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InN films with In and N polarities grown by molecular beam epitaxy are studied by photoreflectance (PR). No PR feature is observed at 293 K. At 50 K, for N-polar InN, a broad PR feature with Franz-Keldysh oscillations (FKOs) is observed. The surface electric field (312 kV/cm) and band gap (0.682 eV) are deduced from analyzing FKO extremes. However, some narrow PR features are observed for In-polar InN and three transition energies are obtained, but no FKO is observed. These indicate that the surface electric field (or surface band bending) of In-polar InN is smaller than that of N-polar InN

Temperature-dependent photoreflectance (PR) measurements are employed to characterize the conduction band structure of In0.54Ga0.46P1−yNy (y=0 and 0.02) grown on GaAs substrates. The band gap and the upper subband E+ transition are observed in InGaPN as predicted by the band anticrossing (BAC) model. To investigate the energetic positions of the features in the PR spectra, a Kramers–Kronig analysis is proposed. Based on the PR data and the BAC model, we find that the energy EN of isolated nitrogen states shifts significantly to higher energies with decreasing temperature. Simultaneously, the interaction potential V between the nitrogen states and the unperturbed conduction band also rises to higher values. At 293 K, EN=2.054 eV and V=1.513 eV are determined. The thermal shifts of EN and V are dEN/dT≈−0.43 meV/K and dV/dT≈−0.67 meV/K, respectively. The temperature-dependent EN level and interaction potential V are attributed to the lattice distortions, which can be affected by temperature-induced changes in deformation potential. This information is important for overall validity of the BAC model to dilute nitride InGaPN alloys.

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