Characterization of Hydrogenated Amorphous Silicon Detectors With Clinical Photon and Electron Beams

Flexible hydrogenated amorphous silicon (a-Si:H) detectors are attractive candidates for clinical dosimetry, particularly for applications requiring lightweight devices and operation without external bias. In this work, three flexible a-Si:H detector architectures are experimentally compared under clinical photon and electron beams: a conventional n-i-p diode, a charge selective contact (CSC) detector, and a very thin p-i-n diode. All detectors show excellent dose linearity under both irradiation modalities. However, large differences in sensitivity are observed at zero bias, exceeding two orders of magnitude across architectures. The conventional n-i-p device shows a response that is limited by the internal electric field, while CSC and very thin p-i-n detectors achieve sensitivities in the pC/cGy range without applied bias. Electron beams yield higher charge per unit dose than photons, compatible with a larger local energy deposition in the active layer. The results demonstrate that sensitivity in flexible a-Si:H dosimeters is governed by contact design and intrinsic layer thickness rather than by active volume alone. Taken together, the present results suggest that combining charge selective contacts with thinner intrinsic layers may represent a promising strategy to further enhance zero-bias sensitivity. These findings provide clear design guidelines for the development of flexible dosimeters for surface and transmission measurements in advanced radiotherapy.