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The relationship between band gap and biaxial stress in wurtzite ZnO thin films has been investigated by side-inclination x-ray diffraction technique and optical absorbance spectrum as well as ab initio calculation. The experimental result shows that differing from other semiconductor thin films with hexagonal structure, such as GaN, the band gap of ZnO thin films increases with the increase in biaxial tensile stress. For explaining the difference, ab initio calculation is performed to simulate the relationship between band gap and biaxial stress of wurtzite ZnO and GaN. The calculated result indicates that the band gap of ZnO increases under biaxial tensile stress but GaN is opposite, supporting our experimental result. The band offset calculation shows that the conduction-band minimum (CBM) and the valence-band maximum (VBM) of ZnO and GaN offset to low energy under biaxial tensile stress. The VBM offset of ZnO is larger than the CBM, responsible for the increase in band gap. The VBM offset of GaN is smaller than the CBM, responsible for the decrease in band gap. The difference between ZnO and GaN is attributed to the strong p-d coupling in valence band of ZnO, but strong p-p coupling in valence band of GaN. [ABSTRACT FROM AUTHOR]

Ga-doped ZnO (GZO)/graphene multilayer film was fabricated on the polyethylene terephthalate substrate at room temperature. The obtained GZO/graphene multilayer showed a transparence of 75% at 550nm and a sheet resistance of 721Ω/sq. Our findings indicate that the graphene intermediate layer plays a critical role in improving the conductivities of GZO. Under a tensile strain, the sheet resistance of the GZO electrode without graphene exhibited a sharp increase owing to the plenty of cracks formed in the GZO layer. In contrast, the GZO/graphene multilayer displayed a relatively stable and low resistance during the tensile deformation due to the excellent mechanical and electrical stabilities of the graphene. [ABSTRACT FROM AUTHOR]

The changes in the microstructure of ZnO nanowire were studied after exposure to different radiation doses of energetic x-rays. Detailed structural, composition and optical analyses were carried out. It was found that the surface composition changed and defects were formed in the irradiated ZnO nanowires. The structural change of ZnO nanowires after thermal treatment was also studied and similar defects were observed. It is proposed that phonon-induced localized heating is the main reason for the observed changes in microstructure. Finally, the field emission properties of ZnO nanowires before and after x-ray radiation were studied. It was found that the increase of work function and change in morphology induced by the irradiation were the reasons for the observed change in field emission properties. [ABSTRACT FROM AUTHOR]

Valence-band offset (VBO) of n-ZnO/p-NiO heterojunction has been investigated by x-ray photoelectron spectroscopy. Core levels of Zn 2p and Ni 2p were used to align the VBO of n-ZnO/p-NiO heterojunction. It was found that n-ZnO/p-NiO heterojunction has a type-II band alignment and its VBO is determined to be 2.60±0.20 eV, and conduction-band offset is deduced to be 2.93±0.20 eV. The experimental VBO value is in good agreement with the calculated value based on the electron affinity of ZnO and NiO. [ABSTRACT FROM AUTHOR]

The valence-band offset of ZnO/MgO (111) heterojunction has been directly measured by x-ray photoelectron spectroscopy. Excluding the strain effect, the valence-band offset is determined to be 0.87±0.20 eV, and the conduction-band offset ΔEC is deduced to be -3.59±0.20 eV, indicating that ZnO/MgO heterojunction has a type-I band alignment. The conduction-band and valence-band offset of MgO/ZnO is used to interpret the origination of p-type conduction in undoped MgxZn1-xO alloy and deeper acceptor level in undoped and N-doped p-type MgxZn1-xO alloy than in ZnO. [ABSTRACT FROM AUTHOR]

Our Raman measurement indicates that the intensity of the peaks (510 and 645 cm-1) related to nitrogen concentration is enhanced in MgZnO compared with that in ZnO. Using first-principles band structure methods, we calculated the formation energy and transition energy level for nitrogen acceptor in ZnO and random MgxZn1-xO (with x=0.25) alloy. Our calculations show that the incorporation of nitrogen can be enhanced as Mg is alloyed into ZnO, which agrees with our experiments. The acceptor energy level deeper in the alloy ascribes to the downward shift of the valence-band maximum edge in the presence of magnesium. [ABSTRACT FROM AUTHOR]

We report room temperature ferromagnetism enhancement of Cu-doped ZnOS (Zn1−xCuxO1−ySy) alloy thin films with high hole concentration. The Zn0.91Cu0.09O0.92S0.08 alloy thin films with a hole concentration of 4.3 × 1019 cm−3 show the strongest magnetization of 1.5μB/Cu. First-principles calculation shows that high hole concentration stabilizes the ferromagnetic ordering in the Zn1−xCuxO1−ySy system, indicating a strong correlation between ferromagnetic stability and hole concentration. These results suggest that the Zn1−xCuxO1−ySy alloy with high hole concentration is promising to find applications in spintronic devices. [ABSTRACT FROM AUTHOR]