Gate stability of GaN-Based HEMTs with P-Type Gate

status: publishe

Prediction of chemical composition and peroxide value in unground pet foods by near-infrared spectroscopy

The massive development of the pet food industry in recent years has lead to the formulation of hundreds of canine and feline complete extruded foods with the objective of meeting both the needs of the animals and numerous demands from pet owners. In the meantime, highly variable raw material compositions and the industry's new production techniques oblige manufacturers to monitor all phases of the extrusion process closely in order to ensure the targeted composition and quality of the products. This study aimed at evaluating the potential of infrared technology (visible and near-infrared spectrophotometer; 570-1842 nm) in predicting the chemical composition and peroxide value (PV) of unground commercial extruded dog foods. Six hundred and forty-nine commercial extruded dog foods were collected. For each product, an unground aliquot was analysed by infrared instrument while a second aliquot was sent to a laboratory for proximate analysis and PV quantification. The wide range of extruded dog food typologies included in the study was responsible for the wide variability observed within each nutritional trait, especially crude fibre and ash. The mean value of the 208 pet foods sampled for PV quantification was 17.49 mEq O2/kg fat (min 2.2 and max 94.10 mEq O2/kg fat). The coefficients of determination in cross-validation of NIRS prediction models were 0.77, 0.97, 0.83, 0.86, 0.78 and 0.94 for moisture, crude protein, crude fat, crude fibre, ash and nitrogen-free extract (NFE) respectively. PV prediction was less precise, as demonstrated by the coefficient of determination in cross-validation (0.66). The results demonstrated the potential of NIRS in predicting chemical composition in unground samples, with lower accuracy for moisture and ash, while PV prediction models suggest use for screening purposes only

Effects of dislocation density on injection and temperature sensitivity of InGaN LED emission spectra: a combined experimental and simulation approach

The aim of this paper is to describe a combined simulation and characterization activity carried out on blue LEDs grown on templates with different threading dislocation densities (TDDs)

Nadir creatinine as a predictor of renal outcomes in PUVs: A systematic review and meta-analysis

Background: Posterior urethral valves (PUVs) represent the most severe pediatric obstructive uropathy, responsible for chronic renal failure in up to 65% of cases and progression to end-stage kidney disease (ESKD) in about 8%–21% of patients. Unfortunately, renal outcomes have poorly improved over time. The key point is to identify patients at risk; thus, several prenatal and postnatal prognostic factors have been analyzed to improve clinical outcomes. Postnatal nadir creatinine seems to accurately predict long-term renal prognosis, but there is no definitive evidence to support this finding. Objective: We performed a systematic review with meta-analysis to analyze the predictive value of nadir creatinine on long-term renal function in infants with PUVs. Methods: We conducted this systematic review according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. PubMed and Cochrane Library were systematically searched for studies published from January 2008 to June 2022. All the articles were checked independently by two reviewers in two steps. Results: A total of 24 articles were screened, and 13 were included for data extraction. Data from 1,731 patients with PUVs were analyzed, with a mean follow-up of 5.5 years; of these, on average, 37.9% developed chronic kidney disease (CKD) and 13.6% developed ESKD. All the articles evaluated nadir creatinine as a predictor of CKD, most using a level of 1 mg/dL, with statistical significance at the 5% level. The relative risk of developing CKD in patients with creatinine values higher than the nadir cutoff considered was 7.69 (95% CI: 2.35–25.17, I2 = 92.20%, p < 0.001). Conclusions: Nadir creatinine is the best prognostic factor for long-term renal function in patients affected by PUV. A value above the cutoff of 1 mg/dL should be considered a significant predictor for the risk of CKD and ESKD. Further studies are needed to define different nadir creatinine cutoffs for better stratification of the different CKD stages and for the development of reliable scores, which include the association of several variables

Buffer breakdown in GaN-on-Si HEMTs: A comprehensive study based on a sequential growth experiment

Abstract The aim of this work is to investigate the breakdown mechanisms of the layers constituting the vertical buffer of GaN-on-Si HEMTs; in addition, for the first time we demonstrate that the breakdown field of the AlN nucleation layer grown on a silicon substrate is equal to 3.2 MV/cm and evaluate its temperature dependence. To this aim, three samples, obtained by stopping the epitaxial growth of a GaN on Silicon stack at different steps, are studied and compared: Si/AlN, Si/AlN/AlGaN, full vertical stack up to the Carbon doped buffer layer. The current-voltage (IV) characterizations performed at both room temperature and high temperature show that: (i) the defectiveness of the AlN nucleation layer is the root cause of the leakage through an AlN/Silicon junction, and causes the vertical I-V characteristics to have a high device-to-device variability; (ii) the first AlGaN layer grown over the AlN, beside improving the breakdown voltage of the whole structure, causes the leakage current to be more stable and uniform across the sample area; (iii) a thick strain-relief stack and a carbon-doped GaN buffer enhance the breakdown voltage up to more than 750 V at 170 °C, and guarantee a remarkably low device-to-device variability. Furthermore, a set of constant voltage stress on the Si/AlN sample demonstrate that the aluminum nitride layer shows a time dependent breakdown, with Weibull-distributed failures and a shape factor greater than 1, in line with the percolation model

degradation of gan on gan vertical diodes submitted to high current stress

Abstract GaN-on-GaN vertical devices are expected to find wide application in power electronics, thanks to the high current densities, the low on-resistance and the high breakdown voltage. So far, only few papers on the reliability of GaN-on-GaN vertical devices have been published in the literature. This paper investigates the degradation of GaN-on-GaN pn diodes submitted to stress at high current density. The study was carried out by means of electrical characterization and electroluminescence (EL) measurements. We demonstrate that: (i) when submitted to stress at high current density, the devices show significant changes in the electrical characteristics: an increase in on-resistance/turn-on voltage, an increase in the generation/recombination components, the creation of shunt-paths. (ii) the increase in on-resistance is strongly correlated to the decrease in the EL signal emitted by the diodes. (iii) the degradation kinetics have a square-root dependence on time, indicative of a diffusion process. The results are interpreted by considering that stress induces a diffusion of hydrogen from the highly-p-type doped surface towards the pn junction. This results in a decrease in hole concentration, due to the creation of Mg H bonds, and in a lower hole injection. As a consequence, on-resistance increases while EL signal shows a correlated decrease

Correlating electroluminescence characterization and physics-based models of InGaN/GaN LEDs: Pitfalls and open issues

Electroluminescence (EL) characterization of InGaN/GaN light-emitting diodes (LEDs), coupled with numerical device models of different sophistication, is routinely adopted not only to establish correlations between device efficiency and structural features, but also to make inferences about the loss mechanisms responsible for LED efficiency droop at high driving currents. The limits of this investigative approach are discussed here in a case study based on a comprehensive set of current- and temperature-dependent EL data from blue LEDs with low and high densities of threading dislocations (TDs). First, the effects limiting the applicability of simpler (closed-form and/or one-dimensional) classes of models are addressed, like lateral current crowding, vertical carrier distribution nonuniformity, and interband transition broadening. Then, the major sources of uncertainty affecting state-of-the-art numerical device simulation are reviewed and discussed, including (i) the approximations in the transport description through the multi-quantum-well active region, (ii) the alternative valence band parametrizations proposed to calculate the spontaneous emission rate, (iii) the difficulties in defining the Auger coefficients due to inadequacies in the microscopic quantum well description and the possible presence of extra, non-Auger high-current-density recombination mechanisms and/or Auger-induced leakage. In the case of the present LED structures, the application of three-dimensional numerical-simulation-based analysis to the EL data leads to an explanation of efficiency droop in terms of TD-related and Auger-like nonradiative losses, with a C coefficient in the 10−30 cm6/s range at room temperature, close to the larger theoretical calculations reported so far. However, a study of the combined effects of structural and model uncertainties suggests that the C values thus determined could be overestimated by about an order of magnitude. This preliminary attempt at uncertainty quantification confirms, beyond the present case, the need for an improved description of carrier transport and microscopic radiative and nonradiative recombination mechanisms in device-level LED numerical models

Modeling the electrical characteristics of InGaN/GaN LED structures based on experimentally-measured defect characteristics

Defects can significantly modify the electro-optical characteristics of InGaN light-emitting diodes (LEDs); however, modeling the impact of defects on the electrical characteristics of LEDs is not straightforward. In this paper, we present an extensive investigation and modeling of the impact of defects on the electrical characteristics of InGaN-based LEDs, as a function of the thickness of the quantum well (QW). First, we demonstrate that the density of defects in the active region of III-N LEDs scales with increasing thickness of the InGaN QW. Since device layers with high indium content tend to incorporate more defects, we ascribed this experimental evidence to the increased volume of defects-rich InGaN associated to thicker InGaN layers. Second, we demonstrate that the current-voltage characteristics of the devices are significantly influenced by the presence of defects, especially in the sub turn-on region. Specifically, we show that the electrical characteristics can be effectively modeled in a wide current range (from pA to mA), by considering the existence of trap-assisted tunneling processes. A good correspondence is obtained between the experimental and simulated electrical characteristics (I-V), by using-in the simulation-the actual defect concentrations/activation energies extracted from steady-state photocapacitance, instead of generic fitting parameters

The 2018 GaN Power Electronics Roadmap

Gallium nitride (GaN) is a compound semiconductor that has tremendous potential to facilitate economic growth in a semiconductor industry that is silicon-based and currently faced with diminishing returns of performance versus cost of investment. At a material level, its high electric field strength and electron mobility have already shown tremendous potential for high frequency communications and photonic applications. Advances in growth on commercially viable large area substrates are now at the point where power conversion applications of GaN are at the cusp of commercialisation. The future for building on the work described here in ways driven by specific challenges emerging from entirely new markets and applications is very exciting. This collection of GaN technology developments is therefore not itself a road map but a valuable collection of global state-of-the-art GaN research that will inform the next phase of the technology as market driven requirements evolve. First generation production devices are igniting large new markets and applications that can only be achieved using the advantages of higher speed, low specific resistivity and low saturation switching transistors. Major investments are being made by industrial companies in a wide variety of markets exploring the use of the technology in new circuit topologies, packaging solutions and system architectures that are required to achieve and optimise the system advantages offered by GaN transistors. It is this momentum that will drive priorities for the next stages of device research gathered here