Large out-of-plane piezoelectric response of wurtzite InN under biaxial strain

Following the general strategy of 'strain engineering', ab initio calculations based on density functional theory (DFT) were performed to investigate the behavior of wurtzite indium nitride under an equibiaxial strain, applied in the basal plane. The evolution of structural, electronic, elastic and piezoelectric properties was investigated over both compressive and tensile strains up to 10%. To overcome the inherent shortcoming of DFT in reproducing band gaps, pseudo-potentials modified à la Christensen were used. A wurtzite to graphitic-like phase transition was found to take place at a tensile strain of +6% and identified to be of the first order. This transformation was found to be accompanied with a direct–indirect band gap transition. In the wurtzite structure, a non-linear enhancement of the out-of-plane piezoelectric constant was evidenced in the expansion regime where its value, near the phase transition, attains several times that of the strain free structure. This large piezoelectric response is very attractive for practical applications, such as piezoelectric sensors and resonators. Substrate candidates for growing pseudomorphic wurtzite InN with a suitable strain and appreciable critical thickness are discussed. (paper)