SnSe crystal grown by dvt method were studied for the photodetector application. Here results for different colors show differences. But mainly it is observed that rise time of the pulse is higher than decay time. Why? What is the wavelength dependency of photodetector?
It may be due to surface defects. If the surface is not smooth then there are chances that photo activated charge carriers recombine with the defects before making it to the other electrode. Therefore it is taking more time to rise and less time to decay.
Yes may be it's right. But here some many changes with different lights sources.. so why that type of behavior shown?
I don't know pecularities of SnSe crystals, but generally one may note: 1) at some wavelength range you might see photoresponse defined by trap absorptions, such traps may have widely different time constants 2) light colours may have widely different penetration depth 3) the light be strong enough to change resistivity of the materail dramatically and so changing dielectric relaxation constant which may e.g. change rise/fall time.
Geerally in phtoconductors there are at least 3 important time constnts at play a) Lifetime of non-equlibrium Carriers B) Dielectric Relaxation Time C) Charge collection Time.
In addition, the light intensity might be such that significatly impacts those constants.
Also, you may have 'quadratic recombination' : when light induced concentration of holes and electrons is much bigger than in the dark the decay is not exponencial but proportioal to squar of carrier concetration dN/dt =-K* N^2, and that may give you different rise/fall times too.
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