Dynamic band alignment modulation of ultrathin WOx/ZnO stack for high on/off ratio field-effect switching applications.

A two-dimensional (2D) WOx/ZnO stack reveals a unique carrier transport behavior, which can be utilized as a novel device element to achieve a very high on/off ratio (>106) and an off current density lower than 1 nA cm-2. These unique behaviors are explained by a dynamic band alignment between WOx and ZnO, which can be actively modulated by a gate bias. The performance of FET utilizing the WOx/ZnO stack is comparable to those of other 2D heterojunction devices; however, it has a unique benefit in terms of process integration because of very low temperature process capability (T < 110 °C). The high on/off switching with extremely low off current density utilizing the dynamic band alignment modulation at the WOx/ZnO stack can be a very useful element for future device applications, especially in monolithic 3D integration or flexible electronics.

ZnO composite nanolayer with mobility edge quantization for multi-value logic transistors.

A quantum confined transport based on a zinc oxide composite nanolayer that has conducting states with mobility edge quantization is proposed and was applied to develop multi-value logic transistors with stable intermediate states. A composite nanolayer with zinc oxide quantum dots embedded in amorphous zinc oxide domains generated quantized conducting states at the mobility edge, which we refer to as "mobility edge quantization". The unique quantized conducting state effectively restricted the occupied number of carriers due to its low density of states, which enable current saturation. Multi-value logic transistors were realized by applying a hybrid superlattice consisting of zinc oxide composite nanolayers and organic barriers as channels in the transistor. The superlattice channels produced multiple states due to current saturation of the quantized conducting state in the composite nanolayers. Our multi-value transistors exhibited excellent performance characteristics, stable and reliable operation with no current fluctuation, and adjustable multi-level states.

Gate-Controlled Graphene-Silicon Schottky Junction Photodetector.

Various photodetectors showing extremely high photoresponsivity have been frequently reported, but many of these photodetectors could not avoid the simultaneous amplification of dark current. A gate-controlled graphene-silicon Schottky junction photodetector that exhibits a high on/off photoswitching ratio (≈104 ), a very high photoresponsivity (≈70 A W-1 ), and a low dark current in the order of µA cm-2 in a wide wavelength range (395-850 nm) is demonstrated. The photoresponsivity is ≈100 times higher than that of existing commercial photodetectors, and 7000 times higher than that of graphene-field-effect transistor-based photodetectors, while the dark current is similar to or lower than that of commercial photodetectors. This result can be explained by a unique gain mechanism originating from the difference in carrier transport characteristics of silicon and graphene.

High-pressure oxygen annealing of Al2O3 passivation layer for performance enhancement of graphene field-effect transistors.

High-pressure annealing in oxygen ambient at low temperatures (∼300 °C) was effective in improving the performance of graphene field-effect transistors. The field-effect mobility was improved by 45% and 83% for holes and electrons, respectively. The improvement in the quality of Al2O3 and the reduction in oxygen-related charge generation at the Al2O3-graphene interface, are suggested as the reasons for this improvement. This process can be useful for the commercial implementation of graphene-based electronic devices.