Solid-State Electronics, Vol.65-66, 38-44, 2011
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/mm(2). An extremely small thickness of the front-entrance window dead layers was achieved for a 1.8 nm B-layer deposition at 700 degrees 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 key electron energies and stable performance is observed provided that the perimeter isolation-oxide is not exposed. (C) 2011 Elsevier Ltd. All rights reserved.
Keywords:Silicon photodiodes;Electron detection;Low-energy electrons;Boron deposition;Ultrashallow junctions;Responsivity;Electron signal gain;Electron irradiation;Dark current degradation