# US 5,710,435 A · Photomultiplier having a photocathode comprised of semiconductor material > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,710,435 A - Document ID: US5710435A - Status: Granted - Kind: A - Application number: 08/580,057 - Filed: 1995-12-20 - Granted: 1998-01-20 - Earliest claimed: 1994-12-21 - Assignees: Hamamatsu Photonics K.K. - Inventors: Minoru Niigaki; Toru Hirohata; Tomoko Suzuki; Masami Yamada - Web page: https://patentgrep.com/patent/US5710435A ## CPC - H01J 1/34: Photo-emissive cathodes (H01J1/35 takes precedence) - H01J 43/08: Cathode arrangements (construction of photo cathodes H01J40/06, H01J40/16, H01J47/00, H01J49/08) - H01J 2201/3423: Semiconductors, e.g. GaAs, NEA emitters - H01J: ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS (spark-gaps H01T; electric arc lamps H05B31/00; particle accelerators H05H) ## Abstract A photoelectric emission surface which is excellent in stability and reproducibility of photoelectric conversion characteristics and has a structure capable of obtaining a high photosensitivity is provided. A predetermined voltage is applied between an upper surface electrode and a lower surface electrode by a battery. Upon application of this voltage, a p-n junction formed between a contact layer and an electron emission layer is reversely biased. A depletion layer extends from the p-n junction into the photoelectric emission surface, and an electric field is formed in the electron emission layer and a light absorbing layer in a direction for accelerating photoelectrons. When incident light is absorbed in the light absorbing layer to excite photoelectrons, the photoelectrons are accelerated by the electric field toward the emission surface. The photoelectrons obtain an energy upon this electric field acceleration, and are transited, in the electron emission layer, to a conduction band at a higher energy level, and emitted into a vacuum. ## Claims ### Claim 1 A photomultiplier having a photocathode for emitting electrons in correspondence with light incident on said photocathode, wherein said photocathode comprises: (a) a substrate of p-type InP, which has a carrier concentration of not less than 1.times.10.sup.18 cm.sup.-3 ; (b) a first layer of p-type InGaAsP, which has a carrier concentration of not more than 5.times.10.sup.16 cm.sup.-3, being in contact with said substrate; (c) a second layer of p-type InP, which has a carrier concentration of not more than 5.times.10.sup.16 cm.sup.-3, being in contact with said first layer; (d) a third layer of n-type InP, which has a carrier concentration of not less than 1.times.10.sup.18 cm.sup.-3, being in contact with said second layer; (e) an upper surface electrode having an opening, being in contact with said third layer; (f) an active layer for decreasing a work function of said second layer, being in contact with a remaining exposed surface of said second layer; and (g) a lower surface electrode being in contact with said substrate. ### Claim 2 (depends on 1) A photomultiplier according to claim 1, wherein said active layer is comprised of Cs. ### Claim 3 (depends on 1) A photomultiplier according to claim 1, wherein said active layer is made of a material selected from the group consisting of CsO and CsF. ### Claim 4 (depends on 1) A photomultiplier according to claim 1, further comprising: a) a sealed vessel which accommodates said photocathode; b) a first stage dynode arranged in said sealed vessel; c) a focusing electrode arranged between said first stage dynode and said photocathode; d) a plurality of dynodes including an ultimate stage dynode and arranged contiguously from said first stage dynode; and e) an anode arranged near said ultimate stage dynode. ### Claim 5 (depends on 1) A photomultiplier according to claim 1, wherein a potential higher than that of said lower surface electrode is applied to said upper surface electrode. ### Claim 6 (depends on 4) A photomultiplier according to claim 4, further comprising an internal conductive film coated on an inner wall of said sealed vessel to surround a space between said focusing electrode and said photocathode and electrically connected to said upper surface electrode. ### Claim 7 (depends on 1) A photomultiplier according to claim 1, further comprising: a) a sealed vessel which accommodates said photocathode, having a predetermined portion through which the light is input to said photocathode; and b) a transparent electrode coated on an inner surface of said predetermined portion of said sealed vessel and electrically connected to said lower surface electrode. ### Claim 8 A photomultiplier having a photocathode for emitting electrons in correspondence with light incident on said photocathode, wherein said photocathode comprises: (a) a substrate of a first conductivity type semiconductor, having a predetermined carrier concentration; (b) a first layer of a first conductivity type semiconductor, having a first carrier concentration, being in contact with said substrate; (c) a second layer of a first conductivity type semiconductor, having a second carrier concentration, being in contact with said first layer; (d) a third layer of a second conductivity type semiconductor, having a third carrier concentration, being in contact with said second layer; (e) an upper surface electrode being in contact with said third layer; (f) an active layer for decreasing a work function of said second layer, being in contact with a remaining exposed surface of said second layer; and (g) a lower surface electrode being in contact with said substrate. ### Claim 9 (depends on 8) A photomultiplier according to claim 8, wherein an energy bandgap of said substrate is larger than that of said first layer, and the energy bandgap of said second layer is larger than that of said first layer. ### Claim 10 (depends on 8) A photomultiplier according to claim 8, wherein an energy bandgap of said third layer is equal to that of said second layer. ### Claim 11 (depends on 8) A photomultiplier according to claim 8, wherein the third concentration is higher than 1.times.10.sup.18 cm.sup.-3. ### Claim 12 (depends on 8) A photomultiplier according to claim 8, wherein said substrate is p-type InP, the predetermined carrier concentration is not less than 1.times.10.sup.18 cm.sup.-3, said first layer is p-type InGaAsP, the first carrier concentration is not more than 5.times.10.sup.16 cm.sup.-3, said second layer is p-type InP, the second carrier concentration is not more than 5.times.10.sup.16 cm.sup.-3, said third layer is n-type InP, and the third carrier concentration is not less than 1.times.10.sup.18 cm.sup.-3. ### Claim 13 (depends on 8) A photomultiplier according to claim 8, wherein said active layer is comprised of Cs. ### Claim 14 (depends on 8) A photomultiplier according to claim 8, wherein said active layer is comprised of a material selected from the group consisting of CsO and CsF. ### Claim 15 (depends on 8) A photomultiplier according to claim 8, further comprising: a) a sealed vessel for accommodating said photocathode; b) a first stage dynode arranged in said sealed vessel; c) a focusing electrode arranged between said first stage dynode and said photocathode; d) a plurality of dynodes including an ultimate stage dynode and arranged contiguously from said first stage dynode; and e) an anode arranged near said ultimate stage dynode. ### Claim 16 A photocathode comprising: (a) a substrate of a first conductivity type semiconductor, and having a predetermined carrier concentration; (b) a first layer of a first conductivity type semiconductor, having a first carrier concentration, being in contact with said substrate; (c) a second layer a first conductivity type semiconductor, having a second carrier concentration, being in contact with said first layer; (d) a third layer consisting of a semiconductor of a second conductivity type, having a third carrier concentration, being in contact with said second layer; (e) an upper surface electrode being in contact with said third layer; (f) an active layer for decreasing a work function of said second layer, being in contact with a remaining exposed surface of said second layer; and (g) a lower surface electrode being in contact with said substrate. ### Claim 17 (depends on 16) A photocathode according to claim 16, wherein an energy bandgap of said substrate is larger than that of said first layer, and the energy bandgap of said second layer is larger than that of said first layer. ### Claim 18 (depends on 16) A photocathode according to claim 16, wherein an energy bandgap of said third layer is equal to that of said second layer. ### Claim 19 (depends on 16) A photocathode according to claim 16, wherein the third concentration is higher than 1.times.10.sup.18 cm.sup.-3. ### Claim 20 (depends on 16) A photocathode according to claim 16, wherein said substrate is p-type InP, the predetermined carrier concentration is not less than 1.times.10.sup.18 cm.sup.-3, said first layer is p-type InGaAsP, the first carrier concentration is not more than 5.times.10.sup.16 cm.sup.-3, said second layer is p-type InP, the second carrier concentration is not more than 5.times.10.sup.16 cm.sup.-3, said third layer is n-type InP, and the third carrier concentration is not less than 1.times.10.sup.18 cm.sup.-3. ### Claim 21 (depends on 16) A photocathode according to claim 16, wherein said active layer is Cs. ### Claim 22 (depends on 16) A photocathode according to claim 16, wherein said active layer is comprised of a material selected from the group consisting of CsO and CsF. ### Claim 23 (depends on 16) A photocathode according to claim 16, wherein said upper surface electrode having a point contact with said third layer.