Shiyang Zhu

A BEEM study of Schottky barrier height distributions of ultrathin CoSi2/n-Si(100) formed by solid phase epitaxy

The spatial distributions of the Schottky barrier heights of ultrathin CoSi2 films (~10 nm) on n-Si(100), obtained by multilayer solid state reaction of Co/Ti/n-Si, Co/a-Si/Ti/n-Si, Ti/Co/a-Si/Ti/n-Si and Co/n-Si systems, are studied by ballistic electron emission microscopy (BEEM) and spectroscopy (BEES) at low temperature (~-80 °C). The barrier heights determined from BEEM spectra range between 520 meV and 700 meV, with an approximate Gaussian distribution. The mean barrier heights of the epitaxial CoSi2 /Si contacts are 0.60-0.61 eV, lower than the 0.64 eV for polycrystalline CoSi2 /Si contacts. Adding a thin amorphous Si interlayer (1 nm) slightly increases the probability of higher barrier heights, while a thin Ti capping layer (1 nm) has no significant influence on the mean barrier height. The BEEM results are compared to those from I -V /C -V measurements.

Rectifying characteristics of sputter-deposited SiGe diodes

Schottky and pn junction diodes with good rectifying characteristics have been prepared based on the polycrystalline SiGe (poly-SiGe) thin film deposited by the ion-beam-sputtering (IBS) technique. Boron and phosphorus diffusion techniques have been used to dope and crystallize as-deposited amorphous SiGe film. Rectification ratios as high as 4000 and 1800 have been achieved in Pt/n-poly-SiGe and Ti/p-poly-SiGe Schottky diodes, respectively, while rectification ratio higher than 1500 and breakdown voltage higher than 200 V have been achieved in poly-SiGe pn junction diodes. Schottky barrier height has been determined to be 0.62 and 0.59 eV for Pt/n-poly-Si0.81Ge0.19 and Ti/p-poly-Si0.81Ge0.19 contacts, respectively, which indicates that the band alignment of poly-SiGe may be substantially different from that of epitaxial SiGe.

I-V-T studies on ternary silicide Co/sub 1-x/Ni/sub x/Si/sub 2//n-Si Schottky contacts

Ternary silicide Co/sub 1-x/Ni/sub x/Si/sub 2//n-Si(100) contacts with different x value were formed by solid phase reaction of Co/Ni bilayer and substrate Si. Their Schottky barrier properties were studied using the current voltage-temperature (I-V-T) measurements range from 100 to 300K. The I-V-T curves show three typical types, which can be related to the barrier height inhomogeneity. A clean trend is found that the barrier height inhomogeneity increases with increasing the annealing temperature. Ni incorporation reduces not only the silicidation temperature, but also the temperature at which the contact becomes inhomogeneity.

Nucleation of CoSi/sub 2/ and MnSi/sub 1.7/ in the Co/Mn/Si ternary system

Silicide formation is studied for the ternary Co-Mn-Si system. At low temperatures, a mixed Co/sub 1-x/Mn/sub x/Si silicide is formed. It is found that the nucleation temperature of the Si-rich phases is increased by alloying: the nucleation temperature of CoSi/sub 2/ is increased by the presence of a small amount of Mn, while the nucleation temperature of MnSi/sub 1.7/ is increased in the presence of a small amount of Co. The nuclei could be observed using optical microscopy and atomic force microscopy. The influence of alloying on the nucleation of CoSi/sub 2/ and MnSi/sub 1.7/ is explained based on the effect of entropy of mixing.

Ion-bombardment effects on PtSi/n-Si Schottky contacts studied by ballistic electron emission microscopy

Ballistic electron emission microscopy has been used to study physical damage effects on PtSi/n-Si Schottky contacts. The physical damages are introduced into Si substrates by ion bombardment with well-defined energies in an ion-milling process. Schottky barrier height (SBH) distribution is measured on the subsequently formed PtSi/n-Si Schottky diodes. The results show that mean SBH decreases with ion energy in a square-root relation. A simple SBH model is developed to consider image-force lowering effect for a semiconductor with a step-function distribution of donor concentration. The model is successfully used to explain quantitatively the experimental relation between SBH and ion energy.