According to KAUST, it’s researchers have demonstrated that by varying the atomic composition of boron-nitride-based alloys, they can enable tuning of polarisation.
When an electric field is applied to a single atom, it shifts the centre of mass of the cloud of negatively charged electrons away from the positively charged nucleus it surrounds. In a crystalline solid, electric dipoles of all atoms come together to create electric polarisation, and in some material, a spontaneous polarisation can occur without an external electric field. The latter is strongly dependent on the structure and composition of the atomic crystal. Piezo electrics can change polarisation when physically deformed.
If a way to control the polarisation in such materials could be developed, KAUST researchers are suggesting it would have potential use in computer memory.
The KAUST team explored one approach to polarisation engineering at the interface between boron-nitride-based alloys.
To investigate the electronic properties of the ternary alloys boron aluminum nitride and boron gallium nitride, the team used software called the Vienna ab initio Simulation Package. They explored how they change as boron replaces aluminum and gallium atoms, respectively.
Visiting student Kaikai Liu, said: "We calculated the spontaneous polarisation and piezoelectric constants of boron nitride alloys within a newly proposed theoretical framework and the impact of the polarisation at junctions of these two materials.”
According to the team, they have demonstrated that spontaneous polarisation changes very nonlinearly with increasing boron content. This is due to the volume deformation of the alloy's unusual atomic structure, known as wurtzite.
The nonlinear change of the piezoelectric polarisation is less pronounced, but apparently evident, and occurs due to the large difference in atomic spacing between boron nitride and both aluminum nitride and gallium nitride.
Apparently, boron aluminum nitride or boron gallium nitride can become nonpiezoelectric when the boron content is more than 87% and 74%, respectively.
The team say that their work shows that a range of spontaneous and piezoelectric polarisation constants could be made available by changing the boron content. They suggest that this could be useful for developing optical and electronic junction devices formed at the interface between conventional nitride semiconductors and either boron aluminum nitride or boron gallium nitride.
The team’s next steps will be to ‘experimentally test the proposed junctions’ in a hope to create much better device performance.
