Learning Forum

[Mariah Ha]

Hello,

I am trying to study the impulse response of a photodiode to a light pulse. Is it better to import an optical generation rate from FDTD or use a delta generation rate in charge?

[Khashayar Ghaffari]

Hi Are you interested in this analysis to characterize bandwidth? If so I would recommend looking into the transient analysis provided in the vertical photodetector example (published in the Appendix of the article). Here we use the imported optical generation rate from FDTD, and perform a Fourier transform of the impulse current response, to obtain bandwidth. The description in the article and the calculations available in the associated script should be insightful.

[Mariah Ha]

Thank you for the great help. Yes i am using those scripts and simulation examples to get some insights and i did nearly the same approch of importing the optical generation. But then i realized that there is a delta generation which i did not try to use before, and my question is can I use it as a shortcut to obtain an impulse and frequency response ?

[Khashayar Ghaffari]

The delta source can also be used to measure the impulse response of the system. This is particularly useful when characterizing the Internal Quantum Efficiency. For this, the location of the source is swept across the simulation region to obtain the weighting function profile according to the Green's function. To seen an example of this approach and find more information please check the CMOS image sensor example here (specifically step 4).