摘要:

An approach for the dipole relaxation in polymers is treated considering the dipole–dipole interaction between the molecules. The thermally stimulated depolarization peak parameters, i.e., the activation energyE, the pre‐exponential factor &tgr;0, and the dipole interaction strength parameterq, were evaluated using the iterative technique. Good results are obtained in comparison with other methods. A linear relationship between the activation energy and the logarithm of the pre‐exponential factor of the relaxation times is existing confirming the operation of the compensation law. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359738

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Photoreflectance spectra have recently been obtained for a range of single strained Si1−xGexepilayers for 0.12<x<0.24, which are buried under a Si cap. Spectra measured at different positions on a sample wafer showed pronounced changes in the SiGe line shape. Here these changes are shown to be due to phase shifts arising from changing optical interference effects caused by variations in the Si cap thickness. The phase shifts are determined accurately using a Kramers–Kronig analysis and are interpreted in terms of a multiple‐reflection treatment incorporating a calculation of the Seraphin coefficients. This allows the Si cap thiakness changes to be determined and compared to the0results of speatroscopic ellipsometry measurements. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359739

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Low‐temperature photoluminescence spectroscopy was used to study AlxGa1−xAs intrinsic epitaxial layers in the range of aluminum content between 0.45<x<0.9 in the region where the band gap minimum is indirect. Nonintentionally doped samples were grown by liquid phase epitaxy very near the saturation temperature (∼800 °C). The heterostructures consisted of an AlxGa1−xAs layer grown on top of a GaAs Si‐doped (n∼2×1018cm−3) substrate with orientation (100) 2° toward the (110). There is little information on the zero phonon excitonic lines for Al compositionsx≳0.6, because the appearance of these lines depends on several factors such as internal strength, crystalline defects, and impurities. In our samples the excitonic lines were observable up tox=0.9. Transitions related to bound‐to‐free carrier as well as their phonon replicas were observable too. The data obtained from the spectra fitted with multigaussian lines allowed us to estimate the dependencies on the Al composition,x, of the bound exciton peak, the bound exciton binding energy, and the exciton localization energy. The acceptor ionization energy attributed to carbon residual impurities in As sites and its dependence onxwas also obtained. Fitting by Gaussian lines the phonon region, the PL spectra fitted better with the TO(X) AlAs‐type branch rather than the LO(X) AlAs‐type, with a linear dependence withxin the studied range. The phonon energies of the GaAs type seem to behave almost constant and it was difficult to assign them to the LO(X) GaAs type or to TO(X) GaAs type due to the scatter of the data for high values ofx. Other phonon replicas from the bound exciton and the electron‐to‐acceptor carbon transition (e‐A°) coincide with the LO(X) AlAs type and TA(X), TA(X)+LA(X) and two LA(X) phonon energies. All the dependencies we present here are valid for aluminum compositions in the range 0.48<x<0.90. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359740

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Crystal defects, such as dislocations, introduce electronic states into semiconductors and thereby degrade the desired electronic behavior of semiconductor devices. Special processing precautions are therefore pursued to minimize dislocation densities in semiconductor materials. When light irradiates a semiconductor, incident photons with appropriate wavelengths excite electrons and holes into traps such as point defects and dislocations. This modification of the population of charged defects can modify the flow stress required to propagate dislocations. This effect manifests itself as an inhibition of dislocation motion in type II‐VI compound semiconductors; whereas in type III‐V semiconductors light can enhance dislocation mobility. This effect is known as photoplasticity. In this article we report on the basic characteristics of photoplasticity in CdS and show how it can be exploited to reduce dislocation densities in semiconductor materials. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359741

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The behavior of Ar plasma‐induced defects deactivating Si donors in GaAs has been studied. We have applied photoreflectance spectroscopic analysis combined with stepwise wet etching to the depth profiling of defects and succeeded in determining the concentrations and profiles of defects in the sub‐surface layer for the first time. We found that the point defects responsible for deactivation undergo electronically enhanced diffusion under the circumstance of photoexcited carriers, demonstrating that the ultraviolet light from plasma is a cause of the deep penetration of defects far beyond the stopping range of ions. We also found that the generation of these point defects is enhanced by photoexcited carriers and that diffusing point defects are trapped by the background defects or impurities, forming immobile complexes. We propose a model in which self‐interstitials are the most probable point defects responsible for deactivation. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359742

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Zinc selenide layers grown by molecular beam epitaxy (MBE) and doped with ZnO have been characterized using low temperature photoluminescence (PL) measurements as a function of excitation level, temperature, and laser energy (i.e., selectively excited donor‐acceptor pair luminescence or SPL), as well as reflectance measurements. An O‐related donor‐to‐acceptor (D0−A0) pair band is clearly observed in all of the ZnO‐doped layers, whose position varies from 2.7196 to 2.7304 eV, depending on the excitation level. The same peak occurs in a number of undoped, As‐doped, and Ga‐doped MBE samples, showing that O can occur as a residual impurity. Temperature‐dependent measurements reveal the existence of a corresponding conduction band‐to‐acceptor (e−A0) peak at 2.7372 eV (39.8 K), confirming the existence of the acceptor level. The binding energy of this acceptor is about 84±2 meV, which is 27 meV shallower than that of N. The SPL measurements reveal four excited states of the shallow acceptor level, separated from the 1s3/2ground state by 48.2 (2p3/2), 57.1 (2s3/2), 64.3 (2p5/2:&Ggr;7), and 67.7 meV (3p3/2:&Ggr;8), respectively (all values ±1 meV). These energies fit well to conventional effective mass theory, which demonstrates that this O‐related acceptor level is effective‐mass‐like. However, luminescence and secondary ion mass spectrometry show that the ZnO doping technique introduces shallow donor impurities into the material in addition to O acceptors, specifically high levels of chemical contaminants (mainly B and Ga) originating from the doping source. This effect may account for the lack of reproducibility in obtainingp‐type conduction with ZnO doping, and suggests that more effective O incorporation methods should be devised. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360739

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have carried out a comprehensive study of the Raman spectra ofa‐Si:H films produced by the glow discharge (GD) and radio frequency sputtering (RFS) deposition techniques. The results show that the short‐range disorder (bond‐angle deviation), as measured by the width of the TO band (&Ggr;TO), is larger in RFS than in GDa‐Si:H films. The intermediate‐range disorder (dihedral angle deviation), as measured by the ratio of the intensity of the TA band to that of the TO band (ITA/ITO), is generally larger in RFS than in GDa‐Si:H films. However, while theITA/ITOvalues of RFS films remain relatively close to those of GD films when the interior is probed, the near surface of RFS films shows much larger values evidencing the existence of a significant disorder gradient along the growth axis. Together, these results indicate that the network order and homogeneity of RFS amorphous silicon is lower than those of GD for substrate temperatures that produce the hydrogenated material. These structural differences are interpreted in terms of the differences between the two film growth processes and are believed to be the reason for the poorer transport properties of RFSa‐Si:H films. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359743

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Compositional distributions of films laser depositedinvacuoat energy densities <1 J/cm2were found to be partly different from previous observations and theories. Analyzing them, we have inferred that evaporation processes at low energy densities contain decomposition of the target materials and evaporation of the decomposed materials. Based on these analyses, we have concluded that pulsed laser codeposition was one of best pulsed laser deposition methods. To realize this using one laser source, a modified version of pulsed‐laser‐deposition rapid‐sequential‐pulsed‐laser deposition, is introduced. The dependence of YBa2Cu3O7films properties on deposition conditions is discussed. Elimination of particulates is demonstrated and good electrical and crystallographic properties as well as suppression of precipitates were achieved in films having the correct stoichiometric composition. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359744

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Silicon carbide (SiC) films have been grown on 4 in. diam (100) silicon wafers by atmospheric pressure chemical vapor deposition, using propane, silane, and hydrogen. X‐ray photoelectron spectroscopy data confirm that the films are stoichiometric SiC, with no major impurities. X‐ray diffraction and transmission electron microscopy (TEM) data indicate that the films are single‐crystalline cubic polytype (3C) across the 4 in. substrates. With the exception of slip lines near the edge of the wafers, the films appear featureless when observed optically. The nitrogen concentration, as determined by secondary ion mass spectroscopy, is 4×1018cm3. Cross‐sectional TEM images show a fairly rough, void‐free interface. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359745

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Direct writing of micronscale gold tracks on alumina samples is possible by local thermal decomposition of a metallopolymer spread all over the substrate surface, induced by a tightly focused cw Ar+laser beam. The polymer decomposition occurs at low laser powers and leads to the formation of very pure deposits as shown by SEM+EDS analyses. The influence of laser scan speed and laser power on the carbon contamination and the resistivity of the deposits has been investigated. Line profiles have also been studied as a function of laser scan speed and laser power. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359746

出版商:AIP    

年代:1995

数据来源: AIP