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18 Sep 1995

Volume 67, Issue 12, pp. 1639-1787

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Spectra of third‐order optical nonlinear susceptibilities of epitaxial chloro‐indium‐phthalocyanines

H. Tajalli, J. P. Jiang, J. T. Murray, N. R. Armstrong, A. Schmidt, M. Chandross, S. Mazumdar, and N. Peyghambarian

Appl. Phys. Lett. 67, 1639 (1995); http://dx.doi.org/10.1063/1.114730 (3 pages) | Cited 20 times

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We have measured the third harmonic generation spectra of epitaxial chloro‐indium phthalocyanine (ClInPc) thin films. The χ(3) spectrum in the wavelength range of 970–1650 nm reveals resonance features of ClInPc. Theoretical analysis of the third‐order nonlinear optical channels in phthalocyanine allows the assignment of the observed resonances to three‐ and two‐photon resonances of χ(3). © 1995 American Institute of Physics.
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42.65.An Optical susceptibility, hyperpolarizability
42.70.Jk Polymers and organics
78.66.Qn Polymers; organic compounds

Properties of deep photoluminescence bands in SiGe/Si quantum structures grown by molecular beam epitaxy

I. A. Buyanova, W. M. Chen, A. Henry, W.‐X. Ni, G. V. Hansson, and B. Monemar

Appl. Phys. Lett. 67, 1642 (1995); http://dx.doi.org/10.1063/1.115042 (3 pages) | Cited 4 times

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The appearance of broad photoluminescence (PL) bands in the energy range 0.70–0.96 eV in SiGe/Si heterostructures is shown to be related to the ion bombardment during the molecular beam epitaxy. From the optically detected cyclotron resonance, polarization, and postgrowth treatments, the PL is shown to be composed of at least two components. No evidence of lattice distortion is found for the main PL band, while the low energy tail is believed to arise from lattice distorted regions. Both PL centers are demonstrated to originate from the SiGe quantum wells by PL excitation measurements. © 1995 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
71.55.Ht Other nonmetals
78.55.Hx Other solid inorganic materials

Direct modulation and optical confinement factor modulation of semiconductor lasers

A. Frommer, S. Luryi, D. T. Nichols, J. Lopata, and W. S. Hobson

Appl. Phys. Lett. 67, 1645 (1995); http://dx.doi.org/10.1063/1.115043 (3 pages) | Cited 3 times

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A method for modulation of semiconductor lasers based on the modulation of the optical confinement factor is demonstrated. Using this method, an enhanced −3 dB bandwidth is observed in agreement with the small signal rate equation analysis. A modulation response that drops at high frequencies slower than the conventional direct current modulation response is achieved. © 1995 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Fc Modulation, tuning, and mode locking

Degradation studies of proton‐implanted vertical cavity surface emitting lasers

Y. Michael Cheng, Robert W. Herrick, Pierre M. Petroff, Mary K. Hibbs‐Brenner, and Robert A. Morgan

Appl. Phys. Lett. 67, 1648 (1995); http://dx.doi.org/10.1063/1.115044 (3 pages) | Cited 4 times

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We analyze the degradation process of proton‐implanted, top‐emitting vertical cavity surface emitting lasers using cross‐sectional cathodoluminescence. The spatially resolved luminescence characteristics of the active regions, and p‐ and n‐distributed Bragg reflector (DBR) mirrors before and after degradation of the devices are presented. Degradation has been observed not only in the active regions, but also remarkably in the p‐DBR mirror stacks. We show that a significant minority carrier population is present in the p mirror under normal operating conditions to drive the degradation observed in the p mirror. © 1995 American Institute of Physics.  
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42.55.Px Semiconductor lasers; laser diodes
42.60.-v Laser optical systems: design and operation

Design, fabrication, and test of wide‐angle low‐loss Y‐junction hybrid polymer couplers

Tsang‐Der Ni, Dana Sturzebecher, Mike Cummings, and Barry Perlman

Appl. Phys. Lett. 67, 1651 (1995); http://dx.doi.org/10.1063/1.115045 (2 pages) | Cited 4 times

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Optical couplers are key components for signal distribution in optoelectronic transmitter/receiver modules. A new low‐loss large‐angle Y‐junction hybrid polymer optical coupler incorporating an integrated microprism has been fabricated and demonstrated experimentally for use in a mixed‐signal module environment. The results show that the radiation loss is small with relatively wide branching angle as compared to a conventional Y‐junction coupler.
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42.79.Gn Optical waveguides and couplers

Neutral‐donor‐bound exciton recombination dynamics in GaN grown by metalorganic chemical vapor deposition

G. D. Chen, M. Smith, J. Y. Lin, H. X. Jiang, M. Asif Khan, and C. J. Sun

Appl. Phys. Lett. 67, 1653 (1995); http://dx.doi.org/10.1063/1.115046 (3 pages) | Cited 33 times

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Neutral‐donor‐bound exciton recombination (I2) dynamics have been studied by photoluminescence in an unintentionally doped n‐type GaN epitaxial layer grown by metalorganic chemical vapor deposition. The luminescence emission line shape, peak position, and intensity as functions of temperature have been measured. In particular, time‐resolved emission spectroscopy has been employed to study the dynamic processes of the bound exciton recombination, from which the temperature and the emission energy dependencies of the recombination lifetime of this transition have been obtained. © 1995 American Institute of Physics.
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78.47.-p Spectroscopy of solid state dynamics
78.55.Cr III-V semiconductors

Measurement of free‐space terahertz pulses via long‐lifetime photoconductors

F. G. Sun, G. A. Wagoner, and X.‐C. Zhang

Appl. Phys. Lett. 67, 1656 (1995); http://dx.doi.org/10.1063/1.115047 (3 pages) | Cited 16 times

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Antennas based on commercially available GaAs as a photoconductor with a subnanosecond photocarrier lifetime have been used to detect subpicosecond free‐space electromagnetic radiation (THz pulses). At low optical gating intensities (≤1 mW/100 μm2), GaAs based antennas exhibit a higher responsivity and signal‐to‐noise ratio than typical antennas based on radiation‐damaged silicon‐on‐sapphire. © 1995 American Institute of Physics.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
78.47.-p Spectroscopy of solid state dynamics

Effects of doping in polymer light‐emitting diodes

D. B. Romero, M. Schaer, L. Zuppiroli, B. Cesar, and B. François

Appl. Phys. Lett. 67, 1659 (1995); http://dx.doi.org/10.1063/1.115048 (3 pages) | Cited 58 times

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We observed a dramatic improvement in the performance of polymer light‐emitting diodes (LEDs) upon light doping of the organic layer. The LEDs betrayed symmetrical electrical and light‐emission characteristics. Their turn‐on voltage is lower and their external quantum and power conversion efficiencies are higher by nearly an order of magnitude when compared with devices that utilized a nominally undoped organic layer. We attributed these results to the modification of the tunneling barrier in metal–polymer–metal junctions due to the presence of an induced polarization electric field associated with the ionized dopant counterions and charged polymer chains. © 1995 American Institute of Physics.
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78.60.Fi Electroluminescence
85.60.Jb Light-emitting devices

Waveguide version of an asymmetric Fabry–Perot modulator

B. Pezeshki, J. A. Kash, and F. Agahi

Appl. Phys. Lett. 67, 1662 (1995); http://dx.doi.org/10.1063/1.115049 (3 pages) | Cited 1 time

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We show that the high contrast property of vertical cavity asymmetric Fabry–Perot modulators can also be obtained in a waveguide geometry. Increasing the absorption in one arm of a waveguide directional coupler causes the transmission through the other arm to decrease, go to zero, and then increase again. Thus, by adjusting the coupling length and the absorption, an infinite contrast ratio can theoretically be obtained with a low insertion loss. The waveguide geometry is not only more convenient than normal incidence for fiber‐based devices, but also provides a larger optical bandwidth. We present the design equations and provide a first order model of device operation. © 1995 American Institute of Physics.
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42.79.Hp Optical processors, correlators, and modulators

Study of apparent Faraday rotation of an optically anisotropic system

Hong‐Zhou Ma, Liang‐Yao Chen, Shi‐Ming Zhou, Yu‐Xiang Zheng, Ya‐Dong Wang, You‐Hua Qian, and Chen‐Jia Chen

Appl. Phys. Lett. 67, 1665 (1995); http://dx.doi.org/10.1063/1.115050 (3 pages)

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We present a formula which can be used to analyze the anisotropic and apparent Faraday effect occurring in a material having an optically anisotropic property. By using the formula the real Faraday parameter can be obtained. For example, we have used the formula to study the anisotropic Faraday effect of a single‐crystal Cd0.55Mn0.45Te measured with the spectroscopic ellipsometer and rotating‐analyzer‐type Kerr apparatus. The calculated data were in good agreement with the experimental results. © 1995 American Institute of Physics.    
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78.20.Ls Magneto-optical effects

Room‐temperature optically pumped blue‐green vertical cavity surface emitting laser

H. Jeon, V. Kozlov, P. Kelkar, A. V. Nurmikko, C.‐C. Chu, D. C. Grillo, J. Han, G. C. Hua, and R. L. Gunshor

Appl. Phys. Lett. 67, 1668 (1995); http://dx.doi.org/10.1063/1.115051 (3 pages) | Cited 19 times

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Surface emitting laser operation at room temperature at λ=496 nm by ps pulsed optical injection has been demonstrated in a II–VI separate confinement heterostructure containing three 80 Å thick (Zn,Cd)Se quantum wells (QW). The vertical cavity was formed by low loss, dielectric, distributed Bragg mirrors, yielding a quality factor for the structure of approximately Q≊2000. The room‐temperature threshold excitation corresponds to an absorbed optical energy density of 1.4 μJ/cm2 or, equivalently, to an estimated electron‐hole pair density of 1×1012 cm−2. At T=200 K, quasicontinuous wave operation was obtained at an average output power of up to 1 mW and an output/input conversion efficiency of 20%. © 1995 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.-v Laser optical systems: design and operation

Transport mechanisms in infinite layer phase compounds grown by molecular beam epitaxy

X. M. Xie, C. Hatterer, V. Mairet, C. F. Beuran, C. Coussot, C. Deville Cavellin, B. Eustache, P. Laffez, X. Z. Xu, and M. Laguës

Appl. Phys. Lett. 67, 1671 (1995); http://dx.doi.org/10.1063/1.115052 (3 pages) | Cited 5 times

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Thin films of infinite layer compounds were prepared by molecular beam epitaxy. Defect layers were incorporated into the structure in order to dope the infinite layer phase. Hole type doping is usually observed. Resistivity measurements show that the conduction mechanisms change gradually with increasing doping level, from activational type to variable range hopping (or a mechanism governed by the Coulomb interaction between localized electrons) and then further to a mechanism related to weak localization which can be described by Δρ=T−S, where the exponent S ranges from 0.5 to 1.5. © 1995 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
74.25.F- Transport properties
74.72.-h Cuprate superconductors

Effective piezoelectric activity of zinc oxide films grown by radio‐frequency planar magnetron sputtering

B. Wacogne, M. P. Roe, T. J. Pattinson, and C. N. Pannell

Appl. Phys. Lett. 67, 1674 (1995); http://dx.doi.org/10.1063/1.115053 (3 pages) | Cited 21 times

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We present a study of the effective piezoelectric activity of thin ZnO films produced by radio‐frequency (rf) planar magnetron sputtering. The energetic plasma particles which bombard the substrate in the above deposition system increase the substrate temperature, thus causing a gradual variation in film structure during the beginning of the film growth. As a result, a precursor layer is formed which consists of small randomly oriented crystallites, exhibiting poor piezoelectric activity. Hence, the film thickness responsible for piezoelectric activity is generally less than the physical thickness of the film and is adjacent to a layer having different acoustic impedance. This leads to an increase in the resonant frequency of the film. For example, a film designed to have a half‐wave resonance at 288 MHz, was found to be resonant at 332 MHz. The poorly structured initial layer meant in this typical case that only 87% of this film volume exhibited piezoelectric activity. Investigations based on the substrate temperature, the optical losses, scanning electron microscope imaging, and rf electrical behavior are presented in this letter. © 1995 American Institute of Physics.
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43.35.Ns Acoustical properties of thin films
43.38.Zp Acoustooptic and photoacoustic transducers
77.65.Bn Piezoelectric and electrostrictive constants
81.15.Cd Deposition by sputtering

Heteroepitaxial growth of highly conductive metal oxide RuO2 thin films by pulsed laser deposition

Q. X. Jia, X. D. Wu, S. R. Foltyn, A. T. Findikoglu, P. Tiwari, J. P. Zheng, and T. R. Jow

Appl. Phys. Lett. 67, 1677 (1995); http://dx.doi.org/10.1063/1.115054 (3 pages) | Cited 15 times

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Highly conductive ruthenium oxide (RuO2) has been epitaxially grown on LaAlO3 substrates by pulsed laser deposition. The RuO2 film is (h00) oriented normal to the substrate surface. The heteroepitaxial growth of RuO2 on LaAlO3 is demonstrated by the strong in‐plane orientation of thin films with respect to the major axes of the substrate. High crystallinity of RuO2 thin films is also determined from Rutherford backscattering channeling measurements. Electrical measurements on the RuO2 thin films demonstrate a quite low room‐temperature resistivity of 35±2 μΩ cm at deposition temperatures of above 500 °C. © 1995 American Institute of Physics.
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68.55.-a Thin film structure and morphology
73.61.-r Electrical properties of specific thin films
81.15.Fg Pulsed laser ablation deposition

Scanning tunneling microscopy study of CdTe(001)

L. Seehofer, G. Falkenberg, R. L. Johnson, V. H. Etgens, S. Tatarenko, D. Brun, and B. Daudin

Appl. Phys. Lett. 67, 1680 (1995); http://dx.doi.org/10.1063/1.115055 (3 pages) | Cited 21 times

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Atomic resolution scanning tunneling microscope images of the (2×1) and c(2×2) reconstructions of CdTe(001) are presented. Both reconstructions can be described by a structural model in which the surface is terminated with 0.5 ML twofold‐coordinated Cd atoms. Step edges, domain boundaries and various types of point defects are characterized. The measurements indicate that the surface atoms are highly mobile at room temperature. © 1995 American Institute of Physics.
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
68.35.B- Structure of clean surfaces (and surface reconstruction)

Heterojunctions of solid C70 and crystalline silicon: Rectifying properties and barrier heights

K. M. Chen, K. Wu, Y. Chen, Y. Q. Jia, S. X. Jin, C. Y. Li, Z. N. Gu, and X. H. Zhou

Appl. Phys. Lett. 67, 1683 (1995); http://dx.doi.org/10.1063/1.115056 (3 pages) | Cited 11 times

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Heterojunctions of solid C70 and n‐ or p‐type crystalline Si have been made. Current–voltage measurements show that both C70/n‐Si and C70/p‐Si contacts are rectifying but their directions of rectification are opposite to each other. Thermal activation measurements at a fixed forward bias show an exponential dependence of current on the reciprocal of temperature, from which we determine the effective barrier height as 0.23 eV for C70/n‐Si and 0.27 eV for C70/p‐Si. Relative dielectric constant of solid C70 was determined to be 4.96 through the study of high‐frequency capacitance–voltage characteristics for Ti/C70/p‐Si structures. © 1995 American Institute of Physics.
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73.40.Cg Contact resistance, contact potential
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

GaN grown by molecular beam epitaxy at high growth rates using ammonia as the nitrogen source

Z. Yang, L. K. Li, and W. I. Wang

Appl. Phys. Lett. 67, 1686 (1995); http://dx.doi.org/10.1063/1.115057 (3 pages) | Cited 53 times

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The 9.5 eV bond energy of the nitrogen molecule makes it very difficult to break it up into atoms and incorporate in III–V nitride compounds grown by molecular beam epitaxy (MBE). By comparison, it is relatively easy to dissociate ammonia due to the existence of a catalytic effect on the GaN surface when there is Ga present. Using ammonia as the nitrogen source, we have achieved high quality GaN by MBE at a growth rate as high as 1 μm/h. This is an order‐of‐magnitude faster than previously reported using electron‐cyclotron resonance plasma‐assisted growth. Most importantly, our results indicate that there is no intrinsic limit to the growth rate of GaN using ammonia, a situation similar to that of conventional III–V MBE using gas sources. The unintentional n‐type doping as low as 2×1017 cm−3 at room temperature. In addition, room‐temperature hole densities of 4×1017 cm−3 in Mg‐doped GaN films have been achieved without postgrowth annealing. Low‐temperature photoluminescence for both undoped and Mg‐doped GaN are dominated by near band‐edge emissions without deep‐level related luminescence, indicative of high quality materials. © 1995 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Alignment of defect dipoles in polycrystalline ferroelectrics

W. L. Warren, D. Dimos, G. E. Pike, K. Vanheusden, and R. Ramesh

Appl. Phys. Lett. 67, 1689 (1995); http://dx.doi.org/10.1063/1.115058 (3 pages) | Cited 53 times

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Using electron paramagnetic resonance (EPR), we show the alignment of defect dipoles along the direction of the spontaneous polarization in polycrystalline BaTiO3 ceramics by subjecting the capacitors to a dc bias at elevated temperatures. The alignment is demonstrated to occur via orientation dependent EPR signals in the polycrystalline perovskite lattice. The alignment of the defect dipoles is found to strongly enhance the light sensitivity of the defects. This observation may have important implications for photorefractive applications. © 1995 American Institute of Physics.
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61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
77.80.-e Ferroelectricity and antiferroelectricity
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Preparation of a La0.5Sr0.5CoO3/PbZr0.56Ti0.44O3/La0.5 Sr0.5CoO3 multilayer structure on SrTiO3(100) and LaAlO3(100) substrates using the sol‐gel method

Fan Wang, Antti Uusimäki, and Seppo Leppävuori

Appl. Phys. Lett. 67, 1692 (1995); http://dx.doi.org/10.1063/1.115059 (3 pages) | Cited 10 times

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A sol‐gel spin‐coating procedure was established to prepare La0.5Sr0.5CoO3/ PbZr0.56Ti0.44O3/La0.5Sr0.5CoO3 multilayer structure on SrTiO3(100) and LaAlO3(100) substrates. The films were characterized by means of x‐ray diffraction, scanning electron microscopy, and electrical measurements. The results showed the advantages of the sol‐gel processing in compositional control as well as in oriented growth of films. A high remnant polarization was obtained in the films prepared with this procedure. © 1995 American Institute of Physics.  
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Reflection high‐energy electron diffraction study of the molecular beam epitaxial growth of CaF2 on Si(110)

W. K. Liu, X. M. Fang, and P. J. McCann

Appl. Phys. Lett. 67, 1695 (1995); http://dx.doi.org/10.1063/1.115060 (3 pages) | Cited 3 times

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Molecular beam epitaxial growth of CaF2 on Si(110) was studied using reflection high‐energy electron diffraction (RHEED) and scanning electron microscopy (SEM). An optimum substrate temperature range exists between 800 and 900 °C within which (110)‐oriented epitaxy can be sustained. At the initial growth stage, long strips of CaF2 parallel to the [110] direction are formed due to the growth anisotropy on the (110) surface. This is followed by the development of low‐energy {111} facets, producing a ridged and grooved surface morphology. Growth then proceeds via the stacking of {111} planes on the sidewalls of the ridges. This surface morphology is believed to result from the combination of favorable energetics in exposing the low‐energy {111} facets and the presence of twinned crystallographic domains. © 1995 American Institute of Physics.
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61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Fabrication of a thin film of an inorganic:organic composite via laser assisted molecular beam deposition

W. M. K. P. Wijekoon, M. Y. M. Lyktey, P. N. Prasad, and J. F. Garvey

Appl. Phys. Lett. 67, 1698 (1995); http://dx.doi.org/10.1063/1.115061 (2 pages) | Cited 10 times

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Thin films of a hybrid organic:inorganic [silica: N‐4‐(4‐nitrophenyl)‐(s)‐prolinol] composite were fabricated by mixing the constituents in the gas phase via the technique of laser assisted molecular beam deposition. UV visible and infrared spectra indicate that the organic chromophore is trapped within the silica matrix without degradation. This approach will enable the fabrication of thin films of a variety of hybrid organic: inorganic composite materials which would otherwise be difficult to fabricate. © 1995 American Institute of Physics.
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78.66.Sq Composite materials
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Room‐temperature synthesis of copper germanide phase by ion beam mixing

S. Dhar, T. Som, Y. N. Mohapatra, and V. N. Kulkarni

Appl. Phys. Lett. 67, 1700 (1995); http://dx.doi.org/10.1063/1.115021 (3 pages) | Cited 11 times

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This letter reports room‐temperature synthesis by ion beam mixing of the ϵ1‐Cu3Ge phase which is a promising candidate for interconnect and contact material in very large scale integrated circuit technology. The resistivity of the mixed sample was found to be nearly the same as the one obtained from thermally prepared films. We briefly discuss the likely mechanisms of phase formation and conclude that reaction kinetics dominates over thermodynamic forces during phase formation. The sequence of phase formation is explained by effective heat of formation rule. © 1995 American Institute of Physics.
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61.80.Jh Ion radiation effects
81.30.Bx Phase diagrams of metals, alloys, and oxides
85.40.Hp Lithography, masks and pattern transfer

The role of transient ion‐induced defects in ion beam‐assisted growth

B. K. Kellerman, E. Chason, J. A. Floro, S. T. Picraux, and J. M. White

Appl. Phys. Lett. 67, 1703 (1995); http://dx.doi.org/10.1063/1.115022 (3 pages) | Cited 9 times

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Low‐energy ion bombardment, concurrent with growth, can control and improve many aspects of film growth, but confirming the atomistic mechanism responsible for these effects has been difficult. We present a simple picture of ion beam‐assisted deposition as the interaction of growth‐induced and ion‐induced surface defects (adatoms and vacancies). We use kinetic Monte Carlo simulations to demonstrate that low‐energy ion bombardment in conjunction with growth produces a smoother surface morphology than either growth or ion bombardment alone by destabilizing surface clusters and promoting step flow growth. © 1995 American Institute of Physics.
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61.80.Jh Ion radiation effects
68.55.-a Thin film structure and morphology
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Diamond polytypes in the chemical vapor deposited diamond films

Sanjay Bhargava, H. D. Bist, S. Sahli, M. Aslam, and H. B. Tripathi

Appl. Phys. Lett. 67, 1706 (1995); http://dx.doi.org/10.1063/1.115023 (3 pages) | Cited 16 times

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Micro‐Raman spectroscopy and x‐ray diffraction measurements have been used to identify the presence of hexagonal diamond polytypes in chemical vapor deposited diamond films. The presence of additional reflections, in addition to the normal cubic diamond reflections in the diffraction spectra and bands at 1306 and 1193 cm−1 in the Raman spectra, are attributed to the presence of diamond 6H polytype. The presence of the 1324 cm−1 band in addition to the main diamond peak in the expanded spectra is attributed to regions with hexagonal symmetry, thus supporting the presence of hexagonal diamond polytypes. The compressive strain in diamond layers on the Si substrate is believed to create regions of hexagonal symmetry and vice versa. © 1995 American Institute of Physics.  
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Characterization of SiGe quantum wire structures by cathodoluminescence imaging and spectroscopy

V. Higgs, E. C. Lightowlers, N. Usami, T. Mine, S. Fukatsu, and Y. Shiraki

Appl. Phys. Lett. 67, 1709 (1995); http://dx.doi.org/10.1063/1.115024 (3 pages) | Cited 2 times

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SiGe quantum wire (QWR) structures grown by gas source molecular beam epitaxy have been characterized by cathodoluminescence (CL) imaging and spectroscopy. At T≊5 K, the CL spectra obtained with a focused beam contain SiGe luminescence features associated with electron‐hole plasma recombination. When the electron beam is defocused three separate SiGe no‐phonon luminescence features and their transverse optic phonon replicas are observed. These features are related to recombination in the SiGe (100) quantum wells (QWs), SiGe (111) QWs, and the SiGe QWRs. The high generation rates associated with the focused electron beam quenches the luminescence and results in electron‐hole plasma recombination in the adjacent SiGe (100) QWs, and saturation of the radiative processes. Defocusing the electron beam reduces the injection level and nonradiative processes, enabling the SiGe bound exciton features to be observed. Monochromatic CL imaging of the SiGe (100) QWs show that at low temperatures the CL image is broadened by exciton diffusion and becomes sharper at higher temperatures (T=50–70 K) reflecting nonexcitonic recombination. © 1995 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.60.Hk Cathodoluminescence, ionoluminescence
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