Infrared absorption by pairs of group III and V impurities in silicon

Infrared absorption bands, shifted to regions of lower energies relative to narrow lines of transitions of impurities to excited states, are investigated in silicon doped with group III and V impurities in concentrations above 10¹⁶ cm^?3. It is found that the band structure is peculiar to each of the investigated impurities but independent of their concentrations, and the absorption coefficients in the bands increase approximately quadratically with concentration. This leads one to infer that the bands are caused by the excitation of charge carriers bound on impurity pairs localized within several Bohr radii.     

Quantitative piezospectroscopy of group V impurities in Germanium

The deformation potential constant, ξ_u, of the lowest conduction band of germanium is found to be 16.4 ± 0.2 eV from the splitting of the 2p₀ line of arsenic impurity under uniaxial stress. The same value is found for Ξ_u of the lower ground state.     

High resolution spectroscopy of the A-band absorption structure

Experimental evidence on the triplet structure of the A absorption band in KBr: T1 is given. The results are obtained by means of the high resolution derivative technique that allowed us to reveal the true structure of the band without applying any external perturbation to further remove the degeneracy of electronic levels. A computer best fit was also used to obtain the parameters of the three subbands in the normal as well as in the derivative spectrum.     

High resolution absorption spectroscopy of NO2

The absorption cross-section of NO₂ has been measured above the 3979 predissociation limit in the region of 3920 and 3950 and in the discretely structured areas around 4112 and 4140 . Spectra were taken in a dual-beam arrangement using a tunable, pulsed dye laser with 0.05 bandwidth (FWHM). This represents an improvement of at least a factor of three over the resolution employed in previous studies. Below 3979 , the spectra are continous with occasional diffuse rotational lines superimposed. The spectra taken above 4100 reveal a wealth of structural complexity. We report here absolute cross-sections taken at 300 . The work above 4100 was also performed at 250 . Only slight variations in the measured cross-sections are observed between these two temperatures.     

High speed logic gate using two-photon absorption in silicon waveguides

The switching speed of conventional silicon-based optical switching devices based on plasma dispersion effect is limited by the lifetime of free carriers which introduce either phase or absorption changes. Here we report an all-optical logic NOR gate which does not rely on free carriers but instead uses two-photon absorption. High speed operation was achieved using pump induced non-degenerate two-photon absorption inside the submicron size silicon wire waveguides. The device required low pulse energy (few pJ) for logic gate operation.     

Device for measuring doping impurities of Groups III and V in high-purity silicon by long-wavelength spectroscopy

An experimental installation for analyzing electrically active impurities in high-purity silicon by investigating low-temperature transmission spectra withcompensation for donor-acceptor impurities is fabricated. The applicability of the method for studying both high-purity and doped silicon wafers is shown.Software for automatically computing the concentration of impurities is developed.     

Gettering of metallic impurities in photovoltaic silicon

 This work addresses the issue of structural defect-metallic impurity interactions in photovoltaic silicon and their effect on minority carrier diffusion length values. Aluminium and phosphorus segregation gettering studies were performed on photovoltaic silicon in order to gain insight into these interactions and quantify the effect of gettering on solar cell performance. Integrated circuit grade silicon was also studied for comparative purposes. Additionally, a novel rapid thermal annealing technique, designed to dissolve metallic impurity precipitates, and Deep Level Transient Spectroscopy were utilized to determine the as-grown impurity concentration in both grades of materials. Significant differences in gettering responses between the two grades of silicon are observed. Gettering treatments greatly improve I.C. grade silicon with a specific gettering temperature providing the optimal response. Photovoltaic grade silicon does not respond as well to the gettering treatments and, in some cases, the material degrades at higher gettering temperatures. The degradation is primarily observed in dislocated regions of multicrystalline photovoltaic silicon. Additionally, these dislocated regions were found to possess the highest as-grown metallic impurity concentration of all the materials studied. The dislocation-free photovoltaic silicon has a higher diffusion length relative to dislocated silicon but could not be improved by the gettering methods employed in this study. A model is presented to describe these phenomena where the high concentration of metallic impurities at dislocations produce relatively low minority carrier diffusion lengths as well as the degrading response with higher gettering temperatures while microdefects create an upper limit to the photovoltaic grade material’s diffusion length. Received: 21 June 1996/Accepted: 2 September 1996     

X-ray absorption study of light emitting silicon nanocrystals

X-ray absorption spectra obtained by total electron yield (TEY) at the Si absorption K-edge have been measured to have chemical and structural information about Si nanocrystals (Si-nc) produced by plasma-enhanced chemical vapour deposition (PECVD). The TEY technique has been employed to investigate the formation of Si-nc and the modification of the silica matrix as a function of annealing temperature (500–1250°C) and of silicon content in the film (35–46 at%). The amount of silicon present in the Si-nc has been evaluated by TEY. Thanks to Rutherford backscattering spectrometry measurements, the amount of Si atoms bonded to oxygen and to nitrogen, incorporated by PECVD, has been assessed. A compositional model that interprets the experimental findings is presented.     

High resolution X-ray studies of porous PbTe layers on silicon substrates

The structure of PbTe films after anodic electrochemical etching in Norr electrolyte is studied by high resolution X-ray diffractometry and reflectometry. Lattice defects before and after etching are estimated. The quantitative parameters of the pores are determined. The advantage of the complex application of high resolution X-ray methods for the determination of the real structure of lead-telluride porous films is shown.     

High resolution optogalvanic study in nitrogen discharge

Doppler limited high resolution spectrum in the wavelength region 17224 to 17236 cm⁻¹ of the first positive system (B ³Π _g −A ³Σ _u ⁺ ) of the N₂ molecule is recorded by optogalvanic spectroscopic technique using a single mode ring dye laser. It is observed that the intensity and line width of the rotational line increase with the discharge current. Dependence of the collision broadening coefficient on the current was also evaluated.     

电解精炼制备太阳级硅杂质行为研究

在氟化物电解质体系下,把Cu与冶金级多晶硅熔配成合金作为阳极,利用杂质与硅析出电位的差别,通过控制电解工艺条件和参数,对冶金硅进行了电解精炼提纯研究.结果表明,阳极铜硅合金对硅中的杂质有滞留作用,且在大电流密度下Cu不会随着合金中硅的减少而溶解到电解质中;预电解对电解质净化效果明显,XRF分析表明P含量从10降为1ppmw;阴极电沉积的硅呈颗粒状,并与电解质混杂,随着电解时间的延长,分散的硅的颗粒聚集成1—2cm直径的大尺寸硅球.ICP-AES分析表明,最后得到的产物硅与冶金级硅相比,硼含量由12·7降低到2·2ppmw,磷含量由98·6减少到4·1ppmw,说明电解精炼除杂进行多晶硅的提纯是有效和可行的.     

Nature of conduction via impurities in uncompensated silicon

The static conductivity σ(E) and photoconductivity (PC) at radiation frequencies ħω=10 and 15 meV in Si doped with shallow impurities (density N=10¹⁶−6×10¹⁶ cm⁻³, ionization energy ε₁≃45 meV) with compensation K=10⁻⁴−10⁻⁵ in electric fields E=10–250 V/cm are measured at liquid-helium temperatures T. Special measures are taken to prevent the high-frequency part of the background radiation (ħω>16 meV) from striking the sample. It is found that the conductivity σ(E) is due to carrier motion along the D ⁻ band, which is filled with carriers under the influence of the field E. In fields E<E _q (E _q ≃100–200 V/cm) the carrier motion consists of hops along localized D ⁻ states in a 10–15 meV energy band below the bottom of the free band (energy ε=ε₁); for E>E _q carriers drift along localized D ⁻ states with energy ε∞ε₁−10 meV. An explanation is proposed for the threshold behavior of the field dependence of the photo-and static conductivities. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 4, 232–236 (25 August 1997)     

A comparative study of nonrelativistic and relativistic 5d atoms as impurities in silicon

A comparison is made between calculations performed nonrelativistically and relativistically for W, Re, Os, Ir, Pt, Au and Hg as substitutional impurities in silicon. The calculations were carried out using the relativistic extended Hückel method. The direct and indirect relativistic effects upon the 5d-like levels and band-gap levels are analysed.     

Near-field effect in the absorption spectrum of impurities in crystals

The effect of the near-field interaction of shallow donors in GaAs on the intracenter absorption spectrum of impurities has been considered. It has been shown that the near-field interaction leads to broadening of the absorption line, which increases with the donor density. The absorption line shape is no longer Lorentzian: its low-frequency wing becomes more prolonged than the high-frequency wing.     

An EPR study of optical absorption of the oxygen-vacancy pair in electron-irradiated silicon

The negative charge state of the vacancy-oxygen pair (Si-B1) in irradiated silicon was populated by illumination with polarized light, from which the direction of the electric dipole moment was determined to be near 〈110〉 perpendicular to the (Si-O-Si) bond axis. Energy dependence of the alignment suggests the presence of an optical absorption band at λ = 1.30 μm.     

Infrared absorption of various isolated impurities in GaAs

We have calculated the infrared absorption at the local mode frequency for various isolated impurities such as B, Al, Mg, Si, C, and P in GaAs. To calculate the local mode frequency we take into account the effects from impurity mass defect and local force constant shifts and use the symmetry properties of the lattice. To calculate the absorption we consider contributions to the dipole moment from impurity and nearest neighbour charges and from charge migration effects. We suggest a physical model which accounts for impurity and nearest neighbour charges and polarizabilities.     

A rutherford scattering study of the diffusion of heavy metal impurities in silicon to ion-damaged surface layers

Rutherford backscattering of 1.75 and 2 MeV ⁴He⁺ ions has been utilized to study the high temperature gettering of Fe, Co, Ni, Cu and Au from silicon by ion-damaged surface layers. In a typical experiment a metal film was evaporated onto one side of a silicon wafer (125 microm thick) which had received ion implantation damage (10¹⁶/cm² Si⁺ ions at 100 keV) on the opposite side; the wafer was then annealed at 900°C, usually for 30 min. The results of such experiments show that the metals studied may be divided into two classes, those which are gettered slowly - Fe, Co, and Au, and those gettered rapidly - Cu and Ni. Fe, Co, and Au were found at levels of 1×10¹³?1×10¹⁴/cm² in the damaged layer, whereas Cu and Ni appeared at levels of 6×10¹⁴ to 5 ×10¹⁶cm². The gettered level of Au, one of the “slow” group, was increased ten-fold by an equal increase in the anneal time to 300 min. The gettered Cu and Au exhibited double peaks in the scattered ion spectra, corresponding to metal concentrated at the most heavily damaged region (end of range for Si implant) and also at the outer surface, with a separation of ~ 1300 Å. A simple model is proposed to explain the slow and fast gettering, based on published interstitial diffusivities and solubilities of the five elements studied.Rutherford scattering has proven to be well suited for the quantitative identification of low levels of impurities on Si surfaces and for impurities gettered at damaged layers close to the surface.     

A valence bond theory of off-center impurities in silicon

We present the first cluster calculations which explicitly include electronic correlation effects in the study of impurities in Si (e.g., nitrogen and oxygen). The calculations provide a natural explanation of the observed off-center features of these impurities in terms of dangling bonds, lone pairs and bond pairs - concepts which, in contrast to the usual molecular orbital and band theories, are well-defined within the context of the correlated wave functions used here.