PHOTOSENSITIVE SEMICONDUCTOR DEVICE

1,231,493. Photo-electric devices. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. 28 June, 1968 [1 July, 1967], No. 30939/68. Heading H1K. A radiation-sensitive PN junction between a surface region and a wall isolated part of a layer epitaxially deposited on a substrate of opposite type is disposed above a more heavily doped zone of the same type as the layer buried in the surface of the substrate. A typical device (Fig. 2) is made by oxidizing the surface of a 3 ohm cm. P-type silicon wafer in wet oxygen conventionally forming a mask therefrom, prediffusing arsenic derived from an arsenic-doped silicon source through an aperture therein and continuing diffusion in oxygen to form an N+ zone 12, 10 Á deep. Boron is then diffused in similar manner through an aperture at the site of isolation wall 4, and after removal of the masking 0À3 ohm. cm. N-type silicon is epitaxially deposited to a depth of 10 Á. over the treated wafer face. After forming an oxide mask on the layer surface as above boron is diffused in to join up with that which has diffused outwards during epitaxial deposition to complete isolation wall 4.' P zone 5 and N+ contact zone 11 are then formed by successive masked diffusions of boron and phosphorus. Finally apertures for contacts are etched in the oxide and aluminium vapour deposited overall and shaped by photolithographic techniques to provide contacts 7, 8 with lateral extensions serving to facilitate attachment of leads or connection to other circuit elements in the wafer and to optically mask the edges of the PN junction. In a modification a further N region is diffused into zone 5 to provide an NPN structure, which with appropriately connected contacts may be used as a phototransistor or optoelectronic transistor, or as two photodiodes responding to different spectral regions connected in series or or parallel. A photothyristor is formed by providing another P region. In all cases one or more of the junctions may be a heterojunction between, for instance, A III By compounds. The junction 15 should lie more than two minority carrier diffusion lengths beneath the layer substrate 14 to prevent leakage currents.