Resonant Diode

RESONANT DIODE

• It is a device that has two tunneling junctions. Its I-V characteristic shows negative differential resistance characteristic. 

Definition

A resonant tunneling diode (RTD) is a diode with resonant tunneling structure. The electrons can tunnel through some resonant states at certain energy levels.

Principle

When electron (wave) incident with energy equal to energy level of a potential well of thin barrier, then the tunneling reaches its maximum value. This is known as resonant tunneling.

Structure of RTD

A typical resonant tunneling diode structure is made by using n-type GaAs for the regions to the left and right of both barriers (regions 1 and 5) (Fig. 7.14).

The intrinsic GaAs is for the well region (region 3) and Al Ga As or Al As for the barrier material (regions 2 and 4).

Working 

Tunneling control

Tunneling is controlled by applying a bias voltage across the device.

Without applied bias

For the case of no applied bias, the energy band diagram is shown in fig. 7.15(a).

Practically it is very difficult to control the barrier height as well as the width of the potential well to match with the energy of the electron. This energy matching and hence resonant tunneling could be achieved by. biasing the potential barriers.

With applied bias

When voltage is applied, the band diagram shifts and if the voltage is varied until the quantized discrete energy level corresponding to the potential well matches with the energy of the electron wave, resonant tunneling occurs. Such behavior is shown in fig. 7.15(b).

Current - Energy characteristic for a resonant tunneling diode

When the incident electron energy E is very different from the energy of a discrete state En, transmission is low. As E tends to En, transmission will increase, becoming a maximum when E = En.

As E increases, tunneling will increase, reaching a peak when E = E1. After that point, a further increase in E will result in a decreasing current, as shown in Fig. 7.16.

This decrease of current with an increase of bias is called negative resistance. Further peaks and valleys will occur as E approaches, and then moves across other discrete energy states.

Application and uses of Resonant Tunneling Diodes (RTD)

1. One area or active application is building oscillators and switching devices that operate at tera hertz frequencies. 

2. RTDs are very good rectifiers.

3. They are used in digital logic circuits. 

4. They are also used in inverters, memory cells and transistors (Resonant Tunneling Transistors (RTTs)

Advantages

• Resonant Tunneling diodes are very compact.

• They are capable of ultra-high-speed operations because the quantum tunneling effect through the very thin layers is a very fast process.