Trion transfer in mixed-dimensional heterostructures

Abstract

Charged excitons, or trions, offering unique spin and charge degrees of freedom, have primarily been investigated in doped systems where charges are long considered indispensable. Here, we present an alternative route to ultra-efficient trion emission from an intrinsic, defect-free semiconductor via a transfer mechanism. By exciting trions in two-dimensional tungsten-diselenide donors and transferring them into one-dimensional carbon-nanotube acceptors in mixed-dimensional heterostructures, we circumvent the usual carrier requirement, overcoming intrinsic Auger-quenching limitations. Benefitting from a reservoir effect induced by dimensional heterogeneity, this process achieves trion emission efficiencies increased by over 100-fold compared to conventional doping-based approaches, and remains robust across diverse doping conditions. Our findings extend the exciton transfer paradigm to the three-body quasiparticles, offering a new platform for advancing excitonic physics and trion-based optoelectronic/spintronic applications.

Figures (5)

• Figure 1: Universal trion emission in CNT/WSe$_2$ heterostructures. a A schematic of a suspended CNT/WSe$_2$ heterostructure. b A typical optical image of a CNT/2L WSe$_2$ sample. The CNT is indicated by the broken red line. The scale bar represents 3 $\mu$m. c The PLE map of the pristine (13,2) CNT. d The PLE map of the (13,2) CNT/2L WSe$_2$ heterostructure, where the tube differs from that in (c). e The PL spectra of the (13,2) CNT/2L WSe$_2$ heterostructure in (d) at excitation under $E_{22}$ (blue, 1.420 eV) and $T_{\mathrm{WSe_2}}$/$X_{\mathrm{WSe_2}}$ (red, 1.634 eV), respectively. f Normalized PLE spectra of integrated $E_{11}$ emission (blue) and $T_{\mathrm{CNT}}$ emission (red) in (d). The PL emission is integrated over a 10 meV-wide spectral window centered at the $E_{11}$ or $T_{\mathrm{CNT}}$ energies. g Chirality-dependent PL spectra at $T_{\mathrm{WSe_2}}$/$X_{\mathrm{WSe_2}}$ excitation. We define a heterostructure nomenclature where (9,7) CNT/3L WSe$_2$ is represented by (9,7)/3L. h Energy separation as a function of 1/Diameter from different samples. Green, orange, red, and purple symbols represent the heterostructures with 1L, 2L, 3L, and 4L WSe$_2$, respectively. The excitation power is 10 $\mu$W. The black line is a fit.
• Figure 2: PL excitation images for revealing trion transfer process. a--c Normalized PL intensity maps from the (9,7) CNT/3L WSe$_2$ sample whose PL spectrum is shown in Fig. \ref{['Fig1']}g. The PL images are constructed by integrating PL emission over a 30 meV-wide spectral window centered at $E_{11}$ energy (a, b) and $T_{\mathrm{CNT}}$ energy (c). The excitation is at $E_{22}$ (1.459 eV, a), $X_{\mathrm{WSe_2}}$ (1.653 eV, b), and $T_{\mathrm{WSe_2}}$ (1.653 eV, c). The excitation power is 10 $\mu$W. d The corresponding reflectivity image. The excitation is at $E_{22}$ (1.459 eV). e--g Energy level diagrams showing the three processes occurring in a--c, respectively. GS indicates the ground state. h Line profiles taken from a--c, as indicated by the white broken lines. The grey, blue, and red symbol-line plots are the experimental results from a, b, and c. The blue and red lines are corresponding fits. The scale bars in a--d represent 1 $\mu$m. The CNT is indicated by the broken green lines in a--d.
• Figure 3: Comparison between free-carrier induced trions and transfer-induced trions. a PL spectra of the (10,5) CNT/3L WSe$_2$ sample at powers of 2, 15, and 45 $\mu$W from left to right. The excitation is at $X_{\mathrm{WSe_2}}$/$T_{\mathrm{WSe_2}}$ energy. b Integrated PL intensity as a function of the laser power for $E_{11}$ and $T_{\mathrm{CNT}}$, respectively. The PL emission is integrated over a 50 meV-wide spectral window centered at the $E_{11}$ or $T_{\mathrm{CNT}}$ energies. c Schematic image of the suspended gated-CNT structure. d PL spectra of the (10,5) gated CNT without (blue) and with $V_g = -0.8$ V (red). The excitation power is 300 $\mu$W and the excitation energy is $E_{22}$. e Schematic image of the CNT/CuPc hybrid. f PL spectra of the pristine (10,5) CNT (blue) and the (10,5) CNT/26-nm-thick CuPc hybrid (red). The excitation powers are 100 $\mu$W for the pristine CNT, 300 $\mu$W for the CNT/CuPc hybrid, and the excitation energy is $E_{22}$. g Schematic image of the CNT/WSe$_2$ heterostructure. h PL spectra of the (10,5) CNT before (blue) and after the formation of the heterostructure with a 1L WSe$_2$ flake (red). The excitation power is 10 $\mu$W and the excitation energy is $E_{22}$ for the pristine tube and $X_{\mathrm{WSe_2}}$/$T_{\mathrm{WSe_2}}$ for the heterostructure. i$T_{\mathrm{CNT}}$ efficiency and $E_{11}$ efficiency from the three different structures. Green dots are from nine different CNT/WSe$_2$ heterostructures with an excitation power of 10 $\mu$W at $X_{\mathrm{WSe_2}}$/$T_{\mathrm{WSe_2}}$ energy. Brown symbol-line plots are from four suspended gated-CNT samples obtained by sweeping $V_g$ from 0 V to the positive side (light-brown two measured at 100 $\mu$W and dark-brown two at 300 $\mu$W). The excitation energy is $E_{22}$. Blue dots are from different CNT/CuPc samples. Light, medium, and dark blue indicate CuPc deposition thicknesses of 7, 16, and 26 nm, respectively. The excitation power is 300 $\mu$W and the excitation energy is $E_{22}$.
• Figure 4: Trion transfer in gated CNT/WSe$_2$ heterostructures. a A schematic of a suspended gated CNT/WSe$_2$ heterostructure. b An optical image of the (10,5) CNT/3L WSe$_2$ device. The scale bar represents 10 $\mu$m. c PL spectra as a function of gate voltage. The excitation power is 2 $\mu$W and the excitation energy is $X_{\mathrm{WSe_2}}$/$T_{\mathrm{WSe_2}}$ at 1.642 eV. d PL peak area for $T_{\mathrm{CNT}}$ (red) and $E_{11}$ (blue) in c as a function of gate voltage. The peak area is obtained by Lorentzian fitting at each $V_g$.
• Figure 5: Trion transfer in CNT/doped WSe$_2$ heterostructures. a A schematic of a suspended CNT/WSe$_2$ heterostructure. b PL spectra of the (11,3) CNT before (orange) and after the formation of the heterostructure with a 1L doped WSe$_2$ flake (green). The excitation power is 10 $\mu$W and the excitation energy is $E_{22}$. c Quenching factor $Q$ for three structures. Error bars are the standard error of the mean. d The PLE map of the (11,3)/1L doped WSe$_2$ heterostructure. The excitation power is 10 $\mu$W. e The PL spectra of the (11,3)/1L doped WSe$_2$ heterostructure at $E_{22}$ (1.540 eV, 40 $\mu$W, blue) and $X_{\mathrm{WSe_2}}$/$T_{\mathrm{WSe_2}}$ (1.634 eV, 9 $\mu$W, red), respectively. f Integrated PL intensity of $T_{\mathrm{CNT}}$ as a function of the laser power at $E_{22}$ (blue) and $X_{\mathrm{WSe_2}}$/$T_{\mathrm{WSe_2}}$ (red) from the (11,3)/1L doped WSe$_2$ heterostructure. The $T_{\mathrm{CNT}}$ emission is integrated over a 50 meV-wide spectral window centered at the peak energy.