Effect of electromechanical coupling on the pressure coefficient of light emission in group-III nitride quantum wells and superlattices

We investigate the influence of the direct and converse piezoelectric effect, i.e., electromechanical coupling (EC), on the strain and the built-in electric field in hexagonal group-III nitride heterostructures under hydrostatic pressure. Particularly, we derive the analytic formulas for pressure dependences of the strain tensor components and the built-in electric field in wurtzite heterostructures, taking into account the EC effect. Then, we calculate pressure coefficients of the light emission, dE(E)/dP, in various GaN/AlGaN and InGaN/GaN superlattices and quantum wells (QWs). Generally, our calculations reveal that taking into account the EC leads to the decrease of the pressure derivative of the built-in electric field in the QW region, which further causes an increase of the dE(E)/dP. The contribution of the EC to dE(E)/dP depends significantly on the geometry, composition, and strain state of heterostructures. We have found that the largest influence of the EC on dE(E)/dP is for GaN/AlN heterostructures. In GaN/AlGaN structures, the contribution of the EC to dE(E)/dP grows with an increasing well width and Al concentration in the barriers. A larger influence of the EC on dE(E)/dP is observed for the structures with strained barriers than with strain wells. Interestingly, for InGaN/GaN heterostructures grown coherently on GaN substrates, the effect of the EC on dE(E)/dP is negligible.