HEMT - High Electron Mobility Transistor

Introduction to HEMT :

The full form of HEMT is High Electron Mobility Transistor. It is the sort of field effect transistor utilized to provide a combination of low noise figure and very high levels of performance at microwave frequencies. 

High electron mobility transistors (HEMTs) have gained a lot of attention in recent years because of their enhanced electron transport for high speed and high power applications. HEMT devices are outperforming traditional fieldeffect transistors (FETs) in terms of high frequency performance, power density, and efficiency.

The HEMT or High Electron Mobility Transistor is used for very high frequency microwave applications where performance is essential.


Construction of HEMT (High Electron Mobility Transistor) :

To Construct an HEMT, the specialized P-N Junction is used. It is the main key element which is known as a hetero-junction and consists of a junction that uses different materials either side of the junction. Instead of the p-n junction, a metal-semiconductor junction (reverse-biased Schottky barrier) is used, where the Schottky barriers allows fabrication to close geometrical tolerances. The most common materials used aluminium gallium arsenide (AlGaAs) and gallium arsenide (GaAs).

Cross Section of HEMT

Aluminium Gallium Arsenide (AlGaAs) and Gallium Arsenide (GaAs) are the most widely used materials. Gallium Arsenide is commonly utilized because it has a high level of basic electron mobility and has greater mobilities and carrier drift velocities than Si.

In the diagram above, an intrinsic layer of Gallium Arsenide is laid down on top of a semi-insulating layer of Gallium Arsenide. This is around 1 micron thick. Then, on top of this layer, a very thin coating of intrinsic Aluminium Gallium Arsenide with a thickness of 30 to 60 Angstroms is applied. The primary function of this layer is to keep the Hetero-junction interface separate from the doped Aluminium Gallium Arsenide region.

The doped layer of Aluminium Gallium Arsenide about 500 Angstroms thick is set down above this as shown in the diagram. The exact thickness of this layer is required and special techniques are required for the control of the thickness of this layer.


HEMT Operation

How HEMTs Works?

The functioning of the HEMT differs from that of other types of FETs, and as a result,  it can provide significantly better performance than typical junction or MOS FETs, particularly in microwave RF applications.  

Electrons from the n-type region move through the crystal lattice and many remain close to the hetero-junction. These electrons form a layer that is only one electron thick form which is a two dimensional electron gas. Within this region the electrons are able to move freely because there are no other donor electrons or other items with which electrons will collide and the mobility of the electrons in the gas is very high.

The bias voltage provided to the gate generated as a Schottky barrier diode is used to modulate the number of electrons in the channel formed from the 2 D electron gas, and so controls the device's conductivity.The width of the channel can be changed by the gate bias voltage.


Advantages of HEMT:

HEMTs have several advantages over conventional FETs, including:

1. Higher electron mobility: The use of a heterojunction allows HEMTs to achieve much higher electron mobilities than conventional FETs. This makes them ideal for high-frequency applications, where the ability to switch signals quickly is important.

2. Lower noise figure: HEMTs have a lower noise figure than conventional FETs. This makes them ideal for applications where low noise is important, such as radar systems and satellite receivers.

3. Higher power handling capability: HEMTs can handle more power than conventional FETs. This makes them ideal for applications where high power is required, such as power amplifiers for mobile devices.


Applications of HEMT:


1. HEMTs are used in applications where microwave millimeter wave communications is conducted.

2.HEMT devices are used in a wide range of RF design applications including cellular telecommunications, radar, imaging, as well as radio astronomy. 

3. HEMTs are used where high gain at high frequencies is required along with low noise values. They are also used in voltage converter applications. 

4.HEMT devices are widely used in small signal amplifiers, power amplifiers, oscillators and mixers operating at frequencies up to 60 GHz.


Future of HEMTs

The future of HEMTs looks bright. As the demand for high-frequency devices continues to grow, HEMTs are likely to become even more widely used. HEMTs are also being developed for new applications, such as quantum computing and terahertz communications.


This is all about HEMT (High Electron Mobility Transistor) and its applications. If you have any queries on this topic leave the comments below.

 


We hope you liked this article on HEMT Working and Operation, we will keep on posting post articles on various electronics topics, so bookmark and keep visiting our Site. Thank you.