Jian-Jhou Zeng

Current transport mechanism of heterojunction diodes based on the reduced graphene oxide-based polymer composite and n-type Si

The present work reports the fabrication and detailed electrical properties of heterojunction diodes based on n-type Si and poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonate) (PEDOT:PSS) having the reduced graphene oxide (RGO). This heterojunction diode showed a good rectifying behavior with an ideality factor of 1.2. A photocurrent decay model is presented that addresses the charge trapping effect and doping mechanisms for composite PEDOT:PSS films having RGO sheets. The enhanced dark conductivity was observed by incorporating RGO into PEDOT:PSS. For heterojunction diodes, the high photocurrent density originates from efficient hole transport combined with electron trapping with long-second lifetime.

Tuning the work function of graphene by ultraviolet irradiation

Graphene layers grown by chemical vapor deposition were, respectively, irradiated for 0, 20, 40, and 60 min by an ultraviolet light source in order to experimentally study the change in the work function of graphene. The dependences of the work function and carrier concentration upon ultraviolet irradiation have been found. It is shown that ultraviolet irradiation may lead to oxygen desorption, thus reducing the hole density and work function of graphene. Based on the well-known expression for the Fermi energy of Dirac fermions, the Fermi velocity of graphene was extracted to be about 5.2 Multiplication-Sign 10{sup 5} m/s.

Schottky barrier inhomogeneity for graphene/Si-nanowire arrays/n-type Si Schottky diodes

The current–voltage characteristics of graphene/Si-nanowire (SiNW) arrays/n-type Si Schottky diodes with and without H2O2 treatment were measured in the temperature range of −150 ∼ 150 °C. The forward-bias current-voltage characteristics were analyzed on the basis of thermionic emission theory. It is found that the barrier height decreases and the ideality factor increases with the decreased temperatures. Such behavior is attributed to barrier inhomogeneities. It is shown that both Schottky barrier inhomogeneity and the T0 effect are affected by H2O2 treatment, implying that charge traps in the SiNWs have a noticeable effect on Schottky barrier inhomogeneity for graphene/SiNWs/n-type Si diodes.

Enhancement of the carrier mobility of poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonate) by incorporating reduced graphene oxide

The investigation of poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonate) (PEDOT:PSS) having the reduced graphene oxide (RGO), denoted RGO-doped PEDOT:PSS shows that conductivity of RGO-doped PEDOT:PSS samples is 27 times higher than that of PEDOT:PSS at 300 K. The improved electrical conductivity is considered to mainly come from the mobility enhancement. The carrier mobility in RGO-doped PEDOT:PSS samples exhibits unexpectedly strong temperature dependence, implying the domination of tunneling (hopping) at low (high) temperatures. An exhibition of high mobility of RGO-doped PEDOT:PSS samples is attributed to the increased spacing between molecules.

Tuning the work function of graphene by nitrogen plasma treatment with different radio-frequency powers

Graphene prepared by the chemical vapor deposition method was treated with nitrogen plasma under different radio-frequency (rf) power conditions in order to experimentally study the change in the work function. Control of the rf power could change the work function of graphene from 4.91 eV to 4.37 eV. It is shown that the increased rf power may lead to the increased number of graphitic nitrogen, increasing the electron concentration, and shifting the Fermi level to higher energy. The ability to controllably tune the work function of graphene is essential for optimizing the efficiency of optoelectronic and electronic devices.

Hybrid diodes based on n-type Ge and conductive polymer doped by graphene oxide sheets with and without reduction treatment

The authors present a hybrid diode based on n-type Ge and poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonate) (PEDOT:PSS) having the reduced graphene oxide (RGO) or graphene oxide (GO) sheets. It is found that conductivity of RGO-doped PEDOT:PSS films increases with increasing the reduction temperature of GO sheets. The improvement of electrical conductivity is considered to mainly come from the carrier mobility enhancement. In addition, the ideality factor of n-type Ge/RGO-doped PEDOT:PSS diodes decreases with increasing the reduction temperature of GO sheets. The device-performance improvement originates from high-mobility hole transport combined with long-lifetime electron trapping in the RGO-doped PEDOT:PSS film. However, GO doping may lead to decreased conductivity, owing to the large number of the oxygen-related defects in GO sheets. The device-performance degradation originates from low-mobility hole transport combined with short-lifetime electron trapping in the GO-doped PEDOT:PSS film.

Effects of reduction temperature on the optoelectronic properties of diodes based on n-type Si and reduced graphene oxide doped with a conductive polymer

The effect of reduction temperature on the optoelectronic properties of diodes based on n-type Si and reduced graphene oxide (RGO) doped with a conductive polymer [poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonate) (PEDOT:PSS)] was examined in this study. It is found that conductivity of RGO-doped PEDOT:PSS films increases with increasing reduction temperature of graphene oxide (GO) sheets. The improvement of electrical conductivity is considered to mainly come from the carrier mobility enhancement. In addition, the ideality factor of n-type Si/RGO-doped PEDOT:PSS diodes decreases with increasing reduction temperature of GO sheets. The device-performance improvement originates from high-mobility hole transport combined with long-lifetime electron trapping in the RGO-doped PEDOT:PSS film. In addition, note that a suitable reduction temperature is an important issue for improving the device performance.