Pub Date : 2023-12-15DOI: 10.3952/physics.2023.63.4.7
P. Sai, M. Dub, V. Korotyeyev, S. Kukhtaruk, G. Cywiński, W. Knap
This study reviews recent advances in the modern field of terahertz plasmonics concerning the control of resonant properties of grating-gate plasmonic crystal structures. Particularly, we conducted both experimental and theoretical investigations of AlGaN/GaN grating-gate structures with a focus on investigations of the resonant structure of transmission spectra associated with plasmon excitations in two-dimensional electron gas at different modulation degree of concentration profiles. Two distinct resonant phases of the plasmonic crystal structure were analyzed. The first one, the delocalized phase, is observed in the case of a small modulation degree of electron gas. In this phase, we found that plasmonic resonant absorption of incident radiation occurs across the entire grating-gate structure, with domination in the gated regions of the electron gas. In contrast, the second phase, the localized one, is realized at a strong modulation of the electron concentration profiles when the gated regions of the electron gas are completely depleted. Here, plasmon resonances are characterized by the spatial localization of absorption of incident radiation exclusively within the ungated regions of the electron gas. Moreover, in the localized phase, we observed the unexpected blue shift of plasmon resonant frequency with an increase of gate voltage. This observation was explained by the result of ‘edge gating effect’ and additional shrinking of the concentration profile of the electron gas in the ungated region. We demonstrate that the correct description of both phases requires rigorous electrodynamic simulations and cannot be achieved solely in the frameworks of simplified single-mode or single-cavity models.
{"title":"THz properties of grating-gate plasmonic crystals crystals","authors":"P. Sai, M. Dub, V. Korotyeyev, S. Kukhtaruk, G. Cywiński, W. Knap","doi":"10.3952/physics.2023.63.4.7","DOIUrl":"https://doi.org/10.3952/physics.2023.63.4.7","url":null,"abstract":"\u0000 \u0000 \u0000This study reviews recent advances in the modern field of terahertz plasmonics concerning the control of resonant properties of grating-gate plasmonic crystal structures. Particularly, we conducted both experimental and theoretical investigations of AlGaN/GaN grating-gate structures with a focus on investigations of the resonant structure of transmission spectra associated with plasmon excitations in two-dimensional electron gas at different modulation degree of concentration profiles. Two distinct resonant phases of the plasmonic crystal structure were analyzed. The first one, the delocalized phase, is observed in the case of a small modulation degree of electron gas. In this phase, we found that plasmonic resonant absorption of incident radiation occurs across the entire grating-gate structure, with domination in the gated regions of the electron gas. In contrast, the second phase, the localized one, is realized at a strong modulation of the electron concentration profiles when the gated regions of the electron gas are completely depleted. Here, plasmon resonances are characterized by the spatial localization of absorption of incident radiation exclusively within the ungated regions of the electron gas. Moreover, in the localized phase, we observed the unexpected blue shift of plasmon resonant frequency with an increase of gate voltage. This observation was explained by the result of ‘edge gating effect’ and additional shrinking of the concentration profile of the electron gas in the ungated region. We demonstrate that the correct description of both phases requires rigorous electrodynamic simulations and cannot be achieved solely in the frameworks of simplified single-mode or single-cavity models. \u0000 \u0000 \u0000","PeriodicalId":18144,"journal":{"name":"Lithuanian Journal of Physics","volume":"126 4","pages":""},"PeriodicalIF":0.6,"publicationDate":"2023-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138999527","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-12-15DOI: 10.3952/physics.2023.63.4.8
M. Jokubauskaitė, G. Petrusevičius, A. Špokas, B. Čechavičius, E. Dudutiene, R. Butkutė
The results of a comparative study on how the design of multiple quantum structures containing a parabolic barrier profile affects optical properties are presented. All quantum well (QW) structures were grown by molecular beam epitaxy (MBE) on semi-insulating GaAs substrates. The investigated samples consisted of (i) double parabolic quantum wells (type A) or (ii) multiple (two or three) rectangular quantum wells surrounded by parabolic barriers (type B). The optical quality of samples was characterized performing room-temperature (RT-PL) and temperaturedependent photoluminescence (TD-PL) measurements. The investigation aimed at the optimization of a multiple quantum well (MQW) structure design for application in the gain region of near infrared (NIR) laser diodes (LDs) revealed benefits of both double parabolic quantum wells and a mixed design (rectangular MQW with parabolic barriers). The PL band position for all samples was registered in the vicinity around 1.19 eV, which corresponds to the Bi content in QW of ~4.4%. It was shown that all structures of type A exhibit an intense emission, while the intensity of photoluminescence measured for the samples of type B depends on the number of QWs. The weaker intensity of the PL signal from two QWs inserted between parabolic barriers was explained by a larger point defect density at low temperature grown inner GaAs barriers. The room-temperature PL intensity of the structure with three GaAsBi QWs embedded in one parabolic AlGaAs barrier was the highest one. The shift of PL peak position to lower energies (1.16 eV) was attributed to the slightly higher bismuth concentration, 4.9%.
{"title":"Effects of parabolic barrier design for multiple GaAsBi/AlGaAs quantum well structures","authors":"M. Jokubauskaitė, G. Petrusevičius, A. Špokas, B. Čechavičius, E. Dudutiene, R. Butkutė","doi":"10.3952/physics.2023.63.4.8","DOIUrl":"https://doi.org/10.3952/physics.2023.63.4.8","url":null,"abstract":"\u0000 \u0000 \u0000The results of a comparative study on how the design of multiple quantum structures containing a parabolic barrier profile affects optical properties are presented. All quantum well (QW) structures were grown by molecular beam epitaxy (MBE) on semi-insulating GaAs substrates. The investigated samples consisted of (i) double parabolic quantum wells (type A) or (ii) multiple (two or three) rectangular quantum wells surrounded by parabolic barriers (type B). The optical quality of samples was characterized performing room-temperature (RT-PL) and temperaturedependent photoluminescence (TD-PL) measurements. The investigation aimed at the optimization of a multiple quantum well (MQW) structure design for application in the gain region of near infrared (NIR) laser diodes (LDs) revealed benefits of both double parabolic quantum wells and a mixed design (rectangular MQW with parabolic barriers). The PL band position for all samples was registered in the vicinity around 1.19 eV, which corresponds to the Bi content in QW of ~4.4%. It was shown that all structures of type A exhibit an intense emission, while the intensity of photoluminescence measured for the samples of type B depends on the number of QWs. The weaker intensity of the PL signal from two QWs inserted between parabolic barriers was explained by a larger point defect density at low temperature grown inner GaAs barriers. The room-temperature PL intensity of the structure with three GaAsBi QWs embedded in one parabolic AlGaAs barrier was the highest one. The shift of PL peak position to lower energies (1.16 eV) was attributed to the slightly higher bismuth concentration, 4.9%. \u0000 \u0000 \u0000","PeriodicalId":18144,"journal":{"name":"Lithuanian Journal of Physics","volume":"68 10","pages":""},"PeriodicalIF":0.6,"publicationDate":"2023-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138998933","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-12-15DOI: 10.3952/physics.2023.63.4.6
H. Yuan, Q. Ul-Islam, H. Roskos
A detector of electromagnetic radiation may benefit – if its sensor area is small – from the application of a substrate lens, which focusses the radiation onto the active sensing area of the device and thus enhances its responsivity. The use of such a lens, attached directly onto the detector backside in order to avoid reflection losses, requires that the detector substrate and backside be transparent to the radiation. However, if this is not the case, one may like to place instead a superstrate lens onto the front side of the detector. It may even be of interest to use both a substrate and a superstrate lens if the detector needs to be illuminated with two beams, e.g. for heterodyne detection, where one beam provides the local-oscillator signal. The use of a superstrate lens is, however, often hindered or impeded by an uneven surface topography or by the presence of bonding wires on the front side of the detector. Here, we address this issue and explore the use of paraffin wax to form or attach superstrate lenses. In the first case, which is the main topic of this contribution, we exploit the surface tension of liquid paraffin, brought onto the detector, to sculpt the wax itself into a lens. In the second case, only addressed conceptually here, we use paraffin to form a thin intermediate layer which also acts as an adhesive for the attachment of a plastic or silicon lens. In both cases, the application of liquid paraffin allows one to fill out an uneven detector surface and to embed wires without breaking them. We investigate the use of wax for the case of CMOS TeraFETs – detectors of terahertz radiation based on field-effect transistors – embedded into antenna structures. We describe the processing steps and analyze the performance of a TeraFET equipped with such a wax superstrate lens for front-side beam coupling.
{"title":"Superstrate-lens integration using paraffin wax on top of semiconductor-based THz detector chips","authors":"H. Yuan, Q. Ul-Islam, H. Roskos","doi":"10.3952/physics.2023.63.4.6","DOIUrl":"https://doi.org/10.3952/physics.2023.63.4.6","url":null,"abstract":"\u0000 \u0000 \u0000A detector of electromagnetic radiation may benefit – if its sensor area is small – from the application of a substrate lens, which focusses the radiation onto the active sensing area of the device and thus enhances its responsivity. The use of such a lens, attached directly onto the detector backside in order to avoid reflection losses, requires that the detector substrate and backside be transparent to the radiation. However, if this is not the case, one may like to place instead a superstrate lens onto the front side of the detector. It may even be of interest to use both a substrate and a superstrate lens if the detector needs to be illuminated with two beams, e.g. for heterodyne detection, where one beam provides the local-oscillator signal. The use of a superstrate lens is, however, often hindered or impeded by an uneven surface topography or by the presence of bonding wires on the front side of the detector. Here, we address this issue and explore the use of paraffin wax to form or attach superstrate lenses. In the first case, which is the main topic of this contribution, we exploit the surface tension of liquid paraffin, brought onto the detector, to sculpt the wax itself into a lens. In the second case, only addressed conceptually here, we use paraffin to form a thin intermediate layer which also acts as an adhesive for the attachment of a plastic or silicon lens. In both cases, the application of liquid paraffin allows one to fill out an uneven detector surface and to embed wires without breaking them. We investigate the use of wax for the case of CMOS TeraFETs – detectors of terahertz radiation based on field-effect transistors – embedded into antenna structures. We describe the processing steps and analyze the performance of a TeraFET equipped with such a wax superstrate lens for front-side beam coupling. \u0000 \u0000 \u0000","PeriodicalId":18144,"journal":{"name":"Lithuanian Journal of Physics","volume":"4 38","pages":""},"PeriodicalIF":0.6,"publicationDate":"2023-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139001022","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-12-13DOI: 10.3952/physics.2023.63.4.5
K. Stanaitis, K. Redeckas, A. Bielevičiūtė, M. Bernatonis, D. Jokubauskis, V. Čižas, L. Minkevičius
The ever-increasing popularity of the terahertz (THz) frequency range reveals the increasingly obvious applicability limiting factor – the price of the final setup. This study is intended to contribute to the solution by evaluating the THz frequency range suitability of the optical components, fabricated using two easily accessible materials – high impact polystyrene (HIPS) and paraffin. The primary analysis using time-domain spectroscopy (TDS) revealed promising results, as both materials had sufficient refractive indexes of n ≈ 1.55 and a high transmittance. That allowed one to assume the feasibility of creating a low-cost THz frequency range lens. Lenses of focal lengths of f = 20, 30, 40 mm were fabricated using extrusion 3D printing and paraffin moulding. The produced lenses showcased the satisfactory beam focusing ability, comparable to that of already existing much less cost-efficient solutions. The THz imaging using the fabricated lenses has successfully been realized, proving the applicational possibilities of the imaging system with the proposed low-cost components employed.
太赫兹（THz）频率范围日益普及，揭示了一个日益明显的应用限制因素--最终装置的价格。本研究旨在通过评估光学元件在太赫兹频率范围内的适用性来解决这一问题，这些元件是使用两种容易获得的材料--高抗冲聚苯乙烯（HIPS）和石蜡--制造的。使用时域光谱法（TDS）进行的初步分析表明，这两种材料都具有足够的折射率（n ≈ 1.55）和较高的透射率，因此结果很有希望。这使我们可以假设制造低成本太赫兹频率范围透镜的可行性。利用挤压 3D 打印和石蜡模塑技术制造了焦距为 f = 20、30 和 40 毫米的透镜。制造出的透镜显示出令人满意的光束聚焦能力，可与现有成本效率低得多的解决方案相媲美。使用所制造的透镜成功实现了太赫兹成像，证明了使用所提议的低成本组件的成像系统的应用可能性。
{"title":"Study of the low-cost HIPS and paraffin-based terahertz optical components","authors":"K. Stanaitis, K. Redeckas, A. Bielevičiūtė, M. Bernatonis, D. Jokubauskis, V. Čižas, L. Minkevičius","doi":"10.3952/physics.2023.63.4.5","DOIUrl":"https://doi.org/10.3952/physics.2023.63.4.5","url":null,"abstract":"\u0000 \u0000 \u0000The ever-increasing popularity of the terahertz (THz) frequency range reveals the increasingly obvious applicability limiting factor – the price of the final setup. This study is intended to contribute to the solution by evaluating the THz frequency range suitability of the optical components, fabricated using two easily accessible materials – high impact polystyrene (HIPS) and paraffin. The primary analysis using time-domain spectroscopy (TDS) revealed promising results, as both materials had sufficient refractive indexes of n ≈ 1.55 and a high transmittance. That allowed one to assume the feasibility of creating a low-cost THz frequency range lens. Lenses of focal lengths of f = 20, 30, 40 mm were fabricated using extrusion 3D printing and paraffin moulding. The produced lenses showcased the satisfactory beam focusing ability, comparable to that of already existing much less cost-efficient solutions. The THz imaging using the fabricated lenses has successfully been realized, proving the applicational possibilities of the imaging system with the proposed low-cost components employed. \u0000 \u0000 \u0000","PeriodicalId":18144,"journal":{"name":"Lithuanian Journal of Physics","volume":"14 3","pages":""},"PeriodicalIF":0.6,"publicationDate":"2023-12-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139004853","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-12-13DOI: 10.3952/physics.2023.63.4.3
P. Kizevičius, S. Orlov, K. Mundrys, V. Jukna, L. Minkevičius, G. Valušis
High numerical apertures can result in distortions appearing in a single-shot image, rendering the acquisition of usable images challenging, if not outright impossible. However, in the realm of single-pixel imaging, various strategies can be employed to effectively inspect objects with an excellent resolution, contrast and brightness. Recent advancements in flat photonic components have facilitated the development of compact nonparaxial imaging systems, which show great promise, particularly in the THz range of wavelengths. These innovations hold the potential to advance fields such as communication, material inspection and spectroscopy. In this study, we delve into the imaging of semi-transparent objects with varying levels of detail. Furthermore, we introduce a nonparaxial design for a flat hyperbolical lens and evaluate its performance in these imaging scenarios, comparing it to structured illumination techniques involving Airy, Bessel, and common thin lens configurations. We present findings regarding potential improvements in imaging attributable to the nonparaxial hyperbolical lens.
{"title":"On nonparaxial single-pixel imaging of semitransparent objects using flat diffractive optics","authors":"P. Kizevičius, S. Orlov, K. Mundrys, V. Jukna, L. Minkevičius, G. Valušis","doi":"10.3952/physics.2023.63.4.3","DOIUrl":"https://doi.org/10.3952/physics.2023.63.4.3","url":null,"abstract":"\u0000 \u0000 \u0000 \u0000 \u0000 \u0000High numerical apertures can result in distortions appearing in a single-shot image, rendering the acquisition of usable images challenging, if not outright impossible. However, in the realm of single-pixel imaging, various strategies can be employed to effectively inspect objects with an excellent resolution, contrast and brightness. Recent advancements in flat photonic components have facilitated the development of compact nonparaxial imaging systems, which show great promise, particularly in the THz range of wavelengths. These innovations hold the potential to advance fields such as communication, material inspection and spectroscopy. In this study, we delve into the imaging of semi-transparent objects with varying levels of detail. Furthermore, we introduce a nonparaxial design for a flat hyperbolical lens and evaluate its performance in these imaging scenarios, comparing it to structured illumination techniques involving Airy, Bessel, and common thin lens configurations. We present findings regarding potential improvements in imaging attributable to the nonparaxial hyperbolical lens. \u0000 \u0000 \u0000 \u0000 \u0000 \u0000","PeriodicalId":18144,"journal":{"name":"Lithuanian Journal of Physics","volume":"58 8","pages":""},"PeriodicalIF":0.6,"publicationDate":"2023-12-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139004357","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-12-13DOI: 10.3952/physics.2023.63.4.2
I. Lukosiunas, J. Nikitina, D. Gailevičius, L. Grinevičiūtė, K. Staliūnas
The development of devices based on compact waveguides is a rapidly evolving field. A unique variation of such devices is the Fano-like resonance dielectric spectral and spatial filtre, made from a dielectric conformal thin film on a surface relief grating. It can be used in a normal (or oblique) angle-of-incidence configuration. This device facilitates directional selectivity, which is useful for transverse-mode cleaning in short optical cavities. It can also be enhanced by using leaky-mode effects to produce even sharper spectral features. However, a perfect spatial filtre should be as invariant as possible in the spectral and enhanced angular domains. Here, we solved the inverse design problem to produce such an effect. Numerically, we tuned the surface profile of the substrate grating, assuming a conformal layer on top. This resulted in trapezoidal relief patterns followed by narrow flat-top angular features. The combination of leaky mode effect and enhanced device topology will enable efficient and useful devices with a bandwidth of 50 nm and even more in the future.
{"title":"Guided mode resonances for angular and spectral filtering","authors":"I. Lukosiunas, J. Nikitina, D. Gailevičius, L. Grinevičiūtė, K. Staliūnas","doi":"10.3952/physics.2023.63.4.2","DOIUrl":"https://doi.org/10.3952/physics.2023.63.4.2","url":null,"abstract":"\u0000 \u0000 \u0000The development of devices based on compact waveguides is a rapidly evolving field. A unique variation of such devices is the Fano-like resonance dielectric spectral and spatial filtre, made from a dielectric conformal thin film on a surface relief grating. It can be used in a normal (or oblique) angle-of-incidence configuration. This device facilitates directional selectivity, which is useful for transverse-mode cleaning in short optical cavities. It can also be enhanced by using leaky-mode effects to produce even sharper spectral features. However, a perfect spatial filtre should be as invariant as possible in the spectral and enhanced angular domains. Here, we solved the inverse design problem to produce such an effect. Numerically, we tuned the surface profile of the substrate grating, assuming a conformal layer on top. This resulted in trapezoidal relief patterns followed by narrow flat-top angular features. The combination of leaky mode effect and enhanced device topology will enable efficient and useful devices with a bandwidth of 50 nm and even more in the future. \u0000 \u0000 \u0000","PeriodicalId":18144,"journal":{"name":"Lithuanian Journal of Physics","volume":"10 2","pages":""},"PeriodicalIF":0.6,"publicationDate":"2023-12-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139005530","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-12-13DOI: 10.3952/physics.2023.63.4.4
J. Vyšniauskas, K. Ikamas, D. Vizbaras, A. Lisauskas
Here, we report on numerical modelling of AlGaN/GaN HEMT terahertz detectors using a two-dimensional solver based on three Boltzmann transport equation (BTE) moments and the Poisson equation. We use the Synopsys TCAD Sentaurus program package, which offers a wide material database and the possibility to include traps and polarization charges for the formation of the channel without any doping. The implications of different levels of model simplifications are addressed both analytically and numerically. We calculated the current responsivity R, to THz radiation on the drain voltage in the frequency range 0.01-3.0 THz for three AlGaN layer thicknesses d= 15, 20 and 25 nm and different gate lengths. We demonstrate that only a hydrodynamic model can reproduce the change in the sign in current responsivity at the gate voltage UG9 (R1 = 0 at UG = UG0). The energy flux factor in the energy balance equation determines this effect. For the simulated structures, we find that the noise equivalent power may be as low as 0.1 pW/VHz at 0.04 THz and 10 pW/VHz at 3.0 THz.
{"title":"Two-dimensional hydrodynamic modelling of AlGaN/GaN transistor-based THz detectors","authors":"J. Vyšniauskas, K. Ikamas, D. Vizbaras, A. Lisauskas","doi":"10.3952/physics.2023.63.4.4","DOIUrl":"https://doi.org/10.3952/physics.2023.63.4.4","url":null,"abstract":"\u0000 \u0000 \u0000Here, we report on numerical modelling of AlGaN/GaN HEMT terahertz detectors using a two-dimensional solver based on three Boltzmann transport equation (BTE) moments and the Poisson equation. We use the Synopsys TCAD Sentaurus program package, which offers a wide material database and the possibility to include traps and polarization charges for the formation of the channel without any doping. The implications of different levels of model simplifications are addressed both analytically and numerically. We calculated the current responsivity R, to THz radiation on the drain voltage in the frequency range 0.01-3.0 THz for three AlGaN layer thicknesses d= 15, 20 and 25 nm and different gate lengths. We demonstrate that only a hydrodynamic model can reproduce the change in the sign in current responsivity at the gate voltage UG9 (R1 = 0 at UG = UG0). The energy flux factor in the energy balance equation determines this effect. For the simulated structures, we find that the noise equivalent power may be as low as 0.1 pW/VHz at 0.04 THz and 10 pW/VHz at 3.0 THz. \u0000 \u0000 \u0000","PeriodicalId":18144,"journal":{"name":"Lithuanian Journal of Physics","volume":"4 2","pages":""},"PeriodicalIF":0.6,"publicationDate":"2023-12-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139004186","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-12-13DOI: 10.3952/physics.2023.63.4.1
J. Jorudas, D. Seliuta, L. Minkevičius, V. Janonis, L. Subačius, D. Pashnev, S. Pralgauskaitė, J. Matukas, K. Ikamas, A. Lisauskas, E. Šermukšnis, J. Liberis, V. Kovalevskij, I. Kašalynas
Asymmetrical shaping of AlGaN/GaN heterostructures containing a conductive layer of two-dimensional electron gas (2DEG) was used for the development of bow-tie (BT) diodes for room temperature terahertz (THz) detection. Considering operation of the THz BT diode in the unbiased mode as preferable for practical applications, we investigated the diodes with an obvious asymmetry of IV characteristics, which was found to be more pronounced with the decrease of an apex width, resulting in the sensitive THz detection. A nonuniform heating of carriers in a metalized leaf of the BT diode was attributed as the main mechanism that caused the rectification of THz waves. The responsivity and noise-equivalent power (NEP) at the fundamental antenna frequency of 150 GHz were up to 4 V/W and 2 nW/√Hz, respectively. Such high sensitivity of BT diodes allowed us to measure for the first time the response spectrum of the asymmetric BT antenna demonstrating fundamental and higher order resonances in good agreement with finite-difference time-domain simulation data in a broad spectrum range. The detailed investigation of the lowand high-frequency noise characteristics of AlGaN/GaN BT diodes revealed that only thermal noise needs to be considered for the unbiased operation, the value of which was relatively low due to a high density of 2DEG enabling low resistivity values. Moreover, we observed that the responsivity of BT diode scales with its resistance, revealing that tapering of the diode apex below a few microns could be ineffective in applications which require low NEP values.
{"title":"Terahertz bow-tie diode based on asymmetrically shaped AlGaN/GaN heterostructures","authors":"J. Jorudas, D. Seliuta, L. Minkevičius, V. Janonis, L. Subačius, D. Pashnev, S. Pralgauskaitė, J. Matukas, K. Ikamas, A. Lisauskas, E. Šermukšnis, J. Liberis, V. Kovalevskij, I. Kašalynas","doi":"10.3952/physics.2023.63.4.1","DOIUrl":"https://doi.org/10.3952/physics.2023.63.4.1","url":null,"abstract":"\u0000 \u0000 \u0000Asymmetrical shaping of AlGaN/GaN heterostructures containing a conductive layer of two-dimensional electron gas (2DEG) was used for the development of bow-tie (BT) diodes for room temperature terahertz (THz) detection. Considering operation of the THz BT diode in the unbiased mode as preferable for practical applications, we investigated the diodes with an obvious asymmetry of IV characteristics, which was found to be more pronounced with the decrease of an apex width, resulting in the sensitive THz detection. A nonuniform heating of carriers in a metalized leaf of the BT diode was attributed as the main mechanism that caused the rectification of THz waves. The responsivity and noise-equivalent power (NEP) at the fundamental antenna frequency of 150 GHz were up to 4 V/W and 2 nW/√Hz, respectively. Such high sensitivity of BT diodes allowed us to measure for the first time the response spectrum of the asymmetric BT antenna demonstrating fundamental and higher order resonances in good agreement with finite-difference time-domain simulation data in a broad spectrum range. The detailed investigation of the lowand high-frequency noise characteristics of AlGaN/GaN BT diodes revealed that only thermal noise needs to be considered for the unbiased operation, the value of which was relatively low due to a high density of 2DEG enabling low resistivity values. Moreover, we observed that the responsivity of BT diode scales with its resistance, revealing that tapering of the diode apex below a few microns could be ineffective in applications which require low NEP values. \u0000 \u0000 \u0000","PeriodicalId":18144,"journal":{"name":"Lithuanian Journal of Physics","volume":"13 2","pages":""},"PeriodicalIF":0.6,"publicationDate":"2023-12-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139004893","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-11-26DOI: 10.3952/physics.2023.63.3.6
J. Jorudas, H. Rehman, G. Fedorov, M. Cojocari, P. Karvinen, A. Urbanowicz, I. Kašalynas, L. Y. Matzui, Y. Svirko, P. Kuzhira
Pyrolyzed photoresist films (PPFs), which are formed via vacuum annealing of a photoresist without a catalyst, can be employed for fabrication of graphitic nanostructures by using conventional lithographic techniques. Such approach allows for reduction of technological steps required for fabrication of conductive micro- and nanoelectrodes for different applications. However, the operation frequency range of PPF electrodes is still unknown. Here, we report the results of the comparative study of PPF structures fabricated by electron beam lithography prior and after the annealing process with preference to the first approach. By performing the comparative measurements of PPF transport properties we found that both pre-and post-processed PPFs possess the same conductivities at dc-current and in the frequency range from 0.2 to 1.5 THz. Moreover, we achieved the sheet resistance of 150 nm thick PPFs as low as 570 Ω/sq, which is comparable to that of commercially available chemical vapour deposited (CVD) graphene. These findings open a path for a simple, reproducible and scalable fabrication of graphitic nanocircuits, nanoresonators and passive components suitable for applications in frequencies up to few terahertz.
{"title":"Pyro lyzed photoresist thin film: effect of electron beam patterning on DC and THz conductivity","authors":"J. Jorudas, H. Rehman, G. Fedorov, M. Cojocari, P. Karvinen, A. Urbanowicz, I. Kašalynas, L. Y. Matzui, Y. Svirko, P. Kuzhira","doi":"10.3952/physics.2023.63.3.6","DOIUrl":"https://doi.org/10.3952/physics.2023.63.3.6","url":null,"abstract":"Pyrolyzed photoresist films (PPFs), which are formed via vacuum annealing of a photoresist without a catalyst, can be employed for fabrication of graphitic nanostructures by using conventional lithographic techniques. Such approach allows for reduction of technological steps required for fabrication of conductive micro- and nanoelectrodes for different applications. However, the operation frequency range of PPF electrodes is still unknown. Here, we report the results of the comparative study of PPF structures fabricated by electron beam lithography prior and after the annealing process with preference to the first approach. By performing the comparative measurements of PPF transport properties we found that both pre-and post-processed PPFs possess the same conductivities at dc-current and in the frequency range from 0.2 to 1.5 THz. Moreover, we achieved the sheet resistance of 150 nm thick PPFs as low as 570 Ω/sq, which is comparable to that of commercially available chemical vapour deposited (CVD) graphene. These findings open a path for a simple, reproducible and scalable fabrication of graphitic nanocircuits, nanoresonators and passive components suitable for applications in frequencies up to few terahertz.","PeriodicalId":18144,"journal":{"name":"Lithuanian Journal of Physics","volume":"37 1","pages":""},"PeriodicalIF":0.6,"publicationDate":"2023-11-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139235106","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-11-26DOI: 10.3952/physics.2023.63.3.5
V. Čižas, N. Alexeeva, K. Alekseev, G. Valušis
Semiconductor superlattices are very well-known structures due to their specific electron transport properties, making them extremely attractive to be employed in electronic or optoelectronic devices. The interest in such structures has been recently additionally stirred up due to the first successful experimental demonstration of parametric gain in GaAs/AlGaAs superlattices, resulting in the generation of harmonics, half-harmonics and fractional harmonics. This invention paves the way for a successful realization of superlattice-based generators and amplifiers up to the terahertz frequency range. Despite the emerging experimental results and decade-long theoretical research, unresolved aspects, related to the physical processes inside the superlattices, persist. Lately, the biasing effect was extensively analysed for the case of degenerate processes in the superlattice; however, the non-degenerate case was left out of frame until now. Within this research, we further expand the boundaries of previous investigation by exploring the differences of non-degenerate processes. The study uncovers the asymmetry appearance of the probe field vs. relative phase dependences as well as the possibility of parametric fractional frequency generation. Finally, the concept of energy reflow between two participating probes is predicted and discussed.
{"title":"Sum-frequency generation and amplification processes in semiconductor superlattices","authors":"V. Čižas, N. Alexeeva, K. Alekseev, G. Valušis","doi":"10.3952/physics.2023.63.3.5","DOIUrl":"https://doi.org/10.3952/physics.2023.63.3.5","url":null,"abstract":"Semiconductor superlattices are very well-known structures due to their specific electron transport properties, making them extremely attractive to be employed in electronic or optoelectronic devices. The interest in such structures has been recently additionally stirred up due to the first successful experimental demonstration of parametric gain in GaAs/AlGaAs superlattices, resulting in the generation of harmonics, half-harmonics and fractional harmonics. This invention paves the way for a successful realization of superlattice-based generators and amplifiers up to the terahertz frequency range. Despite the emerging experimental results and decade-long theoretical research, unresolved aspects, related to the physical processes inside the superlattices, persist. Lately, the biasing effect was extensively analysed for the case of degenerate processes in the superlattice; however, the non-degenerate case was left out of frame until now. Within this research, we further expand the boundaries of previous investigation by exploring the differences of non-degenerate processes. The study uncovers the asymmetry appearance of the probe field vs. relative phase dependences as well as the possibility of parametric fractional frequency generation. Finally, the concept of energy reflow between two participating probes is predicted and discussed.","PeriodicalId":18144,"journal":{"name":"Lithuanian Journal of Physics","volume":"23 1","pages":""},"PeriodicalIF":0.6,"publicationDate":"2023-11-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139235679","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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