Jin Ke-Xin

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.

Dendrite to symmetry-broken dendrite transition in directional solidification of non-axially oriented crystals

In this paper, the morphological transition from dendrite to symmetry-broken dendrite is investigated in the directional solidification of non-axially-oriented crystals using a quantitative phase-field model. The effects of pulling velocity and crystal orientation on the morphological transition are investigated. The results indicate the orientation dependence of the symmetry-broken double dendrites. A dendrite to symmetry-broken dendrite transition is found by varying the pulling velocity at different crystal orientations and the symmetry-broken multiple dendrites emerge as a transition state for the symmetry-broken double dendrites. The state region during the transition can be well characterized through the variations of the characteristic angle and the average primary dendritic spacing.

Ferroelectricity in hexagonal YFeO3 film at room temperature

In this paper we report the leakage current, ferroelectric and piezoelectric properties of the YFeO3 film with hexagonal structure, which was fabricated on Si(111) substrate by a simple sol-gel method. The leakage current test shows good characteristics as the leakage current density is 5.4×10−6 A/cm2 under 5 V. The dominant leakage mechanism is found to be an Ohmic behavior at low electric field and space-charge-limited conduction at high electric field region. The P–E measurements show ferroelectric hysteresis loops with small remnant polarization and coercive field at room temperature. The distinct and switchable domain structures on the nanometer scale are observed by piezoresponse force microscopy, which testifies to the ferroelectricity of the YFeO3 film further.

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.

The Rectifying Property and Photovoltaic Effect in the La0.8Ag0.2MnO3/SrTiO3-Nb Heterojunction

A p—n junction composed of Ag+-doped manganite La0.8Ag0.2MnO3(LAMO) and Nb-0.5wt%-doped SrTiO3(STON) was fabricated using the pulsed laser deposition method. The heterojunction exhibits a good rectifying property over a wide temperature range from 20 to 390 K. The minimum diffusion potential and the lowest leakage currents under different negative voltages both occur at 320 K, which is around the metallic-insulator transition temperature of the LAMO film. The photovoltage rises with the decreasing temperature and wavelength of the laser beam. Under the illumination of a 473 nm laser beam, the photovoltage grows as the light power increases and seems to be saturated at about 300 mW. The maximum Voc is 0.76 V, which is close to the diffusion voltage.

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.