Deep traps determining the non-radiative lifetime and defect band yellow luminescence in n-GaN

Abstract

Deep traps spectra measurements were performed for a group of n-GaN films grown by metalorganic chemical vapor deposition (MOCVD) on sapphire using standard MOCVD and two versions of lateral overgrowth techniques, the epitaxial lateral overgrowth (ELOG) and pendeo epitaxy (PE). Deep levels transient spectroscopy with electrical (DLTS) or optical (ODLTS) injection showed that in all cases the dominant electron traps were the well known Ec-0.56 eV centers. DLTS spectra taken with constant illumination indicate that not only has this trap a high density and electron capture cross section, but that it also has a high hole capture cross section and thus can be an efficient recombination center. Comparison with diffusion length measurements supports this conclusion. Among the hole traps the most prominent centers are the traps near Ev+0.9 eV. However, direct estimate of the electron capture cross section by these traps give very low values close to 10−22 cm2 thus excluding the Ev+0.9 eV traps from the list of potential lifetime killers, despite the high density of these centers. Annealing at 800 °C of one of the PE samples led to an increase of the concentration of the Ev+0.9 eV traps, the increase of the centers with optical ionization energy 1.3 eV density (observed in photocapacitance), and also to increased intensity of yellow luminescence band.