Guo Haizhong

Colossal Magnetoresistive p-n Junctions of Te-Doped LaMnO3/Nb-doped SrTiO3

We have fabricated colossal magnetoresistive (CMR) p-n junctions made of Te-doped LaMnO3 and Nb-doped SrTiO3 with laser molecular beam epitaxy. The I-V characteristics of the La0.9Te0.1MnO3/SrNb0.01Ti0.99O3 p-n junctions as a function of applied magnetic field (0-5xa0T) were experimentally studied in the temperature range 77-300xa0K. The results indicate that the p-n junction exhibited the CMR behaviour. The magnetoresistance (MR) is positive at 220xa0K and 300xa0K, while it displays a negative MR at 77xa0K. For a positive bias, the MR ratios (ΔR/R0, ΔR = RH-R0) are 7.5% at 0.1xa0T and 18% at 5xa0T for 300xa0K, 5% at 0.1xa0T and 33% at 5xa0T for 220xa0K, -14% at 0.1xa0T and -71% at 5xa0T for 77xa0K. For a negative bias, the MR ratios are 6.3% at 0.1xa0T and 10.8% at 3xa0T for 300xa0K, 5.1% at 0.1xa0T and 15% at 3xa0T for 220xa0K, -19% at 0.1xa0T and -72% at 5xa0T for 77xa0K. The CMR behaviour of the p-n junction is different from those of the LaMnO3 compound family.

Structure and electrical characteristics of Nb-doped SrTiO3 substrates

The studies on structure and electrical characteristic of Nb-doped SrTiO3 (SNTO) substrates by XRD, Hall measurements, R-T and SEM, show that the SNTO substrates with the same Nb-doping concentration have different electrical properties because of the nonuniformity of Nb-doping. The uniformly doped high-quality substrates are extremely important for fabricating multilayer structure and devices. In addition, the experimental results also provide us with SEM method to judge the uniformity of conducting material.

Structure, Electrical, and Optical Properties of Nb-doped BaTiO3 Thin Films Grown by Laser Molecular Beam Epitaxy

Structure, electrical, and optical properties of Nb-doped BaTiO3 (Nb:BTO) thin films on MgO substrates grown by laser molecular beam epitaxy with increasing Nb content were investigated. The Nb:BTO thin films with high crystallinity are epitaxially grown on MgO substrates. With more Nb-doped content, the impurity phases are found in Nb:BTO thin films. Hall measurement at room temperature confirms that the charge carriers of the Nb:BTO thin films are n-type. When the Nb-doped content increases, the carrier concentration and carrier mobility increase. Meanwhile the optical transmittance decreases with the increase of the Nb-doping, and the width of the forbidden band in each group is not affected by the presence of Nb in the samples. Raman spectra show that the structural phase transition may occur with the increase of the Nb-doping content, in the meantime more defects and impurities exist in the Nb:BTO thin films.

N-Doped LaAlO3/Si(100) Films with High-k, Low-Leakage Current and Good Thermal Stability

High quality amorphous N-doped LaAlO3 (LaAlON) films have been deposited on Si (100) in nitrogen gas by laser molecular beam epitaxy. The chemical nature and physical distribution of N in LaAlON films has been performed by x-ray photoemission spectroscopy. Compared with LaAlO3, a significant improvement in the interfacial quality and leakage current density was obtained by nitrogen additive. At gate voltage +1 V, the leakage current density of the LaAlON film with an equivalent oxide thickness as thin as 2 nm is obtained to be 2.9×10−6 A/cm2, which decreases almost two orders of magnitude from that of LaAlO3 film with the same thickness. Moreover, high-resolution transmission electron microscope analysis show that the LaAlON sample is still amorphous with a very sharp interface between the LaAlON layer and the Si substrate after annealed at 900 degrees C for 60 s.