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26 Jun 1989

Volume 54, Issue 26, pp. 2619-2730

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Nanometer scale wire structures fabricated by diffusion‐induced selective disordering of a GaAs(AlGaAs) quantum well

Hal A. Zarem, Peter C. Sercel, Michael E. Hoenk, John A. Lebens, and Kerry J. Vahala

Appl. Phys. Lett. 54, 2692 (1989); http://dx.doi.org/10.1063/1.101037 (3 pages) | Cited 6 times

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A shallow zinc diffusion technique is used to selectively disorder a GaAs quantum well creating nanometer scale wire structures. Spectrally resolved cathodoluminescence images of the structures are presented as well as local spectra of cathodoluminescence emission from the structures. Blue shifting of the luminescence from the wire structures is observed.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.35.Fx Diffusion; interface formation
78.60.Hk Cathodoluminescence, ionoluminescence

Improvement in the crystalline quality of heteroepitaxial GaAs on Si films grown by modulated molecular beam epitaxy

Henry P. Lee, Xiaoming Liu, Shyh Wang, Thomas George, and Eicke R. Weber

Appl. Phys. Lett. 54, 2695 (1989); http://dx.doi.org/10.1063/1.101018 (3 pages) | Cited 11 times

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GaAs films were grown on Si substrates by a two‐step method in which a thin buffer layer was first deposited using a modulated molecular beam epitaxy (MBE) technique followed by a thick layer grown by conventional molecular beam epitaxy. The film quality was evaluated using 77 K photoluminescence (PL) and double‐crystal x‐ray rocking curves. It was found that GaAs films grown in this way have a superior crystalline quality compared to the films prepared by normal two‐step MBE. To investigate the nucleation of this buffer layer, thin GaAs layers (150 Å) were grown on Si substrates and examined by plan‐view and cross‐sectional transmission electron microscope. A thin, two‐dimensional nucleation pattern was found in this sample, in clear contrast to the three‐dimensional nucleation islands found in samples grown by conventional MBE. This showed conclusively that modulated beam molecular beam epitaxy resulted in a more uniform and two‐dimensional nucleation during the initial stage of the growth as speculated earlier and is believed to be the reason for the improvement of the crystalline quality of the overgrown layer.
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68.55.-a Thin film structure and morphology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
07.79.Cz Scanning tunneling microscopes
61.05.-a Techniques for structure determination
78.55.Cr III-V semiconductors

Silicon loss and transient etch rate in selective reactive ion etching of oxide overlayers

G. S. Oehrlein and R. Kalish

Appl. Phys. Lett. 54, 2698 (1989); http://dx.doi.org/10.1063/1.100673 (3 pages)

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Silicon dioxide to silicon etch selectivity in reactive ion etching (RIE) employing fluorocarbon gases is due to the formation of a fluorocarbon film on the substrate. This implies that etch selectivity is not achieved instantly but that the substrate will exhibit a transient etch rate and hence material loss during the film formation period. The amount of silicon lost during overetching for CF4/H2 RIE was determined by Rutherford backscattering spectrometry employing a buried marker. For standard etching conditions, about 7 nm of silicon is lost within the first minute of overetching as compared to 1.5 nm expected from steady‐state etch rate data. The Si etch rate varies strongly as a function of time and decreases by a factor of greater than 10 within the first 30 s of overetching to approach a steady‐state value.
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81.05.Kf Glasses (including metallic glasses)
81.65.-b Surface treatments
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
68.55.-a Thin film structure and morphology

Two‐dimensional hole gas in Si/Si0.85Ge0.15/Si modulation‐doped double heterostructures

P. J. Wang, F. F. Fang, B. S. Meyerson, J. Nocera, and B. Parker

Appl. Phys. Lett. 54, 2701 (1989); http://dx.doi.org/10.1063/1.101019 (3 pages) | Cited 28 times

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Si/Si0.85Ge0.15/Si p‐type modulation‐doped double heterostructures have been grown by the ultrahigh vacuum/chemical vapor deposition technique, and mobility enhancement has been observed at low temperatures. For heterostructures with Si layers doped with boron to ∼1×1019 cm−3, hole mobilities of ∼900 cm2/V s at 14 K have been obtained. No carrier freeze‐out behavior has been observed at low temperatures. The existence of two‐dimensional hole gas was determined by the tilted‐field Shubnikov–de Haas measurement. Both Si/SiGe and SiGe/Si heterointerfaces were found to be equivalent and of excellent interfacial quality. The valence‐band maximum of Si0.85Ge0.15 alloy has been estimated to be ≂0.95 meV higher than that of Si. A hole effective mass of 0.44±0.03m0, which is consistent with the interpolation of the bulk band structures for the Si0.85Ge0.15 alloy, has been obtained for the heterostructure.
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73.20.At Surface states, band structure, electron density of states
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.50.Dn Low-field transport and mobility; piezoresistance
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Broadband 8–12 μm high‐sensitivity GaAs quantum well infrared photodetector

B. F. Levine, G. Hasnain, C. G. Bethea, and Naresh Chand

Appl. Phys. Lett. 54, 2704 (1989); http://dx.doi.org/10.1063/1.101002 (3 pages) | Cited 70 times

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Broadband GaAs/AlxGa1−xAs quantum well infrared detectors grown by molecular beam epitaxy have been demonstrated which are sensitive over the λ=8–12 μm atmospheric window spectral region. These are the first high‐detectivity bound state to extended state quantum well detectors which are peaked at λ=10 μm. The spectral bandwidth (Δν/ν) of these devices is three times larger than our earlier λ=8 μm device. The detectivity D∗ is background limited at T=50 K with D∗=1×1010 cm (Hz)1/2 /W, and a noise equivalent temperature change of NEΔT=0.01 K.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
78.66.-w Optical properties of specific thin films
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures

Band‐gap shifts in silicon‐germanium heterojunction bipolar transistors

J. C. Sturm, E. J. Prinz, P. M. Garone, and P. V. Schwartz

Appl. Phys. Lett. 54, 2707 (1989); http://dx.doi.org/10.1063/1.101003 (3 pages) | Cited 11 times

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The band gap of the base of Si1−xGex strained‐layer base heterojunction bipolar transistors has been investigated using minority‐carrier transport measurements. We have found a band‐gap reduction of 131 meV for a base of Si0.82Ge0.18, which is in reasonable agreement with theoretical calculations. Our measurements for a base of Si0.85Ge0.15 show a band‐gap reduction less than predicted, suggesting a reduction of strain in the structure.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.50.Dn Low-field transport and mobility; piezoresistance
85.30.Pq Bipolar transistors

Measurements of the magnetic penetration depth in YBa2Cu3O7−δ thin films by the microstrip resonator technique

Steven M. Anlage, Hsuan Sze, Howard J. Snortland, Shuichi Tahara, Brian Langley, Chang‐Beom Eom, M. R. Beasley, and Robert Taber

Appl. Phys. Lett. 54, 2710 (1989); http://dx.doi.org/10.1063/1.101547 (3 pages) | Cited 42 times

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We have utilized the superconducting microstrip resonator technique to measure the magnetic penetration depth in high Tc oxide thin films in the 1–25 GHz regime. This technique is particularly well suited for thin films, where the absolute value of the penetration depth can be accurately determined. Results for high Tc superconducting thin films show that the value of the penetration depth is sensitive to the preparation conditions of the film, and the temperature dependence is that expected of conventional superconductors.
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74.70.-b Superconducting materials other than cuprates
74.25.Ha Magnetic properties including vortex structures and related phenomena
73.50.Mx High-frequency effects; plasma effects
74.78.-w Superconducting films and low-dimensional structures

Superconducting (Nd,Ce)2CuO4 thin films grown by rf magnetron sputtering

Hideaki Adachi, Shigenori Hayashi, Kentaro Setsune, Shin‐ichiro Hatta, Tsuneo Mitsuyu, and Kiyotaka Wasa

Appl. Phys. Lett. 54, 2713 (1989); http://dx.doi.org/10.1063/1.101548 (3 pages) | Cited 12 times

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Thin films of an electron‐doped‐type (Nd,Ce)2CuO4 system have been prepared by rf magnetron sputtering and subsequent annealing. The films showed a highly oriented structure with the c axis normal to the film plane. They exhibited superconductivity after the reducing treatment by heating at 800–900 °C in vacuum. The resistivity of the films was fairly low with metallic characteristics, and the sign of the Hall coefficient was negative in the normal state. The sharp superconducting transition with zero resistivity at 22 K was observed for the film of Nd/Ce/Cu:1.855/0.145/1.2.
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74.78.-w Superconducting films and low-dimensional structures
74.70.-b Superconducting materials other than cuprates
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.40.Rs Electrical and magnetic properties related to treatment conditions

Dynamics of laser‐ablated particles from high Tc superconductor YBa2Cu3Oy

Osamu Eryu, Kouichi Murakami, Kohzoh Masuda, Atsuo Kasuya, and Yuichirô Nishina

Appl. Phys. Lett. 54, 2716 (1989); http://dx.doi.org/10.1063/1.100674 (3 pages) | Cited 57 times

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The dynamics of light‐emitting particles produced by the excimer laser ablation of the high Tc superconductor YBa2Cu3Oy has been investigated by means of space/time resolved optical measurements near the surface region with a space resolution of 100 μm and a time resolution of 0.1 ns. Two distinct components of ablated particles were observed: one with high average velocities over 5×106 cm/s and the other with slow velocities, depending on laser energy density. The position of the maximum emission intensity in the slower component moved away from the surface and was further delayed from the time of maximum laser intensity as the laser energy density increased. If the incident laser was tilted from the normal of the target surface, the spatial distribution of the luminous plume inclined toward the incident laser beam. These results suggest that the slower component consists of light‐emitting particles resulting from the fragmentation of clusters ejected from the surface.
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79.20.Ds Laser-beam impact phenomena
74.78.-w Superconducting films and low-dimensional structures
74.70.-b Superconducting materials other than cuprates
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Epitaxial growth and critical current density of thin films of YBa2Cu3O7−x on LaAlO3 substrates

A. Mogro‐Campero, L. G. Turner, E. L. Hall, M. F. Garbauskas, and N. Lewis

Appl. Phys. Lett. 54, 2719 (1989); http://dx.doi.org/10.1063/1.101549 (3 pages) | Cited 35 times

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Thin films of the high‐temperature superconductor YBa2 Cu3 O7−x have been produced on (100) LaAlO3 substrates by coevaporation and furnace annealing. A 14‐μm‐wide and 400‐μm‐long constriction patterned on a 0.8‐μm‐thick film had a zero resistance transition temperature of 90 K, a transition width of 1.5 K, and a critical current density of 8×104 A cm−2 at 77 K. Although x‐ray diffraction shows a definite c‐axis alignment normal to the substrate plane, further analysis reveals that c‐axis alignment in the substrate plane is also present. The detailed microstructural picture is revealed by transmission electron microscopy: a continuous layer, about 0.2 μm thick adjacent to the substrate, with c axis normal to the substrate plane, and the remaining top portion of the film, with the c axis in the film plane. In spite of the bilayer structure, the film remains epitaxial (the axes of the superconductor are parallel to the 〈100〉 directions of the substrate).
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74.78.-w Superconducting films and low-dimensional structures
74.70.-b Superconducting materials other than cuprates
74.25.Sv Critical currents
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Y‐Ba‐Cu‐O thin films prepared by flash evaporation

M. Ece and R. W. Vook

Appl. Phys. Lett. 54, 2722 (1989); http://dx.doi.org/10.1063/1.101550 (3 pages) | Cited 6 times

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Oriented‐Y‐Ba‐Cu‐O thin films with thicknesses between 0.6 and 0.7 μm have been deposited on magnesium oxide substrates by the flash evaporation method. The deposition was made by dropping powders of sintered Y1 Ba2 Cu3 O7−x onto a resistively heated tungsten boat. The as‐deposited films were then annealed at 930 °C in oxygen for 60 min. Annealed films were superconductors above 77 K and x‐ray diffraction showed a preferred c‐axis orientation. Increasing the annealing temperature to 945 °C improved the texture of the films and the transition temperature of the superconductivity.
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74.78.-w Superconducting films and low-dimensional structures
74.70.-b Superconducting materials other than cuprates
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation

Acoustoelectric effects in ceramic high‐temperature superconductors using a separate medium structure

M. N. Abedin, S. C. Tiersten, and P. Das

Appl. Phys. Lett. 54, 2725 (1989); http://dx.doi.org/10.1063/1.101551 (3 pages) | Cited 1 time

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The interaction of the surface acoustic wave (SAW) with a bulk ceramic high‐temperature superconductor is investigated using a contactless separate medium structure. The superconductor is part of a sandwich structure consisting of a y‐cut z‐propagating LiNbO3 SAW delay line. An acoustoelectric voltage is observed across the superconductor above the transition temperature. The magnitude of this voltage exhibits large changes as a function of temperature. As the temperature decreases through the superconductive transition, the acoustoelectric voltage vanishes abruptly. The transition temperature for the acoustoelectric voltage is in agreement with resistivity measurements performed on the same sample.
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72.50.+b Acoustoelectric effects
74.70.-b Superconducting materials other than cuprates
43.35.-c Ultrasonics, quantum acoustics, and physical effects of sound
73.50.Rb Acoustoelectric and magnetoacoustic effects
77.65.Dq Acoustoelectric effects and surface acoustic waves (SAW) in piezoelectrics
43.35.Pt Surface waves in solids and liquids

Diamond films for laser hardening

S. Albin, L. Watkins, K. Ravi, and S. Yokota

Appl. Phys. Lett. 54, 2728 (1989); http://dx.doi.org/10.1063/1.101004 (3 pages) | Cited 5 times

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Diamond has many unique physical properties useful as thin‐film coatings for laser optics. The calculated value of the laser‐induced stress resistance parameter of diamond is orders of magnitude higher than any other material and, therefore, diamond films should have a higher laser damage threshold. This is confirmed by laser damage experiments carried out on free‐standing polycrystalline diamond films. Materials susceptible to laser damage can be protected by diamond thin‐film coatings to enhance the damage threshold. This is demonstrated in the case of diamond coated silicon substrate.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.66.-w Optical properties of specific thin films
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
81.90.+c Other topics in materials science (restricted to new topics in section 81)
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