▁gate ▁voltage . ▁One ▁should ▁be ▁aware , ▁though , ▁that ▁the ▁F ET - m ob ility ▁is ▁significantly ▁larger ▁than ▁the ▁TO F ▁mob ility ▁because ▁of ▁the ▁charge ▁car rier ▁concentration ▁in ▁the ▁transport ▁channel ▁of ▁a ▁F ET ▁( see ▁below ). ▁Other ▁ways ▁to ▁determine ▁the ▁charge ▁car rier ▁mob ility ▁involves ▁meas uring ▁space ▁charge ▁limited ▁current ▁( S CLC ) ▁flow ▁and ▁" car rier ▁extra ction ▁by ▁linear ly ▁increasing ▁voltage ▁( CE LI V ). ▁ ▁In ▁order ▁to ▁character ize ▁the ▁morph ology ▁of ▁sem icon duct or ▁films , ▁one ▁can ▁apply ▁atomic ▁force ▁micro sc opy ▁( AF M ) ▁sc anning ▁electron ▁micro sc opy ▁( SE M ) ▁and ▁Gra zing - inc idence ▁small - angle ▁scatter ing ▁( G IS AS ). ▁ ▁Char ge ▁transport ▁In ▁contrast ▁to ▁organ ic ▁cry st als ▁investig ated ▁in ▁the ▁ 1 9 6 0 - 7 0 s , ▁organ ic ▁sem icon duct ors ▁that ▁are ▁now ad ays ▁used ▁as ▁active ▁media ▁in ▁opt oe lect ron ic ▁devices ▁are ▁usually ▁more ▁or ▁less ▁dis ordered . ▁Com b ined ▁with ▁the ▁fact ▁that ▁the ▁struct ural ▁building ▁blocks ▁are ▁held ▁together ▁by ▁compar atively ▁weak ▁van ▁der ▁Wa als ▁forces ▁this ▁pre cludes ▁charge ▁transport ▁in ▁del ocal ized ▁val ence ▁and ▁condu ction ▁bands . ▁Instead , ▁charge ▁carri ers ▁are ▁local ized ▁at ▁mole cular ▁entities , ▁e . g . ▁o lig