Optoelectronics is key to many technologies that help improve our quality of life and protect the planet, including photovoltaics (solar panels), LEDs, and fast data transmission. With optoelectronics, we can reduce energy use, support sustainable power, and build better lasers and photodetectors. There are multiple applications in medicine, including less invasive treatments for a variety of conditions.
Advanced semiconductor materials are vital for the further development of optoelectronics, including:
- III-IV compound semiconductors
- Organic and perovskite semiconductors
- 2D materials
Using these materials can improve efficiency, lower costs, and provide unique qualities that support the development of new technologies.
Here are some semiconductor materials and the uses to which they have been put or for which they show spectacular potential:
III-V Compound Semiconductors
III-V compound semiconductors are alloys containing elements from groups III and V in the periodic table (no IV elements are involved). There are thus a variety of materials in this group with different properties. In general, however, they offer a lot of potential in laser and LED applications where they provide high output power and improved efficiency.
Some examples include:
- GaN (gallium nitride), which scientists use to create blue and ultraviolet lasers
- InN (iridium nitride), which is being studied for use in high-speed optoelectronics and solar cells
- GaAs (gallium arsenide), which is used in high-frequency applications such as fiber optics, DVD players, and cellphones
The materials have been known for a long time, but they are really starting to come into their own. III-V compound solar cells have achieved a conversion efficiency of 47.1%, far higher than silicon-based cells and showing potential to break the key 50% conversion threshold. This, of course, means that more power can be achieved from a smaller area. Smaller solar cells reduce the environmental footprint of solar cell production. It also helps reduce the environmental costs of end-of-life disposal, which is becoming a growing problem as more and more systems reach the end of their lives. The costs of these cells remain high but are coming down all the time. They might also allow for larger and heavier solar-powered aerial vehicles and solar-powered cars, given they combine very high efficiency with reduced weight.
Organic Semiconductors
Organic semiconductors are so-called because they are primarily based on carbon and oxygen. They may be single molecules, short-chain oligomers, or polymers. Their conduction mechanisms are quite different, resulting in some interesting potential applications. Additionally, they tend to cost much less to produce and are incredibly versatile, resulting in many potential uses.
One primary application is spin transport. This is used to create spin valves that tune resistance from low to high, although more work needs to be done to make these reliable at room temperature. More practical uses are in photodetection, photovoltaic devices, and organic light-emitting diodes. They are critical for next-generation electronic and energy devices, including thin-film transistors and biomimetics.
Organic materials are also easily printable, as they can be incorporated into inks. Organic light-emitting diode (OLED) technology is already in regular use in phones and digital cameras. Because it is lighter, has better flexibility, and offers higher performance in terms of color and contrast, it is likely to dominate the market.
However, developers must work to reduce the release of toxic volatile organic compounds, particularly halogenetic solvents, during production. This has proved to be an obstacle in the way of expanding organic semiconductor production, adding costs and slowing the build-out of facilities. Techniques are being developed to solve this by using less toxic solvents and potentially by synthesizing products in water, as is done with other conducting polymers.
Perovskite Semiconductors
Perovskite semiconductors have an organometallic halide or oxide structure that absorbs and emits light, making them hugely valuable for solar cells and LEDs. They also cost less to produce and are highly efficient.
A recent study demonstrated that a spray-on ink could be used to create patterned structures in perovskite semiconductors, which is a much cheaper and safer approach than photolithography. This promises to make faster chips from different supply lines and sources, as well as reduce production costs.
Metal-halide perovskite semiconductors give exceptional quantum yields for photoluminescence, and scientists employ them widely, including in x-ray scintillators. A stable continuous-wave pumped perovskite laser has demonstrated its potential at room temperature. Perovskite materials are also particularly useful in health and medical systems in general.
Again, perovskite costs less to produce and offers plenty of efficiency. “Painted” perovskite promises to reduce costs even further. Manufacturers can even avoid hard-to-find materials used in photolithography, such as neon. It is significantly more efficient than silicon and even more so when combined with silicon.
2D Materials
2D materials are being studied for use in optoelectronics applications. These materials include graphene and transition metal dichalcogenides (TMDs). The latter material demonstrates atomic-scale thickness, favorable electrical and mechanical properties, direct bandgap, and strong spin-orbit coupling.
These materials also show a large variety of physical properties and varied bandgaps. They are particularly well suited for integration into optoelectronic circuits. Heterostructures are being studied for use in broadband optoelectronics, as well as other uses such as ubiquitous electronics.
Graphene has unique optical properties, which show potential for a wide variety of applications. One key consideration is the potential for solid-state lighting and ultrafast optical switching. Exfoliated molybdenum sulfide (MoS2), for example, can produce intense, stable light for use in LEDs. Also, 2D selenides have a wide variety of applications, including optical switching.
2D materials also have the obvious advantage of being useful at the nanoscale. As electronic devices become smaller and electronics are embedded in even more everyday objects, this helps reduce space and weight.
Overall, using these advanced semiconductor materials in optoelectronics applications leads to improved performance, increased efficiency, and lower cost. Scientists must do much more research to optimize the use of these and other advanced materials. They will likely find even more uses for some of these materials over the next few years. Next-generation optoelectronics will both require and come out of studies of these materials, making for a very exciting time in this field.
