Although it’s not as tricky as producing new drugs for medicine, developing new materials for commercial electronics is usually no sure thing. There is a long path of testing and development between the first prototype material and something that can be manufactured in large quantities and used in a variety of products. On top of that, there are usually many competing new materials with similar or sometimes even identical properties. In electronics, for example, graphene transistors, spintronic semiconductors and various memristor approaches all vie for the commercial jackpot. To that list can now be added photonic crystals.
Developed by researchers at the University of Illinois (Champaign-Urbana, USA) and published in Nature Materials [24 July 2011, paywalled, Epitaxial growth of three-dimensionally architectured optoelectronic devices] photonic crystals are materials that have molecular structures which can control or manipulate light (as photons). This makes them interesting for use in light-based applications such as lasers, solar power and LEDs. Most photonic crystals are photonically but not electrically active. That’s what sets this new material apart. Paul Braun, who led the research, highlights the difference:
“We’ve discovered a way to change the three-dimensional structure of a well-established semiconductor material to enable new optical properties while maintaining its very attractive electrical properties.”
What they did was take a common electronics semiconductor material, gallium arsenide, and use it to fill out a photonically active crystal structure. The gallium arsenide adds the electrical properties. What’s unusual in the approach is that the gallium arsenide filler ‘grows’ up from the bottom of the crystalline structure to the top, something like filling up a structure with water. This is called epitaxial deposition, a common process in the electronics industry but usually on two-dimensional surfaces. This photonic crystal material is three-dimensional, which is unusual for the epitaxial process.
When the crystal structure is full, the supporting material is removed, leaving a gallium arsenide structure that is both photoelectronically active and an electrical semiconductor. The research team tested the material’s properties by constructing a Light Emitting Diode (LED) as a demonstration.
This epitaxial approach is reminiscent of similar techniques in synthetic biology, where an artificial framework is filled by growing biological material within it until a complete organ is created. The advantage to the approach is that almost any kind of structure can be constructed – custom designed as needed – and filled with a variety of materials, often layered for special properties. The approach is also more reliable (produces fewer flaws) that more common ‘top down’ deposition. In short, these photonic crystals appear to be dual functioned, highly flexible and scalable – key features if the material is to become successful in the commercial electronics market.
The process looks good and the researchers have demonstrated it can be turned into a successful application. The question from here on is whether the material can compete with the efficiency of existing semiconductors (silicon) or have special properties to compete with, say, graphene devices. The research work now turns to ‘tuning’ the photonic crystal production process for maximum efficiency and attempt to develop ways in which the material can be used in a variety of products. The results, probably in a couple of years (or more) will determine whether this particular new optoelectronic material will become a commercial success.