[“Source” Observation Series] Application of Keithley in Particle Beam Detection Based on Perovskite System

Ionizing radiation such as X-rays and gamma rays has been widely studied and applied in various fields such as medical imaging, non-destructive testing, and scientific research.

Therefore, it is very important to detect this high-energy radiation with highly sensitive and low-cost materials and devices. Compared with commercial silicon (Si) and amorphous selenium (a-Se), halide perovskites have many advantages, such as large light absorption coefficient, high resistivity, small leakage current, high mobility, and simple synthesis and processing, making them promising candidates for radiation detection.

Radiation detectors based on perovskite systems have the following main advantages over traditional detectors:

● High sensitivity: All-inorganic metal halide perovskites have a high X-ray attenuation coefficient and can effectively absorb, for example, X-rays, improving detection sensitivity.

● Direct conversion: Perovskite materials can directly convert X-rays into electrical signals, avoiding the secondary photoelectric conversion in indirect detectors, thereby improving the photoelectric conversion efficiency.

● High spatial resolution: Due to the direct conversion characteristics, perovskite X-ray detectors can achieve higher spatial resolution.

● Low radiation dose: High sensitivity means that clear images can be obtained at a lower X-ray dose, which helps reduce radiation risks.

● Excellent carrier transport performance: Perovskite materials have high carrier mobility and long carrier lifetime, which is conducive to improving detection efficiency.

● Material stability: All-inorganic perovskites have better stability than organic-inorganic hybrid perovskites.

● Controllability: The composition and structure of perovskite materials can be flexibly controlled to meet different application requirements.

● Simple preparation process: Compared with traditional semiconductor materials, perovskite materials can be prepared through simple processes such as solution method, which is conducive to reducing costs and achieving large-area preparation.

Research based on the perovskite system mainly includes material development, electrode engineering, energy band engineering, etc., with the goal of developing devices with higher sensitivity, lower detection limit, and faster response time. At the same time, research is also conducted on large-area process preparation to improve stability and yield, and to be environmentally friendly and pollution-free, continuously reducing costs and accelerating the commercialization process.

Tektronix/Keithley provides professional and high-precision electrical measuring instruments, which are widely used in the research of perovskite systems. Among them, 6514/6517B is used for dark current measurement, and different bias excitations can be applied to the device, and the dark current test accuracy can reach the aA level. The basic parameters of traditional perovskite Qe, open-circuit voltage, circuit current, etc. can be measured using a photovoltaic simulation system, and all electrical parameters can be tested using the 2450 series source meter. In the research of large-scale perovskite detector arrays, 2612B and 3706 are also provided to achieve addressing of array units and high-precision detection of photogenerated current, providing full verification of the design architecture and performance for large-scale imaging chips.

Case 1: Heteroepitaxial passivation of Cs2AgBiBr6 wafers to suppress ion migration for X-ray imaging

X-ray detectors are widely used in medical imaging and product inspection. Perovskite halides show excellent performance in direct X-ray detection. However, ion migration causes large noise and baseline drift, which limits the detection and imaging performance. This work introduces bismuth oxide bromide (BiOBr) as a heteroepitaxial passivation layer to prepare (Cs2AgBiBr6) multi-wafers to suppress ion migration.

In this case, 6517B is used to standardize the device noise, i.e. dark current, as shown in Figure e. This provides sufficient test margin for the device's extreme performance and ensures accurate characterization of the new device's performance (the device noise density is 6 orders of magnitude away from the actual noise density of 6517B).

Case 2: Cross-array perovskite photodetectors prepared by vapor deposition for dynamic imaging

Characterization of the photodetector crossbar array: For static imaging, the array was tested using a multi-channel scanning system. A Keithley 3706A switch card (Keithley 3730 matrix card) was used to select the rows and columns to determine the pixels to be tested, and a Keithley 2612B source meter was used to measure the current vs. voltage characteristics.

The responsiveness of the device current under different biases tested using 2612B; the characteristic curve of the upper blocking diode in the device structure;

The schematic diagram of the 4X4 array test is realized by using 3706 and 2612B. By gating different devices, the photocurrent of each perovskite device is collected sequentially, and finally the image is processed and displayed.

Advantages of Keithley instruments in this application:

1. 6517B multifunction instrument, measures voltage at high input impedance, low current (<1pA), charge and high resistance, beyond the capabilities of traditional digital multimeters. Resistance measurement up to 1016Ω; built-in ±1kV voltage source with bias sweep capability;

6517B

2.2612B series source meter high-precision dual-channel source meter, dual-channel high-precision capability, 100nV voltage resolution, 100fA current resolution.

2612B

3.3706 matrix switch, with high-performance system switch, can contain 6 card slots in the compact 2U high housing, which can easily meet the needs of medium and high channel number applications and realize intensive switching and measurement solutions.

3706

4.TSP-Link programmable interface and built-in processor make intelligent instruments possible. TSP scripts are stored inside the instrument, and the instrument completes the test autonomously, reducing the bus communication time with the host computer and improving the throughput, which is especially important for large-scale production lines.