Doping is a process of mixing sum impurity in a iinsulator andthen that acts like conductor...The materials which are said tobehave like this are called semi conductor . it is very often toknow that when we add some impurity ,the bonding inside the semiconductor just breaks and rejoins itself with new commer electronsof the impurity...major semi conductors are GaAs,Si,Ge ...we cannotice out that if 1 electron is added to silicon(si),it reffers toa conductivity of 10 million electrons...so just think of thisexample,when we add extra impurity...what wouldhappen?????????resulting a great vacancy for electrons tocontinueue their activities. Coming to depletion region...it isjust a smaal region where ions are formed + on N types and - to PTypes .though it is very small but it cannot be neglected ....Hencewe improve the ratio of impurity added.....the free electronsavailable are also in a huge number so a litttle space for theDepletion region remains there but it never ends....i-e depletionregion can not be removed finally