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Due to its remarkable tolerance to high energy ionizing radiation, GaN has recently attracted attention as a promising material for dosimetry applications. However, materials issues that lead to persistent photoconductivity, poor sensitivity, and requirements for large operational voltages have been hurdles to realization of the full potential of this material. Here we demonstrate that the introduction of a two‐dimensional electron gas channel, through the addition of AlGaN/GaN heterointerfaces, can be used to create intrinsic amplification of the number of electrons that can be collected from single ionization events, yielding exceptionally large sensitivities in ultralow dose rate regimes. Furthermore, anomalous photo‐responses, which severely limit response times of GaN‐based devices, can be eliminated using these heterostructures. Measurements using focused monochromatic synchrotron radiation at 1–20 keV, as well as focused 20 MeV protons, reveal that these devices provide the capability for high sensitivity and resolution real time monitoring, which is competitive with and complementary to state‐of‐the‐art detectors. Therefore, AlGaN/GaN heterostructure devices are extremely promising for future applications in fields ranging from high energy physics to medical imaging.

Gallium nitride has a remarkable tolerance to high energy ionizing radiation, but its full potential has not yet been realized due to material issues that lead to persistent photoconductivity, poor sensitivity, and requirements for large operational voltages. However, J. D. Howgate et al. (pp. 1562–1567) demonstrate that the introduction of a two‐dimensional electron gas channel, through the construction of AlGaN/GaN heterointerfaces, can be used to create “photomultiplier” equivalent amplification, while eliminating persistent photoconductivity, under operation with single volt bias at room temperature. These results are extremely promising for future ionizing radiation detector technologies for applications ranging from high energy physics to medical imaging. This is demonstrated on the front cover image, where a 3 × 3 mm flashlight bulb was scanned with ultra‐low dose rate (thousands of photons per second) focused X‐rays, clearly revealing the 50 μm thick spiral filament and the cavity in which it is mounted. Furthermore, such an image could be obtained within milliseconds via device miniaturization using conventional microelectronics techniques that allow for fabrication of integrated two‐dimensional pixel detectors. These extreme sensitivities could, for example, enable patient exposures to harmful ionizing radiation to be dramatically reduced or offer low power personal dosimeters capable of giving real‐time warning to radiation exposure.