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19 Apr 1993

Volume 62, Issue 16, pp. 1857-1992

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Narrowing of the intersubband absorption spectrum by localization of continuum resonances in a strong electric field

Carlo Sirtori, Jerome Faist, Federico Capasso, Deborah L. Sivco, and Alfred Y. Cho

Appl. Phys. Lett. 62, 1931 (1993); http://dx.doi.org/10.1063/1.109517 (3 pages) | Cited 15 times

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Direct observation of strong localization of continuum resonances in the presence of an electric field is reported. Our structure consists of doped GaInAs quantum wells cladded by AlInAs/GaInAs quarter wave electron stacks and by AlInAs barriers. In a strong electric field of the appropriate polarity the first continuum resonance is strongly confined above the wells by the high reflectivity λ/4 stacks and by the field‐induced triangular potential barrier, while the second continuum resonance becomes localized in the latter. This manifests itself in a strong narrowing of the intersubband absorption spectrum as a function of the electric field as a greater fraction of the oscillator strength is concentrated into a transition from the ground state of the well to a quasibound state in the continuum.
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78.66.Fd III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Unimportance of siloxene in the luminescence of porous silicon

S. L. Friedman, M. A. Marcus, D. L. Adler, Y.‐H. Xie, T. D. Harris, and P. H. Citrin

Appl. Phys. Lett. 62, 1934 (1993); http://dx.doi.org/10.1063/1.109518 (3 pages) | Cited 27 times

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Near‐edge‐ and extended‐x‐ray absorption fine structure measurements, as well as luminescence excitation and emission spectra, were obtained from samples of porous Si and siloxene. Combined, these data establish that, contrary to a recently proposed explanation, siloxene is not generally responsible for the observed room‐temperature luminescence in porous Si.
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78.55.Hx Other solid inorganic materials
78.70.Dm X-ray absorption spectra

Dependence of the optical properties of semiconductor alloys on the degree of long‐range order

Su‐Huai Wei, David B. Laks, and Alex Zunger

Appl. Phys. Lett. 62, 1937 (1993); http://dx.doi.org/10.1063/1.109496 (3 pages) | Cited 95 times

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Many III‐V semiconductor alloys exhibit spontaneous [111] alternate monolayer ordering when grown from the vapor phase. This is manifested by the splitting of the valence‐band maximum and by a reduction in the direct band gap. We show here how these features can be used to deduce quantitatively the degree of long‐range order in a given sample. Examples are given for Ga0.5In0.5P and Ga0.5In0.5As alloys.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.55.-a Thin film structure and morphology
78.66.Fd III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Transient phosphorus diffusion from silicon and argon implantation damage

Martin D. Giles

Appl. Phys. Lett. 62, 1940 (1993); http://dx.doi.org/10.1063/1.109497 (3 pages) | Cited 15 times

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We have investigated transient enhanced diffusion of phosphorus in silicon following implantation with silicon or argon ions at low doses. Both conditions show uphill diffusion of phosphorus due to the defect gradients, but the resulting profiles are quite different because of differences in the initial defect distributions. These experiments support an interstitial pair diffusion mechanism for phosphorus and show the importance of bulk recombination in determining defect distributions for argon damage annealing.
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66.30.J- Diffusion of impurities
66.30.Lw Diffusion of other defects
61.80.Jh Ion radiation effects
61.72.Cc Kinetics of defect formation and annealing

Preparation of CuInS2 films by sulfurization of Cu‐In‐O films

Takahiro Wada, Takayuki Negami, and Mikihiko Nishitani

Appl. Phys. Lett. 62, 1943 (1993); http://dx.doi.org/10.1063/1.109498 (3 pages) | Cited 12 times

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CuInS2 thin films are prepared by using a newly developed two‐stage process comprised of a first process by which Cu‐In‐O films are prepared from a Cu2In2O5 target by a pulsed laser deposition, and a second process by which the prepared Cu‐In‐O films are transformed into CuInS2 films by applying an annealing in a H2S gas. The characteristics of thus obtained CuInS2 films are determined by using an x‐ray diffractometer, an energy dispersive x‐ray spectrometer, and a scanning electron microscope, in addition to a spectrophotometer. The CuInS2 film with chalcopyrite‐type structure is obtained when it is annealed at a temperature higher than 400 °C. The effect of annealing temperature on its structural and optical properties is being analyzed.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.-a Thin film structure and morphology
78.66.Hf II-VI semiconductors

Second‐harmonic generation using heavy‐hole/light‐hole intersubband transitions in asymmetric quantum wells

Xiaohua H. Qu and Harry Ruda

Appl. Phys. Lett. 62, 1946 (1993); http://dx.doi.org/10.1063/1.109499 (3 pages) | Cited 14 times

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Second‐harmonic generation (SHG) from semiconductor quantum‐well (QW) structures has recently attracted a great deal of research interest. In this letter we present a study of SHG in AlGaAs/GaAs QWs based on heavy‐hole/light‐hole intervalence subband transitions. The enhancement of the SHG efficiency over bulk material is discussed. Both the sign and the magnitude of the second‐order susceptibility of the well may be controlled; in this fashion, we demonstrate how long‐range quasiphase matching of the SHG is then possible.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.66.Fd III-V semiconductors

Novel fabrication method for nanometer‐scale silicon dots and wires

G. S. Chen, C. B. Boothroyd, and C. J. Humphreys

Appl. Phys. Lett. 62, 1949 (1993); http://dx.doi.org/10.1063/1.109500 (3 pages) | Cited 30 times

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We have discovered that a thin film of SiO2 can be directly reduced to Si under electron beam irradiation. The application of this effect to the fabrication of nanometer‐sized Si dots and wires is demonstrated. In particular, if SiO2 is irradiated with a high intensity 100 keV electron beam of nanometer scale, then a column of Si is formed which can be as small as 2 nm in diameter. If the beam is moved in a straight line, then a very thin wire of Si is formed. These columns and wires are formed directly under electron irradiation with a dose of ≥3×109 C m−2 and no resists or chemical development are required.
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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
61.80.Fe Electron and positron radiation effects

Gigantic negative transconductance and mobility modulation in a double‐quantum‐well structure via gate‐controlled resonant coupling

Y. Ohno, M. Tsuchiya, and H. Sakaki

Appl. Phys. Lett. 62, 1952 (1993); http://dx.doi.org/10.1063/1.109501 (3 pages) | Cited 32 times

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Transport of two‐dimensional electrons in a novel double‐quantum‐well (DQW) field‐effect transistor was systematically studied with emphasis on the effect of resonant interaction. By introducing ionized impurities appropriately into one of the QWs, wave‐function‐dependent scattering process was sensitively controlled by the gate voltage Vg. A prominent valley structure was observed in the channel conductance −Vg characteristics at resonance with the peak‐to‐valley ratio of 3 at 4.2 K. This nonlinear characteristic is caused by the deformation of electron wave functions in the DQW and is found to be well explained by the theoretical calculation. The DQW structure can be utilized for both negative transconductance and velocity modulation devices.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.40.Gk Tunneling
85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling

Γ‐X intervalley transfer in single AlAs barriers under hydrostatic pressure

Y. Carbonneau, J. Beerens, L. A. Cury, H. C. Liu, and M. Buchanan

Appl. Phys. Lett. 62, 1955 (1993); http://dx.doi.org/10.1063/1.109502 (3 pages) | Cited 17 times

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We have investigated the contribution of Γ‐X intervalley transfer to the tunneling current in single AlAs barrier heterostructures grown on a GaAs substrate by measuring I‐V characteristics at low temperature and under hydrostatic pressure up to 9 kbar. The application of hydrostatic pressure affects the contribution of the Γ‐X transfer process to the total tunneling current at a given bias voltage. Experimental results are compared with current‐voltage characteristics calculated with a model taking into account the Γ‐X transfer at heterointerfaces. Only transfer processes involving the longitudinal X valley in AlAs are considered in the calculations. Very good agreement is found for low bias conditions at all pressures.
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73.40.Gk Tunneling
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Microcavity effects in the photoluminescence of GaAs microcrystals

S. Juen, K. Überbacher, J. Baldauf, K. F. Lamprecht, and R. A. Höpfel

Appl. Phys. Lett. 62, 1958 (1993); http://dx.doi.org/10.1063/1.109503 (3 pages) | Cited 1 time

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We have fabricated submicron GaAs crystals by pulverization of bulk material. Size selected crystals exhibit modified photoluminescence spectra with blue shifts of up to 10 meV. The observed behavior is explained by the enhancement and the inhibition of spontaneous emission in a three‐dimensional optical microcavity formed by a semiconductor microcrystal.
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78.55.Cr III-V semiconductors
42.50.-p Quantum optics

Influence of oxygen incorporation on the properties of magnetron sputtered hydrogenated amorphous germanium films

B. Schröder, A. Annen, T. Drüsedau, H. Freistedt, P. Deák, and H. Oechsner

Appl. Phys. Lett. 62, 1961 (1993); http://dx.doi.org/10.1063/1.109504 (3 pages) | Cited 11 times

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Hydrogenated amorphous germanium‐oxygen alloy films (a‐Ge1−xOx:H) with 10−5≤x≤0.4 were prepared by reactive dc‐magnetron sputtering at substrate temperatures of 320 and 420 K in an Ar/H2/O2 atmosphere. No influence of the added oxygen on any material properties could be detected for an oxygen partial pressure p(O2)≤3×10−4 mTorr corresponding to x≤10−4 (unintentional contamination regime). Between 2×10−4≤x≤5×10−3 the dark conductivity of the films linearly increases with x (doping regime). In this regime the optical gap and the hydrogen content remain unchanged, while midgap absorption and Urbach energy weakly increase indicating the increase of network disorder and defect density due to the Fermi level shift caused by the oxygen doping. Maximum conductivity of 8×10−3 Ω−1 cm−1 is achieved for x≊0.02. For x≳0.05 the conductivity and the hydrogen content drop, defect density and Urbach energy strongly increase, and the pronounced increase of the optical gap points to the formation of an alloy (alloy regime).
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73.61.Jc Amorphous semiconductors; glasses
71.55.Jv Disordered structures; amorphous and glassy solids
81.15.Cd Deposition by sputtering

Effect of thermionic‐field emission on effective barrier height lowering in In0.52Al0.48As Schottky diodes

Yasunari Umemoto, William J. Schaff, Hyunchang Park, and Lester F. Eastman

Appl. Phys. Lett. 62, 1964 (1993); http://dx.doi.org/10.1063/1.109638 (3 pages) | Cited 2 times

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The effective lowering of the Schottky barrier height in In0.52Al0.48As diodes under reverse bias conditions is investigated by fitting experimental reverse‐bias I‐T relationships to the thermionic‐field emission theory. This lowering can be explained by thermionic‐field emission without assuming a lack of Fermi level pinning. The electron effective mass deduced experimentally from the fitting procedure ranges from 0.072m0 to 0.087m0, which is comparable to the published data. The effective barrier height is largely dependent on the temperature range of the current. The amount of the lowering is dependent on the electron effective mass, but not on the zero‐field Schottky barrier height.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Gk Tunneling
85.30.Tv Field effect devices

Chemically deposited epitaxial Si1−xGex thin film growth at atmospheric pressure

H. Kühne

Appl. Phys. Lett. 62, 1967 (1993); http://dx.doi.org/10.1063/1.109505 (3 pages) | Cited 1 time

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A so‐called ‘‘three‐partial‐rates’’ model of Si1−x Gex chemical vapor deposition that describes total growth rate as well as layer composition is applied to experimental data obtained at atmospheric pressure in hydrogen along with germane. The kind of silicon source gas was varied in that investigation using silane, dichlorosilane, and disilane, whereas all the other deposition conditions were maintained constant. Theoretical expectations drawn on the background of the above model agree fairly well with the experimental findings. All the experimental results this letter is related to were independently obtained and published [T. I. Kamins and D. J. Meyer, Appl. Phys. Lett. 61, 190 (1992)].
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68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Negative absolute conductivity in quantum wires

R. Mickevicius, V. Mitin, Michael A. Stroscio, and M. Dutta

Appl. Phys. Lett. 62, 1970 (1993); http://dx.doi.org/10.1063/1.109506 (3 pages)

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The effect of negative absolute conductivity in quasi‐one‐dimensional quantum wire structures is obtained by the Monte Carlo simulation. This negative conductivity is associated with inelastic optical phonon scattering leading to an asymmetric electron distribution function established under conditions of intensive electron photoinjection. Simulation results suggest that quantum wires are ideal for the experimental observation of negative absolute conductivity. The oscillations of photoconductivity as a function of injection energy can reveal the spectrum of optical phonons in quantum wires which differs considerably from that in bulk materials.
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72.20.Dp General theory, scattering mechanisms
72.40.+w Photoconduction and photovoltaic effects
63.20.K- Phonon interactions

Lattice location and electrical activity of ion‐implanted Sn in InP

Per Kringhøj and Gerd Weyer

Appl. Phys. Lett. 62, 1973 (1993); http://dx.doi.org/10.1063/1.109507 (3 pages) | Cited 8 times

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The lattice location and electrical activity of ion implanted Sn in InP after rapid thermal annealing has been determined by, respectively, Mössbauer spectroscopy using the 119mSn isomer and differential Hall resistivity measurements. Sn is preferentially located on the In sublattice for concentrations below 2×1019 cm−3 resulting in a high electrical activation and mobility. For Sn concentrations above 2×1019 cm−3, in addition different electrically inactive Sn complexes are observed. No indication of a Sn location on P‐sublattice sites has been found.
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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

Room‐temperature measurements of strong electroabsorption effect in GexSi1−x/Si multiple quantum wells grown by remote plasma‐enhanced chemical vapor deposition

S. S. Murtaza, R. Qian, D. Kinosky, R. Mayer, A. F. Tasch, S. Banerjee, and J. C. Campbell

Appl. Phys. Lett. 62, 1976 (1993); http://dx.doi.org/10.1063/1.109508 (3 pages) | Cited 4 times

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We have used photocurrent measurements to demonstrate a strong electroabsorption effect in GexSi1−x/Si multiple quantum wells grown by remote plasma‐enhanced chemical vapor deposition. Large voltage‐induced shifts in absorption are observed at room temperature in the wavelength range from 1.2 to 1.58 μm. We anticipate that the results can be extended to fabricate GexSi1−x optoelectronic devices operating at room temperature.
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78.66.Db Elemental semiconductors and insulators
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Enhancement of photoluminescence from DX centers in AlGaAs heterostructures

G. Livescu, M. T. Asom, L. Luther, J. L Zilko, K. D. C. Trapp, and E. Finkman

Appl. Phys. Lett. 62, 1979 (1993); http://dx.doi.org/10.1063/1.109509 (3 pages) | Cited 4 times

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Selectively excited room‐temperature photoluminescence spectra of InGaAs‐GaAs‐AlGaAs quantum well heterostructures reveal a broad line at midgap energies originating in the Si doped AlGaAs. When carriers are photoexcited directly in the wells, this line is dramatically enhanced at the expense of the quantum well line, indicating carriers escape from the wells. The broad emission and its enhancement can be explained in terms of recombination between electrons trapped at DX centers in AlGaAs and holes transferred into AlGaAs from the neighboring wells. We also observe the broad emission by direct over‐the‐gap photoexcitation of very highly doped Si:AlGaAs. The doping dependence consistently correlates this line to DX centers.
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78.55.Cr III-V semiconductors
71.55.Eq III-V semiconductors

Doping‐induced selective area photoluminescence in porous silicon

A. J. Steckl, J. Xu, H. C. Mogul, and S. Mogren

Appl. Phys. Lett. 62, 1982 (1993); http://dx.doi.org/10.1063/1.109510 (3 pages) | Cited 23 times

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The incubation time (ti) for the onset of porous Si formation by stain etching in HF:HNO3:H2O was observed to be a strong function of dopant type and concentration. For B‐doped p‐Si, ti increased significantly with substrate resistivity (ρ), from ∼0.5 min for 0.004 Ω cm to ∼9 min for 50 Ω cm. P‐doped n‐Si substrates exhibited a ti which decreased with increasing ρ, from ∼10 min for 0.15 Ω cm to ∼8 min for 20 Ω cm. We have utilized the difference in ti between n‐ and p‐type Si to produce selective area photoluminescence (PL) by Ga+ focused ion beam (FIB) implantation doping and B+ broad beam implantation doping of n‐type Si. Using 30 kV FIB Ga+ implantation, PL patterns with submicrometer resolution have been obtained for the first time.
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81.65.-b Surface treatments
78.55.Hx Other solid inorganic materials
85.45.-w Vacuum microelectronics

Giant magnetoresistance in melt spun Cu‐Co alloys

J. Wecker, R. von Helmolt, L. Schultz, and K. Samwer

Appl. Phys. Lett. 62, 1985 (1993); http://dx.doi.org/10.1063/1.109511 (3 pages) | Cited 101 times

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Cu1−xCox alloys with x=0.1 and x=0.2 have been prepared by conventional melt spinning. The rapid solidification process results in an extended solubility of Co in Cu although some Co precipitates already during quenching. In the as‐quenched ribbons, the magnetoresistance (MR) is only of the order of 1.5%. It increases dramatically with the controlled nucleation and growth of Co precipitates from the supersaturated Cu matrix. The highest MR of 11% at 300 K occurs for Cu90Co10 after an aging at about 440 °C when the Co clusters are superparamagnetic. Saturation is possible only after a higher annealing or at lower measuring temperatures. For the optimally annealed samples the MR increases to 36% at 30 K.
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72.15.Gd Galvanomagnetic and other magnetotransport effects
75.50.Tt Fine-particle systems; nanocrystalline materials
81.40.Rs Electrical and magnetic properties related to treatment conditions

Erbium laser ablation: The effect of dynamic optical properties

Joseph P. Cummings and Joseph T. Walsh

Appl. Phys. Lett. 62, 1988 (1993); http://dx.doi.org/10.1063/1.109512 (3 pages) | Cited 22 times

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Ablation characteristics of Q‐switched Er:YAG (λ=2.94 μm) and Er:YSGG (λ=2.79 μm) lasers have been compared. For equivalent fluences per pulse, the Er:YAG laser radiation cuts deeper craters into a tissue phantom than the Er:YSGG laser radiation. The Er:YAG laser irradiation created lower plume velocities than Er:YSGG laser irradiation. The data have been interpreted in terms of a dynamically changing absorption coefficient model and suggest that, in contradistinction to low‐intensity water absorption spectra, the effective absorption coefficient during ablation is greater at 2.79 than at 2.94 μm.
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87.50.W- Optical/infrared radiation effects

New model for a capacitance increase of a capacitor with hemispherical grains

Naoto Matsuo

Appl. Phys. Lett. 62, 1991 (1993); http://dx.doi.org/10.1063/1.109513 (2 pages) | Cited 2 times

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A new model that clarifies the dependence of the increase of a storage capacitance of the hemispherical grains (HSGs) capacitor both on the grain size and the oxide nitride oxide (ONO) thickness is proposed and discussed. This model assumes the effective area with a constant ONO thickness on the grain. The ratios of the storage capacitance of the HSGs capacitor to that of the conventional stacked capacitor calculated by this model coincide with the experimental data at the different ONO thickness and the different grain size. It is because the effective area increases that the ratios of the storage capacitance increase as the grain size becomes large and the ONO thickness becomes small.
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85.30.Tv Field effect devices
84.32.Tt Capacitors
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