A resonant tunneling diode (RTD) is a type of diode with a resonant tunneling structure that allows electrons to tunnel through various resonant states at certain energy levels. RTDs can be fabricated using many different types of materials (such as III-V, type IV, II-VI semiconductors) and different types of resonant tunneling structures (such as heavily doped pn junction in Esaki diodes, double barriers, triple barriers, quantum wells, quantum wires or quantum dots).
The image above shows the operation of a double barrier resonant tunneling diode. The region between the two barriers acts as a quantum well with discrete energy states. Resonant tunneling through the double-barrier structure occurs when the energy of the electrons flowing from the source (left) coincides with one of the discrete energy levels in the well. The position of the bounded states within the well can be modulated with a gate bias . This results in what can be seen in the I-V characteristics of peak current and valley current. The region with the reducing current is known as a negative differential resistance region.