Profiling the temperature distribution in AlGaN/GaN HEMTs with nanocrystalline diamond heat spreading layers

Reduced performance in Gallium Nitride (GaN) based high electron mobility transistors (HEMTs) as a result of self-heating has been well-documented. A new approach, termed “diamond-before-gate" is shown to improve the thermal budget of the deposition process and enables large area diamond without degrading the gate metal NCD capped devices had a 20% lower channel temperature at equivalent power dissipation

Vertical conduction properties of few-layer epitaxial graphene / n-type 4H-SiC heterojunctions at cryogenic temperatures

Vertical diodes of epitaxial graphene on n 4H-SiC were investigated. The graphene Raman spectraexhibited a higher intensity in the G-line than the 2D-line, indicative of a few-layer graphene film.Rectifying properties improved at low temperatures as the reverse leakage decreased over six ordersof magnitude without freeze-out in either material. Carrier concentration of 10 16 cm 3in the SiCremained stable down to 15 K, while accumulation charge decreased and depletion width increasedin forward bias. The low barrier height of 0.08 eV and absence of recombination-induced emissionindicated majority carrier field emission as the dominant conduction mechanism

Investigation of the Epitaxial Graphene/p-SiC Heterojunction

There has been significant research in the study of in-plane charge-carrier transport in graphene in order to understand and exploit its unique electrical properties; however, the vertical graphene–semiconductor system also presents opportunities for unique devices. In this letter, we investigate the epitaxial graphene/p-type 4H-SiC system to better understand this vertical heterojunction. The I–V behavior does not demonstrate thermionic emission properties that are indicative of a Schottky barrier but rather demonstrates characteristics of a semiconductor heterojunction. This is confirmed by the fitting of the temperature-dependent I–V curves to classical heterojunction equations and the observation of band-edge electroluminescence in SiC

Improved GaN-based HEMT performance by nanocrystalline diamond capping

As a wide-bandgap semiconductor, gallium nitride (GaN) is an attractive material for next-generation power devices. To date, the capabilities of GaN-based high electron mobility transistors (HEMTs) have been limited by self-heating effects (drain current decreases due to phonon scattering-induced carrier velocity reductions at high drain fields). Despite awareness of this, attempts to mitigate thermal impairment have been limited due to the difficulties involved with placing high thermal conductivity materials close to heat sources in the device. Heat spreading schemes have involved growth of AIGaN/GaN on single crystal or CVD diamond, or capping of fullyprocessed HEMTs using nanocrystalline diamond (NCD). All approaches have suffered from reduced HEMT performance or limited substrate size. Recently, a "gate after diamond" approach has been successfully demonstrated to improve the thermal budget of the process by depositing NCD before the thermally sensitive Schottky gate and also to enable large-area diamond implementation

Rapid Weight Gain in Pediatric Refugees after US Immigration

Prior studies of immigrants to the United States show significant weight gain after 10 years of US residence. Pediatric refugees are a vulnerable population whose post-immigration weight trajectory has not been studied. We examined the longitudinal weight trajectory of 1067 pediatric refugees seen in a single university based refugee health program between the dates of September 3, 2012 and September 3, 2014 to determine how quickly significant weight gain occurs post-arrival. The most recent BMI was abstracted from the electronic health record and charts reviewed to obtain serial BMI measurements in 3 year increments after the date of US arrival. The mean arrival BMI percentile for all refugees was 47th percentile. This increased significantly to the 63rd percentile within 3 years of US arrival (p < 0.01). This rapid increase was largely attributable to African and South and Southeast Asian refugees. The overall prevalence of age and sex adjusted obesity rose from 7.4 % at arrival to 18.3 % within 9 years of US immigration exceeding the pediatric US national obesity prevalence of 16.9 %. Pediatric refugees are at increased risk of rapid weight gain after US immigration. Targeted interventions focused on prevention of weight gain in specific populations are warranted.12 month embargo; First Online: 08 July 2016This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Rapid Weight Gain in Pediatric Refugees after US Immigration

Prior studies of immigrants to the United States show significant weight gain after 10 years of US residence. Pediatric refugees are a vulnerable population whose post-immigration weight trajectory has not been studied. We examined the longitudinal weight trajectory of 1067 pediatric refugees seen in a single university based refugee health program between the dates of September 3, 2012 and September 3, 2014 to determine how quickly significant weight gain occurs post-arrival. The most recent BMI was abstracted from the electronic health record and charts reviewed to obtain serial BMI measurements in 3 year increments after the date of US arrival. The mean arrival BMI percentile for all refugees was 47th percentile. This increased significantly to the 63rd percentile within 3 years of US arrival (p < 0.01). This rapid increase was largely attributable to African and South and Southeast Asian refugees. The overall prevalence of age and sex adjusted obesity rose from 7.4 % at arrival to 18.3 % within 9 years of US immigration exceeding the pediatric US national obesity prevalence of 16.9 %. Pediatric refugees are at increased risk of rapid weight gain after US immigration. Targeted interventions focused on prevention of weight gain in specific populations are warranted.12 month embargo; First Online: 08 July 2016This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Degradation mechanisms of 2 MeV proton irradiated AlGaN/GaN HEMTs

Proton-induced damage in AlGaN/GaN HEMTs was investigated using energy-dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM), and simulated using a Monte Carlo technique. The results were correlated to electrical degradation using Hall measurements. It was determined by EDS that the interface between GaN and AlGaN in the irradiated HEMT was broadened by 2.2 nm, as estimated by the width of the Al EDS signal compared to the as-grown interface. The simulation results show a similar Al broadening effect. The extent of interfacial roughening was examined using high resolution TEM. At a 2 MeV proton fluence of 6 × 1014 H+/cm2, the electrical effects associated with the Al broadening and surface roughening include a degradation of the ON-resistance and a decrease in the electron mobility and 2DEG sheet carrier density by 28.9% and 12.1%, respectively