6,159 research outputs found
Solcore: A multi-scale, python-based library for modelling solar cells and semiconductor materials
Computational models can provide significant insight into the operation
mechanisms and deficiencies of photovoltaic solar cells. Solcore is a modular
set of computational tools, written in Python 3, for the design and simulation
of photovoltaic solar cells. Calculations can be performed on ideal,
thermodynamic limiting behaviour, through to fitting experimentally accessible
parameters such as dark and light IV curves and luminescence. Uniquely, it
combines a complete semiconductor solver capable of modelling the optical and
electrical properties of a wide range of solar cells, from quantum well devices
to multi-junction solar cells. The model is a multi-scale simulation accounting
for nanoscale phenomena such as the quantum confinement effects of
semiconductor nanostructures, to micron level propagation of light through to
the overall performance of solar arrays, including the modelling of the
spectral irradiance based on atmospheric conditions. In this article we
summarize the capabilities in addition to providing the physical insight and
mathematical formulation behind the software with the purpose of serving as
both a research and teaching tool.Comment: 25 pages, 18 figures, Journal of Computational Electronics (2018
Oscillating propagators in heavy-dense QCD
Using Monte Carlo simulations and extended mean field theory calculations we
show that the -dimensional spin model with complex external fields has
non-monotonic spatial correlators in some regions of its parameter space. This
model serves as a proxy for heavy-dense QCD in dimensions.
Non-monotonic spatial correlators are intrinsically related to a complex mass
spectrum and a liquid-like (or crystalline) behavior. A liquid phase could have
implications for heavy-ion experiments, where it could leave detectable signals
in the spatial correlations of baryons.Comment: 16 pages, 9 figures, updated to match published versio
Pure Space-Charge-Limited Electron Current in Silicon
Phosphorus diffusion on π‐type silicon is used to fabricate n^+πn^+ structures of base widths between 3 μ and 60 μ with π‐type resistivities of 300 Ω⋅cm and 8 kΩ⋅cm. The V‐I characteristics of the structures are measured at room temperature and at liquid‐nitrogen temperature. The change in current for constant applied voltage is also observed in that temperature range.
The results are interpreted in terms of simple models based on the assumption that pure space‐charge‐limited current of electrons is present. The models describe well the characteristics measured on 300‐Ω⋅cm samples, except for the range of small biases on the thinnest samples. It is concluded that the drift velocity of electrons at 78°K tends towards saturation at 1.0×10^7 cm∕sec ± 10%. The current observed at this temperature actually reaches this value. The critical electric field at 78°K is 10^3 V∕cm±30% but the meaning of this concept for electrons in silicon is vague. The temperature dependence of the current at fixed bias voltages is in general agreement with the variation of the low field mobility. Results obtained on 8‐kΩ⋅cm samples need clarification. Effects of breakdown and trapping are not observed
Modeling Changes in Measured Conductance of Thin Boron Carbide Semiconducting Films Under Irradiation
Semiconducting, p-type, amorphous partially dehydrogenated boron carbide films (a-B10C2+x:Hy) were deposited utilizing plasma enhanced chemical vapor deposition (PECVD) onto n-type silicon thus creating a heterojunction diode. A model was developed for the conductance of the device as a function of perturbation frequency (��) that incorporates changes of the electrical properties for both the a-B10C2+x:Hy film and the silicon substrate when irradiated. The virgin model has 3 independent variables (R1, C1, R3), and 1 dependent variable (��). Samples were then irradiated with 200 keV He+ ions, and the conductance model was matched to the measured data. It was found that initial irradiation (0.1 displacements per atom (dpa) equivalent) resulted in a decrease in the parallel junction resistance parameter from 6032 Ω to 2705 Ω. Further irradiation drastically increased the parallel junction resistance parameter to 39000 Ω (0.2 dpa equivalent), 77440 Ω (0.3 dpa equivalent), and 190000 Ω (0.5 dpa equivalent). It is believed that the initial irradiation causes type inversion of the silicon substrate changing the original junction from a p-n to a p-p+ with a much lower barrier height leading to a lower junction resistance component between the a-B10C2+x:Hy and irradiated silicon. Additionally, it was found that after irradiation, a second parallel resistor and capacitor component is required for the model, introducing 2 additional independent variables (R2, C2). This is interpreted as the junction between the irradiated and virgin silicon near ion end of range
Mechanism of the photovoltaic effect in 2-6 compounds Progress report, 1 Oct. 1968 - 31 Mar. 1969
Heat treatment, illumination and darkness effects, and photovoltaic properties of Cu2S-CdS heterojunction
Radiation effects studies for the high-resolution spectrograph
The generation and collection of charge carriers created during the passage of energetic protons through a silicon photodiode array are modeled. Pulse height distributions of noise charge collected during exposure of a digicon type diode array to 21 and 75 MeV protons were obtained. The magnitude of charge collected by a diode from each proton event is determined not only by diffusion, but by statistical considerations involving the ionization process itself. Utilizing analytical solutions to the diffusion equation for transport of minority carriers, together with the Vavilov theory of energy loss fluctuations in thin absorbers, simulations of the pulse height spectra which follow the experimental distributions fairly well are presented and an estimate for the minority carrier diffusion length L sub d is provided
Assessment of active dopants and p-n junction abruptness using in-situ biased 4D-STEM
A key issue in the development of high-performance semiconductor devices is
the ability to properly measure active dopants at the nanometer scale. 4D
scanning transmission electron microscopy and off-axis electron holography have
opened up the possibility of studying the electrostatic properties of a p-n
junction with nm-scale spatial resolution. The complete description of a p-n
junction must take into account the precise evolution of the concentration of
dopants around the junction, since the sharpness of the dopant transition
directly influences the built-in potential and the maximum electric field.
Here, a contacted silicon p-n junction is studied through in-situ biased
4D-STEM. Measurements of electric field, built-in voltage, depletion region
width and charge density in the space charge region are combined with
analytical equations as well as finite-element simulations in order to evaluate
the quality of the junction interface. The nominally-symmetric, highly doped
() junction presents an electric
field and built-in voltage much lower than expected for an abrupt junction.
These experimental results are consistent with electron holography data. All
measured junction parameters are compatible with the presence of an
intermediate region with a graded profile of the dopants at the p-n interface.
This hypothesis is also consistent with the evolution of the electric field
with bias. These results demonstrate that in-situ biased 4D-STEM enables a
better understanding of the electrical properties of semiconductor p-n
junctions with nm-scale resolution.Comment: 13 pages, 5 figure
Analysis and evaluation in the production process and equipment area of the low-cost solar array project
It was found that the Solarex metallization design and process selection should be modified to yield substantially higher output of the 10 cm x 10 cm cells, while the Westinghouse design is extremely close to the optimum. In addition, further attention to the Solarex pn junction and base high/low junction formation processes could be beneficial. For the future efficiency improvement, it was found that refinement of the various minority carrier lifetime measurement methods is needed, as well as considerably increased sophistication in the interpretation of the results of these methods. In addition, it was determined that further experimental investigation of the Auger lifetime is needed, to conclusively determine the Auger coefficients for the direct Auger recombination at high majority carrier concentrations
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