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Low resistance n+GaN contact materials were experimentally studied for GaN HEMT applications by selective area epitaxy regrowth on a patterned SiC substrate. Epitaxy was performed by metal organic chemical vapor deposition using 100% H2 or 100% N2 as the carrier gas. Thin film characterization demonstrated that n+GaN grown in N2 carrier gas has a superior morphology with improved crystalline quality to that grown in H2 carrier gas. The results also indicated that the surface morphology of n+GaN grown in N2 carrier gas is less sensitive to mask pattern density and micro-loading effects with Si doping concentrations up to 1 × 1020/cm3. Secondary ion mass spectrometry analysis shows that C and O impurity levels in n+GaN are one order of magnitude lower with N2 carrier gas than with H2. The electrical measurement of transmission line model structures shows an n+GaN sheet resistance of 15 Ω/sq and an Ohmic metal to n+GaN contact resistance of 0.02 Ω-mm for structures grown in N2 carrier gas. These values represent 7.1× and 2.5× improvements compared to H2 carrier gas.

AlScN is attractive as a lattice-matched epitaxial barrier layer for incorporation in GaN high electron mobility transistors due to its large dielectric constant and polarization. The transport properties of polarization-induced two-dimensional (2D) electron gas of densities of [Formula: see text]/cm2 formed at the AlScN–GaN interface is studied by Hall-effect measurements down to cryogenic temperatures. The 2D electron gas densities exhibit mobilities limited to ∼300 cm2/V s down to 10 K at AlScN/GaN heterojunctions. The insertion of a ∼2 nm AlN interlayer boosts the room temperature mobility by more than five times from ∼300 cm2/V s to [Formula: see text] cm2/V s, and the 10 K mobility by more than 20 times to ∼6980 cm2/V s at 10 K. These measurements provide guidelines to the limits of electron conductivities of these highly polar heterostructures.

Background: Hesitancy towards the coronavirus disease 2019 (COVID-19) vaccine has been a topic of considerable concern in recent months. Studies have reported hesitancy within the general population and specific facets of the health care system. Little evidence has been published about vaccine hesitancy among Emergency Medical Services (EMS) providers despite them having played a frontline role throughout the pandemic. Methods: A 27-question survey examining vaccination decisions and potential influencing factors among EMS providers was created and disseminated. Responses from providers who declined a COVID-19 vaccine were compared with responses from providers who did not decline a COVID-19 vaccine. Results: Across 166 respondents, 16% reported declining a COVID-19 vaccine. Providers who self-identified as men, providers who reported conservative or conservative-leaning beliefs, and providers surrounded by environments where the vaccine was discussed negatively or not encouraged are significantly more likely to decline a vaccine (P <.01). Providers who have declined a vaccine reported significantly greater levels of concern about its safety, effectiveness, and development (P <.01). Conclusion: This study answers key questions about why some EMS providers might be declining COVID-19 vaccinations. Initiatives to improve vaccination among EMS providers should focus on the areas highlighted, and further studies should continue to examine vaccine hesitancy among EMS providers as well as in other populations.

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