Abstract
In this paper homopolar and heteropolar heterojunctions have been analysed. The energy band discontinuities at heteropolar heterojunctions have been obtained self-consistently by analysing the charge induced at the interface. The crucial point of the analysis is the flow of charge between both semiconductors as a function of the difference in energy between their charge neutrality levels. For homopolar heterojunctions interface relaxation is discussed and it appears to be a function of the state of occupation of the interface. The analysis gives a relaxation of 4% for the 111-GeGaAs interface.