Multivalley two-dimensional electron system in an AlAs quantum well with mobility exceeding 
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Chung, Yoon Jang; Rosales, K. A. Villegas; Deng, Hao; Baldwin, K. W.; West, K. W.; Shayegan, M.; Pfeiffer, L. N.

doi:10.1103/physrevmaterials.2.071001

Cited by 23 publications

(16 citation statements)

References 40 publications

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“…1A. Our mate-rial platform is a very low disorder, dilute 2DES confined to a modulation-doped, 21-nm-wide AlAs quantum well (ε = 10) [24]. The 2D electrons in our sample occupy two in-plane conduction-band valleys with longitudinal and transverse effective masses m l = 1.1, and m t = 0.20, leading to an effective in-plane band mass m equal to (m l m t ) 1/2 = 0.46 [25].…”

Section: Resultsmentioning

confidence: 99%

Observation of Spontaneous Ferromagnetism in a Two-Dimensional Electron System

Hossain,

Ma,

Rosales

et al. 2020

Preprint

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What are the ground states of an interacting, low-density electron system? In the absence of disorder, it has long been expected that as the electron density is lowered, the exchange energy gained by aligning the electron spins should exceed the enhancement in the kinetic (Fermi) energy, leading to a (Bloch) ferromagnetic transition. At even lower densities, another transition to a (Wigner) solid, an ordered array of electrons, should occur. Experimental access to these regimes, however, has been limited because of the absence of a material platform that supports an electron system with very high-quality (low disorder) and low density simultaneously. Here we explore the ground states of interacting electrons in an exceptionally-clean, two-dimensional electron system confined to a modulation-doped AlAs quantum well. The large electron effective mass in this system allows us to reach very large values of the interaction parameter rs, defined as the ratio of the Coulomb to Fermi energies. As we lower the electron density via gate bias, we find a sequence of phases, qualitatively consistent with the above scenario: a paramagnetic phase at large densities, a spontaneous transition to a ferromagnetic state when rs surpasses 35, and then a phase with strongly non-linear current-voltage characteristics, suggestive of a pinned Wigner solid, when rs exceeds 38. However, our sample makes a transition to an insulating state at rs 27, preceding the onset of the spontaneous ferromagnetism, implying that, besides interaction, the role of disorder must also be taken into account in understanding the different phases of a realistic dilute electron system.

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Section: Resultsmentioning

confidence: 99%

Observation of Spontaneous Ferromagnetism in a Two-Dimensional Electron System

Hossain,

Ma,

Rosales

et al. 2020

Preprint

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“…This, in turn, will affect the device characteristics like slope efficiency in lasers, energy conversion efficiency in the solar cells and the overall operation lifetime of any device. As the above device characteristics strongly depend on the QW materials purity, the quest to obtain pure multi QW structures is ongoing now [6][7][8][9]. That is why the major efforts are concentrated on the fabrication of high-quality QW structures on the base, most frequently of the alloy Ga 1−x Al x As [8,9].…”

Section: Introductionmentioning

confidence: 99%

Electron spectra in double quantum wells of different shapes

2022

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We suggest a method for calculating electronic spectra in ordered and disordered semiconductor structures (superlattices) forming double quantum wells (QW). In our method, we represent the solution of Schr\"odinger equation for QW potential with the help of the solution of the corresponding diffusion equation. This is because the diffusion is the mechanism, which is primarily responsible for amorphization (disordering) of the QW structure, leading to so-called interface mixing. We show that the electron spectrum in such a structure depends on the shape of the quantum well, which, in turn, corresponds to an ordered or disordered structure. Namely, in a disordered substance, QW typically has smooth edges, while in ordered one it has an abrupt, rectangular shape. The present results are relevant for the heterostructures like GaAs/AlGaAs, GaN/AlGaN, HgCdTe/CdTe, ZnSe/ZnMnSe, Si/SiGe, etc., which may be used in high-end electronics, flexible electronics, spintronics, optoelectronics, and energy harvesting applications.

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“…If the mobility is limited by short-range neutral disorder (e.g., interface roughness or lattice defects), then this phenomenon of higher mobility in n-SiGe and n-AlAs than in n-GaAs would not happen. The question therefore arises why the existing best 2D GaAs holes [18] , 2D AlAs electrons [19], and 2D Si-Ge electrons [20,21] have much lower mobility than the ones predicted in our theory as shown in Fig. 2.…”

Section: Theory and Resultsmentioning

confidence: 61%

Density-dependent two-dimensional optimal mobility in ultra-high-quality semiconductor quantum wells

Ahn,

Sarma

2021

Preprint

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We calculate using the Boltzmann transport theory the density dependent mobility of twodimensional (2D) electrons in GaAs, SiGe and AlAs quantum wells as well as of 2D holes in GaAs quantum wells. The goal is to precisely understand the recently reported breakthrough in achieving a record 2D mobility for electrons confined in a GaAs quantum well. Comparing our theory with the experimentally reported electron mobility in GaAs quantum wells, we conclude that the mobility is limited by unintentional background random charged impurities at an unprecedented low concentration of ∼ 10 13 cm −3 . We find that this same low level of background disorder should lead to 2D GaAs hole and 2D AlAs electron mobilities of ∼ 10 7 cm 2 /V s and ∼ 4 × 10 7 cm 2 /V s, respectively, which are much higher theoretical limits than the currently achieved experimental values in these systems. We therefore conclude that the current GaAs hole and AlAs electron systems are much dirtier than the state of the arts 2D GaAs electron systems. We present theoretical results for 2D mobility as a function of density, effective mass, quantum well width, and valley degeneracy, comparing with experimental data.

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Multivalley two-dimensional electron system in an AlAs quantum well with mobility exceeding 2×106cm2V−1

Cited by 23 publications

References 40 publications

Observation of Spontaneous Ferromagnetism in a Two-Dimensional Electron System

Observation of Spontaneous Ferromagnetism in a Two-Dimensional Electron System

Electron spectra in double quantum wells of different shapes

Density-dependent two-dimensional optimal mobility in ultra-high-quality semiconductor quantum wells

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