排序方式: 共有55条查询结果,搜索用时 15 毫秒
41.
A. Raisanen L. J. Brillson A. Franciosi R. Nicolini L. Vanzetti L. Sorba 《Journal of Electronic Materials》1995,24(3):163-169
We performed 1—2 keVcathodoluminescence measurements and He-Ne and HeCd excited photoluminescence studies of ZnSe/GaAs( 100)
heterostructures grown by molecular beam epitaxy. Our goal was to investigate the deep level electronic structure and its
connection with the heterojunction band offsets. We observed novel deep level emission features at 0.8, 0.98, 1.14, and 1.3
eV which are characteristic of the ZnSe overlayer and independent in energy of overlayer thickness. The corresponding deep
levels lie far below those of the near-bandedge features commonly used to characterize the ZnSe crystal quality. The relative
intensity and spatial distribution of the deep level emission was found to be strongly affected by the Zn/Se atomic flux ratio
employed during ZnSe growth. The same flux ratio has been shown to influence both the quality of the ZnSe overlayer and the
band offset in ZnSe/GaAs heterojunctions. In heterostructures fabricated in Se-rich growth conditions, that minimize the valence
band offset and the concentration of Se vacancies, the dominant deep level emission is at 1.3 eV. For heterostructures fabricated
in Zn-rich growth conditions, emission by multiple levels at 0.88,0.98, and 1.14 eV dominates. The spectral energies and intensities
of deep level transitions reported here provide a characteristic indicator of ZnSe epilayer stoichiometry and near-interface
defect densities. 相似文献
42.
By introducing electric displacement (D) into the FDTD model, material-independent perfectly matched layer (MIPML) absorbers are developed. With the help of this MIPML, Berenger's PML absorbing boundary condition can be successfully extended to anisotropic dielectric media with arbitrary tensor permittivity. Validation of the proposed technique is carried out through a numerical example 相似文献
43.
Salo J. Meltaus J. Noponen E. Westerholm J. Salomaa M.M. Lonnqvist A. Saily J. Hakli J. Ala-Laurinaho J. Raisanen A.V. 《Electronics letters》2001,37(13):834-835
A computer-generated binary amplitude hologram is used to transform an initial Gaussian electromagnetic field with spherical phase front at 310 GHz into a nondiffracting Bessel beam. The beam profile is measured with the help of a near field scanner. In contrast to the situation in the optical region, both amplitude and phase information is readily obtainable from the generated field 相似文献
44.
A simple 64 element planar array antenna, with H-plane sidelobes below -35 dB at larger angles than 19° from boresight and a gain above 30.4 dBi, is presented for the band 37.0-39.5 GHz. The radiating elements are fed in parallel by a waveguide feed network. The H-plane sidelobe level is reduced by using a combination of arrays, the zero in the element radiation pattern, and amplitude tapering 相似文献
45.
Hienonen S. Vainikainen P. Raisanen A.V. 《Antennas and Propagation Magazine, IEEE》2003,45(4):124-129
A passive intermodulation (PIM) near-field XY scanner for the GSM900 frequency band has been constructed to localize distortion sources in antennas and in other open structures. The equipment should be able to measure distortion levels down to -115 dBm with an input power of 2/spl times/20 W, since the noise floor of a GSM900 base station is typically around -110 dBm. The sensitivity is limited either by thermal noise or by residual intermodulation distortion, depending on the probe coupling. Various causes of residual intermodulation distortion in the passive intermodulation near-field measurement are considered and evaluated. Sensitivity measurements of the scanner have been carried out on two test devices. Sensitivities of -112 dBm and -110 dBm have been achieved with an electric and a magnetic field probe, respectively. 相似文献
46.
Hakli J. Koskinen T. Ala-Laurinaho J. Raisanen A.V. 《Antennas and Propagation, IEEE Transactions on》2005,53(12):3940-3948
Manufacturing of large computer-generated submillimeter wave holograms with high pattern accuracy has been the main challenge in the development of hologram based compact antenna test ranges (CATRs). Illumination of the hologram with a shaped beam produced by a dual reflector feed system (DRFS) simplifies the hologram manufacturing by eliminating the narrow slots in the hologram pattern. In this paper, the design of a shaped dual reflector feed for a hologram CATR is described. The simulated and measured illumination field amplitude and phase at 310 GHz are presented and compared to the desired hologram illumination. The measured amplitude is within /spl plusmn/0.5 dB from the design objective in the most significant central region of the illuminating beam. Measurement results of the quiet-zone field of a demonstration CATR illuminated by the DRFS are presented and compared to the measured quiet-zone amplitude and phase of a hologram fed directly with a corrugated horn. The quiet-zone diameters of the both holograms are over 0.25 meters and the measured root mean squared (rms) amplitude and phase ripples are below /spl plusmn/0.4 dB and /spl plusmn/5/spl deg/, respectively. Further improvements to the hologram CATR, such as greater tolerance to manufacturing errors, are also discussed. 相似文献
47.
48.
Different types (pyramidal, convoluted, wedge, flat) of absorber panel made by several manufacturers have been measured at 107 and 183 GHz. These measurements revealed a rapid degradation of the quality of absorbers from 107 to 183 GHz: reflectivity increased nearly 10 dB. The best absorbers have reflectivities below -40 dB at 107 GHz and about -35 dB at 183 GHz.<> 相似文献
49.
Koistinen O.P. Valmu H.T. Raisanen A. Vdovin V.F. Dryagin Y.A. Lapkin I.V. 《Microwave Theory and Techniques》1993,41(12):2232-2236
A total power radiometer for monitoring the stratospheric ozone spectral line at 110 GHz is presented. Special features such as a cooled planar Schottky mixer as the front end and efficient reduction of standing waves in the quasi-optics are discussed in detail. The noise temperature of the receiver is 530 K (single sideband), and the total bandwidth of the receiver is 1 GHz. A dual acoustooptical spectrometer is used for the signal detection 相似文献
50.
Reflectivity measurements of various commercial absorbers atmillimetre and submillimetre wavelengths
Several absorbers made from new materials, and intended for frequencies up to 1THz, are commercially available. Reflectances of these absorbing panels, measured at 200, 300, 400, 500, and 600 GHz with different incident angles, are presented 相似文献