Piezoelectric energy harvesting is used to convert mechanical vibrations into electrical energy. This is done using a piezoelectric crystal, in which cyclic stresses (applied in the appropriate direction) are used to generate an a.c. voltage. For this to work effectively, the material should have both a high piezoelectric coefficient and a low dielectric constant. Unfortunately, it has so far proven very difficult to find a material that can fulfil both criteria, resulting in very limited device output powers. However, our recent predictions suggest that performance may be improved dramatically using new (Sc,Al,Ga)N materials, in which both high piezoelectric coefficients and low dielectric constants may be achieved. To test the potential of this unexplored material system, we are currently growing thin films of (Sc,Al,Ga)N materials by MBE, for use in improved proof-of-principle energy harvesting devices.
Fig. 1. In-plane stresses produce out-of-plane crystal distortions, which can be used to generate a voltage