Surface versus Bulk Doping Effects on Second Harmonic Generation from Bi₂Se₃

Abstract

Different effects of the bulk and surface doping on the nonlinear response of topological insulator Bi2Sex are studied by comparing the second harmonic generation (SHG) from bulk single crystalline samples of different Se proportion, and using field‐effect transistor devices based on Bi2Se3 ultrathin films. While the SHG signal decreases with the bulk electron density, it increases when more electrons are injected through the gate. The former effect is attributed to the screening of the space charge region near the surface, and the latter is due to the doping of the surface energy band into the non‐parabolic region as well as the enhancement of the electrostatic field across the space charge region.

Time-Resolved Second-Harmonic Generation in Topological Insulator Bi2Te3: Competing Contributions from Dirac Surface States, Surface Photovoltage, and Band Bending

“…Although eq depicts two contributions to I shg 0 , nonlinear second-harmonic experiments in Bi 2 Se 3 and Bi 2 Te 3 crystals have reported the dominant effect of χ (3) E dc over χ (2) , the later being negligible at lower doping concentration . This can also be qualitatively understood from the relation of nonlinear polarization ( P (2) (2ω)) oscillating at the frequency of 2ω to the displacement ( x (2) (2ω)) and carrier density ( n ) as P false( 2 false) ( 2 ω ) = prefix− n e x false( 2 false) ( 2 ω ) = ϵ 0 χ false( 2 false) ( 2 ω , ω , ω ) E 2 ( ω ) However, the effect of χ (2) can indeed be enhanced by increasing the surface carrier density using a circularly polarized probe beam that acts as a perturbation to the Hamiltonian of the topological surface states given by H = ℏv F ( k x σ y – k y σ x ) + M σ z .…”

“…Although eq 1 depicts two contributions to I shg 0 , nonlinear second-harmonic experiments in Bi 2 Se 3 and Bi 2 Te 3 crystals have reported the dominant effect of χ (3) E dc over χ (2) , the later being negligible at lower doping concentration. 28 This can also be qualitatively understood from the relation of nonlinear polarization (P (2) (2ω)) oscillating at the frequency of 2ω to the displacement (x (2) (2ω)) and carrier density (n) as 29…”

Nanocarbon Photonics and Optoelectronics

“…The contributions (in total amount of 13) of this Special Section are presented by a Feature Article and twelve Original Papers devoted to the problem of electrostatic confinement of massless Dirac particles, non‐linear optical effects in non‐carbon nano‐structured matters such as topological insulator Bi 2 Se x and Ag/Pd nanocomposite films, particularities in field electron emission from micro‐tips decorated by nanoparticles, usage of graphene transfer technique for printing of micro‐ and nanoscale optical components on convex lenses, preparation and optical characterization of carbon nanotubes, different aspects related to graphene and graphenic materials formation, application of graphene materials for THz components, and creation of the color centers in diamond micro‐needle crystallites …”