Determination of the complex refractive index and optical bandgap of CH3NH3PbI3 thin films

We report the complex refractive index of methylammonium lead iodide CH3NH3PbI3 perovskite thin films obtained by means of variable angle spectroscopic ellipsometry and transmittance reflectance spectrophotometry in the wavelength range of 190 amp; 8201;nm to 2500 amp; 8201;nm. The film thickness and roughness layer thickness are determined by minimizing a global unbiased estimator in the region where the spectrophotometry and ellipsometry spectra overlap. We then determine the optical bandgap and Urbach energy from the absorption coefficient, by means of a fundamental absorption model based on band fluctuations in direct emiconductors. This model merges both the Urbach tail and the absorption edge regions in a single equation. In this way, we increase the fitting region and extend the conventional amp; 945; amp; 8463; amp; 969; 2 plot method to obtain accurate bandgap value

Capacitance voltage curve simulations for different passivation parameters of dielectric layers on silicon

Abstract Surface passivation is a widely used technique to reduce the recombination losses at the semiconductor surface. The passivating layer performance can be mainly characterized by two parameters: The fixed charge density ( Q ox ) and the interface trap density ( D it ) which can be extracted from Capacitance-Voltage measurements (CV). In this paper, simulations of High-Frequency Capacitance-Voltage (HF-CV) curves were developed using simulated passivation parameters in order to examine the reliability of measured results. The D it was modelled by two different sets of functions: First, the sum of Gaussian functions representing different dangling bond types and exponential tails for strained bonds. Second, a simpler U-shape model represented by the sum of exponential tails and a constant value function was employed. These simulations were validated using experimental measurements of a reference sample based on silicon dioxide on crystalline silicon (SiO 2 /c-Si). Additionally, a fitting process of HF-CV curves was proposed using the simple U-shape D it model. A relative error of less than 0.4% was found comparing the average values between the approximated and the experimentally extracted D it ’s. The constant function of the approximated D it represents an average of the experimentally extracted D it for values around the midgap energy where the recombination efficiency is highest

Capacitance voltage curve simulations for different passivation parameters of dielectric layers on silicon

Surface passivation is a widely used technique to reduce the recombination losses at the semiconductor surface. The passivating layer performance can be mainly characterized by two parameters: The fixed charge density (Q ox) and the interface trap density (D it) which can be extracted from Capacitance-Voltage measurements (CV). In this paper, simulations of High-Frequency Capacitance-Voltage (HF-CV) curves were developed using simulated passivation parameters in order to examine the reliability of measured results. The D it was modelled by two different sets of functions: First, the sum of Gaussian functions representing different dangling bond types and exponential tails for strained bonds. Second, a simpler U-shape model represented by the sum of exponential tails and a constant value function was employed. These simulations were validated using experimental measurements of a reference sample based on silicon dioxide on crystalline silicon (SiO2/c-Si). Additionally, a fitting process of HF-CV curves was proposed using the simple U-shape D it model. A relative error of less than 0.4% was found comparing the average values between the approximated and the experimentally extracted D it's. The constant function of the approximated D it represents an average of the experimentally extracted D it for values around the midgap energy where the recombination efficiency is highest

Band fluctuations model for the fundamental absorption of crystalline and amorphous semiconductors a dimensionless joint density of states analysis

We develop a band fluctuations model which describes the absorption coefficient in the fundamental absorption region for direct and indirect electronic transitions in disordered semiconductor materials. The model accurately describes both the Urbach tail and absorption edge regions observed in such materials near the mobility edge in a single equation with only three fitting parameters. An asymptotic analysis leads to the universally observed exponential tail below the bandgap energy and to the absorption edge model at zero Kelvin above it, for either direct or indirect electronic transitions. The latter feature allows the discrimination between the absorption edge and absorption tails, thus yielding more accurate bandgap values when fitting optical absorption data. We examine the general character of the model using a dimensionless joint density of states formalism with a quantitative analysis of a large amount of optical absorption data. Both heavily doped p type GaAs and nano crystalline Ga 1 x Mn x N, as examples for direct bandgap materials, as well as amorphous Si H x , SiC H x and SiN x , are modeled successfully with this approach. We contrast our model with previously reported empirical models, showing in our case a suitable absorption coefficient shape capable of describing various distinct materials while also maintaining the universality of the exponential absorption tail and absorption edg

Estimation of the effective nominal power of a photovoltaic generator under non-ideal operating conditions

The nominal power is an essential parameter for evaluating the general state of a photovoltaic plant. The American Society for Testing and Materials, the International Electrotechnical Commission and other works propose procedures that allow estimating the nominal power of a photovoltaic generator in outdoor conditions. These procedures generally require monitoring days with ideal conditions, particularly clear sky days with high irradiance values and low wind speeds. These restrictions can limit the available number of monitoring days, especially in places with frequent cloud formations. In this work, a 109.44 kW photovoltaic plant was monitored for six months in Granada, Spain. Its nominal power is first estimated applying a referential procedure reported in the literature for large PV plants under the required ideal climatic conditions. In order to overcome the restrictions for estimating the nominal power, we propose a new procedure applicable not only for ideal but also for non-ideal conditions, such as found on partially cloudy days. This new procedure applies non-parametric statistics to find the most probable value of the nominal power within a single monitoring day. A statistical analysis indicates that it reliably estimates the nominal power at non-ideal conditions while preserving the same estimation accuracy as under ideal conditions.This work received financial support by the Concytec – World Bank project “Mejoramiento y Ampliación de los Servicios del Sistema Nacional de Ciencia Tecnología e Innovación Tecnológica” 8682-PE, through its executing unit PROCIENCIA, contract N◦045-2018- FONDECYT-BM-IADT-MU. José Angulo acknowledges the financial support given by Concytec under the Ph.D. scholarship program with contract N◦236-2015-FONDECYT. The PUCP vicechancellorship for research also provided under the contract no. CAP-2021-A-0028/PI0737. Additionally, part of this work has been financed by the “Agencia Andaluza de Cooperación Internacional para el Desarrollo” of the Junta de Andalucía (Andalusian Autonomous Government), through the project “Emergiendo con el Sol” under expedient code 2012DEC02

Single-photon emission from InGaAs quantum dots grown on (111) GaAs

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Appl. Phys. Lett. 96, 093112 (2010) and may be found at https://doi.org/10.1063/1.3337097.In this letter, we demonstrate that self-organized InGaAs quantum dots (QDs) grown on GaAs (111) substrate using droplet epitaxy have great potential for the generation of entangled photon pairs. The QDs show spectrally sharp luminescence lines and low spatial density. A second order correlation value of g(2)(0)<0.3 proves single-photon emission. By comparing the power dependence of the luminescence from a number of QDs we identify a typical luminescence fingerprint. In polarization dependent microphotoluminescence studies a fine-structure splitting ranging ≤40eV down to the determination limit of our setup (10eV) was observed.DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, Bauelement

Silicon interface passivation studied by modulated surface photovoltage spectroscopy

We demonstrate that the modulated surface photovoltage spectroscopy (modulated SPS) technique can be applied to investigate interface states in the bandgap, i.e. interface passivation, of crystalline silicon coated with a downshift layer such as hydrogenated aluminum nitride with embedded terbium ions by suppressing straylight with a cut-off filter. Different hydrogen contents influence the surface photovoltage spectra at photon energies below the bandgap of crystalline silicon. Modulated SPS reveals that at higher hydrogen content there is a lower signal and, thus, a lower density of surface defect states. Our experiments show that modulated SPS can become a powerful tool for characterizing defect states at interfaces which cannot be easily studied by other methods

Bandgap Engineering of Amorphous Hydrogenated Silicon Carbide

This research was funded by the Research Management Office (DGI) of the Pontificia Universidad Católica del Perú (PUCP). The authors have been supported by the PUCP under the PhD scholarship program Huiracocha (J A Guerra) and by the National Council of Science and Technology (CONCYTEC) under the scholarships granted to the PUCP (J R Angulo and J Llamoza). The author would like to thank Prof Dr H P Strunk, F Benz and Dr Y Weng of the University of Stuttgart for the TEM measurements.Consejo Nacional de Ciencia, Tecnología e Innovación Tecnológica - Concyte

INTERFACE ISSUES OF ALL PECVD SYNTHESIZED ALOX SINX PASSIVATION STACKS FOR SILICON SOLAR CELLS

The interface passivation of a AlOx a SiNx H stacks deposited on p type silicon by in line plasma enhanced chemical vapor deposition is investigated by means of charge carrier lifetime, field dependent surface photovoltage and capacitance voltage measurements as well as Fourier transform infrared spectroscopy. To control the quality of the interface, we performed different wet chemical surface preparation steps prior to a AlOx a SiNx H stack deposition. Our investigation is focusing on the interface passivation upon post deposition thermal treatments such as annealing at 425 C and firing at 860 C as applied in the silicon solar cell industry. We demonstrate that the interface recombination is mainly controlled by the interface state density as demonstrated by the correlation between the surface recombination velocity and interface state density inferred from lifetime and SPV measurements. The increase of the negative charge density after thermal steps as revealed by capacitance voltage measurements correlates with the increase of the density of negatively charged AlO4 tetrahedra as revealed by infrared spectroscopy suggesting that the tetrahedrally coordinated Al contribute to the formation of the negative charg