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Duttagupta S.,Solar Energy Research Institute of Singapore | Duttagupta S.,National University of Singapore | Lin F.,Solar Energy Research Institute of Singapore | Wilson M.,Semilab SDI LLC | And 4 more authors.
Progress in Photovoltaics: Research and Applications | Year: 2014

Extremely low upper-limit effective surface recombination velocities (Seff.max) of 5.6 and 7.4 cm/s, respectively, are obtained on ∼1.5 Ω cm n-type and p-type silicon wafers, using silicon nitride (SiNx) films dynamically deposited in an industrial inline plasma-enhanced chemical vapour deposition (PECVD) reactor. SiNx films with optimised antireflective properties in air provide an excellent Seff.max of 9.5 cm/s after high-temperature (>800 °C) industrial firing. Such low Seff.max values were previously only attainable for SiNx films deposited statically in laboratory reactors or after optimised annealing; however, in our case, the SiNx films were dynamically deposited onto large-area c-Si wafers using a fully industrial reactor and provide excellent surface passivation results both in the as-deposited condition and after industrial-firing, which is a widely used process in the photovoltaic industry. Contactless corona-voltage measurements reveal that these SiNx films contain a relatively high positive charge of (4-8) × 1012 cm-2 combined with a relatively low interface defect density of ∼5 × 1011 eV-1 cm-2. Copyright © 2012 John Wiley & Sons, Ltd.

Davis K.O.,University of Central Florida | Jiang K.,Robert Bosch GmbH | Wilson M.,Semilab SDI LLC | Demberger C.,Robert Bosch GmbH | And 4 more authors.
Physica Status Solidi - Rapid Research Letters | Year: 2013

Using a high throughput, in-line atmosphere chemical vapor deposition (APCVD) tool, we have synthesized amorphous aluminum oxide (AlOx) films from precursors of trimethyl-aluminum (TMA) and O2, yielding a maximum deposition 150 nm min-1 per wafer. For p-type crystalline silicon (c-Si) wafers, excellent surface passivation was achieved with the APCVD AlOx films, with a best maximum effective surface recombination velocity (Seff,max) of 8 cm/s following a standard industrial firing step. The findings could be attributed to the existence of large negative charge (Qf ≈ -3 × 1012 cm-2) and low interface defect density (Dit ≈ 4 × 1011 eV-1 cm-2) achieved by the films. This data demonstrates a high potential for APCVD AlOx to be used in high efficiency, low cost industrial solar cells. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Wilson M.,Semilab SDI LLC | Savtchouk A.,Semilab SDI LLC | Lagowski J.,Semilab SDI LLC | Kis-Szabo K.,Semilab Zrt | And 4 more authors.
Energy Procedia | Year: 2011

We present a version of microwave photoconductance decay, μPCD, measurement of lifetime in silicon photovoltaics which enables simultaneous determination of the carrier decay lifetime, τeff, and injection level, Δn, with the capability of scanning over a broad range of steady state generation including 1 sun. The present μPCD version, referred to as QSS-μPCD, is a refined bias light PCD. It combines scanning of near steady-state generation, G, and pulsed laser μPCD parameter free determination of τeff, for any given G. By reversing the quasi-steady-state photoconductance QSSPC procedure the injection level is determined as Δn=Gτeff. This is achieved for the first time without a requirement for absolute photoconductance calibration or the requirement for carrier mobility values. Moreover, the approach enables tuning measurement to optimize conditions for achieving exponential transients and for elimination of the interference from trapping and space charge conductance modulation. The unique advantage of simultaneous determination of τeff, and Δn permits the use of the Kane and Swanson method for measurement of the emitter saturation current, J0. Using spatially resolved μPCD capability, mapping of J0 is demonstrated. © 2010 Published by Elsevier Ltd.

Wilson M.,Semilab SDI LLC | Edelman P.,Semilab SDI LLC | Lagowski J.,Semilab SDI LLC | Olibet S.,ISC Konstanz | Mihailetchi V.,ISC Konstanz
Solar Energy Materials and Solar Cells | Year: 2012

Excess carrier photoconductance decay lifetime, measured under small perturbation conditions imposed on steady-state generation, offers an attractive and parameter free alternative to quasi-steady-state photoconductance, QSSPC. A recent version of this technique referred to as QSS-μPCD is based on microwave reflectance PCD monitoring. For this technique, it is critically important to maintain a mono-exponential decay over a large range of steady-state light intensity. Toward that goal we present QSS-μPCD with stringent quality of decay control, QDC. The quality of decay parameter, QD (ideally QD=1) measures the direction and magnitude of departures from an ideal exponential transient and enables tuning toward an optimal range of experimental variables, both apparatus and wafer dependent, whereby QD is within 1±Δ where Δ defines the QDC limits. Within QDC limits, the small perturbation effective decay lifetime, τ eff.d, enables accurate determination of important silicon PV parameters, up to about 25 suns, including J 0 and the steady-state lifetime, τ eff.ss. Two J 0 procedures are compared. The ingenious analytical procedure adopted from Basore and Hansen (1990) [2] enables direct determination of J 0. The second J 0 procedure uses integration of τ eff.d over illumination intensity. The results are self-consistent and they show excellent correlation with Sinton QSSPC results. © 2012 Elsevier B.V. All rights reserved.

Wilson M.,Semilab SDI LLC. | Edelman P.,Semilab SDI LLC. | Savtchouk A.,Semilab SDI LLC. | D'Amico J.,Semilab SDI LLC. | And 2 more authors.
Journal of Electronic Materials | Year: 2010

In crystalline silicon, above-bandgap illumination can transform defects into strong recombination centers, degrading minority-carrier lifetime and solar cell efficiency. This light-induced degradation (LID) is due primarily to boron-oxygen and iron-boron defects, and can be reversed using thermal treatments that are distinctly different for each type of defect. Combining illumination and thermal treatment, we have designed an accelerated light-induced degradation (ALID) cycle that, within minutes, transforms defects into the distinct states needed to isolate individual contributions from boron-oxygen dimers (BO 2i) and interstitial iron (Fe i). In this cycle, the concentrations of BO 2i and Fe i are determined using surface photovoltage (SPV) diffusion length measurement. The ALID cycle uses reversible defect reactions and gives very good repeatability of wafer-scale mapping of BO 2i and Fe i in photovoltaic (PV) wafers and final solar cells. © 2010 TMS.

An example semiconductor wafer includes a semiconductor layer, a dielectric layer disposed on the semiconductor layer, and a layer of the metal disposed on the dielectric layer. An example method of determining an effective work function of a metal on the semiconductor wafer includes determining a surface barrier voltage of the semiconductor wafer, and determining a metal effective work function of the semiconductor wafer based, at least in part, on the surface barrier voltage.

Methods for fast and accurate mapping of passivation defects in a silicon wafer involve capturing of photoluminescence (PL) images while the wafer is moving, for instance, when the wafer is transported on a belt in a fabrication line. The methods can be applied to in-line diagnostics of silicon wafers in solar cell fabrication. Example embodiments include a procedure for obtaining the whole wafer images of passivation defects from a single image (map) of photoluminescence intensity, and can provide rapid feedback for process control.

Semilab SDI LLC | Date: 2015-10-09

A method that includes: illuminating a wafer with excitation light having a wavelength and intensity sufficient to induce photoluminescence in the wafer; filtering photoluminescence emitted from a portion of the wafer in response to the illumination; directing the filtered photoluminescence onto a detector to image the portion of the wafer on the detector with a spatial resolution of 1 m1 m or smaller; and identifying one or more crystallographic defects in the wafer based on the detected filtered photoluminescence.

Semilab SDI LLC | Date: 2015-05-04

In an example implementation, a method includes illuminating a wafer with excitation light having a wavelength and intensity sufficient to induce photoluminescence in the wafer. The method also includes detecting photoluminescence emitted from a portion of the wafer in response to the illumination, and detecting excitation light reflected from the portion of the wafer. The method also includes comparing the photoluminescence emitted from the portion of the wafer and the excitation light reflected from the portion of the wafer, and identifying one or more defects in the wafer based on the comparison.

An example method of characterizing a semiconductor sample includes measuring an initial value, V_(in), of a surface potential at a region of a surface of the semiconductor sample, biasing the semiconductor sample to have a target surface potential value (V_(0)) of 2V or less, and depositing a monitored amount of corona charge (Q_(1)) on the region of the surface after adjusting the surface potential to the target value. The method also includes measuring a first value, V_(1), of the surface potential at the region after depositing the corona charge, determining the first change of surface potential (V_(1)=V_(1)V_(0)), and determining the first capacitance value C_(1)=Q_(1)/V_(1), and characterizing the semiconductor sample based on V_(0), V_(1), V_(1), Q_(1 )and C_(1).

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