Lu Huibin

Laser molecular beam epitaxy system and its key technologies

The laser molecular beam epitaxy system and its key technologies have been successfully developed in China. Atomically regulated unit-cell by unit-cell homoepitaxial SrTiO3 (STO) and heteroepitaxial BaTiO3 (BTO) films and STO/BTO superlattices were fabricated on STO (100) substrates by the laser molecular beam epitaxy. The fine streak patterns and more than 1000 cycles of undamping intensity oscillation were obtained by using in-situ reflection high-energy electron diffraction. The surfaces of films are atomically smooth.

Quantum well infrared detector with grating enhancement

Abstract We have investigated theoretically enhanced quantum well IR detector. The field enhancement expressions are given by means of the perturbation method. The quantum efficiency and enhancement ratio have been obtained for a doped GaAs/AlGaAs quantum well structure at λ = 10 μm for different grating periods. We explained why Goossen and Lyon only observed a small enhancement.

Study of resonant excitation of infrared surface second harmonic at the GaAs-Al interface.

By using a tunable TEA CO(2) laser and by grating coupling at the interface of GaAs-Al, we have obtained, for the first time to our knowledge, second-harmonic generation from a resonantly excited infrared surface polariton. The experimental results provided a dispersion relation that compares well with theoretical calculations. The deduced value of chi(2), 5.9 x 10(-7) esu, agrees well with other measurements.

Acceptor Concentration Effects on Photovoltaic Response in the La1-xSrxMnO3/SrNbyTi1-yO3 Heterojunction

Photovoltaic response in the heterojunction of La1−xSrxMnO3/SrNbyTi1−yO3 (LSMO/SNTO) is analyzed theoretically based on the drift-diffusion model. It is found that the decrease of acceptor concentration in the La1−xSrxMnO3 layer of heterojunction can increase the peak value of photovoltaic signal and the speed of photovoltaic response, whereas the changing of donor concentration in the SrNbyTi1−yO3 layer has no such evident effect. Furthermore, the result also indicates that the modulation of Sr doping in La1−xSrxMnO3 is an effective method to accommodate the sensitivity and the speed of photovoltaic response for LSMO/SNTO photoelectric devices.

Effects of DC magnetic field upon the properties of a HTS microstrip antenna at 4.2 K

Abstract A circular polarized microstrip antenna with a working frequency of 6.26 GHz was fabricated from YBCO HTS films. The transmission coefficient and circular polarization ratio of the antenna at different external magnetic field B were measured at 4.2 K. The experimental results showed that its transmission coefficient and circular polarization ratio hardly changed with B up to 1 T. It is concluded that the field-induced increase of surface resistance of YBCO films would not influence the microwave properties of this antenna at B ⩽ 1T and T = 4.2 K.

Growth mode of Cu-rich particles on laser-ablated YBa2Cu3O7 thin films

The microstructure of the laser-ablated YBa2Cu3O7 (YBCO) thin film deposited on heated (100) SrTiO3 substrate was examined by transmission electron microscope. The particles on the film mainly consist of CuO and few CuYO2. Most of these non-superconducting particles nucleate on or near the surface of the film and protrude about 100-400 nm in height. A large amount of a-axis YBCO grains also exist in the film, which nucleate at the substrate surface and grow perpendicularly above the c-axis YBCO film. The YBCO thin film deposited under low oxygen pressure has very different microstructure compared with YBCO thin film deposited under high oxygen pressure.

Intersubband Third-Order Nonlinearities in a GaAs/AlGaAs Step Quantum Well Structure by Phase Conjugation Method

In this letter, we present the observation of phase conjugation at 9.27 μm in a GaAs/AlGaAs multiple step quantum well structure. The response is caused by the nearly resonant intersubband transition. The magnitude of χ(3) determined by this phase conjugation method is about 8 × 10-5 esu and the phase conjugate reflectivity η is about 6 × 10-3 uncorrected for Fresnel reflections.

Study of the properties of infrared intersubband transition in doped GaAs/AlxGa1-xAs multiple quantum wells

The properties of intersubband transition of GaAs/AlxGa1-xAs multiple quantum wells with various well widths and doped-well concentrations have been studied. Both theoretical and experimental results are in good agreement. For the appropriate well width and higher doping concentration, we directly observed two intersubband absorption peaks from E1 → E2 and E2 → E3 transitions in well. The experimental results and theoretical analysis are given.

Fabrication of MgB2 superconducting films by different methods

Abstract MgB2 superconducting films have been successfully fabricated on single crystal MgO (111) and c-AL2O3 substrates by different methods. The film deposited by pulsed laser deposition is c-axis oriented with zero resistance transistion temperature of 38.4K, while the other two films fabricated by chemical vapor deposition and electrophoresis are c-axis textured with zero resistance transistion temperature of 38 K and 39 K, respectively. Magnetization hysteresis measurements yield critical current density J c of 107 A/ cm2 at 15K in zero field for the thin film and of 105 A/ cm2 for the thick film. For the thin film deposited by chemical vapor deposition, the microwave surface resistance at 10 K is found to be as low as 100µΩ, which is comparable with that of a high-quality high-temperature superconducting thin film of YBCO. * Supported by the Major State Basic Research Development Program of China (Grant No. 1999064604)

EFFECTS OF THE QUALITY OF SUBSTRATE ON THE STRUCTURE AND SUPERCONDUCTING PROPERTIES OF Yba 2 Cu 3 O 7-x THIN FILM

We have systematically investigated the structures, morphologies, microwave surface resistance, DC performances and the substrate qualities of three YBa2Cu3O7-x(YBCO) thin films 30 mm in diameter. The three samples deposited by the same process have been proved of different properties. It has been shown that the structure and superconducting properties of the thin film depend strongly on the quality of substrate.