Theory of Resonant Tunnelling and Surface Superlattices

Abstract

One of the attractive features of working with constrained-dimensionality devices is the ability of applying textbook quantum mechanics to their understanding, and still achieving a reasonable degree of success in this task. Perhaps the classic example of this is tunnelling, particularly in the case of the resonant-tunnelling device. The concept of tunnel diodes goes back several decades, and is implemented in very heavily doped p−n junction diodes. In this case the tunnelling is through the forbidden gap region, and involves electrons making transitions from the conduction band to the valence band, and vice versa. In the present context, however, we are concerned with fabricating tunnel barriers by band-gap engineering. Thus, we can separate two GaAs regions by a thin barrier region of GaA1As, and the tunnel barrier is formed by the conduction (and valence) band discontinuity. In this sense, the barrier formed is a textbook example, and the results on tunnelling current can be calculated in a straightforward manner.