Publications (580)1851.85 Total impact
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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.Physical Review Letters 03/2007; 98(6):066805. · 7.73 Impact Factor  [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 L03/2007; 
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.03/2007;  [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 403/2007;  [Show abstract] [Hide abstract]
ABSTRACT: We present finite frequency conductivity measurements on ultra high mobility twodimensional electron systems in GaAs/AlGaAs. At low temperature T03/2007;  [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.03/2007;  [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.Physical Review B 01/2007; 75(3):033314. · 3.66 Impact Factor  [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.Applied Physics Letters 01/2007; 90. · 3.79 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We have fabricated undoped pchannel GaAs/AlxGa1−xAs heterostructure fieldeffect transistors with nearly ideal drain currentvoltage characteristics, using atomiclayerdeposited Al2O3 as the dielectric, and measured their transport properties. At 0.3K, the densities and mobilities of the two dimensional holes can be tuned up to 2.9×10 11 /cm 2 and 6.4×10 5 cm 2 /Vs respectively. The variable density high mobility twodimensional hole system provides a large parameter space for the study of twodimensional physics. Appl. Phys. Lett. 90, 112113 (2007) High mobility twodimensional electron gases (2DEGs) have benefited research in condensed matter physics and brought about many interesting physical phenomena [1]. Conventionally there are two ways of realizing 2DEGs. Modulationdoping is the most widely used technique for GaAs/Al x Ga 1−x As heterostructures, in which electrons transfer from dopants in the barrier layer to the heterojunction interface and form the high mobility 2DEG. Metaloxidesemiconductor fieldeffect transistors (MOSFETs) are quite popular for Sibased systems, utilizing a high quality thermal oxide not available in other semiconductors. In a MOSFET, the 2DEG is induced at the interface of the semiconductor and the amorphous oxide by an electric field. The nature of disorder in the two types of 2DEGs is significantly different and is expected to have impact on their physical properties. Fabrication of enhancementmode (emode) GaAs transistors has proved to be a difficult task, primarily due to the lack of a good thermal oxide on GaAs surfaces [2]. The heterostructureinsulatedgate field effect transistor (HIGFET), whose insulating layer is molecular beam epitaxy (MBE) grown Al x Ga 1−x As, is so far the only widely studied GaAsbased emode device [3, 4]. Different variations of the HIGFET have also been demonstrated [5–8]. However, the insulating layer has an intrinsically small barrier height. Significant leakage current flows at large gate voltages and limits the tunable density range of the 2D carriers.Applied Physics Letters 01/2007; 90. · 3.79 Impact Factor  [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.International Journal of Modern Physics B 01/2007; 21(0809). · 0.46 Impact Factor  [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.International Journal of Modern Physics B 01/2007; 21:12191227. · 0.46 Impact Factor  [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.Annals of the New York Academy of Sciences 12/2006; 581(1):160  168. · 4.38 Impact Factor  [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 .Solid State Communications 12/2006; · 1.53 Impact Factor  [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.Journal of Applied Physics 12/2006; · 2.21 Impact Factor  [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.Physica E Lowdimensional Systems and Nanostructures 12/2006; · 1.86 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The powerlaw increase of the conductivity with temperature in the nominally insulating regime, recently reported for the dilute twodimensional holes [condmat/0603053], is found to systematically vary with the carrier density. Based on the results from four different GaAs heterojunctioninsulatedgate fieldeffecttransistor samples, it is shown that the power law exponent depends on a single dimensionless parameter, the ratio between the mean carrier separation and the distance to the metallic gate that screens the Coulomb interaction. This dependence suggests that the carriers form a correlated state in which the interaction effects play a significant role in the transport properties.11/2006; 
Article: Metalinsulator Transition of 2D Electrons in a Modulation Doped Si/Si1xGex Heterostructure
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ABSTRACT: We report the observation of the apparent metalinsulator transition (MIT) of twodimensional electrons in a high quality modulation doped Si/Si1xGex heterostructure. The critical density nc, at which the thermal coefficient of its low temperature resistivity changes sign, is 0.32×1011 cm2, much smaller than the nc of ~ 0.8×1011cm2 seen in clean SiMOSFET's. This is consistent with previous observations in 2D holes in GaAs that nc decreases with decreasing disorder.09/2006;  [Show abstract] [Hide abstract]
ABSTRACT: The authors design and demonstrate an InGaAs/InGaAsP quantum well infrared photodetector for highspeed infrared detection. The InGaAsP is selected as the barrier material to provide a large photoconductive gain, and the well is made of InGaAs/InP superlattice to achieve a broadband absorption. These features are expected to increase the photocurrent of the detector under a broadband source. For quantitative comparison, we also fabricate a quantum well GaAs/AlGaAs superlattice detector with a similar spectrum. Dark current noise measurement indicates that the gain of the InGaAs/InGaAsP detector is 4.6 times larger than that of the reference detector, thus confirming the present design concept.Applied Physics Letters 08/2006; 89(8):0811280811283. · 3.79 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The melting temperature ($T_m$) of a solid is generally determined by the pressure applied to it, or indirectly by its density ($n$) through the equation of state. This remains true even for helium solids\cite{wilk:67}, where quantum effects often lead to unusual properties\cite{ekim:04}. In this letter we present experimental evidence to show that for a two dimensional (2D) solid formed by electrons in a semiconductor sample under a strong perpendicular magnetic field\cite{shay:97} ($B$), the $T_m$ is not controlled by $n$, but effectively by the \textit{quantum correlation} between the electrons through the Landau level filling factor $\nu$=$nh/eB$. Such melting behavior, different from that of all other known solids (including a classical 2D electron solid at zero magnetic field\cite{grim:79}), attests to the quantum nature of the magnetic field induced electron solid. Moreover, we found the $T_m$ to increase with the strength of the sampledependent disorder that pins the electron solid.Nature Physics 05/2006; · 19.35 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: In a high quality twodimensional electron system of density n ˜1x10^11 cm2 and mobility mu˜10 x10^6 cm^2/Vs, at the temperature (T) of 1.2K, the diagonal magnetoresistance, Rxx, shows a strictly linear magnetic (B) field dependence, except for sharp spikes at B fields where the integer quantum Hall effect develops. As T is lowered to ˜ 35 mK, the main feature of Rxx is now dominated by multiple minima and peaks, due to the formation of integer and fractional quantum Hall states. However, when plotting Rxx at the evendenominator fillings (nu=1/4, 1/2, 3/4, and 3/2) as a function of B field, the same linear B field dependence is recovered. Interestingly, this linear magnetoresistance cannot be understood under the composite fermion model. Rather, it can be explained in terms of a slight, unintentional electron density gradient in our sample: Practically all Rxx features can be reproduced quantitatively through Rxy. We will discuss the implications of this finding.03/2006;
Publication Stats
13k  Citations  
1,851.85  Total Impact Points  
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Institutions

1983–2014

Princeton University
 • Department of Electrical Engineering
 • Department of Physics
Princeton, New Jersey, United States


2004–2012

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


2002–2010

National High Magnetic Field Laboratory
Tallahassee, Florida, United States


2008

Purdue University
 Department of Physics
West Lafayette, IN, United States


2005

NASA
Washington, West Virginia, United States


1998–2005

Columbia University
 Department of Physics
New York City, NY, United States 
AT&T Labs
Austin, Texas, United States


2002–2004

Florida State University
 Department of Physics
Tallahassee, Florida, United States


2001

JDS Uniphase Corporation
Milpitas, California, United States


1995–1996

The University of Tokyo
 Institute of Industrial Science
Tokyo, Tokyoto, Japan


1989–1990

Massachusetts Institute of Technology
 Department of Electrical Engineering and Computer Science
Cambridge, Massachusetts, United States


1984

Harvard University
Cambridge, Massachusetts, United States


1982–1983

Max Planck Institute for Solid State Research
Stuttgart, BadenWürttemberg, Germany
