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27 Sep 1993

Volume 63, Issue 13, pp. 1715-1856

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Electron beam‐enhanced etching of InAs in Cl2 gas and novel in situ patterning of GaAs with an InAs mask layer

S. Miya, T. Yoshida, Y. Kadoya, B. Akamatsu, H. Noge, H. Kano, and H. Sakaki

Appl. Phys. Lett. 63, 1789 (1993); http://dx.doi.org/10.1063/1.110663 (3 pages) | Cited 4 times

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We propose and demonstrate a novel in situ patterning process of GaAs and GaAs/AlGaAs heterostructures in which a thin InAs layer is used as an electron‐beam resist layer for Cl2 gas etching in ultrahigh vacuum environment. It has been found that the etch rate of InAs by Cl2 gas is far lower (by a factor of 500) than that of GaAs but this etch rate can be enhanced by electron beam irradiation by a factor of 20, allowing the pattern formation in the InAs mask layer. By delineating a stripe pattern in the InAs resist and subsequently etching in situ the GaAs underneath, we have successfully formed a fine V groove. Since this process is clean and damage free, it is suited for the fabrication of quantum structures in which high‐quality etch/regrowth interfaces are required.
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81.65.-b Surface treatments
61.80.Fe Electron and positron radiation effects
85.40.Hp Lithography, masks and pattern transfer

Oriented nucleation and growth of diamond films on β‐SiC and Si

R. Kohl, C. Wild, N. Herres, P. Koidl, B. R. Stoner, and J. T. Glass

Appl. Phys. Lett. 63, 1792 (1993); http://dx.doi.org/10.1063/1.110664 (3 pages) | Cited 59 times

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Oriented diamond nuclei prepared by bias‐enhanced microwave plasma chemical vapor deposition on β‐SiC and Si were characterized by x‐ray texture diffractometry. In both cases, x‐ray pole figures reveal an epitaxial relation between the orientation of diamond nuclei and the substrate. However, the angular spread of the nuclei orientation is rather large, amounting to 9°–13° (FWHM) in both polar and azimuthal directions. When growing thick diamond films on top of these already oriented diamond nuclei, the evolution of the orientational order depends critically on the growth conditions. In the case of 〈100〉 oriented nuclei, growth conditions which favor the formation of a 〈100〉 fiber texture can even improve the degree of orientational order, whereas other growth conditions result in a deterioration of the epitaxial relationship.
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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
61.05.cf X-ray scattering (including small-angle scattering)
61.05.cj X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc.

Calculation of InAs/AlSb(001) band offsets: Effect of strain and interfacial atomic structure

R. G. Dandrea and C. B. Duke

Appl. Phys. Lett. 63, 1795 (1993); http://dx.doi.org/10.1063/1.110665 (3 pages) | Cited 18 times

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The band offsets of strained InAs grown on an AlSb(001) substrate are calculated for both the In‐Sb and Al‐As interfaces. A valence band offset of 0.19 eV (AlSb valence max higher) is calculated within first‐principles local density functional theory, independent of the type of interfacial bonding. Short‐period superlattices with identical InAs and AlSb lengths but differing only in the type of interfacial bond exhibit, however, quantum‐confined states that can differ by 0.25 eV, and this is explained in terms of the superlattice wave functions. The 0.13 eV strain‐induced decrease in the InAs gap leads to an extremely small energy difference of 0.04–0.10 eV between the InAs conduction minimum and the AlSb valence maximum, and presents a possible explanation for the increase in the InAs quantum well charge seen with increasing temperature.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
78.66.Fd III-V semiconductors
68.55.-a Thin film structure and morphology

Submicron contact hole filling by electron bias sputtering

Jin Onuki and Masayasu Nihei

Appl. Phys. Lett. 63, 1798 (1993); http://dx.doi.org/10.1063/1.110666 (3 pages)

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A new electron bias sputtering method capable of filling Al into submicron contact holes without degradation of the quality has been developed for the formation of reliable interconnections of very large scale integrated circuits. The method features intermittent electron irradiation to enhance Al flow during sputtering. The Al film deposited contains little Ar and has low resistivity. Contact holes with 0.4‐μm diameter and 0.9‐μm depth can be filled with Al.
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85.40.Ls Metallization, contacts, interconnects; device isolation
81.15.Cd Deposition by sputtering

Reversible electron‐beam writing on a submicron scale in a superionic amorphous film

J. M. Oldale and S. R. Elliott

Appl. Phys. Lett. 63, 1801 (1993); http://dx.doi.org/10.1063/1.110667 (3 pages) | Cited 7 times

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The direct writing of patterns in amorphous silver chalcogenide materials by electron‐beam exposure is reported. At sufficiently low beam‐current densities, the written patterns comprise regions depleted of silver; complete hole drilling of films does not occur. The phenomenon is postulated to arise from a combination of thermal gradient and electronic excitation effects.
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61.80.Fe Electron and positron radiation effects
85.40.Hp Lithography, masks and pattern transfer

Dependence of conduction‐band effective mass on quaternary alloy composition of (In0.52Al0.48As)z(In0.53Ga0.47As)1−z lattice matched to InP

L. A. Cury, J. Beerens, and J. P. Praseuth

Appl. Phys. Lett. 63, 1804 (1993); http://dx.doi.org/10.1063/1.110668 (3 pages) | Cited 13 times

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Cyclotron resonance measurements were carried out on high quality (In0.52Al0.48As)z(In0.53Ga0.47As)1−z thick layers grown on InP substrates by molecular beam epitaxy. The measurements were performed at 60 K and we were able to obtain the electron effective mass dependence with z in the whole range of composition 0≤z≤1. Using the band‐gap values as obtained from photoluminescence measurements on the same samples at 60 K, nonparabolicity corrections were taken into account to obtain the effective mass m0∗ at the conduction band edge. A nonlinear variation m0∗ with z could be inferred from our experimental data. The expression m0∗(z)/me=0.043+0.042z−0.016z2, which includes a quadratic dependence in z (or a so‐called bowing parameter), gives a very good fit to our experimental data.  
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71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
73.61.Ey III-V semiconductors

Novel method for rejuvenating and fabricating stable Se/GaAs surfaces

T. Scimeca, K. Prabhakaran, Y. Watanabe, F. Maeda, and M. Oshima

Appl. Phys. Lett. 63, 1807 (1993); http://dx.doi.org/10.1063/1.110669 (2 pages) | Cited 1 time

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Rejuvenation of the oxidized Se/GaAs surface has been realized by deposition of a thin Al layer. The results provided by synchrotron radiation photoelectron spectroscopy show that upon Al deposition, oxygen originally bound to Ga segregates to the surface and forms a more thermodynamically stable Al oxide species. In addition, a reduction in band bending is realized suggesting that this method may be useful as a means of fabricating a wide range of passivated overlayer/Se/GaAs interfaces.
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81.65.-b Surface treatments
73.20.At Surface states, band structure, electron density of states
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.35.Md Surface thermodynamics, surface energies

Terahertz electromagnetic transients as probes of a two‐dimensional electron gas

W. J. Walecki, D. Some, V. G. Kozlov, and A. V. Nurmikko

Appl. Phys. Lett. 63, 1809 (1993); http://dx.doi.org/10.1063/1.110670 (3 pages) | Cited 5 times

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We demonstrate the application of terahertz electromagnetic transients to the study of the dynamical conductivity of a two‐dimensional, high mobility electron gas in modulation‐doped GaAs quantum wells. The transient response of such an electron system on a picosecond time scale occurs in a regime where the implications of electron–electron interaction effects need be considered.
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78.47.-p Spectroscopy of solid state dynamics
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Transport study of ZnSe:N employing Zn(Se,Te) graded contacts

Y. Fan, J. Han, L. He, J. Saraie, R. L. Gunshor, M. M. Hagerott, and A. V. Nurmikko

Appl. Phys. Lett. 63, 1812 (1993); http://dx.doi.org/10.1063/1.110671 (3 pages) | Cited 17 times

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Hall effect measurements for temperatures ranging from 77 to 320 K on a series of p‐ZnSe films grown on GaAs substrates are reported. The ZnSe epilayers were doped using a nitrogen plasma source during growth by molecular beam epitaxy. A Zn(Se,Te) graded band‐gap layer was used to provide ohmic contacts over the temperature range of the measurements. The activation energy of nitrogen in ZnSe at the infinite dilution limit was found to be 114 meV, and compensation ratios ranged from 6% to 11%.
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73.61.Ga II-VI semiconductors
71.55.Gs II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

A quantum‐dot refrigerator

H. L. Edwards, Q. Niu, and A. L. de Lozanne

Appl. Phys. Lett. 63, 1815 (1993); http://dx.doi.org/10.1063/1.110672 (3 pages) | Cited 20 times

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A cryogenic refrigeration scheme is presented which utilizes the discrete energy levels of quantum dots to customize the electronic Fermi–Dirac distribution, cooling a small but macroscopic reservoir to far below the ambient temperature. Several physical limitations of this scheme are discussed within the context of a model device constructed from a two‐dimensional electron gas. These are explored in a simple example where, at an ambient operating temperature of 150 mK, this quantum‐dot refrigerator can achieve a cooling power of 1 μW/cm2, a base temperature of 10 mK, and a cooling efficiency of 35%.
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85.80.Fi Thermoelectric devices
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment
73.40.Gk Tunneling
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Planar single‐facet teardrop‐shaped AlxGa1−xAs‐GaAs quantum well heterostructure laser

S. J. Caracci, M. R. Krames, M. J. Ries, and N. Holonyak

Appl. Phys. Lett. 63, 1818 (1993); http://dx.doi.org/10.1063/1.110673 (3 pages) | Cited 6 times

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Data are presented demonstrating the laser operation of an AlxGa1−xAs‐GaAs quantum well heterostructure (QWH) crystal patterned into a smoothly curved folded resonator, a ‘‘teardrop’’‐shaped resonator, with a single output facet. A deep AlxGa1−xAs native oxide formed entirely through the top confining layer is utilized to produce a large effective index step for lateral optical confinement. The teardrop‐shaped laser operates primarily in a TM (transverse magnetic) longitudinal mode polarized with a TM/TE (transverse electric) power ratio of 7:1. Continuous wave 300 K threshold currents as low as ∼127 mA, external differential quantum efficiencies of η∼15%, and total output power in excess of 75 mW (uncoated facet) are achieved.
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42.55.Px Semiconductor lasers; laser diodes
42.60.-v Laser optical systems: design and operation

Dissociative adsorption of Si2H6 on silicon at hyperthermal energies: The influence of surface structure

J. R. Engstrom, L.‐Q. Xia, M. J. Furjanic, and D. A. Hansen

Appl. Phys. Lett. 63, 1821 (1993); http://dx.doi.org/10.1063/1.110674 (3 pages) | Cited 34 times

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The reactions of Si2H6 with the (100) and (111) surfaces of silicon have been investigated employing supersonic molecular beam scattering techniques. Incident translational energy has been found to influence strongly the probability of dissociative adsorption (SR) on both surfaces. The reaction on the Si(111) surface is distinct from that observed on Si(100) concerning the dependence of SR on the substrate temperature and the incident angle. In particular, the reaction on the (111) surface shows sensitivity to the surface phase transformation (7×7)→(1×1) that occurs above 825 °C. Both the dangling bond density and the effective corrugation of the surface are important in determining the reaction probability.
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Graded band‐gap Cu(In,Ga)Se2 thin‐film solar cell absorber with enhanced open‐circuit voltage

Miguel Contreras, John Tuttle, Dahong Du, Yi Qi, Amy Swartzlander, Andrew Tennant, and Rommel Noufi

Appl. Phys. Lett. 63, 1824 (1993); http://dx.doi.org/10.1063/1.110675 (3 pages) | Cited 5 times

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An important development in polycrystalline Cu(In,Ga)Se2 (CIGS) thin‐film photovoltaic solar cells is the attainment of a high voltage device simultaneous with state‐of‐the‐art conversion efficiency. This letter describes a CIGS‐based solar cell that demonstrates an open‐circuit voltage (Voc) approaching 700 mV and a total‐area conversion efficiency of 12.2%. The high value of Voc was achieved by grading In/Ga through the absorber by a computer‐controlled physical vapor deposition (PVD) process that utilizes variable metal fluxes.  
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84.60.Jt Photoelectric conversion
73.50.Pz Photoconduction and photovoltaic effects
73.61.Ga II-VI semiconductors
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Dislocation density reduction in CdZnTe(100) on GaAs using strained layer superlattices

J. L. Reno, Saket Chadda, and Kevin Malloy

Appl. Phys. Lett. 63, 1827 (1993); http://dx.doi.org/10.1063/1.110676 (3 pages) | Cited 1 time

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We have inserted Cd0.91Zn0.09Te/CdTe(100) strained layer superlattices of various periods into Cd0.955Zn0.045Te grown on GaAs(100). X‐ray diffraction was used as a means to optimize the period of the strained layer superlattice to maximize the quality of the material. Transmission electron microscopy demonstrated that a dramatic decrease (a total of five orders of magnitude) in the dislocation density occurred due to the insertion of the strained layer superlattices. The dislocation density achieved is in a range usable as a substrate material for HgCdTe infrared detectors.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Gamma‐rays irradiation: An effective method for improving light emission stability of porous silicon

J. S. Fu, J. C. Mao, E. Wu, Y. Q. Jia, B. R. Zhang, L. Z. Zhang, G. G. Qin, G. S. Wui, and Y. H. Zhang

Appl. Phys. Lett. 63, 1830 (1993); http://dx.doi.org/10.1063/1.110677 (3 pages) | Cited 21 times

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We report a study on gamma irradiated porous Si. The electron paramagnetic resonance study on porous Si irradiated by gamma rays shows that the observed signals come from an intrinsic defect, a Si dangling bond, at the interface of Si/SiOx in porous Si. The photoluminescence measurements show that the gamma irradiation not only increases the intensity of the photoluminescence but also greatly improves its stability. The spectra of the Fourier transform infrared absorption show that the gamma irradiation is an effective method for accelerating oxidation of porous Si. All experimental results can be explained by the increase of the oxidation layer thickness which decreases the nonradiative recombination probability of electron‐hole pairs.
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78.55.Hx Other solid inorganic materials
61.80.Ed γ-ray effects
76.30.Mi Color centers and other defects
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Electroabsorption of InAsP/InP strained multiple quantum wells for 1.3 μm waveguide modulators

H. Q. Hou, A. N. Cheng, H. H. Wieder, W. S. C. Chang, and C. W. Tu

Appl. Phys. Lett. 63, 1833 (1993); http://dx.doi.org/10.1063/1.110806 (3 pages) | Cited 30 times

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We report the electroabsorption property of InAsP/InP strained multiple quantum wells (MQWs), grown by gas‐source molecular beam epitaxy, for 1.3 μm modulator applications. Very sharp excitonic absorption at room temperature was observed. Electroabsorption measurements performed for a ring‐shaped p‐i‐n diode, consisting of 10‐period InAs0.41P0.59(100 Å)/InP(150 Å) strained MQWs, reveal a significant red shift of the absorption peak with increasing reverse biases due to the quantum‐confined Stark effect. This large energy shift (e.g., ∼18 meV at an external field of 57 kV/cm) is well accounted for in the ‘‘effective well‐width’’ model. The change of the absorption coefficient at a 22 meV detuning is as large as 3510 cm−1 with a small residual absorption, which can be very useful for 1.3 μm waveguide modulators.
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78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
42.79.Hp Optical processors, correlators, and modulators
42.65.Pc Optical bistability, multistability, and switching, including local field effects

InGaAs/InGaAsP integrated tunable detector grown by chemical beam epitaxy

F. S. Choa, W. T. Tsang, R. A. Logan, R. P. Gnall, T. L. Koch, C. A. Burrus, M. C. Wu, Y. K. Chen, and R. Kapre

Appl. Phys. Lett. 63, 1836 (1993); http://dx.doi.org/10.1063/1.110678 (3 pages) | Cited 5 times

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By controlling the thickness of the grating depth with chemical beam epitaxy (CBE) growth time, we report in this letter the design and performance of an integrated tunable detector. A carefully designed tunable active filter, which allows only one below threshold Fabry–Perot mode for operation, is integrated with a waveguide detector. The full tuning range of this kind of tunable device can now be utilized for system applications.
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42.79.Sz Optical communication systems, multiplexers, and demultiplexers
85.60.Gz Photodetectors (including infrared and CCD detectors)

Surface morphology of metalorganic vapor phase epitaxy grown GaAs observed by atomic force microscopy

C. C. Hsu, T. K. S. Wong, and I. H. Wilson

Appl. Phys. Lett. 63, 1839 (1993); http://dx.doi.org/10.1063/1.110679 (3 pages) | Cited 11 times

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Steps of monolayer height (0.28 nm) are observed by atomic force microscope on a metalorganic vapor phase epitaxy grown GaAs surface. Monolayer terrace width was found to be as large as 430 nm, the same as the vicinal substrate surface. The growth mechanism is according to the classical Burton–Cabrera–Frank theory. We may have a larger (≳500 nm) terrace width and surface diffusion length if an exactly oriented [100] substrate is used.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.-a Thin film structure and morphology
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

Defect and strain redistribution in InxGa1−xAs/GaAs multiple quantum wells studied by resonant Raman scattering

J. Wagner, E. C. Larkins, N. Herres, J. D. Ralston, and P. Koidl

Appl. Phys. Lett. 63, 1842 (1993); http://dx.doi.org/10.1063/1.110680 (3 pages) | Cited 5 times

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Resonant Raman scattering by longitudinal optical (LO) phonons in the GaAs barriers of InxGa1−xAs/GaAs multiple quantum well structures has been used to study the onset of strain relaxation as the number of quantum wells is increased. The intensity of scattering from one and two GaAs LO phonons for excitation in resonance with the GaAs E0+Δ0 band gap is found to be highly sensitive to the formation and/or redistribution of defects and the buildup of strain in the barriers, and thus to strain relaxation in the InxGa1−xAs quantum wells. This behavior allows us to detect the onset of strain redistribution, even in samples where the frequencies of both the GaAs LO phonon in the barrier layers and the GaAs‐like LO phonon in the InxGa1−xAs quantum wells show no measurable shift. Here, the GaAs LO phonon frequency observed in structures with fully strained InxGa1−xAs wells and unstrained GaAs barriers is used as a reference.
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68.55.-a Thin film structure and morphology
78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
63.50.-x Vibrational states in disordered systems

Formation of epitaxial Tl2Ba2CaCu2O8 thin films at low temperature in pure argon

S. L. Yan, L. Fang, Q. X. Song, J. Yan, Y. P. Zhu, J. H. Chen, and S. B. Zhang

Appl. Phys. Lett. 63, 1845 (1993); http://dx.doi.org/10.1063/1.110805 (3 pages) | Cited 47 times

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Mirror‐like Tl2Ba2CaCu2O8 thin films have been reproducibly prepared on (001)LaAlO3 substrates by dc magnetron sputtering using 80% argon and 20% oxygen and post‐annealing at temperatures of 720–760 °C in 1 atm pure argon. X‐ray diffraction patterns of θ‐2θ scans, ϕ scans, and Read camera photographs prove that the thin films are strongly textured with the c‐axis perpendicular to the substrate surfaces and epitaxially grown to the substrate with Tl2Ba2CaCu2O8(100) parallel to the LaAlO3(100). The zero resistance temperatures are in the range of 105.2–108.6 K for the 0.2–1.0‐μm‐thick films. The critical current density of 5.3×106 A/cm2 at 77 K has been obtained at zero magnetic field for a 0.4‐μm‐thick film.
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
68.55.-a Thin film structure and morphology
81.15.Cd Deposition by sputtering

Pulsed laser deposition of thick YBa2Cu3O7−δ films with Jc≥1 MA/cm2

S. R. Foltyn, P. Tiwari, R. C. Dye, M. Q. Le, and X. D. Wu

Appl. Phys. Lett. 63, 1848 (1993); http://dx.doi.org/10.1063/1.110653 (3 pages) | Cited 89 times

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Using pulsed laser deposition, YBa2Cu3O7−δ (YBCO) films ranging in thickness from 0.065 to 6.4 μm have been deposited on yttria‐stabilized zirconia substrates with an intermediate layer of CeO2. The thinnest films have critical current densities of over 5 MA/cm2 at 75 K with zero applied field; as film thickness is increased, Jc decreases asymptotically to 1 MA/cm2. X‐ray analysis of a 2.2‐μm‐thick film shows that the YBCO is predominantly c‐axis oriented and textured in‐plane, while a Rutherford backscattering spectrometry minimum channeling yield of ≊75% indicates that the film contains disordered material at this thickness.
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74.78.-w Superconducting films and low-dimensional structures
81.15.Fg Pulsed laser ablation deposition
68.55.-a Thin film structure and morphology
74.72.-h Cuprate superconductors

Atomic resolution scanning tunneling microscopy with a gallium arsenide tip

G. Nunes and N. M. Amer

Appl. Phys. Lett. 63, 1851 (1993); http://dx.doi.org/10.1063/1.110654 (3 pages) | Cited 20 times

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A scanning tunneling microscope which uses a gallium arsenide tip has been successfully constructed. Atomic resolution is demonstrated by the imaging of the Si(111)‐7×7 surface in ultrahigh vacuum. Details of the tip preparation are given and the tip tunneling current characteristics are discussed.
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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)

High power microwaves at 9 GHz from an extended length cavity in a coaxial beam geometry

T. J. Davis, L. Schächter, and J. A. Nation

Appl. Phys. Lett. 63, 1854 (1993); http://dx.doi.org/10.1063/1.110655 (3 pages)

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Experiment and simulation demonstrate high power microwave generation at 9 GHz using a 9‐cm‐diam, 400‐keV, 7‐kA annular electron beam. The beam is propagated in a coaxial drift tube between inner and outer conductors, a configuration which increases the available beam current and reduces the surface fields from existing high power sources. The microwave interaction is provided by an extended length loaded cavity, overcoming the limitations of radiative loss and low quality factor usually imposed by the coaxial geometry. A coupler samples 25 MW of the total 200 MW produced by the beam‐cavity interaction. Simulations indicate that the 7% efficiency can be significantly improved by optimizing the interaction length.
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84.40.Fe Microwave tubes (e.g., klystrons, magnetrons, traveling-wave, backward-wave tubes, etc.)
52.59.Px Hard X-ray sources
41.60.-m Radiation by moving charges
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