Piezoelectric Franz–Keldysh effect in strained GaInN/GaN heterostructures

Pseudomorphic ${\mathrm{Ga}}_{\text{1−x}}{\mathrm{In}}_x$ N/GaN single heterostructures in the composition range $\text{0<x<0.2}$ have been investigated by photoreflectance and photoluminescence spectroscopy. Strong Franz–Keldysh oscillations near the band gap of the ternary film are observed and attributed to a large constant piezoelectric field of up to 0.63 MV/cm. This allows an accurate determination of the electric field. A significant redshift between the optical band gap from photoreflectance and the luminescence maximum is observed. Luminescence is proposed to originate in the indirect transitions between the electric field tilted band edges in GaInN. The presence of this field is expected to dominate the bandstructure and the recombination and transport processes in strained nitride structures. We find no evidence for large inhomogeneities or phase separation in this material.