Where do Electrons escape from ?
The electrons generated in the thin n - type AlGaAs layer drop completely into the GaAs layer to form a depleted AlGaAs layer , because the heterojunction created by different band - gap materials forms a quantum well ( a steep canyon ) in the conduction band on the GaAs side where the electrons can move quickly without colliding with any impurities because the GaAs layer is undoped , and from which they can not escape .