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Title:Low-temperature growth of silicon and silicon-germanium alloy by ultrahigh vacuum ion-beam sputter deposition
Author(s):Lee, Nae-Eung
Doctoral Committee Chair(s):Greene, Joseph E.
Department / Program:Materials Science and Engineering
Discipline:Materials Science and Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Engineering, Materials Science
Abstract:The use of energetic (average energy $\simeq$ 18 eV), rather than thermal, Si beams increased Si(001) epitaxial thicknesses t$\rm\sb{e}$ by up to an order of magnitude over the growth temperature range $\rm T\sb{s}=80{-}300\sp\circ$C yielding t$\rm\sb{e}$ = 10 nm-1.2 $\mu$m at a growth rate R = 0.1 nm-s$\sp{-1}$. The overall increase in t$\rm\sb{e}$ is attributed primarily to more effective filling of interisland trenches which form during growth in the low adatom mobility two-dimensional multilayer mode and which provide preferential sites for the nucleation of the terminal amorphous phase. The evolution of surface roughness was found to be inconsistent with conventional scaling and hyperscaling laws and led to the formation of mounds separated by a well-defined length scale. In addition, Sb doping $\rm(\langle E\sb{Sb}\rangle\simeq14$ eV), corresponding to a steady-state surface coverage of only ${\simeq}4\times10\sp{-5}$ ML leading to bulk concentration of ${\simeq}2\times10\sp{18}$ cm$\sp{-3}$, at $\rm T\sb{s}=250{-}300\sp\circ$C increased the rate of surface roughening and decreased epitaxial thickness t$\rm\sb{e}$ by a factor of $\sbsp{>}{\sim}$2.
Sb incorporation probabilities $\rm\sigma\sb{Sb}$ during Si(001) homoepitaxy ranged from $\simeq$1 for $\rm T\sb{s}\le550\sp\circ$C to $\simeq$0.1 at $\rm T\sb{s}=750\sp\circ$C with no indication of surface segregation. These $\rm\sigma\sb{Sb}$ values are one to three orders of magnitude larger than for co-evaporative Sb doping during MBE where extensive Sb surface segregation is observed. The incorporated Sb exhibited complete electrical activity at $\rm T\sb{s}\le400\sp\circ$C and temperature-dependent (15-300 K) electron mobilities were equal to the bulk Si values.
High-quality epitaxial $\rm Si\sb{1-x}Ge\sb{x}(001)$ alloy films, with $\rm0.15\le x\le0.30,$ were grown on Si(001) at $\rm T\sb{s}$ ranging from 300 to 550$\sp\circ$C using hyperthermal Si $\rm(\langle E\sb{Si}\rangle\simeq18$eV) and Ge $\rm(\langle E\sb{Ge}\rangle\simeq15$ eV) beams at R = 0.1 nm-s$\sp{-1}$. Critical layer thicknesses $\rm h\sb{c}$ for strain relaxation in $\rm Si\sb{0.7}Ge\sb{0.3}(001)$ was increased rapidly with decreasing $\rm T\sb{s},$ from 35 nm at $\rm T\sb{s}=550\sp\circ$C to 650 nm at 350$\sp\circ$C compared to an equilibrium value of $\simeq$8 nm, primarily due to kinetic limitations in dislocation nucleation and propagation.
The evolution of surface roughness in epitaxial $\rm Si\sb{0.7}Ge\sb{0.3}(001)$ alloys grown on Si(001) showed strain-induced surface roughening dominates in alloys grown at $\rm T\sb{s}\sbsp{>}{\sim}450\sp\circ$C where surface roughness initially increases with increasing film thickness through coherent islanding and then decreases with island coalescence and surface smoothening due to strain relaxation, whereas at very low growth temperatures $\rm(T\sb{s}\le250\sp\circ$C), surfaces roughens kinetically, due to limited adatom diffusivity, but at far lower rates than in the higher-temperature strain-induced regime. There is an intermediate growth temperature range, however, over which the alloy film surfaces remain extremely smooth even at thicknesses near critical values for strain relaxation.
Issue Date:1996
Rights Information:Copyright 1996 Lee, Nae-Eung
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9702576
OCLC Identifier:(UMI)AAI9702576

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