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29 Jun 1992

Volume 60, Issue 26, pp. 3203-3322

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Modulation excitation spectroscopy: A method to determine the symmetry of electronic states

G. Armelles, M. I. Alonso, P. Castrillo, and P. S. Domínguez

Appl. Phys. Lett. 60, 3277 (1992); http://dx.doi.org/10.1063/1.106718 (3 pages) | Cited 1 time

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In this letter we present a new method to determine the character of the optical transitions. We apply this method to a single quantum well of GaAs/AlGaAs. We compare a conventional photoluminescence excitation (PLE) spectrum and a piezomodulated PLE spectrum. The observed relative intensity of the light‐hole and heavy‐hole transitions is different in the former case than in the latter. This method allows us to assign the character of the optical transitions using only one measurement, and is very sensitive and selective.
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78.55.Cr III-V semiconductors
77.65.-j Piezoelectricity and electromechanical effects
78.66.Fd III-V semiconductors
78.66.Hf II-VI semiconductors

Simultaneous blue and green second harmonic generation in quasiphase matched LiNbO3 waveguide

Xiaofan Cao, Ramakant Srivastava, and Ramu V. Ramaswamy

Appl. Phys. Lett. 60, 3280 (1992); http://dx.doi.org/10.1063/1.106719 (3 pages) | Cited 4 times

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We report the first simultaneous quasiphase matched second harmonic generation (SHG) of blue (433 nm) and green (532 nm) light in LiNbO3 channel waveguides. Up to 0.45 mW (0.25 mW) of blue (green) light was obtained stimultaneously with an efficiency of 22%/W (28%/W). This result is made possible by using a 6.8 μm period domain inversion grating which serves as a first‐order (second‐order) grating for green (blue) generation simultaneously. We also show that further enhancement in the SHG performance can be obtained by choosing the appropriate grating depth.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.79.Nv Optical frequency converters

Study of interface composition and quality in AlSb/InAs/AlSb quantum wells by Raman scattering from interface modes

I. Sela, C. R. Bolognesi, L. A. Samoska, and H. Kroemer

Appl. Phys. Lett. 60, 3283 (1992); http://dx.doi.org/10.1063/1.106720 (3 pages) | Cited 26 times

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We have studied the interface structure and the quality of molecular‐beam‐epitaxy grown AlSb/InAs/AlSb quantum wells through Raman scattering from interface vibrational modes from single quantum wells. A series of samples was grown by varying the growth temperature and the interface composition (by forcing either a light AlAs or a heavy InSb interface bond configuration at each InAs/AlSb interface). We have observed the InSb modes for all the samples and related the intensity and shape of the interface modes to the structure and quality of the interfaces. This work demonstrates that a single interface heterostructure can be probed by Raman scattering.
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68.35.Ja Surface and interface dynamics and vibrations
68.55.-a Thin film structure and morphology
78.30.Fs III-V and II-VI semiconductors

Metal‐oxide‐semiconductor characteristics of chemical vapor deposited Ta2O5 films

G. Q. Lo, D. L. Kwong, and S. Lee

Appl. Phys. Lett. 60, 3286 (1992); http://dx.doi.org/10.1063/1.106721 (3 pages) | Cited 32 times

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This letter describes the metal‐oxide‐semiconductor characteristics of chemical vapor deposited Ta2O5 films. With the passivation of bottom ultrathin SiO2 layer (∼3.4 nm), an excellent interface (i.e., low fixed charge and interface state densities) has been achieved. In this study, different top dielectrics such as SiO2 and Si3N4 were used to be compatible with conventional polycrystalline Si‐gate process. By using top dielectrics deposited on Ta2O5, such as SiO2 and Si3N4, the leakage current is found to be greatly suppressed by three orders of magnitude for −Vg. For +Vg, the leakage current behaviors are believed to be governed by the Fowler–Nordheim tunneling through the bottom SiO2 layer. Under high‐field stress, however, interface state generation was found to be enhanced with the presence of the top dielectric layer.
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85.30.Tv Field effect devices
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

High mobility hydrogenated and oxygenated microcrystalline silicon as a photosensitive material in photovoltaic applications

M. Faraji, Sunil Gokhale, S. M. Choudhari, M. G. Takwale, and S. V. Ghaisas

Appl. Phys. Lett. 60, 3289 (1992); http://dx.doi.org/10.1063/1.106722 (3 pages) | Cited 12 times

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Hydrogenated and oxygenated microcrystalline silicon (mc‐Si:O:H) is prepared by rf glow discharge method with a mixture of silane, hydrogen, and oxygen. It is observed that the Hall mobility for the films can be ∼35 cm2 V−1 s−1 under optimal oxygen contents. When used as i layer in a p‐i‐n solar cell configuration, the corresponding solar cell exhibited a 7.8% efficiency with a fill factor of 0.53 over 1‐mm‐diam spots. Further improvements are indicated from the solar cell characteristics.
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84.60.Jt Photoelectric conversion
73.50.Pz Photoconduction and photovoltaic effects
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Maskless growth of InP stripes on patterned Si (001): Defect reduction and improvement of optical properties

M. Grundmann, A. Krost, D. Bimberg, O. Ehrmann, and H. Cerva

Appl. Phys. Lett. 60, 3292 (1992); http://dx.doi.org/10.1063/1.106723 (3 pages) | Cited 3 times

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Metalorganic vapor phase epitaxy of InP stripes on narrow Si (001) stripes of widths down to 0.6 μm, oriented along 〈110〉, bound by V‐grooves with {111}‐sidewalls is studied. If the InP‐stripe width is smaller than ≊4.5 μm, a complete suppression of APDs occurs. In addition, stacking faults are found not to terminate at the (001) InP surface but on {111} side planes. A smoother surface morphology and an increase of quantum efficiency by a factor 1.5–2 result. The thermal strain is observed to be partly relieved with decreasing stripe width. Lateral strain and band‐gap homogeneity is directly imaged using cathodoluminescence. Si incorporation into the InP‐layers is low and of the order of 1016 cm−3.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.66.Fd III-V semiconductors
78.66.Hf II-VI semiconductors
68.55.-a Thin film structure and morphology

Microluminescence depth profiles and annealing effects in porous silicon

S. M. Prokes, J. A. Freitas, and P. C. Searson

Appl. Phys. Lett. 60, 3295 (1992); http://dx.doi.org/10.1063/1.106724 (3 pages) | Cited 56 times

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Cross‐sectional microluminescence measurements for 1 Ω cm 70 μm porous silicon samples show a continuous decrease of the photoluminescence band as a function of sample depth. No spectral shift is observed. For samples annealed at 390 °C, in addition to spectral intensity reduction, we observe the same redshift in all luminescence spectra independent of depth. A study of this luminescence redshift as a function of annealing temperature reveals a striking similarity to results observed for optical band gap shrinking of a‐Si:H as a function of hydrogen loss during annealing.
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78.55.Hx Other solid inorganic materials
81.40.Tv Optical and dielectric properties related to treatment conditions

Novel infrared detector concept utilizing controlled epitaxial doping profiles

H. C. Liu, J.‐P. Noël, Lujian Li, M. Buchanan, and J. G. Simmons

Appl. Phys. Lett. 60, 3298 (1992); http://dx.doi.org/10.1063/1.106725 (3 pages) | Cited 5 times

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A novel infrared detector concept is proposed and experimentally demonstrated. Because of the flexibility provided by modern epitaxial growth techniques, we use thin heavily doped Si layers for infrared absorption via free‐carrier‐related processes, and the active region is sandwiched in a p‐n junction. Silicon‐based materials for long‐wavelength infrared applications are highly desirable because of the possibilities for advanced Si circuit technology.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Preparation of superconducting Ba2YCu3O7−y‐Ag composite films on sapphire by the dipping pyrolysis process

T. Manabe, W. Kondo, S. Mizuta, and T. Kumagai

Appl. Phys. Lett. 60, 3301 (1992); http://dx.doi.org/10.1063/1.106696 (3 pages) | Cited 2 times

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Superconducting Ba2YCu3O7−y(BYCO)‐Ag composite films were prepared on sapphire substrates without a buffer layer by the dipping pyrolysis process. Prefired films of a BaCO3‐Y2O3‐CuO‐Ag mixture (Ba:Y:Cu:Ag=2:1:3:0.2 in molar ratio) were heat treated at 740 °C under a low oxygen partial pressure [p(O2)=2×10−4 atm] followed by O2 annealing at 450 °C. The resulting 0.8–1.8 μm thick films showed high superconducting transition temperatures of Tc, zero=88–89 K.
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74.70.-b Superconducting materials other than cuprates
74.78.-w Superconducting films and low-dimensional structures
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Sputtering of YBa2Cu3O7−δ/NdAlO3/YBa2Cu3O7−δ trilayers

W. Rauch, H. Behner, G. Gieres, B. Sipos, R. J. Seeböck, O. Eibl, R. Kerner, G. Sölkner, and E. Gornik

Appl. Phys. Lett. 60, 3304 (1992); http://dx.doi.org/10.1063/1.106674 (3 pages) | Cited 8 times

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Epitaxial YBa2Cu3O7−δ/NdAlO3/YBa2Cu3O7−δ‐trilayers were grown by sputtering from stoichiometric targets. The YBa2Cu3O7−δ (YBCO) films were deposited by dc‐magnetron sputtering. For the NdAlO3 films, rf‐magnetron sputtering was used. The individual YBCO films revealed critical‐current densities up to 3×106 A/cm2 at 77 K. The bilayer and trilayer structures were characterized by x‐ray diffraction, Rutherford backscattering spectroscopy, and transmission electron microscopy (TEM). The channel yield χmin of the YBCO film on top was 15% for an in situ deposited trilayer. The epitaxial growth of the subsequent layers was proved by cross‐sectional TEM. Although the NdAlO3 layer contained misoriented grains, the top YBCO layer grows in single orientation over these areas. Preliminary electrical measurements show that NdAlO3 is a useful insulating dielectric for microelectronic applications.
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74.70.-b Superconducting materials other than cuprates
74.78.-w Superconducting films and low-dimensional structures
81.15.Cd Deposition by sputtering
85.25.Qc Superconducting surface acoustic wave devices and other superconducting devices

Critical current behavior in the Sb2O3‐doped YBa2Cu3O7−δ superconductor

S. Jin, T. H. Tiefel, R. A. Fastnacht, and G. W. Kammlott

Appl. Phys. Lett. 60, 3307 (1992); http://dx.doi.org/10.1063/1.106675 (3 pages) | Cited 7 times

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The effect of Sb2O3 doping on Tc and Jc behavior of the polycrystalline YBa2Cu3O7−δ superconductor has been studied. While the overall Jc remained relatively low, the addition of a small amount of Sb2O3 (e.g., 0.5 wt %) noticeably improved transport Jc at 77 K by a factor of ∼6 at H=0 and of ∼80 at H=200 Oe. The magnetization hysteresis (ΔM) at H=0.9 T also increased by a factor of ∼3. The Jc improvement, which occurs in spite of the increased porosity, reduced grain size, and slightly suppressed Tc in the Sb2O3‐doped samples, is attributed to the stronger coupling at grain boundaries in view of the significantly reduced field dependence of transport Jc. Another beneficial effect of the Sb2O3 doping, i.e., accelerated kinetics of oxygen absorption during the tetragonal‐orthorhombic transformation, is also discussed. The Sb2O3 doping, if properly optimized, may be useful for alleviating both the grain boundary weak‐link behavior and the oxygen‐supply problem typically present in thick, dense, or metal‐clad YBa2Cu3O7−δ superconductors.
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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

Superior microwave properties by post‐annealing YBa2Cu3O7 thin films at low oxygen partial pressure

A. Mogro‐Campero, L. G. Turner, A. M. Kadin, and D. S. Mallory

Appl. Phys. Lett. 60, 3310 (1992); http://dx.doi.org/10.1063/1.106676 (3 pages) | Cited 10 times

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YBa2Cu3O7 (YBCO) thin films with improved properties have been recently reported by post‐annealing in a low partial pressure of oxygen, similar to that used by in situ methods, compared to the usual post‐annealing in 1 atm of oxygen. Here it is shown that the improvements extend to the microwave surface resistance. The surface resistance was measured at close to 10 GHz; the scaled value at 10 GHz and at 77 K is 240 μΩ. This value is as low as has been reported for YBCO thin films measured around 10 GHz made by any method, and is two orders of magnitude lower than the surface resistance of copper at the same temperature and frequency.
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74.25.N- Response to electromagnetic fields
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
74.70.-b Superconducting materials other than cuprates

Control of grain alignment to fabricate long Y‐Ba‐Cu‐O superconductors with high current density

V. Selvamanickam, C. Partsinevelos, A. V. McGuire, and K. Salama

Appl. Phys. Lett. 60, 3313 (1992); http://dx.doi.org/10.1063/1.106677 (3 pages) | Cited 22 times

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A directional solidification method has been developed to grow YBa2Cu3Ox samples in excess of 55 mm in length with uniform grain alignment and a‐b planes oriented parallel to the sample length. Using a furnace configuration that yields a negative lateral gradient, the YBa2Cu3Ox grains have been forced to nucleate and grow along the axis instead of at an angle to the sample length. X‐ray pole figures analyses along the entire length at different sections show that the a‐b planes are aligned parallel to the sample length with deviations less than 5° along the growth direction. Transport critical current density (Jc) measurements over the entire length and at different sections of the sample reveal a uniform current density in excess of 7000 A/cm2 at 1.5 T and 77 K.
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81.10.Fq Growth from melts; zone melting and refining
74.70.-b Superconducting materials other than cuprates
84.71.Ba Superconducting magnets; magnetic levitation devices

Pressure‐assisted zinc bonding of microcrystalline Sm2Fe17Nx powders

C. Kuhrt, K. O’Donnell, M. Katter, J. Wecker, K. Schnitzke, and L. Schultz

Appl. Phys. Lett. 60, 3316 (1992); http://dx.doi.org/10.1063/1.106678 (3 pages) | Cited 16 times

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Highly coercive isotropic magnets were prepared by pressure‐assisted Zn bonding of microcrystalline Sm2Fe17Nx powders. Mechanically alloyed and two‐step heat treated powder was mixed with elemental Zn powder and compacted by uniaxial pressing at elevated temperatures. The maximum room‐temperature coercivity of such magnets was 34.7 kA/cm (43.6 kOe), which represents an increase by about 50% relative to that of the starting powder. The density was about 80% of the theoretical value resulting in a relatively low remanence of 0.4 T. This was achieved after compaction using parameters optimized with respect to coercivity, i.e., a Zn content of 20 wt. % (referred to the 2:17:N weight), a temperature of 425 °C and a pressure of 270 MPa. The coercivity increase induced by compaction with Zn presumably originates from improved magnetic decoupling of the 2:17:N grains which is caused by the paramagnetic Fe3Zn7 phase formed at the grain boundaries within the powder particles.
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75.50.Vv High coercivity materials
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
81.40.Rs Electrical and magnetic properties related to treatment conditions

High speed, nondestructive readout from thin‐film ferroelectric memory

Sarita Thakoor

Appl. Phys. Lett. 60, 3319 (1992); http://dx.doi.org/10.1063/1.106679 (3 pages) | Cited 25 times

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High speed, polarization direction dependent photoresponse from ferroelectric lead zirconate titanate (PbZr0.53Ti0.47O3) thin films, sandwiched between conducting electrodes to form a memory capacitor, is reported. Laser pulses with a full width at half maximum of ∼10 ns at 532 nm wavelength are utilized to readout the photoresponse signal from individual polarized elements. Such readout is repeated over a million times, with no detectable degradation in the photoresponse or the remanent polarization, suggesting its potential as a nondestructive readout (NDRO) of nonvolatile polarization state in thin‐film ferroelectric memories. In principle, both electronic as well as thermal mechanisms could be triggered by such photon exposure of ferroelectric thin films. A comparison of the photoresponse from capacitors with semitransparent and opaque top electrodes suggests that the observed NDRO signal is primarily due to thermally triggered mechanisms.
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85.60.-q Optoelectronic devices
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
FREE

Erratum: ‘‘Monitoring material grain size by laser‐generated ultrasound’’ [Appl. Phys. Lett. 59, 3530 (1991)]

A. Aharoni, M. Tur, and K. M. Jassby

Appl. Phys. Lett. 60, 3322 (1992); http://dx.doi.org/10.1063/1.107452 (1 page)

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Abstract Unavailable
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61.72.Mm Grain and twin boundaries
43.35.-c Ultrasonics, quantum acoustics, and physical effects of sound
99.10.Cd Errata
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