Abstract Body: The next generation of solid-state power electronics will increasingly utilize the AlxGa1-xN system, benefitting from its large and direct band gap, high switching speed, and high FOM. Formation of selective-area p-type regions is critical for field management and remains a significant challenge for higher-voltage next-generation architectures. Activation of the p-type dopant Mg, especially in the case of ion-implanted AlxGa1-xN, requires temperatures high enough to cause significant diffusion of the dopant, potentially distorting the doped region shape. Microwave annealing has been shown to induce both dopant activation and diffusion, especially for rapid drive-in of B in Si1 Diffusion dynamics induced by microwave annealing can diverge from those suggested by the bulk thermal condition of the sample. This has been attributed to interaction of the microwave beam with ionized defects and dopants in the material, permitting higher diffusion of electrically charged (ionized) species in the lower-temperature bulk2. This makes understanding Mg redistribution in GaN due to microwave annealing in both implanted and in-situ doped material of critical importance to the continued development of selective-area doping. In order to better understand this diffusion and activation behavior, a study was conducted of spatially resolved Mg distribution in in-situ doped and implanted GaN grown by metalorganic chemical vapor deposition (MOCVD) and annealed by gyrotron microwave beam. Annealing conditions between 1160–1410 °C were performed for durations between 30–65 s in total using a quasi-gaussian beam intensity profile and a 2.5 cm beam raster across the sample surface. Low-temperature PL spectra were measured and used as a proxy for acceptor activation before and after annealing of doped GaN. At the locations of PL measurements on samples, depth profiles of [Mg] were taken using dynamic secondary ion mass spectroscopy (D-SIMS). Beyond concentrations of around 1016 cm-3, the intensity of PL bands is not linearly related to the density of acceptors in the material3, however PL spectra have been shown to indicate the presence of conductivity type, provided initial knowledge of the growth condition. The as-implanted [Mg] profile of all samples shows a profile of 1×1019 cm-3 to a depth of 250 nm with a quasi-Gaussian tail. The in-situ doped as-grown [Mg] of 7×1019 cm-3 remains constant from the surface to the p-GaN layer depth of ~120 nm before annealing, and the profile does not appreciably change after annealing. After annealing implanted samples above 1350 °C, diffusion of Mg dopant is observed to vary spatially across the sample, correlating approximately with the beam shape and raster. To understand potential correlation of such diffusion with PL bands, measurements on the same location as SIMS measurement was performed. PL measurements show the characteristic near-band edge (NBE) luminescence at 3.47 eV and Mg-acceptor-related UVL at 3.27 eV in all spectra. In the 2.2–2.4 eV range, either the VN-related GL2 band or the CN-ON-related YL band is dominant. Relative intensity of these bands varies across the sample area, however no correlation of PL activity with Mg diffusion is observed. We show that while PL activity reflects the presence of MgGa and other optically active defects within the laser excitation depth (~92 nm), (anneal-induced) diffusion has no significant impact on [Mg] within this depth, and therefore that diffused Mg deeper in the sample (200–800 nm) does not necessarily impact PL activity. This may be due in part to the upper limit of PL sensitivity to acceptor concentration3. This work was funded by a grant from ARPA-E PNDIODES program, grant #DE-FOA-001691 under the direction of Dr. Isik C. Kizilyalli. [1] Kohli, P., et al. (2002). J. of Electron. Mat., 31(3), 214-219. [2] Booske, J. H., Cooper, R. F., & Dobson, I. (1992). J. Mat. Research, 7(2), 495-501. [3] Reshchikov, M. A., et al. (2017). Scientific reports 7(1), 1-11.

Microwave-Induced Annealing, Its Impact on Mg Diffusion and Photoluminescence Activity in Implanted and In Situ Doped GaN

This talk will review applications of the Cs+ Low Temperature Ion Source (LoTIS). This ion source enables high precision FIB imaging and machining, and also high-yield secondary ion mass spectrometry (SIMS)

Applications of the Cesium Low Temperature Ion Source

A two-dimensional array of transmissive microshutters is designed in which light throughput can be digitally modulated at each pixel. This function is important for certain instruments, such as the near infrared spectrometer to be carried on the James Webb Space Telescope, microscopes, telephoto lenses, or digital light processors.

Transmissive Microshutter Arrays

UD Mass Spectrometry Core Facility

Glucocorticoid Production in the Nervous and Immune Systems: Evidence for a Local HPA Axis HomologThe hypothalamic-pituitary-adrenal (HPA) axis is a critical stress response system in vertebrates. The hypothalamus secretes corticotropin-releasing hormone (CRH), which binds its receptor (CRH-R1) in the anterior pituitary. The anterior pituitary then secretes adrenocorticotropic hormone (ACTH), which binds its receptor (MC2R) in the adrenal glands and stimulates secretion of glucocorticoids into the bloodstream. Glucocorticoids are critical modulators of neural and immune system development. During early development (postnatal day (PND) 2 to 12), mice show decreased adrenal glucocorticoid secretion at baseline and in response to stressors, termed the stress hyporesponsive period (SHRP) (1). Traditionally, glucocorticoids have been thought to be synthesized only in the adrenal glands. However, recent evidence demonstrates that glucocorticoids are also produced in extra-adrenal tissues, such as the brain and lymphoid organs (2). This may be of particular importance during the SHRP, as local production allows glucocorticoid modulation of specific tissues and cells, without general effects throughout the organism. Importantly, the factors that regulate local glucocorticoid production remain unknown. To study the regulation of local glucocorticoid production, we examined whether mediators of the HPA axis are locally expressed at baseline and in response to an immune stressor. We assessed systemic and local glucocorticoid levels in neonatal (PND5) C57BL/6J mice 4hr after an immune challenge with lipopolysaccharide (50µg/kg i.p.) or vehicle control. We examined blood, microdissected brain regions (prefrontal cortex, hippocampus, hypothalamus), and lymphoid organs (thymus, spleen, bone marrow). A panel of 7 steroids was measured via liquid chromatography tandem mass spectrometry (LC-MS/MS). Gene expression of Crh, Crh-R1, Pomc, and Mc2r was quantified via qPCR. Preliminary data indicate that corticosterone was 2-fold higher in tissues than in blood after an immune stressor. The thymus expressed all genes of interest, supporting the existence of a local HPA axis “homolog” in the thymus. Brain, spleen and bone marrow expressed a subset of the genes of interest. These exciting data demonstrate that all the mediators of the HPA axis are locally expressed within the thymus, likely to regulate thymocyte development and reactivity. Greater understanding of local glucocorticoid production will provide crucial insight into neural and immune development and function. Reference: (1) Sapolsky et al., Brain Res Rev. 1986 11(1):65-76. (2) Taves et al., Endocrinology. 2015 156(2):511-522.

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Microwave-Induced Annealing, Its Impact on Mg Diffusion and Photoluminescence Activity in Implanted and In Situ Doped GaN

Applications of the Cesium Low Temperature Ion Source

Transmissive Microshutter Arrays

UD Mass Spectrometry Core Facility

Glucocorticoid Production in the Nervous and Immune Systems: Evidence for a Local HPA Axis Homolog

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