Self-consistent model of transport in quantum well tunneling structures

Pötz, W.

doi:10.1063/1.344257

Cited by 85 publications

(48 citation statements)

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“…14 The purpose of this paper is to provide a simple description of the nonunitary evolution of a ballistic nanostructure's active region due to the injection of carriers from the contacts. Carrier injection from the contacts into the active region is traditionally described by either an explicit source term, such as in the single-particle density matrix, 15,16,17,18,19,20 Wigner function 2,3,21,22,23,24,25,26,27,28,29 and Pauli equation 30,31 transport formalisms, or via a special self-energy term in the ubiquitous nonequilibrium Green's function formalism. 32,33,34,35,36,37 In this work, the problem of contact-induced decoherence is treated using the open systems formalism: 38 we start with a model interaction Hamiltonian that describes the injection of carriers from the contacts, and then deduce the resulting nonunitary evolution of the active region's many-body reduced statistical operator in the Markovian approximation.…”

Section: Introductionmentioning

confidence: 99%

Decoherence due to contacts in ballistic nanostructures

Knežević

2008

Phys. Rev. B

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The active region of a ballistic nanostructure is an open quantum-mechanical system, whose nonunitary evolution (decoherence) towards a nonequilibrium steady state is determined by carrier injection from the contacts. The purpose of this paper is to provide a simple theoretical description of the contact-induced decoherence in ballistic nanostructures, which is established within the framework of the open systems theory. The active region's evolution in the presence of contacts is generally non-Markovian. However, if the contacts' energy relaxation due to electron-electron scattering is sufficiently fast, then the contacts can be considered memoryless on timescales coarsened over their energy relaxation time, and the evolution of the current-limiting active region can be considered Markovian. Therefore, we first derive a general Markovian map in the presence of a memoryless environment, by coarse-graining the exact short-time non-Markovian dynamics of an abstract open system over the environment memory-loss time, and we give the requirements for the validity of this map. We then introduce a model contact-active region interaction that describes carrier injection from the contacts for a generic two-terminal ballistic nanostructure. Starting from this model interaction and using the Markovian dynamics derived by coarse-graining over the effective memory-loss time of the contacts, we derive the formulas for the nonequilibrium steady-state distribution functions of the forward and backward propagating states in the nanostructure's active region. On the example of a double-barrier tunneling structure, the present approach yields an I-V curve that shows all the prominent resonant features. We address the relationship between the present approach and the Landauer-Büttiker formalism, and also briefly discuss the inclusion of scattering.

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Section: Introductionmentioning

confidence: 99%

Decoherence due to contacts in ballistic nanostructures

Knežević

2008

Phys. Rev. B

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“…The relation between the electrostatic drop and asymptotic charge neutrality is already implicit in the original form of the Landauer formula 16,17 I = T R ∆φ, and has been explored by some authors over the years 18,19 until very recently 20 . In Ref.…”

Section: Introductionmentioning

confidence: 99%

Asymptotic self-consistency in quantum transport calculations

2005

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Ab-initio simulations of quantum transport commonly focus on a central region which is considered to be connected to infinite, periodic leads through which the current flows. The electronic structure of these distant leads is normally obtained from an equilibrium calculation, ignoring the self-consistent response of the leads to the current. We examine the consequences of this, and show that the electrostatic potential, ∆φ, is effectively being approximated by the difference between electrochemical potentials, ∆µ, and that this approximation is incompatible with asymptotic charge neutrality. In a test calculation for a simple metal-vacuum-metal junction, we find large errors in the non-equilibrium properties calculated with this approximation, in the limit of small vacuum gaps. We provide a simple scheme by which these errors may be corrected.

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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 …”

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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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Self-consistent model of transport in quantum well tunneling structures

Cited by 85 publications

References 28 publications

Decoherence due to contacts in ballistic nanostructures

Decoherence due to contacts in ballistic nanostructures

Asymptotic self-consistency in quantum transport calculations

Resonant tunneling magnetoresistance in coupled quantum wells

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