Photogeneration (Excitation menu)
The photogeneration options allow you to apply photoexcitation to the device, either as a photogeneration profile supplied via an external file, or using one or both of two light sources which can illuminate either the front or rear surface of the device.
When using the light sources, PC1D internally calculates the photogeneration rate within the device. At each incident wavelength, after accounting for incident-surface reflection, the light is absorbed in the device using the absorption coefficients for each region. If enabled, some light will be lost due to free carrier absorption. If the device has texture, then the photons do not travel parallel to the solution direction (x). The direction they travel makes a different angle with respect to x near the front surface than near the back. Both angles are calculated using the facet angle and the index of refraction for the material of region 1, with the transition between these two angles assumed to occur abruptly when x exceeds one-sixth of the facet depth. If the internal reflectance for the surface opposite the incident surface is non-zero, then some photons reflect from that surface with either the same angle at which they arrived (specular) or randomly-directed (diffuse). If the internal reflectance at the incident surface is non-zero, then some of this reflected light gets trapped within the device until it eventually is either absorbed in the device or fails to be reflected from one surface of the other.
One photogeneration option is to supply an external ASCII file with suffix GEN that contains photogeneration information. This file should have two values on each line, separated by one or more spaces or by a tab. The first value is a position representing the distance of that location from the front surface, in μm. The second value is the cumulative photogeneration rate in the device between the front surface and that position, in carrier-pairs per second per square cm of projected area. Both the position and photogeneration values must be monotonically increasing functions within the file, and both must start with a value of 0.0 on the first line. Photogeneration information provided for positions beyond the rear surface of the device are ignored. If the device is thicker than the last entry in the file, then no photogeneration is assumed beyond the last position defined in the file.
Primary/Secondary Illumination Intensity
These commands open a dialog box to examine or modify the magnitude and time dependence of light incident on the device, and to select whether the light is incident on the front or rear surface of the device. To use either of the illumination sources, you must first Enable that source from within this dialog box. Different values of illumination source intensity can be specified for steady state versus transient conditions. Changing the intensity between its steady-state and initial transient value causes a step change in intensity at t=0. Setting the final transient value different from the initial transient value causes the intensity to sweep linearly from the initial to the final value during the course of the transient solution. The values entered correspond to the total power density normally incident on the surface of the device, measured in W/cm2. One standard "terrestrial sun" corresponds to an intensity of 0.1 W/cm2.
When a simple linear ramp of intensity is inadequate, time-dependent light intensity values can be entered from an external ASCII data file having a filename suffix LGT. Each line in the file should contain two values, separated by one or more spaces or by a tab. The first is a time, in seconds. The second is an intensity value with units of W/cm2. The lines must have monotonically increasing time values. The maximum number of lines in the file is 200. The time values in this file do not affect the time step size or number of time steps used in the solution. Rather, an intensity value is interpolated from the LGT file for each point in time specified in the Mode command.
Primary/Secondary Illumination Spectrum
The illumination spectrum choices are Monochrome, Black-Body, or External.
The Monochrome option allows you to specify that all of the incident power occurs at a single wavelength. Different values of wavelength can be specified for steady state versus transient conditions. Changing the wavelength between its steady-state and initial transient value causes a step change in wavelength at t=0. Setting the final transient value different from the initial transient value causes the wavelength to sweep linearly from the initial to the final value during the course of the transient solution.
The Black-Body option allows you to invoke a black-body spectrum corresponding to a specified temperature. The spectrum is actually implemented as a group of discrete wavelengths, so you must declare the number of discrete wavelengths (maximum 200) and the range of wavelengths to include. You can artificially limit the wavelength range to simulate the effect of a filtered spectrum. The total power density in the black-body spectrum incident on the device is adjusted to match the values specified for illumination intensity. Note that for a given temperature, there is a limit to the intensity that can be obtained from a black body source; however, PC1D does not verify whether this limit has been exceeded.
The External option allows you to supply an external ASCII file that defines a spectral distribution, represented as a group of discrete wavelengths. These files have suffix SPC. Several important spectrums are provided with PC1D, including the air-mass 1.5 direct and global ASTM solar spectrums, and the extraterresrial solar spectrum. These files contain two values on each line, separated by one or more spaces or a tab. The first value is a wavelength in nm, and the second is a power density in W/cm2 (NOT spectral density, W/mm/cm2). The entries must be in order of increasing wavelength, with a maximum of 200 wavelengths allowed The power densities are scaled as necessary so that the total light intensity for the spectrum as a whole equals the value specified for illumination intensity.