Influence of a SiO2 ultrathin film on n-ZnO/p-silicon nanowires photodiodes has been investigated. With a SiO2 thin layer, the diode characteristics can be significantly improved, which exhibits high responsivity under a reverse bias. Based on the electron conversion efficiency measurement, we show that the ultrathin SiO2 layer with positive fixed charges not only acts as a hole blocking layer but also helps the photogenerated electrons to tunnel through the barrier. In addition, the SiO2 layer can effectively passivate the defects generated by wet etching process. It is expected that our approach can be extended to many other nanoscale heterojunction devices.
The electron transport behavior in chemically reduced graphene oxide (rGO) sheets with different thicknesses of 2, 3, and 5 nm was investigated. The four-probe method for the sheet resistance (R(S)) measurement on the intensively reduced graphene oxide samples indicates an Arrhenius characteristic of the electron transport at zero magnetic field B = 0, consistent with previous experimental results on well-reduced GO samples. The anticipated variable range hopping (VRH) transport of electrons in a two-dimensional electron system at low temperatures was not observed. The measured R(S) of the rGO samples are below 52 kΩ/square at room temperature. With the application of a magnetic field up to 4 T, negative magnetoresistance in the Mott VRH regime was observed. The magnetotransport features support a model based on the spin-coupling effect from the vacancy-induced midgap states that facilitate the Mott VRH conduction in the presence of an external magnetic field.
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