Huafang Li

Biaxially textured Al film growth on CaF2 nanostructures toward a method of preparing single-crystalline Si film on glass substrates.

We report the room temperature growth of biaxially textured Al films and further demonstrate the use of these Al films in preparing single-crystalline Si layers on glass substrates. The formation of the biaxial texture in Al film relies on the existence of the CaF(2) buffer layer prepared using oblique angle physical vapor deposition, which consists of single-crystalline nanorods with caps that are in the form of inverted nanopyramids. The single-crystalline Si film was obtained upon crystallization of the amorphous Si film deposited through physical evaporation on the biaxially textured Al film. This method of preparing single-crystalline Si film on glass substrate is potentially attractive for being employed in silicon technology and in fabrication of low-cost electronic devices.

Bias-temperature stress of Al on porous low-k dielectrics

Abstract Aluminum has been perceived as a stable electrode for the reliability test of dielectric films. In this letter, using energy dispersive X-ray spectroscopy method, Al ions were detected in the dielectric after Al/SiCOH/SiO 2 /Si capacitor was subjected to bias-temperature stress (BTS). We investigated the impact of the drifted Al to the stability of the dielectrics by studying the leakage current of the capacitor. We showed that the increase of leakage current after BTS falls into the Poole–Frenkel conduction regime, indicating the Al ions act as electronic traps inside SiCOH. Our results question the compatibility between Al and low- k dielectrics.

Orientation Modulated Epitaxy of Cu Nanorods on Si(1 0 0) Substrate

Epitaxial growth of Cu nanorod films on hydrogen-terminated Si(100) substrates by oblique angle deposition (OAD) was investigated. It is found out that the crystallographic orientation of Cu nanorod films exhibits a 45° in-plane rotation with respect to the substrate. When the incident angle of deposition was increased from normal to 80°, the distribution of Cu(111) poles is observed to spread out gradually, whereas the spread in poles is severe beyond 80°, indicating higher epitaxy quality for Cu deposited at lower incident angles. In addition, two sets of twin poles are induced at high-incident angles, while one set can be suppressed by altering flux direction 45° azimuthally about substrate normal. The mechanism of epitaxy development in the OAD grown Cu films is explained.

Nanolamellar structure obtained by simple crystallization of an amorphous cobalt-based magnetic alloy

A novel modulated nanolamellar structure with a lamellar spacing of about 5 nm was obtained by simple heat treatment of an initially amorphous Co/sub 65/Si/sub 15/B/sub 14/Fe/sub 4/Ni/sub 2/ magnetic alloy. The crystallographic characteristics of this nanolamellar structure were investigated using selected area diffraction pattern, Kikuchi maps, convergent beam electron diffraction, and X-ray diffraction techniques. The crystal structure of the lamellae was found to be a novel phase with a C-base centered orthorhombic crystal structure of a=0.74 nm, b=1.07 nm, and c=0.77 nm, the nanolamellar structure was modulated along the (0 0 1) plane. High-resolution transmission electron microscopy observations showed negligible lattice mismatch between neighboring lamellae. Electron energy loss spectroscopy mapping showed a periodic variation of boron composition corresponding to the nanolamellar periodicity. The formation of the nanolamellar structure was found to be due to spinodal decomposition within the grains formed by crystallization of the alloy.

Quasi-single Crystal Semiconductors on Glass Substrates Through Biaxially Oriented Buffer Layers

High efficiency photovoltaic devices are normally fabricated on single crystalline substrates. These single crystalline substrates are expensive and volume production for widespread usage has not been realistic. To date, large volume production of solar cells is on less expensive noncrystalline substrates such as glass. Typically the films grown on glass are polycrystalline with less than ideal efficiency. It was proposed that a dramatic gain in the efficiency may be achieved if one uses a biaxially oriented buffer layer on glass to grow biaxial semiconductor films to fabricate solar devices compared to that of films grown directly on glass. Biaxial films are not exactly single crystal but have strongly preferred crystallographic orientations in both the out-ofplane and in-plane directions. Typically the misorientation between grains can be small (within a few degrees) and may possess low carrier recombination rate. In this paper we shall discuss growth techniques that would allow one to produce biaxial buffer layers on glass. A specific strategy using an atomic shadowing mechanism in an oblique angle deposition configuration that allows one to grow biaxial buffer layers such as CaF2 on glass substrate will be discussed in detail. Results of heteroepitaxy of semiconductor materials such as CdTe and Ge on these biaxial buffer/glass substrates characterized by x-ray pole figure, reflection high energy electron diffraction (RHEED) pole figure and transmission electron microscopy (TEM) will be presented.

Dislocation reduction in CdTe epilayers grown on silicon substrates using buffered nanostructures

High performance HgCdTe IR detector fabrication on silicon substrates first requires low defect density CdTe buffer layers to be grown on silicon. The objective of this paper is to demonstrate dislocation reduction in CdTe epitaxial layers grown on silicon substrate by using intermediate nanocrystalline CdTe buffer layers. Colloidal synthesis of high quality CdTe nanocrystals was accomplished and spin coating of these CdTe nanocrystals as buffer layers on silicon substrates was carried out. CdTe layers were grown on these buffered substrates by metalorganic chemical vapor deposition (MOCVD). However, the incomplete removal of SiO2 on silicon substrate (by chemical treatment) prevented the exact orientation of the nanocrystals with the silicon substrate and over layer growth of continuous single crystal CdTe epitaxial film. Two new approaches were further investigated: (i) First a thin film of Ge was grown on Si, followed by the deposition of thin SiO2 followed by nanopatterning using block co-polymer (BCP) lithography. Transmission electron microscopy (TEM) showed defect reduction in the CdTe layers grown on these substrates, but the x-ray rocking curves over a larger area gave wider full width half maximum values compared to that of layers grown on blanket surfaces. This was attributed to non uniform nanopatterning in these initial studies; (ii) SiO2 coated silicon substrates were nanopatterned using interference lithography with a honeycomb array of holes. These substrates will be used for the selective growth of germanium and CdTe by MOCVD.