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PbZr0.2Ti0.8O3 (PZT) gate insulator with the thickness of 30 nm is grown by pulsed laser deposition (PLD) in AlGaN/GaN metal–insulator–semiconductor high electron mobility transistors (MIS-HEMTs). The ferroelectric effect of PZT AlGaN/GaN MIS-HEMT is demonstrated. The polarization charge in PZT varies with different gate voltages. The equivalent polarization charge model (EPCM) is proposed for calculating the polarization charge and the concentration of two-dimensional electron gas (2DEG). The threshold voltage (Vth) and output current density (IDS) can also be obtained by the EPCM. The theoretical values are in good agreement with the experimental results and the model can provide a guide for the design of the PZT MIS-HEMT. The polarization charges of PZT can be modulated by different gate-voltage stresses and the Vth has a regulation range of 4.0 V. The polarization charge changes after the stress of gate voltage for several seconds. When the gate voltage is stable or changes at high frequency, the output characteristics and the current collapse of the device remain stable. [ABSTRACT FROM AUTHOR]

Two types of enhancement-mode (E-mode) AlGaN/GaN metal–insulator–semiconductor high-electron-mobility transistors (MIS-HEMTs) with different gate insulators are fabricated on Si substrates. The HfO2 gate insulator and the Al2O3 gate insulator each with a thickness of 30 nm are grown by the plasma-enhanced atomic layer deposition (PEALD). The energy band diagrams of two types of dielectric MIS-HEMTs are compared. The breakdown voltage (VBR) of HfO2 dielectric layer and Al2O3 dielectric layer are 9.4 V and 15.9 V, respectively. With the same barrier thickness, the transconductance of MIS-HEMT with HfO2 is larger. The threshold voltage (Vth) of the HfO2 and Al2O3 MIS-HEMT are 2.0 V and 2.4 V, respectively, when the barrier layer thickness is 0 nm. The C–V characteristics are in good agreement with the Vth's transfer characteristics. As the barrier layer becomes thinner, the drain current density decreases sharply. Due to the dielectric/AlGaN interface is very close to the channel, the scattering of interface states will lead the electron mobility to decrease. The current collapse and the Ron of Al2O3 MIS-HEMT are smaller at the maximum gate voltage. As Al2O3 has excellent thermal stability and chemical stability, the interface state density of Al2O3/AlGaN is less than that of HfO2/AlGaN. [ABSTRACT FROM AUTHOR]

Low temperature photoisomerization of stilbene and 1,4-diphenyl-1,3-butadiene derivatives was found to vary depending on the organic glass employed in such studies. Examination of the combined results showed that the variation was more likely to arise from the rigidity of the organic glass at the temperature of irradiation rather than the composition of the organic glass; that is, the observed results are consistent with the possible softening of the glass that surrounds the excited substrate in the same manner as detected in the photolysis of ethyl iodide reported by Porter and co-workers. These observations successfully account for the apparent "disagreement" of reports from the Hawaii and the Florida State groups on the mechanism of photoisomerization in low temperature glasses.

A new class of tetrathiafulvalene (TTF)-based microstructures fabricated by coordinative self-assembly has been successfully prepared by a solution process. The morphology of the TTF coordination polymers is readily tuned by the variation of metal ions. Upon incorporation of Pb(2+) and Zn(2+) ions, one-dimensional (1D) wirelike microstructures and spherical polymer particles were achieved, respectively. These results indicate that the coordinative approach pursued in this work, in which the building blocks of 1 are linked in a coordination polymer chain by association with metal ions, is an efficient and versatile approach to produce more mechanically robust micro- and nanometer-sized coordination polymer materials. More interestingly, the neutral coordination polymers are conductive and magnetic at room temperature without external manipulation. Such conductivity is reminiscent of the behavior of the neutral conductive TTF in single crystals.