Increasing Impurity Concentration Research Articles

Potential variations around grain boundaries in impurity-doped BaSi2 epitaxial films evaluated by Kelvin probe force microscopy

Potential variations around the grain boundaries (GBs) in antimony (Sb)-doped n-type and boron (B)-doped p-type BaSi2 epitaxial films on Si(111) were evaluated by Kelvin probe force microscopy. Sb-doped n-BaSi2 films exhibited positively charged GBs with a downward band bending at the GBs. The average barrier height for holes was approximately 10 meV for an electron concentration n ≈ 1017 cm−3. This downward band bending changed to upward band bending when n was increased to n = 1.8 × 1018 cm−3. In the B-doped p-BaSi2 films, the upward band bending was observed for a hole concentration p ≈ 1018 cm−3. The average barrier height for electrons decreased from approximately 25 to 15 meV when p was increased from p = 2.7 × 1018 to p = 4.0 × 1018 cm−3. These results are explained under the assumption that the position of the Fermi level Ef at GBs depends on the degree of occupancy of defect states at the GBs, while Ef approached the bottom of the conduction band or the top of the valence band in the BaSi2 grain interiors with increasing impurity concentrations. In both cases, such small barrier heights may not deteriorate the carrier transport properties. The electronic structures of impurity-doped BaSi2 are also discussed using first-principles pseudopotential method to discuss the insertion sites of impurity atoms and clarify the reason for the observed n-type conduction in the Sb-doped BaSi2 and p-type conduction in the B-doped BaSi2.

Detection of Corrosion-Induced Tensile Stress in Aluminum

The enhancement of mechanical degradation by corrosion is the basis for damage processes such as stress corrosion cracking. Corrosion-induced degradation has been attributed to a wide variety of mechanisms.1 Here we show that high-resolution in situ stress measurements during Al corrosion reveal corrosion-induced tensile stress generation, leading to surface plasticity. This finding is evidence that corrosion can directly bring about plasticity, and may be relevant to mechanisms of corrosion-induced degradation. The present measurements are possible because of the unprecedented curvature resolution achievable through the present phase-shifting curvature interferometry method, which permit the monitoring of stress during extended periods of corrosion of thick metal samples.2,3 Al samples were 1 mm thick hard 5N Al sheets or 25 mm thick 5N annealed foils bonded to Si wafers. Some sheet samples were cold worked to 35 % thickness reduction. A reflective gold film was applied to the back side of each sample, which was in contact with air while the front side was exposed to solution. Curvature changes were measured by monitoring interference between two laser beams, each of which reflected twice on the gold surface. Curvature was converted to force per sample width using the Stoney equation.2 The force per width is the integrated in-plane stress through the sample thickness. The obtainable curvature resolution of 10-3 km-1is about 10 times higher than state-of-the-art deflectometry techniques. Thus, while thin metal films on wafers are typically employed in the latter experiments, stress in bulk samples can be measured with curvature interferometry.Fig. 1 shows that the Al samples exhibited large rates of alkaline corrosion-induced tensile stress increase, qualitatively similar to those measured previously on evaporated thin films.4At the outset of dissolution, force increased approximately linearly with time until a plateau was reached at 10-20 min. The plateau force was highest for the cold-worked sheet and smallest for the annealed foil. The yield stress of these samples was determined from Vickers hardness measurements, and found to scale linearly with the plateau stress (inset). Therefore, the plateaus in Fig. 1 apparently correspond to the onset of plastic flow. The preceding linear increase of force may correspond to the buildup of elastic stress to the yield stress. Similar force transients were observed in 1 M NaOH using Al samples with increased impurity content, and with 5N Al samples in solutions of lower pH. The plateau stress increased with impurity concentration and pH (i. e. metal dissolution rate).Tensile stress buildup during corrosion was modeled in terms of diffusion of Al atoms from near-surface dislocations to the metal-oxide interface. The force evolution was predicted based on the requirement of zero net strain resulting from additive contributions from elastic strain, plastic strain associated with power-law creep and diffusion-induced strain. Fitting the model to the force transients yielded values of the Al diffusivity. The elevated values of the fit diffusivity suggested significant rates of metal vacancy injection during the corrosion process. ACKNOWLEDGMENTThis work was supported by the National Science Foundation through NSF-CMMI-100748.REFERENCES1. R. C. Newman, in Corrosion Mechanisms in Theory and Practice,P. Marcus, Editor, p. 499 (2002).2. O. O. Çapraz, K. R. Hebert, and P. Shrotriya, J. Electrochem. Soc., 160,D501 (2013).3. O. O. Çapraz, P. Shrotriya and K. R. Hebert, J. Electrochem. Soc., 161,D256 (2014).4. K. R. Hebert, J. H. Ai, G. R. Stafford, K. M. Ho and C. Z. Wang, Electrochim. Acta, 56, 1806 (2011).Figure 1. Force per width evolution during dissolution of 5N Al samples in aqueous 1 M NaOH solutions at room temperature. In the inset, the force per width at the plateau is plotted vs. the sample yield stress.

Si purity control and separation from Si–Al alloy melt with Zn addition

During solidification refining of Si, the eutectic alloy ultimately solidifies and becomes enriched with impurity elements according to their small segregation coefficients, which may contaminate the primary Si through the cooling process. Combined with analysis of the morphology of the primary Si, the contamination mechanism was verified for a Si–63.8wt%Al alloy using various cooling rates in the final cooling stage (873–293K). By a quenching treatment, the B content in Si was decreased from the initial content of 14.8 to 1.4ppmw, which is quite close to the value predicted by Scheil’s equation. Si cooled down at a rate of 1K/min showed an increase in impurity content (e.g., B: 4.2ppmw) owing to solid-state back-diffusion. In order to prevent such contamination, Zn was added to the Si–Al melt at 873K, which decreased the eutectic temperature and separated Si from the alloy. A final Si amount of 94.1wt% was recycled without further contamination.

Effect of composition on sinter-crystallization and properties of low temperature co-fired α-cordierite glass–ceramics

Abstract This article investigates effect of composition, including SiO 2 and impurity defined to contain K 2 O, Na 2 O, Fe 2 O 3 , etc., from K-feldspar, on sinter-crystallization and properties of the low temperature co-fired α-cordierite glass–ceramics. Increasing impurity content from 5.72 wt% to 9.16 wt% leads to enhanced crystallinity, formation of leucite and more pores but the crystallinity and porosity decreased with a further increase to 10.8 wt%. The main impurity K 2 O is critical for formation of α-cordierite and leucite. Only α-cordierite was precipitated from the glasses with different SiO 2 contents but an increase of SiO 2 content slightly improves their densification. The impurity and SiO 2 contents greatly affect the properties of glass–ceramics. Notably, some glass–ceramics from K-feldspar show high densification at low temperature, low dielectric constant (6–8), low loss (about 0.005), appropriate linear CTEs (4.32–5.87 × 10 −6 K −1 ) and flexural strength (above 100 MPa), all of which meet the requirements of LTCC substrates.

Effect of impurities on the hydrolysis of low-concentration titanyl sulfate solutions

Hydrolysis of titanyl sulfate solutions with TiO2 concentrations of 140–180 g/L was investigated. The effects of the concentrations of impurities present in ilmenite, for example iron(II), magnesium, and aluminium, on hydrolytic conversion, and on the morphology and composition of the hydrolysates, were examined. The results showed that with increasing impurity concentrations, the conversion was gradually decreased, but still maintained at ~95 %. The concentrations of these impurity ions substantially affected the morphology of the hydrolysates. The higher the concentrations of the impurities were, the more irregular and non-uniform were the hydrolysate particles. When iron-to-titanium dioxide (Fe/TiO2) mass ratios in the precipitate liquors were >0.50, the hydrolysates became very compact and difficult to filter and disperse. It was found that the hydrolysate crystallites first formed primary particles which had a very similar particle sizes of 30–50 nm, despite different concentrations of titanium and the impurity ions used. The primary particles further aggregated and formed secondary aggregates probably via sulfate bridge bonds. The concentrations of the impurities substantially affected the amounts of hydrated SO3 adsorbed by the hydrolysates, which increased with increasing impurity concentrations, resulting in increased agglomeration of the primary particles.

(Invited) Thermochromic Phase Transitions in VO2-Based Thin Films for Energy-Saving Applications

Materials that contribute to more sustainable technologies are in high demand, and the highest impact can be made in the structures that are most ubiquitous. Widely implemented, thermochromic ‘smart’ building windows have the potential to save energy by reducing the heating and cooling loads on HVAC systems.1,2 Exploiting a crystalline phase transition in VO2, these window coatings shift from infrared transparent on cold days when solar heating is desirable to infrared reflective as the ambient temperature increases. In pure VO2, this transition occurs at 68°C, but the incorporation of 1-5% cation impurities can depress the transition temperature to Earth ambient temperatures.In this talk we describe our results on infrared thermochromism in V1-xMxO2thin films, for M = Ta, Nb, W, Hf, and others. To efficiently screen the vast compositional space of transitional metal impurities in VO2, we employ a combinatorial materials technique for both material synthesis and characterization. Thin film libraries of continuously varying composition are prepared by pulsed laser deposition (PLD) from two or more unary metal oxide targets, e.g. V2O5 and Ta2O5. Taking advantage of the spatial non-uniformity of deposition rates from each target, we produce library samples of composition V1-xMxO2where x can vary from <0.01 to 0.3 across a single 3” diameter wafer. A special high-throughput spectroscopic reflectance measurement apparatus has been constructed for screening these libraries for thermochromic transitions. A thermoelectric heater/chiller with a 3” diameter plate maintains library temperature at a setpoint between 5°C and 85°C, while near infrared (NIR) reflectance measurements are made at many library locations, and hence many unique compositions. In Figure 1, for each composition represented on the V1-xTaxO2 sample library, the NIR reflectance switches from a low reflectance state to a high reflectance state, a consequence of the crystalline phase transition that occurs. The transition is reversible with a <10°C hysteresis, and the material returns to its low reflectance state as the material is cooled back to 20°C. As the Ta impurity content increases, the transition temperature decreases.Figure 2 shows depression of transition temperatures in VO2 due to the incorporation of Nb or Ta. Both are found to effect a temperature depression that is linear with concentration at -4 °C/atomic percent. Additionally, the higher valence state impurities, such as W, Nb, and Ta, depress the VO2transition temperature while Hf incorporation has little to no effect.‘Smart’ window coatings enabled by the metal-insulator phase transition in lightly-substituted VO2have significant energy-saving potential in terms of decreased heating and cooling needs for commercial and residential buildings. Critically, the NIR transmission/reflection switch occurs due to ambient temperature, and so the technology is passive, requiring no external controls or power systems.

Low-Temperature Electron Spectra of Impurities in Naphtalene Crystals

This work relates to the study of vibrational structures in the electron spectra of naphthalene crystals with impurities of b- and a-naphthalene fluorine with concentrations of 10^−4 to 10 wt.% at a temperature at 4.2 K. It is determined that, at low impurity concentrations, the spectra have a doublet structure and consist of narrow quasilines with initial values of v01 = 31322 cm^−1 and v02 = 31226 cm^−1, which are resonance-coincident in the absorption and fluorescence spectra. It is demonstrated that if the impurity concentration increases, the series of narrow quasilines appear in the areas of the 0-0 transitions of the impurity centers of both types together with the doublet structure. A part of these quasilines is polarized predominantly along the b-axis of a naphthalene crystal. The model is proposed for impurity centers, which induce the generation of new spectral bands. This model is based on the interaction of translation-nonequivalent impurity molecules in the elementary lattice cell of a naphthalene crystal. At high impurity concentrations, the resonance-symmetric wide spectral bands appear in the absorption and fluorescence spectra. The analysis of the results obtained is performed with consideration for the Franck–Condon interaction and the Herzberg–Teller interaction.

Analysis of Structural and Electrical Properties of Iron Sulfide (FeS2)Thin Films doped with Aluminum and Strontium impurities

Abstract: Thin films of iron sulfide (FeS2) prepared by CBD technique were doped with aluminum (Al: 0.020.04M) and strontium (Sr: 0.02-0.04M) impurities at room temperature of 26 C. X-Ray diffraction (XRD) and four-point probe were used to analyze the structural and electrical properties of the thin films. The XRD results show that 0.02M of strontium impurities produced polycrystalline structure of the thin films with diffraction peak values located at Bragg’s angles, 2Θ of 14.71, 25.03 and 34.95, while the un-doped polycrystalline FeS2 thin films have diffraction peaks at 2Θ values of 19.81, 24.43, 31.45 and 36.73. Clearly, the contributing inphase reflections for the different diffraction angles occur from different orientations of lattice planes and/or different crystallite sizes caused by the Sr impurity. On the other hand, 0.02M of aluminum dopant produced mono-crystalline structure of the FeS2 thin film with 2Θ value of 24.97 o and a broadened full width at half maximum (FWHM). It is remarkable that the single peak of the mono-crystal due to Al impurity coincides with the highest intensity and sharper peak of the un-doped FeS2 thin film. The electrical resistivity of the thin films decreased while the conductivity increased with increase in impurity concentrations with non-uniform changes occurring from 0.02M for both impurities. The film thickness remained between 0.09-0.1μm but showed a more dramatic increase with impurity concentration from 0.02M for both impurities.

Simulation of erosion of the tungsten wall by impurities in the divertor plasma

Divertor is a component that directly contacts the plasma in tokamak. To ensure the lifetime of the device, it is necessary to reduce the erosion of the divertor wall by plasma. In this work, a particle-in-cell model is used to study the influences of plasma temperature and impurity concentration on the erosion of tungsten divertor wall by carbon and beryllium ions. The steady-state sheath, particle and energy fluxes to the wall, and the energies and angle of the incident ions can be obtained. Then, these data can be used as the input parameters for the plasma-surface interaction model, to evaluate the erosion rate of the plate based on the empirical formulas for physical sputtering. It is found that the erosion by heating plays a negligible role under the plasma condition of this work. Due to the low physical sputtering threshold energy of tungsten by impurities and the impurity ions accelerated by sheath, the physical sputtering of the tungsten by the impurities plays an dominant role in the total erosion. In addition, the erosion rate increases with the increase of plasma temperature and impurity concentration.

Effect of growth temperature on the impurity incorporation and material properties of N-polar GaN films grown by metal-organic chemical vapor deposition

We have investigated the influence of growth temperature on N-polar GaN epitaxial layers deposited on sapphire substrates by metal-organic chemical vapor deposition (MOCVD). The GaN films were grown at various temperatures (1050°C, 1000°C, 950°C, 900°C). The sheet resistivity of the GaN film was 2153ohm/□ at 950°C, which is 6 times higher than that at 1050°C (361ohm/□). Secondary ion mass spectroscopy (SIMS) measurement confirmed that the increase of carbon impurity concentration was responsible for the above phenomena. High-resolution X-ray diffraction (HRXRD), photoluminescence (PL) and Raman measurements showed that the GaN film quality did not deteriorate seriously at low growth temperature, implying that reducing the growth temperature would be a feasible method to obtain highly insulating N-polar GaN films. However, further reducing the growth temperature to 900°C led to the sharp increase of oxygen impurity concentration and the decrease of sheet resistivity. This mechanism is explained in detail.

Surface‐activating‐bonding‐based low‐resistance Si/III‐V junctions

The electrical properties of pn junctions, with various semiconductor materials with different doping concentrations fabricated by using surface-activated-bonding (SAB), were investigated by measuring their current-voltage ( I-V ) characteristics. The I-V characteristics of p + -GaAs/ n ++ -Si, p + -GaAs/ n + -Si, p + -Si/ n + -Si, p ++ -Si/ n + -InGaP, and p + -Si/ n + -InGaP junctions showed ohmic-like properties. The interface resistance and the resultant electrical loss decreased with increasing impurity concentration at the interface. These results demonstrate the significance of SAB for fabricating tandem solar cells.

General model for calcite growth kinetics in the presence of impurity ions

The concentrations of Sr, Mg and other elements in calcite are widely used to infer the conditions of mineral growth. However, such inferences are dependent on the mechanisms that govern the incorporation of minor constituents into the calcite lattice during growth. A particularly confusing observation is that both Sr and Mg are readily incorporated into growing calcite crystals at low concentrations but inhibit calcite growth at higher concentrations. Here we show that the growth rate dependence of Sr and Mg incorporation into calcite, as well the inhibitory effects on calcite growth of both incorporating and non-incorporating ions, can be predicted with an ion-by-ion crystal growth model where ion attachment is confined to kink sites on the crystal surface.The exchange of ions between active growth (kink) sites on the mineral surface and aqueous solution governs both the efficiency of incorporation of minor constituents and the kinetics of mineral precipitation. Ions such as Sr and Mg in calcite, that are not stoichiometric constituents, may attach to kink sites and impede crystal growth by either blocking propagation of the kink (kink blocking), or if incorporated into the growing mineral, straining the local crystal lattice, and hence increasing the mineral solubility (incorporation inhibition). Here we investigate the effects of including these growth inhibition mechanisms into a microscopic model for crystal growth based on kink creation, propagation and collision (CPC) theory. This model predicts that kink blocking by either incorporated or non-incorporated ions causes an exponential decrease in mineral growth rate with increasing impurity concentration, while incorporation inhibition results in more complicated functional forms of the growth rate effect depending on the thermodynamics of the solid solution. Applying this model to existing data on the partitioning of strontium and magnesium into calcite and the simultaneous effects on growth kinetics and mineral composition, we find that strontium uptake inhibits growth by enhancing mineral solubility while magnesium inhibits growth primarily by kink blocking. Our model should be widely applicable to understanding the impurity content of a large range of sparingly soluble minerals that form by precipitation from aqueous solutions.

Systematic study of photoluminescence, lyoluminescence and mechanoluminescence in Ce3+‐ and Eu3+‐activated Li3PO4 phosphors

Li3 PO4 phosphor was prepared using a modified solid-state diffusion technique. In this work, photoluminescence, lyoluminescence and mechanoluminescence studies were carried out in a Li3 PO4 microcrystalline powder doped with different rare earths. In photoluminescence studies, characteristic emission of Ce and Eu was observed. The lyoluminescence glow curves of Li3 PO4 microcrystals show that lyoluminescence intensity initially increases with time and then decreases exponentially. The decay time consists of two components for all masses. The dependence of decay time, especially the longer component, on mass has been investigated. Experiments on γ-irradiated crystals have proved that the light emission originates from the recombination of released F-centres with trapped holes (V2-centres) at the sulfuric acid-solid interface. Incorporation of bivalent alkali in solid lithium phosphate leads to an enhancement of lyoluminescence. A possible explanation for the experimental results has been attempted. The phosphor has a mechanoluminescence single glow peak. Mechanoluminescence intensity under various loading conditions was investigated. It is observed that mechanoluminescence intensity increases with increasing impurity concentration and increasing piston impact velocity. The results may be considered as only being of academic interest in solid-state materials.

Effects of Different Organic Acids on Solubility and Metastable Zone Width of Zinc Lactate

Effects of three different organic acids including racemic malic acid, succinic acid, and citric acid, which act as an impurity on the solubility and metastable zone width of zinc lactate (ZnL2), have been studied. The results show that the presence of all examined impurities increases the solution solubility and the values of solubility increase with increasing impurity concentration. The introduction of impurity also leads to a reduction on the metastable zone width, and the reductions are pronounced when the impurity concentration increased. Further, experimental data of metastable zone width were analyzed using the expression of the Nývlt’s approach and self-consistent Nývlt-like approach, which can be expressed in the form: ln(ΔTmax/T0) = Φ + β ln b, with intercept Φ = {(1 – m)/m}ln(ΔHd/RTlim) + (1/m)ln(f/KT0) and slope β = 1/m. Here T0 and Tlim are the saturation and nucleation temperature, respectively. m is the apparent nucleation order, and K is a new nucleation constant related to the factor f defined as the number of stable nuclei per unit volume, ΔHd, the heat of dissolution and R the gas constant. Comparing to the former one, the latter approach provides a more satisfactory estimation for the metastable zone width at varying saturation temperature T0. The constant β for specific system reveals independence of the temperature, while the constant Φ increases with increasing saturation temperature. In addition, both constants are proportional to the impurity concentration. Crystal habits of final products are also influenced in the presence of impurities, but the crystal structures are barely changed.

Origin of ferromagnetism in Zn-doped SnO2 from first-principles study

Density-functional calculations are carried out to study the magnetic properties and electronic structures of Zinc-doped SnO2 systems with and without oxygen (tin) vacancies. The magnetic moment increases almost linearly with the increase of impurity concentration (from 4% to 25%) in the cases without oxygen and tin vacancies. The induced magnetic moments mainly come from the first shell oxygen atoms surrounding the doped Zn atom. The magnetic moments become smaller (larger) when oxygen (tin) vacancy is introduced, which is not as seen in Co and Ni doped SnO2 systems. Oxygen (tin) vacancy defects are easily formed at the nearest distance from the doped Zn atom and the largest possible magnetic moments will appear at the concentration of Zn atom between 6.25% and 12.5%. The calculated results also show that Zn–Zn are ferromagnetically coupled, and how the magnetic moments vary with Zn–Zn distance when only two Zn atoms were doped into a SnO2 supercell. However, Zn–Zn show anti-ferromagnetic coupling when three Zn atoms are doped in the same SnO2 supercell. The results may be helpful for further study on TMs doped SnO2 systems.

Effect of transition-metal substitution in iron-based superconductors

We study theoretically the effect of transition-metal (TM) substitution in iron-based superconductors through treating all of the TM ions as randomly distributed impurities. The extra electrons from TM elements are localized at the impurity sites. In the meantime the chemical potential shifts upon substitution. The phase diagram is mapped out and it seems that the TM elements can act as effective dopants. The local density of states (LDOS) is calculated and the bottom becomes V-shaped as the impurity concentration increases. The LDOS at the Fermi energy ρ(ω = 0) is finite and reaches the minimum at the optimal doping level. Our results are in good agreement with scanning tunneling microscopy experiments.

Features of structure and property formation for cold-rolled low-carbon steels for automobile manufacture in relation to the degree of reduction during cold rolling

Features are established for preparation of high category (VOSV (extremely specially hard drawing), VOSV-T) rolled product of low-carbon steel 08Yu using small degrees of reduction during cold rolling. Production solutions are developed based on them for improving a set of mechanical properties. The effect of impurities on steel 08Yu properties is studied and recommendations are developed for correcting technology in order to provide high steel stamping properties with an increased impurity content.

Infrared Tunable Multichannel Filter in a Doped Semiconductor-Dielectric Photonic Crystal Heterostructure

A design of near- to mid-infrared tunable multichannel filter (MCF) based on the doped semiconductor-dielectric photonic crystal (PC) heterostructure is proposed. Here, a strongly extrinsic semiconductor, <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> -type germanium ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> -Ge), is used as one of the constituent layers. The occurrence of multichannel feature originates from the negative-permittivity in the highly doped <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> -Ge. The existence of tunable feature is due to its concentration-dependent permittivity. It is of interest to find that, in such MCFs, the number of channels, i.e., the number of resonant transmission peaks, is directly related to the stack number, and these peaks are located within the pass band of the ideal host PC. The multiple channels are blueshifted as the impurity concentration increases. This design suggests an alternative of engineering the pass band for realizing an MCF instead of engineering photonic band gap in a PC containing photonic quantum well structure as a defect. Our analysis is made based on the transfer matrix method together with the Bloch theorem.

Correlated disorder in a Kondo lattice

Motivated by recent experiments on Yb-doped CeCoIn5, we study the effect of correlated disorder in a Kondo lattice. Correlations between the impurities are considered at the two-particle level. We use a mean-field theory approximation for the Anderson lattice model to calculate how the emergence of coherence in the Kondo lattice is impacted by correlations between impurities. We show that the rate at which disorder suppresses coherence temperature depends on the length of the impurity correlations. As the impurity concentration increases, we generally find that the suppression of coherence temperature is significantly reduced. The results are discussed in the context of available experimental data.

Impurities in thin-film silicon: Influence on material properties and solar cell performance

The influence of oxygen and nitrogen impurities on the material properties of a-Si:H and μc-Si:H films and on the corresponding solar cell performances was studied. For intentional contamination of the i-layer the impurities were inserted by two contamination sources: (i) directly into the plasma through a leak at the chamber wall or (ii) into the gas supply line. The critical oxygen and nitrogen concentrations for silicon solar cells were determined as the lowest concentration of these impurities in the i-layer causing a deterioration of the cell performance. Similar critical concentrations for a-Si:H and μc-Si:H cells in the range of 4–6×1018cm−3 for nitrogen and 1–5×1019cm−3 for oxygen by applying a chamber leak are observed. Similar increase of conductivity with increasing impurity concentration in the a-Si:H and μc-Si:H films is found. A more detailed study shows that the critical oxygen concentration depends on the contamination source and the deposition parameters. For a-Si:H cells, the application of the gas pipe leak leads to an increased critical oxygen concentration to 2×1020cm−3. Such an effect was not observed for nitrogen. For μc-Si:H, a new deposition regime with reduced discharge power was found where the application of the gas pipe leak can also result in an increase of the oxygen concentration to 1×1020cm−3.