Importance of space-charge effects in resonant tunneling devices

Cahay, M.; McLennan, Michael; Datta, Supriyo; Lundstrom, Mark

doi:10.1063/1.98097

Cited by 161 publications

(42 citation statements)

References 10 publications

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“…2 shows that, in the nonpolar case, the depletion and inversion regions that arise at nonzero bias do not inhibit current as the direction of the slope coincides with the movement of the electrons. 38,39 …”

Section: B Tunneling Barriermentioning

confidence: 99%

Polarization-balanced design of heterostructures: Application to AlN/GaN double-barrier structures

2011

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Inversion and depletion regions generally form at the interfaces between doped leads (cladding layers) and the active region of polar heterostructures like AlN/GaN and other nitride compounds. The band bending in the depletion region sets up a barrier that may seriously impede perpendicular electronic transport. This may ruin the performance of devices such as quantum-cascade lasers and resonant-tunneling diodes. Here we introduce the concepts of polarization balance and polarization-balanced designs: A structure is polarization balanced when the applied bias match the voltage drop arising from spontaneous and piezeolectric fields. Devices designed to operate at this bias have polarization-balanced designs. These concepts offer a systematic approach to avoid the formation of depletion regions. As a test case, we consider the design of AlN/GaN double-barrier structures with AlxGa 1−x N leads. To guide our efforts, we derive a simple relation between the intrinsic voltage drop arising from polar effects, average alloy composition of the active region, and the alloy concentration of the leads. Polarization-balanced designs secure good filling of the ground state for unbiased structures, while for biased structures with efficient emptying of the active region they remove the depletion barriers.

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Section: B Tunneling Barriermentioning

confidence: 99%

Polarization-balanced design of heterostructures: Application to AlN/GaN double-barrier structures

2011

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“…3 are band diagrams of QD-RTD structure in the case of with and without InAs dots, respectively, obtained by solving the Schrödinger and Poisson equations self-consistently in the device. [9] As an approximation, the InAs dot layer can be simply treated as the InAs quantum well for qualitative discussions. Fig.…”

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confidence: 99%

High photoexcited carrier multiplication by charged InAs dots in AlAs∕GaAs∕AlAs resonant tunneling diode

Wang

Hou

Xiong

et al. 2008

Applied Physics Letters

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We present an approach for the highly sensitive photon detection based on the quantum dots (QDs) operating at temperature of 77K. The detection structure is based on an AlAs/GaAs/AlAs double barrier resonant tunneling diode combined with a layer of self-assembled InAs QDs (QD-RTD). A photon rate of 115 photons per second had induced 10nA photocurrent in this structure, corresponding to the photo-excited carrier multiplication factor of 10 7 . This high multiplication factor is achieved by the quantum dot induced memory effect and the resonant tunneling tuning effect of QD-RTD structure. * Electronic address: luwei@mail.sitp.ac.cn 1 There is currently great interest in exploring highly sensitive photon detection methodologies for potential use in remote sensing, spectroscopy, and even quantum information. [1] For the very high sensitivity, the photon detection will be in the photon counting mode, even in single photon counting mode. In order to approach the photon counting mode, very high photo-excited carrier multiplication factor is a basic requirement. Recently it has been demonstrated that structure of resonant tunneling diodes containing a layer of self-assembled quantum dots (QD-RTD) may be used as a very high photo-excited carrier multiplication device under the forward bias[2] at liquid helium temperature for single photon detection with the effective multiplication factor in the order of 10 8 .[3] This very high multiplication factor is caused by the storage effect of photo-excited hole in QD near RTD structure. This storage effect can also be achieved by the electrical bias, which presents a pronounced memory effect in current-voltage (I-V ) characteristics of QD-RTD device. [4,5] In this letter, we report that the memory phenomenon, induced by the electrical bias, can be used to enhance the photo-excited carrier multiplication factor in QD-RTD structure. The tunneling current passing through the QDs has been used in the multiplication process, so that the operating temperature has been increased from liquid helium (4.2K) in early report [3,6,7] to liquid nitrogen (77K) in present work.The samples in our experiment were grown by molecular beam epitaxy (MBE) on semiinsulated GaAs (100) substrate. The material layers, from top to bottom, were piled as: a 50nm highly n-doped GaAs (2 × 10 18 cm −3 ) as top contact layer, a 150nm i-GaAs absorber layer, a layer of self-assembled InAs quantum dots capped by 10nm GaAs, a 2nm GaAs spacer layer, a 11ML AlAs barrier, a 8nm GaAs quantum well, a 11ML AlAs barrier, a 20nm GaAs spacer layer, a 430nm graded n-doped GaAs as bottom contact layer (from 1 × 10 16 to 1 × 10 18 cm −3 ), a 15nm AlAs etch-stop layer, a 400nm GaAs buffer layer, and finally a semi-insulating GaAs (100) substrate. In order to investigate the density of QDs, another QD layer of same growing condition was deposited at the surface. The surface morphology was characterized by atomic force microscopy (AFM) as shown in Fig. 1 (a).The density of QDs is about 5.7 × 10 10 cm −2 , with the QDs' siz...

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“…30 The whole structure is considered to be sandwiched between two leads consisting of n-doped GaN ͑n = 1.4ϫ 10 18 cm −3 ͒ of 12 nm width. The effect of the polarization charges at the interfaces 30 is neglected and all simulations are performed at low temperatures T = 4.2 K. We include 3 nm thick undoped GaN buffer layers between the leads and the active structure, which causes an upward band bending at zero bias.Following the classic treatments of ͑two barriers͒ RTDs, [31][32][33] APPLIED PHYSICS LETTERS 89, 242101 ͑2006͒ …”

mentioning

confidence: 99%

“…Following the classic treatments of ͑two barriers͒ RTDs, [31][32][33] APPLIED PHYSICS LETTERS 89, 242101 ͑2006͒…”

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Resonant tunneling magnetoresistance in coupled quantum wells

Ertler

Fabian

2006

Applied Physics Letters

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A three barrier resonant tunneling structure in which the two quantum wells are formed by a magnetic semiconductor is theoretically investigated. Self-consistent numerical simulations of the structure predict giant magnetocurrent in the resonant bias regime as well as significant current spin polarization for a considerable range of applied biases. The requirements for large magnetocurrent are spin resolved resonance levels as well as asymmetry ͑spatial or magnetic͒ of the coupled quantum wells. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2402878͔Semiconductor spintronics offers additional functionalities to the existing electronics technology by combining charge and spin properties of the current carriers. 1 Spin dependent resonant tunneling in double barrier heterostructures has been investigated both experimentally and theoretically with a magnetic quantum well ͑QW͒ made of semimetallic ErAs ͑Refs. 2 and 3͒ or dilute magnetic semiconductors ͑DMSs͒ such as GaMnAs ͑Refs. 4-9͒ or ZnMnSe ͑Refs. 10 and 11͒. Such diodes have been used as spin filters or spin detectors and effective injection of spin-polarized electrons into semiconductors has been demonstrated by employing interband tunneling devices based on GaMnSb. 12,13 A theoretical investigation of resonant tunneling through a nonmagnetic double barrier structure, e.g., AlAs/ GaAs/ AlAs, sandwiched between two bulk ferromagnetic DMSs, e.g., GaMnAs, shows a tremendous enhancement of the tunneling magnetoresistance ͑TMR͒ for low voltages if the thickness of the QW is properly tuned. 14 The effect has been demonstrated to be as high as 10 000% for generic parabolic bands and when including a more realistic kp band structure model still very high TMRs of about 800% have been obtained. 14 Such structures have already been grown and studied experimentally. 4,15,16 Here we propose to use magnetic resonant tunneling diodes ͑RTDs͒ comprising coupled magnetic QWs and three nonmagnetic barriers, as spintronic devices offering large magnetocurrents ͑MCs͒. Corresponding nonmagnetic three barrier structures have been experimentally studied, [17][18][19][20] while electric field domain formation in magnetic multiple QWs was theoretically investigated in Ref. 21. The magnetic three barrier structure allows to establish parallel ͑P͒ and antiparallel ͑AP͒ magnetization configurations and to observe MC. The QWs are assumed to be made of ferromagnetic semiconductors. 5,22 We consider here generic parabolic n-type ferromagnetic QWs, though one expects to observe similar effects in coupled p-type ferromagnetic QWs. Several suitable n-type ferromagnetic semiconductors have been reported: 1 HgCr 2 Se 4 , 23 CdCr 2 Se 4 , 24 CdMnGeP 2 , 25 or most promising ZnO and GaMnN; 22,27 the latter two are believed to exhibit room temperature ͑RT͒ ferromagnetism. To be specific we perform our numerical simulations for GaMnNbased structures.However, it is still controversial if the reported RT ferromagnetism in transition metal doped GaN and ZnO is due to non-resolved precipitates or n...

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Importance of space-charge effects in resonant tunneling devices

Cited by 161 publications

References 10 publications

Polarization-balanced design of heterostructures: Application to AlN/GaN double-barrier structures

Polarization-balanced design of heterostructures: Application to AlN/GaN double-barrier structures

High photoexcited carrier multiplication by charged InAs dots in AlAs∕GaAs∕AlAs resonant tunneling diode

Resonant tunneling magnetoresistance in coupled quantum wells

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