A new silicon electron detector technology for Scanning Electron Microscopy, based on ultrashallow p+n boron-layer photodiodes, features nm-thin anodes enabling low-energy electron detection with record-high sensitivity down to 200 eV. Designs with segmented, closely-packed photodiodes and through-wafer apertures allow flexible configurations for optimal material and/or topographical contrasts. A high scanning speed is obtained by growing a well-controlled, lightly-doped, tens-of-microns-thick epi-layer for low capacitance, and by patterning a conductive grid directly on the photosensitive surface for low series resistance.