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Abstract This work demonstrates the capability to crystallize YAG via femtosecond pulsed laser. Challenges in using melt‐quench glass are shown to restrict glass composition and have not yielded YAG via femtosecond laser crystallization. An alternative glass‐making technique was used to fabricate a range of compositions not otherwise possible. Glasses of YAG with added silica in the range of 0–20 mol% were tested under the laser to explore the allowable deviation from stoichiometric YAG. Raman spectroscopy and Electron backscatter diffraction indicated successful fabrication of YAG, and usage of combined excitation emission spectroscopy (CEES) allowed probing of erbium doped compositions. 

Erbium doped single crystals of lithium niobate were grown within the bulk of 0.075 Er2O3 – 37 Li2O – 37 Nb2O5 – 26 SiO2 glass using a femtosecond pulsed laser. Combined excitation emission spectroscopy was used to show incorporation of erbium into the laser written crystal lattice. Laser power and scanning speed were held constant at optimized values, while bulk sample temperature was systematically varied to study the impact on the crystal growth. Using electron backscatter diffraction to study the transverse cross-sections of grown crystals, control over the lattice rotation rates and crystal size were realized. Unlike changing other parameters, a range of temperatures were found to have substantial impacts on crystal growth, without inhibiting the ability to maintain single crystal formation over long distances. 

Traditional PhD training in STEM fields places a strong emphasis on developing doctoral students' academic skills, encompassing research, academic writing, as well as sharing of knowledge through publications and conference presentations, etc. However, with the ever evolving expectations of graduate training, particularly in applied fields, the demand for PhD has transcended the confines of academia. For instance, nearly 90% of engineering PhDs will not enter academia, which underscores the discrepancy between the current PhD training programs and the preparation of students for future careers. To better support doctoral students especially for those who intend to pursue positions in industry including corporate R&D labs, national labs, defense organizations, healthcare institutes, etc., Lehigh University launched an innovative program called Pasteur Partners PhD (P3) specifically for the training of such doctoral students. It is a student-centered doctoral training program based on use-inspired research in partnership with industry. A preliminary evaluation of the P3 program, which was developed with support from NSF’s IGE program, revealed that students benefited significantly from gaining practical skills through industry involvement such as co-advising, resulting in a clearer understanding of how the industry operates, which, in turn, enhanced their employability in the industry [1]. The University administration also provided significant support for the program. However, a broader implementation of P3 encountered challenges and hesitancy from faculty members. Mostly the senior faculty who already had preexisting connections with industry and junior faculty from certain departments were more receptive to joining the P3 program than others. Could this be a result of the prevailing emphasis of the graduate education system on research output (publications) rather than the training of students for their subsequent careers? What other reasons could there be for the faculty’s lack of enthusiasm for the training of their PhD students following P3 track? To answer above questions and examine the challenges and obstacles that the faculty members feel for student centered doctoral training from an institutional and system perspective, we are conducting a survey specifically targeting faculty members in STEM fields. It seeks to comprehensively understand faculty members’ perspective on the primary objectives of doctoral training within different STEM fields. By exploring these objectives, the survey aims to uncover how they vary across disciplines and what faculty members perceive as the most significant goals in their areas of expertise. Moreover, the survey is designed to shed light on the challenges and hurdles faced by faculty members in their pursuit of these training objectives. Faculty participants are encouraged to identify and articulate the specific obstacles they encounter, whether they pertain to institutional constraints, resource limitations, demands of perceived professional success or other factors that impede the realization of these goals. In addition, the survey takes a close look at the resources that faculty members believe would be beneficial in addressing these challenges and improving the effectiveness of doctoral training. This insight is essential for designing support systems that can empower faculty to contribute to the training of doctoral workforce for the benefit of society at large. The survey seeks to gain valuable perspectives on the qualities and skills considered essential for the success of PhD students. These insights will inform curriculum development and help prepare students better for a wider range of career paths. The results of the survey, currently underway, are presented. 

Abstract Eu-doped Gallium nitride (GaN) is a promising candidate for GaN-based red light-emitting diodes, which are needed for future micro-display technologies. Introducing a superlattice structure comprised of alternating undoped and Eu-doped GaN layers has been observed to lead to an order-of-magnitude increase in output power; however, the underlying mechanism remains unknown. Here, we explore the optical and electrical properties of these superlattice structures utilizing terahertz emission spectroscopy. We find that ~0.1% Eu doping reduces the bandgap of GaN by ~40 meV and increases the index of refraction by ~20%, which would result in potential barriers and carrier confinement within a superlattice structure. To confirm the presence of these potential barriers, we explored the temperature dependence of the terahertz emission, which was used to estimate the barrier potentials. The result revealed that even a dilutely doped superlattice structure induces significant confinement for carriers, enhancing carrier recombination within the Eu-doped regions. Such an enhancement would improve the external quantum efficiency in the Eu-doped devices. We argue that the benefits of the superlattice structure are not limited to Eu-doped GaN, which provides a roadmap for enhanced optoelectronic functionalities in all rare-earth-doped semiconductor systems. 

For the development of III-nitride-semiconductor-based monolithic micro-light-emitting diode (LED) displays, Eu,O-codoped GaN (GaN:Eu,O) is a promising material candidate for the red LEDs. The luminescence efficiency of Eu-related emission strongly depends on the local atomic structure of Eu ions. Our previous research has revealed that post-growth thermal annealing is an effective method for reconfiguring luminescent sites, leading to a significant increase in light output. We observed the preferential formation of a site with a peak at ∼2.004 eV by the annealing process. In this study, we demonstrate that it is a previously unidentified independent site (OMVPE-X) using combined excitation–emission spectroscopy and time-resolved photoluminescence measurements. In addition, we perform excitation power-dependent photoluminescence measurements and show that this OMVPE-X site dominates the emission at a low excitation power region despite its small relative abundance, suggesting a high excitation efficiency. Most importantly, applying our annealing technique to an LED exhibits a reasonably increased electroluminescence intensity associated with OMVPE-X, confirming that this site has a high excitation efficiency also under current injection. These results demonstrate the importance of OMVPE-X as a notable luminescent site for brighter and more efficient GaN:Eu,O-based LEDs.