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31 Oct 1994

Volume 65, Issue 18, pp. 2245-2365

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Novel surface gate structure to induce sharp potential barriers in two‐dimensional electron systems

J. P. Lu, X. Ying, and M. Shayegan

Appl. Phys. Lett. 65, 2320 (1994); http://dx.doi.org/10.1063/1.112730 (3 pages) | Cited 3 times

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A novel surface gate structure, consisting of a central gate and two side gates, is proposed to generate an effectively sharp potential barrier for two‐dimensional electrons confined to a semiconductor heterojunction deep below the sample surface. The side gates are biased at a higher potential than the central gate to enhance the large‐wave‐vector Fourier components of the potential and therefore to compensate partially for the strong decay, due to fringing fields, of these components as a function of the distance below the surface. The reflection coefficient calculated for the proposed potential barrier exhibits strong oscillations as a function of barrier height, much stronger than a conventional single gate. The results suggest that the proposed gate structure should find use in realization of an electron interferometer which can serve as a building block for novel electron interference devices. © 1994 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Ultrafast band‐edge carrier dynamics in In0.65Ga0.35As

Wayne S. Pelouch and L. A. Schlie

Appl. Phys. Lett. 65, 2323 (1994); http://dx.doi.org/10.1063/1.112963 (3 pages) | Cited 4 times

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The ultrafast band‐edge carrier dynamics in In0.65Ga0.35As/GaAs are studied using a transmission correlation technique in the 77–300 K temperature range. The experiment is performed using a femtosecond optical parametric oscillator tunable in the 1.5–1.8 μm spectral range with sub‐100‐fs pulses. Rapid recovery (≤10 ps) of the nonlinear absorption is observed, suggesting an exceptionally high rate of recombination predominantly due to dislocations at the InGaAs/GaAs heterojunction. The phonon‐scattering time is experimentally identified and measured to be 200–400 fs.
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78.47.-p Spectroscopy of solid state dynamics
78.66.Fd III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Parallel quantum point contacts fabricated with independently biased gates and a submicrometer airbridge post

M. E. Sherwin, J. A. Simmons, T. E. Eiles, N. E. Harff, and J. F. Klem

Appl. Phys. Lett. 65, 2326 (1994); http://dx.doi.org/10.1063/1.112731 (3 pages) | Cited 6 times

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Using an integrated airbridge and submicrometer gate post technology, coupled quantum point contacts (QPCs) arranged in a parallel configuration were fabricated. The airbridge and gate post are fabricated by e‐beam lithography and Ti/Au evaporation in a single step. Gate post diameters as small as 0.1 μm have been achieved. The two QPCs are fabricated with two conventional gates and a central airbridged gate, each of which can be biased independently. Conductance measurements clearly exhibit coupling of the two QPCs, as the quantized conductance steps are in units of 4 e2/h. Independent measurements of each QPC show conductance steps in units of 2 e2/h.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
85.40.Hp Lithography, masks and pattern transfer

Influence of oxygen impurity in the intrinsic layer of amorphous silicon solar cells

Masao Isomura, Toshihiro Kinoshita, Yoshihiro Hishikawa, and Shinya Tsuda

Appl. Phys. Lett. 65, 2329 (1994); http://dx.doi.org/10.1063/1.112732 (3 pages) | Cited 8 times

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The influence of oxygen impurity in the i layer of hydrogenated amorphous silicon (a‐Si:H) solar cells is studied. At the initial state, the dark conductivity, and photoconductivity of a‐Si:H films increase and the conversion efficiency of the solar cells drops as the oxygen concentration increases. After the light soaking, these film properties become independent of the oxygen concentration, but the conversion efficiency of a‐Si:H solar cells is still influenced by the oxygen impurity. The dominant effect of the oxygen impurity in a‐Si:H solar cells is a modification of the electric field distribution in the i layer, due to the donorlike states created by oxygen. © 1994 American Institute of Physics.
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71.55.Jv Disordered structures; amorphous and glassy solids
72.40.+w Photoconduction and photovoltaic effects
84.60.Jt Photoelectric conversion

Lateral photovoltaic effect in porous silicon

Daniel W. Boeringer and Raphael Tsu

Appl. Phys. Lett. 65, 2332 (1994); http://dx.doi.org/10.1063/1.112733 (3 pages) | Cited 9 times

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Porous silicon has received considerable attention for its potential as a silicon‐based visible light emitter. In this letter we introduce the lateral photovoltaic effect in porous silicon and show its origin in amphoteric dangling bond traps at the porous silicon surface, which also play a role in the light‐induced photoluminescence degradation. The use of the lateral photoeffect for a wide area position‐sensitive visible light detector is demonstrated. The lateral photoeffect also provides a new electrical technique to study the atmospheric interactions of porous silicon, with possible applications for vapor detection. © 1994 American Institute of Physics.
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72.40.+w Photoconduction and photovoltaic effects
78.55.Hx Other solid inorganic materials
85.60.Gz Photodetectors (including infrared and CCD detectors)

Low temperature limits to molecular beam epitaxy of GaAs

Richard P. Mirin, James P. Ibbetson, Umesh K. Mishra, and Arthur C. Gossard

Appl. Phys. Lett. 65, 2335 (1994); http://dx.doi.org/10.1063/1.112734 (3 pages) | Cited 14 times

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We report reflection high‐energy electron diffraction oscillations during molecular beam epitaxy of GaAs at temperatures as low as 125 °C using As2 as the arsenic source. At a substrate temperature of 200 °C, the As:Ga ratio is shown to be the critical parameter which determines the amplitude of these oscillations. The largest amplitude oscillations are obtained when the As:Ga ratio is about 1:1. In order for these oscillations to occur, the arriving atoms must have some surface mobility. Monte Carlo simulations show that step density oscillations with a period corresponding to one monolayer are expected if the incident atoms are allowed to move as little as one lattice site upon arrival at the surface. © 1994 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Experimental study of forward current transients in amorphous silicon p‐i‐n structures

B. Yan, A. Eliat, and G. J. Adriaenssens

Appl. Phys. Lett. 65, 2338 (1994); http://dx.doi.org/10.1063/1.112737 (3 pages) | Cited 2 times

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The delay time of forward current onset from initial electron space‐charge‐limited current to recombination‐limited current in a‐Si:H p‐i‐n devices was studied as a function of bias voltage, temperature and illumination intensity. The results show that the delay time and the initial electron current are related by a power law, td∝I−γSCLC, where γ is a temperature‐independent constant. The value of γ is sensitive to the device properties such as the thickness of the intrinsic layer and the density of states. For a good quality device with 3.74 μm intrinsic layer, γ=0.70±0.05, while for a thin one deposited in the same conditions, γ changes to 0.99±0.05. A physical interpretation is presented. © 1994 American Institute of Physics.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.80.Ng Disordered solids
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.40.+w Photoconduction and photovoltaic effects

Experimental study of an In0.53Ga0.47As–InP resonant plasma waveguide modulator for medium‐infrared light

J. Stiens, C. De Tandt, W. Ranson, R. Vounckx, P. Demeester, and I. Moerman

Appl. Phys. Lett. 65, 2341 (1994); http://dx.doi.org/10.1063/1.112739 (3 pages) | Cited 3 times

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We report on the first experimental study of a medium‐infrared waveguide modulator based on the coupling between a dielectric grating coupler and an In0.53Ga0.47As–InP waveguide, operating near cut off, and containing a resonant semiconductor plasma. The prototype designed for demonstrating this novel effect was grown by metalorganic chemical vapor deposition. The experimental results show low power (225 mW), low voltage (15 V) operation for obtaining a modulation depth of 30%. The overall transmission efficiency is, however, rather low (0.5%) due to the wet chemical etching techniques used for defining the grating structure. © 1994 American Institute of Physics.
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42.79.Hp Optical processors, correlators, and modulators
72.30.+q High-frequency effects; plasma effects

Relaxation and H coverage of ammonium fluoride treated Si(111)

M. Copel, R. J. Culbertson, and R. M. Tromp

Appl. Phys. Lett. 65, 2344 (1994); http://dx.doi.org/10.1063/1.112740 (3 pages) | Cited 12 times

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Using medium energy ion scattering and elastic recoil detection, we have studied silicon surfaces prepared by ex situ NH4F wet etching. We report direct measurements of relaxation and hydrogen coverage of the passivated Si(111)‐(1×1) surface. For Si(111), nearly ideal, unreconstructed surfaces are obtained, terminated by a single atomic layer of hydrogen. Silicon backscatter yields agree closely with simulations of a bulk truncation, with an inward relaxation of the outermost layer of 0.075±0.03 Å. On the other hand, Si(001) prepared by NH4F solution shows severe roughening. © 1994 American Institute of Physics.
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81.65.-b Surface treatments
68.35.B- Structure of clean surfaces (and surface reconstruction)

Homogeneous and inhomogeneous linewidths of excitons in partially ordered Ga0.52In0.48P

P. Grossmann, J. Feldmann, E. O. Göbel, P. Thomas, D. J. Arent, K. A. Bertness, and J. M. Olson

Appl. Phys. Lett. 65, 2347 (1994); http://dx.doi.org/10.1063/1.112742 (3 pages) | Cited 8 times

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We report picosecond four‐wave mixing experiments on Ga0.52In0.48P grown by organometallic vapor phase epitaxy on GaAs substrates. The spectral behavior of the homogeneous linewidth in the range of the inhomogeneously broadened band gap excitonic resonance is found to be different for a more disordered as compared to a partially ordered structure. Whereas the former shows the normal alloy behavior, the behavior of the partially ordered sample supports the assumption that its structure consists of ordered domains with varying degrees of order. This means, in particular, that the main origin of the inhomogeneous broadening is different for the disordered and ordered case. In addition, a polarization dependence of the four‐wave mixing signal is only observed for the more disordered sample. © 1994 American Institute of Physics.
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78.47.-p Spectroscopy of solid state dynamics
78.66.Fd III-V semiconductors
71.35.-y Excitons and related phenomena

Enhanced Jc’s of YBa2Cu3O7−x–Ag ex situ annealed coevaporated films on LaAlO3 (100) substrates

T. Clausen, M. Ejrnæs, M. Olesen, K. Hilger, J. L. Skov, P. Bodin, A. Kühle, and I. Chorkendorff

Appl. Phys. Lett. 65, 2350 (1994); http://dx.doi.org/10.1063/1.113038 (3 pages) | Cited 6 times

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A 5× increase of the critical current density (Jc) at 77 K was obtained by coating a coevaporated 500 nm thick Y, BaF2, Cu film with 50 nm Ag prior to the ex situ annealing. Jc increased from 0.2 for uncoated samples to 1 MA/cm2 for the Ag‐coated sample without severely affecting the zero resistance transition temperature (Tc0). Scanning electron microscopy showed that the surface morphology was improved and that the normally observed trellislike structure was greatly reduced. By combining electron microscopy and sputter assisted Auger analysis it was found that the Ag nucleated in droplets on the surface of the superconductor with only small amounts of Ag in the superconductor matrix. X‐ray diffraction confirmed that the Ag‐coated film was highly c‐axis oriented. The increase in Jc is believed to be due to the improved surface properties of the superconductor, indicating that a larger amount of the film is c‐axis oriented or that the single‐crystalline grains are larger. © 1994 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.25.Sv Critical currents
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Operation of bicrystal junction high‐Tc direct current‐SQUID in a portable microcooler

Neeraj Khare and P. Chaudhari

Appl. Phys. Lett. 65, 2353 (1994); http://dx.doi.org/10.1063/1.112743 (3 pages) | Cited 9 times

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A bicrystal junction high‐Tc direct current‐SQUID has been operated successfully at 77 K in a portable battery operated microcooler. The microcooler products magnetic signals which are harmonics of 43 Hz and a band of frequencies from 400 Hz to 4 kHz. It is possible to operate the SQUID in a flux‐locked‐loop mode using a 10 kHz modulation signal. The performance of the SQUID in the microcooler, in the frequency range 1–10 Hz, is almost identical to that in a Dewar. © 1994 American Institute of Physics.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
07.55.-w Magnetic instruments and components
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment

Correlation between distribution of outgrowths and microwave surface resistance for YBa2Cu3O7 thin films

Y. J. Tian, L. Li, L. P. Guo, J. Z. Liu, Z. X. Zhao, S. F. Xu, H. B. Lu, Y. L. Zhou, Z. H. Chen, D. F. Cui, and G. Z. Yang

Appl. Phys. Lett. 65, 2356 (1994); http://dx.doi.org/10.1063/1.112744 (3 pages) | Cited 13 times

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A model was proposed to describe the effects of surface outgrowths on the microwave surface resistance of high Tc superconducting thin films. Calculated with experimental data the microwave surface resistance at 10 GHz for c‐axis oriented YBa2Cu3O7 thin films with no outgrowths could be as low as 70 and 4 μΩ at 77 and 4.2 K, respectively. The effect of the orientation of the surface outgrowths on the microwave loss has been discussed. © 1994 American Institute of Physics.
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74.25.N- Response to electromagnetic fields
74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures

Vertical cavity amplifying photonic switch

R. Raj, J. L. Oudar, and M. Bensoussan

Appl. Phys. Lett. 65, 2359 (1994); http://dx.doi.org/10.1063/1.112745 (3 pages) | Cited 4 times

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A 30 dB gain with multi‐GHz modulation bandwidth is obtained in an optically pumped vertical cavity Fabry–Pérot structure. This device may be called a vertical cavity amplifying photonic switch (VCAPS). The amplification configuration has been used for a direct measurement of the carrier induced refractive index change over the absorption as well as the gain regime. © 1994 American Institute of Physics.
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42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.79.-e Optical elements, devices, and systems

Highly monochromatic electron point‐source beams

Roger Morin and Hans‐Werner Fink

Appl. Phys. Lett. 65, 2362 (1994); http://dx.doi.org/10.1063/1.112746 (3 pages) | Cited 6 times

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We have evaporated Cs atoms onto ultrasharp W field emitter tips that act as point sources for electrons. Significant current increases associated with individual atomic adsorption events have been observed while using these tips in the field emission mode. This indicates that only a small number of atoms is involved in the emission process. The decoration of the tip apex with several tens of Cs atoms leads to an emission voltage of only one‐fourth of that required for the pure W emitter. The spread of the energy distribution of the emitted electrons is reduced by a factor of 3 compared to the pure W point‐source tip. Thus we have devised a fairly monochromatic electron source with a full width at half‐maximum energy spread of 100 meV. © 1994 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
07.78.+s Electron, positron, and ion microscopes; electron diffractometers
41.75.Fr Electron and positron beams
FREE

Erratum: ‘‘Photopumped long wavelength vertical‐cavity surface‐emitting lasers using strain‐compensated multiple quantum wells’’ [Appl. Phys. Lett. 64, 3395 (1994)]

C. H. Lin, C. L. Chua, Z. H. Zhu, F. E. Ejeckam, T. C. Wu, Y. H. Lo, and R. Bhat

Appl. Phys. Lett. 65, 2365 (1994); http://dx.doi.org/10.1063/1.113091 (1 page)

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Abstract Unavailable
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
68.55.-a Thin film structure and morphology
99.10.Cd Errata
FREE

Erratum: ‘‘Cr4+: Gd3Sc2Ga3O12 passive Q‐switch for the Cr3+: LiCaAlF6 laser [Appl. Phys. Lett. 64, 2329 (1994)]

Yen‐Kuang Kuo, Yang Yang, and Milton Birnbaum

Appl. Phys. Lett. 65, 2365 (1994); http://dx.doi.org/10.1063/1.113097 (1 page)

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Abstract Unavailable
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Fc Modulation, tuning, and mode locking
99.10.Cd Errata
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