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Houten, H. van; Williamson, J.; Broekaart, M.; Foxon, C.T.; Harris, J. J.

doi:10.1103/physrevb.37.2756

Cited by 69 publications

(34 citation statements)

References 5 publications

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“…By applying different Dingle temperatures, 0.6 K and 2 K, to the carriers originating from the two-fold and four-fold valleys respectively, the 7 K model is able to reproduce the unresolved spin degeneracy and the absence of oscillations from the higher energy valleys seen in the data. Differing scattering times are commonly observed in two component electron systems with different densities [15].…”

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confidence: 99%

Integer Quantum Hall Effect on a Six-Valley Hydrogen-Passivated Silicon (111) Surface

2007

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We report magneto-transport studies of a two-dimensional electron system formed in an inversion layer at the interface between a hydrogen-passivated Si(111) surface and vacuum. Measurements in the integer quantum Hall regime demonstrate the expected sixfold valley degeneracy for these surfaces is broken, resulting in an unequal occupation of the six valleys and anisotropy in the resistance. We hypothesize the misorientation of Si surface breaks the valley states into three unequally spaced pairs, but the observation of odd filling factors, is difficult to reconcile with noninteracting electron theory.PACS numbers: PAC Nos. 73.43.Qt, 71.70.Di The silicon field effect transistors (FETs) that are at the heart of contemporary microelectronics rely on mobile electrons or holes confined at the interface between Si and a higher bandgap barrier material. This barrier in metal oxide silicon (MOS) FETs is SiO 2 , an amorphous material which introduces inevitable disorder at the Si-SiO 2 interface and limits the carrier mobility in these devices. A crystalline interface can be created using epitaxial SiGe-Si layers in which mobilities can be over an order of magnitude higher than the best MOS-FET devices [1], but this technique is limited to the [100] oriented surfaces [2]. Recently a new technique for Si crystalline interfaces has been demonstrated [3] in which a Si interface is passivated with a monolayer of hydrogen and the barrier material is a vacuum. While the inertness and high degree of atomic perfection of these surfaces has been known for some time [4,5,6], the development of high mobility electronic devices on H-Si enables the exploration of two-dimensional (2D) physics of novel Si surface orientations and may one day allow quantum devices to be engineered at the atomic scale using surface manipulation techniques [7].We report here the first detailed magneto-transport studies of a 2D electron system (2DES) at a H-Si(111) surface gated through a vacuum barrier. Electron mobilities are an order of magnitude higher (24, 000cm 2 /Vs) than Si(111) MOSFETs, enabling the observations of the integer quantum Hall effect (IQHE). In the effective mass approximation the ground state for a 2DES on the Si(111) surface is six-fold degenerate with each Si conduction band valley contributing an equal number of carriers, (Fig. 1d) [8,9,10] and six [11,12] along with isotropic resistivities for both. Subsequent proposals [11,13] have tried to explain these anomalous observations, but to date conclusive experimental results are still lacking.The high mobility 2DES can be created by contact bonding two individual Si substrates [3] (Fig. 1a). One is the H-Si(111) substrate (float zone, p-type, ρ ∼ 10 Ω-cm) which has four phosphorous contacts forming a 1-mmwide square with sides oriented parallel to the [110] and [112] crystallographic directions (Fig. 1b and 1c). The second is a silicon-on-insulator (SOI) substrate which acts as the remote gate, where an electric field can be controlled within an etched cavity. The Si(111) surf...

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Integer Quantum Hall Effect on a Six-Valley Hydrogen-Passivated Silicon (111) Surface

2007

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“…Hall effect measurements performed at 4.2 K give a hole density of 3:8 Â 10 11 cm À2 and a mobility of 120,000 cm 2 =V s. The measurements shown here were performed in a 3 He/ 4 He dilution refrigerator with a base temperature of 70 mK, at which the mobility is 200,000 cm 2 =V s. Fig. 1 shows the longitudinal resistivity r xx as a function of the magnetic field.…”

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“…3. The positive, parabolic magnetoresistance is characteristic of the classical Drude magnetoresistance in a system with two subbands of different mobilities [4,1].…”

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Strong spin–orbit interactions in carbon doped p-type GaAs heterostructures

Grbić¹,

Leturcq²,

Ihn³

et al. 2008

Physica E: Low-dimensional Systems and Nanostructures

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“…From the low-field magnetoresistivity, τ 1 and τ 2 are obtained. Early studies on scattering times in two-subband systems relied on the assumption of two independent electronic systems with additive conductivities σ = σ 1 + σ 2 with σ i = n i e 2 τ i /m, quantitatively explaining a measured positive magnetoresistance [4,8,9] (e,m electron charge and effective mass).…”

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Variation of elastic scattering across a quantum well

et al. 1999

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The Drude scattering times of electrons in two subbands of a parabolic quantum well have been studied at constant electron sheet density and different positions of the electron distribution along the growth direction. The scattering times obtained by magnetotransport measurements decrease as the electrons are displaced towards the well edges, although the lowest-subband density increases. By comparing the measurements with calculations of the scattering times of a two-subband system, new information on the location of the relevant scatterers and the anisotropy of intersubband scattering is obtained. It is found that the scattering time of electrons in the lower subband depends sensitively on the position of the scatterers, which also explains the measured dependence of the scattering on the carrier density. The measurements indicate segregation of scatterers from the substrate side towards the quantum well during growth.The striking success of Ga [Al]As semiconductor heterostructures originates from the extremely high mobilities obtained in these materials. One key ingredient for the fabrication of such samples is modulation doping, where dopants and electrons are spatially separated. At low temperatures, impurity scattering, alloy scattering and interface roughness scattering limit the electron mobility [1]. If more than one subband is occupied, intersubband scattering takes place in addition [2,3].Information on the relevant scattering processes is usually obtained by measuring how quantum (τ q ) and Drude scattering times (τ ) vary with carrier density n S . For two-dimensional electron gases (2DEGs) realized in AlGaAs heterostructures, it is found that impurity scattering is dominant. In this case, one finds τ ∝ n γ S , with γ between 1 and 1.5, depending on the distance between the dopants and the 2DEG [1].In a two-subband system with subband densities n 1 and n 2 , the Drude scattering times τ i of subband i are usually found to increase monotonically with n i [4,5]. Recent results show that in a parabolic quantum well (PQW), τ 1 may also slowly decrease, i.e. γ < 0, when a second subband is occupied [6]. In this paper, we investigate this unusual dependence and show that it may be due to a certain arrangement of the ionized impurities.The PQW, grown by molecular beam epitaxy (MBE), is a 760Å wide Al x Ga 1−x As layer with x varying parabolically between 0 and 0.1 [7] (inset of Fig. 1a). In the center of the well, a three monolayer thick Al 0.05 Ga 0.95 As layer forms a potential spike. The well is embedded symmetrically in 200Å of undoped Al 0.3 Ga 0.7 As spacer layers and remote Si-doping layers on both sides. On the surface side, the donors are provided by 11 sheets, each with a Si donor density of nominally 5·10 15 m −2

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Magnetoresistance in a GaAs-AlxGa1−

Cited by 69 publications

References 5 publications

Integer Quantum Hall Effect on a Six-Valley Hydrogen-Passivated Silicon (111) Surface

Integer Quantum Hall Effect on a Six-Valley Hydrogen-Passivated Silicon (111) Surface

Strong spin–orbit interactions in carbon doped p-type GaAs heterostructures

Variation of elastic scattering across a quantum well

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