Coulomb blockade and negative magnetoresistance of ultrasmall ferromagnetic tunnel junctions are studied based on the Feynman path integral approach. It is shown that the change in magnetoresistance is considerably enhanced in the Coulomb blockade regime. This is due to the nonlinear current-voltage characteristics caused by the higher order tunneling processes which set in since negative magnetoresistance tends to make Coulomb blockade unstable. Results obtained are qualitatively in good agreement with recent experimental findings. Coulomb blockade and the magnetoresistance in ultrasmall ferromagnetic double junction are also discussed briefly.
{"title":"Coulomb blockade and higher order tunneling effect on magnetoresistance in ultrasmall ferromagnetic tunnel junctions","authors":"S. Iwabuchi, T. Tanamoto, R. Kitawaki","doi":"10.1109/LDS.1998.714538","DOIUrl":"https://doi.org/10.1109/LDS.1998.714538","url":null,"abstract":"Coulomb blockade and negative magnetoresistance of ultrasmall ferromagnetic tunnel junctions are studied based on the Feynman path integral approach. It is shown that the change in magnetoresistance is considerably enhanced in the Coulomb blockade regime. This is due to the nonlinear current-voltage characteristics caused by the higher order tunneling processes which set in since negative magnetoresistance tends to make Coulomb blockade unstable. Results obtained are qualitatively in good agreement with recent experimental findings. Coulomb blockade and the magnetoresistance in ultrasmall ferromagnetic double junction are also discussed briefly.","PeriodicalId":326271,"journal":{"name":"Proceedings. Second International Workshop on Physics and Modeling of Devices Based on Low-Dimensional Structures (Cat. No. 98EX199)","volume":"30 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1998-03-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131790622","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In this paper, we present a unified picture which can describe transport phenomena independent on applied electric field. Based on the unified picture and by means of the Monte Carlo simulation, we calculate drift velocities of electrons in a superlattice, taking LO phonon scattering and impurity scattering into account. When impurity density is low or electric field is high, electrons are easily accelerated to the edge of the Brillouin zone, and Bloch oscillation is realized. As a result of the Bloch oscillation, localized Stark-ladder states are formed and hopping transport between the Stark-ladder states is realized. With increasing impurities, electrons are scattered frequently and delocalization of Stark-ladder states takes place. In this case, band transport described in the momentum-space becomes important. Crossover between band transport and hopping transport is investigated and discussed.
{"title":"Complemental theory for vertical transport in semiconductor superlattices","authors":"M. Morifuji, A. Sakamoto, C. Hamaguchi","doi":"10.1109/LDS.1998.714535","DOIUrl":"https://doi.org/10.1109/LDS.1998.714535","url":null,"abstract":"In this paper, we present a unified picture which can describe transport phenomena independent on applied electric field. Based on the unified picture and by means of the Monte Carlo simulation, we calculate drift velocities of electrons in a superlattice, taking LO phonon scattering and impurity scattering into account. When impurity density is low or electric field is high, electrons are easily accelerated to the edge of the Brillouin zone, and Bloch oscillation is realized. As a result of the Bloch oscillation, localized Stark-ladder states are formed and hopping transport between the Stark-ladder states is realized. With increasing impurities, electrons are scattered frequently and delocalization of Stark-ladder states takes place. In this case, band transport described in the momentum-space becomes important. Crossover between band transport and hopping transport is investigated and discussed.","PeriodicalId":326271,"journal":{"name":"Proceedings. Second International Workshop on Physics and Modeling of Devices Based on Low-Dimensional Structures (Cat. No. 98EX199)","volume":"16 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1998-03-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131024988","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The design principle for completely negative-chirp operation of an electroabsorption (EA) modulator in the 1.55 /spl mu/m window is studied theoretically in InGaAsP strained quantum well (QW) structures for strain ranging from compressive to tensile. The small-signal chirp parameter for TE polarization is evaluated from calculated EA spectra based on k/spl middot/p theory and their Kramers-Kronig transformed refractive index changes. It is found that both compressive and tensile strain in the well layer reduce the chirp parameter The compressive-strained QW lowers the chirp parameter to nearly zero or negative values, the amount of the reduction being proportional to strain amount. In a tensile-strained QW, almost continuously negative values irrespective of applied electric fields occur at an optimized amount of strain.
{"title":"Design and analysis of low-chirp electroabsorption modulators using bandstructure engineering","authors":"T. Yamanaka, K. Yokoyama","doi":"10.1109/LDS.1998.714531","DOIUrl":"https://doi.org/10.1109/LDS.1998.714531","url":null,"abstract":"The design principle for completely negative-chirp operation of an electroabsorption (EA) modulator in the 1.55 /spl mu/m window is studied theoretically in InGaAsP strained quantum well (QW) structures for strain ranging from compressive to tensile. The small-signal chirp parameter for TE polarization is evaluated from calculated EA spectra based on k/spl middot/p theory and their Kramers-Kronig transformed refractive index changes. It is found that both compressive and tensile strain in the well layer reduce the chirp parameter The compressive-strained QW lowers the chirp parameter to nearly zero or negative values, the amount of the reduction being proportional to strain amount. In a tensile-strained QW, almost continuously negative values irrespective of applied electric fields occur at an optimized amount of strain.","PeriodicalId":326271,"journal":{"name":"Proceedings. Second International Workshop on Physics and Modeling of Devices Based on Low-Dimensional Structures (Cat. No. 98EX199)","volume":"94 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1998-03-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126101700","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Recent progress of the "nanofabrication" technology has opened up exciting possibilities of constructing novel quantum nanoelectronics directly based on the quantum mechanics where wave-particle motions of individual electrons are controlled by artificial quantum structures such as quantum wells, quantum wires, quantum dots and single and multiple tunneling barriers so as to realize devices with new functions and higher performances. This paper discusses the present status and key issues of research on the compound semiconductor quantum nanoelectronics, introducing recent results obtained by author's group at Research Center for Interface Quantum Electronics (RCIQE) as specific examples. Since electrons manifest predominantly either wave-nature or particle-nature depending on their environments, one can conceptually envisage two kinds of nanoelectronics in the quantum regime, i.e., "quantum wave electronics" and "single electronics". A particular emphasis is paid here on single electronics because of its promising prospects. Main topics include prospects, expected roles and nano-fabrication issues of compound semiconductor single electron devices as well as key issues on compound semiconductor quantum wave devices.
{"title":"Status and key issues for compound semiconductor nanoelectronics","authors":"H. Hasegawa","doi":"10.1109/LDS.1998.713841","DOIUrl":"https://doi.org/10.1109/LDS.1998.713841","url":null,"abstract":"Recent progress of the \"nanofabrication\" technology has opened up exciting possibilities of constructing novel quantum nanoelectronics directly based on the quantum mechanics where wave-particle motions of individual electrons are controlled by artificial quantum structures such as quantum wells, quantum wires, quantum dots and single and multiple tunneling barriers so as to realize devices with new functions and higher performances. This paper discusses the present status and key issues of research on the compound semiconductor quantum nanoelectronics, introducing recent results obtained by author's group at Research Center for Interface Quantum Electronics (RCIQE) as specific examples. Since electrons manifest predominantly either wave-nature or particle-nature depending on their environments, one can conceptually envisage two kinds of nanoelectronics in the quantum regime, i.e., \"quantum wave electronics\" and \"single electronics\". A particular emphasis is paid here on single electronics because of its promising prospects. Main topics include prospects, expected roles and nano-fabrication issues of compound semiconductor single electron devices as well as key issues on compound semiconductor quantum wave devices.","PeriodicalId":326271,"journal":{"name":"Proceedings. Second International Workshop on Physics and Modeling of Devices Based on Low-Dimensional Structures (Cat. No. 98EX199)","volume":"18 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1998-03-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132237663","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In this paper a device consisting of a quantum dot (QD) and a heterobipolar transistor (HBT) is proposed. The quantum dot, which is then used as a memory cell, is designed to contain about hundred electrons. The trapped charge, which is adjacent to the HBT-collector, influences the transistor collector current. Depending on whether an npn or pnp transistor is used, the current can respectively be modulated by the dot-charge induced collector band-bending or by the change in the transistor gain. The current variation can be sensed to recognize the state of the dot. The HBT is a vertical device and its lateral dimensions can be further reduced. This will result in the realization of memory circuits with increased in-plane packing densities. Preliminary modeling results will be presented showing the basic parameters to be achieved. In particular, the open problem areas are to be discussed in order to ultimately achieve such the required technological capability.
{"title":"A basic quantum dot element: Proposal of a HBT-dot cell for high-packing density memory circuits","authors":"H. Hartnagel, K. Mutamba, A. Sigurdardóttir","doi":"10.1109/LDS.1998.713912","DOIUrl":"https://doi.org/10.1109/LDS.1998.713912","url":null,"abstract":"In this paper a device consisting of a quantum dot (QD) and a heterobipolar transistor (HBT) is proposed. The quantum dot, which is then used as a memory cell, is designed to contain about hundred electrons. The trapped charge, which is adjacent to the HBT-collector, influences the transistor collector current. Depending on whether an npn or pnp transistor is used, the current can respectively be modulated by the dot-charge induced collector band-bending or by the change in the transistor gain. The current variation can be sensed to recognize the state of the dot. The HBT is a vertical device and its lateral dimensions can be further reduced. This will result in the realization of memory circuits with increased in-plane packing densities. Preliminary modeling results will be presented showing the basic parameters to be achieved. In particular, the open problem areas are to be discussed in order to ultimately achieve such the required technological capability.","PeriodicalId":326271,"journal":{"name":"Proceedings. Second International Workshop on Physics and Modeling of Devices Based on Low-Dimensional Structures (Cat. No. 98EX199)","volume":"23 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1998-03-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115592404","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：