Luo Bing-Cheng

Rectifying and Photovoltage Properties of ZnO:A1/p-Si Heterojunction

An A1-doped ZnO/p-Si heterojunction is fabricated by a laser molecular beam epitaxy technique. The abnormally high ideality factors (n ≫ 2) of the prepared heterojunction are observed in the interim bias voltage range. A theoretical model is proposed to understand the much higher ideality factor of the special heterojunction diode. The ZnO:A1 film shows metal-like conductivity with the electrical resistivity about 6.56 × 10−4 Ω·cm at room temperature. The temperature dependence of the photovoltage indicates that the photovoltaic effect of the A1-doped ZnO based heterojunction can be changed by the intrinsic metal-semiconductor transition at 120 K.

Leakage Current and Photovoltaic Properties in a Bi2Fe4O9/Si Heterostructure

A heterostructure composed of a Bi2Fe4O9 film and an n-type Si substrate is fabricated. The characteristics of leakage current density versus electric field are investigated and the leakage current density is about 6×10−6 A/cm2 at an electric field of 200 kV/cm at 300 K. A strong photovoltaic effect is observed when the heterostructure is exposed to a laser pulse with a wavelength of 532 nm and a power of 6 mW/mm2. It is found that the peak photovoltages initially increase with decreasing temperature, followed by a decrease at T < 210 K. These results reveal that the heterostructure is a promising candidate for photovoltaic devices that are compatible with Si integrated circuits.

The Photovoltaic Properties of BiFeO3La0.7Sr0.3MnO3 Heterostructures

An epitaxial BiFeO3/La0.7Sr0.3MnO3 (BFO/LSMO) multiferroic heterostructure is grown on an LaAlO3 (001) substrate by laser molecular beam epitaxy, and its photovoltaic properties are investigated. It is found that the photocurrent is significantly increased under illumination, and the short-circuit photocurrent has a linear relationship with the laser intensity. Furthermore, when the ferroelectric polarization of the BFO layer is switched, the short-circuit photocurrent and open-circuit voltage can be switched. These results are discussed by considering the contributions from the ferroelectric polarization and the electrode/film interface.

Photoinduced Resistance Change in an Oxygen-Deficient La0.9Sr0.1MnO3−δThin Film

Photoinduced resistance change (ΔR/R) in an oxygen-deficient La0.9Sr0.1MnO3−δ thin film is studied. At room temperature, the resistance change of about 30% and response time of about 75 ns are observed under the illumination with a 532 nm laser pulse of 7 ns and light power of 750 mW. It is also found that ΔR/R changes with the light power. The phenomena are explained in terms of the photoinduced hole carriers and localized insulator-to-metal transition, which may have potential applications in optoelectronic devices.

Dielectric loss of half-doped manganite La0.5Ca0.5MnO3

The dielectric loss tanδ of half-doped manganite La0.5Ca0.5MnO3 is investigated using Greens function technique. The La0.5Ca0.5MnO3 is described by the Kondo-lattice model in the double exchange limit, taking into account the Jahn—Teller distortion and the super-exchange interaction between the localized electrons. It is found that the intensity of tanδ decreases with increasing |eJT|, V, and U. It is also observed that the transition temperature TP rises as |eJT| and U increase. It is worth noting that TP remains unchanged and the strength of tanδ increases with increasing g. The calculated dielectric loss results are explained theoretically, and these behaviors are in qualitative agreement with the experimental results.

Transport and magnetoresistance effect in an oxygen-deficient SrTiO3/La0.67Sr0.33MnO3 heterojunction

An oxygen-deficient SrTiO3/La0.67Sr0.33MnO3 heterojunction is fabricated on an SrTiO3 (001) substrate by a pulsed laser deposition method. The electrical characteristics of the heterojunction are studied systematically in a temperature range from 80 K to 300 K. The transport mechanism follows I ∞ exp(eV/nkT) under small forward bias, while it becomes space charge limited and follows I ∞ Vm(T) with 1.49 < m < 1.99 under high bias. Such a heterojunction also exhibits magnetoresistance (MR) effect. The absolute value of negative MR monotonically increases with temperature decreasing and reaches 26.7% at 80 K under H = 0.7 T. Various factors, such as strain and oxygen deficiency play dominant roles in the characteristics.