Spin-on Dopant Research Articles

Rapid fabrication approach for active photonic devices by employing spin-on dopants.

Modulation based on the plasma dispersion effect can be achieved by controlling free carriers in the optical region with the aid of pn junction diodes. The embedded diodes are commonly realized with ion implantation, which is only available in large facilities with significant costs and sparse schedules. A cost- and time-effective method is reported in this study to improve flexibility during the development phase. The suggested process is based on spin-on dopants and free of a hard mask for further simplification. Following the implementation of devices with this method, electrical and optical characterization results are presented.

An experimental investigation of spin-on doping optimization for enhanced electrical characteristics in silicon homojunction solar cells: Proof of concept

The pursuit of enhancing the performance of silicon-based solar cells is pivotal for the progression of solar photovoltaics as the most potential renewable energy technologies. Despite the existence of sophisticated methods like diffusion and ion implantation for doping phosphorus into p-type silicon wafers in the semiconductor industry, there is a compelling need to research spin-on doping techniques, especially in the context of tandem devices, where fabricating the bottom cell demands meticulous control over conditions. The primary challenge with existing silicon cell fabrication methods lies in their complexity, cost, and environmental concerns. Thus, this research focuses on the optimization of parameters, such as, deposition of the spin on doping layer, emitter thickness (Xj), and dopant concentration (ND) to maximize solar cell efficiency. We utilized both fabrication and simulation techniques to delve into these factors. Employing silicon wafer thickness of 625 μm, the study explored the effects of altering the count of dopant layers through the spin-on dopant (SOD) technique in the device fabrication. Interestingly, the increase of the dopant layers from 1 to 4 enhances efficiency, whereby, further addition of 6 and 8 layers worsens both series and shunt resistances, affecting the solar cell performance. The peak efficiency of 11.75 % achieved in fabrication of 4 layers dopant. By using device simulation with wxAMPS to perform a combinatorial analysis of Xj and ND, we further identified the optimal conditions for an emitter to achieve peak performance. Altering Xj between 0.05 μm and 10 μm and adjusting ND from 1e+15 cm−3 to 9e+15 cm−3, we found that maximum efficiency of 14.18 % was attained for Xj = 1 μm and ND = 9e+15 cm−3. This research addresses a crucial knowledge gap, providing insights for creating more efficient, cost-effective, and flexible silicon solar cells, thereby enhancing their viability as a sustainable energy source.

Investigation of Phosphorus Spin on Dopant on SOI Wafer

Silicon on insulator (SOI) wafer has allowed the integrated circuit (IC) industry to create superior, high-performance solutions. In addition, doping techniques are vital in the silicon sector due to the need to regulate the material electrical properties. The spin on dopant (SOD) approach is an alternative method that involves spinning a solution containing dopant onto SOI wafers. This research aims to determine the impact of thermal diffusion temperature and soaking time on sheet resistance of doped SOI wafer using SOD approach. Additionally, the homogeneity of doping was studied by utilizing mapping techniques. Three inches boron-doped SOI wafers were cut and cleaned according to Radio Corporation of America (RCA) standards. N-type dopants of Filmtronics SOD P509 were deposited on SOI wafer by using a spin coater, for 40 seconds at 4,000 revolutions per minute (rpm). The thermal diffusion temperature and soaking time were set between 700°C to 1000°C for 30 to 120 minutes. After thermal diffusion, hydrofluoric acids (HF) were diluted and used to etch samples. All materials were evaluated using a four-point probe, Hall Effect and Atomic Force Microscope (AFM). The results show that when the thermal diffusion soaking time increases, sheet resistance decreases until activated dopants are saturated. When sheet resistance decreases, dopant concentration rises. Temperature and soaking time increase carrier density and surface roughness, while decreasing Hall mobility. From mapping techniques, it shows low non-uniformity value which less than 10% suggests good thermal diffusion control.

Investigation of phosphorus-doping of MgZnO thin films using efficient spin-on dopant process

Phosphorus doped MgZnO thin films were prepared using the RF sputtering technique on a Si wafer, followed by spin-on doping (SOD) and annealing. The SOD is a cheap and non-destructive process in which the dopant film is spun on a Si wafer and placed in the vicinity of deposited undoped MgZnO thin film at a high temperature to perform doping. After doping, the MgZnO thin films were annealed at temperatures such as 700, 800, and 900 °C, which significantly improved morphological, structural, and optical properties. The atomic force microscopy and scanning electron microscopy measurements revealed that phosphorus-doped MgZnO thin films annealed at 800–900 °C have good morphology and large grains. X-ray diffraction spectra demonstrated the (002) orientation of MgZnO thin films. The photoluminescence spectra measured at 20 K demonstrated the acceptor bound exciton peak at 3.47 eV and acceptor binding energy of around 64.34 meV, indicating the formation of shallow acceptor levels by phosphorus doping of MgZnO thin films using the SOD process. In Raman spectroscopy measurement, the peak of E2high phonons mode of MgZnO wurtzite structure was observed around 436 cm−1. The FWHM value of this peak reduces with augmentation annealing temperature, demonstrating improvement in crystallinity. X-ray photoelectron spectroscopy measurement demonstrated the presence of phosphorus atoms in the SOD processed MgZnO thin films, which is again verified by Fourier-transform infrared spectroscopy measurement showing vibration modes of P–O bonds. It was observed that the different properties of SOD-prepared phosphorus-doped MgZnO films were superior to the film prepared using the alternate costly and destructive ion-implantation technique. These findings have revealed that high-quality phosphorus-doped p-type MgZnO thin films by the SOD process are very suitable for UV optoelectronic device applications.

Ex-situ phosphorus-doped polycrystalline silicon passivating contacts for high-efficiency solar cells by physical vapour deposition

We present ex-situ phosphorus-doped polycrystalline silicon (poly-Si) passivating contacts fabricated by the physical vapour deposition method, specifically sputtering. This technique is currently of great interest to the photovoltaics (PV) community due to its low deposition temperature, small footprint, high throughput, and use of low-hazard, solid targets and gases. We optimise the performance of the passivating contacts by adjusting various parameters from the sputtering of amorphous Si films to the formation of the poly-Si layers by a high-temperature thermal diffusion (with phosphorus oxychloride – POCl3, or phosphorus spin-on glass as the dopant sources). For the case of POCl3 diffusion, a high iVoc of ∼720 mV together with a low J0 of 2.6 fA/cm2 after a hydrogenation treatment by atomic layer deposition (ALD) AlOx and forming gas annealing (FGA), and a low contact resistivity ρc of less than 10 mΩ cm2 were achieved. Meanwhile, with spin-on doping, a low average iVoc of ∼600 mV was observed. This variation in performance could be explained by the difference in the crystallinity and the diffusion mechanism of the sputtered Si films after different subsequent thermal diffusion processes. Quokka3 simulations show that cell efficiencies as high as 25% are possible using the optimised passivating contacts. The results demonstrate the potential of these PVD poly-Si films as a promising candidate for future industrial solar cells.

Boron‐doped polysilicon using spin‐on doping for high‐efficiency both‐side passivating contact silicon solar cells

AbstractThis study focuses on boron‐doped p+polysilicon (poly‐Si) passivating contacts using spin‐on doping (SOD). Experimental conditions, including annealing conditions, SOD concentration, and poly‐Si thickness, were controlled to improve passivation. Based on the analysis results, the passivation quality mainly changes with indiffusion and doping concentration, causing Auger recombination and field effects. Meanwhile, grain size also influences the passivation quality but showed marginal characteristics. Through further optimization using an etch back and diffusion barrier, the efficiency of the flat reference solar cell was improved to 17.5% with an open‐circuit voltage of 695 mV using a p+ poly‐Si contact emitter, the highest reported efficiency using SOD on saw‐damage‐etched surfaces. This study includes a detailed analysis of SOD p+ poly‐Si and shows promising results with potential for application in tandem devices. Furthermore, the cell efficiency is expected to increase by controlling the doping profile and application of textured surfaces, selective emitters, and forming gas annealing (FGA).

Unfolding the conductivity reversal n- to p-type in phosphorus-doped ZnO thin films by spin-on dopant (SOD) process

Phosphorus doping induced p-type doping in ZnO thin films based on spin-on dopant (SOD) process is reported in this article. Owing to the reduced dependence on the conventional amenities for diffusion/ion-implantation doping, the SOD process provides a simple and cheap doping method. The effect of SOD process temperature on conductivity ZnO thin films is investigated by altering the temperature from 700°C to 1000°C. Systematic field emission scanning electron microscopy analysis demonstrates the impact of doping temperature on the morphological properties of SOD. The x-ray diffraction measurements reveal that the p-type ZnO thin films had (002) preferred crystal orientation. At the same time, x-ray photoelectron spectroscopy validated the formation of the PZn–2VZn complex, which was responsible for the acceptor behaviour of films. Moreover, the photoluminescence spectra tracked down that the origin of 3.35 and 3.31 eV emission peaks is due to the acceptor bound exciton and free-electron to acceptor level transitions, respectively. Finally, an elevated hole concentration of 2.09 × 1016 cm−3 is achieved with a resistivity of 1.14 Ω-cm at 800°C doping temperature. However, the film doped at 900°C and 1000°C showed n-type behaviour due to the generation of high concentration donor defects. Here, we successfully demonstrate that the SOD process has great potential to produce high-quality p-type ZnO thin films suitable for optoelectronic devices applications.

Process Considerations for selective doping of poly-Si thin films with spin-on dopants and nickel silicide formation for planar thermoelectric devices

The formation of highly doped p-type (boron-doped) and n-type (phosphorus-doped) poly-Si thin films with spin-on dopants on the same wafer poses unique challenges. This work evaluates the pros and cons of different approaches to dopant diffusion, residue removal, and diffusion mask selection when working with spin-on dopants. The experiments have been carried out to optimize the formation of highly doped poly-Si thin films that will form the active layers of a micro-thermoelectric generator (μ-TEG). Building upon previous work on residue removal methods, we report that the residue formation is also dependent on the oxide-silicon surface with a PECVD oxide-Si interface not requiring a post-dopant diffusion nitric acid treatment to achieve a hydrophobic surface. Furthermore, comparing the direct dispense and proximity diffusion methods verifies the existing reports of enhanced diffusion in the latter case. Besides, we observe that doping first with Boron is more conducive than doping first with phosphorus to reduce sheet resistance. We also optimize the contact formation with Ti/Ni thin films and report the mean contact resistivity. Notably, contact annealing precludes the nitric acid treatment requirement even if the surface is hydrophilic after removing dopant residue. Additionally, the sequence of silicidation is observed to be dependent on the doping of the underlying areas.

Formation of emitter by boron spin-on doping from SiO2 nanosphere and properties of the related n-PERT solar cells

In this paper, spin-on doping (SOD) process using commercial boron dopant source was applied to form front p-type emitter on n-type mono-crystalline CZ substrate. Results showed that the thickness of boron rich layer (BRL) decreased from 180 nm to 20 nm with SiO2 nanosphere assisted SOD and the BRL can be removed entirely by further in-situ oxidation. Furthermore, the hole concentration of the emitter reduced from 5.5 × 1019 cm3 to 2.8 × 1019 cm3 by integrating these two processes. In a symmetric sample without BRL, a very low emitter saturation current density of 32 fA/cm2 with implied-Voc over 700 mV was obtained. The minority carrier lifetime got improved more than 30% after diffusion. Finally, n-PERT solar cell with a conversion efficiency of 20.26% was achieved using optimized boron emitter, showing an enhanced conversion efficiency of 0.54%.

Enhanced performance of solar cell with n+ emitter by SiO2 nanospheres assisted liquid phosphorus diffusion

In order to improve the quality of n+ emitter fabricated by phosphorus doping, SiO2 nanospheres were added into a phosphoric acid solution for spin-on doping. Through a complete analysis of the trade-off between the diffusion uniformity and sheet resistance, the particle size of SiO2 nanospheres is selected to be 230 nm. It is found that with the increase of phosphoric acid concentration from 50% to 85%, the average sheet resistance decreases from 128.5 Ω/sq to 18.1 Ω/sq, and the diffusion uniformity increased from 95.2% to 98.5%. In a large concentration range, the surface doping concentration of the emitter will increase with phosphoric acid, but when the concentration of phosphoric acid reaches 80%, the surface doping concentration will be almost unchanged. Nevertheless, different from above, the p-n junction depth has little dependence on the phosphoric acid concentration. Moreover, the efficiencies in the solar cell center and edge are enhanced by 40.54% and 88.08% respectively using SiO2 nanospheres assisted diffusion.

Phosphorus-doped polycrystalline silicon passivating contacts via spin-on doping

Polycrystalline silicon (poly-Si) passivating contacts are promising technologies to promote the efficiency of silicon solar cells, due to their low carrier recombination and low contact resistivity. In this work, we present phosphorus spin-on doping as an alternative doping method to fabricate high performance poly-Si passivating contacts. The influences of thermal treatments and intrinsic amorphous Si thickness on poly-Si passivating contact quality were investigated. A high implied open-circuit voltage of above 730 mV together with a low contact resistivity below 4 mΩ⋅cm2 were obtained for 100 – 230 nm thick poly-Si layers after a thermal treatment at 975 °C for 60 min followed by a forming gas annealing. The promising results presented in this work imply that phosphorus spin-on doping can be an effective doping method alternative to conventional POCl3 diffusion.

Investigation of Spin-on Dopants and Curing Temperature Effect on Dopant Activation

Spin-on dopant technique has been investigated in the paper. The boron and phosphorus were used as p- and n-type dopant sources and were deposited on silicon substrates, followed by the baking process to evaporate the solvents from spin-on dopant layers. The standard drive-in process was applied to diffuse and activate the dopants. The curing temperature varied from 150 to 200 oC to investigate the temperature effect on dopant activation. It is suggested that for our selected spin-on dopant sources, the curing temperature and time of 175 oC and 60 minutes would lead to the best result of dopant activation during drive-in process, evidenced by the lowest sheet resistance, which was measured using four-point probe measurement method. 

Spin-on boron diffusion for n-type silicon wafers using borate esters of D-mannitol

P-emitter formation has been an urgent issue in the fabrication of n-type silicon solar cells. The widely used BBr3 diffusion process has advantages in cost and output but has disadvantages in safety and efficiency. In this work, we report on a new boron ester dopant, which was prepared by the complexation reaction between boron acid and D-mannitol. The boron ester was dissolved in a mixed solution of 1-Methoxy-2-propanol and H2O to be compatible with the spin-on doping process. The mannitol helped to form a continuous B–O–C network, which improved the concentration and homogeneity of the boron dopants in the boron coatings. The composition of the boron source and the diffusion parameters, such as ambiance, period and temperature, were systematically varied to investigate the behaviour during spin-coating and diffusion. By relating these factors to the surface condition of the wafers and the resulting sheet resistance, it was found that the concentration and ratio of the mannitol/boron acid played a key role in the performance. The formed p-emitters could achieve a sheet resistance below 100 Ω/□ with the RSD (Relative Standard Deviation) remaining below 5% under the diffusion condition.

Spin-on doping of phosphorus on Ge with a 9 nm amorphous Si capping layer to achieve n+/p shallow junctions through rapid thermal annealing

In this paper, the Ge surface deterioration after spin-on doping (SOD) of phosphorus (P), (which suffers from moisture etch at high temperature) was effectively alleviated with a 9 nm amorphous Si (a-Si) capping layer (CL). The 9 nm a-Si CL, which will be oxidized and diffused into Ge, can effectively isolate the Ge surface from water vapour leading to insensitivity of the SOD process to the ambient humidity. Due to introduction of Si atoms, the diffusivity of P was greatly retarded. After a drive-in process by rapid thermal annealing (RTA) at 800°C for 1 min, a Ge-rich GeSi n+/p shallow junctions were obtained with a junction depth of 40 nm. A rectification ratio of ~105 was achieved with an electrical activation energy of 0.64 eV for the n+/p diode. These good performances suggest that this technique has great potential for n-type doping in Ge.

Driving-in effect and gettering degradation induced by laser doping using borosilicate glass as dopant source

In the present work, driving-in effect with a low surface doping concentration and a deep junction after laser irradiation is illustrated by using borosilicate glass formed in the boron spin-on dopant diffusion process as dopant source. PC1D simulation results based on the experimental boron doping profiles demonstrate that the doping modification realized by laser irradiation can achieving an efficiency improvement of 0.13% at most. Meanwhile, no amorphous silicon and rare holes are observed after laser irradiation, indicating a relative low laser damage. Root mean square roughness is introduced to characterize the laser damage, whose variation trend with the laser frequency is opposite to that of effective minority carrier lifetime. Besides, unique gettering degradation effect by taking iron concentration as standard is observed, which is attributed to the re-dissolution and re-segregation process during laser irradiation. The present work will be helpful to deepen the understanding of laser boron doping as well as reduce the laser damage and relative high boron concentration induced by laser doping.

Photovoltaic and Physical Characteristics of Screen-Printed Monocrystalline Silicon Solar Cells with Laser Doping and Electroplated Copper

Photovoltaic and physical characteristics of screen-printed monocrystalline silicon solar cells (SPMSCs) were presented with electroplated copper (EPC) as the rear contact. The boron back surface field (B-BSF) formed by spin-on doping and laser doping (LD) was prepared as a seed layer for the EPC. The LD parameters, including the laser focus, laser power, laser speed, and laser line pitch, were investigated. Moreover, the effects of KOH etching on the surface properties after the LD process were explored. Furthermore, to enhance the adhesion between the B-BSF seed layer and EPC contact layer, a laser pinhole process was proposed. Finally, the EPC processes with various electroplating times were addressed. The results revealed that the mechanism of enhancements could be attributed to a continuous B-BSF seed layer and a reduction of series resistance, as well as an increase of open-circuit voltage and adhesion between the B-BSF seed layer and EPC contact layer.

Synthesis of Phosphorus Solution for n+ Si Selective Emitter Solar Cell by Spin on Doping

A strong requirement in manufacturing of high-efficiency solar cells is its cost reduction. One approach of aim is to merge several steps of n+ Si selective emitter processing into one step without degrading the performance of solar cells. By varying the doping level in the selective area, intrinsic fields can be built into solar cells with potential benefits long recognized. In this paper, the spin-on doping (SOD) method was used for the purpose of important tasks, different phosphorus diffusion to form n+ Si selective area consisting of the lightly and heavily doping emitter areas with 35 Ω/sheet and 121 Ω/sheet. The main solution containing different concentrations of phosphorus doped-SOD source was synthesized in this work. The sheet-resistance dependence of n-Si emitter layers on the concentration of phosphorus acid in the SOD solution was studied in term of the volume ration of TEOS: H3PO4, as well as the thermal diffusion temperature. The suitable condition for forming n+ Si selective emitters in one process step is 1000°C diffusion temperature for 30 minutes with the complementary SOD volume ratio of 4:1 and 2:1. SOD solution can be patterned by a screen printing or an inkjet printing.

Phosphorus Doping of Si Nanosheets by Spin-on Dopant Proximity

Low-dimensional silicon (Si) nanostructures have been attracting a significant attention for various applications including electrical, optical, energy devices, and bio-chemical sensors. Two-dimensional Si nanostructures, i.e., Si nanosheets (SiNSs), are promising owing to their extremely large surface area, mechanical flexibility, and band gap modulation. In order to exploit the potentials of SiNSs, the doping of these nanostructures is crucial; however, this has not been yet extensively investigated. In this paper, we report an n-type phosphorus doping of SiNSs using a spin-on dopant proximity technique that was employed to deposit a thin film of phosphosilicate glass by evaporation. Structural and X-ray measurements results reveal that the phosphorus atoms are substitutionally doped and that the crystallinity and structure of the SiNSs are preserved after the doping. Electrical measurements show that the SiNSs are heavily n-type doped. The doping level can be modulated by adjusting the annealing temperature.

Characterization and modeling of thermally-induced doping contaminants in high-purity germanium

High purity germanium (HPGe) is the key material for gamma ray detectors production. Its high purity level (⩽2 · 10−4 ppb of doping impurity) has to be preserved in the bulk during the processes needed to form the detector junctions. With the goal of improving the device performance and expanding the application fields, in this paper many alternative doping processes are evaluated, in order to verify their effect on the purity of the material. In more detail, we investigated the electrical activation of contaminating doping defects or impurities inside the bulk HPGe, induced by both conventional and non-conventional surface doping processes, such as boron ion implantation, phosphorus and gallium diffusion from spin-on doping sources, antimony equilibrium diffusion from a remote sputtered source and laser thermal annealing (LTA) of sputtered antimony. Doping defects, thermally-activated during high temperature annealing, were characterized through electrical measurements. A phenomenological model describing the contamination process was developed and used to analyze the diffusion parameters and possible process thermal windows. It resulted that out-of-equilibrium doping processes confined to the HPGe surface have higher possibilities to be successfully employed for the formation of thin contacts, maintaining the pristine purity of the bulk material. Among them, LTA turned out to be the most promising.

Avoidance of boron rich layer formation in the industrial boron spin-on dopant diffused n-type silicon solar cell without additional oxidation process

In the present work, the properties of boron rich layer (BRL) formed in the boron spin-on dopant diffusion as well as the avoidance of BRL formation without additional oxidation process are studied. The boron concentration distributions characterized by SIMS exhibit the formation and avoidance of BRL with the variation of oxygen content in the boron diffusion process. The existence of BRL can degrade the minority carrier lifetime due to the enhancement of recombination as well as weaken the anti-reflection effect due to the unmatched refractive index of BRL and SiO2/SiNx stack layers. The decreased minority carrier lifetime together with the increased surface reflectance eventually deteriorates the electrical behavior of solar cell with a maximum power conversion efficiency loss of 0.55%. Significantly, the formation of BRL is found to be avoided due to the complete oxidation of excess elemental boron atoms when the oxygen content increases to 10%, contributing to the recovery of solar cells’ electrical performance with an average efficiency of 19.47%. The present work will be helpful to deepen the understanding of BRL and simplify the boron diffusion process for massive cell production.