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Substrate-controlled nucleation and growth kinetics in ultrathin Bi$_2$Te$_3$ films

Damian Brzozowski, Sander R. Hønnås, Egil Y. Tokle, Jørgen A. Arnesen, Ingrid G. Hallsteinsen

Abstract

Metal chalcogenides are promising layered topological materials, yet their electronic performance is often limited by parasitic bulk conduction arising from defects that introduce excess carriers and shift the Fermi level out of the topological regime. Controlling early-stage growth and defect formation is therefore essential for suppressing bulk transport and enhancing surface-state conduction. Here we investigate ultrathin Bi2Te3 films grown by pulsed laser deposition on substrates spanning van der Waals, lattice-matched, and amorphous regimes to determine how substrate-dependent nucleation pathways influence defect formation and electronic transport. Phase-pure, c-axis-oriented Bi2Te3 forms on all substrates, but the growth morphology varies strongly. Layered growth with well-defined quintuple-layer terraces is governed primarily by substrate roughness rather than lattice match: atomically smooth mica and step-terraced SrTiO3 yield continuous terraces, whereas rougher BaF2 and amorphous Si3N4 produce island-structured films. Between the two smooth substrates, the higher surface energy of SrTiO3 enhances adatom adsorption and nucleation density, promoting rapid vertical growth and early Te depletion. Transport measurements reveal n-type conduction with carrier densities of 10e19-10e20 cm-3. The highest carrier density occurs for films on SrTiO3, consistent with defect formation during high-density nucleation, whereas mobility correlates with structural coherence and terrace formation. Weak anti-localization signatures confirm phase-coherent transport in films on mica and SrTiO3. These results show that substrate roughness and nucleation density provide key levers for controlling defect formation and strengthening topological surface transport in Bi2Te3 thin films.

Substrate-controlled nucleation and growth kinetics in ultrathin Bi$_2$Te$_3$ films

Abstract

Metal chalcogenides are promising layered topological materials, yet their electronic performance is often limited by parasitic bulk conduction arising from defects that introduce excess carriers and shift the Fermi level out of the topological regime. Controlling early-stage growth and defect formation is therefore essential for suppressing bulk transport and enhancing surface-state conduction. Here we investigate ultrathin Bi2Te3 films grown by pulsed laser deposition on substrates spanning van der Waals, lattice-matched, and amorphous regimes to determine how substrate-dependent nucleation pathways influence defect formation and electronic transport. Phase-pure, c-axis-oriented Bi2Te3 forms on all substrates, but the growth morphology varies strongly. Layered growth with well-defined quintuple-layer terraces is governed primarily by substrate roughness rather than lattice match: atomically smooth mica and step-terraced SrTiO3 yield continuous terraces, whereas rougher BaF2 and amorphous Si3N4 produce island-structured films. Between the two smooth substrates, the higher surface energy of SrTiO3 enhances adatom adsorption and nucleation density, promoting rapid vertical growth and early Te depletion. Transport measurements reveal n-type conduction with carrier densities of 10e19-10e20 cm-3. The highest carrier density occurs for films on SrTiO3, consistent with defect formation during high-density nucleation, whereas mobility correlates with structural coherence and terrace formation. Weak anti-localization signatures confirm phase-coherent transport in films on mica and SrTiO3. These results show that substrate roughness and nucleation density provide key levers for controlling defect formation and strengthening topological surface transport in Bi2Te3 thin films.
Paper Structure (11 sections, 7 equations, 6 figures, 2 tables)

This paper contains 11 sections, 7 equations, 6 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Method
  3. Results
  4. Substrate-dependent growth and morphology of Bi2Te3
  5. Phase formation and stoichiometry.
  6. Crystallographic orientation and growth rate.
  7. Surface morphology.
  8. Role of substrate surface properties.
  9. Nucleation
  10. Electronic transport
  11. Conclusion

Figures (6)

  • Figure 1: Raman spectra of deposited films. Dashed lines indicate characteristic phonon modes of Bi2Te3.
  • Figure 2: a) XRD wide-scans of the 50 pulse samples, plotted in logarithmic scale. Substrate peaks marked with asterisks. The dashed lines mark $\left( 003n \right)$ peaks of Bi2Te3. b) XRR profiles of the samples. The profiles were used to estimate sample's thickness. The film grown on Si3N4 displays additional, high-frequent reflectivity curves from the Si3N4/Si interface
  • Figure 3: Left panel: 500$\times$500 nm AFM scans of 50 pulse samples. Right panel: height profiles extracted from AFM scans.
  • Figure 4: 500$\times$500 nm AFM scans of 1-pulse films grown on mica (a) and SrTiO3 (b) substrates. The background level is scaled to highlight the bright-colored nucleation sites at the surface.
  • Figure 5: a) Comparison of normalized nucleation density between different growth techniques for van der Waals epitaxy and quasi van der Waals epitaxy. The ranges for MBE, MOVPE, and CVE are taken from Mortelmans2020, while the PLD values are calculated based on the 1-pulse samples. b) Calculated coverage $\theta$ values for all samples discussed.
  • ...and 1 more figures