Nuofu Chen

Bio: Nuofu Chen is an academic researcher from Chinese Academy of Sciences. The author has contributed to research in topics: Thin film & Epitaxy. The author has an hindex of 15, co-authored 66 publications receiving 925 citations. Previous affiliations of Nuofu Chen include North China Electric Power University.

Structural and magnetic properties of insulating Zn1−xCoxO thin films

Abstract: Cobalt-doped ZnO (Zn1-xCoxO) thin films were fabricated by reactive magnetron cosputtering. The processing conditions were carefully designed to avoid the occurrence of Co precipitations. The films are c-axis oriented, and the solubility limit of Co in ZnO is less than 17%, determined by x-ray diffraction. X-ray photoemission spectroscopy measurements show Co ions have a chemical valance of 2+. In this paper, hysteresis loops were clearly observed for Zn1-xCoxO films at room temperature. The coercive field, as well as saturation magnetization per Co atom, decreases with increasing Co content, within the range of 0.07

P-doped p-type ZnO films deposited on Si substrate by radio-frequency magnetron sputtering

Abstract: P-doped ZnO films were deposited on n-Si substrate by radio-frequency magnetron sputtering. Hall measurements revealed that the films annealed in situ at 750°C in an oxygen ambient at a pressure of 1.3×10−3–3.9×10−3Pa showed p-type behavior with a hole concentration of 2.7×1016–2.2×1017cm−3, a mobility of 4–13cm2∕Vs, and a resistivity of 10.4–19.3Ωcm. Films annealed at 750°C in a vacuum or in oxygen ambient at higher pressures (5.2×10−3 and 6.5×10−3Pa) showed n-type behavior. Additionally, the p-ZnO∕n-Si heterojunction showed a diodelike I-V characteristic. Our results indicate that P-doped p-type ZnO films can be obtained by annealing in oxygen ambient at very low pressures.

p-type Zn1−xMgxO films with Sb doping by radio-frequency magnetron sputtering

Abstract: Sb-doped Zn1-xMgxO films were grown on c-plane sapphire ubstrates by radio-frequency magnetron sputtering. The p-type conduction of the films (0.05 <= x <= 0.13) was confirmed by Hall measurements, revealing a hole concentration of 10(15)-10(16) cm(-3) and a mobility of 0.6-4.5 cm(2)/V s. A p-n homojunction comprising an undoped ZnO layer and an Sb-doped Zn0.95Mg0.05O layer shows a typical rectifying characteristic. Sb-doped p-type Zn1-xMgxO films also exhibit a changeable wider band gap as a function of x, implying that they can probably be used for fabrication of ZnO-based quantum wells and ultraviolet optoelectronic devices. (c) 2006 American Institute of Physics.

Ferromagnetism and possible application in spintronics of transition-metal-doped ZnO films

Abstract: This review article first presents a summary of current understanding of the magnetic properties and intrinsic ferromagnetism of transition-metal (TM)-doped ZnO films, which are typical diluted magnetic oxides used in spintronics. The local structure and magnetic behavior of TM-doped ZnO are strongly sensitive to the preparation parameters. In the second part, we discuss in detail the effects of doping elements and concentrations, oxygen partial pressure, substrate and its orientation and temperature, deposition rate, post-annealing temperature and co-doping on the local structure and subsequent ferromagnetic ordering of TM-doped ZnO. It is unambiguously demonstrated that room-temperature ferromagnetism is strongly correlated with structural defects, and the carriers involved in carrier-mediated exchange are by-products of defects created in ZnO. The third part focuses on recent progress in TM-doped ZnO-based spintronics, such as magnetic tunnel junctions and spin field-effect transistors, which provide a route for spin injection from TM-doped ZnO to ZnO. Thus, TM-doped ZnO materials are useful spin sources for spintronics.

Transition metal-doped TiO2 and ZnO?present status of the field

Abstract: There has been considerable recent interest in the design of diluted magnetic semiconductors, with a particular focus on the exploration of different semiconductor hosts. Among these, the oxide-based diluted magnetic semiconductors are attracting increasing attention, following reports of room temperature ferromagnetism in anatase TiO2 and wurtzite ZnO doped with a range of transition metal ions. In this review we summarize the current status of oxide-based diluted magnetic semiconductors, and discuss the influence of growth method, substrate choice, and temperature on the microstructure and subsequent magnetic properties of thin films. We outline the experimental conditions that promote large magnetization and high ferromagnetic Curie temperature. Finally, we review the proposed mechanisms for the experimentally observed ferromagnetism and compare the predictions to the range of available data.

Evidence of oxygen vacancy enhanced room-temperature ferromagnetism in Co-doped ZnO

Abstract: The annealing effects on structure and magnetism for Co-doped ZnO films under air, Ar, and Ar∕H2 atmospheres at 250°C have been systematically investigated. Room-temperature ferromagnetism has been observed for the as-deposited and annealed films. However, the saturation magnetization (Ms) varied drastically for different annealing processes with Ms∼0.5, 0.2, 0.9, and 1.5μB∕Co for the as-deposited, air-annealed, Ar-annealed, and Ar∕H2-annealed films, respectively. The x-ray absorption spectra indicate all these samples show good diluted magnetic semiconductor structures. By comparison of the x-ray near edge spectra with the simulation on Zn K edge, an additional preedge peak appears due likely to the formation of oxygen vacancies. The results show that enhancement (suppression) of ferromagnetism is strongly correlated with the increase (decrease) of oxygen vacancies in ZnO. The upper limit of the oxygen vacancy density of the Ar∕H2-annealed film can be estimated by simulation to be about 1×1021cm−3.