Z. Q. Yao

Room temperature fabrication of p-channel Cu2O thin-film transistors on flexible polyethylene terephthalate substrates

The effects of growth temperature on the microstructure evolution and electrical transport properties of Cu2O films were investigated. Nanocrystalline Cu2O films with modest p-type semiconducting properties (Hall mobilities ∼20 cm2/Vs, hole concentrations ∼1016 cm−3) were successfully prepared at room temperature without post-annealing. Bottom gate and top contact p-channel Cu2O thin-film transistors (TFTs) were constructed on flexible polyethylene terephthalate substrates at room temperature, which shows superior transfer performance (field effect mobility ∼2.40 cm2/Vs and current on/off ratio ∼3.96 × 104). The low processing temperature and the good electrical performance of the p-type Cu2O TFTs suggest their good potential for applications in high-throughput and low-cost electronics.

Selective growth of catalyst-free ZnO nanowire arrays on Al:ZnO for device application

Vertically aligned ZnO nanowire (NW) arrays have been synthesized selectively on patterned aluminum-doped zinc oxide (AZO) layer deposited on silicon substrates without using any metal catalysts. The growth region was defined by conventional photolithography with an insulating template. Careful control of the types of template materials and growth conditions allows good alignment and growth selectivity for ZnO NW arrays. Sharp ultraviolet band-edge peak observed in the photoluminescence spectra of the patterned ZnO NW arrays reveals good optical qualities. The current-voltage characteristics of ZnO NWs∕AZO∕p-Si device suggest that patterned and aligned ZnO NW arrays on AZO may be used in optoelectronic devices.

Energy band engineering and controlled p‐type conductivity of CuAlO2 thin films by nonisovalent Cu‐O alloying

The electronic band structure and p‐type conductivity of CuAlO2 films were modified via synergistic effects of energy band offset and partial substitution of less‐dispersive Cu+ 3d10 with Cu2+ 3d9 orbitals in the valence band maximum by alloying nonisovalent Cu‐O with CuAlO2 host. The Cu‐O/CuAlO2 alloying films show excellent electronic properties with tunable wide direct bandgaps (∼3.46–3.87 eV); Hall measurements verify the highest hole mobilities (∼11.3–39.5 cm2/Vs) achieved thus far for CuAlO2 thin films and crystals. Top‐gate thin film transistors constructed on p‐CuAlO2 films were presented, and the devices showed pronounced performance with Ion/Ioff of ∼8.0 × 102 and field effect mobility of 0.97 cm2/Vs.

p-type conduction in beryllium-implanted hexagonal boron nitride films

p-type conduction in hexagonal boron nitride (hBN) films was achieved by beryllium implantation and subsequent rapid thermal annealing treatment. The dependence of phase composition and electrical properties of hBN films on the implantation fluence and annealing was studied. A maximum resistivity reduction by six orders of magnitude was demonstrated. Hall measurements revealed a corresponding hole concentration of 3×1019 cm−3 and mobility of 27 cm2/V s. The activation energy of Be ions was estimated to be 0.21 eV. It is suggested that hBN is a promising wide bandgap semiconductor for applications in high-temperature electronic devices and transparent conductive coatings.

Study of in-plane orientation of epitaxial AlN films grown on (111) SrTiO3

Substrate temperature and chemical etching were demonstrated to be dominant factors in determining the in-plane orientation of AlN films grown epitaxially on SrTiO3 (STO) (111) substrates by magnetron sputtering. Single-domain epitaxial AlN films were grown at moderate temperatures of 270–370°C with a sharp interface and orientation relationship of [21¯1¯0]AlN∥[01¯1]STO and (0002)AlN∥(111)STO. At temperature above 470°C, an additional 30° in-plane-rotated AlN domain appeared, and increased in percentage with increasing temperature. A model based on the reconstruction of STO (111) surfaces from (1×1) to (3×3)R30° was proposed to account for the formation of this new domain.

Microstructure analysis of c-axis oriented aluminum nitride thin films by high-resolution transmission electron microscopy

The microstructure, in particular, the surface and interface regions, of the c-axis orientated AlN films deposited on Si (100) substrates was studied. The films showed an evolutionary columnar growth process. In contrast to the previous reports, high-resolution transmission electron microscopy revealed that the AlN films grew directly on substrates without an amorphous interlayer, despite the large lattice mismatch between AlN and Si. The occurrence of misoriented and/or amorphous top layer suggested a subsurface growth/relaxation process of the AlN films by reactive sputtering.

Epitaxial growth and structural analysis of AlN/GaN heterostructures

Single crystal AlN thin films were epitaxially grown on GaN/sapphire (0001) substrates on a macroscopic scale by magnetron sputtering. The microscopic structure and orientation degree of the AlN epilayers were studied by high-resolution transmission electron microscopy, high-resolution x-ray diffraction, and reciprocal spacing mapping. It was revealed that the AlN epilayers have high in-plane and out-of-plane orientation degrees and low defect density. The electrical and optical properties of the AlN epilayers were also studied, and the results suggest that the AlN epilayers grown by sputtering may be employed in the fabrication of GaN-based light-emitting diode devices with increased efficiency.