We have measured the evolving three-dimensional ͑3D͒ morphology of patterned SiO 2 stripes on Si substrates induced by 3 MeV O ++ ion irradiation. We develop a 3D constitutive relation to describe anisotropic deformation, densification, and flow. We use this constitutive relation in a finite element model that simulates the experimental morphology evolution, and we find excellent agreement between simulated and measured profiles. The model should be useful in predicting morphology evolution in complex three-dimensional structures under MeV ion irradiation.
High quality homoepitaxial growth of Si on Si(ll1) through an overlayer of Au is shown to occur at 450-500 "C, far below the temperature required for growth of Si of similar quality on bare Si(ll1). Films of unlimited thickness can be obtained with excellent crystalline quality, as revealed by Rutherford backscattering spectrometry ion channeling measurements (~~~"2.2%). A distinct range of Au coverage (0.4-1.0 monolayer) results in the best quality epitaxy, with no measurable amount of Au trapped at either the interface or within the grown films. Cross-sectional transmission electron microscopy reveals that in films grown with Au coverages below and above the optimum range, the predominant defects are twins on (111) planes and Au inclusions, respectively.
A monolayer of Pb mediates high-quality homoepitaxial growth on Si ͑111͒ surfaces at temperatures where growth with other overlayer elements or on bare surfaces leads to amorphous or highly defective crystalline films. Nearly defect-free epitaxy proceeds for film thicknesses up to 1000 Å with no sign that this is an upper limit. The minimum temperature for high-quality epitaxy depends on the substrate miscut. For a 0.2°miscut, the minimum temperature is 340°C. Films grown on substrates miscut 2.3°towards ͓112͔ show good crystalline quality down to 310°C.
The codeposition of Pb during Si (111) molecular beam homoepitaxy leads to high-quality crystalline films at temperatures for which films deposited on bare Si (111) are amorphous. Like other growth mediating elements--commonly called surfactants--Pb segregates to the film surface. Ion channeling and transmission electron microscopy reveal nearly defect-free epitaxy for a Pb coverage of one monolayer and temperatures as low as 310 'C. We have deposited films up to 1000 A in thickness with no indication that this is an upper limit for high-quality epitaxy. However, a decrease in the Pb coverage during growth by only one tenth of a monolayer leads to highly defective films at these temperatures. The codeposition of both As and Pb results in a striking enhancement of the film quality as well. In this case, while the Pb again segregates to the film surface, the As is incorporated into the film with no apparent segregation. Lead-mediated Si epitaxy on As-terminated Si (11) produces high-quality films in which the As remains buried at the substrate-film interface. These results show Pb-mediated Si (11l) homoepitaxy to be a promising strategy for the synthesis of layered structures having abrupt nanoscale dopant profiles.
In molecular-beam epitaxy a monolayer of Pb on the Si(111) surface induces single-crystal growth at temperatures well below those required for similar growth on a bare surface. We demonstrate that the suppression of dopant segregation at the lower temperatures attainable by Pb-mediated growth allows the incorporation of As donors at concentrations reaching a few atomic percent. When Pb and Si are deposited on an As-terminated Si(111) substrate at 350 °C, the Pb segregates to the surface without doping the Si film while the As is buried within nanometers of the substrate–film interface. The resulting concentration of electrically active As, 1.8×1021 cm−3, represents the highest concentration of As donors achieved by any delta-doping or thin-film deposition method.
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