摘要:

SrS:Ce is an intensively investigated phosphor due to its blue‐green electroluminescence, which shows efficient blue emission after filtering. Recently reported devices based on this material have demonstrated a luminous efficiency of 1.6 lm/W. The luminescence properties of SrS:Ce,X (X=Na or Cl) have been studied on powders and thin films. It is shown that a high density of traps in SrS:Ce,X occurs. The interaction of Ce3+with traps gives rise to a phosphorescence. An energy transfer from Ce3+to traps is responsible for an observed luminescence quenching in the presence of high electric fields. Moreover, the traps are electrically active and are involved in the electroluminescence process. The observed energy transfer is proposed to be the dominant excitation mechanism of Ce3+in electroluminescence. It is demonstrated for thin films that the defect density increases with doping; therefore, the luminescence yield is already limited at doping concentrations below the onset of the concentration quenching. Thus, the prepared SrS:Ce,Cl thin films show a lower photoluminescence yield than powders. It is concluded that an undisturbed Ce incorporation into SrS thin films has not been achieved so far, although high electroluminescence efficiencies (1.6 lm/W) have been obtained. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360376

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The structural and electrical properties of radio frequency (rf) sputtered hydrogenated amorphous silicon carbide films are presented in this paper. Films were prepared with sputtering pressurePsvaried from 0.8 to 3 Pa, or with substrate temperatureTsvaried from 100 to 300 °C. For films deposited with an argon plus hydrogen ambient, the deposition rate was found to increase with increase inPsand decrease with an increase inTs. For films prepared with an argon ambient only, the deposition rate increased slightly with an increase inPsorTs. The deposition rate was also approximately two to eight times higher when sputtering was carried out in an argon plus hydrogen ambient than in argon only. Infrared (IR), x‐ray photoelectron (XPS), and Raman spectroscopies were employed in the structural analysis. The IR results showed that the Si–C bond gave the most prominent absorption peak and was affected by changes inPs. The Si–H and SiHnstretching modes were observed in all films, and the amount of Si–H bondsNSi–Hwere found to increase asPsorTswas increased. The C–Hnstretching mode was absent in all films, and this was attributed to the low carbon content in these films.The Si–N stretching mode was suggested to contribute to the extra features between 800 to 1100 cm−1in the IR spectra for films prepared at a higherPs(3 Pa) orTs(300 °C). The stoichiometry of silicon carbide and the film composition were determined by the XPS method. The carbon content of silicon carbide was found to be similar to the target composition and varied only slightly with changes inPsorTs. The Raman spectra showed that only the C–C bond can be detected in all of the films. From the electrical measurements, the film’s conductivity was found to reduce from 4.21×10−9to 4.35×10−11&OHgr;−1 cm−1asPswas increased from 0.8 to 3 Pa; and decreased from 3.81×10−9to 1.31×10−8&OHgr;−1 cm−1whenTswas raised from 150 to 300 °C. The conductivity was found to be related toNSi–H, with higherNSi–Hresulting in lower conductivity. A comparison with data published in the literature suggested that rf sputtering technique was not effective in varying the carbon content in amorphous silicon carbide film. This technique, however, can be used to varyNSi–Hand thus change the structural and electrical properties of the sputtered films. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360377

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Transversely excited atmospheric pressure CO2and modulated continuous‐wave CO2laser marking of soda‐lime and borosilicate glasses has been investigated as a function of laser fluence and pulse duration. Marks are formed by a combination of surface crazing and material removal, the latter occurring predominantly through particles that are fractured from the surface. Various possible fracture mechanisms are analyzed and residual surface stress following rapid laser heating is identified as the most likely cause of microcracking. Scanning electron microscope studies show that relatively large fragments are produced, with a characteristic thickness that is dependent on the laser pulse duration, but that they predominantly remain locked in the surface. Gas phase products evolved during the interaction have also been subject to evaluation using spectroscopy of the luminous plume and fast photography techniques. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360378

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Hydrogenated amorphous silicon (a‐Si:H) films having a thickness of 7 &mgr;m were deposited on molybdenum by dc glow discharge and then capped with a 0.1‐&mgr;m‐thick aluminum (Al) layer by thermal evaporation. Subsequent vacuum annealing at 500–725 °C resulted in the formation of crystalline Si, as observed by Raman scattering and x‐ray diffraction. This was in contrast to the uncappeda‐Si:H films which were still amorphous at the same annealing temperatures, except at ≳700 °C. That the Al capped films were crystalline caused a ten‐fold increase in the dark conductivity in comparison to the uncapped film annealed at the same temperature. The capped films annealed at 500 °C showed a photoresponse (the ratio of the photoconductivity to dark conductivity) of 30, a photoconductivity of 2×10−4(&OHgr; cm)−1, and a carrier diffusion length of 5.3 &mgr;m—values much higher than those of the uncapped films (heated or not). This was due to a large grain size combined with the retention of hydrogen, which passivated the grain boundaries. On the other hand, a significant loss of hydrogen from the capped film at 580 °C, as observed byinsituevolved gas analysis, resulted in the diffusion length reducing to 1.8 &mgr;m and ten‐fold decreases of the photoconductivity and photoresponse. All three parameters increased slightly with a further increase in the annealing temperature from 600 to 680 °C, due to the increase in the grain size. At 695 °C, further hydrogen evolution caused a sharp decrease in the values of these parameters. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360769

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Tungsten (W) films are deposited from tungsten hexafluoride on sputter‐deposited TiN adhesion layers in a cold‐wall chemical vapor deposition reactor. The film resistivity of the W films is found to be thickness dependent. It decreases monotonically with increasing film thickness. Typical resistivity values of 40‐nm‐thick W films are about 19.3–23.4 &mgr;&OHgr; cm, depending on the structure of the underlying TiN layer used. The resistivity of a 980‐nm‐thick W film is 9.8 &mgr;&OHgr; cm. Oxygen and fluorine impurities, as well as structural difference in the W films are found to be the major causes for the resistivity variations. Lowering impurity level and/or increasing W crystallite size can decrease film resistivity. The stress of all the W films is found to be tensile, independent of the structure of the TiN layers. However, the absolute value of the stress is intimately associated with the structure of the TiN layers. The stress values can differ by a factor of more than 2 for the 40‐nm‐thick W films deposited on the different underlying TiN layers. The amplitude of stress also monotonically decreases with increasing film thickness. Consequently, the difference in stress induced by the difference in the underlying TiN layers gradually disappears as the film thickness increases. A strong correlation between the stress and the film texture is found. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360379

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Glass formation between PbO and KF is reported. The influence of composition on thermal stability, density, molar volume, refractive index, optical band gap, Urbach energy, and Pb2+emission spectra are presented. While KF influences thermal stability, the PbO content markedly influences the optical properties due to the formation of strong ‐Pb‐O‐Pb‐ covalent linkages. Increasing PbO content also results in phonon assisted nonradiative decay from1P1and3P1levels to3P0level leading to a marked decrease in the1P1→1S0emission. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360380

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A moment‐based model for the time evolution of extended defect size distributions is introduced as a computationally efficient method for the quantitative modeling of precipitation processes. Because the model accounts for how the size distribution of aggregates changes with time, it is able to account for thermal history effects that are missed by simpler models. However, by considering only the lowest moments of the distribution rather than the full distribution itself, the model can be practically applied to nonhomogeneous systems for which it is impractical to include the full distribution at every point in space. The model is tested by implementing it in a process simulator and applying it to the simultaneous diffusion and activation/deactivation of dopants in silicon. Under the conditions compared, we find that the reduced model is nearly equivalent to a previously studied model [S. T. Dunham, J. Electrochem. Soc.142, 2823 (1995)] maintains the full size distribution and is thus much more computationally intensive. Because the reduced model is derived directly from the more complete model using an energy‐minimizing closure assumption, all parameters retain a physical interpretation and the model can be readily extended to a large range of systems. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360381

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have fabricated and measured the performance of semiconducting YBaCuO thin‐film thermometers on silicon for uncooled bolometric applications. Our YBaCuO thermometers have revealed a change in resistance with respect to temperature (dR/dT) as high as 8.2×103&OHgr;/K atT=294 K and the temperature coefficient of resistance as high as 3.1% K−1over a 60 K range around room temperature which implies an excellent bolometric response. At 294 K the thermometers had a noise voltage of 0.75 &mgr;V/Hz1/2at the frequency of 30 Hz and the bias current of 1 &mgr;A. Using the data above, we calculated that semiconducting YBaCuO bolometers would have a responsivity of 5.5×104V/W and a detectivityD* as high as 1.3×108cm Hz1/2/W for 1 &mgr;A bias current if integrated with a typical thermal isolation structure. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360382

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Analysis of a quantum superconducting kinetic inductance photodetector (QSKIP) structure is presented for operation in a low background environment. We project the QSKIP’s spectral response to be limited by the Cooper pair binding energy, 2&Dgr; or about 32 &mgr;m for YBCO. The QSKIP response and sensitivity are computed from the minimum of the Hamiltonian energy functional and linearized Rothwarf–Taylor equations. Photoresponse and sensitivity expressions are computed in terms of the quasiparticle lifetime and indicate background limited infrared performance at very low photon flux levels. At low temperatures and under background limited infrared performance conditions, the photoresponse is proportional to the number of absorbed photons. Operating the QSKIP in the Meissner state and below 50% of the critical current limits the noise sources to fluctuations in the condensate population. With the noise and photoresponse equations, the QSKIP noise equivalent power is computed in terms of the characteristic lifetimes of: quasiparticle generation; quasiparticle recombination; anharmonic phonon decay; and phonon trapping. The calculated noise equivalent power for a YBCO QSKIP is about 2.5×10−15W/&sqrt;Hz at 9 K. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360383

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Electronic devices exhibiting bistability in the current‐voltage characteristics are considered from a unified viewpoint. We obtain simple relations for the stability of the different branches in the current‐voltage characteristics. Criteria for oscillatory instabilities are discussed, and special conclusions for elements with S‐ or Z‐shaped characteristics are drawn. The stabilization of the middle branch of the double‐barrier resonant‐tunneling diode in a circuit with effectively negative capacitance and negative resistance is derived in a simple way. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360384

出版商:AIP    

年代:1995

数据来源: AIP