Short-range atomic ordering in nonequilibrium silicon-germanium-tin semiconductors

Abstract

The precise knowledge of the atomic order in monocrystalline alloys is fundamental to understand and predict their physical properties. With this perspective, we utilized laser-assisted atom probe tomography to investigate the three-dimensional distribution of atoms in nonequilibrium epitaxial Sn-rich group IV SiGeSn ternary semiconductors. Different atom probe statistical analysis tools including frequency distribution analysis, partial radial distribution functions, and nearest neighbor analysis were employed in order to evaluate and compare the behavior of the three elements to their spatial distributions in an ideal solid solution. This atomistic-level analysis provided clear evidence of an unexpected repulsive interaction between Sn and Si leading to the deviation of Si atoms from the theoretical random distribution. This departure from an ideal solid solution is supported by first principles calculations and attributed to the tendency of the system to reduce its mixing enthalpy throughout the layer-by-layer growth process. 2The assumption that the arrangement of atoms within the crystal lattice is perfectly random is a broadly used approximation to establish the physical properties of semiconductor alloys. This approximation allows one to estimate rather accurately certain thermodynamic as well as material parameters like the excess enthalpy of formation, Vegard-like lattice parameters, and band gaps that are smaller than the composition weighted average (optical bowing). However, it has been proposed that some ternary semiconductors can deviate from this assumed perfect solid solution. Indeed, both calculations and experiments suggested the presence of local atomic order in certain III-V alloys [1][2][3][4][5][6][7][8]. This phenomenon manifests itself when at least one of the elements forming the alloy preferentially occupies or avoids specific lattice sites. This induces short-range order in the lattice with an impact on the basic properties of the alloyed semiconductors [3][4][5][6][7].The recent progress in developing Sn-rich group IV (SiGeSn) ternary semiconductors and their integration in a variety of low dimensional systems and devices have revived the interest in elucidating the atomistic-level properties of monocrystalline alloys [9][10][11][12][13][14][15][16][17][18][19][20]. Interestingly, unlike III-V semiconductors, achieving a direct bandgap in Si GeSn requires a sizable incorporation of Sn 10 . % , which is significantly higher than the equilibrium solubility (<1 at.%). Understanding the atomic structure of these metastable alloys is therefore imperative for implementing predictive models to describe their basic properties. With this perspective, we present a first study of the atomic order in Si Ge Sn alloys (x and y in 0.04 0.19 and 0.02 0.12 range, respectively). We employed Atom Probe Tomography (APT) which allows atomistic level investigations [21][22][23][24] and statistical tools to analyze the three-dimensional (3-D)distributions of the three elements. This analysis unraveled an un...

Influence of growth kinetics on Sn incorporation in direct band gap Ge1−xSnx nanowires

“…Deviation from a perfectly random distribution and observation of short range ordering was previously observed through atom probe tomography in SiGeSn ternary alloy with > 4 at.% Sn content. 20 The induction of impurity atoms into the nanowire lattice can induce defects at which impurities subsequently accumulate. 46 As such, it is imperative to determine the structural quality of the Ge1-xSnx nanowires with large (> 9 at.…”

“…To verify the increased growth rate of these Ge1-xSnx nanowires with increasing Ag content in the nanoparticle, the lengths of these nanowires were compared for similar diameters across the samples. As the nanowires catalysed by Au0.70Ag0.30 were irregular in both diameter and length and highly tapered, they were not included in the length comparison.The mean diameter of the nanowires catalysed with Au, Au0.90Ag0.10 and Au0.80Ag0 20. were in a similar size range; 63.5 ± 17.4 nm, 57.4 ± 15.2 nm and 65.5 ± 16.8 nm respectively.…”

“…Impurity ordering in semiconductor alloys provide an additional engineering of freedom as the ordering is associated with the electronic band structure such as reduction of band gap, degeneracy at the valence band, emission width and lifetime. 20,21 In case of Ge1-xSnx nanowire, a randomly ordered alloy resulted in luminescence with broad line-widths which are not ideal for photonic devices. 12 Therefore, incorporation of a substantial amount (x > 0.09 is desired for direct band gap) of Sn into a 1D…”

“…A perfectly binary/ternary alloy would produce a completely random distribution in terms of atomic ordering of impurities. A deviation from this random distribution can generate "short-range ordering" 20 of at least one of the atomic constituents of the alloy with an impact on the basic properties of the alloyed semiconductors. 22,23 The uniform and relatively ordered distribution of Sn impurities in a 1-D alloy lattice during the VLS nanowire growth can be achieved via the "solute trapping" process, where the impurities are incorporated by solute redistribution at the catalyst-nanowire interface via an increase of chemical potential and deviation of the partition coefficient.…”

Atomically uniform Sn-rich GeSn semiconductors with 3.0–3.5 μm room-temperature optical emission

“…3 respectively, hence about one order of magnitude lower than those reported in recent studies. 5,12,19,26 Detailed insights into the short-range atomic distribution on the scale of a few lattice constants are obtained by performing a series of statistical analyses 27,28 within pre-defined 10 Â 10 Â 10 nm 3 regions in APT maps recorded for GeSn TL [ Fig. 4(a)].…”