Every software package contains a full set of examples suitable for that version and are installed with the software. If you see examples here that are not in your installation you should consider updating to a later version of the software. These examples can be used by beginners and advanced users for product evaluation, teaching purposes, and self-training.

Required Modules

Victory Device

• 2D Simulator
• 2D Optical

The following set of examples demonstrates how to extract device characteristics for general photodetectors. These characteristics are of interest to those involved in the design of PN and PIN photodiodes, avalanche photodiodes, photoconductors, phototransistors, optical FETs and MSMs. These examples focus principally on optoelectronic characteristics as opposed to the purely electronic behaviour of photodetectors (e.g., dark current, capacitance).

The following examples will address a PIN photodetector. The extraction techniques used on the PIN device will equally apply to other photodetector devices. The device for these examples is described in the input file “optoex01.in “. This input file should be run before any of the other examples in this section as it provides the base device structure used in the other examples.

The first section of the input file specifies the mesh. In this case, the mesh is 10 microns by 10 microns. The spacings were chosen to help resolve the P+/N and N/N+ junctions. The space.mult parameter is used to make the mesh coarse for fast simulation. For more accuracy, the value should be set to unity.

The second section of the input file specifies the structure of the device. The device is a square of silicon with an anode extending across the front surface (y=0.0) and a cathode across the bottom. It is uniformly doped N-type at 1.0e14, with heavily doped P+ and N+ regions at the front and back surfaces respectively.

The third section of the input file specifies which material models will be used in the simulation. Here SRH and Auger recombination mechanisms have been specified since they have important effects on the quantum efficiency of photodiodes. Concentration and field dependent mobility models are also specified.

The last section of the input file is used to obtain an initial solution. The initial solution is written to a solution file that is used in all the subsequent photodetector analysis examples. The output file can be viewed using Victory Visual. This shows the structure of the device and the device mesh.

Next example involves characterization of steady state characteristics of the device and demonstrates extraction of DC currents as a function of optical source power. It also demonstrates the use of multi-spectral sources. The source spectrum is described in the file “spectrum.spec “.

Next section of the input file specifies the optic source. In this example the source originates 1 micron above the device and is directed normal to the front surface of the device. The source spectrum is described in the file ” spectrum.spec “. This spectrum is sampled at 5 discrete samples between the wavelengths of 0.5 and 0.8 microns.
Next, we set up the initial operating bias for the simulation. In this case an operating bias of 2.0 volts is chosen.

Next the input file specifies that the optical source intensity will be ramped from 0 to 1 W/cm^2. During this ramp, steady state currents are extracted and saved in the log file.

The results are displayed by Victory Visual. The source photo current is the equivalent current what would be observed if all the light from the source were detected. Available photo current is the equivalent current that would be observed if all the light absorbed were converted to terminal current. The difference between the source and available photo currents is due to part of the light passing all the way through the device. The third curve is the cathode current

Next example deals with time domain response of the device to time dependent optical sources. This example will extract the transient response of the device to an optical source being “turned off “.

First, a normally incident monochromatic source is defined. The wavelength of the source is 623 nm, equivalent to a HeNe laser wavelength.

Next part sets the initial biasing conditions of the device. Here again the device is biased to 2.0 volts.

Then the input file specifies the transient. In this case the DC solution at a source intensity of 0 W/cm^2 is obtained. Then, the source intensity is ramped linearly to 5 over a time of 1 ns. Terminal data is then collected over the next 9 ns. The terminal data is saved to the log file.

The results of the example are viewed in Victory Visual. They compare the available photo current with the cathode current as a function of time. In this case the cathode current lags the source transient by a fraction of a nanosecond.

Next, this input file analyzes the small signal response of the device to a small signal optical source.

The next section of the file specifies that a DC solution at a source intensity of 5 W/cm^2 is obtained. After the DC solution, the small signal response of the device to a small signal optical source of 1 mW/cm^2 is extracted for frequencies ranging from 100KHz to 10THz. The full AC terminal characteristics are saved in the log file.

When the results are viewed in Victory Visual, they show that the device has a cutoff frequency of about 1 GHz.

The final example in this set involves the extraction of spectral response data.

Here a monochromatic wavelength of 100nm is specified. In the last section of the file, solutions are obtained for a 1 W/cm^2 intensity at discrete source wavelengths of 0.1 to 0.8 microns. The lambda parameter was ramped from 0.1 to 0.8 with steps of 0.01. The terminal characteristics and wavelength results are saved to the log file.
The results of the simulation show that the device exhibits good quantum efficiency below a wavelength of about 700 nm.

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