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

Highlights

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Dislocations in MOCVD GaN films are not major lifetime killers.

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Diffusion length are determined by the 0.56 eV electron traps.

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Annealing does not destroy the hole traps responsible for yellow luminescence.

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 E_c-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 E_v+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 E_v+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 E_v+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.

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Graphical abstract

Keywords

• GaN; 
• Deep traps; 
• Non-radiative lifetime; 
• Yellow luminescence; 
• Dislocations
• • • Source:Sciencedirect 
      
      
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