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30 May 1994

Volume 64, Issue 22, pp. 2913-3050

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Externally deposited phase‐compensating dielectric mirrors for asymmetric Fabry–Perot cavity tuning

Z. Karim, C. Kyriakakis, A. R. Tanguay, K. Hu, L. Chen, and A. Madhukar

Appl. Phys. Lett. 64, 2913 (1994); http://dx.doi.org/10.1063/1.111409 (3 pages) | Cited 4 times

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The wavelength dispersion of the phase shift on reflection that is inherent in dielectric Bragg mirrors can be used to phase compensate resonant‐cavity‐based devices such as multiple quantum well asymmetric Fabry–Perot spatial light modulators and vertical cavity surface‐emitting lasers. We demonstrate the post‐growth ability to accurately fine‐tune the location of the Fabry–Perot minima in a resonant cavity by employing either a normal or inverted dielectric mirror configuration. The dielectric multilayer mirrors are composed of alternating quarter‐wave layers of MgF2 and Sb2S3, and exhibit broadband reflectivities.
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42.79.Hp Optical processors, correlators, and modulators
42.79.Fm Reflectors, beam splitters, and deflectors
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
78.66.Li Other semiconductors

High brightness slab waveguide carbon monoxide laser

A. D. Colley, F. Villarreal, H. J. Baker, and D. R. Hall

Appl. Phys. Lett. 64, 2916 (1994); http://dx.doi.org/10.1063/1.111410 (3 pages) | Cited 7 times

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Near diffraction limited output from a slab waveguide carbon monoxide gain medium using a hybrid confocal unstable resonator is described. A device producing a cw output of 80 W in a beam with M2=1.5 has been demonstrated operating with 12% efficiency at −30 °C.
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42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Harmonic generation in ferroelectric liquid crystals: Phase matching loci

Kenneth E. Arnett, Stephan P. Velsko, and David M. Walba

Appl. Phys. Lett. 64, 2919 (1994); http://dx.doi.org/10.1063/1.111411 (3 pages) | Cited 2 times

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Ferroelectric liquid crystals (FLCs), a new class of organic nonlinear materials have a variety of interesting properties and potential applications. Using commercial FLCs and an FLC mixture specifically formulated for enhanced nonlinear optical properties, we studied the room‐temperature global phase‐matching properties for type I and type II frequency doubling of 1.06‐μm radiation. Although the second‐harmonic coefficients of the different FLC mixtures differ by as much as two orders of magnitude, the phase‐matching loci are remarkably similar.
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61.30.-v Liquid crystals
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Switching energy limitation in all‐optical switching due to group velocity dispersion of highly nonlinear optical waveguides

Masaki Asobe, Kazunori Naganuma, Toshikuni Kaino, Terutoshi Kanamori, Satoru Tomaru, and Takashi Kurihara

Appl. Phys. Lett. 64, 2922 (1994); http://dx.doi.org/10.1063/1.111412 (3 pages) | Cited 7 times

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We discuss the limitations of all‐optical switching due to group velocity dispersion (GVD) in highly nonlinear optical waveguides. The lower limit of switching energy is primarily determined by a figure of merit which is the ratio of the nonlinear refractive index to the GVD. GVD values of several kinds of highly nonlinear optical materials are measured, the figure of merit for each material is estimated, and appropriate operational conditions for each material are discussed.
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42.79.Gn Optical waveguides and couplers
42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.55.Px Semiconductor lasers; laser diodes
78.66.Fd III-V semiconductors

Observation of optical response of avalanche photodiodes at photon‐counting light levels

J. H. Hunt and R. B. Holmes

Appl. Phys. Lett. 64, 2925 (1994); http://dx.doi.org/10.1063/1.111413 (3 pages) | Cited 1 time

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We have demonstrated all‐optical spatial light modulation at photon‐counting light levels. Modulation is performed with a silicon avalanche photodiode operating as a Fizeau interferometer with optical thickness modulated by optically initiated, avalanche‐induced heating. Modulation of 32% is achieved with off‐the‐shelf devices with writing beams using as few as 10 photons per pulse. The results represent the first spatially and temporally resolved measurements of avalanche breakdown.
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85.60.-q Optoelectronic devices
42.30.-d Imaging and optical processing

Photoluminescence of zinc‐blende GaN under hydrostatic pressure

S. J. Hwang, W. Shan, R. J. Hauenstein, J. J. Song, M.‐E. Lin, S. Strite, B. N. Sverdlov, and H. Morkoç

Appl. Phys. Lett. 64, 2928 (1994); http://dx.doi.org/10.1063/1.111414 (3 pages) | Cited 18 times

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Photoluminescence spectra of cubic GaN grown on a GaAs substrate by molecular beam epitaxy have been studied as a function of hydrostatic pressure at 10 K. The spectra are abundant in emission structures arising from a variety of radiative recombination processes, such as free‐electron–bound‐hole and donor‐acceptor pair transitions. These emission peaks shift to higher energy with increasing pressure, providing a measure of the pressure coefficient of the band gap of cubic GaN. In addition, a spectral feature, which is superimposed on the other emission peaks and not observable at atmospheric pressure, becomes gradually resolvable as pressure increases. The difference of pressure dependence of this emission from the others suggests that it is associated with a deep center.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
71.55.Eq III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

1‐to‐42 optoelectronic interconnection for intra‐multichip‐module clock signal distribution

Suning Tang and Ray T. Chen

Appl. Phys. Lett. 64, 2931 (1994); http://dx.doi.org/10.1063/1.111415 (3 pages) | Cited 9 times

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In this paper, we present a miniaturized compact three‐dimensional optical fan‐out interconnect suitable for wafer scale very large scale integrated multichip‐module optical clock signal distribution. The demonstrated device employs a thin light‐guiding substrate in conjunction with a two‐dimensional (2D) optical hologram array. The parallel feature among fan‐out beams and the planar compact structure convert the unsolvable three spatial and three angular multiple alignment problem into a single‐step 2D planar one, which greatly enhances the packaging reliability. A new design scheme for reducing throughput power nonuniformity is presented for the first time. A 25 GHz 1‐to‐42 highly parallel fan‐out interconnect was demonstrated with a signal to noise ratio of 10 dB.  
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85.40.Hp Lithography, masks and pattern transfer
85.60.-q Optoelectronic devices

Wave propagation in periodic nonlinear dielectric superlattices

D. Hennig, H. Gabriel, G. P. Tsironis, and M. Molina

Appl. Phys. Lett. 64, 2934 (1994); http://dx.doi.org/10.1063/1.111416 (3 pages) | Cited 16 times

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We investigate wave propagation in a superlattice consistent of dielectric material with a nonlinear Kerr coefficient. We find gaps in the propagating properties of the medium that depend critically on the injected wave power. This property can be used for transmission of information.
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77.55.-g Dielectric thin films
78.66.-w Optical properties of specific thin films
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials

Modal analysis of a Talbot cavity

James R. Leger, Greg Mowry, and Diana Chen

Appl. Phys. Lett. 64, 2937 (1994); http://dx.doi.org/10.1063/1.111417 (3 pages) | Cited 7 times

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Modal analyses of Talbot cavity eigenmodes are performed for a finite diode laser array using a simple finite external mirror and a patterned external mirror. At a full round‐trip Talbot length, the in‐phase and oscillating‐phase modes of the cavity with a simple flat mirror have slightly different thresholds. The increased modal separation from a patterned‐mirror Talbot resonator is shown to be larger than a flat‐mirror resonator with a round‐trip distance of half a Talbot length. In all these cases, steady‐state oscillation is shown to consist of either the in‐phase or oscillating‐phase mode. The inherent flaw of the Talbot resonator suggested by P. Latimer [Appl. Phys. Lett. 62, 217 (1993)] is thus shown to be a simple matter of modal separation rather than a ‘‘violation of the widespread assumption of grating self‐imaging.’’
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42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Fc Modulation, tuning, and mode locking
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Sensitivity analysis for Love mode acoustic gravimetric sensors

Z. Wang, J. D. N. Cheeke, and C. K. Jen

Appl. Phys. Lett. 64, 2940 (1994); http://dx.doi.org/10.1063/1.111976 (3 pages) | Cited 21 times

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An approximate mass sensitivity formula for Love mode sensors is presented. The optimal thickness of the guiding layer, at which the sensitivity, Sfm is maximum for a given frequency or wavelength is obtained. The (Sfm)max can be expressed as −k0/ρ1λ1, where ρ1 is the density, λ1 is the wavelength of the surface transverse wave of the substrate, and k0 is a coefficient determined by the ratio of shear wave velocity and the ratio of density of the substrate to those of the overlayer. The (Sfm)max of the Love mode device can be 20 times higher than that of the shear horizontal SH–surface acoustic wave device fabricated on the same substrate and operating at the same frequency.
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43.20.Mv Waveguides, wave propagation in tubes and ducts
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Laser elemental mass analysis at large distances

Russell J. De Young and Wen Situ

Appl. Phys. Lett. 64, 2943 (1994); http://dx.doi.org/10.1063/1.111418 (3 pages) | Cited 3 times

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A Nd:YAG laser is used to produce a plasma on targets of Al, Cu, Ge, Ag, and a lunar simulant. Ion energies for 1×109 W/cm2 were found to be between 550 and 900 eV. Some of these ions travel down a 11.1‐m evacuated tube to an ion trap 1‐m time‐of‐flight spectrometer producing a mass spectrum of a lunar simulant, demonstrating the ability to analyze targets at significant remote distances.
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82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
79.20.Ds Laser-beam impact phenomena

Bulk‐induced alignment of nematic liquid crystals by photopolymerization

Sukhmal C. Jain and Heinz‐S. Kitzerow

Appl. Phys. Lett. 64, 2946 (1994); http://dx.doi.org/10.1063/1.111419 (3 pages) | Cited 21 times

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A novel technique to produce uniform alignment of nematic liquid crystals is presented. The technique is based on producing an anisotropic polymer network in the bulk nematic liquid crystal by polymerizing a photoresist material. Both uniform planar alignment and homeotropic alignment can be obtained depending on the curing conditions. In the case of planar alignment, the nematic director orientation is governed by the direction of the polarization vector of the linearly polarized ultraviolet light, thus making it possible to produce a defined azimuthal orientation of the nematic director. This technique obviates the need to give any previous treatment to the bounding substrates and as such should be independent of the nature of the substrate.
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61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
78.20.Jq Electro-optical effects

Smoothing effect of GaAs/AlxGa1−xAs superlattices grown by metalorganic vapor phase epitaxy

Xian’gang Xu, Baibiao Huang, Hongwen Ren, and Minhua Jiang

Appl. Phys. Lett. 64, 2949 (1994); http://dx.doi.org/10.1063/1.111422 (3 pages) | Cited 1 time

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GaAs/AlxGa1−xAs (x=0.5, 0.6, 1.0) superlattices used as buffer layers in high electron mobility transistors and photomultiplier devices can smooth out interface roughness. The mechanism of the smoothing effect has been discussed in detail. The initial stage of nucleation on the substrates has been clearly verified by examining the undulations of a 30 nm GaAs layer sandwiched between the substrate and the superlattice.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.-a Thin film structure and morphology
68.35.Fx Diffusion; interface formation

Activation energy for Ostwald ripening of Al2Cu in Al(4 wt. % Cu) thin films using a lateral diffusion couple

E. G. Colgan

Appl. Phys. Lett. 64, 2952 (1994); http://dx.doi.org/10.1063/1.111423 (3 pages) | Cited 1 time

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The activation energy Ea for Ostwald ripening (coarsening) of Al2Cu(Θ phase) precipitates in Al(4 wt. % Cu) thin films was determined using a lateral diffusion couple. A 1 μm thick Al(4 wt. % Cu) blanket film was deposited on lines of Al2Cu embedded in SiO2. With annealing at temperatures between 400 and 450 °C (1.4–2.5 wt. % Cu in solution) for 1 to 80 h, Θ precipitates were dissolved in regions between 10 and 110 μm wide parallel to the Al2Cu lines. The width of this region increased as the square root of the annealing time. The Ea was determined to be 2.5±0.5 eV from an Arrhenius plot. This value is much larger than both the activation energies for Cu lattice and grain‐boundary diffusion in Al. Understanding the coarsening kinetics of Al2Cu is important since the reliability of Al(Cu) metallizations is strongly dependent on the microstructure.
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81.40.Cd Solid solution hardening, precipitation hardening, and dispersion hardening; aging
66.30.Fq Self-diffusion in metals, semimetals, and alloys

Origin and suppression of misfit dislocations in heavily boron‐doped (100) silicon wafers

Ho‐Jun Lee, Young‐Jin Jeon, Chul‐Hi Han, and Choong‐Ki Kim

Appl. Phys. Lett. 64, 2955 (1994); http://dx.doi.org/10.1063/1.111424 (3 pages) | Cited 5 times

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It has been found that misfit dislocations in heavily boron‐doped layers originate from wafer edges. Moreover, the propagation of the misfit dislocation into a region can be suppressed by placing a surrounding undoped region formed by a chemical‐vapor deposited (CVD) oxide ring pattern before boron doping. A heavily boron‐doped layer with no misfit dislocations can be obtained by using a CVD oxide ring up to a boron dose of 5.4×1016 cm2 for an area of 2 cm×2 cm and up to a dose of 1.48×1017 cm2 for an area of 400 μm×400 μm.  
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.35.Fx Diffusion; interface formation
68.35.Dv Composition, segregation; defects and impurities
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Mixing of Fe2O3 markers into amorphous and crystalline alumina

Elizabeth A. Cooper and Michael Nastasi

Appl. Phys. Lett. 64, 2958 (1994); http://dx.doi.org/10.1063/1.111425 (3 pages) | Cited 5 times

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Thin markers of iron oxide embedded between sapphire and amorphous alumina were ion irradiated with Ar in a temperature range of −166 °C to 700 °C. The marker mixing was examined by Rutherford backscattering spectroscopy and found to have both a ballistic and a temperature dependent mixing regime with different levels of ballistic mixing and different temperature dependencies for the amorphous and crystalline matrices.
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64.75.-g Phase equilibria
81.40.-z Treatment of materials and its effects on microstructure, nanostructure, and properties
61.80.Jh Ion radiation effects
68.35.Fx Diffusion; interface formation

Chemical effect of ternary additions on amorphization in Fe‐C systems by mechanical alloying

K. Omuro and H. Miura

Appl. Phys. Lett. 64, 2961 (1994); http://dx.doi.org/10.1063/1.111394 (3 pages) | Cited 5 times

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Mechanical alloying (MA) of elemental powder mixtures of Fe83C17 and Fe58A25C17 (at. %) (A=Cr, Mo, Mn, or Ni) is performed using a planetary ball mill. In the MA processing, the ternary additions Cr, Mo, and Mn lead to the amorphization of MA products. Due to their higher affinity for C and solubility in Fe, they markedly promote the dissolution of C in the Fe‐rich phase under stronger interaction between atoms A and C, in contrast to the addition Ni with lower affinity for C. Also, such additions, Cr, Mo, and Mn, dissolved in the Fe phase together with C suppress the diffusion of C over large distance in MA products and retard recovery processes, like nucleation of competing more stable carbides.
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81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
66.30.Ny Chemical interdiffusion; diffusion barriers

Molecular beam epitaxy of CdF2 layers on CaF2(111) and Si(111)

N. S. Sokolov, S. V. Gastev, S. V. Novikov, N. L. Yakovlev, A. Izumi, and S. Furukawa

Appl. Phys. Lett. 64, 2964 (1994); http://dx.doi.org/10.1063/1.111395 (3 pages) | Cited 2 times

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Cadmium fluoride single crystal layers have been grown on CaF2/Si(111) or Si(111) substrates by molecular beam epitaxy. The structures are expected to have attractive electronic properties. The growth was monitored by reflections high energy electron diffraction (RHEED) techniques. A distinct (√3×√3) R30° superstructure has been observed on the CdF2(111) surface at growth temperatures below 150 °C. RHEED intensity oscillations indicate a two‐dimensional growth mode of CdF2.
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61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)
68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

High dielectric constant (Ba,Sr)TiO3 thin films prepared on RuO2/sapphire

Koichi Takemura, Toshiyuki Sakuma, and Yoichi Miyasaka

Appl. Phys. Lett. 64, 2967 (1994); http://dx.doi.org/10.1063/1.111396 (3 pages) | Cited 74 times

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RuO2 thin films have been prepared onto sapphire by reactive sputtering with Ar+O2 plasma and their application as the bottom electrode in the high dielectric constant (Ba0.5Sr0.5)TiO3 (BST) thin film capacitor has been studied. RuO2 films with rutile structure are obtained with O2 content greater than 0.7. The dielectric constants of the sputtered (Ba0.5Sr0.5)TiO3 films on the RuO2 films are 250 for 49‐nm‐thick film and 460 for 130‐nm‐thick film. These values are comparable with those on Pt and Pd, which are commonly used as the bottom electrodes. No remarkable interdiffusion at the BST/RuO2 interface region and no hillocks at the RuO2 surface were observed, even after BST film deposition at 620 °C. RuO2 is one of the promising materials for use as the bottom electrode for the (Ba0.5Sr0.5)TiO3 thin film capacitor.
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77.55.-g Dielectric thin films
77.22.Ch Permittivity (dielectric function)
73.61.Ng Insulators

Surface roughening transition and critical layer thickness in strained‐layer heteroepitaxy of EuTe on PbTe (111)

G. Springholz, N. Frank, and G. Bauer

Appl. Phys. Lett. 64, 2970 (1994); http://dx.doi.org/10.1063/1.111374 (3 pages) | Cited 11 times

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Heteroepitaxial growth of 2% lattice‐mismatched EuTe on PbTe (111) by molecular beam epitaxy is investigated in the two‐dimensional layer‐by‐layer growth regime combining in situ reflection high‐energy electron diffraction and scanning tunneling microscopy (STM). At the critical layer thickness a distinct surface roughening is observed. The quantitative analysis of STM images yields an increase of the root mean square roughness by a factor of 4 at this roughening transition. Strong evidence is presented that for the used growth conditions this roughening is not caused by strain induced coherent islanding but by misfit dislocations at the onset of strain relaxation.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.-a Thin film structure and morphology
61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)

Electrical properties and poling of BaTiO3 thin films

H. A. Lu, L. A. Wills, and B. W. Wessels

Appl. Phys. Lett. 64, 2973 (1994); http://dx.doi.org/10.1063/1.111375 (3 pages) | Cited 27 times

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Dielectric and ferroelectric properties were measured for both highly a‐axis textured and randomly oriented BaTiO3 thin films deposited on Pt coated MgO substrates via metal‐organic chemical‐vapor deposition. Dielectric constants on the order of ϵ∼10 and an absence of ferroelectric hysteresis were generally observed for the as‐deposited films. Upon applying an electric field exceeding a threshold value of ∼50–100 kV/cm across the film, both the dielectric constant and the ferroelectric hystersis were enhanced significantly as a result of poling. The dielectric constant increased to ϵ∼100, and the spontaneous polarization of the a‐axis textured film reached Ps≥15 μC/cm2. The measured dielectric and ferroelectric properties of the BaTiO3 thin films depended on the microstructure of the films.
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73.61.Ng Insulators
77.80.Dj Domain structure; hysteresis
77.55.-g Dielectric thin films
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Properties of Al2O3 optical coatings on GaAs produced by oxidation of epitaxial AlAs/GaAs films

E. F. Schubert, M. Passlack, M. Hong, J. Mannerts, R. L. Opila, L. N. Pfeiffer, K. W. West, C. G. Bethea, and G. J. Zydzik

Appl. Phys. Lett. 64, 2976 (1994); http://dx.doi.org/10.1063/1.111376 (3 pages) | Cited 13 times

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Auger analysis of oxidized AlAs epitaxial layers grown by molecular‐beam epitaxy reveals that the composition of the films is stoichiometric Al2O3. High optical quality of the films is demonstrated by optical reflection and transmission measurements. A reflectivity of 6% is measured for an antireflection coating on GaAs. Leakage currents in the nA range and resistivities ≳5×1011 Ω cm are deduced from current‐voltage measurements. Capacitance‐voltage measurements on metal‐oxide‐semiconductor structures using the Al2O3 films obtained by oxidizing AlAs, reveal a significant reduction of the interface state density as compared to conventional, electron beam evaporated Al2O3.
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73.61.Ga II-VI semiconductors
78.66.Fd III-V semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
85.30.Tv Field effect devices

Depth distribution of reactive ion etching‐induced damage in InAlAs/InGaAs heterostructures evaluated by Hall measurements

Sambhu Agarwala, Ilesanmi Adesida, Catherine Caneau, and Rajaram Bhat

Appl. Phys. Lett. 64, 2979 (1994); http://dx.doi.org/10.1063/1.111377 (3 pages) | Cited 3 times

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The depth distribution of defects induced by reactive ion etching in InAlAs/InGaAs heterostructures has been determined from the measurements of low‐temperature mobilities of samples with varying two‐dimensional electron gas (2DEG) depth. The sample with a 2DEG depth of 35 nm from the surface showed no change in mobilities or sheet carrier densities, whereas the one with a 2DEG depth of 12.5 nm, etched under the same conditions using HBr plasma at a self‐bias of −100 V, showed a large change in both mobilities and sheet carrier densities. The defect distribution, which was estimated using the reciprocal of mobilities, has been found to be exponential. A 1/e penetration depth of about 7.8 nm has been obtained for HBr plasma for self‐bias voltages between −100 and −200 V and has been found to be independent of etching time. The exponential distribution of defects suggests that either ion channeling or diffusion is the possible mechanism of defect production in regions deeper than the projected ion range.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.65.-b Surface treatments
85.30.Tv Field effect devices
85.40.Hp Lithography, masks and pattern transfer

Formation of new energy bands and minigap suppression by hybridization of barrier and well resonances in semiconductor superlattices

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

Appl. Phys. Lett. 64, 2982 (1994); http://dx.doi.org/10.1063/1.111378 (3 pages) | Cited 6 times

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The first observation of band structure phenomena arising from the degeneracy of barrier and well resonances in suitably designed superlattices is reported. These effects are characterized by the formation of new minibands and the suppression of a minigap at a Brillouin zone boundary leading to striking modifications of the absorption spectrum. The interesting implications of this phenomenon for electronic transport are discussed.
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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

Theoretical study on threshold energy and impact ionization coefficient for electrons in Si1−xGex

Keesoo Yeom, John M. Hinckley, and Jasprit Singh

Appl. Phys. Lett. 64, 2985 (1994); http://dx.doi.org/10.1063/1.111379 (3 pages) | Cited 9 times

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Threshold energy and electron impact ionization coefficients (α) are calculated for unstrained and strained Si1−xGex on {100} silicon substrate using nonparabolic and ellipsoidal band structure for conduction band and k⋅p method for valence band. The threshold energy in the unstrained Si1−xGex is smaller than that in pure silicon due to the reduced band‐gap energy. The strain causes band degeneracy lifting for both the conduction band and valence band. It gives an additional band‐gap narrowing which leads to a much smaller threshold energy. On the basis of these results, the electron impact ionization coefficient is estimated up to 30% germanium using a Monte Carlo simulation. The reduced threshold energy is found to be the most dominant factor in determining α in the strained Si1−xGex. As a result, the strained Si1−xGex has much larger α than pure silicon while the unstrained Si1−xGex does not due to the effect of alloy scattering and the relatively small change of the threshold energy.
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71.20.Nr Semiconductor compounds
71.20.Ps Other inorganic compounds
72.20.Ht High-field and nonlinear effects
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