Growth of quantum wire arrays by MBE on nonplanar substrates

With single-step molecular beam epitaxy growth, GaAs/AlGaAs quantum wire (QW wire) arrays were fabricated over mesas an GaAs nonplanar substrates patterned by conventional photolithography and wet chemical etching. Faceting and surface migration of atoms during crystal growth resulted in lateral variation in the quantum well (QW) layer thickness on different facet planes. This caused the tops of the mesas to be sharp enough to provide lateral quantum-size-effects (QSEs). In conventional photoluminescence (PL), PL with a micro-optical-system, and photoreflectance measurements under different conditions, a large blue shift was observed in the energy level positions for electronic transitions corresponding to QWs at the tops of mesas compared with those corresponding to QWs on nonpatterned areas of the same substrate. The blue shift was in contradiction with the fact that the GaAs QW layers at the tops of mesas were thicker than those on nanpatterned areas, and illustrated the realization of QW wires at the tops of mesas. Calculations also proved that there was a lateral QSE at the tops of mesas and this was further proof for the formation of QW wires there.     

Photonic quantum dots based on Bragg reflectors grown by conformal deposition on patterned substrates

A new approach, that combines the photolithography and conformal deposition techniques, was proposed to fabricate Si-based three-dimensional optical microcavities on patterned substrates. Different from the lateral optical confinement of 3D microcavities by using total internal reflection, Bragg reflectors are used for all three-dimensional optical confinement. From the room temperature photoluminescence spectra, discrete optical modes with obvious side-dependence were observed. With the lateral size decreased from 4.5 μm to 1.5 μm, the modes shift to higher energies and the mode splitting increases, which indicates that 3D optical microcavities act like photonic quantum dots. The numerical calculations of quantized photon states in photonic quantum dots show a quantitative agreement with these observed discrete optical eigenmodes.     

Magnetic anticrossing of 1D subbands in ballistic double quantum wires

We study the low-temperature in-plane magnetoconductance of vertically coupled double quantum wires. Using a novel flip-chip technique, the wires are defined by two pairs of mutually aligned split gates on opposite sides of a  ≤ 1 micron thick AlGaAs/GaAs double quantum well heterostructure. We observe quantized conductance steps due to each quantum well and demonstrate independent control of each 1D wire. A broad dip in the magnetoconductance at  ∼ 6 T is observed when a magnetic field is applied perpendicular to both the current and growth directions. This conductance dip is observed only when 1D subbands are populated in both the top and bottom constrictions. This data is consistent with a counting model whereby the number of subbands crossing the Fermi level changes with field due to the formation of an anticrossing in each pair of 1D subbands.     

Fabrication and characterization of strained InGaAs quantum wires grown on high index V-grooved GaAs substrates by LP-MOVPE

Self-ordered InGaAs/GaAs quantum wires (QWRs) were obtained on (100) GaAs V-grooved substrates by low-pressure metal-organic vapor phase epitaxy. Different structural and optical properties of compressively strained InGaAs wires grown on grooves exhibiting (111)A-like and (311)-like oriented facets were investigated.     

Growth and optical characterization of dense arrays of site-controlled quantum dots grown in inverted pyramids

We report on the growth and optical properties of dense arrays of single GaAs/AlGaAs quantum dot (QD) heterostructures with pitches as small as 300 nm. The samples were grown by organometallic chemical vapor deposition in dense inverted pyramids on {1 1 1}B GaAs substrate pre-patterned using electron beam lithography and wet chemical etching. The growth conditions such as deoxidation and growth temperatures, growth rates, and V/III ratio, had to be chosen quite differently from those employed with micron-size pyramids. Low-temperature micro-photoluminescence and cathodoluminescence spectra of the samples show distinct luminescence from the QDs with a linewidth of less than 1 meV and uniform emission energy for an ensemble of 900 QDs. The possibility of incorporating such QD arrays inside optical microcavity structures is also discussed.     

Elementary excitations in nanochannel arrays of quantum wires

We present an analytical model for the Coulomb interaction effects in quantum wires forming a nanochannel array. We study the elementary excitations (plasmons and electron-hole excitations) of electron arrays forming three-dimensional structures. The plasmon spectrum of boson arrays is also calculated. Our model applies to bulk material with one-dimensional conduction channels as realized in organic or polymer crystals and in nanochannel array glasses.     

Non-linear optical processes involving excited subbands in laser-dressed quantum wires with triangular cross-section

The conduction subband structure of a triangular cross-section GaAs/AlGaAs quantum well wire under intense laser field is theoretically investigated by taking into account a finite confining potential. The calculation of the subband energy levels is based on a two-dimensional finite element method within the effective mass approximation. It is shown that a transversally polarized laser field non-uniformly shifts the subband energy levels and could be used for tuning the intersubband transitions and altering the related optical susceptibilities. We found that the non-resonant laser field allows the magnification and the red- or blueshift of the third-order non-linear susceptibility peaks for particular polarizations of the pump light and proper laser parameter values. The effects of the laser dressing field on the intersubband third harmonic generation and quadratic electro-optical process are discussed.     

Fabrication of BDD quantum node switches on embedded GaAs quantum wires grown by selective MBE

In view of applications to hexagonal binary decision diagram (BDD) LSIs, a first attempt is made to form quantum BDD node switches on selectively grown (SG) embedded quantum wires (QWRs) by molecular beam epitaxy (MBE). SG branch switches controlled by a Schottky wrap gate (WPG) were successfully fabricated by MBE growth and subsequent device processing. Gate control characteristics were studied by gate-dependent Shubnikov–de-Haas measurements, and the behavior was found to be similar to that of devices fabricated on wires by etching. The switch exhibited clear conductance quantization at low temperature, and temperature dependence of the voltage slope of conductance jump was clarified. A Y-branch BDD node device using two SG branch switches was successfully fabricated, and realized clear path switching characteristics.     

Electrical transport properties of graphene-covered-Cu wires grown by chemical vapor deposition

We investigated the field-effect transistor (FET) characteristics of 15-μm graphene-covered copper wires (G-wires). Unlike the previously reported graphene FET, carries initially showed p-type like FET characteristics in two-terminal transport measurements. Our results indicate that the electrical transport processes in a G-wire FET occur in both the heavily p-doped contact and the p-doped radial graphene channel, as a p-channel. The interfacial potential barrier between the contact electrode and the radial graphene channel is small, but there is a radial potential barrier that limits electrical transport through the copper core in chemical vapor deposition (CVD) grown samples. The p-type FET characteristics appeared clearly after the oxidation of the G-wires.     

Anticrossing of spin-split subbands in quasi-one-dimensional wires

In quantum Hall systems, both anticrossings and magnetic phase transitions can occur when opposite-spin Landau levels coincide. Our results indicate that both processes are also possible in quasi-1D quantum wires in an in-plane B field, Bparallel. Crossings of opposite-spin 1D subbands resemble magnetic phase transitions at zero dc source-drain bias, but display anticrossings at high dc bias. Our data also imply that the well-known 0.7 structure may evolve into a spin-hybridized state in finite dc bias.     

High quality GaAs quantum wires grown by flow rate modulation epitaxy

Accepted: 14 October 1997     

渐变掩蔽图形超低压选择区域生长法制备高质量InGaAsP多量子阱材料

采用超低压(22 mbar)选择区域生长(Selective Area Growth, SAG)金属有机化学汽相沉积(Metal-organic Chemical Vapor Deposition, MOCVD)技术成功制备了高质量InGaAsP/InGaAsP多量子阱(Multiple Quantum Well, MQW)材料. 在较小的掩蔽宽度变化范围内(15—30μm)，得到了46nm的光荧光(Photoluminescence, PL)波长偏移量，PL半高宽(Full-Width-at-Half- 关键词： 超低压 选择区域生长 渐变掩蔽图形     

Novel electronic structure of inhomogeneous quantum wires on a Si surface

A one-dimensional system of Si(111)-(5 x 2)-Au is explored using scanning tunneling microscopy and spectroscopy. The chain of Si adatoms called bright protrusions (BP's) is found to be semiconducting with an evanescent state in the gap, which originates from adjoining metallic BP-free segments. A quantitative analysis shows that the evanescent state decays in inverse-Gaussian form, leading to an appearance of a parabolic BP chain, and scales to its chain length. Spatial decay of the state suggests a quadratic band bending and the existence of a Schottky-like potential barrier at the interface driven by charge transfer.     

Long-wavelength luminescence from GaSb quantum dots grown on GaAs substrates

Self-assembled GaSb quantum dots (QDs) with a photoluminescence wavelength longer than 1.3 μm were successfully grown by suppressing the replacement of As and Sb on the surface of the GaSb QDs. This result means that GaSb can thus join InAs or GaInAs as a suitable material for QD lasers for optical communications.     

GaAs multiple quantum well microresonator modulators grown on silicon substrates

We report new results on the modulation characteristics of GaAs/AlGaAs asymmetric Fabry-Perot modulators grown on silicon substrates. We discuss factors affecting device performance and evaluate these by growing p-i-n quantum well diodes, and multilayer reflector stacks on silicon. Using data from these test structures we have designed an asymmetric microresonator modulator and achieve, experimentally, a 40% reflection change with only 5 V and a contrast ratio of 7.4 dB, also with 5 V.Formerly at:Philips Research Laboratories, Redhill, UK     

Alumina capped ZnO quantum dots multilayer grown by pulsed laser deposition

To extend the applicability of ZnO, with the bulk band gap of about 3.3 eV, into deep UV region, we have grown a multilayer of alumina capped ZnO quantum dots of mean in-plane sizes in the range of ∼1.8-3.6 nm at room temperature using alternate Pulsed Laser Deposition. Size dependent blue shift of the band gap of these dots up to ∼4.5 eV is observed in the optical absorbance spectra. The observed blue shift can be understood using the effective mass approximation in weak and strong confinement regimes.     

Characterization of nitrogen-doped ZnO thin films grown by plasma-assisted pulsed laser deposition on sapphire substrates

The crystalline, optical and electrical properties of N-doped ZnO thin films were measured using X-ray diffraction, photoluminescence and Hall effect apparatus, respectively. The samples were grown using pulsed laser deposition on sapphire substrates coated priorly with ZnO buffer layers. For the purpose of acceptor doping, an electron cyclotron resonance (ECR) plasma source operated as a low-energy ion source was used for nitrogen incorporation in the samples. The X-ray diffraction analyses indicated some deterioration of the ZnO thin film with nitrogen incorporation. Temperature-dependent Van der Pauw measurements showed consistent p-type behavior over the measured temperature range of 200–450 K, with typical room temperature hole concentrations and mobilities of 5×10¹⁵ cm⁻³ and 7 cm²/V s, respectively. Low temperature photoluminescence spectra consisted of a broad emission band centered around 3.2 eV. This emission is characterized by the absence of the green deep-defect band and the presence of a band around 3.32 eV.