Boron-layer silicon photodiodes for high-efficiency low-energy electron detection

Silicon photodiodes for use as low-energy electron detectors have been fabricated using a pure-boron technology to form the p+-anode region. The diode I-V characteristics are ideal and uniform over the wafer with low dark currents in the range of 0.6 pA/mm2. An extremely small thickness of the front-entrance window dead layers was achieved for a 1.8 nm B-layer deposition at 700 °C. All other processing layers on the photosensitive surface were removed using selective wet-etching to the B-layer, a process which is studied here with respect to residues and pitting effects that can result from the etching of Al to the B-layer. For the most optimal photodiode, a high relative electron signal gain is obtained: 60% at 500 eV, and 74% at 1 keV. The degradation of the dark current of B-layer photodiodes is examined for 10-min-long irradiation with 1-25 keV electron energies and stable performance is observed provided that the perimeter isolation-oxide is not exposed.