Papers by Keyword: Surface Passivation

Abstract: Mixed-halide perovskite allows to realize conception of light-emitting solar cell (LESC) due to possibility to in-situ change device band structure by formation of dipole layer under applied voltage and intrinsic properties of perovskite ions. LESC has optimized perovskite-based solar cell (SC) architecture, but light-emitting diode (LED) regime performances is still low. Defect passivation can improve LED efficiencies due to reducing nonradiative recombination via defect levels. Solvent annealing allows to regulate film formation process and leads to better morphology and grain size for our application. Defect density is significantly reduced due to this passivation method. Here we demonstrate effect of annealing in vapors of dimethylformamide (DMF), dimethyl sulfoxide (DMSO) and acetonitrile (MeCN) atmosphere on LESC photovoltaic characteristic, electroluminescence (EL) peak wavelength and photoluminescence quantum yield (PLQY) of mixed-halide perovskite film.

Abstract: Passivation treatments applied prior to Mo metallisation on Silicon Carbide (SiC) Schottky rectifier and metal-oxide-semiconductor capacitor (MOSCAP) structures are studied. A control sample and two treatments, comprising of an O₂ oxidation and a phosphorus pentoxide (P₂O₅) deposition, were studied. Electrical characterisation results show that P₂O₅ treatment improves the homogeneity of the diodes, with the ideality factor reducing to 1.02 and the leakage current reducing by three orders of magnitude to 2×10^-5 A/cm². Furthermore, the SBH was lowered by 0.11 eV and the variance of all the P₂O₅ treated Schottky characteristics over the batch reduced. Characterisation by X-ray photoelectron spectroscopy (XPS) showed that the stoichiometry, the Si:C ratio, of the SiC below the contact increased from 0.93:1 before treatment to 0.97:1 after P₂O₅ treatment.

Abstract: The scanning of Silicon Carbide (SiC) epitaxy wafers for defects by ultraviolet (UV) laser or lamps is widely prevalent. In this work, we document the effects of UV light excitation on the SiC epitaxy material. An increase in background photoluminescence (PL) is observed after repeated scans. The effect of this increase on defect detection is shown. Optimal surface treatments to recover the material back to the original state are demonstrated. Further, some surface treatments are proposed which reduce the effect of the UV light excitation and prevent to a large extent the rise in background PL.

Abstract: Thin Al₂O₃ films were deposited on p-type black silicon (b-Si) by using chemical liquid phase deposition (CLD) technique. The influence of annealing temperatures on the structural and optical properties of Al₂O₃ films was investigated. The b-Si with 80-nm Al₂O₃ films exhibits a low total reflectance of 5%. The sample annealed 300 °C exhibits negative fixed charge with the density of 1.5×10¹² cm^-2. With the increasing of annealing temperature, negative shift of C-V curve was observed, indicating the polarity of fixed charge changes to positive, with maximal the density of 8.7×10¹¹ cm^-2. The evolution of the polarity of fixed charge is assigned to the decreasing of O: Al ratio caused by the transition of the crystalline type of Al₂O₃. The change of fixed charge polarity in Al₂O₃ provides a feasible route for both p- and n-type Si passivation in Si solar cells by adjusting the thermal post-treatment.

Abstract: Schottky barrier diodes (SBD) were fabricated on SiC surfaces that had been treated with different surface passivation techniques, so that metal-semiconductor analysis could be used to evaluate the quality of this surface. In this paper, we discuss the results of this study that used Current-Voltage (I-V), Capacitance-Voltage (C-V) and Current-Voltage-Temperature (I-V-T) analysis to look at the impact of untreated oxidation, Nitrous oxide (N₂O) and Phosphorus Silicate Glass (PSG) treatments prior to oxide removal, and the formation of Mo, Ni and Ti diodes. While the results of this study did not reveal any consistent patterns between the different treatments, a Mo diode formed on a surface after PSG treatment, displays exceptionally low leakage (4.44×10^-5 A/cm² at 19°C; 7.26×10^-4 A/cm² at 300°C) given a low barrier height (1.27 eV). Moreover, the barrier heights extracted from C-V analysis before contact annealing show a variation across all the diodes, suggesting that the interface is greatly suffering from Fermi-Level pinning, the result of significant interface traps.

Abstract: Oxidation of a GaAs surface was performed with liquid H₂O₂, gaseous O₂ and O₃ in order to identify the best solution for digital etching. The oxide layer formed with H₂O₂ is Garich and exhibits surface roughening which can be understood by oxide hydrolysis/condensation model. Roughening makes aqueous H₂O₂ irrelevant as an oxidizing agent for repeated oxidation steps. On the other hand, a smooth oxide layer can be obtained with gaseous O₂ and O₃. Thickness of the formed oxide layer is controlled by time exposure to the oxidizing agent. The nature of the oxide was analyzed by XRay Photo-electron Spectroscopy and is also timedependent.

Abstract: Tristrimethylsilylgermane, (Me₃Si)₃GeH, was employed as a molecular model compound for hydrogen terminated Ge(111) surfaces. Time and temperature dependent NMR spectroscopy yielded rate constants for the reaction between (Me₃Si)₃GeH and elemental sulfur and allowed for the determination of the activation energy for this molecular model reaction to mimic germanium surface passivation.

Abstract: A new technique is described by which ionic species can be rapidly transported into oxide films, and once there provide effective and stable field effect passivation to silicon surfaces. Field effect passivation in thermally grown oxide films has been achieved by embedding potassium ions using a combined drift and diffusion mechanism at high temperature. This process has been shown to be over 10 times faster than a pure diffusion process. The resulting passivation stable for periods exceeding 600 days, with lifetimes reaching 1.4 ms, equivalent to a surface recombination velocity (SRV) ≤ 5.7 cm/s, on 1 Ωcm, n-type, FZ-Si.

Abstract: An investigation of the parasitic surface recombination mechanisms in high-lifetime oxidized n-Si is presented. An approximate analytical expression describing recombination at the edge of square shaped specimens is derived. This shows that edge recombination can have a significant effect on the effective lifetime as measured using the transient photo-conductance technique and that for well passivated high quality material edge recombination can be the dominant mechanism in reducing the effective lifetime below the intrinsic level. For 3 x 3 cm² pieces of silicon measured using a Sinton photo-conductance lifetime instrument, it is shown that recombination at the edge of the sample results in an additional component to the measured lifetime of around 16 ms at an injection level of 10¹⁵ cm^-3. When this effect is taken into account measurements of 1 Ωcm FZ-Si show that a SRV as low as 1.5 cm/s is possible when the surface is passivated using a corona charge concentration of +2.2 x 10¹² q/cm² deposited on a 100 nm oxide layer.

Abstract: Silicon photovoltaic (PV) roadmaps indicate the reduction of wafer thicknesses and the need for innovation in wafering method and cell processing. Within this framework, Imec proposes the i²-module device [1], i.e. an heterojunction interdigitated back-contact (HJ i-BC) solar module [2] processed on 40-μm thick epitaxial wafers bonded to carriers by means of silicone. In the i²-module concept, the Rear Side (RS) of the solar cell is passivated while the wafer is bonded to the module glass and the influence of the silicone on the passivation process is reduced by an O₂ plasma realized in an Reactive Ion Etching (RIE) chamber [3]. In this contribution, the effect of different post-bonding cleaning sequences on the passivation of wafers/silicone/glass stacks treated with an O₂ plasma is investigated and a simplified post-bonding cleaning sequence leading to state-of-the-art passivation is proposed.