Nonlinear macroscopic polarization in GaN/AlxGa1-xN quantum wells

Abstract

We present experimental evidence of the nonlinear behavior of the macroscopic polarization in GaN/AlxGa1-xN quantum wells. This behavior is revealed by determining the barrier-well polarization difference as a function of applied hydrostatic pressure. The polarization difference and corresponding built-in electric field in the wells increase with applied pressure at a much higher rate than expected from the linear model of polarization. This result, universally observed in the quantum well structures with different AlN mole fraction in the barriers, is explained by the nonlinear dependence of the piezoelectric polarization in GaN and AlN on the strain generated by pressure.