Fast and sensitive photodiode integrated with other circuits - features an etched trench in which the optical fibre is placed and pin-diode opposite the end of the fibre

摘要

The photo-diode consists of a cathode (10) and an anode (11) contacting highly doped semiconductor regions, and an area of high resistivity for charge generation (9). The semiconductor (3) is pref. Si. The diode features at least on 2 sides vertical, or nearly vertical, parallel surfaces formed by trench walls. Light enters the diode through one of these surfaces, pref. from an optical fibre which has a thickness equivalent to the depth of the trench and is contained at a right angle to the diode surface. The diode wall next to the fibre pref. has an anti-reflection layer or layers, pref. a Si-dioxide/-nitride double layer. The region between the surfaces of the diode has surface layers, pref. more highly doped than the generation region and pref. of opposite type on the 2 sides, electrically connected with at least one electrode. Also claimed is the use of a MOS-structure, without heavier doping than the generation region and a metal or pref. polysi electrode, instead of at least one of these layers. USE/ADVANTAGE - The diodes have high sensitivity because of the use of highly doped material for the detection part together with a high drift field. The use of reflecting layers increases the apparent thickness of the region without requiring a high biasing voltage to maintain field strength, improving also the spectral response. The lowly doped region, e.g. 2x10power 14 cm-3, used for generating charge carriers can be integrated with circuits such as differential amplifiers with good yield on large area wafers because of the use of epitaxy. The diode has a low capacitance and therefore a short reaction time.