International Journal of Modern Physics B

Silicon Germanium is lattice mismatched to Silicon by up to 4.2% depending on the Ge content. Up to a critical thickness elastic strain accommodates the mismatch. The band ordering of SiGe/Si interfaces is strongly influenced by the strain shifting the band ordering from flat conduction band to a type II ordering when proper strain adjustment is performed. As device examples the heterobipolartransistor, hetero field effect transistor and room temperature Esaki tunneling are treated. As key questions for further material development are identified the growth and processing of ultrametastable layers and the strain adjustment by thin virtual substrates.

Antimony diffusion in in-situ doped strained Si_0.9Ge_0.1 epitaxial layers, subjected to point defects injection by rapid thermal anneal in oxygen atmosphere, was investigated as a function of temperature at range from 890°C to 1000°C. In this work, the effect of point defect injection on the diffusion of antimony in silicon and silicon-germanium alloys has confirmed the predominant mechanism for diffusion of Sb in Si and SiGe to be vacancy mediated. Diffusivities were obtained using computer simulations. Activation energies were calculated while the diffusivity of antinomy in SiGe under point defect injection as a function of temperature was presented.

A 75nm Si_0.84Ge_0.16 film was grown at 500°C with Si₂H₆ and GeH₄ precursors. After depositing an oxide layer on the top, the samples were implanted with ions at an energy of 38keV, and a dose of 3.5 × 10¹⁶cm^-2. These implanted samples were annealed in the temperature range from 400°C to 700°C. H redistribution occurs during this process. Meanwhile, great tensile strain was introduced by implantation into the SiGe/Si heterostructure layers and following annealing relieved the strain. High temperature annealing almost fully relaxed the SiGe layer.

Laser induced pattern crystallization technique with pulsed KrF excimer (248 nm) laser was used to irradiation amorphous SiGe films prepared by plasma-enhanced chemical vapor deposition (PECVD) on Si substrates. The surface of laser treated sample was investigated by scanning electron microscopy (SEM), it was found that the film irradiated by KrF excimer composed by well-shaped square periodicity embedded in the a-SiGe matrix, and in each square there are laser induced SiGe nanocrystals. The size of SiGe crystals was estimated to be about 10 nm. The samples were analyzed by X-ray diffraction, Raman spectroscopy and photoluminescence analysis before and after crystallization. The Raman spectrum shows strong Ge-Ge, Si-Ge, and Si-Si vibrations that agree with those of crystalline Si_1-xGe_x alloy. Strong PL with two peaks at 720 nm and 750 nm was observed at room temperature in the crystallized film, whereas the uncrystallized sample emits no peaks. These results indicate that nanometer SiGe alloy were formed and laser-induced technology is an efficient technique to produce nanometer materials.

Capacitance versus voltage (C-V) and deep level transient spectroscopy (DLTS) characterization was performed on rapid thermal oxides (RTO) on Si_0.887Ge_0.113 and Si_0.8811Ge_0.113C_0.0059 alloys. A high interface trap density (~ 10¹²eV^-1cm^-2) and a high apparent doping level were obtained for the SiO₂/Si_0.8811Ge_0.113C_0.0059 samples. The C-V results at different temperatures showed that the high apparent doping levels of the SiO₂/Si_0.8811Ge_0.113C_0.0059 samples might be due to the formation of SiC-related defects introduced by the high temperature oxidation process.

Photoluminescence (PL) of strained SiGe/Si multiple quantum wells (MQW) with flat and undulated SiGe well layers was studied at different temperature. With elevated temperature from 10K, the no-phonon (NP) peak of the SiGe layers in the flat samples has firstly a blue shift due to the dominant transition converting from bound excitons (BE) to free excitons (FE), and then has a red shift when the temperature is higher than 30K because of the narrowing of the band gap. In the undulated sample, however, monotonous blue shift was observed as the temperature was elevated from 10 K to 287 K. The thermally activated electrons, confined in Si due to type-II band alignment, leak into the SiGe crest regions, and the leakage is enhanced with the elevated temperature. It results in a blue shift of the SiGe luminescence spectra.

One has discussed the principle and method of designing the heterojunction structure of n-Si/Si_1-xGe_x HEMT from the lattice match and the energy band discontinuity points, analysed and calculated the HEMT reported by K. Ismail and obtained 2DEG (two Dimension Electron Gas) density n_s essentially according with the experiment data. Final the design of the heterojunction of K. Ismail's HEMT is improved to get a higher 2DEG density n_s.

The real time B-doped thin Si and SiGe epilayers on diameter 3-inch Si substrates were grown by an ultrahigh vacuum chemical vapor deposition (UHV/CVD) system. The substrate temperature during growth was from 550 ~ 780°C. The properties of the epilayers were characterized by secondary ion mass spectrum (SIMS), Fourier transform infrared spectroscopy (FTIR), spreading resistance profile (SRP) and double crystal x-ray diffraction (DCXRD). The carrier concentration in the intrinsic Si epilayer was about 10¹²cm^-3 and the resistivity was as high as about 10000 Ωcm. In addition, the abrupt transition and B-doped concentration of 10¹⁵ ~ 10¹⁹cm^-3 were achieved for Si and SiGe epilayers.

Oxidation study of rf sputtered amorphous and polycrystalline silicon germanium (Si_1-xGe_x) film which was conducted using infrared spectroscopy (FTIR). The oxidation results showed linear oxidation rate of amorphous Si_1-xGe_x and polycrystalline Si_1-xGe_x films in the dry oxygen ambient did not depend on the Ge concentration. We found that Ge nanocrystals were formed from mixed (Si, Ge)O₂ oxides when annealed in forming gas (10%H₂ + N₂) while pure N₂ showed formation of Ge clusters.

Type-II SiGe/Si MQWs (Multi-Quantum Wells) and Self-Organized Ge/Si Islands were successfully grown by a homemade ultra-high vacuum/chemical vapor deposition (UHV/CVD) system. Growth characteristics and PL (photoluminescence) spectra at different temperature were measured. It demonstrated that some accumulation of carriers in the islands results in the increase of the integrated PL intensity of island-related at a certain temperature range.

Si_0.875-yGe_0.125C_y ternary alloy films were grown on Si by ion implantation of C into Si_0.875Ge_0.125 layers and subsequent solid phase epitaxy. It was shown that C atoms were nearly incorporated into substitutional sites and no SiC was formed in the SiGeC films by optimal two-step annealing. There is a prominent effect of C contents on carrier transport properties. Compared with strained Si_0.875Ge_0.125 film, enhanced Hall mobility has been obtained in partially and fully strain compensated Si_0.875-yGe_0.125C_y layer due to the reduction of lattice strain.

Hydrogenated amorphous Ge / amorphous Si multilayers with different thickness of sublayers were prepared on Si wafer by plasma-enhanced chemical vapor deposition and then oxidized at 800°C for various oxidation durations. Intense photoluminescence with multiple peaks was observed for the samples at room temperature. One peak is centered at the wavelength around 755 nm, which is almost unchanged from sample to sample and could be attributed to the luminescence from the defect states located at the interfaces between the formed nano-crystalline Ge and SiO₂. Another peak around 720 nm shows blue shift with increasing the oxidation duration, which may be deduced from the quantum confinement effect of nc-Ge. The luminescence from the samples with the same thickness of SiO₂ sublayers and different thickness of nc-Ge sublayers supported the suggested luminescence origin.

Erbium doped SiO₂ thin films containing Si nanocrystals were fabricated by Si and Er dual implantation into SiO₂ using a metal vapor vacuum arc (MEVVA) ion source. Photoluminescence (PL) intensity was strongly enhanced by the incorporation of nanocrystalline Si (nc-Si) in the SiO₂ films. For samples implanted with a fixed Er dose, there is an optimum Si dose to achieve a maximum 1.54 μm PL peak intensity, and likewise for samples implanted with a fixed Si dose, there is an optimum Er dose to achieve a maximum PL intensity. These results were discussed in terms of energy transfer mechanisms between the photogenerated carriers in the nc-Si and Er ions in the SiO₂ matrix.

Photoluminescence (PL) from Er-implanted hydrogenated amorphous silicon suboxide (a-SiO_X:H〈Er〉(x<2.0)) films was measured. Two luminescence bands with maxima at λ ≅ 750 nm and λ ≅ 1.54μ m, ascribed to the a-SiO_x:H intrinsic emission and Er³⁺ emission, were observed. Peak intensities of the two bands follow the same trend as a function of annealing temperature from 300 to 1000°C. Micro-Raman results indicate that the a-SiO_x:H<Er> films are a mixture of two phases, an amorphous SiO_x matrix and amorphous silicon (a-Si) domains embedded there in. FTIR spectra confirm that hydrogen effusion from a-SiO_x:H<Er> films occurs during annealing. Hydrogen effusion leads to a reconstruction of the microstructure of a-Si domains, thus having a strong influence on Er³⁺ emission. Our study emphasizes the role of a-Si domains on Er³⁺ emission in a-SiO_x:H<Er> films.

ZnO films with (100) preferred orientation are reported for the first time. ZnO films were synthesized on Si(100) substrate by solid-source chemical vapor deposition (SS-CVD) using zinc acetate dihydrate (solid) as a precursor. The structural properties were investigated by X-ray diffraction and atomic force microscopy. Results show that a lower growth temperature and a higher deposition rate will facilitate the formation of (100) texture. The texture coefficient for (100) plane is 3.28.

Zn_1-xMg_xO films were grown on silicon (Si) at various substrate temperatures by pulsed laser deposition (PLD). The structural, surface morphology, composition and photoluminescent properties of the films as functions of substrate temperature were studied. When the substrate temperature was at 650°C, the crystalline quality was the best, and the grain size of the film was largest. These films showed ultraviolet photoluminescence at room temperature. The near-band-edge (NBE) emission peak of the Zn_1-xMg_xO film deposited at 600°C exhibited a larger blue shift (0.40eV) than that of the film deposited at 500°C (0.33 eV). The ratio of near-band-edge (NBE) to defect level (DL) peak intensity was as large as 159.

High growth rate deposition of μc-Si:H film with VHF-PECVD at low temperature has been reported. Investigations showed that growth rates enhanced with higher excitation frequency and working pressure, but increased at first then decreased with the increase of plasma power. Optical emission spectroscopy (OES) was introduced to monitor VHF plasma. The relationship between the growth rates and the OES results has been discussed. Raman spectra were also used to study the a-Si:H/μc-Si:H phase transition. Finally a high growth rate of 2.0nm/s has been obtained through the initially optimized condition.

Polycrystalline silicon germanium (Si_1-xGe_x) films were characterized using x-ray diffraction (XRD) and Raman spectroscopy techniques. The XRD results show that our films consist of Si_1-xGe_x alloy with no cluster of Ge or a Ge rich material embedded in a Si matrix. Comparison of the XRD results of RTA and furnace annealed samples for the same annealing conditions reveal that the latter allow for faster formation of the (200) and (311) crystal planes. Raman spectroscopy results indicate that our films were strain free.

The gallium nitride (GaN) films have been successfully fabricated on silicon (111) substrates through ammoniating Ga₂O₃ films deposited by electrophoresis. The structure and composition of the formed films were characterized by Fourier transform infrared (FTIR) transmission spectroscopy, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results indicate that the films formed in this study are polycrystalline GaN with hexagonal wurtzite structure.

In this paper, we report the fabrication of Si-based double hetero-epitaxial SOI materials Si/γ-Al₂O₃/Si. First, single crystalline γ-Al₂O₃(100) insulator films were grown epitaxially on Si(100) by LPCVD, and then, Si(100) epitaxial films were grown on γ-Al₂O₃(100)/Si(100) epi-substrates using a CVD method similar to silicon on sapphire (SOS) epitaxial growth. The Si/γ-Al₂O₃(100)/Si(100) SOI materials are characterized in detail by RHEED, XRD and AES techniques. The results demonstrate that the device-quality novel SOI materials Si/γ-Al₂O₃(100)/Si(100) has been fabricated successfully and can be used for application of MOS device.

A type of thermo-optic variable optical attenuator based on multimode interference coupler is proposed. The optical field propagation properties of the devices are simulated using finite difference beam propagation method. The propagation loss of the fabricated device is 2-4.2 dB at the wavelength range 1510-1610 nm. The total power consumption is 370 mW and the maximum attenuation is more than 25 dB, which almost can meet the requirements of optical fiber communication systems.

A bulk silicon is an indirect band gap semiconductor, the radiative transitions in silicon involves a electron-hole-phonon three-body processes and is therefore making it an inability of light emission. In order to integrate Si-based microelectronics with optical components, a best solution is to design a Si-based material with direct band-gap. Here we suggest a new Si-based superlattice consists of a nano-silicon layer and a VI-atom monolayer with dimer-structures in the interfaces between silicon and VI-atom layers. The structural formula is VI/Si_m/VI/Si_m/VI, (m = 2n or/and 2n+1,n ≥ 3). A simple form of (2×1) surface reconstruction has been considered in the ab initio calculation of electronic structures for this Si-based superlattices system. It is found from our computational design that a Se/Si₁₀/Se/Si₁₀/Se superlattice has a direct band-gap at Γ point. As a kind of new Si-based materials, the important potential and advantages in optoelectronic applications will be discussed.

Surface segregation and diffusion are the dominant mechanisms for profile smearing. However in the low temperature regime below 600°C diffusion is negligible. We investigated the dopant profile during silicon molecular beam epitaxy (MBE) in silicon (100). A method for measurement of the adlayer density of segregating dopant atoms is suggested. We utilize the results of this experiment to generate very sharp boron profiles. For the doping we use the pre-build up method with constant boron flux.

Intrinsic, P-doped and B-doped hydrogenated nanocrystalline silicon (nc-Si:H) films were fabricated using plasma enhanced chemical vapor deposition (PECVD) system. It's microstructures were characterized by HRTEM. Electrical transport mechanism of nc-Si:H film was investigated: Tunneling effect of electrode/(p)nc-Si:H/(n)c-Si/electrode were electrically characterized. Electronic transport was governed by thermal-assisted tunneling within around 100K-600K and electrons hopping through the local states near the Fermi-level was existed simultaneously under 100K.

Er and Yb have been doped into nanocrystalline Si and ZnO thin films. Sharp and intense photoluminescence (PL) lines related to intra-4f transitions in the rare earth ions were observed. The optical transition dynamics of the rare earth ions were investigated by time-resolved PL measurements. It was demonstrated that a nano-meter sizing of Si widened the energy bandgap and led to an increase of doping densities of the rare earths. It was also shown that the Er-related PL gave rise to different features under direct and indirect excitations indicating a strong interaction of electron-hole pairs in the host with 4f electrons in the rare earth ions. A co-doping effect of Yb and Er into nanocrystalline Si was presented also. Our results suggested a rare earth-rare earth coupling between the Yb³⁺ ions and the Er³⁺ ions, which transferred the energy from Yb to Er and enhanced the 1.54 μm PL of Er.

The γ-Al₂O₃ films were grown on Si (100) substrates using the sources of TMA (Al(CH₃)₃) and O₂ by very low-pressure chemical vapor deposition (VLP-CVD). It has been found that the γ-Al₂O₃ film has a mirror-like surface and the RMS was about 2.5nm. And the orientation relationship was γ-Al₂O₃(100)/Si(100). The thickness uniformity of γ-Al₂O₃ films for 2-inch epi-wafer was less than 5%. The X-ray diffraction (XRD) and reflection high-energy electron diffraction (RHEED) results show that the crystalline quality of the film was improved after the film was annealed at 1000°C in O₂ atmosphere. The high-frequency C-V and leakage current of Al/γ-Al₂O₃/Si capacitor were also measured to verify the annealing effect of the film. The results show that the dielectric constant increased from 4 to 7 and the breakdown voltage for 65-nm-thick γ-Al₂O₃ film on silicon increases from 17V to 53V.

Electrophoretic assembly of porous silicon (PS) has been studied in the present paper. A toluene/porous silicon suspension was prepared by the sonication of anodically etched porous silicon wafers and showed a PL property similar to the as-prepared PS, giving 620nm orange-red photoluminescence emissions. A broad optical absorption band about 286nm arising from scattering and absorption of the light by the PS particles has been observed. The PS particles suspended in toluene drifted towards the positive electrode and have been assembled on the surface of P⁺ Si or indium-tin oxide (ITO) electrodes under a electric field of 100~600V/cm. The assembled PS films showed a quite stable PL property after ageing for 280 days even though there were some oxides revealed by XPS analysis.

Single crystalline GaN is grown on Si(111) by a vacuum reactive evaporation method. X-ray diffraction(XRD), scanning electron microscopy(SEM), photoluminescence measurement (PL), and Hall measurement results indicate that single crystalline wurtzite GaN film is grown on the microcrystalline GaN buffer layer on Si(111) substrate. The photoconductive ultraviolet photodetector with a metal-semiconductor-metal(MSM) structure is prepared on the unintentionally doped n-type GaN film and the properties of the detector are investigated. The detector has a peak photocurrent responsivity at 365nm and a abrupt cut-off curve. The responsivity increased with the increasing of bias voltage. The responsivity saturated when the bias voltage reached 7V. The response time was ms level under normal conditions and dropped with the increase of bias voltage before the bias voltage reached its saturation.

The carrier density of highly [100]-oriented β-FeSi₂ films grown by molecular beam epitaxy (MBE) was smaller than that by the multilayer method. For the MBE grown, undoped n- and p-type β-FeSi₂ films, only one donor (E_D1 = 0.21 eV) and one acceptor (E_A2 = 0.11 eV) levels were obtained from the temperature dependence of the carrier density, in contrast with the fact that two kinds of donor (E_D1 = 0.21 eV and E_D2 = 0.08 eV) and acceptor (E_A1 = 0.19 eV and E_A2 = 0.11 eV) levels were obtained for layers grown by multi-layer method. These results suggest that the decrease of the carrier density in the MBE-grown films is due to disappearance of the E_D2 or E_A1 level.

Results of Induction Coupled Plasma (ICP) etching of as-prepared and annealed PECVD hydrogenated amorphous silicon carbide (a-Si_1-xC_x:H) films using CF₄/O₂ chemistry are presented. The etch rate of the annealed films decreased with an increase in annealing temperature. Infrared spectra for the annealed films showed a significant decrease in the Si-H and C-H bonds, and a pronounced increase in the Si-C bonds. The XRD results showed several poly-crystalline Si-C structure in films annealed at 800°C. ESR spectra show the density of the dangling bonds increased as a function of annealing temperature. The drop in etch rate of the annealed films is due to the reduction in porous structures resulted from dehydrogenation and increased crystallinity of the film.

The interfacial reactions of Ni with polycrystalline Si_0.8Ge_0.2 films at a temperature range of 300-900°C by rapid thermal annealing for 60s are studied. The sheet resistances of the silicide films were relatively low at ~10 ohm/sq for samples annealed below 600°C. X-Ray diffraction results suggested the existence of low resistivity phase Ni(Si_1-xGe_x) in the film. The significant increase in sheet resistance for films annealed at 700-900°C is probably due to the reduction in the density of Ni(Si_1-xGe_x) as a result of fast Ni diffusion at high annealing temperatures. Fast grain boundary diffusion of Ni was suggested to cause the lowering of formation temperature of Ni(Si_1-xGe_x) on polycrystalline Si_1-xGe_x films. Rutherford backscattering results showed that for films annealed at a temperature range of 300-600°C, Ni has reacted with the polycrystalline films. However, at an annealing temperature higher than 700°C, Ni diffused through the whole film.

The optical band gap (E_g) of the boron (B)-doped hydrogenated nano-crystalline silicon (nc-Si:H) films fabricated using plasma enhanced chemical vapor deposition (PECVD) was investigated in this work. The transmittance of the films were measured by spectrophotometric and the E_g was evaluated utilizing three different relations for comparison, namely: αhν=C(hν-E_g)³, αhν=B₀(hν-E_g)², αhν=C₀(hν-E_g)². Result showed that E_g decreases with the increasing of Boron doping ratio, hydrogen concentration, and substrate's temperature (Ts), respectively. E_g raises up with rf power density (P_d) from 0.45W.cm^-2 to 0.60w.cm^-2 and then drops to the end. These can be explained for E_g decreases with disorder in the films.

Buried gadolinium silicide layer was prepared by ion implantation of Gd into n-type Si (100) wafer. It was shown that GdSi₂ grains have been formed during Gd⁺ implantation. An oxygen-free continuous layer of (112) oriented GdSi₂ was obtained after irradiating the sample using a pulsed excimer laser. Comparing with conventional thermal annealing pulsed excimer laser irradiation at energy densities close to the threshold for melting Si surface layer could prepare oxygen-free GdSi₂ buried layer within a preferred region.

Hydrogenated nano-crystalline silicon (nc-Si:H) thin films were prepared by plasma enhanced chemical vapor deposition (PECVD). The variation in the crystallinity, nano-structure and optical characteristics of the nc-Si:H films with deposition variables such as reaction gas, post-deposition heat-treatment and deposition time were investigated; the relationship between the optical nano-structural features of the nc-Si:H films was discussed. The intensity of the PL peak, observed at about ~ 480 nm region, increased with the amount of reaction gas as well as deposition time. On the other hand, PL peaks appear at ~ 580 nm region when the sample was annealed in vacuum, and the intensity of the peaks increased with increasing the annealing time. It's believed that radiative recombination occurred due to the defects of SiO_x in the film.

Cubic boron nitride (c-BN) thin films have been deposited on Si substrates by radio frequency sputter. Sputtering target was hot pressed hexagonal boron nitride of 4N purity. Sputtering gas was the mixture of nitrogen and argon. During depositing c-BN thin films, substrates were biased by dc voltage negatively with respect to ground. By optimizing the deposition conditions, the boron nitride (BN) films containing a large amount of cubic phase were obtained. The samples were characterized with Fourier transformation infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). According to FTIR, the cubic phase content of c-BN thin films was evaluated to be 92. The B/N ratio was estimated to be approximately 1 from XPS. The AFM shows that the c-BN thin films delaminated from Si substrates obviously.

Lithium niobate (LiNbO₃) thin film is an important material for optical waveguide. Recently, particular attention has been paid to the application of LiNbO₃ (LN) thin films. To develop and fabricate integrated optical devices, the growth of thin LN epitaxial films onto silicon substrate is of great importance and particularly attractive. In this paper, LN thin film was grown by pulsed laser deposition (PLD). Stoichiometric LN ceramic is used as a target. Amorphous SiO₂ buffer layer was coated on Si (100) wafer by in-situ themal oxidation before the deposition. The optimized condition of growing LN film on Si (100) by PLD is found: O₂ pressure 30 Pa, substrate temperature 600°C. Only (006) reflection of LN was observed besides the (002) reflection of silicon substrate from XRD pattern. The FWHM (~0.21°) of (006) reflection peak is much narrower than the value reported by Lee [1]. The results of XRD measurement indicate that the LN film was epitaxially grown along the c-axis. Transmission electron microcopy (TEM) patterns confirm that the film has superior crystalline quality. The optical waveguiding properties of the films were demonstrated by a prism coupler method. Fully c-oriented thin film could be grown on silicon substrate by PLD without the buffer layer and the induced electric field.

Silicon solar cells with embedded germanium (Ge) layers deposited as 3-dimensional islands in the Stranski-Krastanov growth mode have been grown by molecular beam epitaxy (MBE) to enhance the efficiency of Si thin film solar cells. The Ge-layers increase the infrared absorption in the base of the cell to achieve higher photocurrent which should overcome the loss in the open circuit voltage due to incorporation of a smaller bandgap material in the heterostructure. Up to 75 layers of Ge, each about 8 monolayers (ML) thick, separated by Si-spacer layers (9-18nm) have been deposited at rather elevated temperatures (700°C) on a standard 10Ωcm p-type Si-substrate. Island densities of 10¹¹cm^-2 have been achieved by use of antimony (Sb) as surfactant. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) were used to characterize the growth of Ge-islands under variuos growth conditions. Photocurrent measurements exhibit a higher photo-response in the infrared regime but a lower open circuit voltage of the fabricated solar cells compared to a Si-reference cell.

The transition to step flow growth on the clean Si(111) (7×7), Si(111)-In and Si(111)-Sb (7×7) surfaces have been investigated using low energy electron microscopy (LEEM). The critical terrace width for step flow on the clean surface displays in Arrhenius behaviour, although with markedly different prefactor and activation energy above and below 750°K. The abrupt change in Arrhenius parameters was revealed by LEEM to correlate with the crossover from homogeneous to heterogeneous island nucleation behavior. The dependence of the critical terrace width upon step orientation is attributed to anisotropic step attachment kinetics. Sb and In surfactants were found to suppress and enhance step flow, respectively, in accordance with expectations. The preparations of Si(111)-Sb (7×7) and Si(111)-In surfaces that are morphologically suitable for step flow growth are also described.

The applications of various optical and electrical characterization techniques to the study of semiconductor quantum dots (QDs) are summarized. Photoconductivity enhancement effect in CdS-PVK nanocomposite is studied by optical absorption, photoluminescence (PL), photoconductivity spectroscopy, and time-resolved PL. It is found that the photoconductivity of the composite is greatly enhanced in comparison with that of a simple mixture of CdS nano-particles and PVK. PL spectra have shown that luminescence from PVK is dramatically quenched by the incorporation of a low density of CdS particles. Time-resolved spectra reveal that the decay of the PL from the dots of the composite in much longer than that in the simple mixture. These have been attributed to a fast carrier transfer mechanism between CdS QDs and PVK matrix. In addition, optical properties of PVP-capped ZnO QDs are investigated in details. Typical PL spectra of PVP-capped ZnO QDs consist of a sharp UV peak located at about 3.45 eV and a broad green emission band centered at 2.34 eV. At certain Zn²⁺/PVP ratios the green emission band is quenched and only strong UV emission remains. This effect is attributed to the surface modification of ZnO quantum dots with PVP. We are able to associate the UV emission from ZnO QDs to localized states by applying temperature and excitation power dependent PL. Finally, the electronic level of molecular beam epitaxy grown self-organized ZnSe QDs embedded in ZnS is determined by applying PL, capacitance-voltage measurement, and deep level transient spectroscopy.

The paper discussed a possibility of using new approaches for in-situ diagnosis growth processes of large crystals as well as solving some specific problems of controlling them. They are based on the current monitoring of changes in the differences of electric potential between growing crystals and crystallization medium. It is obvious that this monitoring reflects such important crystallization processes as accumulation of charge at the crystal interface and electric screening of it, growth of concentration of subphase formation at the interface (later, inclusions), current change in the mass crystallization rate, etc. This change in the rate suggests a new concept of automation of crystal growth processes, based on minimization of the difference in the current and initially predetermined change in Δϕ through inversely-related adjustment of the temperature of crystallization medium. We have experimentally substantiated the possibility of using various outer electric potentials for modification of processes in a double electric layer at the interface and extension of growth period under fairly favorable conditions. The system of low-temperature phase of barium metaborate crystal and molten solution as crystallization medium was taken for a model one.

CuInS₂ films were deposited on float glass substrates by a one-stage reactive RF sputter process using a Cu-In alloy target and H₂S gas. The sputtered films generally have a (112) preferential orientation. X-ray reflectometry was used to measure the thickness, surface density as well as surface roughness of the sputtered films. The surface morphology of the films was studied by scanning electron microscopy. Energy-dispersive X-ray analysis was performed to determine the composition of the films. XPS revealed that the film surfaces remain In-rich with respect to the bulk.

Low-voltage scanning electron microscopy (LV-SEM) enables us to directly examine non-conducting materials with high spatial resolution. Although use of ultra-low-energy electrons can provide further advantages for characterizing delicate samples, lens aberrations rapidly deteriorates the image resolution. The combined use of a retarding field and the probe-forming lens system can improve the image resolution for electrons with very low energies. In commercially available FEG-SEMs, the retarding field can simply be constructed by applying a negative potential to the specimen. Interesting contrast variations have been observed in ultra-low-voltage SEM images. In this short communication, we discuss the application of LV-SEM to examining semiconductor devices and also the recent development of the ultra-low-voltage SEM technique.

Atomic force microscopy was applied to study the formation and growth mechanism of thin multilayers of chromium-molybdenum and chrome prepared by electro-pulse plating, respectively. The chromium-molybdenum and chrome layers were prepared using direct current density of 1.6 mA.mm^-2 and pulse currents with on-off time from 5 to 2000 ms in the bath containing 300gl^-1 of chromic acid and 75gl^-1 ammonium molybdate, and 250gl^-1 of chromic acid and 5gl^-1 of sulfuric acid, respectively. The higher current density enhanced nucleation rate which resulted in refining grain size. The micro-hardness of the pulse plated chrome and chromium-molybdenum alloy layers increased with the duration of on-off time and pulse current density. The average surface roughness of chrome layer is increased with increasing on/off time ratio for a given peak current density and voltage because the growth and dissolution mainly occurs during on-time and off-time, respectively. However, the average surface roughness of chromium-molybdenum alloy layer is decreased with increasing on/off time ratio for a given peak current density and voltage because the alloying element in the layer.

We present a micro-Raman study of alterations in InGaAs/InP epilayers after rapid thermal annealing. Defects consisting of protruding material with typical dimensions of a few microns can be observed on the surface of the annealed samples. Micro-Raman measurements on these defects show that they consist of In_xGa_1-xP alloys, suggesting that phosphorus diffusion from the InP substrate occurs during the RTA cycle. The defect-free region of the epilayer is also altered leading to the formation of an In_1-xGa_xAs_1-yP_y quaternary alloy.

The full energy distribution of backscattered electrons from elastic peak down to true secondary electron peak has been calculated by a Monte-Carlo simulation method by including cascade secondary electrons production. The simulation method is based on the use of a dielectric function for describing electron inelastic scattering and secondary excitation, and the use of Mott cross section for electron elastic scattering. This calculation reproduces well the backscattering background observed in the direct mode of AES. The calculated absolute electron yields have been compared with the available experimental data. The simulation has indicated that, due to the effect of the elastic scattering differential cross section and detection solid angles, the shape of the energy distribution measured with a cylindrical mirror analyzer may differ from the overall energy spectrum of emitted electrons.

Tetrahedral amorphous carbon films have been prepared by magnetic filtered plasma deposition system. The samples were deposited with negative bias voltage V_b range from +20 V to -95 V. The relative fraction of sp³-bonded carbon in these films was qualitatively and quantitatively estimated by a fitting of the Raman and XPS spectra, respectively. Raman results show that the sp³ fraction of the films deposited in the range from -10 V to -50 V was estimated to be more than 80%. The C 1s spectra were consistently decomposed into the two gaussian components, one is at 284.4±0.1 eV corresponding to sp²-hybridized bonds, and another is at 285.2±0.1 eV corresponding to sp³-hybridized bond. The sp³ content can be quantitatively calculated from the integrated area of the respective gaussian peak divided by the total area of the spectra. The comparison of XPS with Raman analysis, the trend of qualitative variation of sp³ content with V_b is in agreement. We concluded that XPS analysis is a useful method for quantitatively calculating sp³ content in hydrogen-free tetrahedral amorphous carbon films.

Band-gap energy of AIN thin films was investigated by room-temperature photoreflectance (PR) spectroscopy. Using rf magnetron sputtering, the reactive gas-timing technique was successfully applied to grow cubic-AIN thin films. The define XRD patterns of all deposited films show orientation of cubic structure in (111) and (200) planes. The PR spectra clearly exhibit a band-gap energy of cubic-AIN depending on the flow rate of N₂ gas. The band-gap transition energies were determined by fitting the PR spectra to theoretical line-shape expression. The band-gap transition energies decreased with increasing flow rate of N₂.

Diagonal self-assembled InAs quantum wire (QWR) arrays with the stacked InAs/In_0.52Al_0.48As structure are grown on InP substrates, which are (001)-oriented and misoriented by 6° towards the [100] direction. Both the molecular beam epitaxy (MBE) and migration enhanced epitaxy (MEE) techniques are employed. Transmission electron microscopy reveals that whether a diagonal InAs QWR array of the stacked InAs/InAlAs is symmetrical about the growth direction or not depends on the growth method as well as substrate orientation. Asymmetry in the diagonal MEE-grown InAs QWR array can be ascribed to the influence of surface reconstruction on upward migration of adatoms during the self-assembly of the InAs quantum wires.

By 532 nm laser pumped PL spectral and Xe pumped fluorescence spectral, characterized InGaAsP/In_0.5(Ga_xAl_1-x)_0.5P quantum well on substrates 2°, 15° tilted to (110) the optical property dependence of substrates tilt. The PL wavelength varies from 755 nm of the quantum well on substrate of 2° to the 780 nm of the quantum well on substrate of 15°. From fluorescence excitation spectral to excite about 760 nm wavelength of quantum well, the absorption light peak wavelength is 508 nm in common, and has another absorption peak wavelength of 622 nm. Excited by 508 nm and 622 nm wavelength, the fluorescence spectral intensity of the 15° quantum well is about 300 and 10⁴ accordingly. Lifetime of charge recombination is about 1.26 ns for this material.

Simulations were performed to model the response of a copper rectangular parallelepiped single crystal with a notch to tensile deformation. Partial dislocations were created near the tip of the notch as we expected. It is hard to see where the dislocations were created by just looking at the displaced positions of atoms, but the creation of dislocations was easily observed by a simulation of X-ray Lang method. Before creation of dislocations, some indication was quite clearly shown. Laue patterns during tensile deformation were also simulated.

The photocurrent of erbium delta-doped InP grown by organometallic vapor phase epitaxy was observed at room temperature. The clear PC spectra of doped samples reflect the high quality formation of ErP quantum structure in InP. The PC spectra of doped sample with different Er exposure duration show that the total number of ErP islands increase with increasing exposure time, reflected in the sharper PC spectra. When applying an electric field, the spectra of the doped sample exhibit significant shift with increasing field.

Polymer low-k materials have been regarded as one of the most promising candidates as interconnect insulator with copper metallization. One of the major problems associated with polymer materials is their poor thermal stability. In this paper, thermal stability of an aromatic hydrocarbon low-k material was studied using TGA, FTIR and thermal desorption-GC-MS techniques. The material is thermally stable at temperatures up to 430°C. At higher temperatures, thermal decomposition of the low-k material is pronounced and the major outgassing species are aromatic compounds and carbon dioxide.

We constructed a novel vacuum system in which the cathode luminescence properties of as-prepared films can be measured in-situ. It has been observed that the Zn-Ga-O films deposited on 500°C ITO by sputtering emits light with wavelength of about 500 nm from an ultra thin Zn-rich layer formed near film surface. The luminescence induced by irradiation of electrons has also been observed for the first time in the organic bilayered TPD/Alq₃ films prepared in thermal evaporation. Its wavelength blue-shifts by about 120 nm in comparison with the electroluminescence of the same materials. The developed vacuum system is useful to characterize various thin films.

A neural network (NN) method has been proposed as a new algorithm for extraction of defect centers parameters in semi-insulating materials from experimental data obtained by photoinduced transient spectroscopy (PITS). The new algorithm is applied to investigate irradiation-induced defect centers in high resistive silicon. The folds on the PITS spectral surface formed due to the presence of defect levels are best fitted with a two-dimensional approximation function with implementation of the NN learning process. As a result, the Arrhenius plots for defect centers are obtained and the parameters of these centers are determined.

A new system 0.1BiFeO₃-0.9SrBi₂Nb₂O₉ thin films have been successfully prepared by an ethanolamine-modified sol-gel technique. The precursor solution was synthesized from compounds, Bi(NO₃)₃·5H₂O, Sr(NO₃)₂, Fe(NO₃)₃·9H₂O and Nb(OC₂H₅)₅ in solution ethylene glycol monomethyl ether. The thin films were deposited on Si single crystal by spinning coating, and heat-treated at temperatures ranging from 400°C to 700°C. Crystallization of thin films occurred at about 500 ~ 600°C and the films exhibit a pure phase of layered perovskite ferroelectric structure. The grain of films is well distributed and the average grain size of the film is about 100nm.

Pb(Zr_xTi_1-x)O₃ (PZT) films were prepared on the ITO coated glass plates in sol-gel dip-coating process and post-annealing at different temperatures. The structural properties of the films were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). It is shown that the PZT ferroelectric thin films with (110) preferential orientation and well-crystallized perovskite structure can be obtained after annealing at 680°C for 30 minutes. The P-E hysteresis loops were measured by the Sawyer-Tower test system with a compensation resistor at room temperature. Values of the remanent polarization (P_r) and the coercive electric field (E_c) are 19.36•C/cm² and 95 kV/cm, respectively, for the prepared PZT thin films. The relative dielectric constant ε_r and the dissipation factor tg• of the PZT thin films are equal to 639 and 0.23, respectively, which were measured in a LCR meter.

Titanium-vanadium oxide films were prepared by the sol-gel method. The effects of vanadium incorporation on the crystallization behavior TiO₂ were investigated by X-ray diffraction analysis. The results showed that anatase and rutile type solid solution Ti_1-xV_xO₂ films were obtained for x < 0.15 and x > 0.15 samples, respectively. Anatase and V₂O₅ were found in x = 0.15 sample. Moreover, it was found that the crystallization of the film increased with increasing amount of vanadium. The electrical properties of Ti_1-xV_xO₂ films were studied by measuring their resistance and Hall mobility. It was revealed that the resistivity of Ti_1-xV_xO₂ films decreased with increasing x when the solid solution was formed, while the resistivity increased when the crystallization of vanadium oxide precipitated. The Hall constant was negative, indicating that Titanium-vanadium oxide is an n-type semiconductor. The evolution of the resistance and Hall mobility was ascribed to the 3d electrons of vanadium.

The Bi_3.25La_0.75Ti₃O₁₂ (BLT) thin films were prepared by metalorganic decomposition method. The effect of grain size on the ferroelectric properties during crystallization were investigated by x-ray diffraction and field emission scanning electron microscope. The grain size and the roughness of BLT films increase with increasing of drying temperature. The leakage current densities of the BLT thin film with large grains are higher than that with small grains. The remanent polarization of BLT increase with increasing grain size. As compared BLT with small grain size, the BLT film with larger grain size shows better fatigue properties. This may be explained that small grained films shows more degradation of switching charge than large grained films.

The intensities of SiH*, and H* of VHF-GD for depositing μc-Si:H were much higher than those of RF-GD for depositing a-Si:H. The SiH* intensity of VHF-GD became higher than its Si* intensity as the hydrogen dilution ratio decreased. The influences of the hydrogen dilution ratio on the plasma optical emission spectra also depended on the reaction pressure, the excitation power as well as the excitation frequency.

The RuO₂·xH₂O/C composites were prepared directly based on a sol-gel process under ultrasonic wave (50Hz). The specific capacitance of pure RuO₂·xH₂O materials obtained by the method reached a value of 760F/g. Physical properties of the material and electrochemical characteristics of electrodes were described.

The micro-defects in semi-insulating gallium arsenide (SI-GaAs) were investigated by means of chemical etching (ultrasonic aided Abtahams-Buiocchi etching, melting KOH etching), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The experimental results showed that the micro-defects in SI-GaAs are micro-precipitates of As with the size of microns. Micro-defects and dislocations have strong interaction, dislocations absorb the micro-defects and micro-defects decorate on the dislocations.

Dc current-voltage (I-V) measurement, Hall measurement, Deep-level transient-spectroscopy (DLTS), and flatband capacitance measurement have been used to investigate electrical activation energies in diamond. However, the deviations still exist in the published activation energies obtained by these methods. In this paper, we report the first measurement of impedance on free-standing diamond films from 0.1Hz to 10MHz up to 300°C. A wide range of CVD materials have been investigated, but here we concentrate on 'black' diamond grown by MWPECVD. The Cole-Cole (Z′ via Z″) plots are well fitted to a RC parallel circuit model and the equivalent Resistance and Capacitance for the diamond films have been estimated using the Zview curve fitting. The results show only one single semicircle response at each temperature measured. It was found that the resistance decreases from 62 MΩ at room temperature to 4 KΩ at 300°C, with an activation energy around 0.15eV. The equivalent capacitance is maintained at the level of 10² pF up to 300°C suggesting that the diamond grain boundaries are dominating the conduction. At 400°C, the impedance at low frequencies shows a linear tail, which can be explained that the AC polarization of diamond/Au interface occurs.

The initial stages of NH₃ exposure on Si (100) & Si (111) at different substrate temperatures and post annealing in different ambient gases have been investigated. On the Si (100) surface, at 850°C and very high (~ 1050°C) temperatures, NH₃ dissociated and nitridized the Si interface. The degree of nitride crystallization has been enhanced at elevated temperature (~ 1050°C). The interfacial trapped density is lower at higher temperature. I-V measurements indicated that the electrical properties are improved as the substrate temperature is raised. The results were directly related to the better interfacial registry. For the Si(111) substrates, the trends are similar to Si(100), but are more prominent.

We prepared the Bi₂Sr₂Ca_n-1Cu_nO_y (Bi-based) whiskers by the method of Al₂O₃-seeded by the method was about 3 times larger than that by the previous method glassy quenched platelets (ASGQP). The maximum growth rate of the whiskers obtained without any Al₂O₃ seeding. From the resistance-temperature (R-T) characteristics, we found that the temperature transition widths of the Bi-2212 and the Bi-2223 phases were about 2K and 4K, respectively. In addition, the whiskers showed that the FWHM (full-width-half-maximum) value of the (0010) XRD peak was less than 0.06°. The critical current density of the whiskers was more than 10⁴A/cm² at 60K and 0T. The results indicate that the whiskers grown by the ASGQP method have good crystallinity and high quality.