{"id":{"repo_id":"cambridge","oai_identifier":"oai:www.repository.cam.ac.uk:1810/390593"},"canonical_url":"https://search.dev.ndltd.org/etd/cambridge/oai:www.repository.cam.ac.uk:1810/390593","repository":{"repo_id":"cambridge","name":"Cambridge University","base_url":"https://api.repository.cam.ac.uk/server/oai/request"},"display":{"title":"Physics and Engineering of Photoelectric Tunable-step Terahertz Detectors Based on High Mobility III-V Semiconductor Structures","abstract":"The terahertz (THz) region is described as electromagnetic waves within the frequency range of v = 0.1–10 THz, lying between the microwave and infrared regions. Sandwiched by conventional electronic and photonic regions, the THz region has been one of the less explored areas for a long time, known as the ‘THz gap’, due to a lack of efficient, cheap, and easy-to-use THz sources and detectors. To shrink the ‘THz gap’, efficient THz detectors with high responsivity, low noise, fast response speed and room operating temperature are of paramount importance. Field effect transistors (FETs) based on two-dimensional electron gases (2DEGs) have shown promising performance as THz detectors over the past few decades. In 2022, a quantum, collision-free phenomenon, the in-plane photoelectric (IPPE) effect, was discovered as a novel detection mechanism in gated 2DEGs, and devices based on this effect, photoelectric tunable-step (PETS) THz detectors, have been proposed as sensitive THz detectors. This thesis focuses on PETS THz detectors that operate based on the in-plane photoelectric effect. The dependence of the IPPE effect on parameters, including antenna geometry, material, heterostructure design, operating temperature, illumination condition, etc., is systematically investigated for room-temperature PETS THz detectors with high responsivity and fast response speed. Firstly, a systematic study on AlGaAs/GaAs-based PETS THz detectors is carried out. A PETS THz detector with a simple dipole antenna is studied as a model system for universal guidance. From the theoretical expression of the IPPE effect, two figures of merit within the 2DEG, the maximum electric field and the radiation-induced ac-potential difference, jointly determine the photoreponse of PETS THz detectors. Dimensions of the dipole-antenna PETS THz detector are optimized through numerical simulation to tune the resonant frequency of the device to the target frequency, and to maximize the two figures of merit. Based on the simulation results, a dipole-antenna PETS THz detector with optimized dimensions is fabricated and characterized. The photoreponse, conductance and response speed are measured at 8 K. It is demonstrated that the optimized dipole-antenna PETS THz detector shows a higher responsivity and a lower noise equivalent power than the previously reported AlGaAs/GaAs-based bowtie-antenna PETS THz detector. The temperature-dependence measurement shows that AlGaAs/GaAs-based PETS THz detectors have a capability of operating up to 75 K. The influence of asymmetric mesa structure is also investigated and indicates that asymmetry of the mesa structure leads to asymmetry of the photoresponse even through the gates on top of the mesa are symmetric. The influence of infrared illumination on AlGaAs/GaAs-based PETS THz detectors is then investigated to enhance device performance. A specialized setup, comprising an RF PCB, a two-piece copper holder that can be easily assembled and an infrared LED with an IR centre-wavelength of λ = 940 nm, is utilized to expose the PETS THz detector to THz radiation from the top while illuminating it with an infrared LED from the backside. Performance of a bowtie-antenna PETS THz detector, including the photoresponse, conductance, electron density, gate leakage, etc., is characterized following incremental illumination in controlled small doses. The persistent photoconductivity effect with a two-stage growth of the electron density in the 2DEG is observed, but there is no obvious parallel conductance based on the magnetotransport measurement. To explain the behaviour of the PETS THz detector under infrared illumination, a hypothesis based on DX-centre excitation is proposed. This thesis demonstrates, for the first time, a room-temperature PETS THz detector based on an AlGaN/GaN heterostructure. It operates at 1.9 THz, higher than that of most previously reported room-temperature AlGaN/GaN-based THz FETs, as the responsivity decreases dramatically for antenna-coupled FETs at higher frequencies. Photoreponse of the device is characterized in detail at both cryogenic temperature (8 K) and room temperature (295 K). The temperature dependence of the AlGaN/GaN-based PETS THz detector reveals that its responsivity exhibits an exponential decline with temperature, similar to the behaviour observed in AlGaAs/GaAs-based devices but with a smaller decay rate. Therefore, AlGaN/GaN-based devices achieve room-temperature operation, while AlGaAs/GaAs-based devices are not capable of operating beyond 75 K. The theoretical temperature dependence of the in-plane photoelectric effect is also investigated. The demonstration of the IPPE effect at room temperature opens wide opportunities for terahertz detection using quantum effects, and its observation in the AlGaN/GaN system suggests its universality in 2D electron gases. Collectively, the findings of this thesis deepen the understanding of the in-plane photoelectric effect and provide a universal guidance for the design of PETS THz detectors with high responsivity, fast response speed and room temperature operation.","abstract_html":"The terahertz (THz) region is described as electromagnetic waves within the frequency range of v = 0.1–10 THz, lying between the microwave and infrared regions. Sandwiched by conventional electronic and photonic regions, the THz region has been one of the less explored areas for a long time, known as the ‘THz gap’, due to a lack of efficient, cheap, and easy-to-use THz sources and detectors. To shrink the ‘THz gap’, efficient THz detectors with high responsivity, low noise, fast response speed and room operating temperature are of paramount importance. Field effect transistors (FETs) based on two-dimensional electron gases (2DEGs) have shown promising performance as THz detectors over the past few decades. In 2022, a quantum, collision-free phenomenon, the in-plane photoelectric (IPPE) effect, was discovered as a novel detection mechanism in gated 2DEGs, and devices based on this effect, photoelectric tunable-step (PETS) THz detectors, have been proposed as sensitive THz detectors. This thesis focuses on PETS THz detectors that operate based on the in-plane photoelectric effect. The dependence of the IPPE effect on parameters, including antenna geometry, material, heterostructure design, operating temperature, illumination condition, etc., is systematically investigated for room-temperature PETS THz detectors with high responsivity and fast response speed. Firstly, a systematic study on AlGaAs/GaAs-based PETS THz detectors is carried out. A PETS THz detector with a simple dipole antenna is studied as a model system for universal guidance. From the theoretical expression of the IPPE effect, two figures of merit within the 2DEG, the maximum electric field and the radiation-induced ac-potential difference, jointly determine the photoreponse of PETS THz detectors. Dimensions of the dipole-antenna PETS THz detector are optimized through numerical simulation to tune the resonant frequency of the device to the target frequency, and to maximize the two figures of merit. Based on the simulation results, a dipole-antenna PETS THz detector with optimized dimensions is fabricated and characterized. The photoreponse, conductance and response speed are measured at 8 K. It is demonstrated that the optimized dipole-antenna PETS THz detector shows a higher responsivity and a lower noise equivalent power than the previously reported AlGaAs/GaAs-based bowtie-antenna PETS THz detector. The temperature-dependence measurement shows that AlGaAs/GaAs-based PETS THz detectors have a capability of operating up to 75 K. The influence of asymmetric mesa structure is also investigated and indicates that asymmetry of the mesa structure leads to asymmetry of the photoresponse even through the gates on top of the mesa are symmetric. The influence of infrared illumination on AlGaAs/GaAs-based PETS THz detectors is then investigated to enhance device performance. A specialized setup, comprising an RF PCB, a two-piece copper holder that can be easily assembled and an infrared LED with an IR centre-wavelength of λ = 940 nm, is utilized to expose the PETS THz detector to THz radiation from the top while illuminating it with an infrared LED from the backside. Performance of a bowtie-antenna PETS THz detector, including the photoresponse, conductance, electron density, gate leakage, etc., is characterized following incremental illumination in controlled small doses. The persistent photoconductivity effect with a two-stage growth of the electron density in the 2DEG is observed, but there is no obvious parallel conductance based on the magnetotransport measurement. To explain the behaviour of the PETS THz detector under infrared illumination, a hypothesis based on DX-centre excitation is proposed. This thesis demonstrates, for the first time, a room-temperature PETS THz detector based on an AlGaN/GaN heterostructure. It operates at 1.9 THz, higher than that of most previously reported room-temperature AlGaN/GaN-based THz FETs, as the responsivity decreases dramatically for antenna-coupled FETs at higher frequencies. Photoreponse of the device is characterized in detail at both cryogenic temperature (8 K) and room temperature (295 K). The temperature dependence of the AlGaN/GaN-based PETS THz detector reveals that its responsivity exhibits an exponential decline with temperature, similar to the behaviour observed in AlGaAs/GaAs-based devices but with a smaller decay rate. Therefore, AlGaN/GaN-based devices achieve room-temperature operation, while AlGaAs/GaAs-based devices are not capable of operating beyond 75 K. The theoretical temperature dependence of the in-plane photoelectric effect is also investigated. The demonstration of the IPPE effect at room temperature opens wide opportunities for terahertz detection using quantum effects, and its observation in the AlGaN/GaN system suggests its universality in 2D electron gases. Collectively, the findings of this thesis deepen the understanding of the in-plane photoelectric effect and provide a universal guidance for the design of PETS THz detectors with high responsivity, fast response speed and room temperature operation.","abstract_has_math":false,"creators":["Chen, Ran"],"institution":"University of Cambridge","degree_name":"Doctor of Philosophy (PhD)","degree_level":"Doctoral","degree_discipline":null,"degree_department":null,"school":null,"contributors":[],"advisors":["Ritchie, David","Michailow, Wladislaw"],"committee_chairs":[],"committee_members":[],"year":2025,"date_issued":"2025-08-04","date_published":"2025-08-04","updated_at":"2026-07-22T22:24:07Z","subjects":["Terahertz technology","Far-infrared detection","Two-dimensional electron gas","In-plane photoelectric effect","Photoelectric tunable-step detector","AlGaAs/GaAs heterostructure","AlGaN/GaN heterostructure"],"languages":["eng"],"rights":[],"rights_urls":["https://www.repository.cam.ac.uk/bitstreams/67dde331-ccf3-436b-aede-674eb176761b/download","http://purl.org/NET/rdflicense/allrightsreserved"],"identifier_entries":[]},"links":{"outbound_url":"https://doi.org/10.17863/CAM.122146","outbound_label":"DOI","outbound_source":"dc:identifier.doi"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.advisor","label":"Advisor","values":["Ritchie, David","Michailow, Wladislaw"]},{"key":"dc:creator","label":"Author","values":["Chen, Ran"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.issued","label":"Date","values":["2025-08-04"]},{"key":"dc:publisher.institution","label":"Dc Publisher Institution","values":["University of Cambridge"]},{"key":"dc:relation.isreferencedby.uri","label":"Dc Relation Isreferencedby URI","values":["https://www.repository.cam.ac.uk/handle/1810/390593"]},{"key":"dc:type","label":"Dc Type","values":["Thesis"]},{"key":"dc:type.qualificationlevel","label":"Dc Type Qualificationlevel","values":["Doctoral"]},{"key":"dc:type.qualificationname","label":"Dc Type Qualificationname","values":["Doctor of Philosophy (PhD)"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Terahertz technology","Far-infrared detection","Two-dimensional electron gas","In-plane photoelectric effect","Photoelectric tunable-step detector","AlGaAs/GaAs heterostructure","AlGaN/GaN heterostructure"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["eng"]},{"key":"dc:rights","label":"Dc Rights","values":["https://www.repository.cam.ac.uk/bitstreams/67dde331-ccf3-436b-aede-674eb176761b/download","http://purl.org/NET/rdflicense/allrightsreserved"]},{"key":"dc:rights.embargodate","label":"Dc Rights Embargodate","values":["2026-10-10"]},{"key":"dc:rights.embargotype","label":"Dc Rights Embargotype","values":["embargo"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.doi","label":"DOI","values":["https://doi.org/10.17863/CAM.122146"]},{"key":"dc:identifier.uri","label":"Identifier URI","values":["https://www.repository.cam.ac.uk/bitstreams/db9af708-ceac-49aa-9040-d570970b012a/download"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["The terahertz (THz) region is described as electromagnetic waves within the frequency range of v = 0.1–10 THz, lying between the microwave and infrared regions. Sandwiched by conventional electronic and photonic regions, the THz region has been one of the less explored areas for a long time, known as the ‘THz gap’, due to a lack of efficient, cheap, and easy-to-use THz sources and detectors. To shrink the ‘THz gap’, efficient THz detectors with high responsivity, low noise, fast response speed and room operating temperature are of paramount importance. Field effect transistors (FETs) based on two-dimensional electron gases (2DEGs) have shown promising performance as THz detectors over the past few decades. In 2022, a quantum, collision-free phenomenon, the in-plane photoelectric (IPPE) effect, was discovered as a novel detection mechanism in gated 2DEGs, and devices based on this effect, photoelectric tunable-step (PETS) THz detectors, have been proposed as sensitive THz detectors. This thesis focuses on PETS THz detectors that operate based on the in-plane photoelectric effect. The dependence of the IPPE effect on parameters, including antenna geometry, material, heterostructure design, operating temperature, illumination condition, etc., is systematically investigated for room-temperature PETS THz detectors with high responsivity and fast response speed. Firstly, a systematic study on AlGaAs/GaAs-based PETS THz detectors is carried out. A PETS THz detector with a simple dipole antenna is studied as a model system for universal guidance. From the theoretical expression of the IPPE effect, two figures of merit within the 2DEG, the maximum electric field and the radiation-induced ac-potential difference, jointly determine the photoreponse of PETS THz detectors. Dimensions of the dipole-antenna PETS THz detector are optimized through numerical simulation to tune the resonant frequency of the device to the target frequency, and to maximize the two figures of merit. Based on the simulation results, a dipole-antenna PETS THz detector with optimized dimensions is fabricated and characterized. The photoreponse, conductance and response speed are measured at 8 K. It is demonstrated that the optimized dipole-antenna PETS THz detector shows a higher responsivity and a lower noise equivalent power than the previously reported AlGaAs/GaAs-based bowtie-antenna PETS THz detector. The temperature-dependence measurement shows that AlGaAs/GaAs-based PETS THz detectors have a capability of operating up to 75 K. The influence of asymmetric mesa structure is also investigated and indicates that asymmetry of the mesa structure leads to asymmetry of the photoresponse even through the gates on top of the mesa are symmetric. The influence of infrared illumination on AlGaAs/GaAs-based PETS THz detectors is then investigated to enhance device performance. A specialized setup, comprising an RF PCB, a two-piece copper holder that can be easily assembled and an infrared LED with an IR centre-wavelength of λ = 940 nm, is utilized to expose the PETS THz detector to THz radiation from the top while illuminating it with an infrared LED from the backside. Performance of a bowtie-antenna PETS THz detector, including the photoresponse, conductance, electron density, gate leakage, etc., is characterized following incremental illumination in controlled small doses. The persistent photoconductivity effect with a two-stage growth of the electron density in the 2DEG is observed, but there is no obvious parallel conductance based on the magnetotransport measurement. To explain the behaviour of the PETS THz detector under infrared illumination, a hypothesis based on DX-centre excitation is proposed. This thesis demonstrates, for the first time, a room-temperature PETS THz detector based on an AlGaN/GaN heterostructure. It operates at 1.9 THz, higher than that of most previously reported room-temperature AlGaN/GaN-based THz FETs, as the responsivity decreases dramatically for antenna-coupled FETs at higher frequencies. Photoreponse of the device is characterized in detail at both cryogenic temperature (8 K) and room temperature (295 K). The temperature dependence of the AlGaN/GaN-based PETS THz detector reveals that its responsivity exhibits an exponential decline with temperature, similar to the behaviour observed in AlGaAs/GaAs-based devices but with a smaller decay rate. Therefore, AlGaN/GaN-based devices achieve room-temperature operation, while AlGaAs/GaAs-based devices are not capable of operating beyond 75 K. The theoretical temperature dependence of the in-plane photoelectric effect is also investigated. The demonstration of the IPPE effect at room temperature opens wide opportunities for terahertz detection using quantum effects, and its observation in the AlGaN/GaN system suggests its universality in 2D electron gases. Collectively, the findings of this thesis deepen the understanding of the in-plane photoelectric effect and provide a universal guidance for the design of PETS THz detectors with high responsivity, fast response speed and room temperature operation."]},{"key":"dc:format.checksum.md5","label":"Dc Format Checksum Md5","values":["f73af3e8a95b4d45679248590fe615e9","87eda9de84448d1f82354d60eee3eb5f"]},{"key":"dc:title","label":"Title","values":["Physics and Engineering of Photoelectric Tunable-step Terahertz Detectors Based on High Mobility III-V Semiconductor Structures"]}]}],"canonical_facts":{"dc:contributor.advisor":["Ritchie, David","Michailow, Wladislaw"],"dc:creator":["Chen, Ran"],"dc:date.issued":["2025-08-04"],"dc:description.abstract":["The terahertz (THz) region is described as electromagnetic waves within the frequency range of v = 0.1–10 THz, lying between the microwave and infrared regions. Sandwiched by conventional electronic and photonic regions, the THz region has been one of the less explored areas for a long time, known as the ‘THz gap’, due to a lack of efficient, cheap, and easy-to-use THz sources and detectors. To shrink the ‘THz gap’, efficient THz detectors with high responsivity, low noise, fast response speed and room operating temperature are of paramount importance. Field effect transistors (FETs) based on two-dimensional electron gases (2DEGs) have shown promising performance as THz detectors over the past few decades. In 2022, a quantum, collision-free phenomenon, the in-plane photoelectric (IPPE) effect, was discovered as a novel detection mechanism in gated 2DEGs, and devices based on this effect, photoelectric tunable-step (PETS) THz detectors, have been proposed as sensitive THz detectors. This thesis focuses on PETS THz detectors that operate based on the in-plane photoelectric effect. The dependence of the IPPE effect on parameters, including antenna geometry, material, heterostructure design, operating temperature, illumination condition, etc., is systematically investigated for room-temperature PETS THz detectors with high responsivity and fast response speed. Firstly, a systematic study on AlGaAs/GaAs-based PETS THz detectors is carried out. A PETS THz detector with a simple dipole antenna is studied as a model system for universal guidance. From the theoretical expression of the IPPE effect, two figures of merit within the 2DEG, the maximum electric field and the radiation-induced ac-potential difference, jointly determine the photoreponse of PETS THz detectors. Dimensions of the dipole-antenna PETS THz detector are optimized through numerical simulation to tune the resonant frequency of the device to the target frequency, and to maximize the two figures of merit. Based on the simulation results, a dipole-antenna PETS THz detector with optimized dimensions is fabricated and characterized. The photoreponse, conductance and response speed are measured at 8 K. It is demonstrated that the optimized dipole-antenna PETS THz detector shows a higher responsivity and a lower noise equivalent power than the previously reported AlGaAs/GaAs-based bowtie-antenna PETS THz detector. The temperature-dependence measurement shows that AlGaAs/GaAs-based PETS THz detectors have a capability of operating up to 75 K. The influence of asymmetric mesa structure is also investigated and indicates that asymmetry of the mesa structure leads to asymmetry of the photoresponse even through the gates on top of the mesa are symmetric. The influence of infrared illumination on AlGaAs/GaAs-based PETS THz detectors is then investigated to enhance device performance. A specialized setup, comprising an RF PCB, a two-piece copper holder that can be easily assembled and an infrared LED with an IR centre-wavelength of λ = 940 nm, is utilized to expose the PETS THz detector to THz radiation from the top while illuminating it with an infrared LED from the backside. Performance of a bowtie-antenna PETS THz detector, including the photoresponse, conductance, electron density, gate leakage, etc., is characterized following incremental illumination in controlled small doses. The persistent photoconductivity effect with a two-stage growth of the electron density in the 2DEG is observed, but there is no obvious parallel conductance based on the magnetotransport measurement. To explain the behaviour of the PETS THz detector under infrared illumination, a hypothesis based on DX-centre excitation is proposed. This thesis demonstrates, for the first time, a room-temperature PETS THz detector based on an AlGaN/GaN heterostructure. It operates at 1.9 THz, higher than that of most previously reported room-temperature AlGaN/GaN-based THz FETs, as the responsivity decreases dramatically for antenna-coupled FETs at higher frequencies. Photoreponse of the device is characterized in detail at both cryogenic temperature (8 K) and room temperature (295 K). The temperature dependence of the AlGaN/GaN-based PETS THz detector reveals that its responsivity exhibits an exponential decline with temperature, similar to the behaviour observed in AlGaAs/GaAs-based devices but with a smaller decay rate. Therefore, AlGaN/GaN-based devices achieve room-temperature operation, while AlGaAs/GaAs-based devices are not capable of operating beyond 75 K. The theoretical temperature dependence of the in-plane photoelectric effect is also investigated. The demonstration of the IPPE effect at room temperature opens wide opportunities for terahertz detection using quantum effects, and its observation in the AlGaN/GaN system suggests its universality in 2D electron gases. Collectively, the findings of this thesis deepen the understanding of the in-plane photoelectric effect and provide a universal guidance for the design of PETS THz detectors with high responsivity, fast response speed and room temperature operation."],"dc:format.checksum.md5":["f73af3e8a95b4d45679248590fe615e9","87eda9de84448d1f82354d60eee3eb5f"],"dc:identifier.doi":["https://doi.org/10.17863/CAM.122146"],"dc:identifier.uri":["https://www.repository.cam.ac.uk/bitstreams/db9af708-ceac-49aa-9040-d570970b012a/download"],"dc:language":["eng"],"dc:publisher.institution":["University of Cambridge"],"dc:relation.isreferencedby.uri":["https://www.repository.cam.ac.uk/handle/1810/390593"],"dc:rights":["https://www.repository.cam.ac.uk/bitstreams/67dde331-ccf3-436b-aede-674eb176761b/download","http://purl.org/NET/rdflicense/allrightsreserved"],"dc:rights.embargodate":["2026-10-10"],"dc:rights.embargotype":["embargo"],"dc:subject":["Terahertz technology","Far-infrared detection","Two-dimensional electron gas","In-plane photoelectric effect","Photoelectric tunable-step detector","AlGaAs/GaAs heterostructure","AlGaN/GaN heterostructure"],"dc:title":["Physics and Engineering of Photoelectric Tunable-step Terahertz Detectors Based on High Mobility III-V Semiconductor Structures"],"dc:type":["Thesis"],"dc:type.qualificationlevel":["Doctoral"],"dc:type.qualificationname":["Doctor of Philosophy (PhD)"]},"updated_at":"2026-07-22T22:24:07Z"}