Indirect Optical Transitions
The Indirect Optical Transitions feature adds an empirical absorption model for silicon to enable easy simulation of optical absorption in photovoltaic devices. The model uses the data from Ref. 46 to obtain the frequency-dependent real and imaginary components of the refractive index of silicon. Alternately, you can choose to specify a user-defined absorption via either supplying an absorption coefficient or the imaginary part of the refractive index — this enables the feature to be used for other materials for which this data is known. The photogeneration due to absorbed photons is then added into the model via a term that contributes to the carrier generation rate. If a multiphysics coupling between the Semiconductor interface and an Electromagnetic Waves interface is active, the refractive index data from the Indirect Optical Transitions feature is automatically used by the Electromagnetic Waves interface for calculating wave propagation. Also, the frequency and magnitude of the electromagnetic wave, which are required in order to calculate the absorption rate, are obtained automatically from the Electromagnetic Waves interface. If multiphysics coupling is not used, these quantities can be specified directly within the Indirect Optical Transitions feature.
Transitions Model
Select a Transitions model — Empirical silicon absorption (Green and Keevers) (the default) or User-defined absorption.
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Empirical silicon absorption (Green and Keevers): This option automatically obtains the frequency-dependent real and imaginary components of the refractive index and computes the absorption and associate carrier generation. This model is most appropriate for intrinsic silicon at temperatures around 300 K.
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User-defined absorption: This option enables the user to specify the absorption. The photogeneration rate is then computed and the extra carriers are added to the model automatically via an extra generation term. You can either supply the imaginary part of the refractive index or the absorption coefficient.
Specify Absorption
This section is available when User-defined absorption is selected as the transitions model.
Select an option from the Specify absorption list — Absorption coefficient (the default) or Refractive index. Then enter the following as required:
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Imaginary part of refractive index n (dimensionless).
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Absorption coefficient α (SI unit: 1/m).
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Real part of the refractive index k (dimensionless).
Optical Excitation Frequency
This section is available if a multiphysics coupling is not used. It enables the frequency of the electromagnetic wave to be specified. If the Empirical silicon absorption (Green and Keevers) transition model is selected, this frequency is used to look up the corresponding refractive index data. For both transition model options the frequency is used in calculating the photogeneration rate.
Select an Excitation frequency — From study (the default), User-defined frequency, or User-defined wavelength.
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For User-defined frequency, enter the excitation frequency, f0 (SI unit: Hz). The default is 375 GHz.
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For User-defined wavelength, enter the wavelength, λ0 (SI unit: m). The default is 800 nm.
Optical Intensity
This section is available if a multiphysics coupling is not used. It enables the magnitude of the electromagnetic wave to be specified.
Enter the Electric field norm, E0 (SI unit: V/m).