Polycrystalline silicon with large disk-shaped grains by Ni-mediated crystallization of doped amorphous silicon

Silicide mediated crystallization (SMC) of p-doped amorphous silicon (a-Si) has been studied. There are the different grain-shapes of crystallization of doped and non-doped a-Si. Non-doped a-Si is crystallized with needle-shaped grains, while it is observed the disk-shaped grains are formed in crystallized doped a-Si. The crystallization of slightly doped a-Si exhibits larger grain size compared with non-doped and heavily doped films. The p-dopant in a-Si suppresses the formation of the NiSi₂ precipitate which act as a crystallization nucleus, causing continuous grain growth and the formation of disk-shaped grains.     

Structural difference of surface and sub-surface native oxides of evaporated amorphous silicon

Evaporated amorphous silicon (a-Si) films, oxidized in air or O₂ at room temperature, present two native oxides with different structures. The surface oxide is constructed from SiO₄-tetrahedron structural units with a 110° O---Si---O angle, which is the common structural unit of stable silicon oxides. The internal oxide has a different structure having a 120° O---Si---O angle. The results of molecular orbital (MO) calculations for (SiO₃)^m− and (SiO₄)ⁿ⁻ anionic clusters support the presence of the two stable structures of silicon oxides and also reveal the importance of the ionic character of the oxidized sites.     

Band offsets of high dielectric constant gate oxides on silicon

High dielectric constant oxides will soon be needed to replace silicon dioxide as the gate dielectric material in complementary metal oxide semiconductor technology. The oxides must have band offsets with silicon of over 1 eV for both electrons and holes in order to have low leakage currents. We have calculated the band offsets for many candidate oxides using the method of charge neutrality levels. Ta₂O₅ and SrTiO₃ have small or vanishing conduction band offsets on Si. La₂O₃, Y₂O₃, Gd₂O₃, ZrO₂, HfO₂, Al₂O₃ and silicates like ZrSiO₄ have offsets over 1.4 eV for both electrons and holes, making them better gate dielectrics. Zirconates are better than titanates as they have wider gaps.     

On absorption spectra temperature dependence in lithium niobate doped with transition metal oxides

Absorption spectra temperature dependence of LiNbO₃ doped with the Cr-, Mn-, Fe, Co-, Ni- and Cu-irons is studied. Band gap variation of the doped lithium niobate against impurity, temperature and light polarization direction is determined.     

Study of the oxygen role in the photoluminescence of erbium doped nanocrystalline silicon embedded in a silicon amorphous matrix

We have produced and studied erbium doped nanocrystalline silicon thin films with different oxygen and hydrogen content in order to evaluate the influence of the matrix on the Er³⁺ emission and on the 0.89 eV and 1.17 eV bands. Films were grown by reactive magnetron sputtering on glass substrates under several different conditions (RF power, Er content and gas mixture composition) in order to obtain different microstructures. The structural parameters and the chemical composition of the samples were obtained by X-ray in the grazing incidence geometry, Raman spectroscopy and Rutherford back scattering analysis. Using X-ray technique combined with Raman spectroscopy information on the crystalline fraction and the average crystallite size of Si nanocrystals was obtained. Dependence of the 0.89 eV and 1.17 eV peaks in Si heterogeneous matrixes on the films crystallinity and O/H ratio has been analyzed.     

Growth monitoring by reflectance anisotropy spectroscopy in MOVPE reactors for device fabrication

Reflectance anisotropy spectroscopy (RAS) has proved its capability to study surface processes during metalorganic vapour phase epitaxy (MOVPE) growth of a variety of III–V compounds. However, these investigations up to now have been mostly restricted to specialized research reactors. Therefore, we studied the feasibility of in-situ monitoring by RAS during growth on two production-type MOVPE reactors: horizontal 2 inch single wafer reactor AIX 200 and Planetary Reactor™ AIX 2000 for 5 × 3 inch. The slight modifications of the reactors necessary to gain normal incidence optical access to the sample do not alter the properties of the grown materials. While in the horizontal reactor the strain-free optical window allows one to obtain well-resolved RAS spectra the signals in the multiwafer reactor are affected by the anisotropy of the ceiling plate. Even in this case RAS spectra can be extracted. First measurements on rotating samples in the horizontal reactor demonstrate the possibility to obtain RAS spectra by multitransient spectroscopy. As an application monitoring of the growth of p-type layers for the base of GaInP/GaAs hetero-bipolar-transistors (HBTs) is discussed. The linear electro-optic effect (LEO) gives information on doping type and doping level. Time-resolved transients at specific energies are used to study the impact of different switching schemes on the properties of the base-emitter interface.     

Optical properties of hydrogenated amorphous silicon films doped with fluorinated gases

Doped amorphous silicon films were prepared by plasma-enhanced chemical vapour deposition of silane and hydrogen mixtures, using phosphorus pentafluoride (PF₅) and boron trifluoride (BF₃) as dopant precursors. The films were studied by UV-vis spectroscopy and their photo and dark conductivity were measured, the latter as a function of temperature. The optical gap of the n-type samples, doped with PF₅, diminished as the concentration of this gas in the plasma was increased. However, the optical gap of p-type samples, doped with BF₃, did not show any appreciable optical gap decrease as the concentration of BF₃ was varied from 0.04% to 4.7%. The dark conductivity of the p-type films at these extremes of the doping range were 7.6 × 10⁻¹⁰ and 3.5 × 10⁻¹ Ω⁻¹ cm⁻¹, respectively.     

Linear and nonlinear optical properties of the optical fiber doped with silicon nano-particles

We report for the first time the realization of the optical fiber doped with silicon nano-particles. Silica glass optical fibers incorporated with silicon nano-particles were fabricated by the modified chemical vapor deposition and the solution doping technique. We found that a broadband absorption appeared at 450–1300 nm and a photoluminescence band appeared at 600–1100 nm upon pumping with the Ar-ion laser, indicating that silicon nano-particles were successfully incorporated in the fiber core. We also estimated the third-order optical nonlinearity of the optical fibers by measuring the fringe shift obtained from the long-period gratings upon pumping with the Ar-ion laser from 477 to 512 nm. Importantly the optical nonlinearity at 1550 nm was found to be ～1.5 × 10^?15 m²/W and we believe that this large optical nonlinearity is caused by the exciton absorption of the silicon particles.     

Effect of illumination on hydrogenated amorphous silicon thin films doped with chalcogens

Hydrogenated amorphous silicon thin films doped with chalcogens (Se or S) were prepared by the decomposition of silane (SiH₄) and H₂Se/H₂S gas mixtures in an RF plasma glow discharge on 7059 corning glass at a substrate temperature 230 °C. The illumination measurements were performed on these samples as a function of doping concentration, temperature and optical density. The activation energy varied with doping concentration and is higher in Se-doped than S-doped a-Si:H thin films due to a low defect density. From intensity versus photoconductivity data, it is observed that the addition of Se and S changes the recombination mechanism from monomolecular at low doping concentration films to bimolecular at higher doping levels. The photosensitivity (σ_ph/σ_d) of a-Si, Se:H thin films decreases as the gas ratio H₂Se/SiH₄ increased from 10^?4 to 10^?1, while the photosensitivity of a-Si, S:H thin films increases as the gas ratio H₂S/SiH₄ increased from 6.8 × 10^?7 to 1.0×10^?4.     

Properties of non‐stoichiometric nitrogen doped LPCVD silicon thin films

The influence of nitrogen on the internal structure and so on the electrical properties of silicon thin films obtained by low‐pressure chemical vapor deposition (LPCVD) was studied using several investigation methods. We found by using Raman spectroscopy and SEM observations that a strong relationship exists between the structural order of the silicon matrix and the nitrogen ratio in film before and after thermal treatment. As a result of the high disorder caused by nitrogen on silicon network during the deposit phase of films, the crystallization phenomena in term of nucleation and crystalline growth were found to depend upon the nitrogen content. Resistivity measurements results show that electrical properties of NIDOS films depend significantly on structural properties. It was appeared that for high nitrogen content, the films tend to acquire an insulator behavior. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

In situ mesa etching and immediate regrowth in a HVPE reactor for buried heterostructure device fabrication

Mesa etching in a hydride vapour-phase epitaxy (HVPE) reactor has been studied. Etched depth, underetching and shape of the mesas have been analysed as a function of partial pressures of active gases (HCl, PH₃ and InCl), stripe orientation and etching temperature. The experimental results show that the depth and undercut can be etched independently. We propose qualitative mechanisms for etching each of the emerging crystallographic planes ((0 0 1), (1 1 0) and {1 1 1}). In situ mesa etching with immediate regrowth was applied to the fabrication of buried heterostructure Fabry–Perot lasers. No surface contamination due to exposure to ambient and low process time are advantages of this technique.     

Mechanism of formation of barium cuprate-based solid solutions with perovskite-like structure doped with cadmium and yttrium oxides

The influence of Y₂O₃ and CdO content on the phase composition, structure, and electrical properties of Y₂O₃-CdO-BaO-CuO ceramics was studied. The concentration limits of the existence of the orthorhombic perovskite-like Y_xBa_{2 ? x} Cd_yCu_{1 ? y} O_{3 + δ} solid solutions (where 0.20 ≤ x ≤ 0.37 and y ≤ 0.2) and their unit-cell parameters are determined.     

Relationship between structure and optical properties in rare earth-doped hafnium and silicon oxides: Modeling and spectroscopic measurements

The SiO₂–HfO₂ binary system is recognized as a promising candidate for Erbium-doped waveguides amplifiers fabrication. Recently, it was demonstrated that Er³⁺-activated 70SiO₂–30HfO₂ planar waveguides with valuable optical and structural properties can be prepared by sol–gel technique with dip-coating processing. The important role played by hafnium in the silica network was evidenced by the particular spectroscopic properties presented by Er³⁺-ions in the silica–hafnia planar waveguides. In this work we present preliminary results on HfO₂–SiO₂ bulk xerogels doped with Eu³⁺ ions, with the aim to go inside the role of hafnium on the rare earth ions local environment. Spectroscopic measurements of the Eu³⁺ photoluminescence emission are given. Numerical simulations by the molecular dynamics method have been performed showing clearly a phase separation for the HfO₂ richer samples. Moreover it is found than the rare earth-doping ions stay preferentially in hafnium rich domains, thus explaining why the rare earth spectroscopic properties are strongly modified.     

Morphotropic series of Bi-containing layered perovskite-like oxides and principles of their systematics

The well-known bismuth-containing layered perovskite-like oxides (BLPO) of composition A _{m ? 1}Bi₂ B _m O_{3m + 3} are divided into morphotropic series. In these series, the a, b, and c parameters of the orthorhombic unit cells and the Curie temperature (T _c ) change monotonically with increasing unstrained interatomic A-O bond lengths, when A are s elements. For compounds in which A are p elements (Pb^II or Bi^III), the a and b unit-cell parameters and T _c , unlike the c unit-cell parameter, deviate substantially from these correlations, with the deviations decreasing with an increase of the m parameter. These facts must be taken into consideration in the search for new BLPO, whose compositions are predicted with the use of the systematics.     

On the investigation of dopant boundaries in silicon device structures by means of SEM-EBIC

The capabilities to study the geometrical construction of silicon devices by the technique of the electron beam induced current (EBIC) are reviewed with particular emphasis to the 2-dimensional determination of dopant boundaries (p-n junctions) including a discussion of demands for such investigations from a microelectronic point of view. The investigations of buried layers and MOS short-channel transistors are outlined. As a substantial topic the preparation of electrically stable surfaces at cleaved samples is discussed and an example of the possibility of cross-sectional analysis for junction delination is briefly given.     

Defects and stresses in MBE-grown GaN and Al0.3Ga0.7N layers doped by silicon using silane

The electric and structural characteristics of silicon-doped GaN and Al_0.3Ga_0.7N layers grown by molecular beam epitaxy (MBE) using silane have been analyzed by the Hall effect, Raman spectroscopy, and high-resolution X-ray diffractometry. It is established that the electron concentration linearly increases up to n = 4 × 10²⁰ cm^?3 with an increase in the silane flow rate for GaN:Si, whereas the corresponding dependence for Al_0.3Ga_0.7N:Si is sublinear and the maximum electron concentration is found to be n = 4 × 10¹⁹ cm^?3. X-ray measurements of sample macrobending indicate a decrease in biaxial compressive stress with an increase in the electron concentration in both GaN:Si and Al_0.3Ga_0.7N:Si layers. The parameters of the dislocation structure, estimated from the measured broadenings of X-ray reflections, are analyzed.     

Silica films on silicon carbide: a review of electrical properties and device applications

This paper reviews the present knowledge on silica films (SiO₂) on silicon carbide (SiC). First, kinetic of thermal oxidation of SiC is described, and the effects of a great number of parameters (various SiC polytypes, substrate type, substrate orientation…) are discussed. Mainly, thermal oxides grown on SiC are close to stoichiometric silica and the oxidation rate depends on the terminal face of the SiC monocrystal. The next four sections discuss the electrical properties of the oxide, and of the oxide/SiC interface, and especially the effects of materials and technological process on the interface state density and the effective oxide charge (Section 5), and the origin of the interface states are discussed in detail ( Section 6). Oxides grown on n-type SiC have electrical properties (in terms of dielectric strength, leakage currents, interface trap, and oxide charges) measured by means of metal-oxide-semiconductor (MOS) structures, similar to oxides grown on silicon. Until recently, p-type SiC MOS structures have had a large equivalent oxide charge and larger interface state densities in spite of many efforts, compared to silicon MOS structures. It seems nevertheless that recent studies have improved the SiO₂/SiC interfacial quality. Aluminum, carbon and alkali species are the main suspected contaminants. Finally, Section 7 presents the applications of oxide films in SiC-based devices: MOS capacitors and MOS field effect transistors (MOSFETs) for microelectronics, MOSFETs for power electronics, and some applications using silica layers as a passivation layer. In spite of a smaller than required carrier mobility in the inversion layer, MOS field effect transistors (MOSFETs) have been demonstrated to operate up to 650°C and integrated circuits based on NMOS and PMOS technologies have been successfully operated up to 300°C. Vertical power MOSFETs are also of importance but their performances are still limited by a specific on-resistance larger than device requirements. The effect of charges present in the oxide on the electrical properties of high voltage diodes is also briefly discussed.