Improvements to amorphous silicon radiation detectors by doping profile changes

Application of thick (~50 μm) amorphous Si p-i-n diodes as direct radiation detectors for minimum ionizing particles is hampered by the need to apply large bias voltages in order fully to deplete the detecting intrinsic layer, which typically contains 5-10×10¹⁴ ionizable dangling bonds per cm³. A voltage of about 1 kV is required to deplete a 50-μm-thick detector and a large field (500 kV/cm) builds up at the p/i contact. This leads to an undesirable leakage current and related noise. These problems can be mitigated by addition of thin doped layers within the intrinsic layers. By insertion of thin p-type layers at equal intervals within the intrinsic layer, the required depletion voltage can be reduced by a factor of at least 1/(n+1), where n is the number of layers inserted. This principle is demonstrated for devices approximately 12 μm in thickness. Electron losses within the p-type layer can be kept to a minimum by choice of a low doping concentration for the introduced p-layers. The electric field at the contacts can also be reduced by doped layers buried in the intrinsic layer close to the main p/i and i/n interfaces