▁p - type ▁do ping ▁where ▁N ▁vac an cies ▁are ▁abund ant ▁due ▁to ▁its ▁high ▁v apor ▁pressure ▁resulting ▁in ▁high ▁Ga ▁d ang ling ▁bond ▁density . ▁These ▁states ▁are ▁close ▁to ▁the ▁condu ction ▁band ▁edge ▁and ▁therefore ▁act ▁as ▁don ors . ▁When ▁p - type ▁accept or ▁dop ants ▁are ▁introduced , ▁they ▁are ▁immediately ▁compens ated ▁for ▁by ▁the ▁N ▁vac an cies . ▁With ▁these ▁shall ow ▁states , ▁their ▁treatment ▁is ▁often ▁considered ▁as ▁an ▁analog ue ▁to ▁the ▁hydro gen ▁atom ▁as ▁follows ▁for ▁the ▁case ▁of ▁either ▁an ion ▁or ▁c ation ▁vac an cies ▁( hole ▁effective ▁mass , ▁m *, ▁for ▁c ation ▁and ▁electron ▁m * ▁for ▁an ion ▁vac an cies ). ▁The ▁binding ▁energy , ▁E c - E db , ▁is ▁▁ ▁where ▁U =- q 2 /( 4 π ε ε rr ) ▁is ▁the ▁electro static ▁potential ▁between ▁an ▁electron ▁occup ying ▁the ▁d ang ling ▁bond ▁and ▁its ▁ion ▁core ▁with ▁ ε , ▁the ▁free ▁space ▁perm itt ivity ▁constant , ▁ ε r , ▁the ▁relative ▁perm itt ivity , ▁and ▁r ▁the ▁electron - ion ▁core ▁separation . ▁The ▁simpl ification ▁that ▁the ▁electron ▁transl ational ▁energy , ▁K E =- U / 2 , ▁is ▁due ▁to ▁the ▁vi rial ▁theorem ▁for ▁cent ros ym metric ▁potential s . ▁As ▁described ▁by ▁the ▁Bo hr ▁model , ▁r ▁is ▁subject ▁to ▁quant ization ▁. ▁The ▁electron ▁momentum ▁is ▁p