Luminescence Band In GaN Research Articles

The GaN(0001) yellow-luminescence-related surface state and its interaction with air

Yellow luminescence (YL) is probably the longest and most studied defect-related luminescence band in GaN, yet its electronic structure or chemical identity remain unclear. Most of the theoretical work so far has attributed the feature to bulk defects, whereas spectroscopic studies have suggested a surface origin. Here, we apply deep level spectroscopy using sub-bandgap surface photovoltage that provides the energy distribution of the surface charge density. Comparison of surface charge spectra obtained under identical conditions before and after various surface treatments reveals the dynamics of the surface charge density. Further comparison with spectra of the entire state obtained using photoluminescence shows how the charge density stored in YL-related defects is eliminated upon a mild anneal in vacuum. This suggests that the YL-related defect involves a certain molecule adsorbed on the GaN surface, possibly in a complex with an intrinsic surface defect. The observed interaction with air strongly indicates that the YL-related deep level is a surface state.

On the Origin of the Yellow Luminescence Band in GaN

The yellow luminescence (YL) band with a maximum at 2.2 eV is the dominant defect‐related luminescence in unintentionally doped GaN. The discovery of the mechanism responsible for this luminescence band and related defects in GaN took many years. Eventually, a consensus has been reached that the CN acceptor is the source of the YL band (the YL1 band) in GaN samples grown by several techniques. Previously suggested candidates, such as VGa, VGaON, CNON, and CNSiGa, should be discarded. At the same time, other defects (such as the VN, BeGa, and CaGa) may cause luminescence bands with positions and shapes not much different from the YL1 band. In GaN containing high concentrations of gallium vacancies, oxygen, and hydrogen, complexes containing these species may also contribute in the red–yellow part of the photoluminescence spectrum. The main controversies related to the YL band are resolved.

Fine Structure of the Carbon-Related Blue Luminescence Band in GaN

Photoluminescence studies reveal three CN-related luminescence bands in GaN doped with carbon: the YL1 band at 2.17 eV caused by electron transitions via the −/0 level of the CN, the BLC band at 2.85 eV due to transitions via the 0/+ level of the CN and the BL2 band at 3.0 eV attributed to the CNHi complex. The BLC band studied here has the zero-phonon line at 3.17 eV and a phonon-related fine structure at low temperatures. The 0/+ level of the CN is found at 0.33 ± 0.01 eV above the valence band, in agreement with recent theoretical predictions. These results will help to choose an optimal correction scheme in hybrid functional calculations.

A carbon-doping related luminescence band in GaN revealed by below bandgap excitation

Carbon doped GaN grown by hydride vapor phase epitaxy was investigated by photoluminescence and photoluminescence excitation spectroscopy covering a broad range of carbon concentrations. Above bandgap excitation reveals typical transitions related to CN and CN−Hi that decrease with increasing carbon concentration. Besides the formation of nonradiative defects, the formation of complexes containing more than one carbon atom is proposed to be responsible for this reduction. Below bandgap excitation reveals an intense emission band around 1.62 eV for [C] >1018cm−3 that is shown by photoluminescence excitation spectroscopy to be most efficiently excited at 2.7 eV. The 1.62 eV transition thermally quenches above 80 K. A configuration-coordinate diagram model is proposed to explain the observed emission, excitation, and thermal quenching behavior. Based on the simultaneous increase in the concentration of tri-carbon complexes, this band is tentatively attributed to a transition involving a deep tri-carbon-related charge state transition level in the GaN bandgap.

Zero-phonon line and fine structure of the yellow luminescence band in GaN

The yellow luminescence band was studied in undoped and Si-doped GaN samples by steady-state and time-resolved photoluminescence. At low temperature (18 K), the zero-phonon line (ZPL) for the yellow band is observed at 2.57 eV and attributed to electron transitions from a shallow donor to a deep-level defect. At higher temperatures, the ZPL at 2.59 eV emerges, which is attributed to electron transitions from the conduction band to the same defect. In addition to the ZPL, a set of phonon replicas is observed, which is caused by the emission of phonons with energies of 39.5 meV and 91.5 meV. The defect is called the YL1 center. The possible identity of the YL1 center is discussed. The results indicate that the same defect is responsible for the strong YL1 band in undoped and Si-doped GaN samples.

Hydrogen-carbon complexes and the blue luminescence band in GaN

The blue luminescence band with a maximum at 3.0 eV and the zero-phonon line at 3.33 eV (labeled BL2) is observed in high-resistivity GaN. Under prolonged ultraviolet (UV) light exposure, the BL2 band transforms into the yellow luminescence (YL) band with a maximum at 2.2 eV. Our hybrid functional calculations suggest that the BL2 band is related to a hydrogen-carbon defect complex, either CNON-Hi or CN-Hi. The complex creates defect transition level close to the valence band, which is responsible for the BL2 band. Under UV illumination, the complex dissociates, leaving as byproduct the source of the YL band (CNON or CN) and interstitial hydrogen.

Nature of yellow luminescence band in GaN grown on Si substrate

High-optical-quality GaN was grown on a (111)Si substrate by metal–organic vapor phase epitaxy using an AlInN buffer layer and an indium doped AlN nucleation layer. The photoluminescence spectra at room temperature showed a strong and narrow edge-emission peak and weak defect-related emission bands. We found four spectral peaks in the green and yellow luminescence bands at G0: 514.5 nm (2.410 eV), G1: 546.5 nm (2.269 eV), Y1: 553.5 nm (2.240 eV), and Y0: 584.5 nm (2.121 eV), independent of the growth methods/conditions. The results suggest that the emission is associated with an intrinsic defect such as a Ga vacancy.

Microcathodoluminescence and electrical properties of GaN epitaxial layers grown on thick freestanding GaN substrates

Microcathodoluminescence (MCL) spectra, MCL imaging, electron beam induced current imaging, capacitance-voltage (C-V) profiling, and deep level transient spectrum measurements with optical injection (ODLTS) were performed on 3-μm-thick GaN epilayers prepared by metal organic chemical vapor deposition on top of thick freestanding GaN crystals grown by hydride vapor phase epitaxy. The GaN substrates showed a dislocation density of around 5×106cm−2 near the back surface and ∼106cm−2 near the Ga surface on which the epitaxy was performed. Dislocations are revealed as broad dark spots in MCL spectra taken on (0001) surface and as dark broad lines on the cleaved surface. The structure of the GaN film is more complicated, showing a pattern of arrowheadlike features of alternating dark-bright contrast. MCL spectra taken in the dark and bright regions indicate that the shallow donors in the dark region are more heavily compensated. The carrier lifetime near defects is greatly reduced. ODLTS spectra of the films show the presence of well known hole traps with activation energy of 0.85eV often associated with the yellow luminescence band in GaN.

Properties of the 3.4 eV Luminescence Band in GaN and its Relation to Stacking Faults

Properties of the 3.4 eV Luminescence Band in GaN and its Relation to Stacking Faults

The Red (1.8 eV) Luminescence in Epitaxially Grown GaN

The 1.8 eV luminescence band in GaN grown by molecular beam epitaxy is studied by photo-luminescence (PL) and magnetic resonance. Optically detected magnetic resonance (ODMR) shows that deep centres with g = 1.98 and g = 2.01 are involved in the recombination. The results of the PL experiments indicate that the 1.8 eV recombination can be further fed by shallow centres like shallow donors or excitons.

Source of the yellow luminescence band in GaN grown by gas-source molecular beam epitaxy and the green luminescence band in single crystal ZnO

In this paper we show that the origin of the yellow luminescence band in GaN and the green luminescence band in ZnO is best explained by a transition between a shallow donor and a deep level. High resolution photoluminescence spectroscopy measurements on GaN (0 0 0 1) films grown by gas-source molecular beam epitaxy are compared with theoretical predictions. These comparisons show that the makeup of the deep level in GaN is most likely a complex consisting of a gallium vacancy, V Ga and a nearest neighbor donor consisting of an oxygen atom on a nitrogen site, O N, or V Ga–O N. By analogy, the makeup of the deep level in ZnO is most likely a complex consisting of a zinc vacancy, V Zn and a nearest neighbor donor consisting of a chlorine atom on an oxygen site V Zn–Cl O. Chlorine is suggested since it is a dominant donor in ZnO and is known to be present in the ZnO growth process.

Dynamical study of the yellow luminescence band in GaN

A comprehensive study of the yellow photoluminescence (YL) in GaN epitaxial films grown by hydrid vapor phase epitaxy and by metal organic vapor phase epitaxy is presented including time-integrated and time-resolved photoluminescence (PL), PL excitation (PLE) and optically detected magnetic resonance (ODMR) experiments. ODMR reveals the participation of shallow and deep double donors based on the analysis of the g-values. This recombination model is supported by time-resolved investigations. PLE spectra show a close connection between the excitation processes of the YL band and of the inner transition of Fe 3+ at 1.293 eV. Two-color stimulation experiments prove energy transfer between YL and the Fe 3+ center by hole transfer, strongly confirming the YL recombination model involving a deep level 1.2 eV above the valence band.

Yellow Luminescence and Associated Odmr in Movpe Gan: A Comparison of Defect Models

ABSTRACTTwo positive ODMR resonances are commonly observed on a luminescence band in GaN at 2.2 eV, one identified as a shallow donor, the other currently unidentified. We here report a study of their dependencies on a variety of experimental parameters, including microwave modulation frequency, microwave power, photoexcitation power and photoexcitation energy. ODMR simulations using two theoretical models are compared to experimental results which are consistent with spin-dependent recombination between the two defects, assuming the donor has a spin-lattice relaxation time shorter than the spin-dependent recombination lifetime. The photoexcitation energy dependence suggests that the spin-dependent recombination associated with the 2.2 eV band is not the same recombination that is responsible for the luminescence. This supports the two stage model put forth by Glaser et al. for the luminescence process.