Question

 

Electronic density of states (DOS) is an important physical quantity that dictates materials’ electronic properties.

(a) Please also provide arguments and descriptions about how the dimensionality of a system can affect its DOS.

(b) Please give two examples of nanostructure or nano‐device that exhibit electronic quantum phenomena, describe their physical property and potential application in detail.

Answer 1

b) The two examples are:

RTD, resonant tunneling diode:

This is a quantum device a conventional heavily doped bipolar semiconductor. Electrons tunnel through two barriers separated by a well in flowing source to drain in a resonant tunneling diode. Tunneling is also known as quantum mechanical tunneling. The flow of electrons is controlled by diode bias. This matches the energy levels of the electrons in the source to the quantized level in the well so that electrons can tunnel through the barriers. The energy level in the well is quantized because the well is small. When the energy levels are equal, a resonance occurs, allowing electron flow through the barriers.

Single electron transistor:

If a pair of conductors, superconductors, or semiconductors are separated by a pair of tunnel barriers (insulator), surrounding a tiny conductive island, like a quantum dot, the flow of a single charge (a Cooper pair for superconductors) may be controlled by a gate. This is a single electron transistor. Increasing the positive charge on the gate, allows an electron to tunnel to the island. If it is sufficiently small, the low capacitance will cause the dot potential to rise substantially due to the single electron. No more electrons can tunnel to the island due the electron charge. This is known at the coulomb blockade. The electron which tunneled to the island, can tunnel to the drain.