Identification of defect‐trap‐related europium sites in gallium nitride

Abstract

We performed site-selective combined excitation-emission spectroscopy (CEES) studies on Eu-doped GaN layers grown using Interrupted Growth Epitaxy (IGE). We identified numerous Eu 3+ incorporation sites, which exhibit different relative emission intensities as the growth conditions are varied. We found defecttrap 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.1 Introduction GaN is one of the most promising semiconductor hosts for rare-earth (RE) based light emitters. It can provide carrier generation to excite the RE, it is transparent to visible RE emission, and it is thermally and chemically rugged. The wide-bandgap and the ability to tailor the bandgap through III-N alloying enable matching this material system to many RE 3+ ions. Electroluminescence from GaN doped with Er, Eu, Pr, Tb, Tm and other REs has been reported [1] exhibiting sharp emission lines from the UV to the near IR. Red, green, and blue light emission is possible with the incorporation of the appropriate REs into GaN, meaning the realization of full color displays operating under a variety of conditions is possible with this host material. Moreover, laser action in Eu-doped GaN has been reported under optical excitation [2], rekindling the hope that an electrically-pumped rare-earth-doped semiconductor laser can be realized.In the pursuit of this goal, it becomes important that all rare-earth ions that are in the laser cavity are effectively excited. The presence of multiple RE incorporation sites can complicate matters by introducing different excitation pathways, which can be site-specific. The overall distribution of these different incorporation sites can be controlled by adjusting the conditions of the GaN growth. To optimize these devices for laser operation requires the detailed characterization of the RE incorporation sites in terms of their energy states and their capability to be electrically excited. Of particular interest would be the study of Eu sites that are strongly coupled to defect or impurity traps, as they would have a high capture cross section for free carriers (trap-mediated excitation) and would be efficiently excited by above-bandgap excitations [3]. This is important because above-gap optical excitation simulates the electron-hole pair pumping that occurs during electrical injection of p-n junction diodes.In this work, we address the task of characterizing the different Eu-incorporation sites over a range of GaN layers that have varying crystal growth parameters, using the site-selective technique of combined excitation-emission sp...

Spectroscopic Analysis of Eu3+ Implanted and Annealed GaN Layers and Nanowires

“…Rare-earth (RE)-doped semiconductors have been widely investigated as a class of materials with promising properties, especially in the optoelectronic area, taking advantage of the remarkable atomic-like intra-4f n transitions of the trivalent charged RE ions. − Gallium nitride (GaN) is a direct wide-bandgap semiconductor with a bandgap energy of 3.4 eV at room temperature . GaN and its ternary alloys are well-established materials in solid-state optics/lighting/optoelectronic applications such as light-emitting diodes (LEDs) and laser diodes (LDs). − Among the main advantages as a host for RE ions, GaN exhibits a high transparency which makes it suitable for the incorporation of the ladder-like RE 3+ electronic energy levels promoting the ion optical activation with reduced luminescence thermal quenching. ,, Furthermore, the 3+ charge state is easily achieved since RE are preferentially on the isovalent Ga site . The large values for both thermal conductivity and breakdown fields provide further benefits for high temperature and high power electronic devices …”

Luminescence properties of MOCVD grown Al0.2Ga0.8N layers implanted with Tb

“…The experimental data were fitted by equation (2) and the results are plotted in Figure 8. In the present case, it was found that for samples implanted with temperatures higher than RT, the activation energy for the population is in good agreement with the one obtained for the de-excitation mechanism of the host defect centre (see Figures 6 and 8), suggesting a correlation between the de-excitation processes of the broad visible band and the increasing Tb 3+ emission intensity.…”

“…Such RE-doped materials constitute auspicious platforms in the optoelectronic field, especially owing to the remarkable atomic-like intra-4f n transitions exhibited by the trivalent charged ions. These transitions can be extended over all the visible range, depending on the RE ion chosen [1][2][3][4].…”