A GaN HEMT with a polarization-graded AlGaN buffer is performed by two-dimensional analysis of drift-diffusion simulations. The bulk trap-induced current collapse of the proposed structure is effectively restrained in contrast to that of conventional HEMTs with a GaN or AlGaN buffer, resulting from the fact that the high and flat back-barrier altitude in the proposed structure prevents the two-dimensional electron gas (2DEG) from spilling over from the channel, with the reduction of hot carriers injecting into the buffer followed by trapping in deep acceptorlike levels. Simultaneously, the off-state breakdown voltage is remarkably enhanced, due to the strong electric breakdown field of the polarization-graded AlGaN buffer and the restraint of the buffer leakage current. In addition, the relationship between the off-state breakdown voltage and the thickness of the polarization-graded AlGaN buffer is analyzed.

The association between T174M polymorphism of angiotensinogen gene and essential hypertension risk remains controversial. We herein performed a meta-analysis to achieve a reliable estimation of their relationship. All the studies published up to May 2013 on the association between T174M polymorphism and essential hypertension risk were identified by searching the electronic repositories PubMed, MEDLINE and EMBASE, Springer, Elsevier Science Direct, Cochrane Library and Google Scholar. Data were extracted and pooled odds ratios (ORs) with 95% confidence intervals (95% CIs) were calculated. Ultimately, nine eligible studies, including 2188 essential hypertension cases and 2459 controls, were enrolled in this meta-analysis. No significant associations were found under the overall ORs for M-allele comparison (M vs. T, pooled OR 0.92, 95% CI 0.62–1.37), MM vs. TT (pooled OR 0.86, 95% CI 0.29–2.51), TM vs. TT n (pooled OR 0.91, 95% CI 0.63–1.32), recessive model (MM vs. TT+TM, pooled OR 0.89, 95% CI 0.35–2.30), dominant model (MM+TM vs. TT, pooled OR 0.91, 95% CI 0.60–1.38) between T174M polymorphism and risk for essential hypertension. This meta-analysis suggested that the T174M polymorphism of the angiotensinogen gene might not be associated with the susceptibility of essential hypertension in Asian or European populations.

A metal-source flow-rate modulation epitaxy method is reported to enhance the hole concentration of Mg-doped AlGaN grown by metal organic chemical vapor deposition. The hole concentration of p-type AlGaN (Al content 0.43) is increased to 2.3 × 1017 cm−3 at room temperature by this method, which is about ten times higher than that of the conventional growth. The resistivity was found to be as low as 12.7 Ω·cm. Furthermore, the effective acceptor activation energy (EA) in the AlGaN films (Al content 0.32–0.43) was determined to be 20–22 meV, several times smaller than EA in p-GaN. Secondary ion mass spectroscopy measurements demonstrated that uniformly Mg-doped AlGaN structures with spatially modulated Al compositions were formed using this technique. It is suggested that the enhancement of hole concentration benefits from the modulation of the valence band edge.

In this paper, crack‐free GaN films with step‐graded AlGaN transition layer and AlGaN superlattice layer as buffer layers were grown on Si(111) substrate by metal‐organic chemical vapor deposition(MOCVD). The combination of both buffers effectively improves the properties of GaN layer. With the optimization of the buffer structures, high quality compressively‐strained GaN layers with thickness up to 3.6 μm have been obtained on Si(111) substrates (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Monolithically integrated enhancement/depletion (E/D)‐mode AlGaN/GaN metal–insulator–semiconductor high electron mobility transistors (MIS‐HEMTs) are being developed for high‐speed mixed‐signal applications. Partially recessed gate combined with buffered gate insulator produce remarkably improved trade‐off between the threshold voltage (1.4 V) and current density (848 mA mm−1) in the E‐mode device. Record peak transconductances of 311 and 248 mA mm−1 are obtained for D‐ and E‐mode MIS‐HEMTs, respectively. A direct‐coupled FET logic (DCFL) 51‐stage ring oscillator implemented using the MIS‐HEMT technique is fabricated, which exhibits high‐speed performance with an oscillation frequency of 908 MHz and a high output voltage swing of 1.48 V.

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