Optical study of GaN epilayer grown by metalorganic chemical vapor deposition and pulsed laser deposition

Unintentionally doped n-type GaN (0 0 0 1) epitaxial layers were grown by metalorganic chemical vapor deposition (MOCVD) and pulsed laser deposition (PLD) on sapphire substrates. As-grown GaN films were irradiated with 75 MeV high-energy Sn5+ ions at the fluence of 1011 cm−2. Both as-grown and irradiated layers were studied by time-resolved photoluminescence (TRPL), photoluminescence (PL) and UV-absorption spectroscopy techniques at room temperature. Surface morphologies of the samples were analyzed by optical microscopy and scanning electron microscopy (SEM). The surface morphologies of the PLD thin films have revealed the presence of GaN nanoparticles. PLD-grown GaN films have shown highest minority carrier lifetime of 20 ns, whereas 1910 ps has been obtained for MOCVD-grown GaN. During high-energy Sn5+ ion irradiation at 1011 cm−2 fluences, the lifetime decreased to 1880 ps and 16 ns for MOCVD-and PLD-grown samples, respectively. Near band-edge emission (NBE) was observed at 3.40 eV by room temperature PL measurement for all the GaN samples. UV-absorption edge was observed at 3.41 eV for MOCVD and 3.40 eV for PLD-grown samples, respectively. The irradiation process has reduced the absorption band edge for both MOCVD-and PLD-grown GaN.