▁ ▁where ▁only ▁the ▁fl uct u ation ▁terms ▁are ▁time ▁dependent . ▁The ▁mob ility ▁fl uct u ations ▁can ▁be ▁due ▁to ▁the ▁motion ▁or ▁to ▁the ▁change ▁of ▁status ▁of ▁defect s ▁that ▁we ▁neglect ▁here . ▁Therefore , ▁we ▁as cribe ▁the ▁origin ▁of ▁g - r ▁noise ▁to ▁the ▁tra pping - det ra pping ▁processes ▁that ▁contribute ▁to ▁ ▁through ▁the ▁other ▁two ▁terms ▁via ▁the ▁fl uct u ation ▁of ▁the ▁electron ▁number ▁ ▁in ▁the ▁energy ▁level ▁ ▁of ▁a ▁single ▁trap ▁in ▁the ▁channel ▁or ▁in ▁its ▁neighborhood . ▁Indeed , ▁the ▁charge ▁fl uct u ation ▁ ▁in ▁the ▁trap ▁generates ▁variations ▁of ▁ ▁and ▁of ▁. ▁However , ▁the ▁variation ▁ ▁does ▁not ▁contribute ▁to ▁ ▁because ▁it ▁is ▁odd ▁in ▁the ▁u ▁direction , ▁so ▁that ▁we ▁get ▁▁ ▁, ▁ ▁from ▁which ▁we ▁obtain ▁▁ ▁, ▁ ▁where ▁the ▁reduction ▁of ▁the ▁integration ▁volume ▁from ▁ ▁to ▁the ▁much ▁smaller ▁one ▁ ▁around ▁the ▁defect ▁is ▁just ified ▁by ▁the ▁fact ▁that ▁the ▁effects ▁of ▁ ▁and ▁ ▁fade ▁within ▁a ▁few ▁multi ples ▁of ▁a ▁screen ing ▁length , ▁which ▁can ▁be ▁small ▁( of ▁the ▁order ▁of ▁nan om eters ▁in ▁graph ene ); ▁from ▁G auss ' s ▁theorem , ▁we ▁obtain ▁also ▁ ▁and ▁the ▁r . h . s . ▁of ▁the ▁equation . ▁In ▁it ▁the ▁variation ▁ ▁occurs ▁around ▁the ▁average ▁value ▁ ▁given ▁by ▁the ▁F erm i - Di rac ▁factor