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Detection of CrB in silicon The determination of the chromium concentration is very important, since chromium is one of the most abundant and also most detrimental defects in silicon. (Alttext kürzen, da zu lang) Lifetime measurements before and after chromium boron pair dissociation is a widely used method for chromium 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 chromium is present as CrB pairs. With light of sufficient energy these pairs can be dissociated in Cri and B. This process is reversible and after some time all CrB pairs are associated again, which takes much longer as for FeB pairs. CrB and Cri have different recombination properties, so that the dissociation has an effect on the measured lifetime. With this effect the chromium concentration can be determined via: \([Cr] = C_{Cr}(\Delta n) \cdot (\cfrac{1}{\tau_{Cr}} - \cfrac{1}{\tau_{CrB}})\) For the chromium determination a calibration factor C is used, which depends on the injection and doping concentration. With the MDPmap and the heated sample stage a determination of the chromium concentration is possible for mc- and mono-Si with a high resolution. 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

Detection of BO2 in silicon Boron-oxygen complexes are one of the main reasons why solar cells degrade, when irradiated with sun light. Hence it is important to measure the boron-oxygen density in silicon fast, destruction free and with a high resolution. The boron-oxygen complexes can be activated by irradiating the sample with light and deactivated by heating the sample at 200 °C for several minutes. This can be used similar to the iron determination, to determine the relative boron-oxygen density by lifetime measurements before and after the activation and deactivation of the defect complex. The boron-oxygen density is determined via: \([BO_{2}] = C_{BO}(\Delta n) \cdot (\cfrac{1}{\tau_{BO}} - \cfrac{1}{\tau_{FeB}})\) For the boron-oxygen determination a calibration factor CBO is used, which depends on the injection and doping concentration. With the MDPmap and the heated sample stage a determination of the boron-oxygen concentration is possible for mc- and mono-Si with a high resolution. 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 material quality of GaAs Besides silicon GaAs is one of the most important materials in modern technology and therefore a method to investigate the material quality is needed. (Alttext kürzen, da zu lang) In contrast to other techniques MD-PICTS (microwave detected photo induced current transient spectroscopy) can detect signals even from thin surface regions (3 µm) of SI GaAs samples and is therefore able to analyze e.g. influence of surface treatments. Figure 1 shows the defect peak of the well-known EL2 defect in samples with different acceptor concentrations. Fig. 1: Detection of the EL2 defect in SI GaAs samples with different acceptor concentrations by MD-PICTS, peak height and sign correlate to the acceptor concentration 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

Silicon photovoltaic – Wafer check after diamond wire sawing Diamond wire sawing (DWS) is an established technology for wafering semiconductor ingots, as it has many advantages over other technologies, such as of slurry cutting. Some of these advantages include faster cutting speeds with higher cutting efficiency, production of thinner wafers with improved thickness uniformity, easier way to filter silicon debris for slurry recycling (if desired), and use of cutting wire for more than one cut. Diamond wire sawing uses a long (hundreds of kilometres) wire, impregnated with diamond flakes (grit) as a cutting medium. The cutting wire is made up of a stainless-steel core (80– 120 µm in diameter) that is coated with diamond flakes (8–25 µm in size) which are then bonded to the wire by a layer of electroplated Ni or a layer of a resin material. The as-sawn DWS wafer might look perfect to the naked eye, but the diamond wire and the strategy of moving the diamond wire through the ingot (speed and reciprocation), has a high impact on the quality of the as-sawn wafers as well as subsequent processes such as lapping, grinding or etching. For PV wafers in particular, there can be a huge difference in the sub surface damage over the as-sawn square wafer and this needs to be accounted for in the damage etch and texturing etch process step that proceeds the DWS process. SPV spectroscopy using the HR-SPS tool provides direct information about the quality of the as-sawn wafers – it can be used to find areas of wire snap-off, wire reciprocation and also provide a map with relation to subsurface damage depth. It is contactless and fast, allowing for an integration of the tool into a process line QC control of as-sawn wafers. Below is a shown an example for a 156 x 156 mm 2 pseudo square DWS PV wafer (n-type monocrystalline, 1-3 Ohm-cm). Figure 1 shows maps of the SPV height across the n-type PV wafer by illuminated with three different photons energies – the penetration depths of the photons into the wafer is approximately 0.1, 10 and 100 mm, respectively. Also shown are the relaxation time constant across the wafer – defined as the logarithmic SPV signal transient decay time after turning off the light. It is clear from the SPV maps (left side) that the wafer has varying degrees of subsurface damage across the wafer; the top part has more subsurface damage than the bottom part and the periphery also has more damage. This is to be expected because of the force of the wire is higher at the periphery of the ingot to be sawn. In the relaxation maps (right side), there is a distinct zone below the centre of the wafer towards the bottom. This distinct centre has a lower than expected relation time (-10%) and this probably marks the reciprocation process start. The SPV and relaxation maps complement each other and give a fingerprint of the state of the as-sawn PV wafer. Fig. 1. SPV maps (right) and relaxation time maps (left) for the same DWS wafer and illuminated with three different energies (wavelengths) Related Solutions and Industries: Epitaxial Layers & Thin Films Matching Products SPS/SPV series HR-SPSmap with fixed energy excitation sources High-Resolution and Sensitive Surface Photovoltage Measurement Solutions Learn more SPS/SPV series HR-SPSmap with variable energy excitation source with a variable energy excitation source 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

Study and monitoring of photocatalytic materials (TiO2) Aim Photocatalytic materials such as TiO 2 are of great interest, for example, for cleaning of industrial wastewater and for water splitting. The identification of directed charge transfer is important for deeper understanding of the role of defect states, defect bands and doping as well as for technology control. Solution SPV spectroscopy in the dc (Kelvin probe, measurement of the contact potential difference, DCPD) and ac (modulated) modes provides information about preferential directed charge separation [1] and allows the investigation of the influence doping on band bending, recombination losses and scavengers (entities accepting electrons or holes) at surfaces. Application example It was shown that TiO 2 can be doped n- and p-type by thermal treatment in reducing or oxidizing atmosphere (figure 1, more in [2]). Figure 2 shows the deposition temperature dependence of defect and band gap transitions in TiO 2 after deposition by cold gas spraying of TiO 2 powder (more in [3]). The evolution of defect bands in TiO 2 caused by incorporation, of nitrogen and their effect on charge transfer was studied in [4]. References [1] Th. Dittrich, S. Fengler, “Surface photovoltage analysis of photoactive materials”, World Scientific, 2020. [2] M. K. Nowotny, et al., „Observation of p-type semiconductivity in titanium dioxide at room temperature”, Materials Letters 64 (2010) 928. [3] I. Hermann-Geppert, et al., „Cold gas sprayed TiO 2 -based electrodes for the photo-induced water oxidation”, ECS Transactions 58 (2014) 21. [4] R. Beranek, et al., „Exploring the electronic structure of nitrogen-modified TiO 2 photocatalysts through photocurrent and surface photovoltage studies”, Chem. Phys. 339 (2007) 11. Fig. 1: 1st (thick) and 2nd (thin) DCPD spectra of reduced (red) and oxidized (blue) TiO2 (rutile). Band gap and defect states marked. Data partially after [2]. Fig. 2: Modulated SPV spectra of cold gas sprayed TiO2 for different temperatures. Data partially after [3]. Related Solutions and Industries: Epitaxial Layers & Thin Films Matching Products SPS/SPV series HR-SPSmap with fixed energy excitation sources High-Resolution and Sensitive Surface Photovoltage Measurement Solutions Learn more SPS/SPV series HR-SPSmap with variable energy excitation source with a variable energy excitation source 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

Contactless detection of bulk polarization phenomena in semiconductors Aim Characterization of bulk polarization phenomena such as the bulk photo-voltaic effect (BPVE) in semiconductors requires the preparation of two electrical contacts on the sample, which inevitably introduces additional defects in the semiconductor-metal interface what is especially challenging for ultrawide bandgap semiconductors with high resistivity. Solution Surface photovoltage (SPV) spectroscopy using a Kelvin probe is used as a nondestructive, contactless method for characterizing the change of the contact potential difference (DCPD) in carbon doped GaN single crystals. By designing a unique setup capable of measuring DCPD up to ± 200 V, large photovoltages could be detected, without the need to deposit electrical contacts. Application example The band gap of GaN is 3.4 eV. As an example, figure 1 shows a spectrum of DCPD for a carbon doped GaN crystal (GaN:C). The corresponding SPV signal reached more than 13 V at 3 eV, i.e., under excitation of certain defect states, SPV signals were much larger than expected from the band gap (for more details see [1]). A change of the direction of DCPD and a signature in the derivative were found near the band gap. Under excitation with a laser diode (445 nm) at higher intensity, the maximum signal was obtained for GaN:C with a carbon concentration of 9×10 18 cm -3 and amounted to about 23 V, far exceeding the band gap (figure 2). Fig.1: Spectra of DCPD and its deriva-tive for a GaN:C crystal. SPV signals are much larger than the band gap for excita-tion in the defect range (data after [1]). Fig. 2: Time dependence of DCPD of a GaN:C crystal measured during illumination with a laser diode at 445 nm and after switching off illumination. References [1] Levine, I., et al. "Bulk photovoltaic effect in carbon-doped gallium nitride revealed by anomalous surface photovoltage spectroscopy." Phys. Rev. B 101 (2020) 245205. Related Solutions and Industries: Epitaxial Layers & Thin Films Matching Products SPS/SPV series HR-SPSmap with fixed energy excitation sources High-Resolution and Sensitive Surface Photovoltage Measurement Solutions Learn more SPS/SPV series HR-SPSmap with variable energy excitation source with a variable energy excitation source 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 photocatalytic materials (BiVO4) Aim Photocatalytic materials such as BiVO 4 are of great interest, for example, for water splitting. Electronic defect states and surface passivation are important limiting factors. Photocatalytic materials can be applied as powders, porous layers or thin films what makes a simple and contactless photoelectric characterization of such materials still challenging. Solution SPV spectroscopy in the dc (Kelvin probe, measurement of the contact potential difference: DCPD) and ac (modulated) modes is a contactless and highly sensitive method allowing to detect very low SPV signals related to charge separation under excitation of defect states for powder, porous and thin film samples [1]. Application example Figure 1 shows spectra of the modulated SPV amplitude for a BiVO 4 thin film, porous layer and powder (see also [2]). The onset of the band gap of BiVO 4 (2.5 eV), the energy parameters of exponential tails and transitions related to defects can be well measured. Figure 2 shows DCPD spectra of porous BiVO 4 layers decorated with V 13 O 15 with and without a passivating cobalt phosphate (Co-Pi) cocatalyst (see also [3]). References [1] Th. Dittrich, S. Fengler, “Surface photovoltage analysis of photoactive materials”, World Scientific, 2020. [2] S. Fengler, et al., „Characterization of BiVO 4 powders and cold gas sprayed layers by surface photovoltage techniques“, Catalysis Today 321 (2019) 34. [3] H. Ren, et al., „Manipulation of charge transport by metallic V 13 O 16 decorated on bismuth vanadate photoelectrochemical catalyst“, Adv. Mater. (2019) 1807204. Fig. 1: Viewgraphs and spectra of the modulated SPV amplitudes for a BiVO4 thin film (black), porous layer (red) and powder (blue). Band gap is marked. Fig. 2: DCPD spectra of porous BiVO4 layers decorated with V13O15 with (red) and without (blue) a cobalt phosphate cocatalyst. Related Solutions and Industries: Epitaxial Layers & Thin Films Matching Products SPS/SPV series HR-SPSmap with fixed energy excitation sources High-Resolution and Sensitive Surface Photovoltage Measurement Solutions Learn more SPS/SPV series HR-SPSmap with variable energy excitation source with a variable energy excitation source 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

Electronic transitions in diamond Aim For further development of optoelectronic devices and other applications based on diamond and nanodiamond, contactless characterization of electronic defect states and electronic transitions in bulk diamond and at diamond surfaces over a wide spectral range is of great interest. Solution Contactless surface photovoltage (SPV) spectroscopy in the Kelvin probe (direct measurement of the contact potential difference, DCPD) and modulated regimes provides information about transitions energies and direction of charge separation in a spectral range from near infrared (< 0.5 eV) up to the deep ultraviolet (> 6 eV) at high sensitivity. Application example Diamond has an ultra-wide indirect band gap of 5.47 eV [1]. Figure 1 shows the DCPD spectrum and its derivative for a polycrystalline diamond sample prepared by CVD. Transitions related to excitation via defect states and transitions around the band gap can be clearly distinguished [2]. For the modulated SPV spectra of another diamond sample, the sensitivity is increased and transitions at 5.258 and 5.544 eV related to absorption assisted by the indirect exciton and transversal optical phonon are well pronounced. Related spectra are like fingerprints and can be used, for example, for inline control in production lines. References [1] C. D. Clark, P. J. Dean, P. V. Harris, “Intrinsic edge absorption in diamond”, Proc. R. Soc. London A 277, 312 (1964). [2] Th. Dittrich and S. Fengler, “Transitions in polycrystalline diamond probed by surface photovoltage spectroscopy”, to be submitted. Figure 1: Spectra of DCPD and its deriva-tive for polycrystalline CVD diamond (data after [2]). Onsets at major defect transitions and around the band gap. Fig. 2: In-phase and phase-shifted by 90° modulated SPV spectra of a diamond crystal. Dotted lines give defect related transitions and transitions Eg - Ex ± hvTO. Related Solutions and Industries: Epitaxial Layers & Thin Films Matching Products SPS/SPV series HR-SPSmap with fixed energy excitation sources High-Resolution and Sensitive Surface Photovoltage Measurement Solutions Learn more SPS/SPV series HR-SPSmap with variable energy excitation source with a variable energy excitation source 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

Resistance measurements on wafers and bricks The resistivity is one of the most important electrical parameters of a material. It is a key parameter for the performance of semiconductor devices as e.g. solar cells and depends on the doping density of the material. (Alttext Kürzen) With MDPmap and MDPingot it is possible to measure the resistivity of wafers or bricks with a high accuracy and a resolution of 1 mm via eddy current measurements. The Eddy current sensor setup has a very good long-term stability, due to a distance correlated internal calibration matrix. Hence, with every resistivity map a geometry map of the surface flatness is measured. The resistivity can be measured simultaneously with the minority carrier lifetime and photoconductivity maps. In case of wafer measurements, the thickness of the sample has to be given by the user. Step width ≥ 1mm Edge exclusion 12 mm Resistivity wafer thickness range 150 ...250 µm Resistivity range can be specified Default setting: 0.5 to 5 Ohm cm Accuracy: < 5 % Repeatability: < 1 % (range of 0.5 until 3 Ohm cm) It is possible to map the sheet resistance of the emitter, in order to investigate the homogeneity of the emitter diffusion. The resistivity of the base has to be given by the user. Sheet resistance measurement with range 0.1-200 Ohm/sq Accuracy at standard sample size, 0.1 - 10 Ohm/sq: < 3 % accuracy 10 - 100 Ohm/sq: < 4 % accuracy 100 – 200 Ohm/sq: < 5 % accuracy Figure 1 to 3 show examples of resistivity maps measured on mc-Si wafers and bricks. Fig 1: Emitter sheet resistance map of a typical mc-Si wafer with emitter diffusion and an average sheet resistance of 85.1 Ohm/sq. Fig. 2: resistivity map of a typical mc-Si wafer for PV applications and an average resistivity of 1.0 Ohm cm Fig. 3: Resistivity map of a typical mc-Si brick for PV applications and an average resistivity of 1.4 Ohm cm Related Solutions and Industries: Epitaxial Layers & Thin Films , Photovoltaic Matching Products MDP series MDPspot Quick and Simple Lifetime Measurement Made Easy 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

Characterization of Ga2O3 Aim Ga 2 O 3 is an ultra-wide band gap semiconductor with a great application potential. The contactless characterization of defect related transitions with high sensitivity is still challenging. Solution Contactless surface photovoltage (SPV) spectroscopy in the dc (Kelvin probe, direct measurement of the contact potential difference, DCPD) and ac (modulated regime) modes provides information about transitions energies and direction of charge separation in a wide spectral range from near infrared (< 0.5 eV) up to the deep ultraviolet (> 6 eV) at high sensitivity. Furthermore, the same perforated electrode can be applied for measurements in dc and ac modes with a charge amplifier (figure 1). Application example Figure 2 shows an example for the measurement of a (negative) DCPD spectrum and the spectrum of the modulated SPV amplitude (in a logarithmic scale) on the same place of a b-Ga 2 O 3 crystal. Transitions at the band gap of b-Ga 2 O 3 at 4.8 eV and defect transitions at 1.6, 2.3, 3.2, 4.0, 4.4 and 4.6 eV are well distinguished whereas the sensitivities for measurements in the dc and ac modes can be rather different for different transitions. References [1] Th. Dittrich, S. Fengler, N. Nickel, “Surface photovoltage spectroscopy over wide time domains for semiconductors with ultrawide bandgap: example of gallium oxide”, Phys. Stat. Sol. A 11 (2021) 2100176. Fig. 1: Scheme for the measurement in dc and ac modes with the same electrode and a charge amplifier [1]. Fig. 2: Spectra of DCPD (blue) and spectrum of the modulated SPV amplitude (red) of a b-Ga2O3 crystal. Onsets at major defect transitions and at the band gap. Related Solutions and Industries: Epitaxial Layers & Thin Films Matching Products SPS/SPV series HR-SPSmap with fixed energy excitation sources High-Resolution and Sensitive Surface Photovoltage Measurement Solutions Learn more SPS/SPV series HR-SPSmap with variable energy excitation source with a variable energy excitation source 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