Luminescence Properties Of GaN Research Articles

Structural, morphology and optical properties of nanocrystalline GaN and AlGaN alloys prepared by EDTA complex route

GaN and AlGaN alloys were prepared by ethylene diamine tetra acetic acid (EDTA) complex route with five different Al molar ratios. The structure, morphology and luminescence properties of GaN and AlxGa1−xN were investigated by PXRD, SEM, EDX, HRTEM, PL and Raman techniques. The PXRD pattern confirms the formation of hexagonal wurtzite structure of GaN and AlxGa1−xN alloys. When Al is alloy with GaN hexagonal shaped particles change into agglomerated spherical and plate-like morphology of AlxGa1−xN as confirmed by SEM analysis. The results also indicate that with increasing Al composition, the morphology of AlxGa1−xN changes. HRTEM analysis shows that particle size decreases from 24 to 10nm, with increasing Al concentration. Raman analysis confirms the presence of E2(high), A1(TO), E1(LO) and A1(LO) phonon frequencies in AlGaN alloy. PL spectra confirms that the energy of the near band edge emission changes from 383 to 337nm with change in Al concentration in AlxGa1−xN samples.

Mosaicity and stress effects on luminescence properties of GaN

AbstractHigh‐resolution X‐ray diffraction (HRXRD) of several GaN layers grown on Si/N treated c ‐plane sapphire substrate by metal‐organic chemical vapour phase deposition (MOCVD) were investigated. Photoluminescence (PL) measurements were carried out at 13 K. GaN mosaicity was studied at different growth stage with a thickness varying from 0.1 to 4.5 µm. Rocking curves of symmetric and asymmetric plane reflections were investigated to determine respectively the tilt and twist mosaic. Using PL spectra and HRXRD scattering a correlation were found between the intensity and the full width at half maximum (FWHM) of the bound exciton neutral donor (I2) with the GaN mosaicity. The I2 intensity increased significantly with increasing the interaction parameter (m) between tilt and twist mosaic, whereas the FWHM of I2 decreased with increasing m. The evolution of the compressive stress with thickness is extracted from HRXRD and correlated with PL measurements. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of β-irradiation on photoluminescence of MOCVD grown GaN

The effect of beta particles interaction on the optical properties of MOCVD grown GaN is reported. A significant change in luminescence properties of GaN is observed after exposing the material with 0.6 MeV beta particles with low dose of 10(12) cm(-2). The results obtained from photoluminescence measurements of irradiated GaN samples in low dose are found contradictory to those reported in literature for samples irradiated with heavy dose (> 10(15) cm(-2)) of electron. An increase in intensity of yellow luminescence has been observed with increasing dose of beta particles which is in disagreement to the already reported results in literature for heavily irradiated samples. A model has been proposed to sort out this inconsistency. The increase in YL intensity at low dose is attributed to the increase in concentration of VGaON complex whereas production of non-radiative VGaON clusters is assumed to justify the decrease in YL intensity at high dose.

Low‐energy charge‐transfer state and optical properties of Eu 3+ ‐doped GaN

We argue that the charge-transfer state of Eu3+ due to an electron transfer from N to Eu plays important roles in the luminescence properties of GaN:Eu3+ grown by gas-source molecular beam epitaxy. On the basis of the excitation spectrum of the Eu3+ luminescence, the excitation mechanism of Eu3+ under the GaN interband excitation is interpreted in terms of the energy transfer from the above charge-transfer state. The intra-4f shell 5D0–7F2 transition strength of Eu3+ in GaN, which is responsible for red luminescence, is large compared with those of most Eu3+-doped oxide materials. This fact can be attributed to the low-energy position of the charge-transfer state of Eu3+ in GaN. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Defect-related luminescence of GaN:Zn films thermally treated in a radio-frequency ammonia plasma

The effect of thermal annealing in nitrogen radicals obtained by the treatment of NH3 in a radio-frequency discharge on the luminescence properties of GaN:Zn films grown by MOCVD/hydride epitaxy on sapphire (0001) substrates is investigated. As the thermal treatment temperature was increased, a steady weakening of the violet (2.88 eV) and near-edge (3.48 eV) photoluminescence bands was observed. As a result of the thermal treatment in nitrogen radicals at 500–750°C, new bands that peaked at 3.27 and 3.42 eV were detected; the intensities of these bands increased with increasing treatment temperature. The mechanism of formation and the origin of all the bands are analyzed comprehensively. It is found that the luminescence bands at 2.88, 3.42, and 3.27 eV are characteristic of the GaN films obtained by practically each technology and are associated with the simple structural defects. The participation of O in the formation of the band at 3.42 eV is proved experimentally.

Luminescence properties of GaN and Al0.14Ga0.86N/GaN superlattice doped with europium

We report the observation of visible photoluminescence and cathodoluminescence of Eu3+ ions implanted in GaN and Al0.14Ga0.86N/GaN superlattice. The sharp characteristic emission lines corresponding to Eu3+ intra-4f6-shell transitions are resolved and observed over the temperature range of 7–330 K. The luminescence shows dominant transitions D50→7F1,2,3 and weaker D50→7F4,5,6 and D51→7F1. The luminescence emission is very weakly temperature dependent. The intensity of Eu3+ emission from Al0.14Ga0.86N/GaN superlattice annealed in N2 is ∼58% stronger than from Eu3+ in the GaN layer. The Al0.14Ga0.86N/GaN superlattice and GaN epilayers may be suitable as a material for visible optoelectronic devices.

Electronic structure of GaN stacking faults

The calculation of the electronic structure of the GaN stacking faults in the framework of the local empirical pseudopotential theory is presented. The stacking faults in both zinc-blende and wurtzite GaN are predicted to introduce electronic levels within the band gap, with the energy (0.13\ifmmode\pm\else\textpm\fi{}0.01) eV above the valence-band top. These levels are found to originate from interface states of heterocrystalline wurtzite (0001)-zinc-blende (111) interfaces. The possible implications of stacking fault electronic states on the luminescence properties of GaN are discussed.

Analysis of two-step-growth conditions for GaN on an AlN buffer layer

Gallium nitride is grown by metalorganic vapor phase epitaxy with and without a low-temperature-grown AlN buffer layer. Variations in the surface morphology and the layer properties are compared between two-step growth and direct growth to study the effects of various growth conditions. It is found that (i) conditions that stabilize the GaN(0001) surface serve as guidelines for obtaining mirrored surfaces, and (ii) raising GaN growth temperature improves crystallographic, electrical, and luminescence properties of GaN. The observed improvement in the layer properties with increase in GaN growth temperature suggests that increasing N2 dissociation pressure does not affect GaN properties. GaN growth conditions are analyzed thermodynamically to show that NH3 in the growth ambients has the potential to suppress thermal dissociation of GaN.

Growth of Si-doped Al xGa 1– xN on (0001) sapphire substrate by metalorganic vapor phase epitaxy

Effects of Si-doping on the electrical and luminescence properties of GaN and A1 0.1Ga 0.9N epitaxial films have been studied. GaN and A1 0.1Ga 0.9N films were grown by MOVPE on (0001) sapphire substrates using A1N buffer layers. SiH 4 was used as Si source gas. The conductivities of n-type A1 0.1Ga 0.9N film were found to be controllable by varying the flow rate of SiH 4 during growth. Cathodoluminescence spectra of both GaN :Si film and A1 0.1Ga 0.9N :Si film are strong near the bandedge emission, and their intensity increases with increasing Si concentration. These results indicate that (1) GaN :Si and A1 0.1Ga 0.9N :Si films grown using A1N buffer layers have a high quality and (2) Si replaces group-III (Ga or A1) elements at lattice sites in the GaN film and also in the A1 0.1Ga 0.9N film.