Spin-on Dopant Research Articles

Large-Area Planar Wavelength-Extended InGaAs p-i-n Photodiodes Using Rapid Thermal Diffusion With Spin-On Dopant Technique

In this letter, we report the large-area planar-type 2.2- $\mu \text{m}$ wavelength-extended InAsP/InGaAs/InAsP p-i-n photodetectors (PDs) using the rapid thermal diffusion (RTD) technique. The zinc-phosphorous-dopant-coating was used as the spin-on dopant source, which was driven into the InAsP/InGaAs heterostructure to form the p-type cap layer of p-i-n diode through the RTD process. The Si/Al2O3 bilayers were deposited as the antireflective coating to improve the responsivity of vertically illuminated the PDs. The 800- $\mu \text{m}$ -diameter PD exhibits a low dark current of $4.1\,\times \,10^{\mathrm {\mathbf {-8}}}$ A ( $8.2\,\times \,10^{\mathrm {\mathbf {-6}}}$ A/cm $^{\mathrm {\mathbf {2}}}$ ) at −10 mV, a cutoff wavelength of 2.2 $\mu \text{m}$ , a quantum efficiency of above 90% in the wavelength range of 1.4–2.0 $\mu \text{m}$ , and a high responsivity of 1.45 A/W at 2- $\mu \text{m}$ wavelength at room temperature. In addition, the PD exhibits good uniformity in the light received area in the illuminated power range of 0.1–2.0 mW.

Spin-on doping of germanium-on-insulator wafers for monolithic light sources on silicon

High electron doping of germanium (Ge) is considered to be an important process to convert Ge into an optical gain material and realize a monolithic light source integrated on a silicon chip. Spin-on doping is a method that offers the potential to achieve high doping concentrations without affecting crystalline qualities over other methods such as ion implantation and in-situ doping during material growth. However, a standard spin-on doping recipe satisfying these requirements is not yet available. In this paper we examine spin-on doping of Ge-on-insulator (GOI) wafers. Several issues were identified during the spin-on doping process and specifically the adhesion between Ge and the oxide, surface oxidation during activation, and the stress created in the layers due to annealing. In order to mitigate these problems, Ge disks were first patterned by dry etching followed by spin-on doping. Even by using this method to reduce the stress, local peeling of Ge could still be identified by optical microscope imaging. Nevertheless, most of the Ge disks remained after the removal of the glass. According to the Raman data, we could not identify broadening of the lineshape which shows a good crystalline quality, while the stress is slightly relaxed. We also determined the linear increase of the photoluminescence intensity by increasing the optical pumping power for the doped sample, which implies a direct population and recombination at the gamma valley.

C-Si solar cells formed from spin-on phosphoric acid and boric acid

This paper reports the fabrication of c-Si based solar cells using spin-on dopants. Solar cells were developed by texturing both surfaces of the c-Si, and forming the p–n junction by spin-coating the n-type dopant followed by rapid thermal processing (RTP). For back surface field formation on the rear side, a similar spin-coating step was undertaken for one cell and e-beam Al deposition for the other. In the case of double-sided spin-coated cell, simultaneous p–n junction and back surface field were formed in one RTP cycle. Without using high performance features in the device, double-sided spin-on doped cell showed Voc of 600 ± 0.01 mV, Jsc of 33.1 ± 0.03 mA/cm2, FF of 74.26 ± 0.06% and efficiency of 14.74%. As compared to single-sided spin-on doped cell, an improvement in efficiency of about 1.3% has been obtained which can be attributed to boron back surface field. Double-sided spin-on process significantly reduces thermal budget and improves throughput. Besides texturization, high efficiency features have not been used in the device. The results clearly demonstrate that c-Si based solar cells are potentially cost effective to manufacture.

Analysis of thin bifacial silicon solar cells with locally diffused and selective back surface field

The aim of this work is to present the development and comparison of thin n+pp+ industrial bifacial silicon solar cells produced with the local screen-printed Al back surface field (BSF) to those with the selective BSF doped with aluminum-boron. To produce solar cells with selective BSF, the boron diffusion based on spin-on dopant was introduced in the process sequence. The thin SiO2 layer (10 nm) thermally grown did not produce good passivation on the rear face and wafers were contaminated during aluminum diffusion in the belt furnace. The implementation of selectively doped BSF improved the efficiency by reflecting minority charge carriers and the wafer contamination by belt furnace was compensated by boron diffusion. The bifacial solar cells with B-Al selective BSF achieved an efficiency of 13.7% / 8.9% (front / rear illumination) and presented lower sensitivity to the belt furnace processing and to the quality of the rear surface passivation.

Spin-on-doping for output power improvement of silicon nanowire array based thermoelectric power generators

The output power of a silicon nanowire array (NWA)-bulk thermoelectric power generator (TEG) with Cu contacts is improved by spin-on-doping (SOD). The Si NWAs used in this work are fabricated via metal assisted chemical etching (MACE) of 0.01–0.02 Ω cm resistivity n- and p-type bulk, converting ∼4% of the bulk thickness into NWs. The MACE process is adapted to ensure crystalline NWs. Current-voltage and Seebeck voltage-temperature measurements show that while SOD mainly influences the contact resistance in bulk, it influences both contact resistance and power factor in NWA-bulk based TEGs. According to our experiments, using Si NWAs in combination with SOD increases the output power by an order of 3 under the same heating power due to an increased power factor, decreased thermal conductivity of the NWA and reduced Si-Cu contact resistance.

Two-Sided Silicon Nanowire Array/Bulk Thermoelectric Power Generator

To improve the output power of n-and p-type Si nanowire array (NWA)/bulk thermoelectric power generators (TEGs) fabricated using metal assisted chemical etching, post-nanowire-etch spin-on-doping (SOD), and arrays on both sides of the bulk are used. Post-process SOD increases the power factor and removes surface depletion/inversion effects while maintaining crystalline NWs. A maximum output power of 3.5 μW for a p-NWA/bulk/NWA TEG with NWA length of 23 and 24 μm is obtained for an external temperature difference of 37 °C and a TEG area of 25 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

Characterization of Deep Junction Fabricated by Laser Doping Using Internal Quantum Efficiency

Internal quantum efficiency of cells after laser assisted processes has been studied in this work. A 1070nm CW laser beam was used for doping a p-type substrate from a predeposited spin-on dopant source. External and internal quantum efficiencies were measured. The IQE of the cell suggests formation of deep junction after laser doping. To study this, PC1D simulation has been done for different junction depth and similar shape of IQE curve is obtained when junction depth is more than 2μm. Laser assisted drive-in was then performed on finished solar cell. The laser beam scan speed was varied and its effect on IQE was measured. The IQE suggests a small variation of junction depth with scan speed however surface quality is expected to be different. From the comparison of PC1D simulation and experimental data, a junction depth of 9μm is obtained for uniform doping profile of the emitter.

A low temperature process for phosphorous doped ZnO nanorods via a combination of hydrothermal and spin-on dopant methods

We demonstrate the fabrication of solution based low temperature-processed p-type ZnO NRs doped with phosphorous by using a spin-on-dopant method coupled with a hydrothermal process. We confirmed the incorporation of phosphorous dopants into a ZnO crystal by analyzing SIMS profiles, together with the evolution of the photoluminescence spectra. It is further revealed that the electrical properties of the p-type ZnO/n-type Si heterojunction diode exhibited good rectifying behavior, confirming that p-type ZnO NRs were successfully formed. In addition, we demonstrate that a piezoelectric nanogenerator with p-type ZnO NRs made on a glass substrate shows large enough power to drive polymer dispersed liquid crystal displays.

Analysis of PV Modules and N-type Silicon Solar Cells with Different Rear Metal Grid

N-type silicon solar cells are being investigated due to the potential to obtain high efficiency. In this solar cell, the front p+ emitter is performed with boron doping and the Al or Al/Ag screen printing pastes don’t reach the development of Ag pastes used to form the front contact in n+pp+ solar cells. Moreover, the rear area covered by metal grid on the phosphorus back surface field may be optimized to increase the silicon solar cell efficiency and reduce the cost production. The goal of this paper is to present the analysis of PV modules and silicon solar cells developed on phosphorus-doped Czochralski wafers with different metal grid on the rear face. The solar cells were processed by using spin-on dopant to obtain the boron emitter and the back surface field was formed by phosphorus diffusion. The front metal grid was formed with Al/Ag paste and the rear area covered by the Ag metal paste was varied from 9% to 53%. Solar cells were manufactured, characterized and sorted taking into account the short-circuit current. Eight PV modules were fabricated using a standard process. Solar cells presented low fill factor. When the Ag/Sn/Cu ribbon was soldered on the front busbars of a solar cell, the fill factor rose from 0.70 to 0.75, causing an increase of 13.2% to 15.0% in the efficiency. Therefore, the fill factor of the PV modules was higher than that of solar cells. The reduction of the metal grid area on the rear face of solar cells did not affect the fill factor and solar cells with low rear metal coverage presented higher short-circuit current. The infrared thermography analysis was performed under a cloudless sky day with modules in the short-circuit condition. All modules presented hot spots and this result was not related to the different metallized rear area. The temperature difference between the solar cells of each photovoltaic module varied from 9°C to 18°C.

Fabrication of c-Si solar cells using boric acid as a spin-on dopant for back surface field

Cost effective solar cells are paramount for solar power to compete with traditional power generation. Here we present results on two low cost, both side textured c-Si solar cells. One solar cell had an Al back surface field (BSF), while the other had boron BSF fabricated by using spin-on boric acid as a p-type dopant. As compared to the Al-BSF solar cell, an improvement in efficiency of 1.7% was observed for a solar cell with boron BSF. Since boron BSF is stronger than Al-BSF, an improvement in efficiency can be attributed to an increase in long wavelength response, collection efficiency and reduced back surface recombination. The boron BSF solar cell showed an efficiency of 12.9% with Voc of 0.56 V, Jsc of 32.2 mA cm−2 and FF of 0.72. These parameters are expected to significantly increase further with the addition of layers such as anti-reflection/passivation layers at the front side, and back surface passivation with local back surface field, etc.

Spin-On Organic Polymer Dopants for Silicon

We introduce a new class of spin-on dopants composed of organic, dopant-containing polymers. These new dopants offer a hybrid between conventional inorganic spin-on dopants and a recently developed organic monolayer doping technique that affords unprecedented control and uniformity of doping profiles. We demonstrate the ability of polymer film doping to achieve both p-type and n-type silicon by using boron- and phosphorus-containing polymer films. Different doping mechanisms are observed for boron and phosphorus doping, which could be related to the specific chemistries of the polymers. Thus, there is an opportunity to further control doping in the future by tuning the polymer chemistry.

Field-induced superfluids and Bose liquids in projected entangled pair states

In two-dimensional incompressible quantum spin liquids, a large enough magnetic field generically induces "doping" of polarized S=1 triplons or S=1/2 spinons. We review a number of cases such as spin-3/2 AKLT or spin-1/2 Resonating Valence Bond (RVB) liquids where the Projected Entangled Pair States (PEPS) framework provides very simple and comprehensive pictures. On the bipartite honeycomb lattice, simple PEPS can describe Bose condensed triplons (AKLT) or spinons (RVB) superfluids with transverse staggered (N\'eel) magnetic order. On the Kagome lattice, doping the RVB state with deconfined spinons or triplons (i.e. spinon bound pairs) yields uncondensed Bose liquids preserving U(1) spin-rotation symmetry. We find that spinon (triplon) doping destroys (preserves) the topological Z_2 symmetry of the underlying RVB state. We also find that spinon doping induces longer range interactions in the entanglement Hamiltonian, suggesting the emergence of (additive) log-corrections to the entanglement entropy.

A novel technique for degenerate p-type doping of germanium

Spin-on dopants offer an expedient, straight forward, and low cost method for doping semiconductors. These sol–gel dopant films contain sufficient impurity content to obtain surface concentrations well above the solubility limit of most semiconductors (e.g., Si, Ge). While much has been published about spin-on dopants for degenerate doping of Si, there is to the authors’ knowledge no report in the literature of such films being used to achieve degenerate p-type doping of Ge, as there are a number of technical challenges associated with this technique. In this work, we present a novel technique for degenerate p-type doping of Ge using Ga spin-on dopant films in a regular horizontal tube furnace. This technique gives both excellent uniformity, higher doping concentrations and better potential for ultra-shallow junctions than diffusion from solid sources, is much preferred to rapid melt/alloyed junctions (especially for optoelectronic applications), and is readily applicable to rapid thermal processing. In this preliminary investigation, we report doping concentrations exceeding 1020cm-3 which are shown to be fully electrically activated. We report on the use of a traditional “pre-dep”/“drive-in” approach, which could be used to give shallow dopant profiles, or tailored dopant concentrations, for a wide variety of electronic and optoelectronic applications, and to form back surface fields in photovoltaic and thermo-photovoltaic devices. Values of 3.4±0.2eV and 3.2±0.4eV are extracted for the activation enthalpies of the diffusion processes into p-type 〈100〉 and n-type 〈211〉 Ge substrates, respectively, which are shown to be in good agreement with previously published data [1,2]. We conclude that Ga is a more suitable dopant for reliable, low-cost, degenerate p-type doping of Ge, rather than B (also investigated in this work), which is known to be problematic.

Fabrication of Simple GaAs Solar Cell by Zn Diffusion Method

We reported the spin-on Zincsilicafilm dopant content of the diffusion process and the formation of the p+ layer were applied to fabricate GaAs solar cells and their characteristics were investigated. The p-n junction was formed by a thermal furnace from the diffusion of zinc into the GaAs substrate. It was found that the GaAs substrate must be covered by a 100-nm-thick SiO2 layer. This reduced the damage to the GaAs substrate surface morphology that occurred during high temperature treatment and made the cleaning of the residual solvate on the surface easier

Nanostructured plasmonics silicon solar cells

We report a plasmonics silicon solar cell design, with the possibility of lower cost and higher efficiency. The proposed solar cell consists of a radial p–n junction silicon nanopillar arrays in combination with metallic nanoparticles resolved at the top of the nanopillars. Relatively simple processing methods such as metal assisted electroless chemical etching and spin-on doping techniques are used for the fabrication of the described devices. Prior to the metallic nanoparticle incorporation, the power conversion efficiency of the solar cell with nanopillar arrays with a height of 800 nm was measured to be 10.7%. Subsequently, the optical and electrical performance of the aforementioned topography was studied as a function of nanopillar height. The observations indicate that the electrical performance of the produced devices degrades with increases in nanopillar height beyond 800 nm, however, the optical performance measurements did exhibit the opposite trend. Upon the incorporation of metallic nanoparticles to the previously fabricated nanopillar arrays, the power conversation efficiency of the combined structure was observed to decrease to 7.31%. This can be attributed due to a reduced open circuit voltage in spite of having a higher fill factor.

Efficiency Improvement of Silicon Nanowire Arrays (NWAs) Thermoelectric Power Generation (TEG) by Spin On Doping (SOD)

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Surface Passivation of Point-Contacted Solar Cells by Inkjet Printing

The oxide passivation of the localized contacts for p-n junction solar cells by inkjet printing is studied by combining the useful of spin-on-doping (SOD) concept for producing n-Si emitter layer. The phosphorus SOD is a precursor for a dopant source as phosphosilicate glass (PSG). The sheet resistance of the n-emitter layer was obtained in the range of 900–20 Ω/square by increasing the diffusion temperature from 800°C to 1000°C. In addition, an inkjet printing method for patterning a SiO2 dielectric on n-Si emitter layer was demonstrated. With using typical printer, the groove and circular patterns of openings were achieved by the modified printer dropping acetone solution as a resist solvent. The SiO2 layer underneath the resist polymer layer was etching in the region of the groove or circular openings for forming the patterns of SiO2 openings. The formed openings in the thin SiO2 can be produced as point contacts for reducing carrier recombination process of silicon solar cell.

Fabrication and characterization of silicon wire solar cells having ZnO nanorod antireflection coating on Al-doped ZnO seed layer

In this study, we have fabricated and characterized the silicon [Si] wire solar cells with conformal ZnO nanorod antireflection coating [ARC] grown on a Al-doped ZnO [AZO] seed layer. Vertically aligned Si wire arrays were fabricated by electrochemical etching and, the p-n junction was prepared by spin-on dopant diffusion method. Hydrothermal growth of the ZnO nanorods was followed by AZO film deposition on high aspect ratio Si microwire arrays by atomic layer deposition [ALD]. The introduction of an ALD-deposited AZO film on Si wire arrays not only helps to create the ZnO nanorod arrays, but also has a strong impact on the reduction of surface recombination. The reflectance spectra show that ZnO nanorods were used as an efficient ARC to enhance light absorption by multiple scattering. Also, from the current-voltage results, we found that the combination of the AZO film and ZnO nanorods on Si wire solar cells leads to an increased power conversion efficiency by more than 27% compared to the cells without it.

Radial p-n Junction Solar Cells by Core-Shell Silicon Nanowire Arrays

ABSTRACTWe first fabricated a p-type single-crystalline SiNW array as the core by statistic electroless metal deposition (SEMD) method[1]. This structure exhibits per excellent absorption efficiency without increasing the diffusion path, indicating 1.75 times greater performance than Si-based planar solar cells under the same condition[2]. Next, we employed a method of spin-on dopant (SOD) to fabricate an n-type layer as an external thin shell, which benefits to decouple the absorption of light from charge transport by allowing lateral diffusion of minority carriers to the p-n junction rather than many microns away as in Si bulk solar cells, and is suitable for our SiNW array with a hydrophilic surface. Finally, our SiNW-based solar cell possesses strong broadband absorption and low reflection from visible light to near IR, in which the highly light trapping mechanism stems from the effective medium theory (EMT) to demonstrate only less than 3% of total reflectance in the range of 500-1100 nm. It also shows conversion efficiency improvement of 20% compared with the planar single-crystalline Si solar cell by the same fabrication processes. The proposed novel photovoltaic device by our core-shell SiNW array revolutionizes the current architecture of solar cells, promising niche points of (1) better absorption, (2) self-antireflection, and (3) low-cost process.

Preparation of n+ emitter on p-type silicon wafer using the spin-on doping method

There is a strong need for cost reduction in manufacturing crystalline silicon solar cells, and one of the approaches is to merge two steps of silicon wafer processing into one step without degrading the performance of solar cells. In this work, we intended to employ the spin-on doping (SOD) method for the purpose of dual tasks, phosphorus diffusion to form n+ emitters and antireflection coating (ARC) to reduce optical reflection. Different from the commercial SOD solutions based on SiO2, we used tetraethylorthosilicate (TEOS) to prepare SOD solutions containing different concentrations of phosphorus acid as the phosphorus doping source. We first investigated the dependence of the sheet resistance of the n+ emitters on the concentration of phosphorus acid in the SOD solution as well as the thermal diffusion temperature and time. It was found that all these three factors can effectively influence the sheet resistance of the n+ emitters, suggesting a relatively easier optimization process for forming n+ emitters using the SOD method. The SOD thin films formed after the thermal diffusion process were found to be SiO2 films. We then investigated the antireflection properties of the as-grown SOD thin films, and found that they can effectively reduce the optical reflection of silicon wafers.