Wide Bandgap Devices

Wide bandgap (WBG) semiconductor materials enable power electronic components to be smaller, faster, and more reliable. They are often more efficient than silicon-based counterparts. These properties result in weight, volume, and life-cycle cost reductions in a wide range of power applications. Furthermore, capabilities enable substantial energy savings in industrial processing and consumer appliances.

Wide bandgap semiconductors also aid in the widespread adoption of electric vehicles and fuel cells, as well as in the integration of renewable energy into the electric grid. Continue reading to learn more about wide bandgap power semiconductors and their most common variants.

An Overview

The development of advanced power electronic devices with outstanding efficiency, reliability, functionality, and form factor will provide a competitive advantage in the deployment of advanced energy technologies.

High power conversion efficiency necessitates the use of low-loss power semiconductor switches. Metal oxide field effect transistors (MOSFETs), IGBTs, and thyristors are examples of power silicon-based switch technology currently in use.

Wide bandgap semiconductors

There are several limitations to silicon-based power semiconductor devices. High voltage devices with a significant critical thickness are required due to the relatively low bandgap and critical electric field. The increased thickness results in devices with high resistance and associated conduction losses, resulting in high losses.

In addition, in most cases, the achievable switching frequency is low. Silicon’s low bandgap contributes to high intrinsic carrier concentrations in silicon-based devices, resulting in high leakage current at high temperatures.

As a result of the development of  WBG Semiconductors devices, new opportunities for greater efficiency have emerged. The fundamental differences in material properties between silicon and semiconductors such as silicon carbide (SiC) and gallium nitride are driving this (GaN).

Higher critical electric fields in these WBG materials allow for thinner, more highly doped voltage blocking layers, which can reduce on resistance in majority carrier architectures by orders of magnitude. Due to the high breakdown electric field and low conduction loss, WBG materials can achieve the same blocking voltage and on resistance while having a smaller form factor.

The reduced capacitance value allows for high frequency operation in WBG devices.

The materials’ low intrinsic carrier concentration allows for low leakage currents and stable high-temperature performance. As a result, WBG Semiconductors pave the way for more efficient, lighter, high-temperature capable, and smaller form factor power converters.

WBG Semiconductors allow devices to operate at significantly higher temperatures, voltages, and frequencies. This contributes to power electronic modules that are significantly more powerful and energy efficient than conventional semiconductor-based modules. To realize the full potential of WBG-based devices, however, intensive and systematic research and development efforts at every stage of the power electronics value chain, as depicted in Figure 1, are required.

Diagram of value chain for power electronics.
Figure 1. Diagram of value chain for power electronics.

SiC and GaN Based Power Semiconductors

When compared to silicon-based devices, the use of silicon carbide (SiC) can reduce on-state resistance by two orders of magnitude. When applied to power conversion systems, it can significantly reduce power loss. SiC devices, such as power semiconductor switches, are used in conjunction with rectifier devices.

Commercial production of SiC-based devices is now possible due to recent advances in substrate quality, epitaxy improvements, optimized device design, advances in increasing channel mobility with nitridation annealing, and optimization of device fabrication processes.

Silicon-based semiconductor switches have been unable to keep up with the power electronics industry’s evolving changes. This necessitates the use of another semiconductor material, gallium nitride, to match the performance of the newer systems (GaN). It is a high electron mobility (HEMT) semiconductor that is expected to see significant advancements in the coming years. GaN is typically grown on top of a silicon substrate, yielding a fundamentally simple, elegant, and cost-effective solution for power switching.

The essential features that makes GaN extra effective include the fact that it can be grown on top of silicon wafers, offers advantage of self-isolation and therefore efficient monolithic power integrated circuits can be fabricated economically, and enhancement mode along with depletion mode are available. GaN’s exceptionally high electron mobility and low temperature coefficient allows very low on-state resistance. This makes it possible to handle tasks benefitted by very high switching speeds.

By David Stanley

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