a high specific detectivity up to 1.5 × 1010 Jones, a fast response speed with a rise time and fall time of ∼8 and 137 µs. The ultrafast and ultranarrow spectra response of self-filtered narrowband photodetector provides a new strategy in high-precision and high-resolution photoelectric detection.

Cascade perovskite single crystal for gamma-ray spectroscopy.

The halide lead perovskite single crystals (HLPSCs) have great potential in gamma-ray detection with high attenuation coefficient, strong defects tolerance, and large mobility-lifetime product. However, mobile halide ions would migrate under high external bias, which would both weaken the gamma-ray response and cause additional noise. Here, we report the gamma-ray PIN photodiodes made of cascade HLPSCs including both ion-formed and electron-hole-formed electrical junctions that could suppress the ions migration and improve the charges collection. Our photodiodes based on cascade HLPSCs (MAPbBr3/MAPbBr2.5Cl0.5/MAPbCl3) show a wide halide-ion-formed depletion layer of ∼52 µm. The built-in potential along the wide ionic-formed junction ensures a high mobility-lifetime product of 1.1 × 10-2 cm2V-1. As a result, our gamma-ray PIN photodiodes exhibit compelling response to 241Am, 137Cs, and 60Co; the energy resolution can reach 9.4%@59.5keV and 5.9%@662keV, respectively. This work provides a new path toward constructing high-performance gamma-ray detectors based on HLPSCs.

Sensitive Thermography via Sensing Visible Photons Detected from the Manipulation of the Trap State in MAPbX3.

Sensitive thermometry or thermography by responding to blackbody radiation is urgently desired in the intelligent information life, including scientific research, medical diagnosis, remote sensing, defense, etc. Even though thermography techniques based on infrared sensing have undergone unprecedented development, the poor compatibility with common optical components and the high diffraction limit impose an impediment to their integration into the established photonic integrated circuit or the realization of high-spatial-resolution and high-thermal-resolution imaging. In this work, we present a sensitive temperature-dependent visible photon detection in Bi-doped MAPbX3 (X = Cl, Br, and I) and employ it for uncooled thermography. Systematic measurements reveal that the Bi dopant introduces trap states in MAPbX3, thermal energy facilitates the carriers jumping from trap states to the conduction band, while the vacancies of trap states ensure the sequential absorption of visible photons with energy less than the band gap. Subsequently, the change of response toward the visible photon is applied to construct the thermograph, and it possesses a specific sensitivity of 2.11% K-1 along temperature variation. As a result, our thermograph presents a temperature resolution of 0.21 nA K-1, a high responsivity of 2.06 mA W-1, and a high detectivity of 2.08 × 109 Jones at room temperature. Furthermore, remote thermal imaging is successfully achieved with our thermograph.

Electrically Modulated Near-Infrared/Visible Light Dual-Mode Perovskite Photodetectors.

Dual-mode photodetectors (PDs) have attracted increasing interest owing to their potential optoelectrical applications. However, the widespread use of PDs is still limited by the high cost of epitaxial semiconductors. In contrast, the solution processability and wide spectral tunability of perovskites have led to the development of various inexpensive and high-performance optoelectronic devices. In this study, we develop a high-performance electronically modulated dual-mode PD with near-infrared (NIR) narrowband and visible light broadband detection based on organic-inorganic hybrid methylammonium lead halide perovskite (MAPbX3; MA = CH3NH3 and X = Cl, Br, and I) single crystals with a pnp configuration. The operating mode of the dual-mode PD can be switched according to voltage bias polarity because the photon absorption region and carrier transport performance are tuned at different bias voltages. The dual-mode PD exhibits a NIR light responsivity of 0.244 A/W and a narrow full width at half-maximum of ∼12 nm at 820 nm at positive voltages and an average visible light responsivity of ∼0.13 A/W at negative voltages. The detectivities of both modes are high (∼1012 Jones), and the linear dynamic range is wide (>100 dB). Our study provides a new method for fabricating multifunctional PDs and can expand their application in integrated imaging systems.

Vertical oxide thin-film transistor with interfacial oxidation.

A vertical oxide thin-film transistor was developed with interfacial oxidation for low voltage operation. The gate metal was used as a spacer for the definition of the transistor's channel as well as the gate electrode. After definition of the vertical side wall, an IGZO (In-Ga-Zn Oxide) layer was deposited, followed by the interfacial oxidation to form a thin gate insulator. Ta was used for the gate material due to the low Gibbs free energy and high dielectric constant of tantalum oxide. A 15 nm tantalum oxide layer was obtained by the interfacial oxidation of Ta at 400 °C under oxygen atmosphere. The thin gate oxide made it possible to operate the transistor under 1 V. The low operation voltage enables low power consumption, which is essential for mobile application.

Effects of Annealing on an IGZO-Metal Interface.

The interface reaction between a metal layer and a layer of amorphous indium-gallium-zinc oxide was investigated. Oxygen atoms at the interface bond to the metal atoms and form metal oxide. The reaction depends on the annealing temperature and ambient conditions. The thickness of the metal oxide at the interface increased with the annealing temperatures. The reaction relies on the Gibbs free energy for oxidation. Ta, which has low Gibbs free energy formed a 33 nm layer of tantalum oxide at an annealing temperature of 450 °C. The HR-TEM and EDX observation showed that the metal oxide thicknesses were 5, 10, and 33 nm at annealing temperatures of 350, 400, and 450 °C, respectively. The thicknesses obtained with both Ar and oxygen gas were 4, 8, and 21 nm, respectively. The lower oxide thicknesses were attributed to the lower number of oxygen vacancies in the IGZO deposited using Ar and oxygen, which was identified by XPS analysis.

Interfacial Oxidized Gate Insulators for Low-Power Oxide Thin-Film Transistors.

Low power consumption is essential for wearable and internet-of-things applications. An effective way of reducing power consumption is to reduce the operation voltage using a very thin and high-dielectric gate insulator. In an oxide thin-film transistor (TFT), the channel layer is an oxide material in which oxygen reacts with metal to form a thin insulator layer. The interfacial oxidation between the gate metal and In-Ga-Zn oxide (IGZO) was investigated with Al, Ti, and Mo. Positive bias was applied to the gate metal for enhanced oxygen diffusion since the migration of oxygen is an important factor in interfacial oxidation. Through interfacial oxidation, a top-gate oxide TFT was developed with low source-drain voltages below 0.5 V and a gate voltage swing less than 1 V, which provide low power consumption.

Effects of Plasma Treatment on the Composition and Phase Changes of Sputter-Deposited SnOx Thin Films.

This study examined the effects of the plasma treatment of CF4 or SF6 on the properties of tin oxide (SnOx) thin films prepared at room temperature using a radio frequency sputtering technique. The properties of the samples were characterized by dynamic-secondary ion mass spectrometry, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and Hall Effect measurements. All untreated samples showed Sn4+ and Sn2+ XPS peak area percentages of 57.6 and 34.6%, respectively, indicating a larger amount of SnO2 phase in the samples than SnO. The samples treated with CF4 plasma exhibited the maximum and minimum Sn4+ and Sn2+ peak areas, respectively, at a treatment time of 35 s. This was attributed to the maximum oxygen atomic percentage at 35 s and the injection of additional carbon and fluorine into the sample with increasing treatment time. On the other hand, in the case of samples treated with SF6 plasma, the Sn4+ peak area increased with increasing treatment time while the Sn2+ peak area decreased. This suggests that SnO2 is a stronger phase for samples treated with SF6 plasma for a longer duration. Furthermore, the changes in the Sn4+ and Sn2+ peak areas of the samples treated with CF4 plasma were much larger than those of the samples treated with SF6 plasma, which indicates that CF4 plasma has a larger impact on the properties of the samples. This difference in impact showed a correlation with the sharper decrease in the number of oxygen vacancies for CF4 plasma-treated samples. These results were attributed to the introduction of additional fluorine and carbon into CF4 plasma-treated samples compared to the SF6 plasma-treated ones. In addition, XRD showed that the plasma treatment did not affect the amorphous phase in the samples.