Growth and characterization of $\alpha$-Sn thin films on In- and Sb-rich reconstructions of InSb(001)

$\alpha$-Sn thin films can exhibit a variety of topologically nontrivial phases. Both studying the transitions between these phases and making use of these phases in eventual applications requires good control over the electronic and structural quality of $\alpha$-Sn thin films. $\alpha$-Sn growth on InSb often results in out-diffusion of indium, a $p$-type dopant. By growing $\alpha -\mathrm{Sn}$ via molecular beam epitaxy on the Sb-rich $\mathrm{c}(4\times 4)$ surface reconstruction of InSb(001) rather than the In-rich $\mathrm{c}(8\times 2)$, we demonstrate a route to substantially decrease and minimize this indium incorporation. The reduction in indium concentration allows for the study of the surface and bulk Dirac nodes in $\alpha$-Sn via angle-resolved photoelectron spectroscopy without the common approaches of bulk doping or surface dosing, simplifying topological phase identification. The lack of indium incorporation is verified in angle-resolved and angle-integrated ultraviolet photoelectron spectroscopy as well as in clear changes in the Hall response.

Figure 1

Surface reconstructions of InSb(001) surface. (a) Top and side view of the In-rich $\mathrm{c}(8\times 2)$ reconstruction following the model of Ref. [28]. (b) Top and side view of the Sb-rich $\mathrm{c}(4\times 4)$ reconstruction using the atomic positions determined in Ref. [29]. RHEED patterns along the [110], $\left[1\overline{1}0\right]$, and [100] directions for (c) the $\mathrm{c}(8\times 2)$ reconstruction with a $4\times , 2\times$, and $2\times$ pattern, respectively, and (d) the $\mathrm{c}(4\times 4)$ reconstruction with a $2\times , 2\times$, and $4\times$ pattern, respectively. In situ STM images of (e) the $\mathrm{c}(8\times 2)$ surface directly after atomic hydrogen cleaning and (f) the $\mathrm{c}(4\times 4)$ surface after the Sb termination procedure.

Figure 2

Surface structure of $\alpha$-Sn(001). (a) RHEED patterns along the [110], $\left[1\overline{1}0\right]$, and [100] directions showing a $2\times , 2\times$, and $1\times$ pattern, respectively, indicative of a mixed ($2\times 1$)/($1\times 2$) reconstruction. In situ STM of 13 BL $\alpha$-Sn grown on (b) InSb(001)-$\mathrm{c}(8\times 2)$ and (c) InSb(001)-$\mathrm{c}(4\times 4)$. Insets are 100 nm x 100 nm measurements under the same conditions.

Figure 3

UPS measurements of 13 BL $\alpha$-Sn films grown on the two different surface reconstructions of InSb(001) at 296 K. Measurements are offset for clarity. (a) Survey UPS measurements at photon energies of 50 eV and 130 eV, normalized to the integrated Sn $4d$ intensity. Zoom-in of (b) the valence band and indium core-level region and (c) the antimony core-level region with the same scan ordering.

Figure 4

UPS measurements of 50 BL $\alpha$-Sn on the $\mathrm{c}(4\times 4)$ reconstruction grown at 253 K and 400 BL $\alpha$-Sn on the $\mathrm{c}(8\times 2)$ reconstruction grown at 80 K. Measurements are offset for clarity. (a) Survey UPS measurements at a photon energy of 90 eV, normalized to the integrated Sn 4d intensity. Zoom-in of (b) the valence band and indium core-level range and (c) the antimony core-level range with the same sample ordering.

Figure 5

ARPES measurements of the 13 BL $\alpha$-Sn films. (a) Band schematic of $\alpha$-Sn in a 3D topological insulatorlike phase. Surface-state measurements at $h\nu$ = 21 eV in the $\overline{\mathbf{X}}-\overline{\mathit{\Gamma }}-\overline{\mathbf{X}}$ direction for 13 BL $\alpha$-Sn grown on (b) InSb(001)-$\mathrm{c}(8\times 2)$ and (c) InSb(001)-$\mathrm{c}(4\times 4)$. Dashed lines corresponding to a linear fit of TSS1 are overlaid on the spectra. (d) Bulk and surface Brillouin zone schematic of $\alpha$-Sn. Bulk band measurements at $h\nu$=127 eV in the $\mathbf{K}-\mathit{\Gamma }-\mathbf{K}$ direction in the vicinity of ${\mathrm{\Gamma }}_{003}$ for 13 BL $\alpha$-Sn grown on (e) InSb(001)-$\mathrm{c}(8\times 2)$ and (f) InSb(001)-$\mathrm{c}(4\times 4)$.

Figure 6

Magnetotransport measurements of 56 BL $\alpha$-Sn films performed at 2 K. (a) Transverse resistance as a function of magnetic field for $\alpha$-Sn films grown on the $\mathrm{c}(8\times 2)$ and $\mathrm{c}(4\times 4)$ surfaces of InSb(001). (b) Zoom-in of (a) showing an additional inflection point in each sample. (c) Longitudinal resistance vs magnetic field for the two samples. Approximate inflection points in transverse geometry measurements are marked.