Key Takeaways & Executive Findings
- •• Pin diodes on sapphire substrates outperform Schottky and GaN-substrate diodes for 0 V bias proton detection. • Achieved minimum detectable proton beam current below 1 pA/cm², demonstrating high sensitivity. • Detector response is linear with proton current and fast (<1 s), suitable for real-time monitoring. • GaN diodes show promise for high spatial resolution proton imaging in proton therapy.
Abstract
GaN diodes for high energy (64.8 MeV) proton detection were fabricated and investigated. A comparison of the performance of GaN diodes with different structures is presented, with a focus on sapphire and on GaN substrates, Schottky and pin diodes, and different active layer thicknesses. Pin diodes fabricated on a sapphire substrate are the best choice for a GaN proton detector working at 0 V bias. They are sensitive (minimum detectable proton beam <1 pA/cm2), linear as a function of proton current and fast (<1 s). High proton current sensitivity and high spatial resolution of GaN diodes can be exploited in the future for proton imaging of patients in proton therapy.
1. Introduction
Proton therapy is an alternative to classical X-ray radiotherapy commonly used for the treatment of cancers. The unique property of protons is their steep stopping profile in matter (Bragg peak) granting to use higher energy doses than in conventional X-ray radiotherapy while strongly limiting the collateral damage of healthy cells during irradiation[1−3]. Nonetheless, in proton therapy and high energy physics, there is a need for proton detectors with high sensitivity and good spatial resolution.
At the moment, high energy protons (typically in the range 60−230 MeV for proton therapy) can be detected by various techniques, such as ionization chambers (e.g. MatriXX by IBA[4]), silicon detectors (faraday cups, silicon strips[5, 6], silicon pin diodes) or scintillators coupled to CCDs (e.g. Lynx by IBA[7]). However, all these approaches have some drawbacks. For example, the ionization chambers have a good dose resolution but their spatial resolution is limited to a minimum of 500 µm (most often 1 mm) and require a bias of a few kilovolts. On the other hand, the scintillators have a limited dynamic range and rapidly saturate at high proton currents. Finally, silicon has a small displacement energy (21 eV) making the silicon-based devices fragile under irradiation by energetic protons.
During conventional radiotherapy treatment the patients are irradiated with dose rates of 0.01−0.05 Gy/s while a promising procedure called FLASH therapy using dose rates higher than 40 Gy/s is currently arousing a strong interest of the medical community. Consequently, the detectors daily used for beam calibration have to withstand several Gy of irradiation each day. Research on new proton detectors made of SiC[8, 9], amorphous silicon[10], and hybrid materials scintillators[11] is currently emerging in order to adapt to the new irradiation conditions.
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Matilde Siviero, Maxime Hugues, Lucas Lesourd, Eric Frayssinet, Shirley Prado de la Cruz, Sebastien Chenot, Johan-Petter Hofverberg, Marie Vidal, Jean-Yves Duboz (2025). GaN diodes comparative study for high energy protons detection. SinoTechIntel Verified Research. https://doi.org/10.1088/1674-4926/25020014
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Frequently Asked Questions
What are the key findings of the study on GaN diodes for proton detection?
The study found that pin diodes fabricated on sapphire substrates are the best choice for GaN proton detectors operating at 0 V bias, offering high sensitivity (minimum detectable proton beam <1 pA/cm²), linear response, and fast response (<1 s).
Why are GaN diodes considered for proton detection in proton therapy?
GaN diodes offer high sensitivity and spatial resolution, and are more radiation-hard than silicon due to higher displacement energy, making them suitable for high-energy proton detection in proton therapy and FLASH therapy.
What are the limitations of existing proton detectors that GaN diodes aim to overcome?
Existing detectors like ionization chambers have limited spatial resolution and require high bias; scintillators saturate at high currents; silicon detectors are fragile under proton irradiation. GaN diodes aim to provide better spatial resolution, lower bias, and higher radiation hardness.
What is the significance of the 0 V bias operation in GaN proton detectors?
Operating at 0 V bias simplifies detector design, reduces power consumption, and avoids the need for high-voltage supplies, making the detector more practical and safer for clinical use.
How does the study compare different GaN diode structures?
The study compared Schottky and pin diodes on sapphire and GaN substrates with different active layer thicknesses, concluding that pin diodes on sapphire substrates provide the best performance for proton detection at 0 V bias.
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