Long, balanced electron and hole diffusion lengths greater than 100 nanometers in the polycrystalline organolead trihalide compound CH3NH3PbI3 are critical for highly efficient perovskite solar cells. We found that the diffusion lengths in CH3NH3PbI3 single crystals grown by a solution-growth method can exceed 175 micrometers under 1 sun (100 mW cm(-2)) illumination and exceed 3 millimeters under weak light for both electrons and holes. The internal quantum efficiencies approach 100% in 3-millimeter-thick single-crystal perovskite solar cells under weak light. These long diffusion lengths result from greater carrier mobility, longer lifetime, and much smaller trap densities in the single crystals than in polycrystalline thin films. The long carrier diffusion lengths enabled the use of CH3NH3PbI3 in radiation sensing and energy harvesting through the gammavoltaic effect, with an efficiency of 3.9% measured with an intense cesium-137 source.

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With the largest band gap energy of all commercial semiconductors, GaN has found wide application in the making of optoelectronic devices. It has also been used for photodetection such as solar blind imaging as well as ultraviolet and even X-ray detection. Unsurprisingly, the appreciable advantages of GaN over Si, amorphous silicon (a-Si:H), SiC, amorphous SiC (a-SiC), and GaAs, particularly for its radiation hardness, have drawn prompt attention from the physics, astronomy, and nuclear science and engineering communities alike, where semiconductors have traditionally been used for nuclear particle detection. Several investigations have established the usefulness of GaN for alpha detection, suggesting that when properly doped or coated with neutron sensitive materials, GaN could be turned into a neutron detection device. Work in this area is still early in its development, but GaN-based devices have already been shown to detect alpha particles, ultraviolet light, X-rays, electrons, and neutrons. Furthermore, the nuclear reaction presented by 14N(n,p)14C and various other threshold reactions indicates that GaN is intrinsically sensitive to neutrons. This review summarizes the state-of-the-art development of GaN detectors for detecting directly and indirectly ionizing radiation. Particular emphasis is given to GaN's radiation hardness under high-radiation fields.

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