Advantages of HEMT | disadvantages of HEMT
This page covers advantages and disadvantages of HEMT. It mentions HEMT advantages or benefits and HEMT disadvantages or drawbacks.
What is HEMT?
HEMT is the short form of High Electron Mobility Transistor. It is advanced version of MESFET with higher electron mobility on the order of 105 cm2/V. This is achieved by modulating-doping technique. The high electron mobility of HEMT helps to achieve higher gain at low noise figure upto frequencies of 60 GHz.
The figure-1 depicts HEMT structure with its construction layers. As shown, hetero-junction structure GaAs-AlGaAs with selecting doping acts as basic building block. On semi-insulating GaAs substrate, buffer layer is provided. Above buffer layer, there are two layers viz. Si doped n-type AlGaAs layer and undoped GaAs layer. 2-DEG is created between undoped layer and doped layer. Refer HBT vs HEMT >> and HEMT drain current calculator >>.
The electron concentration controls both enhancement and depletion mode operations. When temperature decreases, electron mobility increases from 103 cm2/V to 105 cm2/V.
HEMT is also known as TEGFET (Two dimensional Electron GaAsFET) and HFET (Heterojunction FET).
There are different types of HEMTs based on materials used.
• InP HEMT
• AlGaN/GaN HEMT
• AlGaAs/GaAs HEMT
Benefits or advantages of HEMT
Following are the benefits or advantages of HEMT with GaAs-AlGaAs heterojunction:
➨Offers high Gain
➨Offers high Switching Speed
➨Offers low Noise operations
➨Useful over 5 to 100 GHz range
➨Offers higher efficiency
➨Offers high Pmax
➨High electron mobility as mentioned.
➨Small source resistance
➨High gain-bandwidth product, FT due to high electron velocity in large electric fields
➨High transconductance due to small gate-to-channel separation.
➨High output resistance
➨Higher schottky barrier height due to deposition of schottky metal on AlGaAs instead of GaAs.
Drawbacks or disadvantages of HEMT
Following are the disadvantages of HEMT made of GaN:
➨ Gates of GaN HEMT are more resistive. Hence this device requires minimum amount of current to keep it ON. Moreover it is voltage sensitive. Enhancement mode GaN HEMT available in the market, requires applied voltage of 5V or lower.
➨The HEMT devices require highly skilled engineers for development and testing.
➨GaN HEMTs require very high speed drivers. Moreover they require very fast diodes in parallel to minimize losses.