# US 10,374,071 B2 · Heterojunction bipolar transistor > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,374,071 B2 - Document ID: US10374071B2 - Status: Granted - Kind: B2 - Application number: 15/598,456 - Filed: 2017-05-18 - Published: 2018-01-11 - Granted: 2019-08-06 - Earliest claimed: 2016-07-11 - Assignees: Murata Manufacturing Co., Ltd. - Applicants: Murata Manufacturing Co., Ltd. - Inventors: Yasunari Umemoto; Shigeki Koya; Shigeru Yoshida; Isao Obu - Web page: https://patentgrep.com/patent/US10374071B2 ## CPC - H10D 10/821: {Vertical heterojunction BJTs} - H10D 10/021: {of heterojunction BJTs [HBT]} - H10D 62/136: {of heterojunction BJTs (vertical heterojunction BJTs having one or more non-monocrystalline Group IV elements H10D10/861)} - H10D 62/8181: {Structures having no potential periodicity in the vertical direction, e.g. lateral superlattices or lateral surface superlattices [LSS]} - H10D 62/85: being Group III-V materials, e.g. GaAs - H10D: INORGANIC ELECTRIC SEMICONDUCTOR DEVICES ## Abstract A heterojunction bipolar transistor includes a collector layer, a base layer, an emitter layer, and a semiconductor layer that are laminated in this order, wherein the emitter layer includes a first region having an upper surface on which the semiconductor layer is laminated, and a second region being adjacent to the first region and having an upper surface that is exposed, and the first and second regions of the emitter layer have higher doping concentrations in portions near the upper surfaces than in portions near an interface between the emitter layer and the base layer. ## Claims ### Claim 1 A heterojunction bipolar transistor comprising: a collector layer, a base layer, an emitter layer, and a semiconductor layer that are laminated in this order, wherein the emitter layer includes a first region having an upper surface on which the semiconductor layer is laminated, and a second region being adjacent to the first region and having an upper surface that is exposed with respect to the semiconductor layer, the first and second regions of the emitter layer have higher doping concentrations in portions near the upper surfaces than in portions near an interface between the emitter layer and the base layer so as to avoid generation of a conductive region in the second region of the emitter layer and to maintain the second region of the emitter layer to be fully depleted, the emitter layer contains a same main component in both the portions near the upper surfaces and the portions near an interface between the emitter layer and the base layer, and the portions near the upper surfaces have lower doping concentrations than the semiconductor layer. ### Claim 2 (depends on 1) The heterojunction bipolar transistor according to claim 1, wherein the emitter layer has a thickness of 20 nm or more and 60 nm or less. ### Claim 3 (depends on 1) The heterojunction bipolar transistor according to claim 1, wherein the emitter layer has a thickness of 20 nm or more and 40 nm or less. ### Claim 4 (depends on 1) The heterojunction bipolar transistor according to claim 1, wherein the first and second regions of the emitter layer include a plurality of layers including a lower layer and an upper layer that is laminated nearer to the semiconductor layer than the lower layer, and the upper layer has a doping concentration higher than a doping concentration of the lower layer. ### Claim 5 (depends on 4) The heterojunction bipolar transistor according to claim 4, wherein the upper layer has a thickness of 5 nm or more and 26/(t/30) nm or less where t represents a thickness of the emitter layer. ### Claim 6 (depends on 4) The heterojunction bipolar transistor according to claim 4, wherein the upper layer has a doping concentration of 7.5×1017 cm−3 or more. ### Claim 7 (depends on 4) The heterojunction bipolar transistor according to claim 4, wherein the first and second regions of the emitter layer include an intermediate layer between the lower layer and the upper layer, and the intermediate layer has a doping concentration higher than the doping concentration of the lower layer and lower than the doping concentration of the upper layer. ### Claim 8 (depends on 1) The heterojunction bipolar transistor according to claim 1, wherein the first and second regions of the emitter layer include a concentration gradient layer whose doping concentration continuously changes from a base layer side toward a semiconductor layer side of the emitter layer. ### Claim 9 (depends on 7) The heterojunction bipolar transistor according to claim 7, wherein the emitter layer includes, from a base layer side toward a semiconductor layer side of the emitter layer, a lower region, an intermediate region, and an upper region, and the intermediate region has a higher gradient of a doping concentration than the lower region and the upper region. ### Claim 10 (depends on 8) The heterojunction bipolar transistor according to claim 8, wherein the emitter layer includes, from a base layer side toward a semiconductor layer side of the emitter layer, a lower region, an intermediate region, and an upper region, and the intermediate region has a higher gradient of a doping concentration than the lower region and the upper region. ### Claim 11 (depends on 4) The heterojunction bipolar transistor according to claim 4, satisfying Φ s ≥ qN dH ⁢ t H ⁢ 2 2 ⁢ ⁢ ɛ + qN d ⁢ ⁢ L ⁡ ( t ⁢ 2 - t H ⁢ 2 ) 2 ⁢ ⁢ ɛ where t represents a thickness of the emitter layer; tH represents a thickness of the upper layer; NdL represents the doping concentration of the lower layer; NdH represents the doping concentration of the upper layer; Φs represents a surface potential of the emitter layer; ε represents a dielectric constant of the emitter layer; and q represents an electron elementary charge. ### Claim 12 (depends on 1) The heterojunction bipolar transistor according to claim 1, wherein the second region of the emitter layer is covered by an insulating film. ### Claim 13 (depends on 12) The heterojunction bipolar transistor according to claim 12, wherein the insulating film includes a SiN film. ### Claim 14 (depends on 1) The heterojunction bipolar transistor according to claim 1, wherein at least one main component of the semiconductor layer differs from main components of the emitter layer. ### Claim 15 (depends on 1) The heterojunction bipolar transistor according to claim 1, wherein the emitter layer is InGaP. ### Claim 16 (depends on 15) The heterojunction bipolar transistor according to claim 15, wherein the semiconductor layer has a lower region contacting the emitter layer, and the lower region is GaAs. ### Claim 17 (depends on 4) The heterojunction bipolar transistor according to claim 4, wherein at least one main component of the semiconductor layer differs from main components of the emitter layer. ### Claim 18 (depends on 4) The heterojunction bipolar transistor according to claim 4, wherein the emitter layer is InGaP. ### Claim 19 (depends on 18) The heterojunction bipolar transistor according to claim 18, wherein the semiconductor layer has a lower region contacting the emitter layer, and the lower region is GaAs. ### Claim 20 (depends on 1) The heterojunction bipolar transistor according to claim 1, wherein a doping concentration of the portions near the upper surfaces is 3×1018 cm−3 or less. ### Claim 21 (depends on 1) The heterojunction bipolar transistor according to claim 1, wherein a doping concentration of the portions near the upper surfaces is 7.5×1017 cm−3 or more and 3×1018 cm−3 or less.