# US 8,569,800 B2 · Field effect transistor > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,569,800 B2 - Document ID: US8569800B2 - Status: Granted - Kind: B2 - Application number: 13/076,980 - Filed: 2011-03-31 - Published: 2011-10-06 - Granted: 2013-10-29 - Earliest claimed: 2010-03-31 - Assignees: Furukawa Electric Co., Ltd. - Applicants: Nariaki Ikeda; Takuya Kokawa; Masayuki Iwami; Sadahiro Kato - Inventors: Nariaki Ikeda; Takuya Kokawa; Masayuki Iwami; Sadahiro Kato - Web page: https://patentgrep.com/patent/US8569800B2 ## CPC - H10D 62/151: {of IGFETs (of IGFETs having LDD or DDD structure H10D30/601; of thin film transistors H10D30/6713)} - H10D 30/015: {of FETs having heterojunction interface channels or heterojunction gate electrodes, e.g. HEMT} - H10D 30/4755: {having wide bandgap charge-carrier supplying layers, e.g. modulation doped HEMTs such as n-AlGaAs/GaAs HEMTs} - H10D 64/511: {for IGFETs} - H10D 62/8503: {Nitride Group III-V materials, e.g. AlN or GaN} - H10D 64/693: {the insulator comprising nitrogen, e.g. nitrides, oxynitrides or nitrogen-doped materials} - H10P 14/24: using chemical vapour deposition [CVD] - H10P 14/2905: {Silicon, silicon germanium or germanium} - H10P 14/3216: {Nitrides} - H10P 14/3416: {Nitrides} - H10P 14/3444: {P-type} - H10D: INORGANIC ELECTRIC SEMICONDUCTOR DEVICES - H10P: GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10 ## Abstract A field effect transistor includes: a buffer layer that is formed on a substrate; a high resistance layer or a foundation layer that is formed on the buffer layer; a carbon-containing carrier concentration controlling layer that is formed on the high resistance layer or the foundation layer; a carrier traveling layer that is formed on the carrier concentration controlling layer; a carrier supplying layer that is formed on the carrier traveling layer; a recess that is formed from the carrier supplying layer up to a predetermined depth; source/drain electrodes that are formed on the carrier supplying layer with the recess intervening therebetween; a gate insulating film that is formed on the carrier supplying layer so as to cover the recess; and a gate electrode that is formed on the gate insulating film in the recess. ## Claims ### Claim 1 A field effect transistor made of a nitride compound semiconductor, the field effect transistor comprising: a substrate; a buffer layer that is formed on the substrate; a high resistance layer or a foundation layer that is formed on the buffer layer; a carrier concentration controlling layer containing carbon that is formed on the high resistance layer or the foundation layer; a carrier traveling layer that is formed on the carrier concentration controlling layer; a carrier supplying layer that is formed on the carrier traveling layer; a recess that extends from the carrier supplying layer into the high resistance layer or the foundation layer; a source electrode and a drain electrode that are formed on the carrier supplying layer with the recess intervening therebetween; a gate insulating film that is formed on the carrier supplying layer so as to cover the recess; and a gate electrode that is formed on the gate insulating film in the recess, wherein the carrier traveling layer includes a two-dimensional electron gas generated therein due to a difference of bandgap energy between the carrier traveling layer and the carrier supplying layer. ### Claim 2 (depends on 1) The field effect transistor according to claim 1, wherein a carbon concentration of the carrier concentration controlling layer is from 5×1017 cm−3 to 5×1019 cm−3. ### Claim 3 (depends on 1) The field effect transistor according to claim 1, wherein a carrier concentration of the two-dimensional electron gas generated in the carrier traveling layer is 1×1012 cm−2 to 1×1013 cm−2. ### Claim 4 (depends on 1) The field effect transistor according to claim 1, wherein the high resistance layer or the foundation layer is made of GaN containing Mg or carbon. ### Claim 5 (depends on 1) The field effect transistor according to claim 1, wherein the carrier traveling layer is made of undoped GaN and has a thickness of 2 nm or more and 500 nm or less. ### Claim 6 (depends on 1) The field effect transistor according to claim 1, wherein the carrier supplying layer is made of AlGaN having an Al composition ratio of 0.01 to 0.99 and a thickness of 1 nm or more and 50 nm or less. ### Claim 7 (depends on 1) The field effect transistor according to claim 1, further comprising a heterojunction forming layer that is formed between (i) the buffer layer and (ii) the high resistance layer or the foundation layer and that has a bandgap energy different from that of the high resistance layer or the foundation layer. ### Claim 8 (depends on 7) The field effect transistor according to claim 7, wherein the heterojunction forming layer is made of AlGaN having an Al composition ratio of 0.01 to 0.5. ### Claim 9 (depends on 1) The field effect transistor according to claim 1, wherein a carbon concentration of the carrier concentration controlling layer is decreased in a monotonous manner from the high resistance layer or the foundation layer side toward the carrier traveling layer side. ### Claim 10 (depends on 1) The field effect transistor according to claim 1, wherein the carrier traveling layer is made of GaN containing carbon with a concentration of the carbon lower than 5×1017 cm−3. ### Claim 11 A field effect transistor made of a nitride compound semiconductor, the field effect transistor comprising: a substrate; a buffer layer that is formed on the substrate; a high resistance layer or a foundation layer that is formed on the buffer layer; a carrier concentration controlling layer containing carbon that is formed on the high resistance layer or the foundation layer; a carrier traveling layer that is formed on the carrier concentration controlling layer; a carrier supplying layer that is formed on the carrier traveling layer; a recess formed at least in the carrier supplying layer and the carrier traveling layer; a source electrode and a drain electrode that are formed on the carrier supplying layer with the recess intervening therebetween; a gate insulating film that is formed on the carrier supplying layer so as to cover the recess; and a gate electrode that is formed on the gate insulating film in the recess, wherein the carrier traveling layer includes a two-dimensional electron gas generated therein due to a difference of bandgap energy between the carrier traveling layer and the carrier supplying layer, and a carbon concentration of the carrier concentration controlling layer is from 5×1017 cm−3 to 5×1019 cm−3. ### Claim 12 (depends on 11) The field effect transistor according to claim 11, wherein a carrier concentration of the two-dimensional electron gas generated in the carrier traveling layer is 1×1012 cm−2 to 1×1013 cm−2. ### Claim 13 (depends on 11) The field effect transistor according to claim 11, wherein the high resistance layer or the foundation layer is made of GaN containing Mg or carbon. ### Claim 14 (depends on 11) The field effect transistor according to claim 11, wherein the carrier traveling layer is made of undoped GaN and has a thickness of 2 nm or more and 500 nm or less. ### Claim 15 (depends on 11) The field effect transistor according to claim 11, wherein the carrier supplying layer is made of AlGaN having an Al composition ratio of 0.01 to 0.99 and a thickness of 1 nm or more and 50 nm or less. ### Claim 16 (depends on 11) The field effect transistor according to claim 11, further comprising a heterojunction forming layer that is formed between (i) the buffer layer and (ii) the high resistance layer or the foundation layer and that has a bandgap energy different from that of the high resistance layer or the foundation layer. ### Claim 17 (depends on 16) The field effect transistor according to claim 16, wherein the heterojunction forming layer is made of AlGaN having an Al composition ratio of 0.01 to 0.5. ### Claim 18 (depends on 11) The field effect transistor according to claim 11, wherein a carbon concentration of the carrier concentration controlling layer is decreased in a monotonous manner from the high resistance layer or the foundation layer side toward the carrier traveling layer side. ### Claim 19 (depends on 11) The field effect transistor according to claim 11, wherein the recess extends downward from the carrier supplying layer into the high resistance layer or the foundation layer. ### Claim 20 (depends on 11) The field effect transistor according to claim 11, wherein the carrier traveling layer is made of GaN containing carbon with a concentration of the carbon lower than 5×1017 cm−3. ### Claim 21 (depends on 1) The field effect transistor according to claim 1, wherein the two-dimensional electron gas is generated in the carrier traveling layer near an interface between the carrier traveling layer and the carrier supplying layer.