Bulk Lifetime Research Articles

~23% rear side poly-Si/SiO2 passivated silicon solar cell with optimized ion-implanted boron emitter and screen-printed contacts

We report on the understanding and optimization of ion-implanted boron emitters in combination with screen-printed contacts to produce very low recombination current density and high-efficiency cells with rear poly-Si/SiO2 passivated contact. Due to high bulk lifetime in n-base Si and very low recombination in the rear-side n+ passivated contact, recombination in the emitter limits the efficiency potential of manufacturable single-side passivated contact cells. Emitter recombination is governed by recombination under metal contacts (J0e,metal) and in the passivated regions in between (J0e,pass). Emitter profile engineering and dielectric passivation can lower the J0e,pass while paste chemistry and firing conditions can reduce J0e,metal by altering the extent of screen-printing induced emitter surface etching and the percentage of unetched dielectric islands under the metal contacts. We optimized implanted boron profiles, surface concentration and passivation, and junction depth in the sheet resistance range of 48-200 Ω/□ and achieved very low J0e,pass (<15 fA/cm2) for textured boron emitters with Rsheet≥140 Ω/□. Additionally, screen-printing paste and firing optimization reduced J0e,metal from 1172 to 707 fA/cm2 on 170 Ω/□ boron emitter by virtually eliminating emitter surface etching and creating distributed local contacts with unetched dielectric islands (~40% area coverage) underneath the grid lines. This resulted in very low total metallized J0e of 30 fA/cm2 with 3% metal coverage. Our device modeling showed the optimum boron sheet resistance is in the range of 120-170 Ω/□. The simulated results were validated by fabricating fully screen-printed 100 cm2 22.9% efficient bifacial cell with n+ poly-Si/SiO2 passivated rear contact.

Optimization of Mono-Crystalline Silicon Solar Cell Devices Using PC1D Simulation

Expeditious urbanization and rapid industrialization have significantly influenced the rise of energy demand globally in the past two decades. Solar energy is considered a vital energy source that addresses this demand in a cost-effective and environmentally friendly manner. Improving solar cell efficiency is considered a prerequisite to reinforcing silicon solar cells’ growth in the energy market. In this study, the influence of various parameters like the thickness of the absorber or wafer, doping concentration, bulk resistivity, lifetime, and doping levels of the emitter and back surface field, along with the surface recombination velocity (front and back) on solar cell efficiency was investigated using PC1D simulation software. Inferences from the results indicated that the bulk resistivity of 1 Ω·cm; bulk lifetime of 2 ms; emitter (n+) doping concentration of 1×1020 cm−3 and shallow back surface field doping concentration of 1×1018 cm−3; surface recombination velocity maintained in the range of 102 and 103 cm/s obtained a solar cell efficiency of 19%. The Simulation study presented in this article allows faster, simpler, and easier impact analysis of the design considerations on the Si solar cell wafer fabrications with increased performance.

Positron lifetime spectroscopy of defect structures in Cd1–x Zn x Te mixed crystals grown by vertical Bridgman–Stockbarger method

Positron annihilation lifetime spectroscopy was used to examine grown-in defects in Cd1–x Zn x Te mixed crystals as a function of Zn content (x = 0, 0.07, 0.11, 0.49, 0.9, 0.95, 1) and measuring temperature. All samples were prepared using the high-pressure modified vertical Bridgman–Stockbarger method. The crystal structure and material phase were characterized by X-ray diffraction. The positron lifetime spectra reveal the presence of both open volumes and shallow traps regardless of the sample composition. In particular, both average and bulk lifetimes are found to be much higher in ternary alloys (CdZnTe) than those in binary systems (CdTe and ZnTe). This originates from distinct differences in average electron densities and the nature of open-volume defects between binary and ternary samples. Competition in positron trapping with increasing Zn content is observed between defects characteristic for both structural systems. Moreover, a clear correlation is shown between defects and the lattice thermal conductivity of studied samples. The applicability of the positron trapping model to CdTe-based materials is discussed.

Enhancing Defect Tolerance with Ligands at the Surface of Lead Halide Perovskites.

High defect tolerance has been considered a primary reason for the long charge carrier lifetime and high photoluminescence quantum yield in bulk lead halide perovskites (LHPs). On the other hand, surface defects play a critical role in determining charge carrier dynamics and optical properties, especially for LHP nanocrystals and quantum dots. Understanding the nature of surface defects and developing strategy for their effective passivation are thus of strong interest. Focusing on a prototypical LHP, CsPbBr3, our work uses first-principles calculations to reveal that interstitial sites and antisites can have lower formation energies when they form at the surface while simultaneously creating deep trap states within the bandgap. Meanwhile, the formation of halide vacancies is energetically less favorable. On the basis of a new surface defect model, we demonstrate the explicit role of molecular ligands in passivating these defects, which eliminate trap states in favor of shallow states and enhance photoluminescence.

Pathways toward 30% Efficient Single‐Junction Perovskite Solar Cells and the Role of Mobile Ions

Perovskite semiconductors have demonstrated outstanding external luminescence quantum yields, enabling high power conversion efficiencies (PCEs). However, the precise conditions to advance to an efficiency regime above monocrystalline silicon cells are not well understood. Herein, a simulation model that describes efficient p–i–n‐type perovskite solar cells well and a range of different experiments is established. Then, important device and material parameters are studied and it is found that an efficiency regime of 30% can be unlocked by optimizing the built‐in voltage across the perovskite layer using either highly doped (1019 cm−3) transport layers (TLs), doped interlayers or ultrathin self‐assembled monolayers. Importantly, only parameters that have been reported in recent literature are considered, that is, a bulk lifetime of 10 μs, interfacial recombination velocities of 10 cm s−1, a perovskite bandgap () of 1.5 eV, and an external quantum efficiency (EQE) of 95%. A maximum efficiency of 31% is predicted for a bandgap of 1.4 eV. Finally, it is demonstrated that the relatively high mobile ion density does not represent a significant barrier to reach this efficiency regime. The results of this study suggest continuous PCE improvements until perovskites may become the most efficient single‐junction solar cell technology in the near future.

(Invited) Gallium Doped Silicon for High Efficiency Solar Cells

In the past year or so, gallium doped silicon wafers have become a mainstream substrate for solar cell production in China [1], and hence for the world. They offer intrinsically better carrier lifetime stability than boron doped substrates [2] without requiring post-cell production stabilisation processes while requiring only minimal changes to established cell lines. Gallium doped monocrystalline silicon is likely to account for the majority of passivated emitter and rear cell (PERC) production in the coming years.High purity gallium doped silicon has been the subject of much less study than some other silicon material types, and the limits of its performance are not yet well established. In terms of effective carrier lifetime – one of the most important properties for solar cells – the highest reported values are typically around 1 ms. We have conducted a study to evaluate the performance limit of modern Ga doped silicon materials with high quality surface passivation. We find effective lifetime to vary with resistivity and measure effective lifetimes > 9 ms in 11.2 Ωcm material, which is much higher than reported previously. Furthermore, the injection dependence is less strong than in the boron case which may result in a higher fill factor and favourable cell performance in operation.One of Ga doped silicon’s perceived advantages is its stability under illumination relative to B doped silicon which suffers heavily from boron-oxygen light induced degradation if not mitigated. We have monitored the stability of commercial gallium doped PERC cells under illumination (> 3000 h in some cases) using a photoluminescence imaging proxy method. We have shown however that dark annealed Ga doped PERC cells can degrade when exposed to light, albeit on a much smaller scale than B doped PERC, and this degradation occurs due to a reduction in bulk lifetime [3]. We will now present our latest results which show inconsistencies in degradation behaviour between solar cell batches. Surprisingly, cells from one ingot exhibit degradation, then recovery behaviour when annealed at 300 °C, but near stability when not annealed, but, for another ingot, the opposite is observed. We have also investigated the effect of stabilisation processes of the kind typically used to mitigate boron-oxygen degradation. We find these processes make essentially no difference to the degradation behaviour in Ga doped PERC cells. Our investigations using secondary ion mass spectrometry (SIMS) find that commercial Ga doped PERC cells contain detectable levels of boron, and this could play a role in the degradation processes observed.In summary, our work generally confirms the positive effects of a transition from B to Ga doping for solar cells. Any degradation in cell performance under illumination is fairly small, but understanding the reasons for this is one of the most important questions in high purity silicon research at present. We will highlight urgent research in this area necessary to mitigate instability issues which may arise in newly manufactured modules featuring Ga doped silicon solar cells.

Silicon wafers for industrial n-type SHJ solar cells: Bulk quality requirements, large-scale availability and guidelines for future developments

In this work, we derive and discuss the wafer bulk requirements for industrial amorphous/crystalline n-type silicon heterojunction cells. In particular, we investigate in detail the efficiency variations as a function of a) bulk carrier lifetime, b) dark resistivity, as well as c) the ratio of both quantities. To this end, we resort to finite element simulations to calculate how the I(V) parameters vary with the bulk properties listed above. In order to validate the simulation outputs, SHJ cells were processed from several wafer groups specially prepared to span wide ranges of bulk lifetimes and resistivities. Once validated, the simulation results are used to compute the wafer requirements as a function of the targeted efficiency, and the specifications derived therefrom are compared with literature. In this respect, the limits of the bulk lifetime/resistivity ratio, often employed to discuss wafer specifications, are highlighted. Combining the established requirements with statistical data from mass production of Czochralski ingots, we then assess whether or not nowadays commercially available monocrystalline wafers allow for a stable production of high efficiency devices. From a wafer manufacturer's standpoint, we quantify for a fixed cell structure, the room for efficiency improvement expected with further progresses in wafer bulk properties. Last, we also provide an outlook on how wafer requirements shall evolve with cell efficiency up to 25%.

Phosphorous Diffusion Gettering of Trapping Centers in Upgraded Metallurgical‐Grade Solar Silicon

Experimental evidence indicating the beneficial impact of a phosphorous diffusion gettering (PDG) in the reduction of trapping centers is shown, as observed by means of inductively coupled photoconductance (PC) decay and lifetime measurements carried out on upgraded metallurgical‐grade silicon (UMG‐Si) wafers. The presence of trapping species dominating the long time range of the PC decay of UMG material (slow traps), which is effectively removed after a PDG conducted at 780 °C, is detected. Notwithstanding, a second trapping mechanism, characterized by a shorter time constant, still governs the response at very low injection levels after the gettering. Furthermore, the beneficial effect of the PDG is studied as a function of processing time, showing minority carrier bulk lifetime improvements up to 18‐fold, up to the range of 70 μs. Thereby, the way for developing gettering strategies capable of successfully removing trap centers and improving the bulk lifetime of unconventional Si material is paved.

UMG silicon for solar PV: From defects detection to PV module degradation

Upgraded metallurgical grade silicon (UMG-Si) for photovoltaic (PV) solar applications has been manufactured through the metallurgical route by means of the process developed by Ferrosolar. In an ambitious mass production test, performed in commercial solar cells and modules production lines, the silicon was proven to be appropriate for photovoltaics applications (Forniés et al., 2019 Mass production test of solar cells and modules made of 100% umg silicon. 20.76% record efficiency. Energies 12), reaching, in a conventional production line, up to 20.76% of solar cell efficiency with multicrystalline cells made of 100% UMG silicon. In this paper we present more results from the mentioned massive test. Defect engineering is being applied to improve the bulk lifetime of the UMG wafers and to guide in the identification of the limiting defects in the material. Moreover, the modules produced with 100% UMG silicon solar cells were installed together with the modules produced in the same production line with polysilicon material to assess the degradation of the UMG silicon when compared to polysilicon. After 24 months of outdoor PV generation, the degradation, in terms of Performance Ratio at 25 °C (25PR) diminution, has been the same for both types of modules. Additionally, a Life Cycle Assessment (LCA) has been performed for this UMG silicon and state-of-the-art Siemens polysilicon to compare the environmental impact of both silicon feedstocks. The results presented in this paper; chemical analysis of wafers, defect engineering, low degradation, average efficiency and environmental assessment, lead to a complete study of UMG silicon, confirming its potential to be used as raw material for PV applications.

Nickel and gold identification in p-type silicon through TDLS: a modeling study

In Silicon, impurities introduce recombination centers and degrade the minority carrier lifetime. It is therefore important to identify the nature of these impurities through their characteristics: the capture cross sectionσand the defect levelEt. For this purpose, a study of the bulk lifetime of minority carriers can be carried out. The temperature dependence of the lifetime based on the Shockley-Read-Hall (SRH) statistic and related to recombination through defects is studied. Nickel and gold in p-type Si have been selected for the SRH lifetime modeling. The objective of the analysis is to carry out a study to evaluate gold and nickel identification prior to temperature-dependent lifetime measurements using the microwave phase-shift (μW-PS) technique. The μW-PS is derived from the PCD technique and is sensitive to lower impurity concentrations. It has been shown that both gold and nickel can be unambiguously identified from the calculated TDLS curves.

In2O3−Ga2O3 Alloys as Potential Buffer Layers in CdTe Thin-Film Solar Cells

The efficiency of state-of-the-art $\mathrm{Cd}\mathrm{Te}$ solar cells remains limited by the relatively low open-circuit voltage (${V}_{OC}$). Improving the front interface is key towards realizing a higher ${V}_{OC}$ after achieving the necessary bulk carrier density and lifetime. Recent efforts in identifying buffer layers beyond $\mathrm{Cd}\mathrm{S}$ have focused on ${\mathrm{Mg}}_{x}{\mathrm{Zn}}_{1\ensuremath{-}x}\mathrm{O}$, which offers tunability of the band offsets, but often suffers from high interfacial defect densities. ${\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$-based buffer layers demonstrate tremendous improvements in interfacial defect passivation in crystalline silicon and dye-sensitized solar cells, leading to record high ${V}_{OC}$, yet remain largely unexplored in $\mathrm{Cd}\mathrm{Te}$-based devices. Here, we perform hybrid density-functional-theory calculations to investigate pure ${\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ and ${\mathrm{In}\mathrm{Ga}\mathrm{O}}_{3}$ alloys as a window layer in $\mathrm{Cd}\mathrm{Te}$ photovoltaics. We report calculated band offsets for several pairs of solid-solid interfaces comprising transparent conducting oxide (TCO) and $\mathrm{Cd}\mathrm{Te}$ heterojunctions. The results support a large conduction band offset spike of 0.67 eV for the $\mathrm{Cd}\mathrm{Te}/{\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ (100) interface, while the offset is reduced to 0.18 eV for the ${\mathrm{In}\mathrm{Ga}\mathrm{O}}_{3}$ alloy and matches closely with the preferred optimum value of 0.2 eV. Device-level modeling tests of $\mathrm{Cd}\mathrm{Te}$ solar cells integrating our results indicate that the highest efficiency is achieved with ${\mathrm{In}\mathrm{Ga}\mathrm{O}}_{3}$ acting both as a buffer layer and TCO. Our results suggest that alloys of ${\mathrm{In}}_{2}{\mathrm{O}}_{3}$ and ${\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ may be attractive alternatives to ${\mathrm{Mg}}_{x}{\mathrm{Zn}}_{1\ensuremath{-}x}\mathrm{O}$ for tailoring optimal conduction-band offsets of the buffer and TCO layers in high-efficiency $\mathrm{Cd}\mathrm{Te}$ thin-film solar cells.

SMART Cast‐Monocrystalline p‐Type Silicon Passivated Emitter and Rear Cells: Efficiency Benchmark and Bulk Lifetime Analysis

Herein, boron‐doped cast‐monocrystalline silicon wafers that have been fabricated using the Seed Manipulation for ARtificially controlled defect Technique (SMART mono‐Si) are examined. Their suitability for passivated emitter and rear cell (PERC) fabrication is investigated. Applying a zero busbar layout energy conversion efficiencies of η = 21.9% for SMART mono‐Si, η = 22.2% for gallium‐doped Cz‐Si (Cz‐Si:Ga), and η = 22.3% for boron‐doped Cz‐Si (Cz‐Si:B) are achieved at similar doping levels between 0.7 Ω cm ≤ ρB ≤ 1.0 Ω cm. Therefore, SMART mono‐Si PERCs show almost the same performance as Cz‐Si PERCs. Apart from the performance of SMART mono‐Si PERCs, the minority charge carrier bulk lifetime τB of the SMART mono‐Si wafers after different high‐temperature process steps in the PERC process flow is investigated. After emitter formation, this analysis confirms the high material quality of SMART mono‐Si yielding τB ≈ 1.3 ms at an injection level of Δn = 1015 cm−3. The bulk lifetime after firing is similar to the level determined for mCz‐Si:B and Cz‐Si:Ga reference wafers of similar doping level.

Study of open circuit voltage loss mechanism in perovskite solar cells

Open circuit voltage (V oc) loss within perovskite solar cells (PSCs) is undesirable as it reduces the power conversion efficiency of these devices. This report proposes a useful method to study V oc loss mechanisms based on experimental samples. V oc in the radiative limit () of devices is estimated by combining the detailed balance theory and the van Roosbroeck–Shockley relation. Furthermore, V oc loss from bulk recombination can be quantified by introducing the bulk lifetime. Thus, the V oc loss from bulk recombination of MAPbI3 and FASnI3 was estimated as 0.094 V and 0.061 V, respectively. The analysis helps distinguish and quantify the V oc loss of PSCs.

Investigation of bulk and surface minority carrier lifetimes in metamorphic InAsSb grown on GaAs and Si

Monolithic integration of III–V-based optoelectronic devices onto Si wafers provides enormous benefits to many device manufacturing technologies. Therefore, it is essential to understand the effect of limiting factors such as dislocations on the material properties. In this paper, we study the minority carrier lifetimes in mid-wave infrared InAsSb alloys grown on lattice-matched GaSb and lattice-mismatched semi-insulating GaAs and Ge/Si substrates. Time-resolved microwave reflection measurement has been performed to study the carrier dynamics and different recombination mechanisms over the temperature range of 20–300 K at various optical injection levels. The sample on GaAs is found to have a lower lifetime over the entire temperature region than the sample on the Ge/Si substrate. The threading dislocation density values estimated from the lifetime analysis were found to be 2.9±0.2 times larger in the sample on GaAs when averaged over the temperature range of 70–200 K. Furthermore, we studied the contribution of various recombination mechanisms, and it was shown that the lifetime in the sample on GaAs is dominated by the Shockley–Read–Hall recombination up to 140 K, above which the Auger recombination is the limiting factor. This transition temperature is 80 K and 100 K for the samples on GaSb and Ge/Si, respectively. We have also investigated the effect of the surface recombination on the total lifetime. The extracted bulk lifetime was found to be up to 2× higher when the surface effect was excluded.

Nonparabolicity effects on carrier lifetimes in bulk Hg1-xCdxTe alloys and Mid-Infrared 2D Hg1-xCdxTe/CdTe Single Quantum Well Lasers

We report on a theoretical study of nonparabolicity (NP) effects on carrier lifetimes in narrow energy bandgap bulk (3D) Hg 1-x Cd x Te ternary alloys and their related 2D Hg 1-x Cd x Te/CdTe Single Quantum Well (SQW) nanostructures for Mid-infrared (MIR) Laser applications. Carrier lifetime (τ) calculations are performed within both the parabolic and the 4-band CB + HH + LH + SO nonparabolic models. We show that NP affects strongly all three main scattering processes: Auger, Schockley-Read-Hall (SRH), and radiative recombination (RR). At 300 K and in mid-Cd contents (0.4 < x < 0.6) 3D Hg 1-x Cd x Te alloys, Auger 1 is shown to be the dominant τ limiting factor. In 2D Hg 1-x Cd x Te/CdTe SQW nanostructures, we show that RR turns out to be the dominant τ limiting process. This strongly reduced influence of Auger1 process in 2D Hg 1-x Cd x Te/CdTe SQW nanostructures is the result of the strong 2D quantum confinement induced amplification of NP effects via much stronger electron (CB) and all three hole (HH, LH, SO) energy subbands interactions and mixing. As a consequence, NP effects are finally shown to significantly improve all main 2D Hg 1-x Cd x Te/CdTe SQW Laser parameters in the MIR λ range with an optimum at x = 0.45 and for wide enough QW with L z ≥ 100 Å. • Nonparabolicity effects on carrier lifetimes in Hg 1-x Cd x Te 3D and 2D MIR Lasers. • Auger scattering processes are dominant at 300 K in 3D Hg 1-x Cd x Te alloys (0.3 < x < 0.6). • Radiative recombination is dominant 300 K in 2D Hg 1-x Cd x Te/CdTe QW (x ≥ 0.40). • NP affects strongly carrier lifetimes, and consequently, all main laser parameters. • NP improves Laser emission wavelength, optical gain and threshold current densities.

Numerical analysis of tunnel oxide passivated contact solar cell performances for dielectric thin film materials and bulk properties

The performance of tunnel oxide passivated contact (TOPCon) solar cells is evaluated numerically by changing the tunnel dielectric materials. The conventional SiO2, Si3N4, and Al2O3 and the prospective TiO2 and HfO2 have unique tunnel parameters and fixed charge polarities, both of which affect cell performance. The critical tunnel dielectric thickness is determined by the majority-carrier effective mass, with a lighter majority-carrier effective mass capable of easing the tunnel dielectric thickness control at the wider thickness region. The fixed charge should be considered for the higher bulk lifetime condition, with a maximum cell efficiency impact of approximately 0.5%. By adopting p-type bulk with BO-cluster deactivation and higher resistivity as well as an Al2O3 tunnel dielectric thin film of 1 nm, a cell efficiency of 24.77% is achieved, approximately 0.2% higher than the record efficiency of a large-scale TOPCon that adopts FZ-Si bulk.

Pre-Texturing Thermal Treatment for Saw-Damage-Removal-Free Wet Texturing of Monocrystalline Silicon Wafers

The etching of Si wafers significantly influences the efficiency of photovoltaic devices. Texturing can effectively decrease front surface reflection and improve device performance. Saw damage removal (SDR) is necessary to yields uniform random pyramidal surfaces without the appearance of saw marks, it entails significant consumption of chemical solutions and complicated cleaning steps. Herein, an alternative process of pre-texturing thermal treatment was carried out at 800 °C for 10 min, followed by anisotropic texturing, and a uniform pyramidal surface over a large area of the textured surface was obtained without saw marks. Compared with that of as-cut mono-Si wafers (30.7%), the weighted average reflectance of the samples textured with or without thermal treatment decreased to 11.2% and 11.9%, respectively, and further to 3% and 3.4%, respectively, when anti-reflection coatings were applied. In addition, saw marks on the wafer surface were used as gettering sites during thermal treatment, and the bulk lifetime was more than doubled from 42.6 µs before the treatment to 93.8 µs after. The simple, SDR-free method presented herein for enhancing the textural uniformity of Si wafers and, hence, solar cell performance, can be employed on an industrial scale without necessitating additional investment in equipment.

Impact of Substrate Thickness on the Degradation in Multicrystalline Silicon

Light and elevated-temperature-induced degradation (LeTID) is a well-known phenomenon that reduces the bulk lifetime in silicon wafers. The cause of this degradation mechanism is still under investigation. However, a wide range of empirical trends that correlate LeTID with multiple physical and processing parameters have been reported, including the observation that wafers thinner than 120 μm do not show significant LeTID. In this work, we extend that study by varying the thickness of the wafers, the temperature of the firing step, and testing LeTID at the accelerated stability testing conditions. We demonstrate that the extent of degradation reduces with the thickness of the wafer, in agreement with the earlier work. However, silicon wafers with a thickness below 120 μm still suffer from LeTID when fired at sufficiently high temperatures, demonstrating that thinner wafers are not inherently immune to LeTID. By performing accelerated testing using a high-intensity laser and fitting the degradation and regeneration data, we observe that thinner wafers do not necessarily exhibit a faster recovery, as suggested earlier. However, their reduced degradation extent could be a consequence of relatively higher out-diffusion of hydrogen per unit volume in thinner wafers during firing. We further report that the method used for thinning the wafers results in a variation in the surface morphology of the samples, and that may partly be responsible for the observed correlation between the thickness of the wafers and LeTID extent. Finally, we discuss how these new findings can be explained by the involvement of hydrogen and other impurities in LeTID.

Combination of μW-PCD and SPV techniques for bulk and surface defects densities measurements

In semiconductor applications, surface and interface defects play a key-role on the electronic properties of the device. Several non destructive tools can be combined to characterize these defects. From microwave-Photo-Conductivity Decay (μW-PCD) measurements, one can access to an effective measurement of lifetime of minority carriers that characterizes both the surface and the bulk semiconductor material. On the other hand, Surface Photo-Voltage (SPV) is a powerful technique that gives credible bulk lifetime values from minority carriers’ diffusion length measurements. In this paper, we use a nondestructive method by which we determine the surface and bulk defects densities in crystalline silicon wafers by combining μW-PCD and SPV tools using an adequate theoretical approach. We apply this method to three surface morphologies; a mirror-polished sample, a CP4 etched sample and a pyramidal textured sample.

Electron irradiation induced molecular changes in PMMA: A positron spectroscopy study

To examine the positron annihilation parameters with regard to microstructural changes, the positron annihilation lifetime spectroscopy and measurements of the Doppler broadening of annihilation radiation (DBAR) of electron‐irradiated poly(methyl methacrylate) were carried out at room temperature. Trapping rate equations were applied in terms of the positron bulk lifetime as well as the positron lifetime fitting results to investigate the molecular changes due to electron irradiation effects. It was found that the mean positron lifetime shows the same trend as the o‐Ps intensity. In disordered regions, the positronium trapping rate suggests that trapping of o‐Ps increases with increasing electron irradiation fluence until electron fluence reached 5.9 × 1013 electrons/cm2, after which it begins to decrease. The line shape S‐parameter was found to have similar behavior as the o‐Ps intensity, and suggests that poly(methyl methacrylate) undergoes chain scission, followed by cross‐linking, and eventually degradation, due to the electron radiation effects. The results of positron annihilation spectroscopy were verified by X‐ray results, mechanical, and electrical measurements.