Spectroscopy in Polarized and Piezoelectric AlGaInN Heterostructures

Uniaxial wurtzite group-III nitride heterostructures are subject to large polarization effects with significant consequences for device physics in optoelectronic and transport device applications. A central aspect for the proper implementation is the experimental quantification of polarization charges and associated fields. In modulated reflection spectroscopy of thin films and heterostructures of AlGaInN we observe pronounced Franz-Keldysh oscillations that allow direct and accurate readings of the field strength induced by polarization dipoles at the heterointerfaces. In piezoelectric GaInN/GaN quantum wells this dipole is found to induce an asymmetry in barrier heights with a respective splitting of interband transitions. This splitting energy appears to reflect in the transitions of spontaneous and stimulated luminescence in the well. From these experiments the polarization dipole is identified as controllable type-II staggered band offset between adjacent barrier layers which can extend the flexibility in AlGaInN bandstructure design. The derived field values can serve as important input parameters in the further interpretation of the entire system.