Effect of ambient on photoluminescence from GaN grown by molecular-beam epitaxy (original) (raw)
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Intensity dependence of photoluminescence in GaN thin films
Applied Physics Letters, 1994
We report the intensity dependence of band-gap and midgap photoluminescence in GaN films grown by electron cyclotron resonance (ECR) microwave plasma-assisted molecular beam epitaxy. We find that the band-gap luminescence depends linearly while the midgap luminescence has a nonlinear dependence on the incident light intensity. These data were compared with a simple recombination model which assumes a density of recombination centers 2.2 eV below the conduction band edge. The concentration of these centers is higher in films grown at higher microwave power in the ECR plasma.
Photoluminescence of GaN layers studied with two-color spectroscopy
Solid-State Electronics, 2003
We report on the results of an investigation of GaN layers by two-color spectroscopy in the visible and the near infrared (IR) (0.9-2 lm) or mid-infrared (6-18 lm). After primary band-to-band excitation, a secondary beam is used with photon energy to matching ionization energy of levels in the gap. Photoluminescence spectra obtained with and without additional IR illumination are compared for different photon energies. The impact of IR radiation on the donor-related emission is discussed, and the involvement of deep mid-gap states is postulated.
Journal of Applied Physics, 1996
Continuous-wave and time-resolved photoluminescence spectroscopies have been employed to study the band-edge transitions in GaN epitaxial layers grown by plasma assisted molecular beam epitaxy. In addition to the neutral-donor-bound exciton transition ͑the I 2 line͒, a transition line at about 83 meV below the band gap has been observed in an epitaxial layer grown under a lower plasma power or growth rate. This emission line has been assigned to the band-to-impurity transition resulting from the recombination between electrons bound to shallow donors and free holes (D 0 , h ϩ). Systematic studies of these optical transitions have been carried out under different temperatures and excitation intensities. The temperature variation of the spectral peak position of the (D 0 , h ϩ) emission line differs from the band gap variation with temperature, but is consistent with an existing theory for (D 0 , h ϩ) transitions. The dynamic processes of the (D 0 , h ϩ) transition have also been investigated and subnanosecond recombination lifetimes have been observed. The emission energy and the temperature dependencies of the recombination lifetime have been measured. These results have provided solid evidence for the assignment of the (D 0 , h ϩ) transition and show that the motions of the free holes which participated in this transition are more or less restricted in the plane of the epitaxial layer at temperatures below 140 K and that the thermal quenching of the emission intensity of this transition is due to the dissociation of neutral donors. Our results show that time-resolved photoluminescence spectroscopy can be of immense value in understanding the optical recombination dynamics in GaN.
Photoluminescence and Excitation Spectra of Deep Defects in GaN
MRS Proceedings, 2001
ABSTRACTDeep defects responsible for broad bands in the red-to-green range of the photoluminescence (PL) spectrum of undoped and Si-doped GaN grown by molecular beam epitaxy (MBE) and hydride vapor phase epitaxy (HVPE) were studied by employing PL and PL excitation (PLE) methods. In HVPE grown samples, a red luminescence (RL) and a green luminescence (GL) bands were observed, respectively, at about 1.9 and 2.4 eV. Similar in positions but different in properties red and green bands (RL2 and GL2, respectively) dominated in the samples grown in Ga-rich conditions by MBE with radio frequency plasma as a nitrogen source (RF-MBE). A yellow luminescence (YL) with a maximum at about 2.2 eV dominated in the samples with ammonia used as a nitrogen source (NH3-MBE). It has been established from the variation of temperature, excitation intensity and excitation wavelength that the abovementioned five bands are related to different deep-level defects.
Time-resolved photoluminescence study of GaN grown by metalorganic chemical vapor deposition
Journal of Crystal Growth, 2000
We have investigated the time decay of the photoluminescence (PL) at room temperature of high-quality (HQ) and low-quality (LQ) GaN epitaxial layers grown on sapphire by metalorganic chemical vapor deposition. For undoped and Si-doped HQ GaN, the full-width at half-maximum of the (1 0 2) X-ray di!raction curve is 562 and 427 arcsec and the dislocation density is 4;10 and 2;10 cm\, respectively. It is found that the PL of HQ GaN has a higher intensity and decays slower than that of LQ GaN. The PL decay time is found to be much longer in HQ GaN. The dual-exponential decay times are 50 and 250 ps for undoped HQ GaN, and 150 and 740 ps for Si-doped HQ GaN. To our knowledge, the decay times of 150 and 740 ps are the longest ever reported in GaN thin "lms at room temperature. Furthermore, the characteristics of PL decay with di!erent excitation intensities and laser beam focusing conditions are also reported.
Blue photoluminescence activated by surface states in GaN grown by molecular beam epitaxy
Applied Physics Letters, 2001
We have studied the broad blue band, which emerges in the photoluminescence (PL) spectrum of c-plane GaN layers after etching in hot H3PO4 and subsequent exposure to air. This band exhibited a 100 meV blueshift with increasing excitation intensity and a thermal quenching with activation energies of 12 and 100 meV. These observations led us to suggest that surface states may be formed on etched surfaces and cause bandbending, which leads to a shift in transition energy with excitation. The blue PL is related to transitions from the shallow donors filled with nonequilibrium electrons to the surface states, which capture the photogenerated holes. The observed irreversible bleaching of the blue luminescence may be attributed to the metastable nature of the surface states or to the oxygen desorption.
Effects of low energy e‐beam irradiation on cathodoluminescence from GaN
2012
We present cathodoluminescence (CL) studies on low energy e-beam irradiated (LEEBI) metal-organic vapor phase epitaxy (MOVPE) grown GaN films. High intensity LEEBI has been reported to reduce the band-edge photoluminescence intensity of MOVPE grown GaN films. Here we observe similar reduction of band-edge CL intensity with increasing LEEBI dose. The irradiation damage is found to be concentrated in the LEEBI energy dissipation depth by CL depth profiling. We have previously attributed the LEEBI induced reduction of band-edge intensity to the activation of in-grown Ga-vacancies. Here we observe no increase in the relative intensity of defect related yellow or blue CL emission peaks in the LEEBI treated samples. This indicates that blue or yellow emission in undoped GaN is not related to in-grown Ga-vacancies.
Photoluminescence study on GaN homoepitaxial layers grown by molecular beam epitaxy
MRS Internet Journal of Nitride Semiconductor Research, 1996
GaN epitaxial layers on GaN single crystals were grown using molecular beam epitaxy with an NH3 source. The deposited layers were examined by high resolution x-ray diffraction and photoluminescence (PL) spectroscopy. We observed strong and extremely narrow (half-widths of 0.5 meV) lines related to the bound excitons. In the higher energy range we observed three strong lines. Two of them are commonly attributed to free exciton transitions A (3.4785 eV) and B (3.483 eV). Their energetic positions are characteristic of strain-free GaN material.
The GaN yellow-luminescence-related surface state and its interaction with air
Cornell University - arXiv, 2022
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.