The dark and photo current plots as a function of bias voltage obtained from the electrical simulation are compared with the same results from the reference publication (the device with 10um length) in the figures below. To obtain the figures of merit of the detector, including responsivity and multiplication gain, run the script file avalanche_photodetector_FOMs.lsf.Run the script file avalanche_photodetector_IV.lsf to plot and save the photo current results and compare with the reference publication.Click "Quit & Save" to preserve the results for the next step. The simulation will diverge again close to breakdown. Optionally import the generation rate data into the object (the object is preloaded with data) Switch back to Layout mode and enable the optical generation rate object.Run the script file avalanche_photodetector_IV.lsf to plot and save the dark current results and compare with the reference publication.Then you need to click "Quit & Save" to preserve the results for the next step. This is indicative of reaching the breakdown and not a problem in the simulation. Note that the simulation will eventually diverge at a voltage close to the APD's breakdown, at which point the job in the job manager window will get red in color and job status changes to Job error (as shown below). Open and run the electrical simulation file (avalanche_photodetector_electrical.ldev).The average generation rate profile at a cross-section of the device calculated by the optical simulation is illustrated in the figure below. To have a plot of the generation data at the cross section of the device, select the parameter “z” from the list of parameters in the visualizer window and set the “action” field to “plot y axis”. To visualize the exported generation data, right click on “generation rate” analysis group and select “Visualize” then “G_export”.This will calculate the optical generation data and export the data to a file (apd_10um_G_Ge.mat) that will be imported into CHARGE. Right click on "generation rate" analysis group object and select "Run analysis".Open and run the APD simulation file (avalanche_photodetector_optical.fsp) using FDTD.Instructions for running the model and discussion of key results Step 1: Optical simulation An eye diagram is employed to evaluate the quality of the detected signal and its variation as a function of the detector gain (multiplication factor). The performance figures of merit obtained from the previous step are used to define a compact model for the Avalanche photodetector (APD) in INTERCONNECT to simulate the operation of the device for detecting a low power modulated signal. The responsivity and multiplication gain of the detector can be calculated from the photocurrent result. Then, two separate simulations are carried out to obtain the dark current and the photo-current by disabling and enabling the optical generation object, respectively. The optical generation rate data (representing the concentration of photogenerated carriers inside the device) is imported into the electrical simulation. This generation rate is averaged over the length of the device in order to simplify the electrical simulation by performing the simulation at the cross section of the device in a 2D plane. Light absorption in the Ge layer of the detector is simulated in this step (assuming a single mode TE light arriving within the waveguide for detection) and is converted into a generation rate profile which is needed for the electrical simulation in the next step. A compact model based on these parameters is created in INTERCONNECT and evaluated by characterizing the response of the device to a modulated signal. This optical generation data is then fed into the CHARGE solver to characterize various figures of merit (FOM) for Avalanche photodetectors including dark and photocurrent, responsivity and gain. The FDTD solver is used to obtain the optical generation rate profile inside the detector due to light absorption. This example covers the simulation of a Ge-on-Si Avalanche photodetector with Si multiplication layer reported in reference. Understand the simulation workflow and key results The performance figures of merit of the detector obtained from these simulations, including dark current, responsivity and gain, will be incorporated in an APD compact model which will then be used in a simple circuit simulation in INTERCONNECT. The optical simulation will be performed using FDTD and the electrical simulation using CHARGE solver. Simulate an Avalanche photodetector (APD) based on a Ge-on-Si heterostructure with the avalanche multiplication taking place in the Si layer.
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