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

Abstract

The piezoelectric properties of ${\mathrm{Ga}}_{1-x}{\mathrm{In}}_x\mathrm{N}/\mathrm{G}\mathrm{a}\mathrm{N}$ multiple quantum well structures are analyzed in two sets of samples covering the composition range of $0<x<\mathrm{}0.2\mathrm{}$ and well widths $23\hspace{0.5em}\AA <~L_z<~130\hspace{0.5em}\AA .$ In photoreflection spectroscopy we observe Franz-Keldysh oscillations near the barrier band-gap energy and directly derive huge electric field values in the range of $0.23–0.90\hspace{0.5em}\mathrm{M}\mathrm{V}/\mathrm{c}\mathrm{m}.$ The field scales with composition and strain. The onset of Franz-Keldysh oscillations marks a three-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 composition 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 determine the properties of such polarization controlled systems.