Optical Properties Of Silicon Research Articles

The synthesis, characterization and optical properties of silicon and praseodymium doped Y 6MoO 12 compounds: Environmentally benign inorganic pigments with high NIR reflectance

Novel, yellow, brown and brick-red colored, near-infrared reflective pigments based on yttrium molybdate doped with metal ions such as Si 4+ or Pr 4+ are described. Replacing Si 4+ for Y 3+ in Y 6MoO 12 changed the color from light-yellow to dark-yellow and the band gap decreased from 2.60 to 2.45 eV due to O 2p-Mo 4d charge transfer transitions. In contrast, replacing Pr 4+ for Y 3+ changed the color from light-yellow to dark brown and the band gap shifted from 2.60 to 1.90 eV. The coloring mechanism is based on the introduction of an additional 4f 1 electron energy level of Pr 4+ between the valence and conduction bands. The NIR reflectance of the pigments on asbestos cement sheet was measured.

An effective hamiltonian for the optical properties of silicon and germanium

An effective Hamiltonian which yields the observed optical properties of silicon and germanium is presented. The form of the Hamiltonian depends upon crystal symmetry and is based on a Fourier expansion for the energy bands. This Hamiltonian is closely related to the Slater-Koster interpolation scheme and has been applied as an interpolation scheme for experimental data.

Study of the electrical and optical properties of silicon containing oxygen precipitates

The properties of n-type silicon with oxygen precipitates introduced by three-stage annealing were studied by the electron beam induced current (EBIC) method, deep-level transient spectroscopy (DLTS), and photoluminescence (PL). The presence of extended defects with concentration of ≤109 cm−3 is revealed by the EBIC method. The concentration of electrically active defects formed in silicon due to oxygen precipitation is estimated from the EBIC contrast and is compared to that obtained from the DLTS data. Comparing the spectra of samples with oxygen precipitates with those of plastically deformed crystals, we can assume that the DLTS and PL spectra of silicon with oxygen precipitates are mainly determined by dislocations.

Optical properties of gas source MBE grown AlInP on GaAs

Optical properties of silicon (Si) doped Al x In 1− x P grown by gas source molecular beam epitaxy (GSMBE) have been investigated by using photoluminescence (PL). The PL peaks of Al x In 1− x P shift to higher energy side as Al mole fraction increases in direct bandgap region, and the fractions of strained portion have been calculated. Results also show that for direct bandgap Al x In 1− x P both band-to-band (B–B) and donor-to-acceptor (D–A) transition peaks exist, the D–A pair peak shifts to higher energy side as the excitation power increases. A weak PL peak has been observed for indirect bandgap sample, and this peak is noticed to shift to lower energy side as Al mole fraction increases. The thermal activation energies of the impurities also have been estimated by observing the temperature dependence of the PL intensity of the D–A pair peaks.

Plasma synthesis and liquid-phase surface passivation of brightly luminescent Si nanocrystals

While silicon's optical properties are improved at the nanoscale, they also become highly sensitive to the properties of the surfaces and interfaces of silicon nanostructures. For instance, while reported quantum yields for photoluminescence of silicon quantum dots covered by a native oxide are often in the few percent range, quantum yields as high as 30% have been found in quantum dots whose surfaces were passivated by covalently bonded organic molecules. In this paper, we describe an approach that is based on the gas phase synthesis of silicon quantum dots in a nonthermal plasma, and the subsequent organic surface passivation in the liquid phase. Nanocrystals are formed within a few milliseconds with a high mass yield in a nonthermal plasma. Various organic ligands such as octadecene, dodecence, and styrene are grafted onto the nanocrystal surfaces in a reaction known as hydrosilylation. Materials are characterized through transmission electron microscopy, atomic force microscopy, and fluorescence measurements. The particle size distributions are found to be relatively monodisperse and are well controllable through the plasma process parameters. Photoluminescence quantum yields as high as 60–70% have been achieved for particles luminescing in the red range of the visible spectrum.

Optical properties of Si and Ge nanocrystals: Parameter‐free calculations

AbstractThe cover picture of the current issue refers to the Edi‐tor's Choice article of Ramos et al. [1]. The paper gives an overview of the electronic and optical properties of silicon and germanium nanocrystals determined by state‐of‐the‐art ab initio methods. Nanocrystals have promising applications in opto‐electronic devices, since they can be used to confine electrons and holes and facilitate radiative recombination. Since meas‐urements for single nanoparticles are difficult to make, ab initio theoretical investigations become important to understand the mechanisms of luminescence.The cover picture shows nanocrystals of four sizes with tetrahedral coordination whose dangling bonds at the surface are passivated with hydrogen. As often observed in experiments, the nanocrystals are not perfectly spherical, but contain facets. Apart from the size of the nanocrystals, which determines the quantum confinement, the way their dangling bonds are passivated is relevant for their electronic and optical properties. For instance, the passivation with hydroxyls reduces the quantum confine‐ment. On the other hand, the oxidation of the silicon nanocrys‐tals increases the quantum confinement and reduces the effect of single surface terminations on the gap. Due to the oscillator strengths of the lowest‐energy optical transitions, Ge nanocrys‐tals are in principle more suitable for opto‐electronic applica‐tions than Si nanocrystals.The first author, Luis E. Ramos, is a postdoc at the Institute of Solid‐State Physics and Optics (IFTO), Friedrich‐Schiller University Jena, Germany. He investigates electronic and optical properties of semiconductor nanocrystallites and is a member of the European Network of Excellence NANO‐QUANTA and of the European Theoretical Spectroscopy Facility (ETSF).

Strain induced photoluminescence from silicon and germanium nanowire arrays

The optical properties of silicon and germanium nanowires grown within the pores of hexagonal mesoporous silica matrices have been characterised by ultraviolet absorption and photoluminescence (PL) spectroscopy. A clear blue-shift in the PL of the semiconductor composite materials was observed as the diameter of the nanowires decreased from 85 to 22 A. Powder X-ray diffraction revealed that, as the diameter of the confined nanowires decreased, the strain on the crystallographic structure of the nanowires increased, due to escalating lattice expansion, resulting in a shift in the PL maximum to higher energies. The ability to manipulate the optical properties in templated semiconductor nanowires, through strain engineering, has important implications for the design of future optical devices.

Towards controllable optical properties of silicon based nanoparticles for applications in opto-electronics

Size-dependent optical properties of laser-synthesized Si-based nanopowders were investigated by photo-luminescence (PL) and photo-luminescence excitation (PLE) spectroscopy on powder samples annealed in air in the 700–1000 °C temperature range. TEM analysis reveals that at increasing annealing temperature a progressive Si nanoparticle size reduction occurs as a consequence of crystalline core oxidation, and a corresponding blue-shift of the PL emission is observed. The subsequent step is the preparation of nanocomposite materials by nanopowders dispersion and integration into a continuous silica phase by sol–gel processing. Synthesis parameters are adjusted in order to preserve the PL red emission from Si nanostructures. An interesting application would consist in the Er incorporation into the nanocomposite glassy material aiming at the 1.54 μm Er emission sensitization by energy transfer from Si nanostructures to nearby Er ions. However, it was found that Si nanoparticles are completely oxidized at the processing temperatures (1400 °C) required to activate Er emission. Here we demonstrate that better and promising results can be achieved introducing in the sol–gel Si-based nanopowders withstanding higher temperatures.

Structural and optical properties of silicon nanoparticles prepared by pulsed laser ablation in hydrogen background gas

We studied the structural and optical properties of silicon (Si) nanoparticles (np-Si) prepared by pulsed laser ablation (PLA) in hydrogen (H2) background gas. The mean diameter of the np-Si was estimated to be approximately 5 nm. The infrared absorption corresponding to Si-Hn (n=1,2,3) bonds was observed at around 2100 cm-1, and a Raman scattering peak corresponding to crystalline Si was observed at around 520 cm-1. These results indicate that nanoparticles are not an alloy of Si and hydrogen but Si nanocrystal covered by hydrogen or hydrogenated silicon. This means that surface passivated Si nanoparticles can be prepared by PLA in H2 gas. The band-gap energy of np-Si prepared in H2 gas (1.9 eV) was larger than that of np-Si prepared in He gas (1.6 eV) even though they are almost the same diameter. After decreasing the hydrogen content in np-Si by thermal annealing, the band-gap energy decreased, and reached the same energy level as np-Si prepared in He gas. Thus, the optical properties of np-Si were affected by the hydrogenation of the surface of np-Si.

Electrical and optical properties of Si-doped InP grown by solid source molecular beam epitaxy using a valved phosphorus cracker cell

We report on the electrical and optical properties of silicon (Si)-doped InP layers grown by solid-source molecular beam epitaxy using a valved phosphorus cracker cell. Within the range of Si effusion cell temperatures investigated (900–1200 °C), the highest electron concentration obtained was 1.1×1020 cm−3. A saturation phenomenon was observed for the electron concentration at higher Si cell temperatures. 300 and 77 K Hall mobility data were used to determine the compensation ratios by comparing them with the theoretical data. Although the Hall data show that the compensation ratio increases with the increase in carrier concentration, the exact values are not certain because the theoretical calculation overestimates the mobility values at higher carrier concentrations. The saturation phenomenon of electron concentration in InP may be considered due to the Si atoms occupying both the In and P lattice sites, or Si donors located at the interstitial sites. The 300 K Hall mobility and the concentration data measured were found to fit the Hilsum expression well. The mobility values obtained in this study are better than or comparable to reported data in the past, indicating good material quality. 5 K photoluminescence (PL) measurements showed two peaks for the undoped and low doped InP layers corresponding to the neutral donor-bound exciton transitions (D0–X) and the acceptor-related transitions (D–A), respectively. When the doping level was increased, the near-band edge (D0–X) recombination peak becomes broadened and asymmetric due to changes in the donor level density of states and relaxation of the wave vector conservation rule. The full-width at half-maximum (FWHM) value of the PL peak position increased when the doping concentration was increased. An empirical equation was developed to fit this variation, which provides a convenient way of determining the dopant concentration from the experimental FWHM value. The near-band edge peak positions shifted to higher energy with the increase of doping level due to the band filling effect. This shift agreed well with the calculations based on the Burstein–Moss shift and the band gap narrowing effect considering a nonparabolic conduction band.

Optical properties of silicon pigmented alumina films

Plates of Al–Si alloy were anodized in a sulfuric acid solution. This treatment provides a Si–Al2O3 coating growing at a rate of 0.14 μm/min. The Si particles had sizes between 1 and 10 μm, as seen by scanning electron microscopy. Optical measurements showed a continuous decrease of reflectance with increasing film thickness. The reflectance of the Si–Al2O3 coated aluminum could be understood from a four flux radiative transfer theory. In order to explain our measurements, it was found necessary to include a free-carrier term in the dielectric permittivity of Si. The free carriers are probably due to doping with Al. Hence, the relaxation time of the free carriers is determined by scattering from the charged Al impurities.

Optical spectra of Si/Ge-network copolymers: [Si(C6H13)]1−x[Ge(C6H13)]x

Optical properties of silicon- and germanium-based network copolymers, [Si(C6H13)]1−x- [Ge(C6H13) ]x, have been investigated for various Si/Ge compositions (x). The backbone Si/Ge atoms are coordinated by the three other Si/Ge backbone atoms in the polymers. These Si/Ge copolymers show the absorption spectra which are typical of amorphous semiconductors. Their color continuously traverses the visible range with x, which is due to the change of the band gap (Tauc gap) energy as well as to the presence of localized subgap states. The Si/Ge copolymer shows a broad band of luminescence in the visible region. The luminescence band maximum was observed to shift by ∼0.5 eV with change of the Si/Ge ratio.

Porous silicon sheds a new light on OEICs

Research efforts and developments in understanding the origin of the luminescence of porous silicon are reviewed. The fundamental characteristics of porous silicon are outlined. The quantum confinement model, which is used to characterize the luminescence from porous silicon, and porous silicon's optical properties, which show substantial instabilities, are discussed. The research into and applications of electroluminescence using porous silicon are also discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Optical properties of silicon and its oxides

We have measured the inelastic electron scattering spectra of a variety of Si and SiO2 thin films from the fundamental absorption threshold to well above the L-shell thresholds. We have used Kramers–Kronig analyses and sum rules to obtain the dielectric and optical response functions. We compare the optical properties of crystalline and evaporated and hydrogenated amorphous Si, amorphous evaporated SiO and SiO2, and chemical-vapor-deposition SiO2 in both the interband and the L-shell absorption regions. The interband structure in crystalline Si shows three sharp peaks that are blended into a single broad peak in the amorphous samples. At the L threshold crystalline Si also shows more structure than amorphous Si, however, the overall shape in the region well above the threshold is quite similar in the three samples. Above the SiO2 band gap the three oxide samples show strikingly similar behavior.

Time-resolved infrared radiometry of laser-heated silicon

Time-resolved pulsed photothermal radiometry techniques for the study of the thermal and optical properties of silicon are discussed. By the use of a one-dimensional thermal diffusion equation, a theoretical description for the transient thermal radiation can be developed. Results obtained for relatively heavily doped samples (~0.002 Ω-cm) show that the pulsed photothermal radiometry is an excellent remote diagnostic technique for silicon over a wide range of relatively heavy doping levels. For lightly doped samples (~5 Ω-cm), an anomalously large thermal radiation signal is observed that contradicts the predictions of the thermal diffusion model. The phenomenon can be explained by the enhancement of the gray-body emissivity due to laser-generated free carriers. A simple theoretical model for the free-carrier effect is presented.

High quality Si-on-SiO2 films by large dose oxygen implantation and lamp annealing

Ion beam synthesis of a buried SiO2 layer is an attractive silicon-on-insulator technology for high-speed complementary metal-oxide-semiconductor circuits and radiation hardened devices. We demonstrate here a new annealing procedure at 1405 °C that produces silicon films of excellent quality, essentially free of oxygen precipitates and with sharp interfaces between the Si and the SiO2. Buried oxide layers have been formed in Si (100) wafers by implanting 400 keV molecular oxygen at 500 °C to a dose of 1.8×1018 cm−2. Annealing was performed by radiative heating of the back side of each sample to the melt temperature of silicon, TM=1412 °C, so that the buried oxide structure was at 1405 °C. The temperature control relies entirely on the change in optical properties of silicon upon melting. This ensures, without any external feedback, that the surface exposed to the photon flux will remain at TM.

Time-Resolved Ellipsometry and Reflectivity Measurements of the Optical Properties of Silicon During Pulsed Excimer Laser Irradiation

ABSTRACTSeveral advances in time-resolved optical measurement techniques have been made, which allow a more detailed determination of the optical properties of silicon immediately before, during, and after pulsed laser irradiation. It is now possible to follow in detail the time-resolved reflectivity signal near the melting threshold; measurements indicate that melting occurs in a spatially inhomogeneous way. The use of time-resolved ellipsometry allowed us to accurately measure the optical properties of the high reflectivity (molten) phase, and of the hot, solid silicon before and after the laser pulse. We obtain n = 3.8, k = 5.2 (±10.1) at λ = 632.8 nm for the high reflectivity phase, in minor disagreement with the published values of Shvarev et al. for liquid silicon. Before and after the high reflectivity phase, the time-resolved ellipsometry measurements are entirely consistent with the known optical properties of crystalline silicon at temperatures up to its melting point.

A Detailed Examination of Time-Resolved Pulsed Raman Temeperature Measurements of Laser Annealed Silicon

ABSTRACTRaman temperature measurements during pulsed laser annealing of Si by Compaan and co-workers are critically examined. It has been shown previously that the Stokes to anti-Stokes ratio depends critically upon the optical properties of silicon as a function of temperature. These dependences, coupled with the large spatial and temporal temperature gradients normally found immediately after the high reflectivity phase, result in large variations in the calculated temperature depending upon the probe laser pulse width and the pulse-to-pulse and spatial variations in the annealing pulse energy density.

The Characterisation of Laser and Electron Beam Annealed Silicon by Infrared Spectrophotometry

ABSTRACTAn exact model of the IR reflectance and transmission spectra of inhomogeneously doped silicon has been developed. By comparing theoretically and experimentally generated spectra in the range 1.2 to 25 μm, information about the doping profile may be deduced. The technique has been applied to laser and electron beam annealed silicon (as well as furnace annealed) and comparisons made with theoretical profiles and SIMS analysis in the latter case. No values consistent with other published data have been found for the optical properties of silicon at high doping levels (&gt;1020 cm−3).

Structure and optical properties of silicon implanted by high doses of 70 and 310 keV carbon ions

Structure and optical properties of silicon implanted by high doses of 70 and 310 keV carbon ions