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1 Jun 1992

Volume 60, Issue 22, pp. 2711-2813

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Solution‐cast films of polyaniline: Optical‐quality transparent electrodes

Yong Cao, George M. Treacy, Paul Smith, and Alan J. Heeger

Appl. Phys. Lett. 60, 2711 (1992); http://dx.doi.org/10.1063/1.106852 (3 pages) | Cited 133 times

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Optical‐quality transparent conducting films of polyaniline (PANI) and of conducting polyblends of polyaniline with amorphous bulk polymers are described. Using functionalized protonic acids to induce solubility in common organic solvents, PANI and PANI polyblends can be cast from solution, in the conducting form, onto a variety of substrates. The resulting films are clear, and they combine low surface resistance with excellent transparency. By varying the thickness of the film and/or the volume fraction of PANI in the polyblend, the surface resistance can be controlled over an extraordinary broad range.
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42.70.Jk Polymers and organics
78.66.Qn Polymers; organic compounds
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Optical Bloch waves in a semiconductor photonic lattice

P. L. Gourley, M. E. Warren, G. A. Vawter, T. M. Brennan, and B. E. Hammons

Appl. Phys. Lett. 60, 2714 (1992); http://dx.doi.org/10.1063/1.106853 (3 pages) | Cited 9 times

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We have observed multiple optical Bloch waves in a semiconductor photonic lattice. This photonic lattice comprises epitaxial quarter‐wave periodic layers surrounding a periodic quantum‐well region. After growth, the layers are structured laterally into periodic square unit cells by reactive‐ion‐beam etching. When photoexcited, the lattice emits a complex angular distribution of photons that reflects its periodic structure. Scattered light is distributed according to the Laue conditions in analogy with x‐ray diffraction from a bulk crystal. Optical Bloch waves photostimulated in the lattice are analogous to electron Bloch waves in an atomic lattice. These optical Bloch waves exhibit long‐range translational symmetry and local symmetry due to the shape of the unit cell. Interestingly, the far‐field pattern of stimulated emission gives a direct mapping of the allowed Bloch wave vectors in the Brillouin zone. The mapping exhibits a wave‐vector gap at the Bragg condition and may be associated with a photonic energy gap. In addition to measuring the intensity distribution of these Bloch waves, we directly measure the phase of the wave by polarization shearing interferometry.
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42.55.Px Semiconductor lasers; laser diodes
42.30.Kq Fourier optics
42.25.-p Wave optics
78.45.+h Stimulated emission

Observation of phase conjugation at 10.6 μm via intersubband third‐order nonlinearities in a GaAs/AlGaAs multi‐quantum‐well structure

Ilan Gravé, Mordechai Segev, and Amnon Yariv

Appl. Phys. Lett. 60, 2717 (1992); http://dx.doi.org/10.1063/1.106854 (3 pages) | Cited 14 times

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We describe the observation of phase conjugation at 10.6 μm in a GaAs/AlGaAs multi‐quantum‐well‐doped structure. The responsible nonlinear susceptibility χ(3) is due to a nearly resonant intersubband transition. The magnitude of χ(3) is 7×10−5 esu and the phase conjugate reflectivity is a few tenths of a percent.
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
78.66.Fd III-V semiconductors
78.66.Hf II-VI semiconductors

Origin of nonlinear gain saturation in index‐guided InGaAsP laser diodes

Rudolf Frankenberger and Robert Schimpe

Appl. Phys. Lett. 60, 2720 (1992); http://dx.doi.org/10.1063/1.106855 (3 pages) | Cited 8 times

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The spectrum of nonlinear gain saturation of InGaAsP diode lasers with a buried heterostructure is measured by means of modulation spectroscopy. The underlying physical processes are identified through comparison with theoretical spectra. At the laser line, contributions to the coefficient of self‐saturation by spectral hole burning (1.6×10−17 cm3) and carrier heating (1.1×10−17 cm3) of comparable magnitude are found.
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42.55.Px Semiconductor lasers; laser diodes
42.60.-v Laser optical systems: design and operation

In situ real‐time determination of the free‐carrier density in doped ZnSe films during molecular beam epitaxial growth

C. M. Rouleau and R. M. Park

Appl. Phys. Lett. 60, 2723 (1992); http://dx.doi.org/10.1063/1.106856 (3 pages) | Cited 7 times

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The characteristic blue/green cathodoluminescence (CL) emission observed while analyzing doped ZnSe films using the reflection high energy electron diffraction technique during molecular beam epitaxial growth has been detected ex vacuo and its intensity has been quantified. By employing a CdS‐based photoresistor mounted outside the vacuum system it has been determined for the examined case of Cl doped n‐type ZnSe/GaAs films that the CL intensity varies linearly as a function of free‐carrier density in the films. Specifically, log(CL intensity) was found to be proportional to log(free‐electron density) over the room‐temperature free‐electron density range, 1017–5×1018 cm−3. This work demonstrates that the free‐carrier density in doped ZnSe films grown by molecular beam epitaxy can be monitored in real time during growth which should significantly enhance process control.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.60.Hk Cathodoluminescence, ionoluminescence

Optical second‐harmonic generation in laterally asymmetric quantum dots

Jeremy Allam and Mathias Wagner

Appl. Phys. Lett. 60, 2726 (1992); http://dx.doi.org/10.1063/1.106857 (3 pages) | Cited 2 times

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We investigate laterally asymmetric quantum dots (LAQDs) as second‐order nonlinear optical elements in which symmetry‐forbidden intersubband transitions become allowed due to lateral asymmetry. The susceptibility for second‐harmonic generation (χ2ω(2)) of a two‐dimensional LAQD with three equispaced energy levels was studied by calculating the product of the intersubband transition dipole moments. The product was as large as 0.95×10−3 Lx3 for a dot of length Lx confined by an infinite‐potential barrier. The product was increased to 3.0×10−3 Lx3 by varying the aspect ratio (Ly/Lx) of the LAQD and decreasing the barrier height. The lateral asymmetry can be controlled by a gate electrode in semiconductor devices, leading to a device with tunable wavelength and nonlinear coefficients, suitable for quasi‐phase matching in nonlinear optical waveguides.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.66.Fd III-V semiconductors
78.66.Hf II-VI semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Effects of nonuniform well width on compressively strained multiple quantum well lasers

D. Teng, Y. H. Lo, C. H. Lin, and L. F. Eastman

Appl. Phys. Lett. 60, 2729 (1992); http://dx.doi.org/10.1063/1.106858 (3 pages) | Cited 2 times

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We theoretically investigate the effects of nonuniform well widths on compressively strained In0.2Ga0.8As/GaAs multiple quantum well lasers using multiband effective mass theory and density matrix formalism. We find that the well width fluctuations do not degrade the transparency current, differential gain, and linewidth broadening factor. Besides, lasers with intentionally designed chirped well width have much broader gain profiles compared to uniform well lasers. This feature is attractive for applications requiring large gain bandwidth such as tunable lasers, mode‐locked lasers, and wavelength division multiplexed laser arrays.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
85.30.De Semiconductor-device characterization, design, and modeling

Fast intensified‐CCD photography of YBa2Cu3O7−x laser ablation in vacuum and ambient oxygen

David B. Geohegan

Appl. Phys. Lett. 60, 2732 (1992); http://dx.doi.org/10.1063/1.106859 (3 pages) | Cited 196 times

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The propagation of laser ablation plumes from 248 nm laser‐irradiated YBCO into vacuum and 100 mTorr ambient oxygen has been photographed with a gated, intensified CCD array camera system. The thermalization of the laser plasma and onset of shock structures due to collisions with the background gas are investigated from two‐dimensional digitized images of the visible plume emission.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
79.20.Ds Laser-beam impact phenomena

Observation of a new surface mode on a fluid‐saturated permeable solid

Peter B. Nagy

Appl. Phys. Lett. 60, 2735 (1992); http://dx.doi.org/10.1063/1.106860 (3 pages) | Cited 15 times

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Almost ten years ago, S. Feng and D. L. Johnson predicted the presence of a new surface mode on a fluid/fluid‐saturated porous solid interface with closed surface pores [J. Acoust. Soc. Am. 74, 906 (1983)]. We found that, due to surface tension, practically closed‐pore boundary conditions can prevail at an interface between a nonwetting fluid (e.g., air) and a porous solid saturated with a wetting fluid (e.g., water or alcohol). Surface wave velocity and attenuation measurements were made on alcohol‐saturated porous sintered glass at 100 kHz. The experimental results show clear evidence of the new ‘‘slow’’ surface mode predicted by Feng and Johnson.
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43.35.Pt Surface waves in solids and liquids
68.35.Gy Mechanical properties; surface strains
68.43.-h Chemisorption/physisorption: adsorbates on surfaces

Amorphization of Cu0.6Ti0.2Zr0.2 by mechanical alloying

Hen Zhang and D. G. Naugle

Appl. Phys. Lett. 60, 2738 (1992); http://dx.doi.org/10.1063/1.106861 (3 pages) | Cited 3 times

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An amorphous Cu0.6Ti0.2Zr0.2 alloy was synthesized by mechanical alloying of pure elemental powders of Cu, Ti, and Zr in air using a planetary high‐energy ball‐milling machine. The structure and thermal behavior of the powders milled for different times were analyzed by x‐ray diffraction and differential scanning calorimetry. Results indicate that adding Zr into the Cu‐Ti binary system can speed the amorphization. Furthermore, the alloy composition during the milling process may influence the ratio of Zr crystallization products relative to those of Ti.
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81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
61.43.Fs Glasses
61.43.-j Disordered solids
61.44.Br Quasicrystals
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition

Tip artifacts of microfabricated force sensors for atomic force microscopy

P. Grütter, W. Zimmermann‐Edling, and D. Brodbeck

Appl. Phys. Lett. 60, 2741 (1992); http://dx.doi.org/10.1063/1.106862 (3 pages) | Cited 44 times

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It is demonstrated that due to inevitable intrinsic imperfections in the microfabrication process of atomic force microscopy (AFM) tips, images of rough surfaces can be totally dominated by tip artifacts. These images reflect the mesoscopic tip shape as concluded from a comparison of AFM and scanning electron microscopy images of the tip and sample. These tip artifacts have been found on a scale of 20–600 nm, showing the necessity of characterizing the tip shape in order to make reliable sample‐specific statements.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
68.35.B- Structure of clean surfaces (and surface reconstruction)

Cubic silicon cluster

Kazuaki Furukawa, Masaie Fujino, and Nobuo Matsumoto

Appl. Phys. Lett. 60, 2744 (1992); http://dx.doi.org/10.1063/1.106863 (2 pages) | Cited 30 times

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A cubic silicon cluster having eight bonds each terminated by a tert‐butyl substituent, tert‐butyloctasilacubane (TBOSC), is studied. TBOSC was formed and isolated by chemical procedures. The optical properties of TBOSC were measured in comparison with those of bulk silicon. TBOSC is purple and its absorption edge (λg) is observed at 650 nm (1.9 eV) at room temperature. This λg is 0.8 eV larger than that of bulk silicon. It also shows photoluminescence extending to 850 nm at 77 K although bulk silicon shows no photoluminescence.
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78.66.-w Optical properties of specific thin films

Crystallization‐induced stress in silicon thin films

Hideo Miura, Hiroyuki Ohta, Noriaki Okamoto, and Toru Kaga

Appl. Phys. Lett. 60, 2746 (1992); http://dx.doi.org/10.1063/1.106864 (3 pages) | Cited 25 times

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Residual stress change in silicon thin films during crystallization of amorphous silicon is discussed experimentally by detecting the wafer curvature change using a scanning laser microscope. The as‐deposited amorphous‐silicon film shows compressive stress of about 200 MPa. During a crystallization reaction at about 650 °C, a large tensile stress of about 1000 MPa develops in the film due to film shrinkage. The final residual stress of polycrystalline film depends on the film formation process.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
62.20.M- Structural failure of materials
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure

Electrical and structural properties of Ga0.51In0.49P/GaAs heterojunctions grown by metalorganic vapor‐phase epitaxy

E. C. Paloura, A. Ginoudi, G. Kiriakidis, N. Frangis, F. Scholz, M. Moser, and A. Christou

Appl. Phys. Lett. 60, 2749 (1992); http://dx.doi.org/10.1063/1.106865 (3 pages) | Cited 15 times

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Undoped and Se‐doped Ga0.51In0.49P/GaAs single heterojunctions grown by metalorganic vapor‐phase epitaxy (MOVPE) are characterized with deep‐level transient spectroscopy and transmission electron microscopy (TEM). The undoped MOVPE material, grown at 710 °C, is characterized by a deep electron trap with an activation energy that takes values in the range 700–900 meV. Se doping suppresses the formation of this trap when the doping level is higher than 5×1017 cm−3. Furthermore, Se doping suppresses the persistent photoconductivity that is observed in the undoped samples. Finally, analysis with cross‐section TEM reveals that the samples undergo partial spinodal decomposition in a direction nearly vertical to the interface.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
71.55.Eq III-V semiconductors
78.66.Fd III-V semiconductors
78.66.Hf II-VI semiconductors

Silicon epitaxial solar cell with 663‐mV open‐circuit voltage

A. W. Blakers, J. H. Werner, E. Bauser, and H. J. Queisser

Appl. Phys. Lett. 60, 2752 (1992); http://dx.doi.org/10.1063/1.106866 (3 pages) | Cited 20 times

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Silicon films of 20 μm thickness have been grown epitaxially on silicon substrates by liquid‐phase epitaxy. Solar cells fabricated on such layers display open‐circuit voltages as high as 663 mV (AM1.5, 25 °C), a value which exceeds previous data by a large margin. High open‐circuit voltages are a prerequisite for thin‐film solar cells with high efficiencies. Our result has applications to both space cells and to low‐cost terrestrial cells.
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84.60.Jt Photoelectric conversion
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
73.50.Pz Photoconduction and photovoltaic effects

Anomalous magnetoresistance at a mesoscopic bend

D. R. S. Cumming, H. Ahmed, and T. J. Thornton

Appl. Phys. Lett. 60, 2755 (1992); http://dx.doi.org/10.1063/1.106867 (3 pages) | Cited 7 times

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We have carried out magnetoresistance measurements on a mesoscopic cross formed from two split gates on a GaAs/AlGaAs 2DEG and have observed anomalous peaks in the bend resistance before the electron collimation is finally destroyed by the magnetic field. We have considered two possible explanations for this effect, and have rejected the possibility of quantum mechanical effects in favor of a classical one in which we postulate the presence of an impurity close to the center of the active region.
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73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.50.Bk General theory, scattering mechanisms

Thermal stability of Si1−xCx/Si strained layer superlattices

M. S. Goorsky, S. S. Iyer, K. Eberl, F. Legoues, J. Angilello, and F. Cardone

Appl. Phys. Lett. 60, 2758 (1992); http://dx.doi.org/10.1063/1.106868 (3 pages) | Cited 29 times

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The thermal stability of epitaxial silicon‐carbon alloys grown by molecular beam epitaxy on (001) silicon was investigated using high resolution x‐ray diffraction, transmission electron microscopy, and secondary ion mass spectroscopy measurements. Different superlattices, with alloy compositions of Si0.997C0.003, Si0.992C0.008, and Si0.985C0.015, all nominally 6 nm thick, with 24 nm Si spacer layers were employed. Annealing studies determined that there are different pathways to strain relaxation in this material system. At annealing temperatures of 900 °C and below, the structures relax only by interdiffusion, indicating that these layers are stable during typical device processing steps. At temperatures of 1000 °C and above, SiC precipitation dominates with enhanced precipitation in the Si1−xCx layers with the highest initial carbon content.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
66.30.J- Diffusion of impurities
81.40.Gh Other heat and thermomechanical treatments

Identification of segregation from borophosphosilicate glass films during annealing

S. Imai, Y. Yabuuchi, Y. Terai, T. Yasui, C. Kudo, I. Nakao, and M. Fukumoto

Appl. Phys. Lett. 60, 2761 (1992); http://dx.doi.org/10.1063/1.106869 (3 pages) | Cited 4 times

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The structure and crystallinity of a segregation on a borophosphosilicate glass (BPSG) film have been clarified by scanning electron microscopy (SEM), transmission electron microscopy (TEM), transmission electron diffraction (TED), and electron energy loss spectroscopy (EELS). The segregation arises on the BPSG film surface after annealing in nitrogen ambient. Its size is below 0.5 μm. The segregation is identified as crystalline BPO4 from the results of TED and EELS. In this letter, TED pattern of crystalline BPO4 is indicated in detail. The growth mechanism of crystalline BPO4 is proposed on the basis of a series of the results.
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81.40.Gh Other heat and thermomechanical treatments
77.55.-g Dielectric thin films
64.75.-g Phase equilibria

Real‐time monitoring of a surface reaction in germanium film growth

Djula Eres and J. W. Sharp

Appl. Phys. Lett. 60, 2764 (1992); http://dx.doi.org/10.1063/1.106870 (3 pages) | Cited 2 times

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Epitaxial germanium film growth by a surface reaction was investigated using a pulsed molecular jet. Time‐resolved reflectometry was utilized for in situ monitoring of both the formation and the evolution of a chemisorbed layer of digermane. The rate of chemisorption was independent of temperature. Evolution of the adsorption layers occurred by a temperature dependent first order process, believed to be molecular hydrogen desorption. Digital growth of germanium films was demonstrated by periodically refilling the active surface sites liberated by molecular hydrogen desorption between two successive gas pulses. Epitaxial germanium films over 150 nm thick were grown on Si (100) substrates.
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68.55.-a Thin film structure and morphology
68.43.-h Chemisorption/physisorption: adsorbates on surfaces
82.40.-g Chemical kinetics and reactions: special regimes and techniques
82.20.Pm Rate constants, reaction cross sections, and activation energies

Pd/Si plasma immersion ion implantation for selective electroless copper plating on SiO2

Meng‐Hsiung Kiang, Michael A. Lieberman, Nathan W. Cheung, and X. Y. Qian

Appl. Phys. Lett. 60, 2767 (1992); http://dx.doi.org/10.1063/1.106871 (3 pages) | Cited 15 times

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Selective deposition of copper in SiO2 trenches has been carried out using Pd/Si plasma immersion ion implantation and electroless Cu plating. To form the seed layer for electroless Cu plating on SiO2, sputtered Pd and Si atoms were partially ionized by the Ar plasma and then deposited at bottoms of SiO2 trenches; Ar ion beam was then applied to assist the mixing of the deposited Pd/Si films with the SiO2 substrate by recoil implantation. We found a threshold Pd dose of 2×1014/cm2 is required to initiate the electroless plating of Cu. By careful control of the anisotropic etching of the oxide trenches and proper choice of the Pd dose, 1‐μm wide Cu filled lines with flat surfaces suitable for planarized multilevel metallization were successfully fabricated.
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85.40.Ls Metallization, contacts, interconnects; device isolation
85.40.Hp Lithography, masks and pattern transfer
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Ballistic versus diffusive base transport in the high‐frequency characteristics of bipolar transistors

Anatoly A. Grinberg and Serge Luryi

Appl. Phys. Lett. 60, 2770 (1992); http://dx.doi.org/10.1063/1.107470 (3 pages) | Cited 6 times

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The time‐dependent Boltzmann equation is used to calculate the small‐signal complex base transport factor α(ω) for different ratios between the base width W and the scattering mean‐free path lsc. It is shown that the phase trajectory (Re α, Im α) has a universal character both in the diffusion limit (W≫lsc) and the ballistic limit (lsc≫W). In the latter limit, the trajectory is completely determined by the distribution function of minority carriers injected into the base. The complex trajectories are plotted for several model distributions, including the usual thermal distribution and taking into account the injection energy appropriate for a heterojunction bipolar transistor with a wide‐gap emitter.
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85.30.Pq Bipolar transistors
85.30.De Semiconductor-device characterization, design, and modeling
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.30.+q High-frequency effects; plasma effects

Structure of S‐passivated InP(100)‐(1×1) surface

Z. H. Lu, M. J. Graham, X. H. Feng, and B. X. Yang

Appl. Phys. Lett. 60, 2773 (1992); http://dx.doi.org/10.1063/1.106872 (3 pages) | Cited 40 times

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X‐ray absorption near‐edge structure (XANES) is used to determine the structure of the S‐passivated InP(100)‐(1×1) surface. From photon electric polarization‐dependent XANES studies, we found that S forms a bridge bond with two In atoms along the [011] direction, with an In‐S‐In bond angle of 100°. The atomic position of S is found to be close to the tetrahedral site of a phosphorous vacancy.
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81.65.-b Surface treatments
78.70.Dm X-ray absorption spectra
68.35.B- Structure of clean surfaces (and surface reconstruction)

Monitoring ion etching of GaAs/AlGaAs heterostructures by real time spectroscopic ellipsometry: Determination of layer thicknesses, compositions, and surface temperature

A. R. Heyd, R. W. Collins, K. Vedam, S. S. Bose, and D. L. Miller

Appl. Phys. Lett. 60, 2776 (1992); http://dx.doi.org/10.1063/1.106873 (3 pages) | Cited 9 times

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A real time spectroscopic ellipsometry (RTSE) study of the GaAs/AlGaAs/GaAs heterostructure, performed during Ar ion beam etching, provides the instantaneous GaAs and AlGaAs layer thicknesses and etch rates, the Al composition for the alloy layer, the evolution of the thickness and composition of the surface damage layer, and the near‐surface temperature. In addition, combined effects of ion‐induced atomic intermixing and etching inhomogeneity can be assessed as the interfaces are crossed. These results demonstrate the extensive capabilities of the RTSE technique for monitoring semiconductor structures during processing.
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68.55.-a Thin film structure and morphology
07.60.Fs Polarimeters and ellipsometers
81.65.-b Surface treatments
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

GaAs/AlAs quantum wells for electroabsorption modulators

B. Pezeshki, S. M. Lord, T. B. Boykin, and J. S. Harris

Appl. Phys. Lett. 60, 2779 (1992); http://dx.doi.org/10.1063/1.106874 (3 pages) | Cited 16 times

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We demonstrate both theoretically and experimentally that the quantum‐confined Stark effect leads to larger absorption changes in GaAs/AlAs quantum wells compared to the more conventional GaAs/AlGaAs system due to the higher Γ confinement. The lower indirect valleys in AlAs do not degrade the performance and the exciton resonance is maintained at higher‐energy shifts. The improvement in exciton oscillator strength is nearly 50% with a 70‐meV shift. The greater exciton strength at high fields has important applications for optical modulators and switches that operate at the long‐wavelength side of the zero‐bias exciton.
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78.66.Fd III-V semiconductors
78.66.Hf II-VI semiconductors
42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.79.Hp Optical processors, correlators, and modulators

Back‐gated split‐gate transistor: A one‐dimensional ballistic channel with variable Fermi energy

A. R. Hamilton, J. E. F. Frost, C. G. Smith, M. J. Kelly, E. H. Linfield, C. J. B. Ford, D. A. Ritchie, G. A. C. Jones, M. Pepper, D. G. Hasko, and H. Ahmed

Appl. Phys. Lett. 60, 2782 (1992); http://dx.doi.org/10.1063/1.106849 (3 pages) | Cited 22 times

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We have studied the quantized conductance of a one‐dimensional ballistic channel in the two‐dimensional electron gas of a back‐gated GaAs/AlGaAs heterostructure. A standard Schottky split‐gate fabricated with electron‐beam lithography techniques is used to define the one‐dimensional channel, but we incorporate an epitaxially grown in situ back‐gate, situated ∼1 μm below the electron gas, to provide additional control of the carrier density. Quantized conductance steps can be induced by changing the bias on either gate, highlighting the self‐consistent nature of the electrostatics involved. We show that we can, in principle, achieve independent control of the one‐dimensional carrier density and channel width.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.50.Dn Low-field transport and mobility; piezoresistance
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
85.30.Tv Field effect devices
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