Silicon technology is nearing its apex. Meanwhile, faster, more efficient circuits are still in demand. One way forward from here is for researchers and companies to look into different materials to produce the devices of the future.
One material in particular that has piqued the industry’s interest is gallium nitride or GaN, which is already seeing increased use in optoelectronics. In general, GaN transistors are more efficient and faster compared to traditional silicon devices. But, if such is the case, what constraints are preventing it from dethroning silicon?
Here’s a look at where GaN is right now.
Gan Versus Silicon
When looking at the physical properties of GaN, it is easy to see why it is such a promising semiconductor. GaN is a binary III/V direct bandgap semiconductor with a band gap of 3.4eV, which is several times greater than silicon’s band gap of 1.1eV.
GaN’s wider bandgap makes it ideal for optoelectronics and is essential in the production of devices like UV LEDs, wherein frequency doubling is not practical. GaN semiconductors not only have 1000 times the electron mobility of silicon, but they can also operate at higher temperatures while retaining their characteristics (up to 400 degrees Celsius). GaN would be highly desirable in high frequency (THz), high temperature, and high power environments due to these combined properties.
The Problem with GaN
While GaN devices are widely used in the optoelectronics industry (for example, LEDs), they are not widely used in transistors for a variety of reasons. One of the most significant challenges in gallium nitride transistors is that they are typically depletion type devices that turn on when the gate-source voltage is zero, which is problematic because power circuitry and logic rely on both normally on and normally off transistors.
There are currently several proposals for creating GaN devices that are OFF when the gate-source voltage is zero, including the use of fluoride ions, a MIS-type gate stack, a combined GaN and Si device, and the use of a P-type material on top of the AlGaN/GaN heterojunction.
Current GaN Applications
Despite the fact that only a few devices utilize GaN transistors, several companies are attempting to increase demand for GaN-based products. Panasonic, for example, has used its patented X-GaN technology to produce GaN-based transistors in a variety of applications, including power converters (with up to 99 percent efficiency) and replacements for transistors in motor configurations.
Their X-GaN transistors can also be used to completely replace MOSFETs and freewheel diodes, allowing for energy savings while also reducing the physical size of the circuit.
Due to their superior frequency characteristics, GaN transistors are also finding their way into radio applications, speed cameras, military applications, and air traffic controls, all of which require frequencies between 9.2-10GHz at 10kW of power.
Will GaN Replace Silicon?
GaN has many significant advantages over silicon, including greater power efficiency, and faster, better recovery characteristics. While GaN may appear to be a better choice, it will not replace silicon in all applications for some time.
The GaN transistors’ depleted nature is the first barrier to overcome. Effective logic and power circuits require transistors of both normally-on and normally-off types. While normally-off GaN transistors are possible, they either rely on a standard silicon MOSFET or require special extra layers that make shrinking difficult. Because GaN transistors cannot be manufactured on the same scale as silicon transistors, they are currently impractical for use in CPUs and other microcontrollers.
More research is being conducted to improve the efficiency and accessibility of GaN. Panasonic, for example, has patented an AlGaN layer method for fabricating an enhanced GaN transistor. It means that until other companies conduct their own research, any invention or application involving that specific transistor will be dependent on Panasonic. Meanwhile, those other companies are working on their own improved GaN transistor manufacturing methods. The results of these efforts will shape GaN’s future market viability.
GaN device development has been going on since the early 2000s, but GaN transistors are still in their infancy. While there is no doubt that they will eventually replace silicon transistors in power applications, they are still far from being used in data processing applications.
But, if GaN devices can be reduced in sizes (with features smaller than 100nm), they will not only be able to replace silicon for improved power efficiency, but they will also be able to operate at much higher speeds, allowing processor power to continue to rise.