Electromechanical coupling in free-standing AlGaN/GaN planar structures

摘要

The strain and electric fields present in free-standing AlGaN/GaN slabs areexamined theoretically within the framework of fully-coupled continuum elasticand dielectric models. Simultaneous solutions for the electric field and straincomponents are obtained by minimizing the electric enthalpy. We applyconstraints appropriate to pseudomorphic semiconductor epitaxial layers andobtain closed-form analytic expressions that take into account the wurtzitecrystal anisotropy. It is shown that in the absence of free charges, thecalculated strain and electric fields are substantially differently from thoseobtained using the standard model without electromechanical coupling. It isalso shown, however, that when a two-dimensional electron gas is present at theAlGaN/GaN interface, a condition that is the basis for heterojunctionfield-effect transistors, the electromechanical coupling is screened and thedecoupled model is once again a good approximation. Specific cases of thesecalculations corresponding to transistor and superlattice structures arediscussed.