Silicon photodiodes for high-efficiency low-energy electron detection

Solid-state electron detectors have been fabricated using a p⁺n silicon photodiode where the p⁺ region is created by a chemical-vapor deposition (CVD) surface doping from diborane B₂H₆. The as-obtained nm-deep p-type layer is resistant to conventional metal etchants, which allows elimination of both entrance contacts and protection layers from the photosensitive surface. This approach lowers the dead layer energy loss, while keeping near theoretical efficiency at high electron energies. The photodiodes have outstanding performance in terms of electron signal gain at low energies achieving 60% and 74% of the theoretical gain value at 500 eV and 1 keV, respectively. The ideal I-V characteristics and the small over-the-wafer spread of the dark current indicate a defect-free p⁺n junction, as well as a reliable and reproducible process.