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Title: Perfectly tetragonal, tensile-strained Ge on Ge{sub 1-y}Sn{sub y} buffered Si(100)

Abstract

High-quality, tensile-strained Ge layers with variable thickness (>30 nm) have been deposited at low temperature (350-380 deg. C) on Si(100) via fully relaxed Ge{sub 1-y}Sn{sub y} buffers. The precise strain state of the epilayers is controlled by varying the Sn content of the buffer, yielding tunable tensile strains up to 0.25% for y=0.025. Combined Raman analysis and high resolution x-ray diffraction using multiple off-axis reflections reveal unequivocally that the symmetry of tensile Ge is perfectly tetragonal, while the strain state of the buffer ({approx}200 nm thick) remains essentially unchanged. A downshift of the direct gap consistent with tensile strain has been observed.

Authors:
; ; ; ; ; ;  [1];  [2]
  1. Department of Chemistry and Biochemistry, Arizona State University, Tempe AZ 85287 (United States)
  2. (United States)
Publication Date:
OSTI Identifier:
20971810
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 90; Journal Issue: 6; Other Information: DOI: 10.1063/1.2472273; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; BUFFERS; CRYSTAL GROWTH; ENERGY GAP; GERMANIUM; GERMANIUM COMPOUNDS; LAYERS; MOLECULAR BEAM EPITAXY; RAMAN SPECTRA; RESIDUAL STRESSES; SEMICONDUCTOR MATERIALS; STRAINS; TEMPERATURE RANGE 0400-1000 K; THICKNESS; TIN COMPOUNDS; X-RAY DIFFRACTION

Citation Formats

Fang, Y.-Y., Tolle, J., Roucka, R., Chizmeshya, A. V. G., Kouvetakis, John, D'Costa, V. R., Menendez, Jose, and Department of Physics and Astronomy, Arizona State University, Tempe AZ 85287. Perfectly tetragonal, tensile-strained Ge on Ge{sub 1-y}Sn{sub y} buffered Si(100). United States: N. p., 2007. Web. doi:10.1063/1.2472273.
Fang, Y.-Y., Tolle, J., Roucka, R., Chizmeshya, A. V. G., Kouvetakis, John, D'Costa, V. R., Menendez, Jose, & Department of Physics and Astronomy, Arizona State University, Tempe AZ 85287. Perfectly tetragonal, tensile-strained Ge on Ge{sub 1-y}Sn{sub y} buffered Si(100). United States. doi:10.1063/1.2472273.
Fang, Y.-Y., Tolle, J., Roucka, R., Chizmeshya, A. V. G., Kouvetakis, John, D'Costa, V. R., Menendez, Jose, and Department of Physics and Astronomy, Arizona State University, Tempe AZ 85287. Mon . "Perfectly tetragonal, tensile-strained Ge on Ge{sub 1-y}Sn{sub y} buffered Si(100)". United States. doi:10.1063/1.2472273.
@article{osti_20971810,
title = {Perfectly tetragonal, tensile-strained Ge on Ge{sub 1-y}Sn{sub y} buffered Si(100)},
author = {Fang, Y.-Y. and Tolle, J. and Roucka, R. and Chizmeshya, A. V. G. and Kouvetakis, John and D'Costa, V. R. and Menendez, Jose and Department of Physics and Astronomy, Arizona State University, Tempe AZ 85287},
abstractNote = {High-quality, tensile-strained Ge layers with variable thickness (>30 nm) have been deposited at low temperature (350-380 deg. C) on Si(100) via fully relaxed Ge{sub 1-y}Sn{sub y} buffers. The precise strain state of the epilayers is controlled by varying the Sn content of the buffer, yielding tunable tensile strains up to 0.25% for y=0.025. Combined Raman analysis and high resolution x-ray diffraction using multiple off-axis reflections reveal unequivocally that the symmetry of tensile Ge is perfectly tetragonal, while the strain state of the buffer ({approx}200 nm thick) remains essentially unchanged. A downshift of the direct gap consistent with tensile strain has been observed.},
doi = {10.1063/1.2472273},
journal = {Applied Physics Letters},
number = 6,
volume = 90,
place = {United States},
year = {Mon Feb 05 00:00:00 EST 2007},
month = {Mon Feb 05 00:00:00 EST 2007}
}
  • Novel hydride chemistries are employed to deposit light-emitting Ge{sub 1-y}Sn{sub y} alloys with y ≤ 0.1 by Ultra-High Vacuum Chemical Vapor Deposition (UHV-CVD) on Ge-buffered Si wafers. The properties of the resultant materials are systematically compared with similar alloys grown directly on Si wafers. The fundamental difference between the two systems is a fivefold (and higher) decrease in lattice mismatch between film and virtual substrate, allowing direct integration of bulk-like crystals with planar surfaces and relatively low dislocation densities. For y ≤ 0.06, the CVD precursors used were digermane Ge₂H₆ and deuterated stannane SnD₄. For y ≥ 0.06, the Gemore » precursor was changed to trigermane Ge₃H₈, whose higher reactivity enabled the fabrication of supersaturated samples with the target film parameters. In all cases, the Ge wafers were produced using tetragermane Ge₄H₁₀ as the Ge source. The photoluminescence intensity from Ge{sub 1–y}Sn{sub y}/Ge films is expected to increase relative to Ge{sub 1–y}Sn{sub y}/Si due to the less defected interface with the virtual substrate. However, while Ge{sub 1–y}Sn{sub y}/Si films are largely relaxed, a significant amount of compressive strain may be present in the Ge{sub 1–y}Sn{sub y}/Ge case. This compressive strain can reduce the emission intensity by increasing the separation between the direct and indirect edges. In this context, it is shown here that the proposed CVD approach to Ge{sub 1–y}Sn{sub y}/Ge makes it possible to approach film thicknesses of about 1 μm, for which the strain is mostly relaxed and the photoluminescence intensity increases by one order of magnitude relative to Ge{sub 1–y}Sn{sub y}/Si films. The observed strain relaxation is shown to be consistent with predictions from strain-relaxation models first developed for the Si{sub 1–x}Ge{sub x}/Si system. The defect structure and atomic distributions in the films are studied in detail using advanced electron-microscopy techniques, including aberration corrected STEM imaging and EELS mapping of the average diamond–cubic lattice.« less
  • Ge{sub 0.94}Sn{sub 0.06} films with high tensile strain were grown on strain-relaxed In{sub y}Ga{sub 1−y}P virtual substrates using solid-source molecular beam epitaxy. The in-plane tensile strain in the Ge{sub 0.94}Sn{sub 0.06} film was varied by changing the In mole fraction in In{sub x}Ga{sub 1−x}P buffer layer. The tensile strained Ge{sub 0.94}Sn{sub 0.06} films were investigated by transmission electron microscopy, x-ray diffraction, and Raman spectroscopy. An in-plane tensile strain of up to 1% in the Ge{sub 0.94}Sn{sub 0.06} was measured, which is much higher than that achieved using other buffer systems. Controlled thermal anneal experiment demonstrated that the strain was notmore » relaxed for temperatures up to 500 °C. The band alignment of the tensile strained Ge{sub 0.94}Sn{sub 0.06} on In{sub 0.77}Ga{sub 0.23}P was obtained by high resolution x-ray photoelectron spectroscopy. The Ge{sub 0.94}Sn{sub 0.06}/In{sub 0.77}Ga{sub 0.23}P interface was found to be of the type I band alignment, with a valence band offset of 0.31 ± 0.12 eV and a conduction band offset of 0.74 ± 0.12 eV.« less
  • Sn-containing group IV semiconductors create the possibility to independently control strain and band gap thus providing a wealth of opportunities to develop an entirely new class of low dimensional systems, heterostructures, and silicon-compatible electronic and optoelectronic devices. With this perspective, this work presents a detailed investigation of the band structure of strained and relaxed Ge{sub 1−x−y}Si{sub x}Sn{sub y} ternary alloys using a semi-empirical second nearest neighbors tight binding method. This method is based on an accurate evaluation of the deformation potential constants of Ge, Si, and α-Sn using a stochastic Monte-Carlo approach as well as a gradient based optimization method.more » Moreover, a new and efficient differential evolution approach is also developed to accurately reproduce the experimental effective masses and band gaps. Based on this, we elucidated the influence of lattice disorder, strain, and composition on Ge{sub 1−x−y}Si{sub x}Sn{sub y} band gap energy and directness. For 0 ≤ x ≤ 0.4 and 0 ≤ y ≤ 0.2, we found that tensile strain lowers the critical content of Sn needed to achieve a direct band gap semiconductor with the corresponding band gap energies below 0.76 eV. This upper limit decreases to 0.43 eV for direct gap, fully relaxed ternary alloys. The obtained transition to direct band gap is given by y > 0.605 × x + 0.077 and y > 1.364 × x + 0.107 for epitaxially strained and fully relaxed alloys, respectively. The effects of strain, at a fixed composition, on band gap directness were also investigated and discussed.« less
  • The compositional dependence of the cubic lattice parameter in Ge 1-ySn y alloys has been revisited. Large 1000-atom supercell ab initio simulations confirm earlier theoretical predictions that indicate a positive quadratic deviation from Vegard's law, albeit with a somewhat smaller bowing coefficient, θ = 0.047 Å, than found from 64-atom cell simulations (θ = 0.063 Å). On the other hand, measurements from an extensive set of alloy samples with compositions y < 0.15 reveal a negative deviation from Vegard's law. The discrepancy with earlier experimental data, which supported the theoretical results, is traced back to an unexpected compositional dependence ofmore » the residual strain after growth on Si substrates. The experimental bowing parameter for the relaxed lattice constant of the alloys is found to be θ = -0.066 Å. Possible reasons for the disagreement between theory and experiment are discussed in detail.« less
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  • In this letter, we study the structural and magnetic properties of Ge{sub 1-x-y}Sn{sub x}Mn{sub y} films grown on Ge(001) by low temperature molecular beam epitaxy using X-ray diffraction, high resolution transmission electron microscopy, and superconducting quantum interference device. Like in Mn doped Ge films, Mn atoms diffuse during the growth and aggregate into vertically aligned Mn-rich nanocolumns of a few nanometers in diameter. Transmission electron microscopy observations in plane view clearly indicate that the Sn incorporation is not uniform with concentration in Mn rich vertical nanocolumns lower than the detection limit of electron energy loss spectroscopy. The matrix exhibits amore » GeSn solid solution while there is a Sn-rich GeSn shell around GeMn nanocolumns. The magnetization in Ge{sub 1-x-y}Sn{sub x}Mn{sub y} layers is higher than in Ge{sub 1-x}Mn{sub x} films. This magnetic moment enhancement in Ge{sub 1-x-y}Sn{sub x}Mn{sub y} is probably related to the modification of the electronic structure of Mn atoms in the nanocolumns by the Sn-rich shell, which is formed around the nanocolumns.« less