Publications (602)1931.38 Total impact
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ABSTRACT: Microwave cyclotron resonance of lowdensity highmobility twodimensional hole gases of different densities in (100) oriented GaAs/AlGaAs heterostructures has been measured at 4.2 K. The measurements show that the hole effective mass depends strongly on the confining potential. For holes in a 20 nm quantum well, the cyclotron mass decreases from 0.48me at density p = 6.9×1010/cm2 to 0.29me at p = 0.8×1010/cm2. The cyclotron mass for holes confined at a heterojunction is fairly insensitive to the density and has a value of approximately 0.5me.  [Show abstract] [Hide abstract]
ABSTRACT: In a GaAs/AlGaAs quantum well of density 1×1011 cm2 we observed a fractional quantum Hall effect (FQHE) at nu=4/11 and 5/13, and weaker states at nu=6/17, 4/13, 5/17, and 7/11. These sequences of fractions do not fit into the standard series of integral quantum Hall effects of composite fermions (CF) at nu=p/(2mp±1). They rather can be regarded as the FQHE of CFs attesting to residual interactions between these composite particles. In tilted magnetic fields the nu=4/11 state remains unchanged, strongly suggesting it to be spin polarized. The weak nu=7/11 state vanishes quickly with tilt.  [Show abstract] [Hide abstract]
ABSTRACT: We report studies of pinning mode resonances in the low total Landau filling (nu) Wigner solid of a series of bilayer hole samples with negligible interlayer tunneling and with varying interlayer separation d. Comparison of states with equal layer densities (p,p) to single layer states (p,0) produced in situ by biasing, indicates that there is interlayer quantum correlation in the solid at small d. Also, the resonance frequency at small d is decreased just near nu = 1/2 and 2/3, indicating the importance in the solid of correlations related to those in the fractional quantum Hall effects.  [Show abstract] [Hide abstract]
ABSTRACT: The results of experimental transport studies involving a series of five narrow Al <sub>0.1</sub> Ga <sub>0.9</sub> As / Ga As quantum wells with well widths ranging from 7.9 to 33.0 nm are reported. The total transport scattering rate measured in thin Al Ga As / Ga As quantum wells is typically limited by electron scattering from the interfacial roughness of the quantum well. For a relatively low constant electron density (n<sub>e</sub>∼5.8×10<sup>10</sup> cm <sup>2</sup>) , the authors find that interfacial roughness is the dominant scattering mechanism for L≤16.0 nm and describe the data using a finite quantum well model with adjustable interfacial roughness parameters. Temperature dependence data are also presented.  [Show abstract] [Hide abstract]
ABSTRACT: The zerofield temperature dependence of the resistivity of twodimensional holes is observed to exhibit two qualitatively different characteristics for a fixed carrier density for which only the metallic behavior of the socalled metalinsulator transition is anticipated. As T is lowered from 150 to 0.5 mK, the sign of the derivative of the resistivity with respect to T changes from being positive to negative when the temperature is lowered below approximately 30 mK and the resistivity continuously rises with cooling down to 0.5 mK, suggesting a crossover from being metallike to insulatorlike.  [Show abstract] [Hide abstract]
ABSTRACT: The authors demonstrate that a high mobility twodimensional electron gas can be capacitively induced in an undoped Si/Si1xGex heterostructure using atomiclayerdeposited Al2O3 as the dielectric. The density is tuned up to 4.2×1011/cm2, limited by the gate leakage current. The mobility increases with the density rapidly and reaches 5.5×104 cm2/V s at the highest density. The observation of well developed quantum Hall states and twodimensional metalinsulator transition shows that the devices are suitable for twodimensional electron physics studies.  [Show abstract] [Hide abstract]
ABSTRACT: We present a fabrication process and results of transport measurements of a number of pchannel heterojunctioninsulatedgate fieldeffect transistors (HIGFETs). Without intentional doping in HIGFETs, the disorder is likely to be less than that in the modulationdoped samples. We established a process that eliminates the wellknown gate leakage problem. The hole density in our devices can be continuously tuned down to a record low value of 7 × 108 cm2. Remarkably, such a dilute system (with Fermi wavelength approaching 1 mum) exhibits a nonactivated conductivity that grows with temperature approximately as a power law at sufficiently low temperatures. We contrast it with the activated transport found in more disordered samples and discuss possible transport mechanisms in this stronglyinteracting regime.  [Show abstract] [Hide abstract]
ABSTRACT: Wigner solids in twodimensional electron systems in high magnetic field B exhibit a striking, microwave or rf resonance, that is understood as a pinning mode. The temperature, Tm, above which the resonance is absent, is interpreted as the melting temperature of the solid. Studies of Tm for many B and many sample densities n show that Tm is a function of the Landau level filling ν alone for a given sample. This indicates that quantum mechanics figures importantly in the melting. Tm also appears to be increased by larger sample disorder.  [Show abstract] [Hide abstract]
ABSTRACT: The authors have fabricated undoped pchannel GaAs/AlxGa1xAs heterostructure fieldeffect transistors with nearly ideal drain currentvoltage characteristics, using atomiclayerdeposited Al2O3 as the dielectric, and measured their transport properties. At 0.3 K, the densities and mobilities of the two dimensional holes can be tuned up to 2.9x10(11)/cm(2) and 6.4x10(5) cm(2)/V s, respectively. The variable density high mobility twodimensional hole system provides a large parameter space for the study of twodimensional physics. (c) 2007 American Institute of Physics. 
Article: 2D hole transport in GaAs MOSFETs
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ABSTRACT: We have fabricated enhancementmode pchannel GaAs MOSFETs on the (100) surface of undoped GaAs/AlxGa1xAs heterostructures, using atomiclayerdeposited Al2O3 dielectric and Ti/Au gate, and measured their transport properties. The capacitively induced 2D hole density (p), determined from Shubnikovde Haas oscillations, can be tuned from 9x10^9 to 3x10^11cm2 by applying a negative gate bias. Within this range, the effective capacitance is close to that of an ideal parallel plate capacitor, and the leakage current remains virtually zero. The highest possible density is limited by the heterostructure design, not by gate leakage. The 2D hole mobility at T=0.3K increases with p and saturates at 6.3x10^5 cm^2/Vs for p>2.3x10^11cm2. In this talk, we present data on transistor drain currentvoltage characteristics, as well as magneto transport and the quantum Hall effects.  [Show abstract] [Hide abstract]
ABSTRACT: We present finite frequency conductivity measurements on ultra high mobility twodimensional electron systems in GaAs/AlGaAs. At low temperature T  [Show abstract] [Hide abstract]
ABSTRACT: We report measurements of the RF diagonal conductivity, Re[sigmaxx(f)], of ultrahigh mobility 2D electron systems with Landau level (LL) filling factor 4  [Show abstract] [Hide abstract]
ABSTRACT: We have studied the magnetotransport of two dimensional electron systems with various amount of shortrange alloy disorder. Our samples are AlxGa1xAsAl0.32Ga0.68As heterostructures with the Al concentration x ranging from 0 to 0.85%, and the electron mobility varies from 1.2x10^7cm^2/V.s down to 8.9x10^5cm^2 /V.s within this x range. We have two major observations in the high magnetic field regime. First, we have found that the amplitude of the fractional quantum Hall gaps is independent on x. Second, and more surprisingly, we have observed a nu=1 reentrant integer quantum Hall effect (RIQHE) between the Landau level filling factor nu=2/3 and nu=3/5 in the sample with x=0.85%. Between the quantum Hall Plateaus of nu=2/3 and nu=3/5, the Hall resistance is observed to be quantized to h/e^2 while the longitudinal resistance reaches a deep minimum.  [Show abstract] [Hide abstract]
ABSTRACT: The results of experimental transport studies involving a series of thin GaAs/AlGaAs quantum wells with varying well widths will be reported. The mobility, mu, of thin GaAs/AlGaAs quantum wells is typically limited by electron scattering from the interfacial roughness of the quantum well. The total scattering rate due to all scattering mechanisms is determined from the mobility through &1circ;=e/mum^* where m^* is the effective electron mass. Our series of samples consists of well widths of L=7.9, 9.9, 12.9, 16.0 and 33.0 nm. For constant electron density (ne˜5.5x10^10 cm2) we find that interfacial roughness is the dominant scattering mechanism for L  [Show abstract] [Hide abstract]
ABSTRACT: We report spontaneous narrow band oscillations in the high field Wigner solid. These oscillations are similar to the recently seen and yet unexplained oscillations in the reentrant integer quantum Hall states. The currentvoltage characteristic has a region of negative differential resistance in the current biased setup and it is hysteretic in the voltage biased setup. As a consequence of the unusual breakdown, the oscillations in the Wigner solid are of the relaxation type.  [Show abstract] [Hide abstract]
ABSTRACT: In a high mobility twodimensional electron system in Si, near the critical density, $n_c=0.32\times10^{11}$cm$^{2}$, of the apparent metaltoinsulator transition, the conductivity displays a linear temperature ($T$) dependence around the Fermi temperature. When $\sigma_0$, the extrapolated T=0 conductivity from the linear Tdependence, is plotted as a function of density, two regimes with different $\sigma_0(n)$ relations are seen, suggestive of two different phases. Interestingly, a sharp transition between these two regimes coincides with $n_c$, and $\sigma_0$ of the transition is $\sim$ $e^2/h$, the quantum conductance, per square. Toward T=0, the data deviate from linear $\sigma(T)$ relation and we discuss the possible percolation type of transition in our Si sample.  [Show abstract] [Hide abstract]
ABSTRACT: An overview is given of some recent experiments on the localizationdelocalization transition in the integral quantum Hall effect and the new quantum liquid ground states giving rise to the fractional quantum Hall effect.  [Show abstract] [Hide abstract]
ABSTRACT: Cyclotron resonance at microwave frequencies is used to measure the band mass (mb) of the twodimensional holes (2DHs) in carbondoped (100) GaAs/ AlxGa1−xAs heterostructures. The measured mb shows strong dependences on both the 2DH density (p) and the GaAs quantum well width (W). For a fixed W, in the density range (0.4×1011 to 1.1×1011 cm−2) studied here, mb increases with p, consistently with previous studies of the 2DHs on the (311)A surface. For a fixed , mb increases from 0.22me at to 0.50me at , and saturates around 0.51me for .  [Show abstract] [Hide abstract]
ABSTRACT: A SiGe quantum dot singlehole transistor passivated by silicon epitaxial regrowth with extremely stable Coulomb blockade oscillations has been demonstrated. The quantum dot was defined by atomic force microscopy nanopatterning technique and subsequently passivated by the epitaxial regrowth of silicon. Such passivation of the dot avoids any potential defect states on the dot associated with the Si / Si O <sub>2</sub> interface. Coulomb blockade oscillations controlled by side planar gating at ∼0.3 K are reproducible, in sharp contrast with the noisy and irreproducible IV characteristics of unpassivated SiGe quantum dot devices. An additional top gate was used to further tune the Coulomb blockade oscillations, enabling a shift in sidegate voltage of up to three periods.  [Show abstract] [Hide abstract]
ABSTRACT: Recent experiments have shown that twodimensional electron systems with an externally applied magnetic field are an extremely rich ground for manybody physics. In particular, when only two of the Landau levels (LL) are filled an intricate magnetoresistance is found. This result stems from an interesting competition of electronic phases such as fractional quantum Hall liquids, reentrant integer Hall states, and unique quantized states at even denominator LL filling factors. We present a brief review of the transport properties of these electronic phases and discuss in detail the effects of an added inplane magnetic field. (c) 2006 Elsevier B.V. All rights reserved.
Publication Stats
21k  Citations  
1,931.38  Total Impact Points  
Top Journals
 Applied Physics Letters (86)
 Physical review. B, Condensed matter (70)
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Institutions

19822015

Princeton University
 Department of Electrical Engineering
Princeton, New Jersey, United States 
Max Planck Institute for Solid State Research
Stuttgart, BadenWürttemberg, Germany


2004

Sandia National Laboratories
 Semiconductor Material and Device Sciences Department
Albuquerque, New Mexico, United States 
Florida State University
 Department of Physics
Tallahassee, Florida, United States


1998

Columbia University
 Department of Physics
New York City, New York, United States


19871998

AT&T Labs
Austin, Texas, United States
