[FullRangeMan]

What is Gallium Nitride
Gallium nitride is a semiconductor material composed using materials from groups III and V in the periodic table of elements.

Physically, the material is very hard and has a Knoop hardness factor of 14.21 GPa, and GaN has some other interesting physical attributes, but it's the electrical properties that are of interest here.

Gallium nitride has a wide bandgap of 3.5 eV, which is very similar to that of silicon carbide and this makes it very suitable as a semiconductor for various devices.

GaN has some very useful properties that make it ideal for a number of power applications. It can tolerate high operating voltage, handle high power levels, and operate at high frequencies, making it ideal for many RF applications, from mobile communications, 5G, 6G, etc., to aerospace and satellite communications.

     Note on Gallium Nitride:
     Gallium nitride is a semiconductor material that is physically very hard, but it also acts as a semiconductor that has a wide bandgap and allows high levels of power to be used at high frequencies when used in semiconductor devices.

     To manufacture the GaN electronics themselves, gallium nitride needs to be formed into what is often called a pseudo-substrate – it is not possible to make a substrate from GaN itself for chemical reasons.

Typically GaN is deposited on silicon or silicon carbide to give GaN on silicon, often referred to as Gan on Si or GaN on silicon carbide referred to as GaN on SiC.

GaN on silicon devices are cheaper than GaN on silicon carbide, but GaN on SiC offers several advantages:
#= GaN on SiC has higher thermal conductivity: Due to the higher thermal conductivity of silicon carbide, overall GaN on SiC has a higher thermal conductivity, typically three times higher than GaN on silicon. This means that GaN on SiC devices has higher efficiency, higher reliability and higher power density when compared to GaN on silicon devices of the same geometry.

#=  Silicon carbide has lower relative permittivity: The low relative permittivity of silicon carbide means that GaN in SiC devices can have a higher bandwidth than GaN in silicon devices.

Another possible substrate is synthetic diamond. This offers a high level of thermal conductivity, but the cost is much higher than GaN on silicon and GaN on SiC.

GaN (gallium nitride) Field Effect Transistors and HEMTs: what they are and how they work

Gallium nitride is a semiconductor material that is increasingly being used to provide better performance, especially in high-speed and RF FETs and HEMTs.

Gallium nitride, GaN FETs or GaN transistors are increasingly being used in many power modules and devices, as well as in RF power circuit designs. Often the terms GaN HEMT and GaN transistor are used interchangeably.

The high electron mobility of gallium nitride, GaN, allows the fabrication of semiconductor devices that have a low ON resistance value combined with a very high switching frequency capability.

These benefits mean that GaN FETs are being used in many new electronic circuit designs for everything from power systems, to electric vehicles and renewable energy applications, to RF power amplifiers, other RF design circuits and the like.

GaN FETs use the interface between two semiconductor materials to produce a very thin region known as 2DEG (see below for an explanation) to provide very high levels of electron mobility that result in the formation of GaN HEMTs or high electron mobility transistors.

Often, GaN transistor technology is used to manufacture monolithic microwave ICs, MMICs, which provide high levels of performance at microwave frequencies. These benefits mean that GaN FETs are being used in many new circuit designs electronics for everything from power systems, to electric vehicles and renewable energy applications to RF power amplifiers, other RF design circuits and the like.

GaN FETs use the interface between two semiconductor materials to produce a very thin region known as 2DEG (see below for an explanation) to provide very high levels of electron mobility that result in the formation of GaN HEMTs or high electron mobility transistors.

Often, GaN transistor technology is used to manufacture monolithic microwave ICs, MMICs, which provide high levels of performance at microwave frequencies.

[FullRangeMan]

What is 2DEG
There are many informative websites and articles about HEMTs that refer to 2DEG without an explanation of what it is.

In essence, 2DEG stands for two-dimensional electron gas and is a core concept behind HEMT technology.

GaN HEMT basic concept:
GaN FETs or GaN transistors are essentially high electron mobility transistors or HEMTs. The HEMT concept has been known for many years and has been used in other FET technologies.

The chemical structure of gallium nitride is called the “Wurtzite” structure. It is this structure that is key to the HEMT operation of GaN transistors.

The wurtzite structure of the GaN crystal gives the material a piezoelectric effect. This is predominantly achieved because of charged elements within the crystal lattice. If the structure is subjected to tension, the deformation will cause a very small displacement in the atoms in the network that generate an electric field: the higher the tension level, the greater the electric field created.

When the aluminum gallium nitride, AlGaN, layer is grown on top of the gallium nitride, GaN crystal, the interface between the two crystal lattices does not completely coincide and therefore a deformation is set up.

voltage induces a two-dimensional electron gas, 2DEG. This two-dimensional electron gas is highly conductive because the electrons are confined within a very small region at the interface. This practically doubles the electron mobility from about 1000 cm 2 /V ˙ s in normal GaN to between 1500 and 2000 cm 2 /V ˙ s in the 2DEG region. This high electron concentration and mobility is the basis of HEMTs and, in this case, GaN HEMT.

The quality of 2DEG was found to have a significant impact on electronic transport across the interface and therefore on the properties of the final devices.

The flow of electrons through the two-dimensional region – effectively the channel – is controlled by the gate potential in the normal way for a FET.


GaN transistor structure and operation
All GaN FETs or HEMTs employ the same basic technology and utilize the HEMT structure with its two-dimensional electron gas region providing the fundamental mode of operation for the device.

GaN HEMTs are available in depletion mode and enhancement mode varieties.

     Depletion mode: A depletion mode GaN transistor is normally on; and to turn it off, a negative voltage relative to the drain and source electrodes must be applied to the gate.

     Enhancement Mode: Enhancement mode or electronic mode FETs are the ones that are normally disabled. They are activated by applying a positive voltage to the gate relative to the drain and source.

Naturally, the structures of real FETs are slightly different for both types. Furthermore, there are various approaches taken by different manufacturers of these electronic components, but the basic principles of operation are exactly the same.

       Depletion Mode GaN Transistor
The basic structure for a GaN HEMT depletion mode consists of three electrodes, source, drain and gate, as would normally be expected for a field effect transistor.

The source and drain are manufactured so that they are not in the AlGaN layer, but instead they directly contact the GaN region and therefore the 2DEG.
Basic structure concept for a GaN HEMT depletion modeBasic structure concept for a GaN HEMT depletion mode

Since this is a HEMT in depletion mode, this creates a short circuit between the drain and the source.

To reduce the flow of electrons through the 2DEG, a negative potential is applied to the gate relative to the drain and source, this depletes the electron channel, thus reducing the conductivity of the channel.

There are several ways to manufacture these devices. It is possible to create a Schottky gate electrode by depositing a layer of metal directly onto AlGaN using details such as nickel-gold or platinum. A Schottky barrier was created to control the conductivity of the channel.

Deletion-mode GaN HEMTs were also fabricated by using an insulating layer and then depositing a metal gate on top of it. This approach has many similarities to silicon MOSFET technology.

Although depletion mode transistors are applicable in many electronic circuit designs, they tend not to be used for power systems because it is not advisable to have the large current source generally available in power systems, with a device which is short-circuited when turned on.

 Enhancement Mode GaN Transistor
There are several methods that have been used to create enhancement mode GaN transistors. Typically, they are a little more complicated to manufacture, but they tend to be widely used.

There are five main structures that are used for enhancement mode GaN FETs. They are: Cascode Hybrid, Direct Drive Hybrid, Implanted Gate, pGaN Gate and Recessed Gate.

Some of the main framing techniques are described below:
With GaN semiconductor technology developing rapidly due to the advantages it brings to RF design and the design of a number of power projects, there will be more developments in the coming years and new formats and structures for devices.
     Recessed gate structure: The recessed gate structure is created by thinning the AlGaN barrier region above the 2DEG plane. This reduces the voltage generated by the piezoelectric effect in this region. A point is reached where the voltage generated by the strain in the crystal lattice is less than the internal voltage of the metallic Schottky gate and with zero bias the 2DEG plane is eliminated here. Basic structure concept for an advanced mode GaN HEMTSe recessed gate a positive bias is placed on the gate, electrons are attracted back to the interface between the two semiconductor materials and current can flow depending on the bias level.
With GaN semiconductor technology developing rapidly due to the advantages it brings to RF design and the design of a number of power projects, there will be more developments in the coming years and new formats and structures for devices.

GaN Transistor Applications
GaN HEMT or transistor technology is used in many areas of electronic circuit design and RF design. The parameters of the GaN transistors that are produced mean that they are applicable for many different applications where high power, high frequency or high performance or any combination of these parameters are required.

     Power Systems: With everything from switching power supplies, power switching, electric vehicles and the like needing power switching devices, GaN HEMT lends itself to many of these applications. The fast switching and low on-resistance of these devices means efficiency levels are high. The high breakdown voltages also mean that relatively high level switching can be achieved.

RF Power Amplifiers:
  The combination of high power and high speed capability means that GaN FET technology is an ideal candidate for RF power amplifiers. GaN FET technology offers many advantages, from high reliability and high levels of efficiency to the ability to operate at high frequencies. As a result, GaN technology is used in many RF power amplifiers for a wide variety of applications, including mobile communications where it is used, particularly in base stations for 5G, 6G, etc. It is also used in satellite applications where its high reliability and resilience as well as the high levels of efficiency that can be returned are of great interest.

     GaN RF Switches: Another application for GaN FETs is as RF switches. There are many situations where RF switching is required and these electronic components provide the ideal means of switching the RF circuit. They are capable of handling much higher power levels than GaAsFETs, which are also used in RF designs for switching. GaN FETs are capable of using the same basic RF design architecture as GaAsFET switches, but with changes in the values of electronic comments, etc. they have a high level of isolation, excellent linearity, and can handle much higher power levels than GaAsFETs.

     Low-Noise GaN Amplifiers: The high-frequency capability of GaN FETs means they are capable of not only operating as a power amplifier, but also on the receive side as a low-noise front-end amplifier, LNA. In this role, these electronic components are capable of performing well while offering a low noise figure, essential in this role within an RF circuit design. However, in view of their high power capability and overall robustness, they are capable of tolerating high input power levels, unlike GaAsFETs, which can be quite susceptible to overload and ESD. Thus, GaN FETs are beginning to be used in radar installations as one of many examples. An advantage of their high tolerance to RF levels is that a circulator is not always required. Since the circulator will experience loss, this can reduce the overall sensitivity of the receiver as well as absorb some of the transmitter power.

     GaN Mixers: Gallium nitride FETs are also finding use in high-performance RF mixers. Here, the high level of linearity that these electronics can provide and their resilience to high power levels means that they are replacing GaAsFET-based mixers in many new RF designs.

     MMIC: GaN FET technology is also used in many monolithic microwave ICs, MMICs. With MMICs needing to extend their frequency ranges across a variety of RF design blocks, GaN technology is ideal for use in MMICs that provide a variety of RF functions.

There are many areas in which GaN technology is being used, and as the technology develops, there is always the possibility that electronic components using GaN technology could be used in other areas.

Gallium nitride technology is becoming increasingly prevalent in many areas of power and radio frequency circuit design. The devices still cost more than some of their counterparts using older technology, but the benefits sometimes outweigh the cost penalties and in many cases result in a lower overall cost of the item. Hence, GaN FETs or GaN HEMTs are being seen in many RF designs as well as many new circuit designs for power systems.

[FullRangeMan]

GaN Transistor Applications
GaN HEMT or transistor technology is used in many areas of electronic circuit design and RF design. The parameters of the GaN transistors that are produced mean that they are applicable for many different applications where high power, high frequency or high performance or any combination of these parameters are required.

     Power Systems: With everything from switching power supplies, power switching, electric vehicles and the like needing power switching devices, GaN HEMT lends itself to many of these applications. The fast switching and low on-resistance of these devices means efficiency levels are high. The high breakdown voltages also mean that relatively high level switching can be achieved.

RF Power Amplifiers:
  The combination of high power and high speed capability means that GaN FET technology is an ideal candidate for RF power amplifiers. GaN FET technology offers many advantages, from high reliability and high levels of efficiency to the ability to operate at high frequencies. As a result, GaN technology is used in many RF power amplifiers for a wide variety of applications, including mobile communications where it is used, particularly in base stations for 5G, 6G, etc. It is also used in satellite applications where its high reliability and resilience as well as the high levels of efficiency that can be returned are of great interest.

     GaN RF Switches: Another application for GaN FETs is as RF switches. There are many situations where RF switching is required and these electronic components provide the ideal means of switching the RF circuit. They are capable of handling much higher power levels than GaAsFETs, which are also used in RF designs for switching. GaN FETs are capable of using the same basic RF design architecture as GaAsFET switches, but with changes in the values of electronic comments, etc. they have a high level of isolation, excellent linearity, and can handle much higher power levels than GaAsFETs.

     Low-Noise GaN Amplifiers: The high-frequency capability of GaN FETs means they are capable of not only operating as a power amplifier, but also on the receive side as a low-noise front-end amplifier, LNA. In this role, these electronic components are capable of performing well while offering a low noise figure, essential in this role within an RF circuit design. However, in view of their high power capability and overall robustness, they are capable of tolerating high input power levels, unlike GaAsFETs, which can be quite susceptible to overload and ESD. Thus, GaN FETs are beginning to be used in radar installations as one of many examples. An advantage of their high tolerance to RF levels is that a circulator is not always required. Since the circulator will experience loss, this can reduce the overall sensitivity of the receiver as well as absorb some of the transmitter power.

    GaN Mixers: Gallium nitride FETs are also finding use in high-performance RF mixers. Here, the high level of linearity that these electronics can provide and their resilience to high power levels means that they are replacing GaAsFET-based mixers in many new RF designs.

    MMIC: GaN FET technology is also used in many monolithic microwave ICs, MMICs. With MMICs needing to extend their frequency ranges across a variety of RF design blocks, GaN technology is ideal for use in MMICs that provide a variety of RF functions.

There are many areas in which GaN technology is being used, and as the technology develops, there is always the possibility that electronic components using GaN technology could be used in other areas.

Gallium nitride technology is becoming increasingly prevalent in many areas of power and radio frequency circuit design. The devices still cost more than some of their counterparts using older technology, but the benefits sometimes outweigh the cost penalties and in many cases result in a lower overall cost of the item. Hence, GaN FETs or GaN HEMTs are being seen in many RF designs as well as many new circuit designs for power systems.