X-Ray Detection and Spectroscopy Technologies

X-ray detection and spectroscopy technologies have evolved rapidly through advances in semiconductor materials, device architectures and low-noise electronics. Modern spectrometers rely on direct-conversion detectors, which generate electrical signals from incident X-ray photons and enable precise energy discrimination. A range of wide-bandgap semiconductors, including gallium arsenide (GaAs), silicon carbide (SiC) and aluminium gallium arsenide (AlGaAs), have been demonstrated as viable detector materials, each offering distinct benefits in terms of energy resolution, temperature tolerance and radiation hardness. Key performance metrics such as leakage current, charge collection efficiency and full-width at half-maximum (FWHM) energy resolution have been improved by optimising epitaxial growth, device geometry and front-end electronics. Photon counting spectroscopy—where each X-ray photon is individually registered and analysed—has become the method of choice for applications ranging from planetary science and space missions to medical imaging and industrial process control. Recent innovations include the integration of photodiode arrays for spatially resolved spectroscopy, avalanche multiplication to lower detection thresholds and bespoke charge-sensitive preamplifiers to suppress electronic noise. Together, these developments underpin a versatile toolkit for high-precision X-ray analysis across scientific and applied domains.

Research from Nature Portfolio

Recent studies have introduced InGaP (GaInP) p-i-n photodiodes optimised for photon counting X-ray spectroscopy. Devices with 5 µm intrinsic layers and diameters of 200 µm and 400 µm were coupled to low-noise charge-sensitive preamplifiers and tested with an 55Fe source at room temperature. The best spectrometer energy resolution achieved was 900 eV (FWHM) at 5.9 keV for the smaller devices under moderate reverse bias. Detailed noise analysis quantified contributions from dielectric and transistor sources, guiding future improvements in front-end electronics. This work demonstrates the viability of III–V photodiodes in compact, high-resolution X-ray spectrometers suitable for harsh environments and miniaturised platforms.

Research from all publishers

High-temperature GaAs photodiodes with 10 µm intrinsic layers have been characterised between –20 °C and 100 °C, yielding energy resolutions down to 0.66 keV (FWHM) at 5.9 keV and –20 °C. Leakage currents remained low up to 50 kV/cm internal fields, with dielectric noise identified as the dominant broadening mechanism at most temperatures. Complementary work on commercial 4H-SiC Schottky photodiodes has demonstrated room-temperature photon counting spectroscopy with FWHM of 1.8 keV (0.06 mm²) and 3.3 keV (0.5 mm²) at 5.9 keV, leveraging the material’s inherent low dark current and wide bandgap. More recently, Al₀.₆Ga₀.₄As avalanche photodiodes have been shown to achieve energy resolutions of 630 eV and 730 eV (FWHM) at gains of 3.5–5, with avalanche multiplication extending detectable energy down to 1.5 keV. These studies illustrate a trend towards combining material engineering with gain mechanisms to enhance sensitivity and lower detection thresholds for space and laboratory spectrometers.

X-Ray Detection and Spectroscopy Technologies publication trend

The graph below shows the total number of articles in x-ray detection and spectroscopy technologies across all publications each year (not limited to Nature Index journals).

Technical terms

p-i-n photodiode: A semiconductor detector structure with intrinsic layer between p-type and n-type regions, used for direct conversion of X-rays to electrical signals.

Photon counting spectroscopy: A detection mode in which individual X-ray photons are recorded and binned by energy, enabling high spectral resolution and quantitative analysis.

Avalanche photodiode (APD): A photodiode that multiplies the primary charge carriers via impact ionisation, lowering the minimum detectable energy.

Charge-sensitive preamplifier: An electronic front end that converts the charge generated by an X-ray photon into a voltage pulse with minimal added noise.

Energy resolution (FWHM): The full width at half-maximum of a spectral peak, a measure of a spectrometer’s ability to distinguish closely spaced energies.

References

1. InGaP (GaInP) mesa p-i-n photodiodes for X-ray photon counting spectroscopy. Scientific Reports (2017).
2. High temperature GaAs X-ray detectors. Journal of Applied Physics (2017).
3. Soft X-ray detection and photon counting spectroscopy with commercial 4H-SiC Schottky photodiodes. Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment (2016).
4. Al0.6Ga0.4As x-ray avalanche photodiodes for spectroscopy. Semiconductor Science and Technology (2020).
5. Al0.2Ga0.8As 2 × 2 square pixel X-ray photodiode array. Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment (2018).
6. Electronic noise in charge sensitive preamplifiers for X-ray spectroscopy and the benefits of a SiC input JFET. Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment (2015).