Comparison of mobility-limiting mechanisms in high-mobility Si1−<i>x</i>Ge<i>x</i> heterostructures

Monroe, Don; Xie, Y. H.; Fitzgerald, Eugene A.; Silvėrman, P. J.; Watson, George

doi:10.1116/1.586471

Cited by 103 publications

(65 citation statements)

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“…Comparing this quantum scattering time to the transport scattering time τ t , obtained from the mobility through µ = eτ t /m * , we obtain Dingle ratios τ t /τ q ranging from ∼ 80 to ∼ 17 for the 3 deepest quantum wells and a Dingle ratio of ∼ 1.5 for the shallowest quantum well. The large Dingle ratios are indicative that the rate of large angle scattering, caused by background impurities located in the quantum well, is much smaller than the rate of small angle scattering caused by remote impurities, 30 confirming the high quality of the devices presented in this study and the hypothesis that mobility is limited by scattering from charges trapped near the heterostructure surface. The small Dingle ratio of the shallower device implies that the charge centers are in such close proximity to the 2DEG that they induce large angle scattering.…”

Section: Deg Depthsupporting

confidence: 65%

“…dependence on the density, µ ∝ n α , α ≤ 0.3, 30,31,33,34 which is not what we experimentally observe in our devices. Charges accumulating directly underneath the metal gate are also unlikely to be the dominant source of scattering in this device due to the strong shielding the metal gate itself would induce on such charges.…”

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confidence: 38%

“…Interface roughness scattering causes the mobility to decrease with increasing density 7,[30][31][32] and is thus extremely unlikely to be the dominant scattering mechanism in our devices, except near the highest achievable densities in the 100 nm deep device (green dotted line). Scattering from charge centers could arise from many sources in our devices: background impurities in the Si quantum well, background impurities in the SiGe barriers, trapped charges at the Si/SiGe (quantum well / spacer) interfaces, trapped charges at the cap/spacer interface, trapped charges at the amorphous SiO 2 /Si interface, charges trapped at the SiO 2 /Al 2 O 3 interface, or charges trapped at the gate/insulator interface.…”

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confidence: 99%

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Scattering mechanisms in shallow undoped Si/SiGe quantum wells

et al. 2015

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We report the magneto-transport study and scattering mechanism analysis of a series of increasingly shallow Si/SiGe quantum wells with depth ranging from ∼ 100 nm to ∼ 10 nm away from the heterostructure surface. The peak mobility increases with depth, suggesting that charge centers near the oxide/semiconductor interface are the dominant scattering source. The power-law exponent of the electron mobility versus density curve, μ ∝ nα, is extracted as a function of the depth of the Si quantum well. At intermediate densities, the power-law dependence is characterized by α ∼ 2.3. At the highest achievable densities in the quantum wells buried at intermediate depth, an exponent α ∼ 5 is observed. We propose and show by simulations that this increase in the mobility dependence on the density can be explained by a non-equilibrium model where trapped electrons smooth out the potential landscape seen by the two-dimensional electron gas.

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Section: Deg Depthsupporting

confidence: 65%

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confidence: 38%

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confidence: 99%

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Scattering mechanisms in shallow undoped Si/SiGe quantum wells

et al. 2015

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“…We note that in spite of the much improved zero-field mobility, the extracted CF mobility using the resistivity at ν = 1/2 is only ∼ 8. clearly highlighted such effects [31]. In our undoped enhancement-mode FET, the mobility saturates at n = 1.5 × 10 11 /cm 2 and even shows a slight decrease with increasing n [18], indicating that interface roughness scattering becomes important at high densities [32]. This is different from modulation-doped heterostructures where disorder is dominant by remote charge scattering.…”

Section: Fig 1 (A)mentioning

confidence: 60%

Fractional quantum Hall effect of two-dimensional electrons in high-mobility Si/SiGe field-effect transistors

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Tsui

et al. 2012

Phys. Rev. B

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The fractional quantum Hall (FQH) regime of the Si two-dimensional electron system (2DES) in enhancement-mode field-effect transistors of Si/SiGe heterostructures was probed via electrical transport measurements. At n ∼ 2.6 × 10 11 /cm 2 with µ = 1.6 × 10 6 cm 2 /V s, signatures of FQH states at filling factors ν = 4/5, 6/5, and 10/7 were observed, in addition to the FQH states reported in previous studies. The temperature dependence of the FQH states is investigated and comparison is made with previous work done on modulation-doped samples. Results indicate that robustness of the FQH states is dependent on the nature of disorder in the 2DES. 1The discoveries of the integer quantum Hall (IQH) effect[1] and the fractional quantum Hall (FQH) effect [2] have spurred much research on the ground states of two-dimensional (2D) electrons in the presence of strong magnetic fields over the past 30 years. Thanks to to the constantly refined III-V epitaxial technology, the quality of GaAs/AlGaAs heterostructures has been continually improving, leading to the observation of a few tens of FQH states in GaAs [3]. While large in number, most of the FQH states can be understood within the theoretical framework of composite fermions (CFs) [4]. In the CF model, the FQH effect, originally arising from electron-electron interaction, is mapped to the IQH effect arising from Landau quantization of the orbital motion of CFs.Soon after the discoveries of the IQH and FQH effects, it was realized that additional degrees of freedom of 2DESs such as spins, layers, subbands, and valleys, may produce new correlated states which do not exist in a one-component 2DES [5]. Celebrated examples include Skyrmions in systems with small Zeeman splitting [6,7], even-denominator FQH states [8,9], and the excitonic superfluid in bilayer systems [10]. While much effort towards the understanding of the roles of spins, layers, and subbands in the FQH regime has been made using high-quality GaAs quantum wells, experimental studies on the effects of valleys have been relatively sparse, only a few reports on 2D electrons in Si [11,12] and AlAs [13][14][15][16] available, partly due to the less impressive material quality of multi-valley semiconductors.Indeed, the electron mobilities of the devices used in these studies were smaller than that of GaAs by almost two orders of magnitude [3,17]. Nevertheless, looking back at the history of discoveries of new states in GaAs, we may expect that more interesting physical phenomena in multi-valley systems will emerge, once materials with higher mobility are available.Recently, we reported a fabrication process for making undoped (100)-oriented Si/SiGe FETs and observed an electron mobility of 1.6 × 10 6 cm 2 /V s [18], approximately eight times higher than that of typical modulation-doped Si/SiGe quantum wells [19]. Such improvement in material quality naturally prompted us to perform magneto-transport experiments and search for new states in Si 2DESs. In this paper, we focus on the FQH regime ν < 2, where the...

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“…1, we show the fitting (gray trace) to the curve of the mobility versus density following the method used in Ref. [23]. The obtained value for the random impurity density is n i = Fig.…”

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confidence: 99%