Neutron Conversion Layers for Semiconductor Neutron Detectors: A Review of Materials, Thin-Film Deposition Technologies, and Performance Optimization

Semiconductor neutron detectors are compact, low-voltage alternatives to 3He-based detectors, and their detection performance hinges on the conversion layer that transforms neutrons into charged particles. Previous reviews have treated this layer as an auxiliary component rather than as a thin-film engineering problem. Here, four representative conversion materials (6LiF, 10B4C, BN, and Gd) are evaluated against five deposition technologies (magnetron sputtering, vacuum evaporation, solution-based deposition, chemical vapor deposition, and atomic layer deposition) within a four-dimensional framework of areal density, density/uniformity, conformality, and adhesion/interface quality. The comparison shows that performance differences among deposition technologies trace to their deposition mechanisms: PVD processes enable large-area planar films but lack three-dimensional conformality; CVD and ALD coat conformally, but the isotope areal densities they deliver are rarely reported and therefore remain unquantified; solution-based methods scale cheaply but lose efficiency to binder dilution and porosity. Three-dimensional microstructured architectures relax the planar self-absorption constraint, with intrinsic efficiencies well above the ~4–5% ceiling of the single-sided single-layer planar configuration, although device-level validation of conformal deposition rests on only a few reports, principally LPCVD 10B trench filling, with reported intrinsic efficiencies of 16.3 ± 1.6% and 26.1 ± 0.3%, and interfacial dead layers and radiation damage remain key reliability concerns. Magnetron-sputtered 10B4C is currently the most mature option; further progress requires cross-process thin-film benchmarking, device-level testing of conformal coating on 3D microstructures, and semiconductor-grade material quality in emerging functional-integration candidates such as h-BN.