Design engineers should be implementing these state-of-the-art semiconductor materials into their latest projects.
With silicon fast approaching its physical limitations in the semiconductor space, engineers are faced with the task of identifying new materials that can effectively solve today’s technological bottlenecks. The most promising solution to many of the present challenges is provided by compound semiconductors, the next generation of materials delivering the efficiency and performance demanded by applications such as 5G infrastructure, high-capacity data centers, electric and autonomous vehicles, and even the metaverse.
What are compound semiconductors?
Compound semiconductors are everywhere and underpin a vast assortment of today’s technologies that demand the ability to operate at high frequencies, withstand high temperatures, or efficiently emit and detect light. This makes them the indispensable choice in technological segments where standard silicon simply fails to deliver
Rather than attempting to push silicon beyond its physical limits, an alternative is to combine two or more elements to achieve specific performance parameters. These compound semiconductors are split into two groups, the first being the ‘Three-Fives,’ i.e., chemical compounds made up of one or more Group III materials (B, Al, Ga, In) combined with one or more Group V materials (N, P, As, Sb, Bi). Examples of ‘Three-Fives’ include gallium arsenide (GaAs), indium phosphide (InP), and gallium nitride (GaN).
The second ‘Group IV’ compound semiconductors are, as their name would suggest, made up of combinations of Group IV elements (C, Si, Ge, and Sn). Silicon carbide (SiC) and silicon germanium (SiGe) are common examples of Group IV compound semiconductors.
How are compound semiconductors made?
Compound semiconductors are made using a complex manufacturing process called ‘epitaxy’ whereby crystalline layers of the aforementioned compound semiconductor materials are deposited onto a substrate to make a wafer, which is then subsequently used by chip makers to produce semiconductor devices.
By determining the composition and sequence of the layers in epitaxial growth, the optical and electrical properties of the wafer can be finely tuned to deliver very specific performance characteristics.
In fact, an epitaxial wafer can include hundreds of individual layers, each of which may be as thin as two or three atoms. To get this staggeringly complicated process exactly right, epitaxial wafer makers need a tremendous amount of expertise and decades of experience—for example, IQE has been honing its epitaxial know-how for more than 30 years and currently holds around 250 patents.
What advantages can compound semiconductors offer?
Compound semiconductors are making an impact across many applications. For example, they are critical in many wireless applications where they achieve broad bandwidth and low latency whilst maximizing power and efficiency. Compound semiconductors also form a key component in photonics applications, such as 3D sensing and facial recognition.
Despite being more complex to manufacture and requiring a high level of expertise, these III-V compound semiconductor materials significantly outperform silicon. They enable operation at higher frequencies, offer more efficient emission and detection of light, provide a higher breakdown voltage, present better thermal performance, and can withstand higher temperatures.
So, what has changed and why do we now need to focus so much on compound semiconductors? Simply put, whether we like it or not, we are being driven forward by the megatrends of our decade: 5G connectivity, e-mobility, IoT, AR/VR, edge AI, and cybersecurity, which demand more powerful and multifaceted electronics that silicon-only semiconductors simply cannot provide.
There are three key areas in which compound semiconductors outperform standard silicon:
Power & efficiency at high frequencies: The first, and perhaps most important area, is efficiency: compound semiconductors materials are very efficient at high frequencies. Technically, this is since they have higher electron mobility and—as frequency increases—compound semiconductor materials become far more efficient than standard silicon. This makes them the material of choice for high-power, high-frequency applications such as advanced mobile handsets.
The key takeaway here is that it is the high efficiency of compound semiconductor materials that give today’s smartphones their long battery life. Were it not for compound semiconductors, the battery life of next-generation handsets would be measured in minutes rather than hours or days!
Efficient light emission and detection: Secondly, III-V compound semiconductors are extremely efficient emitters and detectors of light, which is something that has been exploited in one of the earliest applications of compound semiconductors materials—LED lighting. For example, the optical efficiency of compound semiconductors materials has enabled the replacement of traditional 100W filament light bulbs with more reliable and flexible 7W LED light bulbs. Imagine the amazing reduction in power consumption when all the light bulbs in the world are factored in. The inherent high efficiency of compound semiconductor materials across myriad applications makes them an essential element on humanity’s path to Net Zero.
The efficient emission and detection of light provided by III-Vs makes them essential for facial and gesture recognition, wearable health monitors, etc. If we also include effective 3D mapping for AR and VR, and ultra-high-resolution displays utilizing micro-LEDs for Metaverse applications, we can see that the scope of optical capability of the Three-Fives is set to play an indispensable role in the future.
Furthermore, by defining their composition, compound semiconductors can be finely tuned to emit or detect specific wavelengths of light. This enabling characteristic has made them the foundation upon which high-speed data communications over optical networks have been built.
Efficient power handling capabilities: Finally, IV compound semiconductors materials such as GaN and SiC have outstanding power handling capabilities, making them ideally suited for power electronic applications from computer power supplies to electric vehicles (EVs) to grid-based voltage conversion. The way forward to Net Zero in the area of transportation is the electrification of vehicles, where compound semiconductor materials are vital, both for the vehicles themselves as well as the charging infrastructure.
And EVs are just one of several important elements of the Net Zero strategy. Consider the fact that the current worldwide energy loss resulting from voltage conversion is equivalent to twice the amount of energy generated by all renewable sources combined. This “silent” loss can be reduced considerably by simply replacing silicon-based power components with compound semiconductor devices.
Opening up new horizons
While thinking at the circuit level is the most natural and familiar approach for system designers, it is important to understand that material optimization will become increasingly central to both device and system-level advancements.
The system designer will, of course, specify a particular property for a device, such as its gain, turn-on or breakdown voltage, etc. However, by working with a materials provider, designers now have the opportunity to evaluate entirely new alternatives to meet their specific requirements, and they may discover out-of-the-box design options that they could not have imagined before!
Let the examples speak for themselves!
To illustrate the value of compound semiconductors, let’s consider just a few examples as follows:
GaN and GaAs for 5G base stations and Wi-Fi 6 routers: The telecoms industry is currently in the midst of rolling out 5G base stations around the world. However, unlike earlier generations, these 5G base stations typically incorporate the power supply unit within an integrated architecture.
Without a separate power supply and with only a single heatsink and less space for cooling, the efficiency of the power system suddenly becomes very important, particularly since operating at elevated temperatures can reduce equipment reliability. This is where the higher power handling efficiencies of compound semiconductors, such as gallium nitride (GaN), are highly valued. Similarly, the superior efficiency of GaAs semiconductors has seen them become an integral part of 5G handsets and the latest Wi-Fi 6 routers.
VCSEL-enabled LiDAR advanced driver assistance systems (ADAS): Compound semiconductors are also becoming increasingly important in automotive applications. To give one example, advanced driver assistance systems (ADAS) utilize LiDAR (light detection and ranging) to ‘see’ what is around them. However, due to the factor of ‘eye safety at street level,’ it is desirable to use longer wavelengths wherever possible. To achieve this, light is generated using a vertical-cavity surface-emitting laser. This VCSEL technology consists of a compound semiconductor-based laser diode that emits a highly efficient optical beam vertically from its top surface, thus saving valuable space on the circuit board.
Power electronics and efficient high-speed data connections: Vehicle electrification also requires highly efficient power electronics that are underpinned by GaN technology, whilst autonomous vehicles will require ultra-reliable high-speed data connections. Once again, compound semiconductors are leveraged to deliver the high bandwidth and low latency required.
What does the future hold?
Looking ahead, many exciting advances in electronic products will be enabled by compound semiconductors. For example, IQE, a company at the forefront of long wavelength photonics (typically more than 1100nm), is developing advanced products based on the InP material. These products are particularly suitable for applications such as environmental gas sensing, health monitoring, and advanced 3D sensing.
As we move into the new era beyond Moore’s Law, the unique properties of compound semiconductors hold the key to overcoming the fundamental limitations of silicon. An important focus will, without a doubt, be placed on integrating compound semiconductors with leading-edge CMOS technology to fuse the advantages of both these approaches and to raise the bar on semiconductor technologies and the amazing products they enable.