The calculation of the electron density starts by assuming that the semiconductor is neutral so that there is a zero charge density in the material. The hole concentration in equilibrium is written as a function of the electron density by using the mass action law. This yields the following relation between the electron density and the ionized impurity densitie

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If you want to calculate light-driven charge generation rate, then I can recommend you to refer this link: http://www.pveducation.org/pvcdrom

Thanks Shaikh and Dowon

I think it is possible to apply laser parameters into the generation formula from

that site Dowon recommended me.