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9 Sep 1991

Volume 59, Issue 11, pp. 1269-1388

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Modulation of carrier distributions in delta‐doped quantum wells

Y. C. Shih and B. G. Streetman

Appl. Phys. Lett. 59, 1344 (1991); http://dx.doi.org/10.1063/1.105303 (3 pages) | Cited 15 times

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We present the modulation effect of carrier distributions in δ‐doped quantum wells (QWs). For identical Si or Be dopant distributions, the carrier distributions are significantly affected by the confinement of QWs having different thicknesses. For both types of carrier we find a QW thickness for maximum confinement, with thicker or thinner wells resulting in less confinement. An extremely narrow capacitance‐voltage profile with a full width at half maximum of 5 Å is observed in Be δ‐doped AlGaAs/GaAs QWs of width 50 Å. The sheet conductivities determined from Hall measurements also exhibit strong dependence on the spatial distribution of carriers. The modulation effects are mainly governed by the subband energy levels and the spatial extent of the carrier wave functions. Photoluminescence spectra reflect the rise of the Fermi energy caused by enhanced confinement of carriers by QWs.
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73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.61.Ey III-V semiconductors
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
78.55.Cr III-V semiconductors

Direct observation of SiH3 on a 1%‐HF‐treated Si(111) surface by scanning tunneling microscopy

Y. Morita, K. Miki, and H. Tokumoto

Appl. Phys. Lett. 59, 1347 (1991); http://dx.doi.org/10.1063/1.105304 (3 pages) | Cited 37 times

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Scanning tunneling microscopy (STM) has been made on an as‐prepared Si(111) surface by the 1%‐HF treatment. The STM images for both the empty and filled states exhibit regular dots with the threefold symmetry on the flat parts of the surface: the distance between dots measures 2.2 Å. The origin of these dots can be ascribed to the H atoms of the trihydride (SiH3) phase on the Si(111) surface. The electrons can tunnel from or to the tail states of the σ (filled) states or the σ∗ (empty) states around the H atoms for the SiH3 radicals, respectively.
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07.79.Cz Scanning tunneling microscopes
61.05.-a Techniques for structure determination
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics

Electroluminescence from a pseudomorphic Si0.8Ge0.2 alloy

D. J. Robbins, P. Calcott, and W. Y. Leong

Appl. Phys. Lett. 59, 1350 (1991); http://dx.doi.org/10.1063/1.105305 (3 pages) | Cited 37 times

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Electroluminescence due to recombination of electrons and holes at the band edges of strained Si1−xGex alloy is reported for the first time. This is demonstrated by comparison of the luminescence energy with the photoconductivity threshold of a p‐i‐n diode incorporating Si0.8Ge0.2, and with the calculated energy gap for the pseudomorphic alloy. The luminescence is strong at low temperature and persists to 220 K. The high intensity of the no‐phonon line relative to the momentum‐conserving phonon replica in the spectrum shows the scattering in the random alloy is a practical and effective mechanism for enhancing the recombination probability in this indirect semiconductor.
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78.60.Fi Electroluminescence
85.60.Jb Light-emitting devices
85.60.Dw Photodiodes; phototransistors; photoresistors
78.66.-w Optical properties of specific thin films

In situ spectroscopic ellipsometry study of the electron cyclotron resonance plasma oxidation of silicon and interfacial damage

Y. Z. Hu, J. Joseph, and E. A. Irene

Appl. Phys. Lett. 59, 1353 (1991); http://dx.doi.org/10.1063/1.105306 (3 pages) | Cited 24 times

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The growth of SiO2 films on Si and the evolution of interfacial damage resulting from electron cyclotron resonance plasma oxidation was studied using in situ during process spectroscopic ellipsometry. Accelerated growth under positive substrate bias indicates that negative atomic species dominate the growth above an oxide thickness of 4 nm. Below this thickness bias appears less important. The interfacial damage is different in both nature and extent from that caused by ions with higher energies. It appears that the damage layer is composed of SiO2 with a‐Si and is due to the oxidation reaction rather than the ions from the plasma.
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81.65.-b Surface treatments
61.80.Jh Ion radiation effects
78.66.-w Optical properties of specific thin films
68.55.-a Thin film structure and morphology

Surface‐relaxation‐controlled mechanism for occurrence of long range ordering in III‐V semiconductor alloys grown by molecular beam epitaxy

S. B. Ogale and A. Madhukar

Appl. Phys. Lett. 59, 1356 (1991); http://dx.doi.org/10.1063/1.105307 (3 pages) | Cited 7 times

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Influence of surface‐atomic relaxations on adsorption processes and the dependence of the relaxations themselves on the chemical constitution of the already grown layers are shown to be the key factors in the occurrence of long range ordering in III‐V semiconductor alloys grown by molecular beam epitaxy. The findings are based on the use of semiempirical potentials for energy minimization and involve surface‐atomistic processes over a range of five monolayers.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.66.Dk Alloys
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Effects of substrate misorientation on anisotropic electron transport in InGaAs/GaAs heterostructures

Q. Sun, C. Lacelle, D. Morris, M. Buchanan, P. Marshall, P. Chow‐Chong, and A. P. Roth

Appl. Phys. Lett. 59, 1359 (1991); http://dx.doi.org/10.1063/1.105308 (3 pages) | Cited 3 times

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The effects of substrate misorientation on anisotropic electrical properties of thick InGaAs layers grown on GaAs by low‐pressure metalorganic vapor phase epitaxy are studied. Hall bar samples oriented along [110] and [110] were cut from layers grown simultaneously on substrates oriented (a) exactly on (001) and (b) at 2° off (001) towards [011]. In layers grown on (001) oriented substrates a very large mobility anisotropy (μ[110]/μ[110]≊ 1000) is observed and attributed mainly to a lattice mismatch induced anisotropy. For the misoriented substrates, the average electron mobility increases by an order of magnitude and shows only a small residual anisotropy in the opposite direction (μ[110]/μ[110] ≊ 0.7).
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73.61.Ey III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.-a Thin film structure and morphology
68.35.Fx Diffusion; interface formation

The mechanism of electron capture by DX centers

Z. Su and J. W. Farmer

Appl. Phys. Lett. 59, 1362 (1991); http://dx.doi.org/10.1063/1.105309 (3 pages) | Cited 11 times

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It has been found that the electron capture transients of the individual DX levels in Si‐doped AlGaAs include two regimes: net capture and redistribution. In this letter, by analyzing both of these regimes, the electron capture kinetics of DX centers are determined for the first time. It is found that the capture rate for an empty state is proportional to the square of the free carrier concentration. These kinetics are predicted only by the negative U model in which two electrons are captured sequentially via an intermediate one‐electron state.
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73.20.Hb Impurity and defect levels; energy states of adsorbed species
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Laser writing and rewriting on YBa2Cu3O7 films

Y. Q. Shen, T. Freltoft, and P. Vase

Appl. Phys. Lett. 59, 1365 (1991); http://dx.doi.org/10.1063/1.105310 (3 pages) | Cited 14 times

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High‐resolution patterning (4 μm) has been achieved on epitaxial thin films of the high‐temperature superconductor YBa2Cu3O7−δ using laser writing. A focused laser beam is applied to write semiconducting patterns on superconducting films in a vacuum or in a nitrogen atmosphere. The semiconducting patterns are shown to be formed by a reduction of the oxygen content due to local heating caused by the laser beam. The process does not cause any structural damage and does not change the surface morphology. When reapplying the same laser beam and rewriting the film in an oxygen atmosphere, it is possible to restore the superconductive properties. The application of this method for production of superconducting microelectronic circuits is discussed.
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85.40.Hp Lithography, masks and pattern transfer
74.78.-w Superconducting films and low-dimensional structures
74.20.Mn Nonconventional mechanisms
74.20.Rp Pairing symmetries (other than s-wave)
74.70.-b Superconducting materials other than cuprates

Preparation of Tl2Ba2CaCu2O8 superconducting thin films on LaAlO3 substrates from metalorganic‐chemical‐vapor‐deposition‐prepared precursor films

J. A. Ladd, B. T. Collins, J. R. Matey, J. Zhao, and P. Norris

Appl. Phys. Lett. 59, 1368 (1991); http://dx.doi.org/10.1063/1.105311 (3 pages) | Cited 8 times

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Single phase Tl2Ba2CaCu2O8 thin films have been deposited on single‐crystal LaAlO3 substrates, (100) orientation, via a two‐step deposition process. First, Ba‐Ca‐Cu‐O precursor films were deposited by metalorganic chemical vapor deposition (MOCVD) using barium, calcium, and copper‐tetramethyl‐heptanedionate, (tmhd)2, source materials under reduced pressure in an oxygen/argon atmosphere. Substrate temperatures were between 500 and 600 °C. Thallium was then incorporated by heating the films in a confined surface configuration with an unfired pellet of Tl2Ba2CaCu2Ox composition at 870 °C for 0.1 h. The resultant films (0.5–1 μm thick) showed a preferred orientation with the c axis normal to the substrate. The superconducting properties were characterized by resistance and mutual inductance versus temperature and by critical current measurements. Zero resistance temperatures as high as 98 K and Jc values close to 1×104 A/cm2 at 77 K were observed.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
74.78.-w Superconducting films and low-dimensional structures
74.25.Sv Critical currents
74.70.-b Superconducting materials other than cuprates

Nonbolometric photoresponse of YBa2Cu3O7−δ films

Mark Johnson

Appl. Phys. Lett. 59, 1371 (1991); http://dx.doi.org/10.1063/1.105312 (3 pages) | Cited 36 times

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Current biased films of YBa2Cu3O7−δ (YBCO) are illuminated by short pulses of laser light and transient voltages are measured for a range of temperature 10 K <T < 250 K. Near the superconducting transition temperature Tc a bolometric response is observed. Below Tc signals are observed that cannot be explained by a bolometric mechanism. These signals, with decay times of the order of hundreds of picoseconds, are characterized and discussed.
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74.25.N- Response to electromagnetic fields
74.70.-b Superconducting materials other than cuprates
73.50.Pz Photoconduction and photovoltaic effects

Large‐area, two‐sided superconducting YBa2Cu3O7−x films deposited by pulsed laser deposition

S. R. Foltyn, R. E. Muenchausen, R. C. Dye, X. D. Wu, L. Luo, D. W. Cooke, and R. C. Taber

Appl. Phys. Lett. 59, 1374 (1991); http://dx.doi.org/10.1063/1.105313 (3 pages) | Cited 46 times

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The in situ excimer‐laser deposition process is demonstrated, for the first time, to be an effective technique for producing superconducting films on both sides of substrate wafers of up to 5 cm in diameter. By exploiting the directed nature of the laser produced plume and controlling its off‐axis composition, thickness and stoichiometric variations of less than ±5% have been obtained over the entire surface. Coatings on 5‐cm‐diam LaAlO3 substrates have uniform transition temperatures of ≥ (R18)90 K on both sides, with a critical current density at 77 K and zero field of 2.5×106 A/cm2. The 10 GHz surface resistance for samples cut from a 5 cm wafer is 40–60 μΩ at 4 K.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
74.70.-b Superconducting materials other than cuprates

Laser deposition of CdS/Y‐Ba‐Cu‐O heterostructures

L. Shi, Y. Hashishin, S. Y. Dong, J. P. Zheng, and H. S. Kwok

Appl. Phys. Lett. 59, 1377 (1991); http://dx.doi.org/10.1063/1.105314 (3 pages) | Cited 1 time

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Pulsed laser deposition was used to grow high‐quality Y‐Ba‐Cu‐O (YBCO) and CdS thin films sequentially on MgO. A temperature window between 200 and 250 °C was found to be suitable for the deposition of CdS on YBCO. The transition temperature of the heterostructure was measured to be 72 K while the single YBCO film had a Tc of 85 K. The degradation was determined to be due to interface reaction, rather than the result of poor deposition conditions. X‐ray measurements indicated that the CdS film was hexagonal and c‐axis oriented. In situ resistivity measurement was used to monitor the film growth dynamics.
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74.78.-w Superconducting films and low-dimensional structures
74.78.Fk Multilayers, superlattices, heterostructures
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Excellent thermal stability of superconducting properties in YBa2Cu3O7 films irradiated by pulsed excimer lasers

Rajiv K. Singh, D. Bhattacharya, S. Harkness, J. Narayan, P. Diwari, Catherine Jahncke, R. Sparks, and M. Paesler

Appl. Phys. Lett. 59, 1380 (1991); http://dx.doi.org/10.1063/1.105315 (3 pages) | Cited 8 times

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We have investigated the microstructure and superconducting properties of YBa2Cu3O7 films irradiated by nanosecond pulsed excimer lasers. The superconducting YBa2Cu3O7 thin films were deposited in situ on (100) LaAlO3 substrates using the pulsed laser evaporation technique. The virgin unirradiated YBa2Cu3O7 films exhibited excellent superconducting properties with Tco (temperature for zero resistance) of 90 K and critical current densities Jc (at 77 K and zero magnetic fields) of approximately 5.0 × 106 A/cm2. The films were further irradiated by a pulsed excimer XeCl laser (λ=308 nm, τ=45×10−9 s) with energy density varying from 30 to 300 mJ/cm2. Excellent thermal stability was observed for YBa2Cu3O7 films on LaAlO3 substrate for laser irradiation at all energy densities between 30 and 300 mJ/cm2, with no deterioration in the Tco values (90±0.3 K). An improvement in the Jc of the films was observed at low‐energy density irradiation, however, for energy densities above the melt threshold the Jc values decreased sharply. The Raman measurements for laser irradiated films showed improvement in the crystallinity of the film with stronger Raman peaks at 140 and 340 cm−1, thus correlating the improvement in Jc to better crystallinity of the films.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
74.78.-w Superconducting films and low-dimensional structures
74.70.-b Superconducting materials other than cuprates
74.25.Sv Critical currents

Crystallinity of a‐axis oriented YBa2Cu3O7−δ thin film epitaxially grown on NdGaO3 (110) by 95 MHz magnetron sputtering

N. Homma, S. Okayama, H. Takahashi, I. Yoshida, T. Morishita, S. Tanaka, T. Haga, and K. Yamaya

Appl. Phys. Lett. 59, 1383 (1991); http://dx.doi.org/10.1063/1.105316 (3 pages) | Cited 21 times

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An a‐axis oriented 400 Å YBa2Cu3O7−δ film has been epitaxially deposited on a NdGaO3 (110) substrate by rf magnetron sputtering using a single YBa2Cu5Ox target. An excitation frequency of 94.92 MHz, seven times as high as the conventionally used 13.56 MHz, results in a lower self‐bias voltage which reduces degradation of films caused by resputtering due to negatively charged oxygen. Sharp streaks corresponding to the c‐axis lattice parameter of YBa2Cu3O7−δ have been observed by reflection high‐energy electron diffraction, showing that the c‐axis is parallel to the surface of the NdGaO3 substrate and the film surface is smooth on an atomic scale. The crystallinity has been characterized by Rutherford backscattering channeling analysis. A minimum yield, χmin of 3.2%, has confirmed excellent crystallinity of the a‐axis oriented film.
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81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
68.35.Fx Diffusion; interface formation

Influence of cobalt substitution on critical currents of YBa2Cu3O7−s

R. G. Kulkarni, G. J. Baldha, G. K. Bichile, D. G. Kuberkar, and Smita Deshmukh

Appl. Phys. Lett. 59, 1386 (1991); http://dx.doi.org/10.1063/1.106383 (3 pages) | Cited 9 times

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Co‐doped YBa2Cu3O7−s samples prepared under identical conditions have been investigated by magnetization measurements as a function of temperature and field exhibiting pronounced M(H) hysteresis loops indicative of large flux pinning even as T approaches Tc. It is believed that the flux pinning arises due to the preferential substitution of Co in Cu(1) site, which acts as pinning center. A critical current density, Jc, of ∼106 A/cm2 is deduced from M(H) data at 13 K in a field of 1.5 kOe for YBa2(Cu1−xCox)3O7−s at x=0.01, which is nearly five times larger than the Jc of the pristine 1‐2‐3. The variation of Jc with atomic percent of Co‐substitution in 1‐2‐3 shows a structural transition (orthorhombic to tetragonal) at 4 at. % of Co indicating structural dependence on Jc.
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74.25.Sv Critical currents
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
74.70.-b Superconducting materials other than cuprates
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