Generation, transport and detection of valley-polarized electrons in diamond

Isberg, Jan; Gabrysch, Markus; Hammersberg, J.; Majdi, Saman; Kovi, Kiran Kumar; Twitchen, Daniel J.

doi:10.1038/nmat3694

Cited by 145 publications

(127 citation statements)

References 26 publications

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“…10 Diamond has six equivalent conduction band valleys oriented along the {100} directions with a uniquely low scattering rate between these valleys. 11,12 Short wavelength lattice vibrations are required for intervalley scattering but these are, in diamond, absent at low temperatures due to the rigid lattice. Electrons in these valleys have a different longitudinal (m l ) and transversal effective mass (m t ), which cause a strong anisotropy in the transport properties of the polarized electrons.…”

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confidence: 99%

Investigation of transferred-electron oscillations in diamond

Suntornwipat

Majdi

Gabrysch

et al. 2016

Applied Physics Letters

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The recent discovery of Negative Differential Mobility (NDM) in intrinsic single-crystalline diamond enables the development of devices for high frequency applications. The TransferredElectron Oscillator (TEO) is one example of such devices that uses the benefit of NDM to generate continuous oscillations. This paper presents theoretical investigations of a diamond TEO in the temperature range of 110 to 140 K where NDM has been observed. Our simulations map out the parameter space in which transferred-electron oscillations are expected to occur for a specific device geometry. The results are promising and indicate that it is possible to fabricate diamond based TEO devices. Published by AIP Publishing. [http://dx.doi.org/10.1063/1.4952766]The carrier drift velocity in semiconductors is normally proportional to the electric field at low fields and saturates at high fields; nonetheless, Gunn observed that the velocity could behave in a different way. He discovered that at high fields, the electron drift velocity in Indium Phosphide and Gallium Arsenide decreased with an increase in the electric field.1,2 This was later called Negative Differential Mobility (NDM) or Negative Differential Resistance (NDR). 3 The phenomenon generally appears in direct bandgap III-V and II-VI semiconductor materials with non-equivalent valleys, such as GaAs, 1 InP, 1 InAs, 4 ZnSe, 5 and CdTe. [5][6][7][8] When increasing the applied electric field, electrons with a lower effective mass at the central conduction band valley are heated up and transferred into satellite valleys where they have a higher effective mass, thus decreasing the drift velocity and causing NDM to occur. This effect is not expected to occur in indirect bandgap materials but has previously been reported for silicon at a temperature below 45 K. 9 Furthermore, the phenomenon has been observed in intrinsic Single-Crystalline Chemical Vapor Deposition (SC-CVD) diamond.10 With an applied electric field of 300 to 600 V/cm in the [100] direction, the NDM effect was observed in a temperature range of 110 to 140 K. Since diamond is an indirect bandgap material, this effect occurs in a somewhat different way. 10Diamond has six equivalent conduction band valleys oriented along the {100} directions with a uniquely low scattering rate between these valleys.11,12 Short wavelength lattice vibrations are required for intervalley scattering but these are, in diamond, absent at low temperatures due to the rigid lattice. Electrons in these valleys have a different longitudinal (m l ) and transversal effective mass (m t ), which cause a strong anisotropy in the transport properties of the polarized electrons. If an electric field is applied in the [100] direction, two valleys are aligned in parallel (on the (100) axis) and four valleys orthogonal to the field (on the (010) and (001) (010) and (001) axes respond with the transversal effective mass (m t ¼ 0.22 m 0 ). 13 At low electric fields, the electron drift velocity is proportional to the field. By increasing the electric field, the ...

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confidence: 99%

Investigation of transferred-electron oscillations in diamond

Suntornwipat

Majdi

Gabrysch

et al. 2016

Applied Physics Letters

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“…In contrast, LaSb with a similar Fermi-surface anisotropy and even higher effective mass ratio shows smaller polarization due. We further point out that the electron-like Fermi surface of LaBi highly resembles that of diamond which has previously been shown to be very effective in generating valley polarized electrons [21].…”

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confidence: 55%

Magnetic field induced strong valley polarization in the three-dimensional topological semimetal LaBi

et al. 2017

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LaBi is a three-dimensional rock-salt-type material with a surprisingly quasi-two-dimensional electronic structure. It The search of an extra degree of freedom has played a significant role in modern technological advancements. In spintronics, one adds the spin degree of freedom in charge devices [1,2], whereas in the magnetoelectric multiferroics, the polarization can be manipulated by a magnetic field and vice versa [3,4]. In recent years, a new field named valleytronics shows great promise particularly in materials with two-dimensional (2D) electronic structures based on their layered crystal structure. For example in graphene, linearly dispersing conical bands (valleys) touch at the high symmetry points of the Brillouin zone (BZ) and one of the exciting aspects for exploiting such a band structure is to occupy (polarize) one valley much larger than another in a controlled fashion. This enables graphene to be used for valley valves and valley filters [5,6]. In contrast to graphene, monolayers of some of the transition metal dichalcogenides (TMDs) inherit broken inversion symmetry with finite band gap. The absence of inversion symmetry and a finite band gap provide crucial electrical and optical control of the valley degree of freedom. [7][8][9]

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“…(13). The 2D spatial extension of this wave function in the xy plane is characterized by the effective Bohr radius a eB .…”

Section: Appendix D: Estimation Of the Effective Bohr Radiusmentioning

confidence: 99%

Valley relaxation in graphene due to charged impurities

Boross

Pályi

2015

Phys. Rev. B

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Monolayer graphene is an example of materials with multivalley electronic structure. In such materials, the valley index is being considered as an information carrier. Consequently, relaxation mechanisms leading to loss of valley information are of interest. Here, we calculate the rate of valley relaxation induced by charged impurities in graphene. A special model of graphene is applied, where the p z orbitals are two-dimensional Gaussian functions, with a spatial extension characterized by an effective Bohr radius a eB . We obtain the valley relaxation rate by solving the Boltzmann equation, for the case of noninteracting electrons, as well as for the case when the impurity potential is screened due to electron-electron interaction. For the latter case, we take into account local-field effects and evaluate the dielectric matrix in the random phase approximation. Our main findings are as follows: (i) The valley relaxation rate is proportional to the electronic density of states at the Fermi energy. (ii) Charged impurities located in the close vicinity of the graphene plane, at distance d 0.3Å, are much more efficient in inducing valley relaxation than those farther away, the effect of the latter being suppressed exponentially with increasing graphene-impurity distance d. (iii) Both in the absence and in the presence of electron-electron interaction, the valley relaxation rate shows pronounced dependence on the effective Bohr radius a eB . The trends are different in the two cases: In the absence (presence) of screening, the valley relaxation rate decreases (increases) for increasing effective Bohr radius. This last result highlights that a quantitative calculation of the valley relaxation rate should incorporate electron-electron interactions as well as an accurate knowledge of the electronic wave functions on the atomic length scale.

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Generation, transport and detection of valley-polarized electrons in diamond

Cited by 145 publications

References 26 publications

Investigation of transferred-electron oscillations in diamond

Investigation of transferred-electron oscillations in diamond

Magnetic field induced strong valley polarization in the three-dimensional topological semimetal LaBi

Valley relaxation in graphene due to charged impurities

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