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17 May 1993

Volume 62, Issue 20, pp. 2459-2586

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Hopping conduction in a free‐standing GaAs‐AlGaAs heterostructure wire

D. G. Hasko, J. R. A. Cleaver, H. Ahmed, C. G. Smith, and J. E. Dixon

Appl. Phys. Lett. 62, 2533 (1993); http://dx.doi.org/10.1063/1.109287 (3 pages)

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We report on the fabrication and electron transport in a novel heterostructure in which layers of AlGaAs and GaAs have been grown after a submicron free‐standing GaAs wire has been formed. Electronic conduction at low temperatures in this material is shown to be consistent with three‐dimensional hopping conduction with a transition to one‐dimensional hopping at temperatures below 1 K.
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72.80.Ey III-V and II-VI semiconductors
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
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
68.55.-a Thin film structure and morphology

Thermally stable oxygen implant isolation of p‐type Al0.2Ga0.8As

John C. Zolper, Albert G. Baca, and Scott A. Chalmers

Appl. Phys. Lett. 62, 2536 (1993); http://dx.doi.org/10.1063/1.109288 (3 pages) | Cited 15 times

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High dose oxygen implantation was used to form high resistivity regions in p‐type Al0.2Ga0.8As. By achieving oxygen concentrations 30 times the grown‐in beryllium concentration we created Al0.2Ga0.8As layers with a sheet resistance of over 1010 Ω/☒ that were stable to 900 °C. Samples implanted with a base dose of 2×1014 cm−2 showed an apparent activation energy for conduction of 0.67 eV after annealing at 800 °C.  
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61.72.uj III-V and II-VI semiconductors
71.55.Eq III-V semiconductors
72.80.Ey III-V and II-VI semiconductors

Strong far‐infrared intersubband absorption under normal incidence in heavily n‐type doped nonalloy GaSb‐AlSb superlattices

L. A. Samoska, Berinder Brar, and H. Kroemer

Appl. Phys. Lett. 62, 2539 (1993); http://dx.doi.org/10.1063/1.109289 (3 pages) | Cited 26 times

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We report on long‐wavelength intersubband absorption under normal incidence in heavily doped binary‐binary GaSb‐AlSb superlattices. Due to a small energy difference between the ellipsoidal L valleys in GaSb and the low‐density‐of‐states Γ minimum, electrons spill over from the first Γ subband into the higher‐energy L subband in GaSb wells, where they are allowed to make an intersubband transition under normally incident radiation. A peak fractional absorption per quantum well of 6.8×10−3 (absorption coefficient α≊8500 cm−1) is observed at λ≊15 μm for a sheet concentration of 1.6×1012 cm−2/well.
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78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Intersubband optical transients in multi‐quantum‐well structures

F. Luc, E. Rosencher, and Ph. Bois

Appl. Phys. Lett. 62, 2542 (1993); http://dx.doi.org/10.1063/1.109290 (3 pages) | Cited 9 times

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We show that optical transients due to the intersubband photoionization of the electrons from quantum wells may be observed by inserting a multi‐quantum‐well structure in the space‐charge layer of a Schottky diode. This method provides a direct measurement of the photoionization cross section of a quantum well. The escape probability of the photoexcited electron from the quantum well can thus be unambiguously deduced. Its variation with the electric field may be described by a simple model based on the statistical fluctuation of the quantum‐well width.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
78.66.Fd III-V semiconductors
85.60.Gz Photodetectors (including infrared and CCD detectors)

Atomic probe microscopy of 3C SiC films grown on 6H SiC substrates

A. J. Steckl, M. D. Roth, J. A. Powell, and D. J. Larkin

Appl. Phys. Lett. 62, 2545 (1993); http://dx.doi.org/10.1063/1.109291 (3 pages) | Cited 8 times

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The surface of 3C SiC films grown on 6H SiC substrates has been studied by atomic probe microscopy in air. Atomic‐scale images of the 3C SiC surface have been obtained by scanning tunneling microscopy (STM). STM has confirmed the 〈111〉 orientation of the cubic 3C layer grown on the {0001} surface of the hexagonal 6H substrate. The nearest‐neighbor atomic spacing for the 3C layer has been measured to be 3.29±0.2 Å, which is within 7% of the bulk value. Shallow terraces in the 3C layer have been observed by STM to separate regions of very smooth growth in the vicinity of the 3C nucleation point from considerably rougher 3C surface regions. These terraces are oriented at right angles to the growth direction. Atomic force microscopy has been used to study etch pits present on the 6H substrate due to high temperature HCl cleaning prior to chemical vapor deposition growth of the 3C layer. The etch pits have hexagonal symmetry and vary in depth from 50 nm to 1 μm.
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Nonlinear interdiffusion in semiconductor superlattices: Case of CdTe/HgTe

A. Tardot, A. Hamoudi, N. Magnea, P. Gentile, and J. L. Pautrat

Appl. Phys. Lett. 62, 2548 (1993); http://dx.doi.org/10.1063/1.109292 (3 pages) | Cited 13 times

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Experiments have been designed to measure the interdiffusion coefficients in CdTe/HgTe (001) superlattices grown by molecular beam epitaxy. The interdiffusion coefficients are deduced from double‐crystal x‐ray diffraction on samples annealed in the 200–240 °C range under a Hg saturated pressure. Our results indicate that the interdiffusion is strongly dependent on concentration with a coefficient given by D(CCd,T)=1.0 exp{[−1.45(±0.1) eV]/(kT)} exp {[−0.55 (±0.1) CCd eV]/(kT)} cm2/s. The activation energies ΔEHgTe≊1.45 eV and ΔECdTe≊2.0 eV are consistent with an interdiffusion process by a vacancy mechanism.
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66.30.Ny Chemical interdiffusion; diffusion barriers
68.55.-a Thin film structure and morphology
68.35.Fx Diffusion; interface formation

Real‐time study of the reflection high energy electron diffraction specular beam intensity during atomic layer epitaxy of GaAs

B. Y. Maa, P. D. Dapkus, P. Chen, and A. Madhukar

Appl. Phys. Lett. 62, 2551 (1993); http://dx.doi.org/10.1063/1.109293 (3 pages) | Cited 3 times

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The intensity behavior of the specular beam in reflection high energy electron diffraction (RHEED) from GaAs (001) is investigated during the exposure of trimethylgallium (TMGa) and tertiarybutylarsine (TBAs) in atomic layer epitaxy (ALE) of GaAs. The temporal behavior of RHEED specular beam intensity corresponding to the transient behavior of the reflectance difference (RD) at 632.8 nm reveals several phases of surface reactions in ALE using TMGa and TBAs. RHEED specular beam intensity relaxation after short exposure to TMGa shows a longer time constant than that observed by RD, suggesting that it is the result of the overall changes in the surface atomic arrangements and morphology whereas the latter is responding to the formation/annihilation of Ga dimers.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)

Polycrystalline silicon thin film transistors on Corning 7059 glass substrates using short time, low‐temperature processing

Gang Liu and Stephen J. Fonash

Appl. Phys. Lett. 62, 2554 (1993); http://dx.doi.org/10.1063/1.109294 (3 pages) | Cited 41 times

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A new fabrication process for polycrystalline silicon thin film transistors on 7059 glass substrates is reported. This unique fabrication process has the advantages of short processing time and low processing temperature (≤600 °C). The processing is based on the key step of using an ultrathin Pd layer, introduced to the surface of the glass prior to the deposition of an a‐Si:H film, to reduce the crystallization time and temperature. It is also based on using an electron cyclotron resonance hydrogen plasma to reduced the passivation time. The n‐channel TFTs produced by this new fabrication process have mobilities of 20 cm2/V s, and off‐currents of 0.5 pA/μm.
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85.30.Pq Bipolar transistors
85.40.Hp Lithography, masks and pattern transfer

Theoretical and experimental studies of the ZnSe/CuInSe2 heterojunction band offset

Art J. Nelson, C. R. Schwerdtfeger, Su‐Huai Wei, Alex Zunger, D. Rioux, R. Patel, and Hartmut Höchst

Appl. Phys. Lett. 62, 2557 (1993); http://dx.doi.org/10.1063/1.109295 (3 pages) | Cited 13 times

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We report first‐principles band structure calculations that show that ZnSe/CuInSe2 has a significant valence band offset (VBO, ΔEv): 0.70±0.05 eV for the relaxed interface and 0.60±0.05 eV for the coherent interface. These large values demonstrate the failure of the common anion rule. This is traced to a stronger Cu,d‐Se,p level repulsion in CuInSe2 than the Zn,d‐Se,p repulsion in ZnSe. The VBO was then studied by synchrotron radiation soft x‐ray photoemission spectroscopy. ZnSe overlayers were sequentially grown in steps on n‐type CuInSe2(112) single crystals at 200 °C. In situ photoemission measurements were acquired after each growth in order to observe changes in the valence band electronic structure as well as changes in the In 4d and Zn 3d core lines. Results of these measurements reveal that the VBO is ΔEv=0.70±0.15 eV, in good agreement with the first‐principles prediction.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Current‐voltage characteristics and interface state density of GaAs Schottky barrier

Keiji Maeda, Hideaki Ikoma, Kenji Sato, and Toshiki Ishida

Appl. Phys. Lett. 62, 2560 (1993); http://dx.doi.org/10.1063/1.109296 (3 pages) | Cited 19 times

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See Also: Erratum

Show Abstract
A density distribution of the interface states in GaAs Schottky barrier was derived for the first time from observed nonideal I‐V characteristics of a GaAs Schottky barrier with an oxidized interface. With increasing forward bias voltage, the ideality factor increases and then decreases after passing a maximum. Fermi level of the interface states shifts with the applied bias in the interfacial layer model adopted for the analysis. The obtained energy level of the interface states is in agreement with a previously reported value. However, the absolute magnitude of the state density is quite small compared with that obtained from the weak dependence of the barrier height on metal work functions. Implications of this result are discussed.
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73.20.At Surface states, band structure, electron density of states
73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Lumped circuit model of two‐dimensional to two‐dimensional tunneling transistors

Y. Katayama and D. C. Tsui

Appl. Phys. Lett. 62, 2563 (1993); http://dx.doi.org/10.1063/1.109297 (3 pages) | Cited 10 times

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A lumped circuit model for the two‐dimensional (2D) to 2D tunneling transistor is proposed. A new concept of virtual separation of nodes is introduced to distinguish the energy of the subband edges and the Fermi energy of the quantum wells in the circuit diagram. The two virtually separated nodes are connected by the quantum capacitance due to the quantum confinement of the electrons in each well. This concept provides a simple and accurate representation of the device operation by the geometrical capacitances, the quantum capacitances, and the voltage dependent tunneling resistance.
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85.30.De Semiconductor-device characterization, design, and modeling
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
73.40.Gk Tunneling

Very low temperature (<400 °C) silicon molecular beam epitaxy: The role of low energy ion irradiation

M. V. Ramana Murty, Harry A. Atwater, A. J. Kellock, and J. E. E. Baglin

Appl. Phys. Lett. 62, 2566 (1993); http://dx.doi.org/10.1063/1.109298 (3 pages) | Cited 39 times

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Concurrent low energy (50–70 eV) ion irradiation during silicon molecular beam epitaxy results in an increased epitaxial thickness at very low temperatures relative to conventional molecular beam epitaxy. Ion irradiation of a (1×1) dihydride‐terminated Si(001) results in a (2×1) reconstruction, indicating irradiation‐induced hydrogen desorption. Conventional molecular beam epitaxial growth is possible on a dihydride‐terminated Si(001) surface following (2×1) reconstruction such that the substrate temperature never exceeds 150 °C; which is not possible without irradiation.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.80.Jh Ion radiation effects

Quantitative study of exciton migration effects on photoluminescence of quantum well

Er‐Xuan Ping

Appl. Phys. Lett. 62, 2569 (1993); http://dx.doi.org/10.1063/1.109299 (3 pages) | Cited 6 times

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The effects, induced by the exciton (EX) migration and the inherent interface roughness, on the photoluminescence (PL) in a quantum well (QW) have been studied by a model which includes the inter‐ and intra‐growth‐island EX transfer. Analytical expressions, showing the redshifting and linewidth reduction in the PL spectrum, are obtained at low and high temperatures. The inconsistency of the PL and PL excitation spectra has been reexamined and quantitatively obtained, under the influence of the EX migration, as a function of the temperature, the quality, and the structure of the QW.
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78.66.-w Optical properties of specific thin films
78.55.-m Photoluminescence, properties and materials
71.35.-y Excitons and related phenomena

Submicron electrically conducting wires produced in polyimide by ultraviolet laser irradiation

H. M. Phillips, S. Wahl, and R. Sauerbrey

Appl. Phys. Lett. 62, 2572 (1993); http://dx.doi.org/10.1063/1.109300 (3 pages) | Cited 12 times

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An array of permanently electrically conducting lines with a width of 0.5 μm and a period of 0.9 μm has been produced in polyimide with a KrF laser using a holographic technique. The electrical resistivity of these submicron structures shows an ohmic characteristic and has a value of less than 0.5 Ω cm, while the resistivity perpendicular to the structures exceeds this value by more than a factor of 107. The temperature dependence of the conductivity in these wires is found to be similar to that found for macroscopic regions of polyimide which show laser induced conductivity.
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72.80.Le Polymers; organic compounds (including organic semiconductors)
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
82.50.-m Photochemistry
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

Voltage noise properties of Nb‐(fine Nb wires)‐NbN thin film short weak links

M. Hatle, T. Kondo, and K. Hamasaki

Appl. Phys. Lett. 62, 2575 (1993); http://dx.doi.org/10.1063/1.109301 (3 pages)

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We have fabricated superconductive Nb‐(fine Nb wires)‐NbN short weak links. We find that their quasiparticle characteristics can be well explained using the theory of T. M. Klapwijk, G. E. Blonder, and M. Tinkham [Physica B and C 109 & 110B 1657 (1982)] based on the Andreev reflection phenomenon at two independent normal metal‐superconductor interfaces for the case of a negligible effective barrier potential. For such devices, there is found no measurable excess noise associated with the Andreev reflection itself and device voltage noise clearly exhibits both thermal and shot noise limits. Although the device structure is fundamentally different, in the whole studied range of bias voltages, the voltage noise properties of our short weak links are found to be qualitatively comparable to those of small‐area tunnel junctions.
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74.50.+r Tunneling phenomena; Josephson effects
74.40.-n Fluctuation phenomena
74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)

Effects of annealing conditions on heavily carbon‐doped InGaAs

W. Y. Han, L. Calderon, Y. Lu, S. N. Schauer, R. P. Moerkirk, H. S. Lee, J. R. Flemish, K. A. Jones, and L. W. Yang

Appl. Phys. Lett. 62, 2578 (1993); http://dx.doi.org/10.1063/1.109302 (3 pages)

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Two heavily carbon doped InGaAs samples (2.20×1019 and 1.92×1019 cm−3) with low In mol fractions (1% and 8%) were annealed with or without silicon nitride caps in H2 containing 0.3% AsH3 over the temperature range 5000–800 °C. Hall effect, secondary ion mass spectroscopy, double crystal x‐ray diffraction, and integrated photoluminescence measurements showed that H outdiffuses over the annealing temperature range when the films were capped with silicon nitride. However, there was almost no net H outdiffusion for uncapped samples annealed in the same ambient and temperature range. Recombination centers formed during high temperature anneals in samples with less In (1%), but did not appear to form as readily in the one with more In (8%).
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61.72.Cc Kinetics of defect formation and annealing
61.72.uj III-V and II-VI semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Fine magnetic domain structure of stressed amorphous metal

K. Koike, H. Matsuyama, W. J. Tseng, and J. C. M. Li

Appl. Phys. Lett. 62, 2581 (1993); http://dx.doi.org/10.1063/1.109303 (3 pages) | Cited 6 times

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The fine magnetic domain structure which appears on a stressed amorphous ribbon is studied using a spin‐polarized scanning electron microscope. The detected domain structure differs from any so far reported. The magnetization direction inside the wavy stripelike closure domain fluctuates along the stripes. We propose two possible models to explain this domain structure.
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75.50.Kj Amorphous and quasicrystalline magnetic materials
75.60.Ch Domain walls and domain structure

Visualization of a gas flow instability in spin coating systems

Sanjay Wahal, Alparslan Oztekin, David E. Bornside, Robert A. Brown, Philip K. Seidel, Paul W. Ackmann, and Franz T. Geyling

Appl. Phys. Lett. 62, 2584 (1993); http://dx.doi.org/10.1063/1.109304 (3 pages) | Cited 5 times

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Flow visualization in the gas above the surface of a rotating wafer in an industrial spin coating apparatus demonstrates the presence of an Ekman‐like flow instability that adversely affects the uniformity of the dried film. Experiments performed with a 6‐in.‐diam wafer and typical operating conditions show 6–8 spiral vortices around the wafer oriented with negative angle, as is indicative of the type II flow instability predicted by linear stability analysis. The critical Reynolds number for onset is in reasonable agreement with the theory.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
47.27.-i Turbulent flows
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