Carbon implantation was performed after high dose(5 x 1016/cm2) Ge implantation into [100] oriented Si substrates to study the effect of sequential implantation on dislocation nucleation. When the nominal peak concentration of implanted C is over 0.55 at%, Dislocations in the SiGe layer containing C are considerably reduced in density after solid phase epitaxial(SPE) annealing at 800°C for 1 hour, compared to the SiGe layer without C. These results suggest that during annealing, C atoms compensate the Geinduced misfit strain which causes dislocation generation in the region of peak Ge concentration. Channeling spectra obtained by RBS analysis show only 5% to 6% minimum back scattering yield as C atoms suppress the dislocation generation.

Raman scattering measurements have been carried out on Si1-xGex/Si SLS. It is found that the Ge–Ge optic phonon frequency shift is proportional to strain in the SiGe film, and the Ge–Ge strain shift coefficient is 408cm−1. Based on these study a new method for analyzing the Raman spectra of SiGe/Si SLS has been proposed. Using the new method we can obtain the composition of the alloy sublayers as well as the strain in SLS. The strain distribution in the SiGe/Si SLS has been discussed, and strain in both SiGe and Si sublayers of the SLS have been calculated.

The range of composition (x) is one of the parameters we often have to measure if Si1-xGex layers are generated by chemical vapour deposition (CVD). It is important in this case, in which way the optical properties of Si1-xGex layers depend on the range of composition. We are interested in using multi-wavelength ellipsometry as a technique for rapid, nondestructive characterization of these samples, without large preparations, especially for series of measurements (2D profiles or wafer-lots). The number of unknown parameters and the multiple solutions are reduced by using several wavelengths during the measurement. The calculation is prepared by the help of parameter-correlation based on results of spectroscopical ellipsometry. To examine the results, thickness and composition were controlled for selected samples by cross-sectional transmission electron microscopy (XTEM) and X-ray double crystal diffractometry (DCD).

The use of both chemical and reactive ion etching for the selective removal of SixGe1-x alloys with respect to both silicon and silicon dioxide has been investigated. We have found that a solution of NH4OH:H2O2:H2O is effective in selectively etching the SixGe1-x films with respect to both of these materials. The chemical composition of the substrate surface after removal of insitu doped SixGe1-x films was evaluated using EDS and SIMS. Diffusion from insitu doped Si0.7Ge0.3, followed by selective removal, was used to demonstrate self-aligned npn dopant profiles with narrow base widths. Reactive ion etching of SixGe1-x alloys was investigated using SF6, CF4, and Cl2 based chemistries. Pressure, power, and gas flow ratios were optimized to provide the least isotropic etch possible for SixGe1-x films containing approximately 40% Ge. Selectivity and degree of anisotropic etching were determined as a function of Ge content for samples with 0% to 100% Ge. Samples were analyzed using SEM and ellipsometry. Highest selectivities were achieved using SF6 and O2.

We have studied the growth of microcrystalline silicon (μc-Si) and amorphous silicon (a-Si:H) by layer by layer deposition technique, where the deposition and the radical exposure are done alternatively. He or hydrogen plasma exposure gives rise to the etching effect of both μc-Si and a-Si:H even though the etch rate by He plasma is much smaller. The long exposure of hydrogen radical on a-Si:H gives rise to the formation of μc-Si at low substrate temperature (Ts), whereas the hydrogen content decreases at high Ts. The growth mechanism of the crystallite is proposed on the basis of experimental results.

The efficient visible tight emitting porous silicon was made using the standard method of anodic oxidation. The characteristic photoluminescence spectra and Raman Scattering spectra of the porous silicon were obtained. A kind of stable yellow powder (not the fragments of the porous silicon thin film the porous structure was still on the crystalline silicon substrate) was taken off from the visible light emitting porous silicon with nonchemical method. The powder can not dissolve in water, alcohol, acetone and some other common solvents, and it still emits efficient visible light after further grinding. The PL spectrum of the powder shows the same peak position, the same shape and the same FW-M as that of the porous silicon wafer. The microstructure of the porous silicon wafer and the microscopic shape of thepowder were studied using the scanningelectron microscopy (SEM) The X–ray photoelectron spectroscopy MSP) shows that the fluorescent powder in the surface layer of the porous silicon is composed of many kinds of elements, such as Si, Q a N and so on. The Si content is only 50% or less in the surface layer of porous silicon. The above–mentioned experiments were performed again on the unpolished surface of the single crystal silicon substrate. So we suggest that the visible luminescence of the porous silicon is from the fluorescent powder maybe not due to the quantum confinement effect in the nm–scate crystalline silicon pillars.

Green photoluminescence (PL) is observed from an as-anodized porous Si wafer immersed in the anodization electrolyte and the PL turns red after the sample is removed from the electrolyte and is blown dry. The PL of porous Si immersed in alcohol exhibits a blue shift and a marked decrease in intensity relatively to dry, as-anodized wafers. However, when the immersed samples are treated with UV for a few minutes, the PL peak shifts to a longer wavelength. Fourier-transform infrared spectroscopy reveals that alkoxy surface species and silicon hydride species backbonded to oxygen atoms appear on the UV-treated samples. Furthermore, the PL characteristics and surface species of the UV-treated samples can be recovered to those of as-anodized wafers by dipping in HF. These results point out the importance of surface chemistry in the luminescence process of porous Si.

We have investigated the properties of light-emitting porous silicon (LEpSi) after standard microelectronic processing steps such as annealing, thermal and chemical oxidation, ion implantation, and reactive ion etching. The nature of the physical and chemical changes induced by these processing steps is studied. After thermal or chemical oxidation, the photoluminescence (PL) from LEpSi is blue shifted and more stable. Low dose dopant implantation essentially keeps the PL spectrum unchanged. Thermal annealing after ion implantation affects the PL intensity differently, depending on the type of ions. Reactive ion etching changes the surface morphology and shifts the PL peak to blue.

Uniform layers of porous silicon have been produced in a photoelectrochemical etch that show intensity enhancements of up to 100 fold, relative to samples etched in the dark. These films can also show fine structure in their photoluminescence (PL) spectra characteristic of longitudinal optical cavity modes. The highly luminescent, uniform porous layer is generated by illumination with blue or green light during the electrochemical etch of singlecrystal (B-doped) Si, and the enhancement is attributed to a localized photochemical etch process. The relevance of the increased PL intensity and interference-induced spectral changes to measurements of the intrinsic emission spectrum of porous Si are discussed.

Photoluminescence (PL) spectra are presented for porous silicon samples formed under various formation conditions in aqueous HF solutions. Formation conditions are chosen that effect maximal changes in morphology of resultant films and that correspond to varying formation electrochemistry. The trends in PL center wavelength and full width at half maximum (FWHM) with formation conditions are examined and compared to the resulting morphology. The PL spectra were observed to be most affected by changes in formation conditions when porous films are formed where the electrochemical process of silicon dissolution changes from a 2e- to 4e- (oxide production) reaction. Under these conditions, decreasing HF concentration and/or increasing current density produces a spectral blue-shift which is proportional to the narrowing of the FWHM. This behavior corresponds to morphology changes which are consistent with the quantum confinement model.

We have studied the electronic relaxation processes in porous silicon using a femtosecond pump and probe pulse–correlation technique at 440–nm wavelength. We have observed photoinduced absorption with a response time on the order of 5 ps. From picosecond luminescence decay measurements and the femtosecond pump and probe experiments, the carrier dynamics corresponding to our excitation conditions in porous Si is clarified as follows: carriers are excited in Si microcrystals and then rapidly thermalize to the surface state within 5 ps. After this, strong luminescence occurs from this state with decay components on the order of 1 ns.

We have studied the origin of the visible photoluminescence (PL) from oxidized porous Si. The hydrogen–passivated surface of porous Si prepared by electrochemical etching is converted to stable silicon oxides by rapid–thermal–oxidization processes. At low oxidation temperature (Tox), the PL spectrum with a peak near 700 nm is observed. At high Tox above 800 °C, a strong blue PL is observed near 400 nm. We discuss the origin of blue and red PL by employing the results of ab initio electronic structure calculations of silicon–oxygen compounds.

Si thin films were deposited on quartz at temperatures ( TD ) ranging from 540 to 640°C. X-ray diffraction indicates that films deposited at TD < 580°C are amorphous, while those deposited above 600°C are poly-crystalline with a <220> texture. The Si films were made porous by stain-etching in HF:HNO3:H2O. Only Si films deposited at 590°C and above show photoluminescence (PL), centered at ∼650-670 nm under UV excitation. Films deposited at TD < 580°C do not luminesce even after very long etch times, which produce a highly porous structure. The PL intensity and the x-ray signal follow a very similar trend with TD. It appears that a minimum level of crystallinity is required for photoemission in porous Si and that a strong relationship exists between them.

We report results of photoluminescence (PL) fatigue and nonlinear optical absorption in anodized porous silicon (PS) samples aged in air for a few months. The fatigue strength is found different for PS emitting below 1.65 eV, in 1.65 - 2.05 eV range and above 2.05 eV, revealing the different nature of PL. A comparison with two special glasses is made, and a possible explanation for PL mechanism in PS is discussed.

We have fabricated stacked-structures comprised of i) fused silica substrates, and ii) near-periodic Si3N4/SiO2 bi-layers by low-temperature, 250°C, remote plasmaenhanced chemical-vapor deposition. Comparing the reflectance of these structures with model calculations, we have been able to identify the effects on the reflectance spectra of departures from i) exact periodicity, ii) not having the constituent dielectric layers each posses an ideal optical path length, OPL, exactly equal to λcentral/4, and iii) the intrinsic dispersion in the dielectric functions of the oxide and nitride materials. We have prepared quasi-periodic structures in which the OPL of the higher index Si3N4 layer was > λcentral/4, and in which the OPL of the lower index SiO2 layer was < λcentral/4. This promotes a second strong reflectance band at an energy that is approximately two times that of the primary band. Calculations have shown that the reflectance values in this band, and near a reflectance minimum on the high energy side of the band, are both very sensitive to changes in the optical properties of the nitride film. We present calculations that demonstrate the effects on the reflectance of this band by a temperature-induced modulation of the optical properties of the oxide and nitride layers.

Synthesis of strain-compensated single-crystal Siy(SnxC1-x)1-y alloy films on silicon (100) substrates has been achieved with compositions of tin and carbon greatly exceeding their normal equilibrium solubility in silicon. Amorphous SiSnC alloys were deposited by molecular beam deposition from solid sources followed by thermal annealing. In situ monitoring of crystallization was done using time-resolved reflectivity. Good solid phase epitaxy was observed for Si0.98Sn0.01C0.01, at a rate about 20 times slower than that of pure silicon. Compositional and structural analysis was done using Rutherford backscattering, electron microprobe, ion channeling, x-ray diffraction, and transmission electron microscopy.

There exists considerable interest in the synthesis of nanocrystalline SiC particles embedded in an a-SixC1−x:H matrix. This study investigated the formation of nanocrystalline SiC by annealing a non-equilibrium a-Si0.35C0.65 alloy sputter deposited onto oxidized (100) Si. Evolution of the microstructure was characterized by thin film sheet resistance measurements, glancing angle X-ray diffraction (GAXRD) and transmission electron microscopy (TEM). It was found that films annealed at temperatures below 850°C remained amorphous. Annealing at temperatures above 850°C resulted in the formation of SiC nanocrystallites, as revealed by GAXRD and TEM. The electrical conductivity also showed an abrupt increase around 950°C. Prolonged annealing resulted in a further increase in conductivity, implying that the transformation continued. Annealing at 1100°C for 3 hours increased the film conductivity by two orders of magnitude relative to the as-deposited film.

The chemical kinetics of laser pyrolysis of Si(CH3)2Cl2 was studied. Besides Si/C deposited on substrate as a needle the main gaseous products were H2 and HCI. The decomposition rate constants of Si(CH3)2Cl2 and the formation rate constants of H2 and HCl were measured. The chemical and physical properties of the Si/C needles were studied by various methods, such as their outer features, elemental analysis, Auger depth profile spectra, X-ray diffraction. Other useful properties, such as electric resistivity, photovoltaic effect and hardness, were also reported. A model for the pyrolysis and the growth process of this Si/C needles was proposed. It should be emphasized that the samples with desired physical properties could be grown by controlling the growth conditions properly -- the laser power and the pressure of Si(CH3)2Cl2.

A novel phase modulator has been designed and analysed, assuming fabrication in a silicon-on-insulator material such as SIMOX. The proposed modulator is based upon a transverse p-i-n structure, utilising the plasma dispersion effect to produce the desired refractive index change in an optical rib waveguide. The device has been studied using the MEDICI two dimensional device simulation package to optimise the injected carrier interaction with the propagating optical mode. Whilst the device is designed to support a single optical mode, it measures several micrometers in cross sectional dimensions, thereby simplifying fabrication and allowing efficient coupling to other single mode devices such as optical fibers. Furthermore the device has an extremely high figure of merit, predicting over 200 degrees of induced phase shift per volt per mm. This implies a short active length together with a low power requirement.

The use of an Electrolyte-SiO2-Si system allows a detailed control of the electron injection from the electrolyte into SiO2 layer, and makes feasible to reach the electron heating in the conduction band of SiO2 before to take place the irreversible breakdown.

The injected and heated electrons enhance the probability of the SiO2 defect excitation as well as the Si-O bond breaking. Both features give raise to the relaxation processes which are responsible of the electroluminescence characteristics of the oxide. So, the measured electroluminescence spectrum presents straightforward information on the defect types, their nature and possible precursor defect behaviour. Results on silicon oxides obtained from different technological processes and treatments, corroborate the above analysis and show the electro-luminescence of SiO2 as an interesting and powerful method to evaluate the SiO2 properties.