We saw that in a heterojunction in which the spike and notch occurred in the conduction band (as in Figure 6.12), it was possible for electrons in the valence band of the narrow-gap material to tunnel a short distance into the forbidden band of the wide-band-gap material. This tunneling induced a dipole that produced a discontinuity in the bands at the junction. Consider a Pn heterojunction such as that in Figure P6.3. Comment on the possibility of tunneling-induced dipoles in this case.

Figure P6.3

Figure 6.12 Equilibrium energy band diagram of an arbitrary Type I Np heterojunction as predicted by the electron affinity model. Electrons from the valence band of semiconductor B can tunnel a short distance into the forbidden gap of A, thus creating an interfacial dipole.

  

Egl Notch Eg2 -Spike Evac Ec Ef Ev