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28 Jun 1993

Volume 62, Issue 26, pp. 3393-3533

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Tristable operation of injection laser diodes coupled to absorbers of narrow spectral bandwidth

Yoshinobu Maeda

Appl. Phys. Lett. 62, 3393 (1993); http://dx.doi.org/10.1063/1.109027 (3 pages) | Cited 2 times

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Tristable longitudinal modes of a laser diode for an injection current were observed. Transmitting these laser lights through an Er‐doped yttrium aluminum garnet crystal, which has an absorption peak of narrow spectral bandwidth, results in changes in these wavelengths of the laser diode that could be converted into intensity changes and take tristable optical outputs for the same injection current value. It is suggested that an optical inverter and memory could be realized and a new type three‐valued logic would be constructed by making use of these phenomena.
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42.60.Fc Modulation, tuning, and mode locking
42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks

Dynamics of the 5 eV optical absorption in SiO2 glass

T. E. Tsai, J. M. Jewell, and J. S. Sanghera

Appl. Phys. Lett. 62, 3396 (1993); http://dx.doi.org/10.1063/1.109028 (3 pages) | Cited 1 time

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The optical absorption at 5 eV in SiO2 glass was observed, using laser calorimetry, to change reversibly depending on the intensity of UV light. The generation and bleaching of an absorption band at 5 eV by two‐ and one‐photon absorption processes, respectively, can explain these reversible changes. This observation supports the structural model of unrelaxed oxygen deficiency center for the 5 eV absorption band in silica.
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78.30.Hv Other nonmetallic inorganics
78.40.Ha Other nonmetallic inorganics
78.66.Jg Amorphous semiconductors; glasses
71.55.Ht Other nonmetals
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Low power (bistable) opto‐electrical threshold switches with high gain based on n‐i‐p‐i doping superlattices

A. Höfler, K. H. Gulden, P. Kiesel, M. Kneissl, B. Knüpfer, P. Riel, G. H. Döhler, G. Tränkle, and G. Weimann

Appl. Phys. Lett. 62, 3399 (1993); http://dx.doi.org/10.1063/1.109029 (3 pages) | Cited 8 times

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We report on the realization of an electro‐optical switch on n‐i‐p‐i doping superlattices for both bistable and step‐like threshold operation at very low input power levels (≂200 pW) and with high opto‐electrical gain (6.8×106). The configuration presented in this letter consists of a (two terminal) photodiode with negative current‐voltage characteristic and a novel three‐terminal photoconductive detector structure. The minimum optical switching power is determined by the reverse dark currents of the devices that are below pA. The switches are suitable for monolithical integration into arrays.
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42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
78.66.Fd III-V semiconductors

Fiber compatible fast acousto‐optic modulator using a gradient index lens as the interaction medium

I. Abdulhalim, C. N. Pannell, and D. N. Payne

Appl. Phys. Lett. 62, 3402 (1993); http://dx.doi.org/10.1063/1.109030 (3 pages) | Cited 3 times

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A novel fiber‐compatible acousto‐optic modulator is described in which the interaction between the optical and acoustic waves occurs in a graded‐index lens which can also function as an ‘‘expanded‐beam’’ fiber‐to‐fiber connector in the case of a half‐pitch device, or as a collimator in the case of a quarter‐pitch device. Initial results using a quarter‐pitch lens are diffraction efficiences of 3%, and diffraction loss of 7%, using 0.5 W power of 80 MHz rf under cw operation and under pulsed operation, using pulse widths down to 40 ns. A 14 ns switching time was measured.
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42.79.Jq Acousto-optical devices
42.79.Hp Optical processors, correlators, and modulators
42.79.Ry Gradient-index (GRIN) devices
42.81.-i Fiber optics

Excimer pumped deuterated L‐arginine phosphate optical parametric oscillator

Gordon Robertson and Malcolm H. Dunn

Appl. Phys. Lett. 62, 3405 (1993); http://dx.doi.org/10.1063/1.109031 (3 pages)

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The first optical parametric oscillator (OPO) using deuterated L‐arginine phosphate is reported herein. The OPO pumped at 308 nm by an XeCl excimer laser generates broadly tunable output over the spectral ranges 415 to 526 nm and 1194 to 743 nm, using a critically phase‐matched type I geometry. A study of the oscillation threshold has been made under conditions of different beam sizes and across the tuning range. A discussion of the damage problem in the material and the implications of 351 nm pumping are also given.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Microscopic studies of semiconductor lasers utilizing a combination of transmission electron microscopy, electroluminescence imaging, and focused ion beam sputtering

R. Hull, D. Bahnck, F. A. Stevie, L. A. Koszi, and S. N. G. Chu

Appl. Phys. Lett. 62, 3408 (1993); http://dx.doi.org/10.1063/1.109032 (3 pages) | Cited 15 times

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The microstructure of semiconductor laser diodes is studied using a combination of focused ion beam sputtering, electroluminescence imaging, and cross‐sectional transmission electron microscopy. Careful control of focused ion beam sputtering allows fabrication of high quality thin membranes for transmission electron microscope imaging, which can be located to submicron accuracy at a given position on the laser active stripe. By correlation with electroluminescence imaging, the membrane may then be positioned at an optically degraded region of the active stripe. In addition, imaging of the complete cross‐sectional laser structure, from substrate to surface contact layers is possible. The applications of these techniques to studies of laser degradation mechanisms are demonstrated and discussed.
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68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)
42.55.Px Semiconductor lasers; laser diodes

Depth profiling of proton exchanged LiNbO3 waveguides by micro‐Raman spectroscopy

Gustavo R. Paz‐Pujalt and David D. Tuschel

Appl. Phys. Lett. 62, 3411 (1993); http://dx.doi.org/10.1063/1.109033 (3 pages) | Cited 9 times

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Z‐cut LiNbO3 wafers were proton exchanged (PE) with pyrophosphoric acid. The polished edges provided a side view of the exchanged region. The region was probed by micro‐Raman spectroscopy by stepping a 488.0 nm laser at intervals as small as 0.2 μm across the edge face starting below the exchanged region and moving towards the wafer surface, thereby traversing the PE region. Profiling revealed significant changes, in the 125–800 cm−1 and 3200–3600 cm−1 frequency ranges. The PE region expanded after annealing at 300 °C indicating proton penetration into the wafer. Continued annealing resulted in the progressive recovery of spectral characteristics resembling unexchanged lithium niobate. Micro‐Raman profiles provide spectroscopic information regarding which vibrational modes are affected by the exchange and the annealing processes as a function of depth.
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66.30.J- Diffusion of impurities
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.30.Hv Other nonmetallic inorganics

Alkaline metal dopants and photodarkening in colored filter glass

T. Yanagawa, H. Nakano, Y. Ishida, and K. Kubodera

Appl. Phys. Lett. 62, 3414 (1993); http://dx.doi.org/10.1063/1.109034 (3 pages) | Cited 2 times

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It is clearly shown for the first time that alkaline metal ions assist the photodarkening effect in colored filter glass. Time responses of samples vary depending on the kind of alkaline metal dopants involved as additive compounds for improving glass quality. Energy relaxation times of photoexcited carriers after laser beam irradiation change following weight quotients of potassium oxides from sodium oxides. The fastest response after irradiation can be obtained when the quotient is approximately two. This quotient corresponds to compositions showing conspicuous mixed‐alkali effects from potassium and sodium.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.70.Ce Glasses, quartz
78.30.Hv Other nonmetallic inorganics
78.40.Ha Other nonmetallic inorganics

AlGaAs/GaAs buried quantum well laser diodes by one time selective metalorganic chemical vapor deposition growth on dielectric window stripes

M. Ogura, Z. Y. Chen, H. Kaneko, S. Fujii, H. Itoh, M. Mori, M. Watanabe, S. Mukai, and H. Yajima

Appl. Phys. Lett. 62, 3417 (1993); http://dx.doi.org/10.1063/1.109621 (3 pages) | Cited 2 times

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AlGaAs graded‐index separate‐confinement heterostructure lasers with lateral mode confinement are realized by one time metalorganic chemical vapor deposition with silicon dioxide stripes as selective masks and current blocking layers. The effect of the active region width on lasing characteristics is investigated. The threshold current and external quantum efficiency are around 12 mA and 70%, respectively, for narrow lasers. Elevated waveguide structure formed by the growth‐rate difference between (100) and sidewall planes was effective for stable lateral mode characteristics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.-v Laser optical systems: design and operation
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Wideband electronically tunable integrated magneto‐optic frequency shifter at X band

Y. Pu and C. S. Tsai

Appl. Phys. Lett. 62, 3420 (1993); http://dx.doi.org/10.1063/1.109035 (3 pages) | Cited 9 times

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A new wideband integrated optical frequency shifter that utilizes noncollinear guided‐wave magneto‐optic (MO) Bragg diffraction from magnetostatic‐forward‐volume waves (MSFVW) in a bismuth‐doped yttrium‐iron‐garnet/gadolinium‐gallium‐garnet (YIG/GGG) waveguide, 6×10 mm2 in size, is reported. Constancy in the output angle of the frequency‐shifted light beam, irrespective of the amount of frequency shift, is facilitated by synchronous tuning of the carrier frequency of the MSFVW and the bias magnetic field using an electronic synchronizer. The device operating at the optical wavelength of 1.302 μm and the carrier frequency centered at X band has demonstrated desirable characteristics including large frequency shift, very large tunable bandwidth, large dynamic range, and fast tuning speed. Specifically, bandwidths of 1.61 and 2.35 GHz and dynamic ranges of 35 and 32 dB at the center carrier frequencies of 6.035 and 11.025 GHz, respectively, and a tuning speed of 50 μs have been accomplished.
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42.79.Nv Optical frequency converters
42.82.Bq Design and performance testing of integrated-optical systems

Two‐photon pumped upconverted lasing in dye doped polymer waveguides

Anadi Mukherjee

Appl. Phys. Lett. 62, 3423 (1993); http://dx.doi.org/10.1063/1.109036 (3 pages) | Cited 63 times

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The first measurements of two‐photon pumped upconverted lasing in a waveguide is reported. Nonlinear dependence of the upconversion signal on the square of the input pump intensity and associated spectral narrowing was experimentally observed in dye‐doped polymer waveguides. The pump wavelength was 736 nm and the center of the lasing spectrum was 570 nm. The spectra shows excitonlike features at 630 and 654 nm not seen in the absorption spectrum.
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42.55.Mv Dye lasers
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Effect of disorder on the optical properties of short period superlattices

J. A. Strozier, Y. A. Zhang, C. Horton, A. Ignatiev, and H. D. Shih

Appl. Phys. Lett. 62, 3426 (1993); http://dx.doi.org/10.1063/1.109037 (3 pages) | Cited 6 times

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The optical properties of disordered short period superlattices are studied using a one‐dimensional tight‐binding model. A difference vector and disorder structure factor are proposed to characterize the disordered superlattice. The density of states, participation number, and optical absorption coefficients for both ordered and disordered superlattices are calculated as a function of energy. The results show that introduction of disorder into an indirect band gap material enhances the optical transition near the indirect band edge.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.66.Fd III-V semiconductors

Electrical characteristics of plasma loaded, radio frequency driven, capacitively coupled electrodes

John Forster

Appl. Phys. Lett. 62, 3429 (1993); http://dx.doi.org/10.1063/1.109038 (3 pages) | Cited 5 times

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A simple, nonlinear circuit model of a plasma sheath was used to study impedance and harmonic generation at a radio frequency (rf) driven electrode immersed in a plasma. The impedance can be estimated from linear expressions of the conduction and displacement currents; i.e., nonlinear effects on impedance are small. Harmonic generation occurs from nonlinearities in the sheath. The harmonic level at the electrode is influenced both by the plasma parameters and the electrical circuitry attached to the electrode. Thus any use of the harmonic levels for a plasma diagnostic must take into account the stray and actual components attached to the electrode.  
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52.80.Pi High-frequency and RF discharges
52.70.Gw Radio-frequency and microwave measurements

Synthesis of diamond from methane and nitrogen mixture

Andrzej Badzian, Teresa Badzian, and S.‐Tong Lee

Appl. Phys. Lett. 62, 3432 (1993); http://dx.doi.org/10.1063/1.109039 (3 pages) | Cited 68 times

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We have found that diamond can be synthesized from a mixture of CH4 and N2 without adding any H2. This new synthesis is sharply different from the common practice of diamond growth by chemical vapor deposition, which uses a hydrogen‐rich mixture of CH4 and H2. In this new approach, nitrogen becomes an active component of microwave plasma leading to diamond growth. Nitrogen participates in abstraction of hydrogen from the diamond surface. We hypothesize that formation of HCN is an indication of hydrogen abstraction that allows diamond to grow from CH4+N2 mixtures. As a consequence of surface processes, the crystal structure of the grown diamond is distorted. The sequence of tetrahedral layers is mixed (cubic and hexagonal) and it suffers from turbostatic disorder. Diamond films were characterized by x‐ray diffraction, Auger electron spectroscopy, x‐ray photoelectron spectroscopy, and Raman spectroscopy.  
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Formation of a C49 TiGe2 phase during annealing a coevaporated Ti0.33Ge0.67 alloy

Q. Z. Hong, K. Barmak, and F. M. d’Heurle

Appl. Phys. Lett. 62, 3435 (1993); http://dx.doi.org/10.1063/1.109040 (3 pages) | Cited 6 times

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The coevaporated, amorphous Ti0.33Ge0.67 alloy crystallizes at 315 °C into a metastable C49 structure, which transforms to the equilibrium C54 structure at higher temperatures around 535 °C. This result differs from that obtained from binary reactions between Ti and Ge where the C49 phase is not observed. The electron diffraction pattern for the C49 phase exhibits extra spots as predicted by Bourret et al. for a large period polytype [A. Bourret, F. M. d’Heurle, F. K. LeGoues, and A. Charai, J. Appl. Phys. 67, 241 (1990)]. Additional evidence for the formation of the C49 TiGe2 is found by annealing a Ti0.33Ge0.67/Ti0.33Si0.67 bilayer. The bilayer crystallizes into a solid solution of C49 TiGe2‐TiSi2 before transforming to a C54 solid solution at lower temperatures than pure C49 TiSi2.
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81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder

Epitaxial diamond thin films on (001) silicon substrates

X. Jiang, C.‐P. Klages, R. Zachai, M. Hartweg, and H.‐J. Füsser

Appl. Phys. Lett. 62, 3438 (1993); http://dx.doi.org/10.1063/1.109041 (3 pages) | Cited 219 times

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Epitaxial (001) diamond film were grown on mirror‐polished single‐crystalline (001) silicon substrates by microwave plasma chemical vapor deposition from a methane/hydrogen gas mixture. The films were characterized by means of scanning electron microscopy, Raman spectroscopy, and x‐ray analysis. The results show that the diamond crystallites are oriented to the silicon substrate with both the (001) planes and the [110] directions parallel to the silicon substrate.
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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.)

Symmetric switching in strong anchoring surfaces of large‐core‐angle ferroelectric liquid crystal

S. S. Bawa, A. M. Biradar, and Subhas Chandra

Appl. Phys. Lett. 62, 3441 (1993); http://dx.doi.org/10.1063/1.109042 (3 pages) | Cited 4 times

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The polymer rubbed, polar surface anchoring effect in a thin homogeneously aligned sample of large‐core (high‐tilt)‐angle ferroelectric liquid crystal which undergoes an isotropic‐chiral nematic‐smectic C∗ phase transition is reported herein. It has been found that symmetric switching characteristics can be obtained by applying an appropriate bias field to the samples even though the difference between the polar anchoring energy on two surfaces is quite large. The temperature dependence of the anchoring strength is also studied in the smectic C∗ phase.
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61.30.-v Liquid crystals

Transmission electron microscopy study of diamond nucleation on 6H‐SiC single crystal with possibility of epitaxy

Li Chang, Tzer‐Shen Lin, Jiun‐Long Chen, and Fu‐Rong Chen

Appl. Phys. Lett. 62, 3444 (1993); http://dx.doi.org/10.1063/1.109043 (3 pages)

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Diamond has been grown on 6H‐SiC single crystal wafers by microwave plasma assisted chemical vapor deposition with a negative bias pretreatment. A high nucleation density of diamond on the substrate has been achieved. Cross‐sectional transmission electron microscopy was employed to study the interfacial microstructure of diamond on 6H‐SiC. Lattice image observations illustrate that diamond is directly formed on the 6H‐SiC substrate. The possibility of local epitaxial nucleation of diamond on the 6H‐SiC substrate and its crystallography are briefly discussed.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology

Synthesis of CeC2 crystals encapsulated within gigantic super fullerenes

Yositaka Yosida

Appl. Phys. Lett. 62, 3447 (1993); http://dx.doi.org/10.1063/1.109044 (2 pages) | Cited 19 times

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A new synthesis of nanometer‐sized crystals encapsulated within gigantic super fullerenes by dc arc evaporation of composite carbon rods containing ∼3 wt % CeO2 is reported. Transmission electron microscopy showed the crystals CeC2 with the CaC2 type structure.  
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61.46.-w Structure of nanoscale materials
81.20.-n Methods of materials synthesis and materials processing

Optical monitoring of nucleation and growth of diamond films

A. A. Smolin, V. G. Ralchenko, S. M. Pimenov, T. V. Kononenko, and E. N. Loubnin

Appl. Phys. Lett. 62, 3449 (1993); http://dx.doi.org/10.1063/1.109045 (3 pages) | Cited 17 times

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Early stages of diamond film deposition on molybdenum substrates using dc arc discharge in CH4/H2 gas mixtures were studied by in situ measurements of optical reflectivity of growing film. Ultrafine diamond grit of ≊200 Å size was used for seeding to increase nucleation density up to 2×109 cm−2 and to produce smooth thin films. Evolution of He‐Ne laser beam reflection at 0.63 μm wavelength is described in terms of Mie scattering by nonabsorbing dielectric spheres in the case of nucleated film and of light interference in the system of continuous diamond film on a metal substrate. During the deposition process the growth rate passes through a minimum at the moment when a minimum roughness is supposed to be achieved.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Growth of InGaAs/GaAs quantum wells with perfectly abrupt interfaces by molecular beam epitaxy

Jean‐Michel Gerard and Guy Le Roux

Appl. Phys. Lett. 62, 3452 (1993); http://dx.doi.org/10.1063/1.109046 (3 pages) | Cited 11 times

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The abruptness of InxGa1−xAs‐on‐GaAs as well as GaAs‐on‐InxGa1−xAs interfaces grown by molecular beam epitaxy is usually intrinsically limited by the surface segregation of indium atoms. The deposition of a one‐monolayer‐thick indium‐rich prelayer of InGaAs (or of a submonolayer amount of InAs) prior to growth of InxGa1−xAs allows, however, the formation of a perfectly abrupt InxGa1−xAs‐on‐GaAs interface, as shown (for x=0.06 and x=0.11) by a detailed study of the surface composition at various stages of the growth of this heterostructure. A thermal annealing can also be performed at the GaAs‐on‐InGaAs interface so as to desorb surface indium atoms and suppress In incorporation in the GaAs overlayer. Both techniques preserve the optical quality of InxGa1−xAs/GaAs quantum wells.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.-a Thin film structure and morphology

Enhancement of Si hole mobility in coupled delta‐doped wells

T. K. Carns, X. Zheng, and K. L. Wang

Appl. Phys. Lett. 62, 3455 (1993); http://dx.doi.org/10.1063/1.109047 (3 pages) | Cited 8 times

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When two or more highly doped, thin (delta‐doped) layers are placed in close proximity to one another it is found that an enhancement of the hole mobility occurs over that of a single delta (δ) layer as well as that of the Si bulk case. Hall mobilities of up to 2400 cm2 V−1 s−1 at 77 K have been obtained with δ layers spaced 200 Å apart compared to a mobility of 280 cm2 V−1 s−1 for the single delta layer. The conductivity of the coupled δ‐doped well exceeds that of comparable uniformly doped bulk layers, especially at lower temperatures. These types of structures show great promise in obtaining high mobilities with high carrier densities for semiconductors grown by simple homoepitaxy.
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73.50.Dn Low-field transport and mobility; piezoresistance
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Polarized electroluminescence spectra of GaxIn1−xP/(Al0.6Ga0.4)0.5In0.5P quantum wells

D. P. Bour, T. L. Paoli, R. L. Thornton, D. W. Treat, Y. S. Park, and P. S. Zory

Appl. Phys. Lett. 62, 3458 (1993); http://dx.doi.org/10.1063/1.109048 (3 pages) | Cited 3 times

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Electroluminescence spectra of 80 Å GaxIn1−xP/(Al0.6Ga0.4)0.5In0.5P quantum wells (QWs), with x=0.3, 0.4, 0.5, and 0.6, are examined. The polarization is anisotropic, and the light‐hole (lh) and heavy‐hole (hh) transitions are resolved at current densities between 1 A/cm2 and threshold. In the compressively strained (x=0.3, 0.4) QWs, the hh is ground state and transverse electric‐mode emission dominates. The lh and hh band edges are reversed for the tensile‐strained QW, however, and the emission is predominantly transverse magnetic. Near threshold, the bandfilling effect is most pronounced in the compressively strained QWs, suggesting a reduced in‐plane hh effective mass. For the most highly compressed QW (x=0.3, λ=707 nm), the threshold current density is 190 A/cm2.
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78.66.Fd III-V semiconductors
78.60.Fi Electroluminescence
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Effects of mixing germane in silane gas‐source molecular beam epitaxy

Ki‐Joon Kim, Maki Suemitsu, Masayoshi Yamanaka, and Nobuo Miyamoto

Appl. Phys. Lett. 62, 3461 (1993); http://dx.doi.org/10.1063/1.109049 (3 pages) | Cited 19 times

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Growth of SiGe gas‐source molecular beam epitaxy (GSMBE) using silane/germane mixture has been investigated for the germane content of 0%, 0.8%, and 2.6%. From detailed measurements on the growth rate, a separation into high‐ and low‐temperature regions of the growth rate, as in silane‐GSMBE system, has been found to exist in this silane/germane system. A simultaneous measurement on the surface hydrogen coverage has revealed that the growth in the low‐temperature region is rate limited by the surface hydrogen desorption process, reasoning the enhanced growth rate with germane in terms of the reduced coverage of the surface hydrogen. All the growth rates followed a same fourth power dependence on the free‐adsorption site, which suggests a validity of the four‐site adsorption model, established for silane‐GSMBE, in silane/germane GSMBE.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Strain relaxation and mosaic structure in relaxed SiGe layers

P. M. Mooney, F. K. LeGoues, J. O. Chu, and S. F. Nelson

Appl. Phys. Lett. 62, 3464 (1993); http://dx.doi.org/10.1063/1.109021 (3 pages) | Cited 35 times

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We report high‐resolution x‐ray diffraction measurements of relaxed Si0.7Ge0.3 layers on (001) Si substrates. Strain was relieved either by a glide‐limited mechanism in structures where the composition was changed abruptly or by a nucleation‐limited mechanism in structures having a compositionally graded intermediate layer. We find that the broadening of the x‐ray peak of the surface alloy layer is similar in both cases, although the threading dislocation densities ranged from 1011 cm−2 to 5×106 cm−2. The effect of the threading dislocations on the x‐ray peak widths is masked by the mosaic structure caused by the network of misfit dislocations underneath the layer.
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68.55.-a Thin film structure and morphology
61.05.cf X-ray scattering (including small-angle scattering)
61.05.cj X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc.
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
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