摘要:

We have investigated the structural properties of ZnSe epilayers that were molecular beam epitaxially grown on (001) GaAs substrates with different tilt angles and tilt directions. We measured the properties of the epilayers by x-ray diffraction, transmission electron microscopy, and etch pit density analysis. Tilting the (001) GaAs substrate toward [010] was very effective in reducing the surface defect density of the ZnSe layers, while tilting toward the [110] direction was of no use. We could observe the increasingly two-dimensional nature of the initial growth mode in the (001) GaAs substrate tilted toward [010]. Growth of a 1.8-&mgr;m-thick ZnSe layer on (001) GaAs tilted 4° toward [010] resulted in a very low surface defect density of 1×104 cm−2.Such a low defect density has seldom been obtained in ZnSe, without growing a GaAs buffer layer below the ZnSe layer. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364372

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We discuss a new method to characterize multilayer structures with grazing-incidence reflectivity measurements using hard x-ray radiation, such asCu-K&agr;orMo-K&agr;radiation. The method is based on the analysis of the reverse Fourier transforms of the reflectivity at the Bragg peaks in q-space, the reflectivity data being obtained from an angular scan (&thgr;−2&thgr;). This method is faster than curve fitting of the reflectivity data, results in an accurate value of the density and thickness of both materials, and needs no pre-assumptions about the material composition and the parameters of the multilayer. The method makes a distinction between interface roughness and layer thickness errors, and is independent of measurement of the critical angle. A minor disadvantage is that only an average value of the layer thickness is determined, rather than the individual layer thicknesses. As an example our method is used to analyze small-angle reflectivity measurements of Mo/Si and Co/C multilayers. The parameters thus obtained are used to model a structure, which is subsequently used to predict the near-normal incidence reflectivity at soft x-ray wavelengths. The accuracy thus found corresponds to a relative error of 5&percent;. The densities of a Mo/Si multilayer are determined independently with critical angle measurements to verify the values obtained from the grazing incidence reflectivity measurements. The results of the analysis of the Co/C multilayer are compared to values obtained using a conventional method based on the kinematical theory. However, the conventional method requires additional data of soft x-ray reflectivity measurements. The new method yields the same values for the multilayer parameters but does not require the extra soft x-ray measurements. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364360

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have investigated the elastic properties of epitaxial MnTe layers using triple axis high resolution x-ray diffraction and reciprocal space mapping. A series CdTe/MnTe superlattices (SLs) grown by molecular beam epitaxy and nearly strain compensated, were deposited on [001]Cd1−xZnxTesubstrates. In order to obtain the MnTe content of these SLs without ana prioriknowledge of the elastic properties of cubic MnTe, annealing experiments were performed to interdiffuse the individual layers into a mixedCd1−xMnx Tealloy layer. For a precise analysis of the data, it was found to be important to determine the in-plane strain of the superlattice layers using reciprocal space maps around symmetric and asymmetric reciprocal lattice points. The value for the Poisson ratio of zinc-blende MnTe was determined to be&ngr;=C11/2C12=0.77±0.15.©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364392

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The orientational crossover phenomena in a radio frequency (rf) sputtering growth of TiN films were studied inin situ, real time synchrotron x-ray scattering experiments. For the films grown with pure Ar sputtering gas, the crossover from the (002)-oriented grains to the (111)-oriented grains occurred as the film thickness was increased. As the sputtering power was increased, the crossover thickness, at which the growth orientation changes from the ⟨002⟩ to the ⟨111⟩ direction, seemed to decrease. The addition ofN2besides Ar as sputtering gas suppressed the crossover, and consequently resulted in the (002) preferred orientation without exhibiting the crossover. We attribute the observed crossover phenomena to the competition between the surface and the strain energy. The x-ray powder diffraction, the x-ray reflectivity, and theex situatomic force microscopy surface topology studies consistently suggest that the microscopic growth front was in fact always the (002) planes. In the initial stage of growth, the (002) planes were aligned to the substrate surface to minimize the surface energy. At later stages, however, the (002) growth front tilted away from the surface by about 60° to relax the strain, which caused the crossover of the preferred growth direction to the ⟨111⟩ direction. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364394

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The annealing behavior of pseudomorphic Si0.603Ge0.397/Si and Si0.597Ge0.391C0.012/Si superlattice structures was studied in the temperature range between 750 °C and 900 °C. Carbon incorporation of 1.2&percent; changes the thermal stability of SiGe structures significantly. It suppresses plastic relaxation due to an effective dislocation pinning. No relaxation of the SiGeC sample was observed during annealing up to 875 °C for 3 h. For comparison the SiGe sample relaxed at 800 °C. Carbon strongly increases the interdiffusion of Ge and Si. The activation energy of this diffusion process for a Ge content of 40&percent; decreases from about 4.8 eV for the pure SiGe to about 2.0 eV with an additional C content of 1.2&percent; assuming a neglectable diffusion of the carbon. This leads to a distinct modification of the Ge profile in the investigated temperature range. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364361

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Silicon carbide films were grown on (100) silicon substrates by deposition of 200-nm-thickC60films, followed by annealing. The predepositedC60is progressively destroyed by annealing, and carbon reacts with silicon to produce SiC. The reaction starts at the interface and continues by diffusion of silicon through the already formed SiC. At the lower temperatures (700 °C), the reaction is localized at the interface. Diffusion of silicon and formation of stoichiometric SiC requires annealing at 800 °C fort⩾100 minand at 900 °C fort⩾25 min.The stoichiometric films are uniform with a grain size of 20–40 nm. A diffusion coefficient of silicon in SiC of4×10−15 cm2/sat 900 °C was determined. Because the diffusion of silicon is faster through preferential paths in the SiC film, such as grain boundaries and other crystalline defects, pits and voids are produced in the silicon substrate when theC60predeposited film covers larger areas. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364395

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Chemical bonding and local order around the different atoms of thick amorphousSiCxNydeposits[0.03⩽x/(x+y)⩽0.67] prepared with chemical vapor deposition at 1000–1200 °C usingTMS–NH3–H2have been investigated using x-ray photoelectron spectroscopy (XPS), Raman spectrometry, Fourier transform infrared spectrometry (FT-IR), electron energy loss spectroscopy (EELS) and29Simagic-angle spinning nuclear magnetic resonance spectrometry (MAS-NMR). XPS analyses have shown that the main bonds are Si–C, Si–N, and C–C, and have suggested the existence of C–N bonds. According to Raman analyses and complementary FT-IR absorption of thin films, the coatings are nonhydrogenated. Si, C and N atomic chemical environments are more complicated than in a mixture of pureSi3N4–SiCphases. The examination of theSi KL2,3L2,3line shapes recorded by XPS have allowed one to state the existence ofSi(C4−nNn)units. Mixed coordination shells around silicon have been confirmed by EELS analyses. Additionally, FT-IR reflection analyses have proved that Si is both bonded with N and C. Indirect indication has been obtained owing to the29SiMAS-NMR analyses of powders. Raman analyses have been conclusive to assume that C–C bonds correspond to a mixedsp3−sp2carbon configuration linked withSi(C4−nNn)tetrahedra with0⩽n⩽4.©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364396

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Deep level defects in electron-irradiated4HSiC epitaxial layers grown by chemical vapor deposition were studied using deep level transient spectroscopy. The measurements performed on electron-irradiatedp+njunctions in the temperature range 100–750 K revealed several electron traps and one hole trap with thermal ionization energies ranging from 0.35 to 1.65 eV. Most of these defects were already observed at a dose of irradiation as low as≈5×1013 cm−2.Dose dependence and annealing behavior of the defects were investigated. For two of these electron traps, the electron capture cross section was measured. From the temperature dependence studies, the capture cross section of these two defects are shown to be temperature independent. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364397

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A surface characterization study using ion scattering spectroscopy (ISS) and x-ray photoelectron spectroscopy (XPS) has been performed on solvent cleaned,n-type GaAs(001) substrates before and after cleaning by ion sputtering and annealing. The native oxide layer on this surface contains large amounts ofAs2O5,As2O3,andGa2O3according to XPS withGa2O3being the predominant species. Before cleaning C is present as hydrocarbons, carbonates, and carbide with hydrocarbons as the predominant chemical state. Ion sputtering converts the hydrocarbons into carbide, which is difficult to remove by further sputtering/annealing cleaning cycles, but O is removed by these cycles. According to ISS data, the outermost atomic layer is enriched in Ga before cleaning, but after cleaning the ISS Ga-to-As atom ratio is about 1:2. The results obtained in this study are consistent with the presence of a layered oxide structure withGa2O3just above the interface. A sputter-cleaned surface initially exhibits an increase in the Ga-to-As surface atom ratio which returns to the initial state with time(∼2 h)as observed by ISS. The Ga-to-As surface atom ratio also increases by annealing at temperatures as low as 180 °C. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364398

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The lifetime of II–VI-based blue-green laser diodes on GaAs substrates is limited by rapid degradation in the active layers. This degradation has been observed as dark defects in the active layer during the laser operation, where defects occurred due to stacking faults that originated from theGa2Se3compounds at the ZnSe/GaAs interface. The reported value of the density of stacking faults of the II–VI lasers was in the order of105 cm−2.To extend the lifetime, surface treatment of the GaAs substrate and control of the interface reaction are necessary. We investigated a new treatment technique using hydrogen-radical and Zn/As fluxes. We fabricated ZnSe-based double-hetero (DH) structures on a treated GaAs substrate and measured the density of dark defects in the light emitter area by electroluminescence microscopy. Chemical bonds at the interface were evaluated by x-ray photoelectron spectroscopy. A dark defect density of less than105 cm−2was obtained when the As-terminated GaAs surface was Zn treated. The Zn treatment prevented the formation of theGa2Se3layers. When we alternated the exposure between Zn and As fluxes, excessZnAsxinterfacial layers were formed and the quality of the DH structure was unacceptable. However, hydrogen-radical exposure before and during the Zn/As treatment effectively removed the excessZnAsxcompounds, and the density of dark defects fell to2×104 cm−2.©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364399

出版商:AIP    

年代:1997

数据来源: AIP