Electric-field strength, polarization dipole, and multi-interface band offset in piezoelectric Ga1-xInxN/GaN quantum-well structures

The piezoelectric properties of Ga1-xInxN/GaN multiple quantum well structu res are analyzed in two sets of samples covering the composition range of 0 <x<0.2 and well widths 23 Angstrom less than or equal to L(z)less than or e qual to 130 Angstrom. In photoreflection spectroscopy we observe Franz-Keld ysh oscillations near the barrier band-gap energy and directly derive huge electric field values in the range of 0.23-0.90 MV/cm. The field scales wit h composition and strain. The onset of Franz-Keldysh oscillations marks a t hree-dimensional critical point that tunes with the electric field and well width. It is found to correspond to a direct interband transition between continuum states controlled in energy by the polarization dipole, i.e., the product of the polarization field and well width. By variation of the comp osition alone the level can be tuned over a large energy range from 3.15 to 3.37 eV. This correspondence provides a direct means to accurately determi ne the properties of such polarization controlled systems.