摘要:

Lead titanate films were fabricated from their oxides and spin coated over alumina (Al2O3) and zinc sulphide (ZnS) substrates. Compositional analysis and surface morphology studies are done by x rays and the scanning electron microscope, respectively. The studies on electrical behavior of these films reveal the existence of phase transition at ∼850° K, which is confirmed as the Curie temperature (Tc) by temperature dependence of the dielectric constant. At room temperature, the real and imaginary parts of the permittivity exhibit a relaxation dispersion up to 100 GHz and indications of a resonance around 200 GHz.

ISSN:0021-8979    

DOI:10.1063/1.353262

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Employing photoluminescence (PL) spectroscopy, we have carried out a detailed study of the characteristics and origin of the 1.681 eV luminescence center in chemical‐vapor‐deposited (CVD) diamond films. In addition to the zero‐phonon line (ZPL), the fine structure of the PL emission spectrum revealed vibronics corresponding to both phonon emission and phonon absorption. Most of the vibronics can be identified with known lattice phonons in a natural diamond, although a few of the peaks appear to be associated with a local vibrational mode. The emission intensity was found to be a strong function of the CH4/H2ratio used to grow the diamond films. Decreasing the methane concentration from 2.0% to 0.25% resulted in an increase of about four orders of magnitude in the PL intensity. It has been found that residual stress on the order of 0.5 GPa in the diamond film quenches the PL emission intensity but has no measurable effects on the peak position and half‐width of the 1.681 eV ZPL. Temperature has a marked influence on the PL emission characteristics. With increasing temperature, the emission intensity decreases, the peak position shifts to lower energy, and the half‐width broadens. Some of these results provide further support to the conclusion arrived at recently by some researchers that the 1.681 eV center, characteristic of ‘‘high‐quality,’’ CVD‐grown diamond films, is not the GR1 center present in radiation‐damaged bulk diamond. The plausibility of the Si‐impurity model, proposed to explain the origin of this 1.681 eV center, was critically examined.

ISSN:0021-8979    

DOI:10.1063/1.353239

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

In this article we present the experimental results for the pressure variation of the refractive index of sapphire up to 16 GPa, obtained with an interferometric method, using the diamond anvil cell. In the range of hydrostatic pressures, up to about 12 GPa, the analysis of the results with the classic Lorentz–Lorenz approach provides a nearly linear relation between polarizability (&agr;) and volume, corresponding to a constant strain polarizability parameter. For pressures above 12 GPa, there is a substantial nonlinear deviation, associated with nonhydrostatic effects inside the diamond anvil cell.

ISSN:0021-8979    

DOI:10.1063/1.353240

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The temperatureTeof photoexcited carriers in semi‐insulating GaAs wafers is determined with high lateral resolution by topographic measurement of the spectrally selected band‐to‐band recombination luminescence intensityIPL. It is also calculated from a detailed balance between carrier excitation and recombination, taking into account optical phonon, electron‐electron, piezoelectric, and acoustic phonon scattering processes. Comparison of the experimental and theoreticalTedata yields the lifetime &tgr; of the photoexcited carriers, which is thus obtained without time‐resolved measurement. The lifetime results are corroborated by comparison of the measured and calculated dependence ofTeon the laser excitation power. The relation betweenTeand &tgr; for given excitation power allows for the generation of two‐dimensional high‐resolution lifetime topograms. The correlation with conventionalIPLtopograms is direct, duplicating the lateral cellular pattern with comparable fluctuation amplitude. From these properties, it is inferred that &tgr; is dominantly determined by inhomogeneously distributed nonradiative recombination centers. Their concentration is low in the walls of the dislocation network and high in the interior of the cells. The statistical evaluation ofTetopograms allows for an application‐oriented comparison of the quality and homogeneity of GaAs wafers.

ISSN:0021-8979    

DOI:10.1063/1.353241

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The study of the excitation efficiency &eegr;excon thin‐film electroluminescent devices with special semiconductor layer—a very thin probe‐doped layer located at different part of the pure ZnS layer—has proved that &eegr;excis not homogeneous across the active layer. Moreover, this variation of &eegr;excdepends on the amount of the transferred charge. At high excitation range, &eegr;excdecreases continuously from the cathode toward the anode of the active layer. This behavior of &eegr;excis related to a space charge located in some part of the ZnS layer and generated by the energetic electrons. This space charge reduces the total efficiency of a conventional device when operating at high excitation range.

ISSN:0021-8979    

DOI:10.1063/1.353242

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Exposing the photorefractive material bismuth silicon oxide (BSO) at low temperatures to 2.4–3.3 eV light produces photochromic absorption bands. In undoped and Fe‐doped BSO these bands appear to consist of a series of overlapping bands ranging from around 1.5 eV in the infrared to near the band edge. The infrared component is always weaker than the visible range contributions. The infrared portion anneals just above 100 K; in some samples this anneal is accompanied by the appearance of additional structure in the visible region. In undoped BSO the major anneal of the photochromic bands takes place above 200 K. If iron is present the photochromic bands are weaker and an anneal stage in the 120–150 K range appears. Bleaching with either 1.51 or 2.28 eV laser light uniformly lowered the photochromic bands in both undoped and Fe‐doped BSO. In BSO:Al the aluminum electronically compensates the deep donor centers responsible for the yellow coloration observed in undoped crystals. At low temperatures, photoexcitation using near band‐edge light produces the same overlapping bands at 1, 1.38, and 2.45 eV that were observed in BGO:Al. These bands anneal together between 80 and 100 K. The [AlO4]0center which causes the coloration observed in smoky quartz is a plausible model for the photochromic bands in BSO:Al.

ISSN:0021-8979    

DOI:10.1063/1.353243

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Hydrogenated amorphous silicon selenium alloy was prepared by plasma enhanced chemical vapor deposition with hydrogen dilution. The alloy films exhibited a low hydrogen content and a dense amorphous network. Light induced photoconductivity degradation and light induced variation of dangling bond density of the alloy films were investigated under 1 sun white light and an intense light illumination. The results show that the amorphous silicon selenium alloy is a stable photovoltaic material.

ISSN:0021-8979    

DOI:10.1063/1.353244

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Reflection–absorption infrared spectroscopy, Auger electron spectroscopy (AES), temperature programmed desorption, and reactive scattering were used to investigate the adsorption and desorption behavior of PEt3on copper and chlorinated copper surfaces under ultrahigh vacuum conditions. No reaction was observed between PEt3and clean Cu(100) or between PEt3and ac(2×2)–Cl overlayer. At temperatures above 320 K, PEt3reacted rapidly with a heavily chlorinated copper surface (10 000 L exposure of Cl2at 300 K). Subsequent examination of the substrate by AES showed removal of chlorine and presumably copper. The remaining chlorine corresponded roughly to 0.5 monolayer coverage. This is consistent with reactive scattering, infrared and AES experiments carried out on thin chlorinated layers (8 L Cl2exposure), where essentially no reaction of PEt3with the surface was observed. The reaction between PEt3and a heavily chlorinated Cu(100) surface yields both ClCu(PEt3)2and Cl2PEt3. These data are consistent with the etching of copper under ultrahigh vacuum conditions at low temperatures by reaction with Cl2and PEt3to form CuCl(PEt3)2.

ISSN:0021-8979    

DOI:10.1063/1.353219

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A closed form analytic solution to the growth characteristics of the separation by implantation of oxygen (SIMOX) buried oxide and silicon film, based on a two‐sided Gaussian approximation to the oxygen implant profile in the SIMOX process, is presented. The model used includes the effects of substrate swelling and sputtering due to the implanted oxygen, as well as the effects of saturation of the oxygen density at the stoichiometric SiO2level in the implanted region. The results of this investigation show that for typical SIMOX implant conditions currently used in high‐current implanters, the total dose of oxygen required to first reach the saturation level is only slightly dependent on the swelling and sputtering effects associated with the oxygen implantation, and that the deviation of the location of the first saturation point from the commonly used implant range can be significantly affected by the implant profile. In addition, it is shown that a ‘‘natural parameter’’GNsat, whereGis the net growth of the substrate per implanted oxygen atom andNsatis the saturation level of oxygen atoms in the buried oxide, can be used to characterize the magnitude of the effects of the implant parameters on the final SIMOX material. It is also shown that the parameterGNsatcan be easily obtained from the slope of aToxvsTsiplot.

ISSN:0021-8979    

DOI:10.1063/1.353220

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Plasma etching has became an indispensible technique for microelectronics device manufacturing. However, its application is often limited by the wafer temperature increase due to the ion bombardment, which may exceed the susceptor temperature by as much as 200 °C when the semiconductor wafer is loosely lying on the cooled susceptor. The aim of this study is to perform an accurate evaluation of heat transfer in an industrial etching reactor, and in particular to point out the critical role of the susceptor/substrate interface in this problem of damageable overheating. The required experimental precision, necessary to reach this goal, is based oninsitutemperature monitoring via fluoroptometry, and on electrical characterization of the plasma to investigate the effective heating power dissipated on the substrate. It is thus shown that the only wafer heating source to be considered is the real electrical rf power dissipated in the plasma, and that the heated substrate evacuates the main part of this power to the cooled susceptor, via thermal conduction through the residual gas present in the interface between these two elements. A non‐negligible part of energy can also be lost via thermal radiation. The thermal conduction through the interface is shown to be strongly dependent on the gas pressure, and the quasilinear rate obtained is evidence for the molecular regime of the gas molecules in this region. The type of gas also strongly affects the interface heat flow, and in a quite uncommon way: an effect of thermal conductance inversion between two different types of gases when the pressure decreases is observed. A criterion is proposed to evaluateaprioriand in a qualitative point of view whether a given couple of gases may exhibit this effect, which consequences are very important from a technological point of view.

ISSN:0021-8979    

DOI:10.1063/1.353221

出版商:AIP    

年代:1993

数据来源: AIP