Researchers at the University of Michigan have made a groundbreaking discovery that reconciles the gap between recent experiments and theory concerning polarization in wurtzite semiconductors, paving the way for the development of smaller, faster, and more efficient electronic devices.
Using Polarization to Our Advantage
The second most produced semiconductor (after silicon) is gallium nitride, which is already used in LED lighting and has been a potential technology for high-power, high-frequency electronic devices. Anticipated to enable the next-generation cell phones and communications systems, this material boasts unprecedented electronic performance based on polarization.
So the research team turned its attention to gallium nitride in its wurtzite crystal phase — a structure now widely used in electronic and optoelectronic devices. Since the crystal forms a hexagonal lattice, it does not possess inversion symmetry which leads to spontaneous polarization and piezoelectric polarization when subjected to mechanical strain. Although both polarizations of the same magnitude and hence the induced polarization gradient across the interface can be suitably exploited for engineering semiconductor device electronic properties.
Connecting Theory and Experiments
For gallium nitride and other materials with the wurtzite structure, up until now, polarizability has been understood only using theoretical predictions. Experiments showed, however, that the induced polarization is ten times larger and reversed in sign compared to what conventional theory predicted.
The trouble behind why theory and experiment were off by so much is that a reference structure was not what we thought it was. While initial attempts to interpret the results using a simple zinc blend structure did not provide a good agreement between experiment and theory, replacing this with a hexagonal reference structure that better focuses on the In_2Se_3 monolayer resulted in very good qualitative agreement.
The preceding literature therefore picked a poor ruler for polarization, which made it impossible to find the correct knife and explain a key piece of the data. Professor Chris Van de Walle at the University of California Santa Barbara originally predicted these much-changed properties theoretically in 2016 on paper that are now experimentally confirmed by us, as well as others,” said Danhao Wang, a research fellow in electrical and computer engineering at U-M and co-corresponding author of the study.
Conclusion
Using these state-of-the-art findings explores a new route and perspective on designing GaN-based electronic/ optoelectronic devices. In addition to the current and anticipated impacts on electronics and optoelectronics, this new physics of polarization can serve as a foundational tool for exploring frontier nitride materials discovery towards next-generation transformational clean energy catalysis along with quantum research and technology. This research is likely to have ongoing influence and gradually bring the next wave of cell phones, communications systems, and a myriad of other electronic devices.
