Xiang Wen-Feng

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.

Structure Stability of LaAlO3 Thin Films on Si Substrates

A series of amorphous and single-crystalline LaAlO3 (LAO) thin films are fabricated by laser molecular-beam epitaxy technique on Si substrates under various conditions of deposition. The structure stability of the LAO films annealed in high temperature and various ambients is studied by x-ray diffraction as well as high-resolution transmission electron microscopy. The results show that the epitaxial LAO films have very good stability, and the structures of amorphous LAO thin films depend strongly on the conditions of deposition and post-annealing. The results reveal that the formation of LAO composition during the deposition is very important for the structure stability of LAO thin films.

Oxygen pressure dependence of properties of epitaxial LaAlO3 films grown on Si(100)

Heteroepitaxial LaAlO3 films were grown on a SrTiO3/Si (100) substrate by laser molecular beam epitaxy under different oxygen pressures, and their properties such as crystallinity and electrical characteristics were experimentally investigated using the various measurement methods. The results show that most properties depend mainly on the deposition oxygen pressure. The crystallinity and the C–V and I–V characteristics can be greatly improved with the increasing oxygen deposition pressure. Moreover, after annealed at 1050 degrees C in N2 ambient, the C–V and I–V characteristics of LAO films deposited at the lower oxygen pressure are also improved due to the decrease of oxygen vacancies in LAO films.

Ni(Pt) germanosilicide contacts formed on heavily boron doped Si1−xGex substrates for Schottky source/drain transistors

The electrical properties of Ni0.95Pt0.05-germanosilicide/Si1−xGex contacts on heavily doped p-type strained Si1−xGex layers as a function of composition and doping concentration for a given composition have been investigated. A four-terminal Kelvin-resistor structure has been fabricated by using the conventional complementary metal–oxide–semiconductor (CMOS) process to measure contact resistance. The results showed that the contact resistance of the Ni0.95Pt0.05-germanosilicide/Si1−xGex contacts slightly reduced with increasing the Ge fraction. The higher the doping concentration, the lower the contact resistivity. The contact resistance of the samples with doping concentration of 4 × 1019 cm−3 is nearly one order of magnitude lower than that of the samples with doping concentration of 5 × 1017 cm−3. In addition, the influence of dopant segregation on the contact resistance for the lower doped samples is larger than that for the higher doped samples.

Formation of Interfacial Layers in LaAlO3/Silicon during Film Deposition

We have studied the interfacial reactions between amorphous LaAlO3 thin films and Si substrates, using high-resolution transmission electron microscopy and x-ray photoelectron spectroscopy. It has been shown that the interfacial layer between LaAlO3 film and Si substrate is SiLaxAlyOz. The depth distributions of La, Si and Al chemical states show that the ratio of La 4d3/2 to Al 2p of the interfacial layer remains unchanged with the depth compared to that of the LaAlO3 film. Moreover, the Si content in the interfacial layer gradually decreases with increasing thickness of the interfacial layer. These results strongly suggest that the Al element is not deficient in the interfacial layer, as previously believed, and the formation of a SiLaxAlyOz interfacial layer is mainly due to the diffusion of Si from the substrate during the LaAlO3 film deposition. With the understanding of the interfacial layer formation, ones can control the interface characteristics to ensure the desired performances of devices using high-k oxides as gate dielectrics.