I have performed the neutron irradiation on the PIN Diode. I have found that the forward bias cut-in volatge has been shifted.
Why these shift been observed in the neutron irradiated PIN Diode?
Please some one explain the phenomena behind the shift in the cut-in voltage of PIN Diode?
To understand the shift, you have to start understanding the effects of neutron radiation (see https://en.wikipedia.org/wiki/Neutron_radiation):
in opposition to the effects on organisms (mainly ionization effects), I'd guess that the effects of 'collision cascades' (https://en.wikipedia.org/wiki/Neutron_radiation#Effects_on_materials) and 'neutron capture' (see https://en.wikipedia.org/wiki/Neutron_capture) are prevalent - both damaging and degrading your previously 'perfect' diode and thus altering the characteristics.
Manoj,
The particle radiation effect on the pin diode was investigated and the results are published in the literature. The colleague Dreher hinted this in his post. I agree with his explanation. However i would like to add some comments:
The neutron irradiation leads to damage in the crystalline structure of the pin diode and produce many geometrical defects. These geometrical defects act as an effective recombination centers reducing the minority carrier lifetime. These defects cause also an increase in the scattering of the mobile charge carriers in their diffusion or drift in the material. Therefore the effective series resistance of the diode increases. The decrease in the minority cattier lifetime causes an increase in the recombination rate and consequently an increase in the reverse saturation current. Based on the theory of the pin diode,the ratio W/L of the diode controls the series resistance of the diode such that the series resistance increases as W/L increases. Where w is the thickness of the I region and L is the diffusion length. The diffusion length L= square root of DTau. D is the diffusion length and the Tau the lifetime. Both decrease with the neutron irradiation..
By inspecting the forward I-V curves one can see that the shift to higher forward voltage by the neutron irradiation, one can conclude that the increase of the series resistance due to the neutron irradiation dominates the increase in the reverse saturation current.
My discussion is based on the the paper given in the link: http://ro.uow.edu.au/cgi/viewcontent.cgi?article=5824&context=engpapers
wish you success
In addition to damage to the crystal structure, depending on the neutron temperature (energy) you may actually be transmuting some of the 30Si (about 3% of natural silicon) to 31P - changing the doping levels. Depending on the exact type of diode, this may cause some shift in the cut-in voltage.
https://en.wikipedia.org/wiki/Doping_(semiconductor)#Neutron_transmutation_doping
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