Low-temperature growth and critical epitaxial thicknesses of fully strained metastable Ge{sub 1{minus}x}Sn{sub x} (x{approx_lt}0.26) alloys on Ge(001)2{times}1

Journal Article · Thu Jan 01 04:00:00 EST 1998 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.366690· OSTI ID:565607

Gurdal, O; Desjardins, P; Carlsson, J R; Taylor, N ^[1]; Radamson, H H; Sundgren, J ^[2]; Greene, J E ^[1]

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1. Materials Science Department, the Coordinated Science Laboratory, and the Materials Research Laboratory, University of Illinois, 1101 West Springfield Avenue, Urbana, Illinois 61801 (United States)
2. Department of Physics, Linkoeping University, S-58183 Linkoeping (Sweden)

Epitaxial metastable Ge{sub 1{minus}x}Sn{sub x} alloys with x up to 0.26 (the equilibrium solid solubility of Sn in Ge is {lt}0.01) were grown on Ge(001)2{times}1 by low-temperature molecular beam epitaxy. Film growth temperatures T{sub s} in these experiments were limited to a relatively narrow range around 100{degree}C by the combination of increased kinetic surface roughening at low temperatures and Sn surface segregation at high temperatures. All Ge{sub 1{minus}x}Sn{sub x} films consisted of three distinct sublayers: the first is a highly perfect epitaxial region followed by a sublayer, with an increasingly rough surface, containing 111 stacking faults and microtwins, while the terminal sublayer is amorphous. Based upon reflection high energy electron diffraction and cross-sectional transmission electron microscopy (XTEM) analyses, critical epitaxial thicknesses t{sub epi}, defined as the onset of amorphous growth, were found to decrease from 1080 {Angstrom} for pure Ge to {approx_equal}35{Angstrom} for alloys with x=0.26. TEM and XTEM analyses revealed no indication of misfit dislocations (except in Ge{sub 0.74}Sn{sub 0.26} samples) and high-resolution x-ray reciprocal lattice mapping showed that epitaxial Ge{sub 1{minus}x}Sn{sub x} layers were essentially fully strained. From an analysis of t{sub epi}(x) results, surface morphological evolution leading to epitaxial breakdown is controlled by kinetic roughening for alloys with x{approx_lt}0.09 and by strain-induced roughening at higher Sn concentrations. We propose that the thermal activation required for the cross-over, reported here for the first time, from kinetic to strain-induced roughening is partially overcome by the fact that kinetic roughening provides local surface chemical potential gradients over lateral length scales which are sufficiently small to initiate strain-induced roughening even at these low temperatures. {copyright} {ital 1998 American Institute of Physics.}

• OSTI ID: 565607
• Journal Information: Journal of Applied Physics, Journal Name: Journal of Applied Physics Journal Issue: 1 Vol. 83; ISSN JAPIAU; ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
GERMANIUM ALLOYS
METASTABLE STATES
MICROSTRUCTURE
MOLECULAR BEAM EPITAXY
STACKING FAULTS
STRAINS
STRUCTURAL CHEMICAL ANALYSIS
THICKNESS
TIN ALLOYS
TRANSMISSION ELECTRON MICROSCOPY
TWINNING