▁for ▁a ▁long ▁time ▁ ▁in ▁a ▁trap ▁if ▁the ▁screen ing ▁length ▁due ▁to ▁the ▁other ▁carri ers ▁is ▁small ▁in ▁comparison ▁to ▁ ▁size . ▁All ▁the ▁above ▁consider ations ▁hold ▁true ▁for ▁any ▁size ▁of ▁, ▁including ▁nan ode v ices . ▁In ▁particular ▁we ▁have ▁a ▁meaning ful ▁case ▁when ▁the ▁device ▁is ▁a ▁right ▁par alle le pip ed ▁or ▁cyl inder ▁with ▁ ▁as ▁later al ▁surface ▁and ▁u ▁as ▁the ▁unit ▁vector ▁along ▁its ▁axis , ▁with ▁the ▁bases ▁ ▁and ▁ ▁located ▁at ▁a ▁distance ▁L ▁as ▁electro des , ▁and ▁with ▁. ▁Indeed , ▁choosing ▁, ▁from ▁the ▁above ▁equation ▁we ▁finally ▁obtain ▁the ▁current ▁, ▁▁ ▁, ▁ ▁where ▁ ▁and ▁ ▁are ▁the ▁components ▁of ▁ ▁and ▁ ▁along ▁. ▁The ▁above ▁equations ▁in ▁their ▁cor pus cular ▁form ▁are ▁particularly ▁suitable ▁for ▁the ▁investigation ▁of ▁transport ▁and ▁noise ▁phen omena ▁from ▁the ▁micro scop ic ▁point ▁of ▁view , ▁with ▁the ▁application ▁of ▁both ▁the ▁analyt ical ▁approaches ▁and ▁numerical ▁statistical ▁methods , ▁such ▁as ▁the ▁Monte ▁Carlo ▁techniques . ▁On ▁the ▁other ▁side , ▁in ▁their ▁collect ive ▁form ▁of ▁the ▁last ▁terms , ▁they ▁are ▁useful ▁to ▁connect , ▁with ▁a ▁general ▁and ▁new ▁method , ▁the ▁local ▁variations ▁of ▁continuous ▁quantities ▁to ▁the ▁current ▁fl uct u ation ▁at ▁the ▁device ▁terminal s . ▁This ▁will ▁be ▁shown ▁in ▁the ▁next ▁sections . ▁ ▁No ise ▁ ▁Sh ot ▁noise ▁Let ▁us ▁first ▁evaluate ▁the ▁P SD ▁