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10 Apr 1989

Volume 54, Issue 15, pp. 1383-1481

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Noncollinear phase‐matched second‐harmonic generation in beta barium borate

G. C. Bhar, S. Das, and U. Chatterjee

Appl. Phys. Lett. 54, 1383 (1989); http://dx.doi.org/10.1063/1.101405 (2 pages) | Cited 8 times

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Noncollinearly phase‐matched second‐harmonic generation is reported for the first time in beta barium borate crystal and compared with existing KDP and KD∗P crystals using Nd:YAG radiation.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.20.-e Optical properties of bulk materials and thin films

Linear electro‐optic effect in sputtered polycrystalline LiNbO3 films

G. Griffel, S. Ruschin, and N. Croitoru

Appl. Phys. Lett. 54, 1385 (1989); http://dx.doi.org/10.1063/1.101406 (3 pages) | Cited 26 times

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Light guiding and modulation was demonstrated in sputtered LiNbO3 films deposited on glass substrates. We report on films’ exceptionally low attenuation (<2 dB/cm) and the highest electro‐optical coefficient reported so far for this kind of film (1.34×10−12 m/V).
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78.66.-w Optical properties of specific thin films
78.20.Jq Electro-optical effects

GaAs double quantum well laser diode with short‐period (AlGaAs)m(GaAs)n superlattice barriers

H. Imamoto, F. Sato, K. Imanaka, and M. Shimura

Appl. Phys. Lett. 54, 1388 (1989); http://dx.doi.org/10.1063/1.100675 (3 pages) | Cited 1 time

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A short‐period (AlGaAs)m(GaAs)n superlattice has been applied to the barrier layers in a single and a multiple quantum well structure prepared by molecular beam epitaxy in order to improve the interface quality. With a 38 Å thin GaAs quantum well without employing aluminum, a low threshold current density of 260 A/cm2, a high characteristic temperature (T0) of 205 K, and a high differential quantum efficiency of 75% have been achieved in a double quantum well ridge waveguide laser diode emitting at 780 nm.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Transverse‐mode‐stabilized ridge stripe AlGaInP semiconductor lasers incorporating a thin GaAs etch‐stop layer

T. Tanaka, S. Minagawa, and T. Kajimura

Appl. Phys. Lett. 54, 1391 (1989); http://dx.doi.org/10.1063/1.100676 (3 pages) | Cited 3 times

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Transverse‐mode‐stabilized ridge stripe AlGaInP semiconductor lasers fabricated using a thin GaAs layer as an etch stop are reproducibly realized. The ridge stripe structure is fabricated utilizing the large difference in etching rates between GaAs/AlGaAs and AlGaInP layers. As a result, the thickness control of the cladding layer adjacent to light absorbing layers is significantly improved. Results show that the GaAs layer is effective as an etch‐stop layer even if the thickness is only 1–2 nm. The total internal loss of the lasers is estimated to be about 20 cm−1 and loss due to the insertion of the GaAs layer is almost negligible. A threshold current of about 50 mA and a stable fundamental transverse mode up to an output power of about 10 mW is attained at room temperature under cw operation. Similar results were obtained when an AlGaAs layer was used instead of GaAs.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
81.65.-b Surface treatments

Electro‐optic switching using total internal reflection by a ferroelectric liquid crystal

M. R. Meadows, M. A. Handschy, and N. A. Clark

Appl. Phys. Lett. 54, 1394 (1989); http://dx.doi.org/10.1063/1.100677 (3 pages) | Cited 22 times

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An electro‐optic switch using total internal reflection by a ferroelectric liquid crystal is reported. The device has rise and fall times of about 150 μs, and causes the optical power in the output beam to be attenuated by a factor of 500 000 in the off state. It does not employ polarizers, and its operation is nearly independent of wavelength. The measurements here cover the 400–1600 nm band.
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78.20.Jq Electro-optical effects
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
42.79.Hp Optical processors, correlators, and modulators
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

High‐efficiency, continuous‐wave, epitaxial surface‐emitting laser with pseudomorphic InGaAs quantum wells

P. L. Gourley, S. K. Lyo, and L. R. Dawson

Appl. Phys. Lett. 54, 1397 (1989); http://dx.doi.org/10.1063/1.100678 (3 pages) | Cited 13 times

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We report the first continuous‐wave (cw) photopumped operation of surface‐emitting lasers comprising pseudomorphic InGaAs quantum wells. The lasers were grown by molecular beam epitaxy and incorporate epitaxial quarter‐wave AlAs/GaAs mirrors surrounding an active region. In the active region, 50 Å InGaAs quantum wells are distributed with half‐wave periodicity to center on cavity standing wave maxima. Lasing is observed from 78 to 250 K in the spectral range 920–950 nm, where the GaAs substrate is transparent. Thresholds were as low as 1.5×104 W/cm2, and overall (differential) output power efficiency was as high as 35% (85%) with up to 60 mW in a low divergence beam. Both periodic gain and biaxial compressive layer strain contribute to the reduced lasing threshold. The laser gain length is only 550 Å (11 quantum wells). The possibility of surface‐emitting lasing in single quantum wells is discussed.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
78.45.+h Stimulated emission

Lasing characteristics of GaAs microresonators

J. L. Jewell, S. L. McCall, Y. H. Lee, A. Scherer, A. C. Gossard, and J. H. English

Appl. Phys. Lett. 54, 1400 (1989); http://dx.doi.org/10.1063/1.100679 (3 pages) | Cited 33 times

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Lasing characteristics of optically pumped 1.5‐μm‐diam GaAs‐AlAs microresonators are reported. Room‐temperature thresholds of 9 pJ were observed. Uniform outputs were obtained from a simultaneously driven 2×2 array.
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42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.55.Px Semiconductor lasers; laser diodes
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Density rescaling procedure for Monte Carlo simulations of electron transport

Y. M. Li, L. C. Pitchford, and T. J. Moratz

Appl. Phys. Lett. 54, 1403 (1989); http://dx.doi.org/10.1063/1.100680 (3 pages) | Cited 8 times

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A practical difficulty in Monte Carlo simulations of electron transport occurs when the electron number density changes significantly over the time or length scale of the simulation. In this letter, we present a simple scaling procedure to resolve this difficulty that is easy to implement and that is exact for linear collision operators. A simulation of electron transport in nitrogen at high electric field strength is included to illustrate this rescaling procedure.
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52.25.Fi Transport properties
51.50.+v Electrical properties (ionization, breakdown, electron and ion mobility, etc.)
52.65.-y Plasma simulation
52.20.Fs Electron collisions

Improved flash γ‐ray uniformity using a Bθ lens diode

T. W. L. Sanford, J. A. Halbleib, J. W. Poukey, C. E. Heath, R. Mock, V. L. Bailey, G. A. Proulx, P. W. Spence, and H. Kishi

Appl. Phys. Lett. 54, 1406 (1989); http://dx.doi.org/10.1063/1.100681 (3 pages) | Cited 1 time

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Significantly improved spatial uniformity of bremsstrahlung radiation, relative to a planar‐anode diode, is obtained on the 3‐MV, 150‐kA HELIA accelerator when a Bθ lens diode is used to actively control the high‐power electron beam at the exit of a coaxial, magnetically insulated transmission line. The advantage of this diode over other diodes which only passively control the beam is that better radiation uniformity for less beam loss is possible. Measurements taken on HELIA are shown to agree with theoretical expectations.
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52.59.Mv High-voltage diodes
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
41.75.Fr Electron and positron beams
41.60.-m Radiation by moving charges

Elastic constants of metal‐insulator superlattices

R. Bhadra, M. Grimsditch, J. Murduck, and Ivan K. Schuller

Appl. Phys. Lett. 54, 1409 (1989); http://dx.doi.org/10.1063/1.100682 (3 pages) | Cited 13 times

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A Brillouin scattering study of elastic properties of NbN/AlN superlattices is presented. Because the coupling of light to surface waves in this system is very weak, we describe a modification of the technique which enhances the scattering efficiency, thereby allowing measurements of a system which is otherwise inaccessible. This particular multilayer superlattice is one of the very few that does not exhibit any elastic anomalies as a function of layer thickness in accordance with the idea that electron transfer may be the mechanism responsible for elastic anomalies in superlattices.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.60.Bs Mechanical and acoustical properties
78.35.+c Brillouin and Rayleigh scattering; other light scattering
68.35.Gy Mechanical properties; surface strains

Hydrogen retention and release dynamics of amorphous carbon films exposed to a hydrogen plasma

H. Sugai, S. Yoshida, and H. Toyoda

Appl. Phys. Lett. 54, 1412 (1989); http://dx.doi.org/10.1063/1.100683 (3 pages) | Cited 11 times

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H2 and DH release was investigated in a pulsed deuterium discharge over a carbon thin‐film deposited wall. A large quantity of hydrogen was desorbed by 300 eV D+2 irradiation from hydrogenated amorphous carbon (a‐C:H) deposited by a hydrogen‐admixed methane discharge. On the other hand, a strong pumping effect was observed in the case of films deposited by a helium‐admixed discharge. The wall pumping effect was attributed to the presence of interstitial vacancies rather than dangling bonds in the films. A linear dependence of the hydrogen release rate on the ion bombarding current suggests that molecular formation is by direct hydrogen abstraction instead of recombination of two free hydrogen atoms. A dynamic model of hydrogen release and retention for a‐C:H layers during hydrogen implantation is proposed. Corresponding calculations yield satisfactory agreement with observations when using appropriate rate constants for trapping and detrapping.
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68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
52.40.Hf Plasma-material interactions; boundary layer effects
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Analytical description for the diffusion and recombination of point defects in silicon

N. E. B. Cowern

Appl. Phys. Lett. 54, 1415 (1989); http://dx.doi.org/10.1063/1.100684 (3 pages) | Cited 6 times

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A simplified analysis is given of point‐defect diffusion in the presence of traps which saturate on recombination. Examples of this phenomenon are self‐interstitial diffusion and gettering in Czochralski silicon, and coupled interstitial‐vacancy diffusion in perfect crystalline silicon. When recombination is diffusion limited, a simple diffusion equation is obtained, with an effective diffusivity math which is an analytical function of the point‐defect and trap concentrations. The physical meaning of this function is described.
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66.30.Dn Theory of diffusion and ionic conduction in solids
66.30.Lw Diffusion of other defects
61.72.jd Vacancies
61.72.jj Interstitials
61.72.J- Point defects and defect clusters

Elastic oscillatory resistances of small contacts

N. García and L. Escapa

Appl. Phys. Lett. 54, 1418 (1989); http://dx.doi.org/10.1063/1.100685 (3 pages) | Cited 36 times

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We discuss the elastic coherent resistances of small contacts or constrictions between reservoirs. These resistances show an oscillatory behavior versus contact size, increase when the size of the contact decreases, and are dominant over the inelastic or residual resistances for realistic values of resistivities, temperature, and purity.
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73.40.Cg Contact resistance, contact potential
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Atomic resolution imaging of electrode surfaces in solutions containing reversible redox species

Michael J. Heben, Reginald M. Penner, Nathan S. Lewis, Moris M. Dovek, and Calvin F. Quate

Appl. Phys. Lett. 54, 1421 (1989); http://dx.doi.org/10.1063/1.100686 (3 pages) | Cited 6 times

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Procedures are described for insulating metal scanning tunneling microscope (STM) tips with either glass or polymer coatings. In solutions containing 0.10 M of a reversible redox couple, Fe(CN)−3/−46, the faradaic limiting current to polymer coated tips was 200–500 pA and that for glass coated tips was <10 pA. For polymer insulated tips, steady‐state currents of 10–100 pA were observed at tip‐sample displacements less than 0.3 μm. The suppression of faradaic current achieved by these coating procedures enabled the collection of the first atomic resolution STM images of highly ordered pyrolytic graphite electrodes in contact with redox‐active electrolytes. Preliminary data for the in situ electrochemical characterization of these tips are also discussed.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
07.79.Cz Scanning tunneling microscopes
61.05.-a Techniques for structure determination
82.45.-h Electrochemistry and electrophoresis

Writing nanometer‐scale symbols in gold using the scanning tunneling microscope

Y. Z. Li, L. Vazquez, R. Piner, R. P. Andres, and R. Reifenberger

Appl. Phys. Lett. 54, 1424 (1989); http://dx.doi.org/10.1063/1.100687 (3 pages) | Cited 77 times

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The conditions required to electroetch nanometer‐sized craters in flat gold substrates with a scanning tunneling microscope operating in air are identified. Reproducible nanometer‐scale modifications of the substrate are possible. Letters and complex symbols with linewidths as small as 2 nm have been written. Experiments show that a good tunneling tip is not destroyed by the writing process.
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81.05.Bx Metals, semimetals, and alloys
07.79.Cz Scanning tunneling microscopes
61.05.-a Techniques for structure determination
07.78.+s Electron, positron, and ion microscopes; electron diffractometers

Catalytic effect of SiO on thermomigration of impurities in SiO2

G. K. Celler and L. E. Trimble

Appl. Phys. Lett. 54, 1427 (1989); http://dx.doi.org/10.1063/1.101407 (3 pages) | Cited 30 times

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We have found that encapsulated thin Si films, adjacent to SiO2, are dissolved at elevated temperatures by a reaction: Si+SiO2→2SiO, with SiO diffusing through the silica network. The presence of SiO in SiO2 in a concentration ≤3 at. % has a profound effect on thermomigration of dopant impurities in the oxide. We propose a model for transport of As‐, Sb‐, P‐, and Ge‐rich precipitates, 50–1000 Å in diameter, based on a reaction between SiO2 and the precipitates that is mediated by a catalytic influence of SiO molecules. Only in the presence of SiO are the bonds in the SiO2 network broken ahead of the drifting clusters and regrown behind them. The model predicts that the migration of precipitates is controlled by diffusivity of SiO in silica, consistent with the narrow range of drift velocities for clusters of different chemical compositions. The data also suggest that SiO2 dissociation at the Si/SiO2 interface is diffusion limited, which explains why decomposition of thin SiO2 in vacuum is spatially inhomogeneous, while thick films used in our experiments react uniformly.
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66.30.J- Diffusion of impurities
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.60.Dv Thermal stability; thermal effects
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Formation of silicon carbide particles behind shock waves

Craig S. Carmer and Michael Frenklach

Appl. Phys. Lett. 54, 1430 (1989); http://dx.doi.org/10.1063/1.100688 (3 pages) | Cited 7 times

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The formation of silicon carbide powder in a 3% SiH4‐3% CH4‐Ar mixture was studied in a shock tube. The experiments were conducted at the temperature of 800–3650 K, pressures of 0.46–4.16 atm, and reaction times of 1–2 ms. The progress of reaction was monitored by the attenuation of a He‐Ne (633 nm) laser beam. Powders collected at the end wall of the tube were identified to be β‐SiC and at high temperatures contained particles having sizes up to 0.5 μm. The large particles had the form of thin single‐crystal platelets with hexagonal and truncated triangular shapes. The transmitted laser light intensity as a function of reaction time exhibited a pronounced minimum at incident shock temperatures above 1700 K. A reaction model is proposed that explains the experimental observations. It is postulated that SiC particles are nucleated homogeneously, along with Si particles. The latter are etched by the products of methane pyrolysis and the chemical species formed by the etching add to the growth of SiC particles.
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81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
68.35.Fx Diffusion; interface formation
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
64.60.Q- Nucleation

Implantation damage and anomalous diffusion of implanted boron in silicon

Qiang Guo, Ximao Bao, Jianming Hong, Yong Yan, and Duan Feng

Appl. Phys. Lett. 54, 1433 (1989); http://dx.doi.org/10.1063/1.101353 (3 pages) | Cited 5 times

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The anomalous diffusion of implanted boron in silicon damaged by self‐implantation has been investigated by cross‐section transmission electron microscopy and secondary‐ion mass spectroscopy. During rapid thermal annealing, bulges in the boron profile are observed at the edges of the defected band and the profile broadening is accompanied by the shrinking of the band. The decay time became unobvious due to the emission of point defects from the edges of the defected band. It is suggested that the anomalous diffusion of boron is related to the point defects produced by implantation and emitted from the defected band.
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61.80.Jh Ion radiation effects
61.72.Bb Theories and models of crystal defects
61.72.uf Ge and Si
66.30.J- Diffusion of impurities

Deep levels in n‐InP grown by molecular beam epitaxy

A. A. Iliadis, S. C. Laih, and E. A. Martin

Appl. Phys. Lett. 54, 1436 (1989); http://dx.doi.org/10.1063/1.100689 (3 pages) | Cited 10 times

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Deep level transient spectroscopy was used to study for the first time the deep traps in n‐InP grown by molecular beam epitaxy (MBE). Three electron traps B1, B2, and B3 were found to be present in the grown layers with activation energies of 0.43, 0.52, and 0.57 eV from the conduction‐band minimum. Based upon our photoluminescence and secondary‐ion mass spectroscopy data, trap B1 at 0.43 eV from the conduction band was linked to Fe atoms that probably form a phosphorus vacancy‐Fe impurity complex. Traps B2 and B3, observed in the low growth temperature sample, were tentatively attributed to native defects resulting from the low temperature of growth. It is concluded that the MBE growth of InP at the high‐temperature regime may improve the material quality.
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73.20.Hb Impurity and defect levels; energy states of adsorbed species
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Heteroepitaxy of GaAs on Si and Ge using alternating, low‐energy ion beams

T. E. Haynes, R. A. Zuhr, S. J. Pennycook, and B. R. Appleton

Appl. Phys. Lett. 54, 1439 (1989); http://dx.doi.org/10.1063/1.100690 (3 pages) | Cited 12 times

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Crystalline GaAs films have been grown epitaxially on silicon and germanium substrates at 400 °C by direct deposition of alternating 69Ga and 75As layers from electromagnetically switched low‐energy ion beams. Positive gallium and arsenic ions were extracted simultaneously from a single ion source and mass analyzed prior to deceleration to a controlled deposition energy of 30 or 40 eV. Atomic layers of gallium and arsenic were deposited alternately by switching the analyzing magnetic field repeatedly to select either the 69Ga+ or 75As+ species. The structure and composition of the resulting layers have been characterized by cross‐section transmission electron microscopy and ion channeling/backscattering spectrometry. The best crystal quality was obtained for a GaAs layer deposited on Ge using a 30 eV beam. This layer gave an ion channeling minimum yield of ≊6%. These results demonstrate the feasibility of growing isotopically pure, single‐crystal compound semiconductor layers at relatively low temperatures by deposition from alternating, fully ionized, low‐energy beams.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
68.55.Nq Composition and phase identification
68.55.-a Thin film structure and morphology

Assessment of oxygen in gallium arsenide by infrared local vibrational mode spectroscopy

J. Schneider, B. Dischler, H. Seelewind, P. M. Mooney, J. Lagowski, M. Matsui, D. R. Beard, and R. C. Newman

Appl. Phys. Lett. 54, 1442 (1989); http://dx.doi.org/10.1063/1.100691 (3 pages) | Cited 65 times

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Two infrared local vibrational mode (LVM) absorption lines occurring at 715 and 845 cm−1 shift to 679 and 802 cm−1 in gallium arsenide doped with 18O, proving that the lines arise from the vibrations of oxygen impurities. The 715 cm−1 line exhibits a triplet 69,71Ga isotope fine structure consistent with that expected from a quasi‐substitional VAs‐O center. The 845 cm−1 line appears as a closely spaced doublet expected for a bonded interstitial oxygen atom.
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63.20.Pw Localized modes
61.72.S- Impurities in crystals
78.30.-j Infrared and Raman spectra
78.40.Fy Semiconductors
71.55.Eq III-V semiconductors

Photosensitivity of the 714 and 730 cm−1 absorption bands in semi‐insulating GaAs: Evidence for a deep donor involving oxygen

H. Ch. Alt

Appl. Phys. Lett. 54, 1445 (1989); http://dx.doi.org/10.1063/1.100692 (3 pages) | Cited 39 times

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The optically induced metastable interconversion processes of the oxygen‐related vibrational modes at 730 and 714 cm−1, bands A and B, have been studied and compared with related properties of the EL2 defect. It is shown that the conversion from A to B is due to a charge exchange with the neutral EL2 level. The reverse process, recovery of band A, is observed after quenching of EL2. Conclusive evidence is presented that the two bands are associated with a donor in the upper half of the band gap. From Hall effect measurements, a trap energy of 0.43 eV below the conduction band is expected. A preliminary calibration of the absorption strength yields defect concentrations of ≊1015 cm−3 in some samples.
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71.55.Eq III-V semiconductors
72.40.+w Photoconduction and photovoltaic effects
78.30.-j Infrared and Raman spectra
78.40.Fy Semiconductors
61.72.sd Impurity concentration
61.72.sh Impurity distribution
61.72.sm Impurity gradients

Observation of ‘‘slow’’ states in conductance measurements on silicon metal‐oxide‐semiconductor capacitors

M. J. Uren, S. Collins, and M. J. Kirton

Appl. Phys. Lett. 54, 1448 (1989); http://dx.doi.org/10.1063/1.100693 (3 pages) | Cited 21 times

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We report the observation of a low‐frequency plateau in conductance measurements on silicon metal‐oxide‐semiconductor capacitors. The signal is consistent with the ‘‘slow’’ states observed by other techniques, in particular those states responsible for 1/f noise in silicon metal‐oxide‐semiconductor field‐effect transistors.
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73.20.Hb Impurity and defect levels; energy states of adsorbed species
72.70.+m Noise processes and phenomena
85.30.Tv Field effect devices
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Neutron‐treated, ultrafast, photoconductor detectors

C. L. Wang, M. D. Pocha, J. D. Morse, M. S. Singh, and B. A. Davis

Appl. Phys. Lett. 54, 1451 (1989); http://dx.doi.org/10.1063/1.100694 (3 pages) | Cited 4 times

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We have investigated homogeneous, photoconductive semiconductors as very fast radiation detectors. We irradiated GaAs, Cr‐doped GaAs, and Fe‐doped InP crystals with 14 MeV neutrons to produce lattice defects that act as fast recombination centers for electrons and holes. Using short‐pulse lasers and 17 MeV linear‐accelerator electrons and bremsstrahlung x rays, we measured the temporal response and sensitivity of these photoconductors as functions of fluence ranging from 1012 to 1016 neutrons/cm2. The carrier lifetime and mobility decrease monotonically as the neutron fluence increases, resulting in faster detector response at the expense of sensitivity. A resolving time of less than 30 ps (full width at half maximum) was measured for the above photoconductors irradiated with ∼1015 neutrons/cm2.
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29.40.Wk Solid-state detectors
61.80.Hg Neutron radiation effects
85.60.Gz Photodetectors (including infrared and CCD detectors)
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Determination of the local Al concentration in AlxGa1−xAs‐GaAs quantum well structures using the (200) diffraction intensity obtained with a 10 Å electron beam

H.‐J. Ou, S.‐C. Y. Tsen, K. T. Tsen, J. M. Cowley, J. I. Chyi, A. Salvador, and H. Morkoç

Appl. Phys. Lett. 54, 1454 (1989); http://dx.doi.org/10.1063/1.100695 (3 pages) | Cited 4 times

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A novel method for determining the local concentration of Al in the AlxGa1−xAs layer of AlxGa1−xAs‐GaAs multiple quantum well structures is reported. By scanning a 10 Å electron beam across the interface, the (200) dark‐field scanning transmission electron microscopy (STEM) image shows the contrast of the AlxGa1−xAs‐GaAs multilayer since the intensity of the (200) diffraction is sensitive to the Al concentration. The line scan intensity profile of the (200) diffraction, along a uniform specimen region of known thickness, shows the intensity variation of the (200) diffraction and reflects the local content of Al in each region. The simulation of the nanodiffraction patterns produces a chart of the (200) diffraction intensity versus the Al concentration for the determination of the local change of the Al concentration. A molecular beam epitaxy grown AlxGa1−xAs‐GaAs specimen (x=0.57 as determined from Raman spectroscopy) is tested and the dark‐field STEM studies show two thin layers of x=0.46 at the 1/3 and 2/3 height level within every AlxGa1−xAs layer.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
07.79.Cz Scanning tunneling microscopes
61.05.-a Techniques for structure determination
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.sd Impurity concentration
61.72.sh Impurity distribution
61.72.sm Impurity gradients
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