High quality, large grain size graphene on polycrystalline nickel film on two inch silicon wafers was successfully synthesized by the chemical vapor deposition (CVD) method. The polydimethylsiloxane (PDMS) stamping method was used for graphene transferring in this experiment. The graphene transferred onto Al2O3/ITO substrates was patterned into macroscopic dimension electrodes using conventional lithography followed by oxygen plasma etching. Experimental results show that this graphene can serve as transparent source and drain electrodes in high performance organic semiconductor nanoribbon organic field-effect transistors (OFETs), facilitating high hole injection efficiency due to the preferred work function match with the channel material: single crystalline copper phthalocyanine (CuPc) nanoribbons. The nanoribbons were grown on top of the patterned graphene via evaporate-deposition to form the FET device. The carrier mobility and on/off current ratio of such devices were measured to be as high as 0.36 cm2/(V s) and 10(4).

Sulfur passivation and subsequent wafer-bonding treatments are demonstrated for III–V semiconductor applications using GaAs–GaAs direct wafer-bonded structures. Two different sulfur passivation processes are addressed. A dry sulfur passivation method that utilizes elemental sulfur vapor activated by ultraviolet light in vacuum is compared with aqueous sulfide and native-oxide-etch treatments. The electrical conductivity across a sulfur-treated 400 - °C-bonded n-GaAs/n-GaAs interface significantly increased with a short anneal (1–2 min) at elevated temperatures (500–600 °C). Interfaces treated with the NH4OH oxide etch, on the other hand, exhibited only mild improvement in accordance with previously published studies in this area. TEM and STEM images revealed similar interfacial microstructure changes with annealing for both sulfur-treated and NH4OH interfaces, whereby some areas have direct semiconductor–semiconductor contact without any interfacial layer. Fitting the observed temperature dependence of zero-bias conductance using a model for tunneling through a grain boundary reveals that the addition of sulfur at the interface lowered the interfacial energy barrier by 0.2 eV. The interface resistance for these sulfur-treated structures is 0.03 Ω·cm at room temperature. These results emphasize that sulfur-passivation techniques reduce interface states that otherwise limit the implementation of wafer bonding for high-efficiency solar cells and other devices.

A novel serpentine channel structure is used to mask the sapphire substrate for the epitaxial growth of dislocation-free GaN. Compared to the existing epitaxial lateral overgrowth methods, the main advantages of this novel technique are: (a) one-step epitaxial growth; (b) up to 4 times wider defect-free regions; and (c) the as-grown GaN film can be transferred easily to any type of substrate. TEM, etch pits and cathodoluminescence experiments are conducted to characterize the quality of as-grown GaN. The results show that the average etch-pit density in the yet-to-beoptimized GaN epi-layers is about 4 Â 10 5 cm À2. The underlying physics of selective nucleation and growth is investigated using the finite element method (COMSOL). It is concluded that the proximity effect dominates the selective growth of GaN on the serpentine channel structure masked sapphire. This novel technique is a promising candidate for the growth of high quality III-nitride and the subsequent high-performance device fabrication including high brightness LED, laser diodes, and high-power, high-efficiency transistors. V

Bonding techniques for direct wafer bonding of III-V materials by various sulfur passivation treatments are presented. A dry sulfur passivation method utilizing elemental sulfur vapor activated by ultraviolet light in high vacuum is adapted for use in wafer bonding. Large area bonding is achieved for GaAs/GaAs and InP/InP with bulk fracture strength achieved after annealing at 400 °C and 300 °C respectively without large compressive forces. X-ray photoelectron spectroscopy measurements of the treated GaAs surface show the reduction of oxide and creation of sulfide bonds prior to bonding. The electrical conductivity across a sulfur bonded GaAs/GaAs interface is greatly improved with a short anneal (1-2 minutes) at elevated temperatures (500-600 °C) and HRTEM images reveal the interface is restructuring at lower temperatures than reported for other bonding techniques.

The second author's last name was mis-spelled. The correct spelling is Khripin.