In this paper, we report the device performance of a high-voltage normally off Al2O3/GaN MOSFET on the Si substrate. Normally off operation is obtained by multiple cycles of O-2 plasma oxidation and wet oxide-removal gate recess process. The recessed normally off GaN MOSFET with 3 mu m gate-drain distance exhibits a maximum drain current of 585 mA/mm at 9 V gate bias. The threshold voltage of the MOSFET is 2.8 V with a standard derivation of 0.2 V on the sample with an area of 2 x 2 cm(2). The gate leakage current is below 10(-6) mA/mm during the whole gate swing up to 9 V and the I-ON/I-OFF ratio is larger than 10(9), indicating the good quality of Al2O3 gate insulator. The MOSFET with 10 mu m gate-drain distance shows a three terminal OFF-state breakdown voltage (BV) of 967 V at zero gate-source bias with a drain leakage current criterion of 1 mu A/mm. The specific ON-resistance (R-ON,R- SP) of the device is 1.6 m Omega . cm(2) and the power figure of merit (BV2/R-ON,R- SP) is 584 MW/cm(2).
Zhou Z, Zeng J, Ma X, Pang X, Yi H, Chen Q, Meltzer M, He M, Rozelle S, Congdon* NG. Accuracy of rural refractionists in western China. Investigative Ophthalmology & Visual Science. 2014;55:154-161.
Although new particle formation accounts for about 50% of the global aerosol production in the troposphere, the chemical species and mechanism responsible for the growth of freshly nucleated nanoparticles remain largely uncertain. Here we show large size growth when sulfuric acid nanoparticles of 4-20 nm are exposed to epoxide vapors, dependent on the particle size and relative humidity. Composition analysis of the nanoparticles after epoxide exposure reveals the presence of high molecular weight organosulfates and polymers, indicating the occurrence of acid-catalyzed reactions of epoxides. Our results suggest that epoxides play an important role in the growth of atmospheric newly nucleated nanoparticles, considering their large formation yields from photochemical oxidation of biogenic volatile organic compounds.