Indium selenide (InSe) has emerged as a promising material for radiation detection, particularly in X-ray and gamma-ray sensing applications. Its high atomic number elements, indium and selenium, contribute to strong photon absorption, making it suitable for detecting high-energy radiation. The material’s layered structure and tunable electronic properties further enhance its potential for efficient charge collection, a critical factor in radiation sensor performance. This article examines the role of InSe in radiation sensing, focusing on its charge collection efficiency and comparing its capabilities with traditional scintillator-based detectors.

The effectiveness of a radiation sensor depends on its ability to absorb incident photons and convert them into measurable electrical signals. InSe excels in this regard due to the high atomic numbers of its constituent elements. Indium has an atomic number of 49, while selenium has an atomic number of 34, giving InSe a higher effective atomic number compared to many conventional semiconductor detectors. This property increases the probability of photoelectric absorption, which is the dominant interaction mechanism for X-rays and gamma rays in the energy range of interest for medical imaging, security screening, and industrial inspection.

Charge collection efficiency is a key metric for evaluating radiation sensor performance. In InSe-based detectors, the layered van der Waals structure allows for efficient carrier transport with reduced trapping and recombination losses. Studies have shown that InSe exhibits high carrier mobility, with electrons demonstrating values exceeding 1000 cm²/Vs in high-quality samples. This high mobility facilitates rapid charge extraction, minimizing signal loss due to carrier trapping. Additionally, the material’s moderate bandgap, typically around 1.3 eV, ensures a balance between dark current suppression and sufficient charge generation upon photon absorption.

The performance of InSe radiation sensors can be further optimized through material engineering. Thickness scaling plays a crucial role in balancing absorption efficiency and charge collection. Thicker InSe layers enhance X-ray absorption but may introduce additional carrier scattering. Research indicates that an optimal thickness exists where absorption is maximized without significantly compromising charge transport. Defect engineering also influences sensor performance, as defects can act as trapping centers. Advances in growth techniques, such as molecular beam epitaxy and chemical vapor deposition, have enabled the production of high-purity InSe with reduced defect densities.

When compared to traditional scintillator-based detectors, InSe offers several advantages. Scintillators convert high-energy photons into visible light, which is then detected by a photomultiplier tube or silicon photodiode. This two-step process introduces inefficiencies, including light yield limitations and optical coupling losses. In contrast, InSe detectors directly convert absorbed photons into electrical signals, eliminating intermediate steps and improving signal-to-noise ratios. Direct detection also enables higher spatial resolution, as the signal generation occurs within the active material rather than being spread through light emission.

Energy resolution is another critical parameter where InSe demonstrates competitive performance. The material’s ability to generate a large number of electron-hole pairs per absorbed photon contributes to improved energy discrimination. For instance, InSe detectors have shown energy resolutions comparable to cadmium zinc telluride (CZT) detectors in the gamma-ray energy range below 200 keV. This makes InSe a viable alternative for applications requiring precise energy measurement, such as nuclear medicine and spectroscopy.

Environmental stability is an important consideration for practical radiation sensors. InSe exhibits better resistance to oxidation compared to other layered semiconductors like black phosphorus, though encapsulation may still be necessary for long-term operation in harsh environments. Advances in passivation techniques have further enhanced the stability of InSe devices, ensuring reliable performance over extended periods.

The fabrication of InSe radiation sensors typically involves the deposition of electrical contacts on high-quality InSe flakes or films. Ohmic contacts are essential to minimize series resistance and ensure efficient charge extraction. Metals such as gold and titanium have been successfully used as contact materials, with annealing steps often employed to improve interface quality. Device architectures may include planar configurations for simplicity or vertically stacked designs to enhance absorption in thinner layers.

In terms of application-specific performance, InSe detectors have been tested in various radiation sensing scenarios. Medical imaging applications benefit from the material’s high absorption efficiency in the diagnostic X-ray range (20-150 keV). Security screening systems can leverage InSe’s ability to discriminate between different materials based on their X-ray absorption signatures. Industrial inspection tools utilizing InSe sensors can detect defects or compositional variations in manufactured components with high sensitivity.

Future developments in InSe radiation sensors may focus on large-area fabrication techniques to enable commercial scalability. While laboratory-scale devices have demonstrated promising results, transitioning to wafer-scale production requires further optimization of growth and processing methods. Heterostructure integration, where InSe is combined with other layered materials, could also enhance performance by tailoring band alignment and charge transport properties.

The potential for flexible InSe-based radiation sensors opens new possibilities for conformal and wearable detection systems. The mechanical flexibility of thin InSe layers allows for integration into non-planar surfaces, which could be advantageous in medical dosimetry or portable radiation monitoring devices. Research in this direction is ongoing, with preliminary results indicating retained sensitivity even under bending conditions.

In summary, indium selenide presents a compelling option for next-generation radiation sensors, offering high absorption efficiency, excellent charge collection, and competitive energy resolution. Its advantages over traditional scintillators include direct detection capabilities and potential for miniaturization. Continued advancements in material quality and device engineering will further solidify its position in the field of radiation detection, addressing the growing demand for high-performance, compact, and versatile sensing solutions.