P-type Wafers Research Articles

Integrating interface engineering and plasmonic effect to boost photoresponse performance of ZnO:Ga/GaN heterojunction self-powered UV photodetectors

The ability to function without an external power supply makes photodetectors highly promising for use in a new generation of wirelessly and independently operated ultraviolet (UV) photodetection and imaging systems. However, self-powered photodetectors' high dark current, inadequate light harvesting, and poor carrier separation prevent them from attaining high-efficiency UV photodetection and imaging. Herein, a high-performance heterojunction UV photodetector consisting of a single Ga-doped ZnO microwire enshrouded by Ag nanowires (AgNWs@ZnO:Ga MW), a MgO electron blocking layer, and a p-type GaN wafer was proposed. Taking full advantage of the interface engineering and plasmonic effects, the AgNWs@ZnO:Ga MW/MgO/GaN photodetector achieves high photodetection performance with an excellent responsivity of 262 mA/W, a remarkable external quantum efficiency of 92.37%, and a high detectivity of 1.966 × 1012 Jones under 370 nm illumination with power density of 0.22 mW/cm2. Furthermore, it also demonstrates ultrafast pulsed photoresponse speed with a rise/fall time of 3.64 μs/252 μs. An UV imaging system is designed based on the AgNWs@ZnO:Ga MW/MgO/GaN self-powered photodetector, allowing for high-quality, accurate, and distinct object imaging. This work combines interface engineering and plasmonic effects for achieving high-performance UV photodetection, which provides a strategic approach to the development of highly efficient optoelectronic devices.

Reducing Time and Costs of FT-IR Studies of the Effect of SiNx, Dopants, and Emitter on Hydrogen Species in Si Wafers and Solar Cell Structures

Accurately measuring the hydrogen content in silicon (Si) solar cells is essential due to its connection to surface degradation and light and elevated temperature induced degradation (LeTID). Fourier Transform-Infrared (FT-IR) spectroscopy provides a quantitative technique for determining the content of various hydrogen species in Si wafers that have undergone various process steps. In this study, we examine both the effect of a silicon nitride (SiNx:H) layer during FT-IR spectroscopic measurements on hydrogen species, as well as the impact of an emitter present during firing on the amount of hydrogen introduced into Si wafers. We find that the presence of SiNx:H during measurements has negligible effects on the measured hydrogen species, potentially simplifying the preparation steps for FT-IR. For the emitter investigation we analyze boron (B)- and gallium (Ga)-doped p-type wafers to detect H-B, H-Ga, Oi-H2, and H2. We observe that hydrogen species initially present in B- and Ga-doped Si wafers differ significantly. Only H-Ga is detected in Ga-doped wafers, while H-B, Oi-H2, and H2 signals are measured in B-doped wafers. Moreover, we cannot confirm an increased release of H through the emitter into the bulk during the firing process. Finally, we conduct measurements at different temperatures and confirm that cryogenic temperatures are more effective for detecting H-B and H2 with concentrations in the 1014 cm-3 range. Nevertheless, useful spectra can still be obtained at liquid nitrogen (N2) temperatures.

Refractive indices and extinction coefficients of p-type doped Germanium wafers for photovoltaic and thermophotovoltaic devices

Our work is primarily driven by the absence of optical parameters for p-type Ge wafers, adaptable to any specific doping value, and, at the same time, able to cover any application from infrared to ultraviolet regime. To address this, we have determined the complex refractive indices of p-type commercial Ge wafers through a wide spectral range (200–25000 nm) employing spectroscopic ellipsometry and transmittance measurements. The doping levels in these wafers vary between 1015 and 1018 cm−3, which are most commonly used in photovoltaic, thermophotovoltaic and optoelectronic applications. Our data fitting procedure resulted in a dielectric function that successfully reproduces not only the critical points associated with interband transitions above the bandgap, but also absorption features below the bandgap connected to intraband processes. Consequently, we obtained the complex refraction indices of these Ge wafers as a function of dopant concentration, and these have been corroborated through experimental reflectance and transmittance measurements. Additionally, we achieved a successful validation of these refractive indices by simulating the external quantum efficiency of Ge single-junction solar cell with two different thickness fabricated on a Ge wafer with a different doping level than those analyzed in this study.

A Detailed Theoretical Analysis of TOPCon/TOPCore Solar Cells Based on p-type Wafers and Prognosticating the Device Performance on Thinner Wafers and Different Working Temperatures

A Detailed Theoretical Analysis of TOPCon/TOPCore Solar Cells Based on p-type Wafers and Prognosticating the Device Performance on Thinner Wafers and Different Working Temperatures

Investigation of the Stability and Insulating Properties of Mineral Oil-Based Surface Modified Silicon Nanofluid

The requirement for high voltage is growing extensively, which has obligated to enhance the dielectric and thermal properties of the insulators. Nanofluids are a new insulating material class that exhibits exceptional thermal and electrical characteristics. The relative permittivity and conductivity of Si nanoparticles (nSi) of diameter 10-30 nm synthesized from the p-type wafer are ideal values for free charge trapping; hence the mixture of mineral oil and nSi has the potential to replace the standard insulating oil. During the pre-breakdown phenomena of the insulator, the nSi in the base fluid act as a charge trap, capable of capturing about 45 electrons with a significantly shorter relaxation time of 1.42 × 10-14 s relative to the streamer propagation time. Oleic acid, an oil-soluble dispersant, improved the dispersion and stability of the nanofluids. The FTIR analysis determined the type of interaction as chelating bidentate between the oleic acid and the nSi surface. The impulse breakdown voltage of the nanofluids revealed the effect of trapping the free charges generated by the molecular ionization on enhancing the impulse breakdown strength. The relative permittivity measurement of the nanofluid followed the Clausius-Mossotti polarization model of a mixed dielectric. Due to increased nanosized pores (with the number of nanoparticles), partial discharge inception voltage and the AC breakdown voltage were reduced with concentration.

Impacts of Wafer Doping Type on Structural and Optical Properties of Black Silicon Fabricated by Metal-Assisted Chemical Etching

In this work, the impacts of wafer doping type on structural and optical properties of black silicon (b-Si) fabricated by metal-assisted chemical etching (MACE) process are investigated. P-type and n-type mono-crystalline silicon (mono c-Si) wafers are etched in an aqueous solution of hydrofluoric acid (HF), silver nitrate (AgNO3) and deionised water (DI H2O) at room temperature and various durations from 5-20 minutes. Surface morphological results demonstrate the formation of b-Si nanowires (NWs) with average lengths of 0.4-0.8 μm for p-type wafers and 0.8-3.0 μm for n-type wafers. The higher length of the NWs for the n-type wafers is due to the minority charge carriers, which lead to a higher etching rate during the MACE process. Within the 300-1100 nm wavelength region, weighted average reflection (WAR) for the p-type and n-type wafers decreases to 6.6% and 6.4%, respectively, after 20 minutes of etching. The corresponding improvement in broadband light absorption results in maximum potential short-circuit current density (Jsc (max)) of 38.2 and 38.8 mA/cm2 for the p-type and n-type b-Si, respectively, which is an of enhancement of 39.9% and 42.1% when compared to the Jsc (max) of planar c-Si reference.

TCAD Analysis of Leakage Current and Breakdown Voltage in Small Pitch 3D Pixel Sensors.

Small-pitch 3D pixel sensors have been developed to equip the innermost layers of the ATLAS and CMS tracker upgrades at the High Luminosity LHC. They feature 50 × 50 and 25 × 100 μm2 geometries and are fabricated on p-type Si-Si Direct Wafer Bonded substrates of 150 μm active thickness with a single-sided process. Due to the short inter-electrode distance, charge trapping effects are strongly mitigated, making these sensors extremely radiation hard. Results from beam test measurements of 3D pixel modules irradiated at large fluences (1016neq/cm2) indeed demonstrated high efficiency at maximum bias voltages of the order of 150 V. However, the downscaled sensor structure also lends itself to high electric fields as the bias voltage is increased, meaning that premature electrical breakdown due to impact ionization is a concern. In this study, TCAD simulations incorporating advanced surface and bulk damage models are used to investigate the leakage current and breakdown behavior of these sensors. Simulations are compared with measured characteristics of 3D diodes irradiated with neutrons at fluences up to 1.5 × 1016neq/cm2. The dependence of the breakdown voltage on geometrical parameters (e.g., the n+ column radius and the gap between the n+ column tip and the highly doped p++ handle wafer) is also discussed for optimization purposes.

Assessing the stability of p+ and n+ polysilicon passivating contacts with various capping layers on p-type wafers

Polysilicon (poly-Si)-on-oxide passivating contact structures (POLO/TOPCon) enable high-efficiency solar cells as they simultaneously provide a very high level of surface passivation and a high conductance for either electrons or holes. The ease of incorporation with existing manufacturing lines and their tolerance for high-temperature processing has increased the wide acceptance of this structure in the PV industry. In this report, we explore the effects of short high-temperature annealing required for effective hydrogenation and formation of ohmic screen-printed contacts across a wide temperature range (636 °C–846 °C) on the stability of passivating contact structures. We study this on p-type c-Si substrates with phosphorus-doped (n-type) or boron-doped (p-type) polysilicon contacts capped with either an AlOx or SiNx coating. Our experimental results show that irrespective of the poly-Si doping type, AlOx-capped samples suffer a loss in surface passivation across the investigated temperature range, while SiNx-capped samples show an improvement at lower annealing temperatures. Above 744 °C, severely ruptured blisters occur for the samples coated with a SiNx layer, leading to lift-off of the poly layer in extreme cases, and in all cases, significant surface passivation losses, up to 99%. A study of the long-term stability of these fired samples under 1-sun illumination @ 140 °C shows that they suffer from both bulk and surface-like instabilities. Two degradation cycles were observed: the first, a boron-oxygen light-induced degradation (BO-LID) observed after 5 min, with capture cross-section ratios of 15.8–19.2, and a slower secondary degradation, similar to light and elevated temperature-induced degradation (LeTID), with maximum degradation reached after ∼ 14 days. The presence of a silicon nitride layer does not appear to influence the kinetics of post-degradation recovery. Our results suggest that the effect of firing may be influenced by the polarity of the bulk c-Si or perhaps the chemistry of the SiNx film and highlight that passivating contact structures based on p-type c-Si may offer better long-term stability than those based on n-type c-Si.

Patterned Ga2O3 nanowires synthesized by CVD method for High-performance self-powered ultraviolet photodetector

High-performance and energy-efficient ultraviolet photodetectors play a critical role in civilian and military fields. Here, patterned growth of highly crystalline straight Ga2O3 nanowires on p-type GaN epitaxial film wafer substrate is achieved by bottom-up technology using an economical chemical vapor deposition method. A self-powered ultraviolet photodetector based on GaN/Ga2O3 nanowires p-n junction for broadband UV detection is constructed by combining spin coating Poly(methyl methacrylate) as an insulating layer and magnetic sputtering an Au thin film as top transparent conductive electrode. This nanowires-film structure device exhibits excellent performance under zero bias voltage, including considerable responsivity of 960 mA W−1, high detectability of 3.82 × 1013 Jones, ultrahigh ultraviolet/visible inhibition ratio (R254 nm/R400 nm) of 7.92 × 103, fast rise/decay time of 4/12 ms and a high photo-to-dark current ratio greater than 104. The self-powered property under zero bias is attributed to the built-in electric field formed between the p-GaN film and the n-Ga2O3 nanowires, which creates a driving force for the rapid separation of photo-generated carriers. The high-performance mainly credits to the device's excellent UV light utilization efficiency and unique interfacial engineering of the p-n junction. This work provides a new avenue for the application of Ga2O3 nanowires in high-performance p-n junction self-powered photodetectors that can operate in harsh environments where it is inconvenient to transmit electric power.

Detailed Study on the Role of Nature and Distribution of Pinholes and Oxide Layer on the Performance of Tunnel Oxide Passivated Contact (TOPCon) Solar Cell

Industrial silicon solar cells are now mostly based on aluminum back surface field (Al-BSF) or passivated emitter rear cell (PERC) technologies on p-type crystalline silicon wafers. Recently tunnel oxide passivated contact (TOPCon) solar cell on p-type Si wafers has attracted attention due to its demonstrated higher efficiency than either Al-BSF or PERC type solar cell. Numerical analysis using 3-D Sentaurus Technology Computer Aided Design (3-D-TCAD) software leads to the enhancement of the efficiency of the p- and n-type TOPCon solar cells by optimizing the size, nature, and number density of pinholes in the oxide layer; thickness of the oxide layer with and without pinholes and B doping concentration in the hole selective p+ poly-Si layer at the rear. Effects of both types of pinholes, either completely through (physical contact) or partially through (localized thinner oxide), are studied on cell performance. Simulation results show that pinholes in tunnel oxide have an advantage in lowering of series resistance and improvement of fill factor. To achieve optimum performance, the size, nature, and number density of pinholes and thickness of the oxide layer should be optimized. Considering both types of pinholes, the efficiency achieved is 25.3% for p-TOPCon and 26% for n-TOPCon. Also, the outputs of simulated p-TOPCon are compared with simulated p-PERC solar cell. The analysis shows that TOPCon solar cell on p-type wafer has significant ability to be adopted for industrial production.

Effects of dopant type and concentration on surface recombination velocity in hydrogen-terminated silicon

Isolating the effects of the type and concentration of the dopant in lightly doped regions in the reaction between hydrogen-terminated silicon surface and atmospheric impurities in air is very difficult. However, changes in the surface recombination sites can be analyzed accurately through recombination lifetime measurements performed using the microwave photoconductive decay method. Thus, we investigated variations in the effective recombination lifetime in hydrogen-terminated silicon surfaces over time in air for different dopant types and concentrations. For both p-type and n-type silicon wafers, surface recombination velocity, S, increased with decreasing resistivity, namely, increasing dopant concentration. The time-dependent variations of the S for the p-type wafers decreased, and those for the n-type wafers increased with decreasing resistivity. Thus, it was shown that the time-dependent variation of the S depends on the type and concentration of the dopant used.

Impacts of hydrogen annealing on the carrier lifetimes in p-type 4H-SiC after thermal oxidation

Thermal oxidation and hydrogen annealing were applied on a 100 μm thick Al-doped p-type 4H-SiC epitaxial wafer to modulate the minority carrier lifetime, which was investigated by microwave photoconductive decay (μ-PCD). The minority carrier lifetime decreased after each thermal oxidation. On the contrary, with the hydrogen annealing time increasing to 3 hours, the minority carrier lifetime increased from 1.1 μs (as-grown) to 3.14 μs and then saturated after the annealing time reached 4 hours. The increase of surface roughness from 0.236 nm to 0.316 nm may also be one of the reasons for limiting the further improvement of the minority carrier lifetimes. Moreover, the whole wafer mappings of minority carrier lifetimes before and after hydrogen annealing were measured and discussed. The average minority carrier lifetime was up to 1.94 μs and non-uniformity of carrier lifetime reached 38% after 4-hour hydrogen annealing. The increasing minority carrier lifetimes could be attributed to the double mechanisms of excess carbon atoms diffusion caused by selective etching of Si atoms and passivation of deep-level defects by hydrogen atoms.

A Comparative Study on p- and n-Type Silicon Heterojunction Solar Cells by AFORS-HET.

Despite the increasing trend of n-type silicon wafer utilization in the manufacturing of high-efficiency heterojunction solar cells due to the superior advantages over p-type counterparts, its high manufacturing cost remains to be one of the most crucial factors, which impedes its market share growth with state-of-the-art silicon heterojunction (SHJ) solar cells demonstrating high conversion efficiencies from various configurations, the prospect of using an n-type wafer is debatable from a cost-efficiency point of view. Hence, a systematic comparison between p- and n-type SHJ solar cells was executed in this work using AFORS-HET numerical software. Front and rear-emitter architectures were selected for each type of wafer with ideal (without defects) and non-ideal (with defects) conditions. For ideal conditions, solar cells with p-type wafers and a front-emitter structure resulted in a maximum conversion efficiency of 28%, while n-type wafers demonstrated a maximum efficiency of 26% from the rear-emitter structure. These high-performance devices were possible due to the optimization of the bandgap and electron-affinity for all passivating and doping layers with values ranging from 1.3 to 1.7 eV and 3.9 to 4 eV, respectively. The correlation between the device structure and the type of wafers as demonstrated here will be helpful for the development of both types of solar cells with comparable performance.

Assessing the Stability of P+ and N+ Polysilicon Passivating Contacts with Various Capping Layers on P-Type Wafers

Assessing the Stability of P+ and N+ Polysilicon Passivating Contacts with Various Capping Layers on P-Type Wafers

Interaction of defects with solar irradiation for devices used ZnO/Ga2O3 heterojunctions in which Ga2O3 prepared using oxidation of the heavily doped p-type GaAs

The effect of the growth condition on the interaction of defects with solar irradiation for devices that use ZnO/Ga2O3 heterojunctions is studied. A Ga2O3 layer was grown on the heavily doped p-type GaAs wafer using a dry oxidation process. The surface of the Ga2O3 film grown with a low O2/N2 gas ratio is very flat, whereas there is a large number of cracks on the surface of the Ga2O3 film grown with a high O2/N2 gas ratio. This is because of the sensitivity of oxidation, nucleation and crystallization to an oxygen annealing ambient. Because of the strong visible-emission absorption for ZnO and Ga2O3 films, the devices that use ZnO/Ga2O3 heterojunctions exhibit the response properties to solar irradiation and photovoltaic behavior. An oxygen vacancy- (VO-), gallium vacancy- (VGa-) and VO-VGa complex-related band model is proposed to describe the transition processes for the photo-generation of carriers and the contribution to the photocurrent.

Engineering of ultra-thin sintered porous silicon virtual substrates for lattice-mismatched growth compliance and epilayer detachability

The air-sensitivity of mesoporous silicon layers etched on p-type wafers was evaluated comparing ambient-oxidized to methyl-capped samples, from which the unaltered pore/interpore sizes were obtained and linked to diffraction patterns and reflectivity data. Sintering of oxide-free nano/mesoporous bilayers produced ultra-thin porous epi-foils with full surface reconstruction at temperatures below 1000 °C. The epi-foils were in-plane tensely strained and exhibited good crystallinity and polished wafer-like surface roughness (RMSmin = 0.23 nm), emerging as potential compliant substrates for crack-free epitaxy of flat heterostructures. Furthermore, they were conveniently formed over a weakly bonded macroporous mesh that provided both structural stability and ease for detachment, establishing sintering below 1000 °C as a promising route to avoid collapsing and premature delamination of ultra-thin films.

Study of Black Silicon Wafer through Wet Chemical Etching for Parametric Optimization in Enhancing Solar Cell Performance by PC1D Numerical Simulation

Black silicon (BSi) fabrication via surface texturization of Si-wafer in recent times has become an attractive concept regarding photon trapping and improved light absorption properties for photovoltaic applications. In this study, surface texturization has been conducted on mono-crystalline Si(100) wafer using a wet chemical anisotropic etching process with IPA:KOH solution to form micro-pyramidal surface structures. Moreover, the optimized properties of the fabricated BSi wafers are used for numerical simulation using PC1D software to analyze the performance of the solar cell and establish the correlation among relevant parameters. Effects such as doping concentration, texturization, passivation, and anti-reflection coating of BSi on the solar cell performance have numerically been investigated. Results show that textured surface obtained from the wet chemical anisotropic etching process has successfully reduced the reflectance of the BSi wafer and surpassed the solar cell efficiency by 2%, which is mainly attributed to the optical confinement of the textured pyramids on the surface with a height of 1–2 μm and angles of 70 degrees. Furthermore, the doping concentration of the p-type wafer and n-type emitter were optimized to be 1 × 1016 cm−3 and 1 × 1018 cm−3, respectively. In the case of device optimization, the SiO2 passivation layer with a refractive index of 1.48 and the Si3N4 ARC layer with a refractive index of 2.015 has been identified as the best combination for the solar cell performance. These optimized parameters eventually result in 23.14% conversion efficiency from numerical simulation for solar cells that use black silicon wafers as fabricated in this study.

Study of the electrical properties of < 100 > Cz p-type solar-grade silicon wafers against the high-temperature processes

Study of the electrical properties of < 100 > Cz p-type solar-grade silicon wafers against the high-temperature processes

The Role of Metal-Catalyzed Chemical Etching Black Silicon in the Reduction of Light- and Elevated Temperature-Induced Degradation in P-Type Multicrystalline Wafers

Light- and elevated temperature-induced degradation (LeTID) of silicon wafers reduces the energy yield of photovoltaic modules in the field. A previous study demonstrated that this degradation is greatly reduced in samples with a surface textured with black silicon formed via reactive ion etching. However, the reason for this reduction is currently not understood. This article extends that result to a range of nano-textures formed using commercial metal-catalyzed chemical etching. Lifetime test structures are fabricated on multicrystalline wafers with six different chemical nano-textures and the results are compared to planar reference samples. The article demonstrates a reduction in the extent of light-induced degradation compared to planar reference samples for all six textures. The extent of LeTID is observed to reduce with decreasing front surface reflectance and increasing front surface area. The article finds that wafer thickness, phosphorus gettering, and fast-firing cannot explain the result.

Simulation-based roadmap for the integration of poly-silicon on oxide contacts into screen-printed crystalline silicon solar cells

We present a simulation-based study for identifying promising cell structures, which integrate poly-Si on oxide junctions into industrial crystalline silicon solar cells. The simulations use best-case measured input parameters to determine efficiency potentials. We also discuss the main challenges of industrially processing these structures. We find that structures based on p-type wafers in which the phosphorus diffusion is replaced by an n-type poly-Si on oxide junction (POLO) in combination with the conventional screen-printed and fired Al contacts show a high efficiency potential. The efficiency gains in comparsion to the 23.7% efficiency simulated for the PERC reference case are 1.0% for the POLO BJ (back junction) structure and 1.8% for the POLO IBC (interdigitated back contact) structure. The POLO BJ and the POLO IBC cells can be processed with lean process flows, which are built on major steps of the PERC process such as the screen-printed Al contacts and the text{Al}_text{2 }text{O}_text{3 }/text{SiN } passivation. Cell concepts with contacts using poly-Si for both polarities (text{POLO}^2-concepts) show an even higher efficiency gain potential of 1.3% for a text{POLO}^2 BJ cell and 2.2% for a text{POLO}^2 IBC cell in comparison to PERC. For these structures further research on poly-Si structuring and screen-printing on p-type poly-Si is necessary.