Fig. 3: Topological p–n junctions.
From: Topological electronics
a Theoretical schematic illustrating the surface of a 3D TI p–n junction with incident, reflected, and transmitted electrons shown with their corresponding spin polarizations. Image taken from ref. 47. b Calculated quantum transport results showing the spin-to-charge ratio, β, at the source and drain contacts as a function of the gate voltage Vp applied to the p-type part of the junction at a fixed gate voltage on the n-type part of the junction. We observe a large enhancement in β at the source contact in a topological p–n junction due to the spin-momentum locking of the surface states of a 3D TI. Image taken from ref. 47. The inset shows that the transmitted current is only non-zero when the incident electrons are normal to the surface of the junction. c A high-angular annular dark field image of two MBE-grown binary 3D TIs, 15 QL of Sb2Te3, and 6 QL of Bi2Te3 in direct contact with one another. Image taken from ref. 49. d Experimentally measured Hall resistance of various heterostructures comprised of 6 QL of Bi2Te3 with differing Sb2Te3 thicknesses. Image taken from ref. 49. e Schematic of a horizontal p–n junction with a Si back gate to tune the location of the chemical potential. On one half of the surface, an electronegative molecule is deposited on the surface to draw out the unintentional bulk carriers allowing greater manipulation of the chemical potential with electrostatic gating48. f Quantum transport measurements of the longitudinal resistance of topological p–n junction as a function of back-gate voltage VG showing a large jump in resistance when there are p–n junctions formed on both the top and bottom surfaces. The jump in resistance is attributed to the spin-momentum locking of the surface states in a 3D TI48.
