MOCVD Growth and Characterization of Be-Doped GaN.

Beryllium has been considered a potential alternative to magnesium as a p-type dopant in GaN, but attempts to produce conductive p-GaN:Be have not been successful. Photoluminescence studies have repeatedly shown Be to have an acceptor level shallower than that of Mg, but deep Be defects and other compensating defects render most GaN:Be materials n-type or semi-insulating at best. Previous reports use molecular beam epitaxy or ion implantation to dope GaN with Be, almost exclusively. Due to the high toxicity of Be organometallics, reports of GaN:Be by metal-organic chemical vapor deposition (MOCVD) have been largely absent. Here, we report a systematic study of growth of GaN:Be by MOCVD. All doped samples show the established UV band and yellow luminescence signature of GaN:Be, and growth conditions resulting in high-quality GaN with stable Be incorporation were established. Our results show that the MOCVD growth technique allows for Be incorporation pathways that have not been possible with previous growth methodologies and is highly promising in achieving p-type conductivity in GaN:Be.

Boronate probe-based hydrogen peroxide detection with AlGaN/GaN HEMT sensor.

The results from this study demonstrate the potential of an AlGaN/GaN high electron mobility transistor sensor for the detection of reactive and transient biological molecules such as hydrogen peroxide. A boronate-based fluorescent probe was used with this device to detect the presence of micromolar levels of hydrogen peroxide typically associated with intracellular processes. The real-time electrical response of the high electron mobility transistor sensor showed a gradual decrease in the two-dimensional electron gas current as the reaction proceeded over time. A corresponding increase in the emission intensity was measured from the fluorescent probe with the progression of the reaction. The fluorescence from the boronate probe was used as an indicator to confirm the detection of hydrogen peroxide. These results demonstrate the dynamic measurement capability of AlGaN/GaN high electron mobility transistor sensors in monitoring real-time reactions of reactive oxygen species such as hydrogen peroxide.

Hillock assisted p-type enhancement in N-polar GaN:Mg films grown by MOCVD.

We report on the enhanced incorporation efficiency of magnesium dopants into facets of hexagonal hillock structures in N-polar GaN, studied by comparative analysis of GaN:Mg films grown by MOCVD on high and low hillock density GaN template layers. Total magnesium concentration in planar regions surrounding a hillock structure is comparable to that within hillock sidewall facets measured at 1.3 × 1019 cm-3 by atom probe tomography, and clustering of Mg atoms is seen in all regions of the film. Within individual hillock structures a decreased Mg cluster density is observed within hillock structures as opposed to the planar regions surrounding a hillock. Additionally, the Mg cluster radius is decreased within the hillock sidewall. The favorable incorporation of Mg is attributed to Mg dopants incorporating substitutionally for Ga during growth of semi-polar facets of the hillock structures. Enhanced p-type conductivity of GaN:Mg films grown on high hillock density template layers is verified by optical and electrical measurement.

3D GaN-based betavoltaic device design with high energy transfer efficiency.

A combined GaN 3D core-shell and planar pin structure is being developed and demonstrated to achieve the highest potential to increase energy transfer efficiency from the source (ηsrc) and power generated per cm2 (PGaN/cm2) in a betavoltaic (BV) device configuration. Physics-based Sentaurus TCAD and Monte Carlo N-Particle extended (MCNPX) software are employed to obtain the maximum ηsrc and PGaN/cm2 by a parametric study of device dimensions coupled with a 63NiCl2 source. Idealized structure dimensions are determined to be 2 µm wide, 4 µm tall GaN pin core-shell mesas, with 63Ni source conformally surrounding the structure with a 2 µm gap for maximum efficiency of energy transfer. For maximizing power deposited (10 µm mesa separation) a 3.75x increase in PGaN/cm2 at approximately half the activity density compared to a planar device is achieved for 4 µm mesa height, with 5.82x improvement in ηsrc.

Metabolic Responses to a Battling Rope Protocol Performed in the Seated or Stance Positions.

Brewer, W, Kovacs, R, Hogan, K, Felder, D, and Mitchell, H. Metabolic responses to a battling rope protocol performed in the seated or stance positions. J Strength Cond Res 32(12): 3319-3325, 2018-The purpose of this study is to compare the levels of oxygen consumption and heart rate responses elicited by a treadmill or cycle V[Combining Dot Above]O2max test with a standing or sitting battling rope protocol (BRP) (treadmill vs. standing BRP) (cycle vs. seated BRP). Forty healthy subjects performed either a ramped V[Combining Dot Above]O2max treadmill or cycle test. At least 3 days later, the subjects who performed the ramped treadmill test did the standing BRP, and the subjects who performed the ramped cycle test did the sitting BRP. Each BRP consisted of 10 sets of 15/45 seconds of work/rest for 10 sets. V[Combining Dot Above]O2peak and HRpeak were recorded. Metabolic responses were significantly lower for the sitting BRP and standing as compared to the HRmax and V[Combining Dot Above]O2max values derived from the bicycle and treadmill tests. The BRP produced a V[Combining Dot Above]O2peak that was 71.87% (sitting) and 68.37% (standing) of the subjects' V[Combining Dot Above]O2max assessed u the bicycle and treadmill protocol. Moderate correlations were found between the V[Combining Dot Above]O2 during the seated (r = 0.61; p = 0.003) and standing (r = 0.43; p = 0.03) BRP and the bicycle and treadmill V[Combining Dot Above]O2max tests, respectively. The HRpeak elicited by the BRP performed in sitting (r = 0.52; p = 0.009) and standing (r = 0.67; p = 0.001) had a moderate correlation with the HRmax derived from the bicycle and treadmill tests. Battling ropes may be a low cost, accessible option to improve cardiovascular endurance for individuals who cannot stand or move their lower extremities in a rhythmic manner to conduct aerobic exercise.