摘要:

A novel method to obtain diffusion-controlled atomic concentration profiles in II–VI semiconductor heterostructures has been developed using high-resolution x-ray diffraction. Measured diffraction spectra are compared with simulations based on direct summation of scattered waves across the heterostructure. In this approach, short-range variations of structural parameters, including the concentrations of the components, interface roughness, etc., can be easily introduced into the simulation routine. The application of the fitting procedure to the experimental spectra taken from variously annealedCdTe/Hg1−xCdxTeheterostructures grown by metal organic chemical vapor deposition, allowed determination of the Hg (or Cd) concentration depth profile as a function of the annealing temperature. As a result, the activation energy and the pre-exponential coefficient for mercury diffusion was found. The diffusion profiles derived from x-ray diffraction spectra were compared with secondary-ions mass spectrometry results, and the advantages of the new method are discussed. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366119

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We describe a new technique to prepare cells of smecticC*films with a uniform bookshelf texture that can be bistably switched. This is achieved with a homeotropic surface coating with weak anchoring properties. The surface of one plate was modulated by parallel stripes of a polymer which hinder flow perpendicular to the stripes. This gives bias to field induced flow effects and enhances alignment by periodic switching. The resulting texture is uniform with smectic layers normal to the cover plates and parallel to the deposited stripes. The stripes also help to reheal textures with defects. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366120

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have studied the strain relaxation inSi1−xGex/Si(001) structures with high electron mobility grown by molecular beam epitaxy. The structures contain aSi1−xGexlayer with linearly graded composition, followed subsequently by a uniform composition bufferSi1−yGey,a thin Si layer serving as two-dimensional electron gas channel, and a modulationn-dopedSi1−xGexlayer. We found that a major part of the graded layer is basically completely strain relaxed, whereas a very thin layer close to the graded-uniform layer interface, as well as the uniform alloy buffer, are just partly relaxed. We performed also model calculations of the strain status of a graded-uniform two-layer system using an equilibrium approach. It is found that for ourSi0.7Ge0.3systems, the residual strains of the samples with different composition, grading rate, and a uniform buffer thickness of 0.6 &mgr;m is almost the same at equilibrium. However, experiments show a clear dependence of the residual strain on the grading rate of the graded buffer. The higher the grading rate, the higher is the residual strain in the constant composition alloy buffer. This indicates that with a lower grading rate, the structure is closer to equilibrium, and is thus, thermally more stable. Furthermore, lower grading rates produce also smoother surfaces. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366281

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A detailed characterization of undoped and heavily boron-dopedSi1−xGexlayers withx=0.21,0.26, and 0.34 grown on (001) Si wafers by solid phase epitaxy is presented. The starting material for solid phase epitaxial growth was prepared by amorphization of epitaxial SiGe-Si heterostructures by ion implantation. In order to obtain doped layers, boron was also implanted into some of the amorphous samples. After regrowth, the strain depth distributions of the SiGe layers were measured using axial channeling angular scans and the defect distributions were observed by high-resolution electron microscopy. A defect-free region ranging from 0 nm (undoped layer ofx=0.34)to 30 nm (doped layer ofx=0.21)in thickness was observed next to the layer-substrate interface. In the upper region of the layers, strain-relieving defects, identified as planar faults, were observed. Some isolated defects were also present at the layer-substrate interfaces of most of the samples. The measured strain depth profiles show that (i) the defect-free regions are not always fully strained; the defects located at the interfaces being responsible for this partial relaxation; (ii) the strain is almost constant throughout the defect-free layers because it cannot be relieved due to the absence of defects; and (iii) the strain progressively decreases towards the sample surfaces in the region of the layer where the strain-relieving defects are located. Comparison between the undoped and boron-doped layers show the consequences of the strain compensation effect due to the incorporation of boron atoms into the lattice. The defect-free regions of the doped layers are thicker and closer to coherency than those in the undoped layers of the same composition and the defect density in the upper region of the layers is significantly reduced. As a result of the strain compensation effect, a 30-nm-thick heavily doped layer withx=0.21is found to be defect free and fully strained throughout its whole thickness although the corresponding undoped layer was partially relaxed and showed strain-relieving defects. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366121

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

CuInxGa1−xSe2thin films, with variousGa/(Ga+In)ratios, suitable for solar cells were processed by selenizing stacked Cu, Ga, and In precursor layers in aH2Sereactor in the temperature range of 400–500 °C. Cu/Ga/In and Cu/In/Ga precursors were obtained by sequential sputtering of the elemental layers. The Cu/Ga/In and Cu/In/Ga precursors, and the selenized films were characterized by scanning electron microscopy, x-ray diffraction, energy dispersive spectroscopy, and Auger electron spectroscopy. The precursors contained only binary and elemental phases in the as-deposited condition and after annealing. The selenized films had a nonuniform distribution of Ga and In. The surface of the selenized films were In rich, while the Mo/film interface in these films was Ga rich. The selenized films withGa/(Ga+In)ratios greater than 0.25 contain graded Ga and In compositions, and the selenized films withGa/(Ga+In)ratios less than 0.6 contain a phase-separated mixture ofCuInSe2andCuGaSe2with theCuInSe2near the surface and theCuGaSe2near the Mo/film interface. Single phase, homogeneousCuInxGa1−xSe2films were obtained by annealing the as-selenized films in argon in the temperature range of 500–600 °C for 60 min. Interdiffusion of In and Ga between theCuGaSe2and theCuInSe2phases was found to be responsible for the homogenization process. This homogenization process does not occur in the presence of a selenium atmosphere. Diffusion measurements yielded similar interdiffusion coefficients for Ga and In. The annealing temperature and time to effect homogenization depends on theGa/(Ga+In)ratio of the absorber films. Films with lowerGa/(Ga+In)ratios require a homogenization temperature of 600 °C or more and films with higherGa/(Ga+In)ratios homogenize at a lower temperature of 400–500 °C, for an annealing time of 60 min.    

ISSN:0021-8979    

DOI:10.1063/1.366122

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Spectroscopic ellipsometry over the spectral range from 700 to 3000cm−1and from 1.5 to 3.5 eV is used to simultaneously determine phase and microstructure of polycrystalline hexagonal and cubic boron nitride thin films deposited by magnetron sputtering on (100) silicon. The results are obtained from a single microstructure-dependent model for both infrared and visible-light thin-film anisotropic dielectric functions. The optical behavior of highc-BN content thin films is described by an effective medium approximation. We obtain the amount ofh-BN within highc-BN content thin films. A thin oriented nucleation layer between the silicon substrate and the highc-BN content layer is demonstrated. The preferential arrangement of the graincaxes within theh-BN thin films are found to be dependent on the growth parameters. The results from the infrared and visible spectral range ellipsometry model are compared to each other and found to be highly consistent. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366123

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Extended x-ray absorption fine structure (EXAFS) measurements ofCo78Cr22, Co86Cr12Ta2,andCo86Cr12Pt2films were made to investigate the local structure and chemistry around Ta and Pt atoms to determine their site distributions in these alloys. Comparisons between the measured data and data collected from experimental standards and calculated using theoretical EXAFS simulation codes indicate that the Ta atoms are preferentially distributed to the Cr-enriched regions of the CoCr media, and the Pt atoms have an effect on the local environment of the Co atoms. Both Ta and Pt introduce a large amount of local structural disorder to the local environments in which they reside. The presence of Ta atoms in the Cr-enriched regions further reduces the magnetization of these regions, which enhances the magnetic isolation of the Co regions from each other. This helps improve the noise characteristics of the films. The portion of the Pt atoms residing in the Co-enriched regions increases the magnetic anisotropy of the films, thereby increasing their coercivity. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366124

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Microwave heating was utilized for solid phase crystallization of amorphous silicon films. The amorphous silicon thin films were deposited in the temperature range of 100–400 °C by plasma enhanced chemical vapor deposition and annealed by microwave heating at 550 °C in nitrogen. Microwave heating lowered the annealing temperature and reduced the annealing time for complete crystallization. For example, thea-Si film deposited at 400 °C was fully crystallized in 3 h at 550 °C. On microwave heating, the hydrogen in the amorphous films diffused out very quickly, but there was no change in structural disorder following hydrogen evolution. The lower temperature crystallization ofa-Si films compared to conventional furnace annealing is due to the interaction between microwave and silicon atoms. The grain size of the crystallized silicon films was in the range of 0.55–0.78&mgr;m, depending on the deposition temperature. These grain sizes are not so small compared to those of Si films crystallized by conventional furnace heating, while the crystallization time is much shorter. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366125

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The presence of undesirable hydrogen-related impurities and the resulting stress instability in chemical vapor deposited silicon dioxide films are important issues. In this work, the bonding nature and stress behavior of relatively low-temperature deposited silicon dioxide films deposited at high rates were investigated. Films were deposited at 1000 Å/min and at a substrate temperature in the 250–350 °C range. A considerable change in stress was observed in these films upon annealing in the 250–400 °C temperature range. Both as-deposited and annealed films were then stored in a cleanroom environment for long periods of time, and their stress was monitored intermittently. In parallel, Fourier transform infrared studies were performed on an identical set of as-deposited and annealed films to investigate changes in the bonding nature of the films during aging. Thus, film stress and their bonding nature were studied concurrently over an extended period of time. Si–H and silanol (Si–OH) were identified as impurities responsible for the observed stress instability of the deposited films. Initial concentrations of these impurities have been observed to vary depending on the deposition conditions. Also, depending on the concentrations of these impurities, both reversible and irreversible bond reconstruction were observed in the films upon annealing. Concomittantly, reversible and irreversible changes in stress were observed in annealed films, the amount of change depending on the impurity type and content. Impurities responsible for reversible and irreversible bond reconstruction were identified. Good correlation between film stress and bonding was observed. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366126

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have investigated the detailed process of agglomeration ofTiSi2thin film on (100) Si substrates as a model system for our recent geometrical model of agglomeration based on the spheroidization at both the surface and film/substrate interface. Agglomeration occurs by a nucleation of holes at grain-boundary vertices as a result of spheroidization at both interfaces and by their subsequent growth along grain boundaries in accordance with the prediction of our model. The critical condition of the ratio of the grain size to film thickness is predicted and confirmed to be between 5 and 6 depending on the magnitude of free-energy barrier. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366127

出版商:AIP    

年代:1997

数据来源: AIP