Range Of Doping Concentrations Research Articles

Spin-dependent scattering and magnetic proximity effect in Ni-doped Co/Cu multilayers as a probe of atomic magnetism

We investigate the spin transport and ferromagnetic resonance properties of giant magnetoresistance (GMR) Co/Cu-Ni multilayers with variable levels of Ni doping in the Cu spacer. We present an experimental evidence for a magnetic-to-diamagnetic transition in the atomic magnetic moment of Ni in the Cu matrix for concentrations below 15 at. % Ni. As its concentration is increased, Ni atoms turn into spin scattering centers, which is manifested experimentally as a step-like change in the GMR of the multilayers. This behavior is observed in multilayers with gradient-doped Cu spacers, where only the inner region was doped with Ni. In the uniformly doped spacers, the GMR decreases monotonously with increasing Ni content, indicating that Ni atoms are magnetic and act as spin relaxation centers in the entire dopant-concentration range studied. We explain the difference in the observed GMR behavior due to a strong magnetic proximity effect in the uniform spacers, which is efficiently suppressed in the gradient spacers. The observed magnetic phase transition is fully supported by our detailed ab initio calculations, taking into consideration structural relaxation in the system as well as potential Ni clustering. Controlling the loss or gain of the atomic magnetism for a specific dopant can be a tool in probing and controlling spin relaxation in materials and devices for spin-valve and spin-torque based applications.

Surface nanosheets evolution and enhanced photoluminescence properties of Al-doped ZnO films induced by excessive doping concentration

Previous reports found Al-doped ZnO nanosheets were formed at a certain preparation condition, but the formation mechanism was vague. In this work, we prepare sol-gel Al-doped ZnO films, and find that films show the obvious nanorods structure on surface of pure ZnO, but the nanorods changes to nanosheets gradually with rising doping concentration. The formation mechanism of nanosheets is clarified, and the doping concentration dependence of morphology is discussed in this paper. In addition, the photoluminescence spectra of all films appear a series of emissions including the near band edge emission (NBE) at 388 nm and several defect emissions (DE) at 396–499 nm. Previous reports proposed that NBE and DE would rise monotonously or decline monotonously with doping. However, this work reveals that the NBE decreases firstly in the range of low doping concentrations and then improves upon excessive doping concentration, due to crystalline quality and optical energy gap --- this reason is different from traditional explanations. Also, DE at different positions show the different variation trends, without the same increase or the same decrease. At excessive doping concentration, both NBE and DE enhance, illustrating the potential application for the enhanced ultraviolet and white light emitting devices.

Influence of Mg2+/Ga3+ doping on luminescence of Y3Al5O12:Ce3+ phosphors

Mg2+/Ga3+ doped Y3Al5O12:Ce3+ phosphors were synthesized through a solid state reaction. The phase and luminescent of the synthesized phosphors were investigated. For Ga3+ codoped Y2.96Ce0.04Al(5−x)GaxO12 phosphors, the emission intensity increases with the increase of Ga3+ concentration up to Y2.96Ce0.04Al4.80Ga0.20O12 and then decreases with a further increase of Ga3+ concentration, but the emission peak shifts to shorter wavelength continuously in the Ga3+ doping concentration range of 0.05–0.25. For Mg2+/Ga3+ codoped Y2.96Ce0.04Al(4.8−y)Ga0.20MgyO12 phosphors, the emission intensity decreases and the emission peak shifts to longer wavelength continuously in the Mg2+ doping concentration range of 0.02–0.12. The emission spectra of Y2.96Ce0.04Al(4.8−y)Ga0.20MgyO12 phosphors demonstrate that the codoped Mg2+/Ga3+ ions not only induce the enhancement of Y2.96Ce0.04Al5O12 emission intensity but also lead to the red shift of Y2.96Ce0.04Al5O12 emission peak. The decay lifetimes decrease in Mg2+/Ga3+ codoped Y2.96Ce0.04Al5O12 phosphors due to defects formed by substitutions of Y3+ by Mg2+/Ga3+.

First-principles study of optical properties of germanium doped with phosphorus and bismuth

Using first-principles calculations based on density functional theory, we investigate the electronic structures and optical properties of germanium doped by phosphorus and bismuth with different concentrations. By analyzing the electronic structures and optical properties of the doped systems, we can theoretically analyze and predict the optical and electrical practical applications of N-doped germanium semiconductors. By analyzing and comparing the densities of electronic states before and after doped, we can draw some conclusions. The conclusions show that the Fermi level moves in the direction of conduction band after being doped. Although germanium is an indirect band gap luminescent material, the doped systems all become direct band gap luminescence. Doping more or less affects various optical properties in different energy ranges. In a low energy range, the dielectric function and refractive index of the doped systems are affected. When the doping concentration is 2.083%, the dielectric function and refractive index of the doped system both have a special change. And the absorption of the doped system is changed in the high energy. As the energy increases after the absorption peak, the absorption of the doped system drops faster. The reflectance of the doped system is affected in all the energy ranges. The reflectance of the doped system increases in medium energy. And the reflectance of the doped system is reduced in low energy and high energy range. However, when the doping concentration is 2.083% and the energy is less than 1.7 eV, the reflectance of the doped system is higher than that of the undoped system. The conductivity of the doped system forms two peaks, adding a peak in low energy. The additional peaks in the systems where the doping concentrations are 1.563% and 2.083% are obvious. The peak of the loss function increases after being doped. However, as the doping concentration increases, the increment of the loss function decreases. As the doping concentration increases, the peak is formed at a higher energy. The conclusions are of significance for guiding the optical applications of N-type doped germanium. According to the conclusions, we can adjust the doping concentration and energy range in the optical applications of N-doped germanium.

Reconstructing photoluminescence spectra at liquid nitrogen temperature from heavily boron‐doped regions of crystalline silicon solar cells

AbstractWhen measured at low temperature (79 K), the photoluminescence (PL) spectra from silicon wafers containing a diffused heavily doped layer exhibit a second peak due to band gap narrowing in the diffused region. This work aims to decompose this peak into components arising from the various doping concentrations within the diffused layer. Whilst the peak position of silicon band‐to‐band PL spectra changes significantly with the doping concentration in silicon, the shape of the spectra also varies strongly with doping concentrations due to the broadening effects of band‐filling and band‐tail states. By measuring PL spectra on a range of uniformly heavily doped wafers, we show that these changes in spectral position and shape can be accurately modelled for doping concentrations above 1 × 1019 cm−3 using simple parameterisations, with minimal impact of variations in excitation intensity or injection level. This allows the PL spectra for a range of arbitrary doping concentrations to be reconstructed. We then show that the PL spectra from a thermally boron‐diffused wafer, in which the boron concentration changes with depth, can be reconstructed based on a superposition of PL spectra arising from the layers of different doping beneath the surface. Furthermore, the scaling factor for each layer can be accurately estimated based on the doping profile and the fraction of incident light absorbed in the layer.

Superconducting phase diagrams of cuprates and pnictides as a key to understanding the HTSC mechanism

This paper reviews experimental phase diagrams of cuprates and pnictides to demonstrate that specific features of the superconducting phase diagrams in both HTSC families can be understood within the framework of the proposed approach, which assumes the formation, under heterovalent doping, of localized trion complexes consisting of a doped carrier and charge transfer (CT) excitons. The geometry of such cells containing CT excitons (CT plaquettes) in the basal plane of the crystal is determined by its crystal structure and the type of dopant, so that the dopant concentration range corresponding to the existence of a percolation cluster of CT plaquettes can be readily determined for each particular compound. These dopant concentration ranges coincide with good accuracy with the experimental ranges of superconducting domes in the phase diagrams of the HTSC compounds considered. The generation of free carriers and the mechanism of superconducting pairing in this pattern is related to biexciton complexes (Heitler–London centers) emerging in neighboring CT plaquettes.

Synthesis and characterization of Fe-doped ZnO thin films deposited by chemical spray pyrolysis

In the present study, iron doped zinc oxide (ZnO:Fe) thin films were prepared by using a simple chemical spray pyrolysis technique by varying the doping concentration in the range, 0–6at.% at a constant substrate temperature of 400°C.The effect of Fe-doping concentration on the physical behavior of ZnO thin films were analyzed and discussed. The X-ray diffraction (XRD) patterns exhibited hexagonal wurtzite crystal structure without any secondary phases for all the films irrespective of the doping concentration. However, the preferential orientation changed from (002) to (101) plane with increase of Fe-doping. The Raman spectroscopy studies showed the peaks at 338cm-1, 438cm-1 and 574cm-1 which are the characteristic vibrational modes of ZnO. The scanning electron microscopic (SEM) images showed irregular shaped grains grown over the substrate surface. The X-ray photoelectron spectroscopy (XPS) studies confirmed the presence of Fe in +3 state in ZnO layers. The Fourier transform infrared (FTIR) spectroscopy data revealed the presence of iron in the doped ZnO films by showing the modes related to iron in addition to ZnO. The optical properties revealed that the films with lower Fe-doping concentration (≤ 2at.%) showed high transmittance and wide band gap than the pure and highly Fe-doped ZnO films. The evaluated band gap showed a red shift upon doping with the energy band gap decreased from 3.24eV to 3.01eV for the investigated doping concentration range. The photoluminescence spectra also showed similar optical behavior with quenching of PL signal intensity of the films. Moreover, all the Fe-doped ZnO films showed ferromagnetic behavior at room temperature.

Non-metal to metal transition in n-type ZnO single crystal materials

The electrical properties of ZnO mono-crystalline materials, either in the form of bulk crystals or epitaxial films, were investigated for a large range of un-intentional or intentional doping concentrations extending from 4.0×1015 cm−3 up to 1.3×1020 cm−3. Hall and resistivity measurements were carried out from 10 K to 300 K, yielding the temperature dependent carrier densities and carrier mobilities. This allowed for an unambiguous determination of the dopant ionization energies, taking into account the concentration of compensation centers. The ionization energy variation as a function of dopant concentration was found to follow Mott's law, being consistent with the hydrogenic behavior of all involved donors; an effective critical Mott's concentration for the insulator to metal transition was found to be around 4.2×1018 cm−3, while the apparent value of the isolated donor ionization energy was determined as being 60 meV.

Effects of V heavy doping on the magnetic and optical properties in anatase TiO2

A half-metal diluted magnetic semiconductor (DMS) can be formed in heavy V-doped TiO2. Contradictory experimental results in the literature have reported about the absorption spectra blueshift and redshift results in heavy V-doped TiO2. This study aims to reveal the mechanism of half-metal DMS in heavy V-doped TiO2 and solve the problem of absorption spectra blueshift and redshift in the doping system. In this study, models of the unit cells of pure anatase TiO2 and two V heavy-doped supercells of Ti[Formula: see text]V[Formula: see text]O2 and Ti[Formula: see text]V[Formula: see text]O2 were constructed based on density functional theory, which uses the first-principles plane-wave ultrasoft pseudopotential method. All models were obtained through geometry optimization. Local density approximation [Formula: see text] was used to calculate the band structure, density of states (DOS), orbital charge and absorption spectrum of the doping system. The calculated results under the condition of electron spin showed that in the heavy doping concentration range, the volume of supercells increases, the total energy and formation energy decrease and the stability of the supercells increases as V doping concentration increases. Furthermore, the interaction of [Formula: see text]–[Formula: see text] states is weaker than that of [Formula: see text]–[Formula: see text] states, which results in the valence band maximum shifting toward the low-energy region, and also the optical bandgap becomes narrower as well as the redshift and intensity of the absorption spectrum become more notable. Noticeably, the hybrid coupling effect of Ti-3[Formula: see text] and V-3[Formula: see text] states becomes stronger, and the magnetic moment increases. The Fermi levels of spin-up band structure within the conduction band, which form the [Formula: see text]-type degenerate semiconductors, and the Fermi levels of spin-down band structure within the bandgap indicate that the doping system has semiconductor features. Therefore, V-doped anatase TiO2 is an extremely promising DMS because of its high electron polarizability of nearly 100%. The calculation results are consistent with the experimental data; these results explain the problems reasonably and adequately. Therefore, the research findings can help solve the contradiction of the redshift and blueshift in the preparation of photocatalysts and half-metal diluted magnetic semiconductors of V heavy-doped anatase TiO2.

A t-butyl modification approach of acceptor moiety for stable deep blue emission in thermally activated delayed fluorescent devices

A t-butyl modification method of an acceptor moiety was developed as a molecular design approach of blue emitters to shift the emission color to deep blue region and to stabilize the emission color according to doping concentration. A phenyl unit of triphenyltriazine acceptor moiety of blue thermally activated delayed fluorescent emitter was modified with either one or two t-butyl units to study the effect of the t-butyl unit on the electroluminescence emission of the blue thermally activated delayed fluorescent emitters. It was found that two t-butyl units introduced in the phenyl unit of the triphenyltriazine shifted the emission color to deep blue emission while keeping the deep blue color over wide doping concentration range.

Dielectric and piezoelectric properties and electrical conductivity of LiNbO3:ZnO crystals in a wide range of dopant concentrations

The dielectric and piezoelectric properties and electrical conductivity of initially multidomain LiNbO3:ZnO crystals have been studied in a wide range of dopant concentrations with the aim of determining the composition range of the anomalous increase in unipolarity. The results demonstrate that the development of spontaneous unipolarity during high-temperature annealing takes place only in LiNbO3:ZnO crystals grown from melts in a “near-threshold” composition range (~5.4 < Cm ≤ 6.76 mol % ZnO). The effect is accompanied by a considerable and reproducible increase in the static piezoelectric modulus d333. The increase in the piezoelectric modulus, Δd333, rises linearly with increasing jump in electrical conductivity, Δσ, near a temperature T* ≈ 800 K.

Solid sampling determination of magnesium in lithium niobate crystals by graphite furnace atomic absorption spectrometry

The vaporization/atomization processes of Mg in high-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS-GFAAS) were investigated by evaporating solid (powder) samples of lithium niobate (LiNbO3) optical single crystals doped with various amounts of Mg in a transversally heated graphite atomizer (THGA). Optimal analytical conditions were attained by using the Mg I 215.4353nm secondary spectral line. An optimal pyrolysis temperature of 1500°C was found for Mg, while the compromise atomization temperature in THGAs (2400°C) was applied for analyte vaporization. The calibration was performed against solid (powered) lithium niobate crystal standards. The standards were prepared with exactly known Mg content via solid state fusion of the oxide components of the matrix and analyte. The correlation coefficient (R value) of the linear calibration was not worse than 0.9992. The calibration curves were linear in the dopant concentration range of interest (0.74–7.25mg/gMg), when dosing 3–10mg of the powder samples into the graphite sample insertion boats. The Mg content of the studied 19 samples was in the range of 1.69–4.13mg/g. The precision of the method was better than 6.3%. The accuracy of the results was verified by means of flame atomic absorption spectrometry with solution sample introduction after digestion of several crystal samples.

Scalable Production of Thermochromic Nb-Doped VO&lt;SUB&gt;2&lt;/SUB&gt; Nanomaterials Using Continuous Hydrothermal Flow Synthesis

The synthesis of effective thermochromic Nb-doped VO2 nanoparticles, containing a range of Nb dopant concentrations (1, 5 and 15 at.% Nb), was carried out via continuous hydrothermal flow process under supercritical water regime. The synthesis method employed here is directly scalable for industrial purposes and the materials may be produced at a rate of kg h-1 in our pilot plant. The thermochromic properties of these materials were studied at variable temperature using UV/Vis spectroscopy. The structure, morphology and particle properties were characterised using powder X-ray diffraction, Raman spectroscopy and transmission electron microscopy. The incorporation of Nb dopant into VO2 was studied X-ray photoelectron spectroscopy. The Nb-doped VO2 materials showed a substantial decrease in metal- To-semiconductor transition temperature (ca. 20 °C) and improved optical features (narrow hysteresis loop, 10 °C difference) compared to undoped VO2 nanoparticles synthesised under similar conditions. A reduction in the MST temperature of 3.6°C per at.% Nb incorporated was estimated from these studies.

On the use of hopping conduction for the determination of dopant concentration in compensated silicon

AbstractThis work explores the possibility to use the mechanism of hopping conduction – and particularly the transition temperature between band and hopping conduction – on low temperature resistivity measurements, for the control of dopants densities in p‐type compensated silicon. This work first establishes a parametric study of the hopping conductivity: the impact of the majority dopant density and of the compensation ratio is investigated. In the range of majority dopant concentration studied (5×1016 cm–3–5×1017 cm–3), a linear relation seems to appear between the majority dopant concentration and the transition temperature, and this, apparently whatever the compensation impurity type or the crystalline structure. It was then shown that both minority and majority dopant densities can be estimated from a single resistivity versus temperature curve. To our knowledge, this work presents the first experimental study of the feasibility of using such mechanisms to collect relevant information on the compensated Si composition. (© 2016 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Reduced oxygen precipitation in heavily arsenic‐doped Cz‐silicon crystals

AbstractOxygen precipitation in heavily arsenic doped Czochralski silicon is investigated for a wide dopant concentration range (from 3 × 1018 cm–3 to 4 × 1019 cm–3) and it is compared with that observed in lightly doped silicon having similar initial oxygen concentration. A lower density of oxide precipitates after an anneal of 4 h at 800 °C followed by 16 h at 1000 °C is measured in the case of arsenic doped samples, in comparison to lightly doped ones, when the dopant concentration exceeds 1.6 × 1019 cm–3. In addition, no radial bands (rings) of precipitation are observed in arsenic‐doped samples, contrary to lightly doped samples grown at the same V/G (ratio between pull rate V and axial thermal gradient G). These findings are explained by considering the role played by vacancies in the formation of oxygen precipitates and the impact of the arsenic concentration on the total concentration of point defects in silicon. Data obtained by computer simulation of microdefect formation in silicon are also presented in support of this explanation. (© 2016 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Experimental optimum design and luminescence properties of NaY(Gd)(MoO4)2:Er3+ phosphors**Project supported by Education Reform Fund of Dalian Maritime University, China (Grant No. 2015Y37), the Natural Science Foundation of Liaoning Province, China (Grant Nos. 2015020190 and 2014025010), the Open Fund of the State Key Laboratory on Integrated Optoelectronics, China (Grant No. IOSKL2015KF27), and the Fundamental Research Funds for the Central Universities, China

Three-factor orthogonal design (OD) of Er3+/Gd3+/T (calcination temperature) is used to optimize the luminescent intensity of NaY(Gd)(MoO4)2:Er3+ phosphor. Firstly, the uniform design (UD) is introduced to explore the doping concentration range of Er3+/Gd3+. Then OD and range analysis are performed based on the results of UD to obtain the primary and secondary sequence and the best combination of Er3+, Gd3+, and T within the experimental range. The optimum sample is prepared by the high temperature solid state method. Photoluminescence excitation and emission spectra of the optimum sample are detected. The intense green emissions (530 nm and 550 nm) are observed which originate from Er3+ 2H11/2→ 4I15/2 and 4S3/2→4I15/2, respectively. Thermal effect is investigated in the optimum NaY(Gd3+)(MoO4)2:Er3+ phosphors, and the green emission intensity decreases as temperature increases.

Effects of dopant type and concentration on the femtosecond laser ablation threshold and incubation behaviour of silicon

In laser micromachining, the ablation threshold (minimum fluence required to cause ablation) is a key performance parameter and overall indicator of the efficiency of material removal. For pulsed laser micromachining, this important observable depends upon material properties, pulse properties and the number of pulses applied in a complex manner that is not yet well understood. The incubation effect is one example. It manifests as a change in the ablation threshold as a function of number of laser pulses applied and is driven by photoinduced defect accumulation in the material. Here, we study femtosecond (800 nm, 110 fs, 0.1-1 mJ/pulse) micromachining of a material with well-defined initial defect concentrations: doped Si across a range of dopant types and concentrations. The single-pulse ablation threshold (Fth,1) was observed to decrease with increasing dopant concentration, from a maximum of 0.70 J/cm2 (+/-0.02) for undoped Si to 0.51 J/cm2 (+/-0.01) for highly N-type doped Si. The effect was greater for N-type doped Si than for P-type, consistent with the higher carrier mobility of electrons compared to holes. In contrast, the infinite-pulse ablation threshold (Fth,inf) was the same for all doping levels and types. We attribute this asymptotic behaviour to a maximum defect concentration that is independent of the initial defect concentration and type. These results lend insight into the mechanism of multipulse, femtosecond laser ablation.

Electrical and Optical Properties of n-Type Indium-Doped CdTe/Mg0.46Cd0.54Te Double Heterostructures

CdTe/Mg0.46Cd0.54Te double heterostructures with n-type In doping concentrations, varied from 1 × 1016 to 7 × 1018 cm−3, have been grown on InSb substrates using molecular beam epitaxy. Secondary ion mass spectroscopy measurements show strong diffusion of In from the InSb substrate to the CdTe buffer layer, while the In concentration is constant in the CdTe layer between the two Mg 0.46Cd0.54Te barrier layers. Capacitance–voltage measurements show that the dopants are 100% ionized for the doping concentration range from 1 × 1016 to 1 × 1018 cm −3. The carrier lifetime decreases with increasing doping concentration (from 0.73 μs for an unintentionally doped sample to 0.74 ns for a 1 × 1018 cm−3 doped sample) due to the decrease of both radiative and nonradiative lifetimes. Decent carrier lifetimes are achieved (∼100 ns) between 1 × 1016 and 1 × 1017 cm−3 doping levels, which is beneficial for developing n-type monocrystalline CdTe solar cells, photodetectors, and other optoelectronic devices. The strongest photoluminescence intensity is observed when the doping concentration is 1 × 1017 cm −3, which corresponds to the highest internal quantum efficiency.

Precise parameterization of the recombination velocity at passivated phosphorus doped surfaces

We investigate the surface recombination velocity Sp at the silicon-dielectric interface of phosphorus-doped surfaces for two industrially relevant passivation schemes for crystalline silicon solar cells. A broad range of surface dopant concentrations together with a high accuracy of evaluating the latter is achieved by incremental back-etching of the surface. The analysis of lifetime measurements and the simulation of the surface recombination consistently apply a set of well accepted models, namely, the Auger recombination by Richter et al. [Phys. Rev. B 86, 1–14 (2012)], the carrier mobility by Klaassen [Solid-State Electron. 35, 953–959 (1992); 35, 961–967 (1992)], the intrinsic carrier concentration for undoped silicon by Altermatt et al. [J. Appl. Phys. 93, 1598–1604 (2003)], and the band-gap narrowing by Schenk [J. Appl. Phys. 84, 3684–3695 (1998)]. The results show an increased Sp at textured in respect to planar surfaces. The obtained parameterizations are applicable in modern simulation tools such as EDNA [K. R. McIntosh and P. P. Altermatt, in Proceedings of the 35th IEEE Photovoltaic Specialists Conference, Honolulu, Hawaii, USA (2010), pp. 1–6], PC1Dmod [Haug et al., Sol. Energy Mater. Sol. Cells 131, 30–36 (2014)], and Sentaurus Device [Synopsys, Sentaurus TCAD, Zürich, Switzerland] as well as in the analytical solution under the assumption of local charge neutrality by Cuevas et al. [IEEE Trans. Electron Devices 40, 1181–1183 (1993)].

Framework to predict optimal buffer layer pairing for thin film solar cell absorbers: A case study for tin sulfide/zinc oxysulfide

An outstanding challenge in the development of novel functional materials for optoelectronic devices is identifying suitable charge-carrier contact layers. Herein, we simulate the photovoltaic device performance of various n-type contact material pairings with tin(II) sulfide (SnS), a p-type absorber. The performance of the contacting material, and resulting device efficiency, depend most strongly on two variables: conduction band offset between absorber and contact layer, and doping concentration within the contact layer. By generating a 2D contour plot of device efficiency as a function of these two variables, we create a performance-space plot for contacting layers on a given absorber material. For a simulated high-lifetime SnS absorber, this 2D performance-space illustrates two maxima, one local and one global. The local maximum occurs over a wide range of contact-layer doping concentrations (below 1016 cm−3), but only a narrow range of conduction band offsets (0 to −0.1 eV), and is highly sensitive to interface recombination. This first maximum is ideal for early-stage absorber research because it is more robust to low bulk-minority-carrier lifetime and pinholes (shunts), enabling device efficiencies approaching half the Shockley-Queisser limit, greater than 16%. The global maximum is achieved with contact-layer doping concentrations greater than 1018 cm−3, but for a wider range of band offsets (−0.1 to 0.2 eV), and is insensitive to interface recombination. This second maximum is ideal for high-quality films because it is more robust to interface recombination, enabling device efficiencies approaching the Shockley-Queisser limit, greater than 20%. Band offset measurements using X-ray photoelectron spectroscopy and carrier concentration approximated from resistivity measurements are used to characterize the zinc oxysulfide contacting layers in recent record-efficiency SnS devices. Simulations representative of these present-day devices suggest that record efficiency SnS devices are optimized for the second local maximum, due to low absorber lifetime and relatively well passivated interfaces. By employing contact layers with higher carrier concentrations and lower electron affinities, a higher efficiency ceiling can be enabled.