Surface Impurity Concentration Research Articles

Specific Features of the Segregation-Related Redistribution of Phosphorus during Thermal Oxidation of Heavily Doped Silicon Layers

A model of the diffusion-segregation redistribution of phosphorus in an SiO2/Si system during thermal oxidation of highly doped silicon layers is developed taking into account the formation of a peak of surface impurity concentration at the interface. The formation of this surface concentration peak is attributed to a change in the free energy of the impurity atoms near the silicon surface. This process is simulated by a diffusion-segregation equation. It is shown that the developed diffusion-segregation model is quite adequate for describing the phosphorus redistribution occurring during the oxidation of uniformly doped silicon layers. For the oxidation of implanted silicon layers, it was found that the segregation coefficient of the phosphorus at the SiO2/Si interface is not constant but depends on time in the same way as the efficiency of transient enhanced diffusion in silicon. This phenomenon is explained by the reactivity of the impurity segregation during the thermal oxidation of silicon, when excess point defects in the implanted silicon layer affect both the oxidation process and the capture of impurity atoms by the growing silicon dioxide.

Piezoresistance measurement on single crystal silicon nanowires

A p-type single crystal silicon nanowire bridge and a four-terminal nanowire element were fabricated by electron-beam direct writing. The piezoresistance was investigated in order to demonstrate the usefulness of these sensing elements as mechanical sensors. The longitudinal piezoresistance coefficient πl[110] was found to be 38.7×10−11 Pa−1 at a surface impurity concentration of Ns=9×1019 cm−3 for the nanowire bridge. The shear piezoresistance coefficient π44 was found to be 77.4×10−11 Pa−1 at Ns=9×1019 cm−3 for the four-terminal nanowire element. These values are 54.8% larger than the values obtained from p+ diffused piezoresistors, which are used in conventional mechanical sensors.

Single crystal silicon nano-wire piezoresistors for mechanical sensors

A p-type silicon (Si) nano-wire piezoresistor, whose minimum cross-sectional area is 53 nm/spl times/53 nm, was fabricated by combination of thermal diffusion, EB (electron beam) direct writing and RIE (reactive ion etching). The maximum value of longitudinal piezoresistance coefficient /spl pi//sub l[011]/ of the Si nano-wire piezoresistor was found to be 48/spl times/10/sup -5/ (1/MPa) at surface impurity concentration of 5/spl times/10/sup 19/ (cm/sup -3/) and it has enough sensitivity for mechanical sensor applications. The longitudinal piezoresistance coefficient /spl pi//sub l[011]/ of the Si nano-wire piezoresistor increased up to 60% with a decrease in the cross sectional area, while transverse piezoresistance coefficient /spl pi//sub t[011]/ decreased with a increase in the aspect ratio of the cross section. These phenomena were briefly investigated based on a hole energy consideration and FEM (finite element method) stress analysis.

Structural characterization of a dimeric dimethylindium azide and its use as a single-source precursor for InN thin films

Dimeric dimethylindium azide, [Me 2In(μ-N 3)] 2 ( 1), was prepared from the reaction of Me 3In with HN 3. A single-crystal X-ray diffraction study reveals that 1 exists as a three-dimensional network of three symmetry-independent azide-bridged, centrosymmetric dimers. In each dimer, the two azido groups lying in the same plane of the (In–N) 2 ring have a linear geometry, and the two indium atoms exhibit a distorted octahedral geometry. InN thin films were grown with 1 on Si(111) substrates in the temperature range 350–450°C in the absence of carrier gas by a low-pressure chemical vapor deposition method. The stoichiometry of the resulting films was determined by X-ray photoelectron spectroscopy (XPS). The films are nitrogen-deficient InN (In:N≈1:0.60) with high surface impurity concentrations (C ≈20%, O ≈27%). The film structure was examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The films appear to be polycrystalline and show diffraction patterns characteristic of the expected hexagonal wurtzite structure.

Pb/ p-PbSe junction: An investigation of current-voltage and capacitance-voltage measurements

Molecular beam epitaxy has been used to grow p-PbSe/CaF 2/Si(111) heterostructures. Using such stuctures, which are fully compatible with standard photolithographic technological procedures, photovoltaic sensors have been realized. The I( V) characteristics of the Pb/ p-PbSe contacts have been investigated experimentally and theoretically over a wide temperature range from 4 to 300 K. Evidence of the contribution of bulk and surface impurity concentrations in the space charge region at high temperature is presented. The Schottky barrier height has been derived from a fit to the experimental data. We used the theory of Padovani and Stratton in the context of Fermi-Dirac statistics. In addition the capacitance-voltage characteristics of Pb/ p-PbSe diodes have been investigated. The Schottky barrier height has been obtained and the existence of an inversion layer at the surface of p-type PbSe layer has been demonstrated.

Control of Surface Concentration of Boron or Phosphorus Employing Ion Shower Doping

An ion shower doping technique has been applied to control the surface concentration of boron or phosphorus on a silicon wafer both for p‐well and n‐well complementary metal oxide semiconductor (CMOS) wafer processes. The dose is controllable in the range from 1012 to and has a proportional relation with the doping time. Both surface impurity concentrations of boron and phosphorus within the range from 1016 to can be obtained, the range required for CMOS wafer processing. Fabricated MOS transistors have shown the characteristics comparable to those obtained from devices fabricated with ion implanters which are conventionally used in the semiconductor industry. As a result, it has been ascertained that ion shower doping can be utilized in the CMOS wafer process.

Visible and near-infrared reflectivity during the ablation period on Peyto Glacier, Alberta, Canada

AbstractModels for calculating glacier mass balance are sensitive to surface reflectivity variation. Fieldwork carried out on Peyto Glacier, Alberta, Canada, contributes to the data set available for ice-reflectivity parameterization in such models. Hemispherical reflectivity in the visible and near-infrared parts of the solar spectrum was obtained for rock, snow and three contrasting glacier surfaces to examine temporal and spatial variations. Glacier-ice near-infrared reflectivity displays only minor spatial variation (0.12–0.17) in comparison with the visible range (0.23–0.40), the latter being influenced primarily by surface impurity content. Surface roughness is of minor importance compared with impurities. Temporal variation of reflectivity was weak at all glacier-ice and rock locations; slight variations observed were due to changes in either solar zenith angle or cloud amount. Snow reflectivity displayed pronounced diurnal asymmetry and a larger response to cloud cover. The minimal temporal variation in glacier-ice reflectivity simplifies its parameterization. This behaviour is additionally useful for satellite-based measurements of the reflectivity field on larger glaciers, as images obtained within a 6 h window centred on solar noon are likely to yield values which are within 2–3% of daily mean values.

Visible and near-infrared reflectivity during the ablation period on Peyto Glacier, Alberta, Canada

AbstractModels for calculating glacier mass balance are sensitive to surface reflectivity variation. Fieldwork carried out on Peyto Glacier, Alberta, Canada, contributes to the data set available for ice-reflectivity parameterization in such models. Hemispherical reflectivity in the visible and near-infrared parts of the solar spectrum was obtained for rock, snow and three contrasting glacier surfaces to examine temporal and spatial variations. Glacier-ice near-infrared reflectivity displays only minor spatial variation (0.12–0.17) in comparison with the visible range (0.23–0.40), the latter being influenced primarily by surface impurity content. Surface roughness is of minor importance compared with impurities. Temporal variation of reflectivity was weak at all glacier-ice and rock locations; slight variations observed were due to changes in either solar zenith angle or cloud amount. Snow reflectivity displayed pronounced diurnal asymmetry and a larger response to cloud cover. The minimal temporal variation in glacier-ice reflectivity simplifies its parameterization. This behaviour is additionally useful for satellite-based measurements of the reflectivity field on larger glaciers, as images obtained within a 6 h window centred on solar noon are likely to yield values which are within 2–3% of daily mean values.

Effect of surface impurities segregation and ion sputtering on ion driven deuterium permeation through copper

The deuterium permeation through a polycrystalline copper membrane driven by an ion beam (3 keV D 2 +) was measured as a function of temperature (573–873 K) and surface impurity concentration. For copper a single-impurity layer can be prepared by combining thermal annealing and argon ion bombardment. The surface recombination coefficient was evaluated from the measured permeation flux. Under assumption that the segregation of sulphur on the surface results in modification of the activation energy for chemisorption, E C, the value of E C was calculated as a function of sulphur concentration.

Quarter-micrometer SPI (Self-aligned Pocket Implantation) MOSFET's and its application for low supply voltage operation

A novel SPI (Self-aligned Pocket Implantation) technology has been presented, which improves short channel characteristics without increasing junction capacitance. This technology features a localized pocket implantation using gate electrode and TiSi/sub 2/ film as self-aligned masks. An epi substrate is used to decrease the surface impurity concentration in the well while maintaining high latch-up immunity. The SPI and the gate to drain overlapped structure such as LATID (Large-Angle-Tilt Implanted Drain) technology allow use of the ultra low impurity concentration in the channel region, resulting in higher saturation drain current at the same gate over-drive compared to conventional device. The carrier velocity reaches 8/spl times/10/sup 6/ cm/sec and subthreshold slope is less than 75 mV/dec, which can be explained by low impurity concentration in the channel and in the substrate. The small gate depletion layer capacitance of SPI MOSFET was estimated by C-V measurement, and it can explain high performance such as small subthreshold slope. On the other hand, the problem and the possibility of low supply voltage operation have been discussed, and it has been proposed that small subthreshold slope is prerequisite for low power device operated at low supply voltage. In addition, the drain junction capacitance of SPI is decreased by 65% for N-MOSFET's, and 69% for P-MOSFET's both compared with conventional devices. This technology yields an unloaded CMOS inverter of 48 psec delay time at the supply voltage of 1.5 V.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Plasmon radiation from a silver surface during ion bombardment

Continuous spectra of plasmon radiation from a Ag surface bombarded by 15 keV H +, He +, O + ions are investigated. The spectra in the region 200–600 nm are characterized by a broad maximum at λ = 330–360 nm depending on the experimental conditions. It is shown that the position of the maximum is very sensitive to the presence of oxygen impurities (0.001–0.05 of a monolayer) introduced either by adsorption or by implantation. The maximum position is sensitive also to ion flux and the type of bombarding ions (sputtering coefficient). This is suggested to be connected with a change in surface impurity concentration associated with a variation of ion beam parameters.

Nonlinear piezoresistance effects in silicon

Nonlinearity of the piezoresistance effects in p- and n-type silicon was measured at room temperature for three surface impurity concentrations and for three crystallographic orientations &amp;lt;100≳, &amp;lt;110≳, and &amp;lt;1̄1̄2≳. Piezoresistance coefficients up to third order in stress were obtained experimentally. Uniaxial stresses up to about 174 MPa were applied with currents flowing either parallel (longitudinal configuration) or perpendicular (transverse configuration) to them. A complete set of nine independent second-order tensor components was determined. The second-order piezoresistance coefficients in various configurations of uniaxial stress, current, and crystallographic orientation were calculated by the sixth rank tensor transformation. The nonlinear piezoresistance effect in n-type silicon was discussed with the many-valley model.

Theoretical study of thin and thick emitter silicon solar cells

We describe a complete theoretical model to calculate the open circuit voltage, the light generated current density, and the conversion efficiency of thin and thick emitter silicon solar cells. We show the importance of the Fermi carrier degeneracy, in addition to the heavy doping effects such as band-gap narrowing and Auger recombination. For example, in contradiction to recent calculations, the conversion efficiency of thin passivated emitter solar cells is shown to be independent of the surface dopant concentration. Also, in agreement with experimental results, but contrary to old conventional cell designs, it is shown that the conversion efficiencies of thick emitter solar cells can be as high as those of thin emitter cells. The last result will occur whenever the emitter is well passivated and the surface impurity concentration is relatively low (Ns=1×1019 cm−3). For non-passivated solar cells it is better to have thin emitters and high surface dopant concentrations (Ns≳2×1020 cm−3) as usual in conventional solar cells.

Matrix-effect correction in oxide crystal Auger electron spectroscopy

A simple model is presented for the calculation of surface elemental composition, surface impurity content and surface chemical termination in complex oxide crystal surfaces. The model is based upon Auger electron spectroscopic measurements and takes electronic inelastic mean free paths or attenuation lengths and bulk crystallographic data into consideration. Different results are obtained when using either the attenuation length or the electronic inelastic mean free path for the surfaces stoichiometric weights. MgO(100), SrTiO 3(100), LaAlO 3(100), and YBa 2Cu 3O 7− x (001) are used as test samples. Uncertainties are estimated at 10–20%.

7631. Selective suppression of photochemical dry etching using elevated surface impurity concentrations: a new technique for self-aligned etching: C I H Ashby et al, J Appl Phys, 68, 1990, 2406–2410

7631. Selective suppression of photochemical dry etching using elevated surface impurity concentrations: a new technique for self-aligned etching: C I H Ashby et al, J Appl Phys, 68, 1990, 2406–2410

Selective suppression of photochemical dry etching using elevated surface impurity concentrations: A new technique for self-aligned etching

High concentrations of recombination-promoting impurities in the near-surface region of a semiconductor can produce virtually complete suppression of carrier-driven photochemical etching processes. In-diffusion of Zn to levels appropriate for ohmic contact formation on GaAs (mid-1020/cm3) has been employed to reduce etching to an undetectable level in n-GaAs with n=1.0×1017 and 1.3×1018/cm3 and to produce a greater than ten-fold reduction in etching of semi-insulating GaAs. Raman spectroscopy of the altered near-surface region shows enhanced electronic scattering, which indicates the presence of a sufficient impurity concentration to suppress etching. Transmission electron microscopy shows the near-surface region to be crystalline without significant numbers of defects following Zn diffusion. Possible applications of this process include self-aligned etching of transistor and laser structures.

The quantum collection efficiency of heavily doped emitters in silicon solar cells

Abstract The importance of the minority carrier degeneracy on the collection efficiency (air mass (AM) 1) of heavily doped emitters in silicon solar cells is shown by means of a simple analytical model. In our calculations we include explicitly the effects of space-dependent mobility, lifetime, band gap narrowing and the Fermi-Dirac statistics for donor concentrations higher than N d = 1 × 10 20 cm −3 . We show that for passivated in emitters the collection efficiency is high and almost independent of the surface dopant concentration. However, for thick emitters ( x j > 2 μm ) it is convenient to have small surface impurity concentrations ( N s 20 cm −3 ) in order to achieve high collection efficiencies. In addition, for non-passivated solar cells the collection efficiency should be higher when the surface impurity concentration is greater, in conjunction with a smaller thickness. All of the above confirm experimental results that both thin and thick emitter solar cells can be made that attain high conversion efficiencies, using an appropriate design.

Effect of Powder Surface Chemistry on the Stability of Concentrated Aqueous Dispersions of Alumina

The surface chemistry differences between two alumina powders is shown to have a significant effect on the properties of concentrated aqueous dispersions of the powders. The initial dispersion pH and magnitude and sign of the initial mobility of the particles (determined by acoustophoresis) are different for the two powders because of differences in surface impurity contents. As a result, the two powders require different amounts of dispersant to achieve stability in dispersions near their isoelectric points. The surface chemistry differences between these two aluminas illustrate the importance of examining ceramic dispersion properties at the concentrations used in processing the material.

Fermi degeneracy and its effects on the open-circuit voltage of silicon solar cells

A theoretical explanation of the high open-circuit voltage (Voc) in n+-p silicon solar cells despite the heavy doping effects (such as Auger recombination and rigid band-gap narrowing) is given. It is shown that, contrary to recent expectations, when the surface impurity concentration is Ns ≥2×1020 cm−3 the open-circuit voltage is approximately the same as that for surface passivated cells with Ns ≤2×1019 cm−3. Furthermore, in the case of high values of Ns the open-circuit voltage becomes almost independent of the surface recombination velocity. Our model shows that these facts are due to the Fermi degeneracy and the internal electric field. Therefore, high concentrations of activated donors should be looked forward to for obtaining high-efficiency n+-p solar cells.

An improved simple procedure for calculating the open-circuit voltage of passivated emitter silicon solar cells

The effects due to band gap shrinkage, Auger and surface recombination, variation of mobility and lifetime of minority carriers, and the electric field (caused by the gradient of effective doping concentration in the emitter) are included in a simple iterative procedure for the computer calculation of the open-circuit voltage of passivated emitter silicon solar cells. It is shown that in order to obtain high conversion efficiencies, the surface impurity concentration has to be reduced by an order of magnitude with respect to conventional n +−p diffused solar cells.