A comparison is presented between Eu implanted and Eu in situ doped GaN thin films showing that two predominant Eu sites are optically active around 620 nm in both types of samples with below and above bandgap excitation. One of these sites, identified as a Ga substitutional site, is common to both types of Eu doped GaN samples despite the difference in the GaN film growth method and in the doping technique. High-resolution photoluminescence (PL) spectra under resonant excitation reveal that in all samples these two host-sensitized sites are in small amount compared to the majority of Eu ions which occupy isolated Ga substitutional sites and thus cannot be excited through the GaN host. The relative concentrations of the two predominant host-sensitized Eu sites are strongly affected by the annealing temperature for Eu implanted samples and by the group III element time opening in the molecular beam epitaxy growth. Red luminescence decay characteristics for the two Eu sites reveal different excitation paths. PL dynamics under above bandgap excitation indicate that Eu ions occupying a Ga substitutional site are either excited directly into the D50 level or into higher excited levels such as D51, while Eu ions sitting in the other site are only directly excited into the D50 level. These differences are discussed in terms of the spectral overlap between the emission band of a nearby bound exciton and the absorption bands of Eu ions. The study of Eu doped GaN quantum dots reveals the existence of only one type of Eu site under above bandgap excitation, with Eu PL dynamics features similar to Eu ions in Ga substitutional sites.

Using combined excitation emission spectroscopy, we performed a comparative study of europium ions in GaN in samples that have been in situ doped during interrupted growth epitaxy (IGE) or conventional molecular beam epitaxy (MBE) as well as samples that were grown using organometallic vapor phase epitaxy (OMVPE) and subsequently ion implanted with Eu ions. Through site-selective resonant excitation, we are able to unambiguously assign all major observed transitions to a combination of different incorporation sites and electron–phonon coupled transitions. We identified at least nine different incorporation sites of Eu ions in GaN and studied how these sites behave under different excitation conditions and how their relative number is modified by different growth and doping conditions. The coupling to phonons has also been studied for a series of Al x Ga1−x N samples with x=0…1. We find that a main site most resembling an unperturbed Eu ion on Ga site is always dominant, while the minority sites are changing substantially in relative numbers and can occur in some samples fairly close in emission intensity to the main site. In terms of the excitation pathway after the creation of electron-hole pairs, we found three types of centers: (1) sites that are dominantly excited through shallow defect traps; (2) sites that are excited through a deep defect trap; (3) sites that cannot be excited at all including the majority of the main sites. We interpret this finding to indicate that the ion in this environment is not very efficient in trapping excitation and that the indirect excitation involving other traps depends on the ion/trap distance. Many of the main sites are far away from these traps and cannot be excited through this channel at all. The efficiency of excitation is highest for the deep traps, indicating that it would be desirable to enrich the respective site, as has been done with some success in the IGE grown samples.

We performed site-selective combined excitation-emission spectroscopy (CEES) studies on Eu-doped GaN layers grown using Interrupted Growth Epitaxy (IGE). We identified numerous Eu3+ incorporation sites, which exhibit different relative emission intensities as the growth conditions are varied. We found defect-trap related Eu sites that can be excited over a wide spectral range and that dominate the photoluminescence spectra for above-bandgap, excitation. Spectra obtained through above-bandgap, excitation, which simulates EL operation, are identical to the emission spectra of these defect-trap related sites, indicating that these particular Eu ions would be the major contributors to electroluminescent (EL) emission in these samples. In resonant excitation, however, the emission from these sites is rather weak suggesting that these are minority sites. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Site-selective combined excitation emission spectroscopy studies have been performed on Eu-doped GaN and numerous sites have been identified. Relative numbers and broadening of these peaks has been investigated for different growth conditions. (c) 2004 Optical Society of America

An improved thick dielectric (TD) layer for inorganic electroluminescent (EL) display devices has been achieved through a composite high-/spl kappa/ dielectric sol-gel/powder route. This composite TD film results in a luminance improvement (up to 10/spl times/) in these TDEL devices with Eu-doped GaN and Mn-doped ZnS phosphor layers. The use of a composite TD film, composed primarily of lead-zirconate-titanate (PZT), results in a significantly higher charge (>3 /spl mu/C/cm/sup 2/) coupling to the phosphor layer. Furthermore, the reduction in porosity of the TD has improved the homogeneity of electric field applied to the phosphor layer, resulting in a steeper luminance-voltage slope. The reduction in porosity has also decreased the diffuse reflection of the TD, which when pigmented, exhibits a diffuse reflectivity of <2% resulting in high display contrast. High luminance levels of up to 3500 cd/m/sup 2/ have been achieved from the ZnS:Mn TDEL devices and 450 cd/m/sup 2/ from GaN:Eu devices. A detailed analysis of the electrical steady-state time-varying characteristics has shown that the electrical performance of TDELs is very similar to TFELs in spite of the physical asymmetry in the device structure. These results demonstrate that three critical requirements for practicality of the TDEL approach (formation on standard display glass, low reflectivity, and electric field homogeneity) can be obtained by careful selection and design of the device materials, fabrication process and device structure.

In this paper, we report on Er-doped ZSG waveguide amplifiers and electroluminescent devices (ELDs). A 3.5 /spl mu/m wide ZSG:Er optical amplifier with a core thickness of 1.1 /spl mu/m and a length of 4.7 cm was fabricated. The refractive index variation with wavelength was obtained using a variable wavelength spectroscopic ellipsometer with a 0.27 /spl mu/m ZSG:Er sample. The results indicate that electroluminescent optical amplifiers in ZSG:Er films are possible.

In this paper we report oil electroluminescent devices fabricated using Eu-doped GaN films grown by interrupted growth epitaxy (IGE). IGE is a combination of conventional molecular beam epitaxy and migration enhanced epitaxy. It consists of a sequence of ON/OFF cycles of the Ga and Eu beams, while the N-2 plasma is kept constant during the entire growth time. IGE growth of GaN:Eu resulted ill significant enhancement in the Eu emission intensity at 620.5 nm. The nitridation of the surface that occurs during the OFF cycle appears to be the dominant process producing the enhancement. Thick dielectric devices fabricated on glass Substrates using IGE-grown GaN:Eu have resulted in luminance of similar to 1000 cd/m(2) and luminous efficiency of similar to 0. 15 Im/W. (c) 2005 Elsevier B.V. All rights reserved.

Site-selective combined excitation emission spectroscopy studies have been performed on Eu-doped GaN and numerous sites have been identified. Relative numbers and broadening of these peaks has been investigated for different growth conditions and for increasing AL content of the AlxGa1-xN alloy.

Time-resolved photoluminescence spectroscopy of rare earth (Eu, Er, Tm) -doped GaN revealed that optical properties and relaxation dynamics depend surprisingly upon excitation energy, pulse width, temperature, and dopant site.

In this paper we report GaN:Eu AC-TDEL devices with high luminance and high efficiency levels obtained through optimized phosphor growth techniques and device structure. The GaN:Eu phosphor is grown using interrupted growth epitaxy (IGE ™). An improved thick dielectric layer for inorganic electroluminescent EL display devices has been achieved through a composite high-κ dielectric sol-gel/powder route. The reduction in thick dielectric porosity has improved the homogeneity of the electric field applied to the phosphor layer, resulting in a steeper luminance-voltage slope with a maximum luminance of ~1,000 cd/m 2 . Furthermore, the reduction in porosity has also decreased the diffuse reflection of the thick dielectric, which when pigmented, exhibits a diffuse reflectivity of <2% resulting in high display contrast.

In this paper, we report on the optimization of TDEL devices in both the phosphor material and the device structure. The TDEL device consists of a metal-insulator-semiconductor-insulator-metal (MISIM) stacked film structure built upon a transparent glass substrate. The high dielectric constant and break down field of PZT thick dielectric film along with the other thin film stacks has enabled a significantly higher charge (>3 μC/cm2) transport across the phosphor layer. Furthermore, the nano-porous PZT film has reduced the intensity of high field points in the device, resulting in a steeper luminance-voltage slope after device turn-on. We have also found that the phosphor electric field of the TDEL surpasses that of a thin film electroluminescent (TFEL) device, resulting in higher efficiencies under same biasing conditions.

In this paper, we discuss the fabrication, operation and aplications of rare-earth-doped GaN electroluminescent devices (ELDs). GaN:RE ELDs. GaN:RE ELDs emit light due to impact excitation of the RE ions by hot carriers followed by radiative relaxation. By appropriately choosing the RE dopant, narrow line width emission can be obtained at selected wavelengths from the ultraviolet to the infrared. The deposition of GaN:RE layers is carried out primarily by MBE. GaN growth mechanism and optimization for RE emission are discussed based on RE concentration, growth temperature, and III-V ratio. We have investigated the optimum growth conditions of RE doped GaN phosphors.

An overview of inorganic EL (iEL) flat panel displays (FPD) is presented. This includes a summary of the key points of iEL device operation and on overview of the impact of new phosphors and dielectric materials critical in EL device operation. This is followed by in-depth review of iEL devices and displays utilizing rare-earth-doped GaN and transition-metal-doped ZnS, in conjunction with high dielectric constant insulating layers. Next, a brief status of companies in the iEL field is given. Finally, speculative concepts on combining inorganic and organic light emitting materials are discussed.