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Photoconductivity When light of sufficient energy is absorbed by a semiconductor, the number of free electrons and holes changes and raises the electrical conductivity of the semiconductor. Photoconductivity When light of sufficient energy is absorbed by a semiconductor, the number of free electrons and holes changes and raises the electrical conductivity of the semiconductor. This increase is called photoconductivity and is dependent of the excess electron and hole concentrations and their mobility via the following equation. [1] \(\Delta\sigma = e \cdot(\mu_{n}\Delta n + \mu_{p} \Delta p)\) [2] \(\Delta\sigma = e \cdot G\) opt \(\cdot \tau \cdot(\mu_{n} + \mu_{p})\) G opt is the optical generation rate, which depends on the incident light intensity, the light spot on the sample and the wavelength. [3] \(G\) opt \(= \alpha \cdot \phi \cdot(1 - R)e^{\alpha x}\) Equation 2 implies that the photoconductivity is proportional to the product of lifetime t and the mobility µ. Therefore, it is also proportional to the square of the diffusion length L, which is defined as: [4] \(L = \sqrt{D \cdot \tau} = \sqrt{\frac{e}{kT} \cdot \mu{\tau}}\) Matching Products MDP series MDpicts pro High-Resolution, Temperature-Dependent Lifetime Measurement System for Precise Material Characterization Learn more MDP series MDPpro 850+ Advanced Solution for Quality Control of Monocrystalline Silicon Ingots, Bricks, and Wafers Learn more MDP series MDPlinescan Versatile OEM Unit for Lifetime Measurements on Silicon Samples, from Bricks to Processed Wafers Learn more MDP series MDpicts Temperature-Dependent Lifetime Measurement System for Advanced Material Analysis Learn more RES series RESmap High-Precision Resistivity Mapping System for Accurate Material Analysis Learn more MDP series MDPmap Precision Lifetime Charachterization with Exceptional Sensitivity Learn more MDP series MDPspot Quick and Simple Lifetime Measurement Made Easy Learn more Get in touch Do not hesitate to contact us – we are available to assist you with any inquiries or requests. Use our inquiry tool or reach out via email: sales @ freiberginstruments.com

Photoconductivity measurements of implanted samples Implantation of B and P are used for many applications in the microelectronic industry, but so far there was no method available to check the homogeneity of these implantations without contacting the samples and (Alttext zu lang) In this case not the lifetime, but the photoconductivity or signal height is the most sensitive parameter for detecting inhomogeneity in implantations. It depends strongly on the resistivity and the lifetime itself. In the MDPmap and MDPingot equipment it is possible to integrate up to 4 lasers with different wavelength. Furthermore it is possible to measure with different pulse length from a very short pulse of only 100 ns, where no carrier diffusion takes place to a pulse length of several ms, where the carriers diffuse into the sample depth. Hence by varying the laser wavelength and the pulse length, it is possible to measure with different penetration. In this case a 660 nm laser with a pulse length of 100 ns was chosen; hence a penetration depth of approximately 4 µs was achieved. Figure 1 shows the implanted P doses in the measured Cz-Si sample and figure 2 demonstrates how the different doses can be distinguished by photoconductivity measurements. Fig. 1: implanted P dosis with a depth of only 2 µm Fig. 2: measured photoconductivity of the sample with different implanted P doses Related Solutions and Industries: Epitaxial Layers & Thin Films Matching Products MDP series MDPmap Precision Lifetime Charachterization with Exceptional Sensitivity Learn more MDP series MDPpro 850+ Advanced Solution for Quality Control of Monocrystalline Silicon Ingots, Bricks, and Wafers Learn more MDP series MDPpro Advanced Lifetime Measurement System for Quality Control and Material R&D on Semiconductors Learn more Get in touch Do not hesitate to contact us – we are available to assist you with any inquiries or requests. Use our inquiry tool or reach out via email: sales @ freiberginstruments.com

Investigation of defect levels in InP InP is applied in high frequency technique, for lasers, communication technique and production of integrated circuits. Hence also for this material methods for defect investigation and quality control are needed. MD-PICTS is a well suited method for the investigation of defect levels in InP. For example investigations on indium phosphide shows that the defect content changes during annealing processes, which may also have an impact on the distribution of electric properties. Whereas the defect content of as-grown samples depends on their position in the crystal, an equivalent set of defect levels is prominent in wafer-annealed samples. Figure 1 shows a comparison of Fe-doped SI-InP samples from different crystal positions. They differ in their characteristic defect levels. The observed peaks in FE-doped InP provided the first proof of iron acting as a recombination center in InP. Fig.1: Comparison of MD-PICTS spectra of as-grown Fe doped SI-InP samples from different crystal positions and thus different FE concentrations. The samples differ in their characteristic defect levels Related Solutions and Industries: Epitaxial Layers & Thin Films Matching Products MDP series HTpicts Advanced High-Temperature Lifetime Measurement System for In-Depth Material Analysis Learn more MDP series MDpicts pro High-Resolution, Temperature-Dependent Lifetime Measurement System for Precise Material Characterization Learn more MDP series MDpicts Temperature-Dependent Lifetime Measurement System for Advanced Material Analysis Learn more Get in touch Do not hesitate to contact us – we are available to assist you with any inquiries or requests. Use our inquiry tool or reach out via email: sales @ freiberginstruments.com

Inline metrology of mc-Si bricks Lifetime measurements are already widely used for material quality control especially in the photovoltaic industry. Taking it one step further, (Alttext zu lang) With the MDPinline ingot it is possible to measure all 4 sides of a brick in under 1 min per side with 1 mm resolution. At the same time a spatial resolved measurement of conduction type changes as well as resistivity linescans are measured. Customer defined brick cut criteria by lifetime, resistivity or conduction type change can be transmitted to the fab database, which allows a fully automated material monitoring for next generation photovoltaic fabs. Furthermore the iron density can be measured on one side of the brick, which takes about 2.5 min. Related Solutions and Industries: Epitaxial Layers & Thin Films Matching Products MDP series MDPpro 850+ Advanced Solution for Quality Control of Monocrystalline Silicon Ingots, Bricks, and Wafers Learn more MDP series MDPpro Advanced Lifetime Measurement System for Quality Control and Material R&D on Semiconductors Learn more Get in touch Do not hesitate to contact us – we are available to assist you with any inquiries or requests. Use our inquiry tool or reach out via email: sales @ freiberginstruments.com

Minority carrier lifetime measurements on SiC In recent years the quality of SiC materials has improved profoundly and hence SiC is becoming more and more a competitor to Si for e.g. high-power devices. Since it is a wide-bandgap semiconductor, SiC has a number of advantages when compared to Si. The minority carrier lifetime is one of the fundamental parameters with regard to the performance of semiconductor devices, especially for the application of SiC in high voltage devices. Hence, it is necessary to perform lifetime engineering to gain the best performance of a certain device. In order to manufacture SiC devices with maximum yield, a material characterization with a high resolution is needed, together with a method to investigate the origin of defects in SiC to further improve the quality. The two contactless and destruction free methods microwave detected photoconductivity (MDP) and photo induced current transient spectroscopy (MD-PICTS) are ideal methods for material quality and defect characterization. The MDPmap combined with a UV-laser (355 nm) is the ideal tool for the spatial investigation of inhomogeneities in the minority carrier lifetime of SiC with a lower limit of 20 ns. MD-PICTS measurements enable the temperature dependent investigation of the photoconductivity transient allowing the determination of the defect activation energy and capture cross sections. With the MD-PICTS system it is possible to measure down to 85 K with a liquid nitrogen bath cryostat or even down to 4 K with a helium cooling system. The upper temperature limit is 800 K and hence also deep trap levels can be investigated. With the additional mapping option small samples (2 x 2 cm) can be mapped at different temperatures. Results Figure 1 and 2 show a minority carrier lifetime map and a photoconductivity transient of a 4H-SiC sample. Both was measured with the MDPmap with a resolution of 100 µm and a 355 nm laser. Figure 3 demonstrates a MD-PICTS spectrum with two detected defect levels with activation energies of 0.12 eV and 0.22 eV. The measurement was conducted with an MDpicts and a liquid nitrogen bath. For more information please read: B. Berger, N. Schüler, S. Anger, B. Gruendig-Wendrock, J. R. Niklas, K. Dornich, physica status solidi A, 1-8. Contactless electrical defectcharacterization in semiconductorsby microwave detected photo inducedcurrent transient spectroscopy (MD-PICTS) and microwave detected photoconductivity (MDP) Fig.1: Minority carrier lifetime map of a 4" SiC wafer Fig.2: Typical photoconductivity transient of a 4H-SiC sample Fig. 3: MD-PICTS spectrum of a 4H-SiC sample, with two trap levels Related Solutions and Industries: Epitaxial Layers & Thin Films Matching Products MDP series MDPmap Precision Lifetime Charachterization with Exceptional Sensitivity Learn more MDP series MDPspot Quick and Simple Lifetime Measurement Made Easy Learn more MDP series MDpicts Temperature-Dependent Lifetime Measurement System for Advanced Material Analysis Learn more Get in touch Do not hesitate to contact us – we are available to assist you with any inquiries or requests. Use our inquiry tool or reach out via email: sales @ freiberginstruments.com

Microwave Detected Photo Induced Current Transient Spectroscopy (MD-PICTS) is a modification of MDP, where temperature dependent measurements of the defect part of the transient are accomplished. In order to investigate defects in semiconductors it is widely spread to use temperature dependent methods as deep level transient spectroscopy (DLTS). Usually for these methods it is necessary to form contacts on the samples, which means the sample itself is often altered due to annealing steps. Furthermore for lot of semiconductors some effort is needed to create ohmic contacts at all. MD-PICTS is a non-destructive, contactless method with which the activation energies and capture cross sections of defects can be determined with a high accuracy. For MD-PICTS measurements the photoconductivity of a sample after the irradiation with light is measured with a resonant microwave cavity. For the determination of the activation energy the temperature dependent change of the photoconductivity transient is determined via a window analysis, which is also used for DLTS measurements (fig. 1). Fig.2 shows a so called MD-PICTS spectrum which results from the window analysis. Every peak in this spectrum is a certain defect in the sample. The temperature shift of the maximum of this peak is plotted in an Arrhenius plot according to this formula of the emission rate: \(e_{n} = \gamma\delta_{n}T^{2}e^{-\frac{E_{A}}{kT}}\) From the slope of the Arrhenius plot (Fig. 3) the activation energy can be determined. With the novel commercially available MD-PICTS equipment it is possible to measure the temperature dependence of the photoconductivity transient in a range from 20…500 K. In the past Si, GaAs, InP, SiC and many more semiconductors have already been successfully investigated with this method. For more information please read: [1] B. Berger, N. Schüler, S. Anger, B. Gruendig-Wendrock, J. R. Niklas, K. Dornich, physica status solidi A, 1-8 Fig. 1: Depiction of the window analysis of the photoconductivity transient Fig. 2: resulting MD-PICTS spectrum Fig. 3: Arrhenius plot Fig. 4: example of a MD-PICTS spectrum of different tempered Cz—Si wafers Related Solutions and Industries: Epitaxial Layers & Thin Films Matching Products MDP series HTpicts Advanced High-Temperature Lifetime Measurement System for In-Depth Material Analysis Learn more MDP series MDpicts pro High-Resolution, Temperature-Dependent Lifetime Measurement System for Precise Material Characterization Learn more MDP series MDpicts Temperature-Dependent Lifetime Measurement System for Advanced Material Analysis Learn more Get in touch Do not hesitate to contact us – we are available to assist you with any inquiries or requests. Use our inquiry tool or reach out via email: sales @ freiberginstruments.com

Trap concentration determination Many lifetime measuring methods as QSSPC, µPCD or CDI, as well as MDP suffer from an anomalous high measured lifetime at very low injections. (Alttext kürzen, da zu lang) With the MDPmap and MDPingot it is possible to measure the photoconductivity as well as the minority carrier lifetime with one measurement and fully automated in a wide injection range. A clever algorithm allows the determination of the trap concentration in the sample. From the injection dependent lifetime curve the lifetime at low injection τ LLI can be determined and the photoconductivity is fitted with the slightly modified model of HORNBECK and HAYNES. The trapping density N T and the activation energy E A are the fitting parameters. First measurement results were obtained on mc- and Cz-Si wafers and a correlation between the trap density and the dislocation density could be confirmed. \(\Delta\delta = e[\tau_{LLI}G_{opt}(\mu_{n}+\mu_{p})+\Delta n_{T}\mu_{p}]\) MDPmap allows to measure injection dependent photoconductivity and lifetime curves with a high resolution, so that the trap density and activation energy of trapping centers can be determined. With this it is possible to investigate the origin of traps and there influence on for example the efficiency of solar cells. For more information read: [1] J. A. Hornbeck and J. R. Haynes, Physical Review 97, 311-321 (1955)[2] D. Macdonald and A. Cuevas, Applied Physics Letters 74, 1710 - 1712 (1999) [3] N. Schüler, T. Hahn, K. Dornich, J.R. Niklas, 25th PVSEC Valencia (2010) 343-346 Photoconductivity versus Gopt for different trap densities and fit of measured photoconductivity curve Related Solutions and Industries: Epitaxial Layers & Thin Films , Photovoltaic , Research and Development Matching Products MDP series MDPmap Precision Lifetime Charachterization with Exceptional Sensitivity Learn more MDP series MDPpro 850+ Advanced Solution for Quality Control of Monocrystalline Silicon Ingots, Bricks, and Wafers Learn more MDP series MDPpro Advanced Lifetime Measurement System for Quality Control and Material R&D on Semiconductors Learn more Get in touch Do not hesitate to contact us – we are available to assist you with any inquiries or requests. Use our inquiry tool or reach out via email: sales @ freiberginstruments.com

Light Beam Induced Current (LBIC) Light Beam Induced Current (LBIC) is a primarily in the photovoltaic sector well established method for the spatial resolved measurement of recombination active defects in ready-progressed solar cells. The proceeding is based on the measurement of the local short circuit current Isc in the cell, which is produced through appropriate excitation. For the measurement the solar cell is contacted and locally irradiated with laser light. Advantages are the simple buildup and the high resolution, disadvantage is the exigency of contacting the sample, for which reason only ready-progressed cells can be examined. Predictions about lifetime, mobility or defect details are possible. From the measured short circuit current the external quantum efficiency can be determined via: \(EQE = \cfrac{I_{SC}\cdot h \cfrac{c}{\lambda}}{P \cdot e}\) where P is the laser power and l the wavelength. The external quantum efficiency depends on the properties of the cell volume but also on the reflection properties of the surface. If the reflection can be neglected the following mechanism determines the EQE: recombination of minority carriers in the volume recombination of minority carriers at the surfaces at the front and the back shunts in the solar cell The internal quantum efficiency IQE includes the reflection of the light at the surface: \(IQE = EQE\cfrac{1}{1 - R(\lambda)}\) In order to determine the diffusion length, it is necessary to measure IQE for at least 4 different wavelengths, which should differ in the penetration depth. The slope of 1/IQE vs. 1/a is the reciprocal of the effective diffusion length. Fig. 1: internal quantum efficiency of a solar cell measured with 4 different wavelength Related Solutions and Industries: Epitaxial Layers & Thin Films , Photovoltaic Matching Products MDP series MDpicts pro High-Resolution, Temperature-Dependent Lifetime Measurement System for Precise Material Characterization Learn more MDP series MDPpro 850+ Advanced Solution for Quality Control of Monocrystalline Silicon Ingots, Bricks, and Wafers Learn more MDP series MDPpro Advanced Lifetime Measurement System for Quality Control and Material R&D on Semiconductors Learn more MDP series MDPmap Precision Lifetime Charachterization with Exceptional Sensitivity Learn more Get in touch Do not hesitate to contact us – we are available to assist you with any inquiries or requests. Use our inquiry tool or reach out via email: sales @ freiberginstruments.com

Iron concentration determination The exact determination of the iron concentration is very important, since iron is one of the most abundant and also most detrimental defects in silicon. (Alttext kürzen, da zu lang)) With the MDPingot and MDPmap series it is possible to measure the iron concentration in bricks and wafers fully automated and with a very high resolution. Lifetime measurements before and after iron boron pair dissociation is a widely used method for iron determination in silicon wafers. In boron doped silicon with a high doping concentration, as it is used for PV applications nearly 100 % of the electrical active iron is present as FeB pairs. With light of sufficient energy these pairs can be dissociated in Fe i and B. This process is reversible and after some time all FeB pairs are associated again. FeB and Fe i have different recombination properties, so that the dissociation has an effect on the measured lifetime. With this effect the iron concentration can be determined via: \([\mathrm{Fe}] = C(\Delta n) \cdot \left( \cfrac{1}{\tau_{\mathrm{Fe}_i}} - \cfrac{1}{\tau_{\mathrm{FeB}}} \right)\) For the iron determination a calibration factor C is used, which depends on the injection, doping concentration and trap concentration, which has to be considered especially in Multicrystalline silicon. With MDP a determination of the iron concentration is possible for mc- and mono-Si with a high resolution and thanks to simulations and years of research, also with a high accuracy. Lifetime map before illumination and resulting iron map Related Solutions and Industries: Epitaxial Layers & Thin Films , Photovoltaic , Research and Development Matching Products MDP series MDPpro 850+ Advanced Solution for Quality Control of Monocrystalline Silicon Ingots, Bricks, and Wafers Learn more MDP series MDPpro Advanced Lifetime Measurement System for Quality Control and Material R&D on Semiconductors Learn more MDP series MDPmap Precision Lifetime Charachterization with Exceptional Sensitivity Learn more Get in touch Do not hesitate to contact us – we are available to assist you with any inquiries or requests. Use our inquiry tool or reach out via email: sales @ freiberginstruments.com

Minority carrier Lifetime maps on 450 mm wafers Since several years, the microelectronic industry is planning to enlarge the wafer size from 300 mm (12 inch) to 450 mm (18 inch) diameter, in order to gain more yield. The technology for the production of such high-quality wafers is now available and only the cost issue of adapting the fabs is still prohibiting the transfer to a larger wafer size. These 450 mm wafers also need to be checked for extrinsic and intrinsic impurities and hence highly spatially resolved lifetime measurements are needed. In cooperation with Fraunhofer IISB , Freiberg Instruments developed a tool for the minority carrier lifetime measurement of 450 mm wafers in the EC-funded project SEA4KET . For the minority carrier lifetime measurement of 450 mm wafers basically the same measurement head as in the MDPmap and MDPpro is used with some adaption for the larger wafer size in the mapping part of the tool. Figure 1 shows one of the first measured lifetime maps of a 450 mm wafer, which clearly shows some handling traces and striations. In figure 2 and 3 the tool, which is situated in the clean room at Fraunhofer IISB is displayed. Fig. 1: minority carrier lifetime map of a 450 mm wafer Fig. 2: Versatile metrology module at Fraunhofer IISB site with implemented minority carrier lifetime measurement head (MDP sensor) in the course of feasibility evaluation activities within SEA4KET project. © Photo: Kurt Fuchs/Fraunhofer IISB Fig. 3: minority carrier lifetime measurement head (MDP sensor) and 450 mm wafer in the course of feasibility evaluation activities within SEA4KET project. © Photo: Kurt Fuchs/Fraunhofer IISB Related Solutions and Industries: Epitaxial Layers & Thin Films Matching Products MDP series MDPpro Advanced Lifetime Measurement System for Quality Control and Material R&D on Semiconductors Learn more MDP series MDPmap Precision Lifetime Charachterization with Exceptional Sensitivity Learn more Get in touch Do not hesitate to contact us – we are available to assist you with any inquiries or requests. Use our inquiry tool or reach out via email: sales @ freiberginstruments.com