Piezoelectric Franz-Keldysh effect in strained GaInN/GaN heterostructures

Pseudomorphic Ga1-x InxN/GaN single heterostructures in the composition ran ge 0 < x < 0.2 have been investigated by photoreflectance and photoluminesc ence spectroscopy. Strong Franz-Keldysh oscillations near the band gap of t he ternary film are observed and attributed to a large constant piezoelectr ic 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 ph otoreflectance and the luminescence maximum is observed. Luminescence is pr oposed to originate in the indirect transitions between the electric field tilted band edges in GaInN. The presence of this field is expected to domin ate the bandstructure and the recombination and transport processes in stra ined nitride structures. We find no evidence for large inhomogeneities or p hase separation in this material. (C) 1999 American Institute of Physics. [ S0021-8979(99)01207-4].