Effects of nitrogen addition on vibrational property of high nitrogen-content GaPN thin films

Structural, vibrational and optical properties of GaP1-xNx films with N contents (x) up to 5.4 at% grown on GaP (001) substrates by MOVPE have been investigated by high resolution X-ray diffraction (HRXRD), micro-Raman spectroscopy and micro-photoluminescence (micro-PL). An average N content was verified by HRXRD to be in a range of 0 to 5.4 at%. All the films are under tensile strain. Smooth surface and fairly flat interface were confirmed by atomic force microscopy (AFM) and scanning electron microscopy (SEM), even though the N atoms were incorporated as high as 5.4 at%. Raman spectra showed the N-related vibrational modes (N-VMs) in range of 440 – 520 cm-1, which is the first validation for GaPN at room temperature. We have investigated the N-VMs Raman intensity (IN-VMs) as a function of N content determined by HRXRD (xXRD). The IN-VMs was found to rise for the GaPN films with higher N incorporation. It is also evident that the N content in the GaPN films determined by Raman spectroscopy technique (xRaman) exhibits a linear dependence on the xXRD. Our results demonstrate that the linear dependence of xRaman on the xXRD provides a useful calibration method to determine the N content in dilute GaPN films with the N content up to 5.4 at%. Room temperature bandgap determined by micro-PL is dramatically reduced, when the N content is increased. A huge band gap bowing parameter of GaPN is calculated to be 10 eV.