Optical Memory in a MoSe2/Clinochlore Device

Abstract

Two-dimensional heterostructures have been crucial in advancing optoelectronic devices utilizing van der Waals materials. Semiconducting transition-metal dichalcogenide monolayers, known for their unique optical properties, offer extensive possibilities for light-emitting devices. Recently, a memory-driven optical device, termed a Mem-emitter, was proposed by using these monolayers atop dielectric substrates. The successful realization of such devices heavily depends on the selection of the optimal substrate. Here, we report a pronounced memory effect in a MoSe₂/clinochlore device, evidenced by an electric hysteresis in the intensity and energy of MoSe₂ monolayer emissions. This demonstrates both population- and transition-rate-driven Mem-emitter abilities. Our theoretical approach correlates these memory effects with internal state variables of the substrate, emphasizing that a clinochlore-layered structure is crucial for a robust and rich memory response. This work introduces a novel two-dimensional device with promising applications in memory functionalities, highlighting the importance of alternate insulators in the fabrication of van der Waals heterostructures.

Keywords: 2D natural materials; MoSe2/clinochlore; charge dynamics; optical memory effect; phyllosilicates.

Figure 1

Clinochlore-based MoSe₂ device. (a) Clinochlore SEM image and EDS chemical maps of its constituent elements in addition to Fe impurity. (b,c) Schematic view; (b) and optical microscopy image (c) of our t-hBN/1L-MoSe₂/clinochlore/Au-electrode device. (d) PL spectra of 1L-MoSe₂ acquired in the clinochlore sample at different gate voltages ranging from −10 to 10 V. X⁰ and X^– emissions are denoted in the PL spectrum at 0 V. (e) Time-resolved PL emission transients recorded for the integrated intensity of excitons and trions in the 1L-MoSe₂ under the application of 5 s rectangular voltage pulses with a 5 V amplitude. Each spectrum was taken over 0.03 s.

Figure 2

Hysteresis effect in the PL emission of the clinochlore device under external voltage sweeps of 18 min period. (a,b) Integrated intensity (in shades of black) and energy shift (in shades of blue) of X⁰ (a) and X^– (b) emissions as a function of the gate voltage, which was subsequently swept 5 times in cycles ranging from −10 to 10 V. Each voltage cycle is presented in a different shade of black or blue for the intensity or energy data, respectively. (c,d) Integrated intensity (in shades of brown) and energy shift (in shades of purple) of X⁰ (c) and X^– (d) emissions, after defect passivation, are shown as a function of the gate voltage. These measurements were detected at σ⁺ and σ^– circular polarizations. The voltage cycle for each detection is presented in a different shade of brown or purple for the intensity or energy data, respectively. For all graphs, green arrows indicate where the measurement initiates and orange arrows denote the direction of the voltage sweep. The energy shift ΔE is relative to the first emission energy measured at 0 V.

Figure 3

Hysteresis effect in the PL emission of the clinochlore device at different conditions of voltage sweep rate, voltage sweep amplitude, and excitation power. (a–d) Integrated intensity (a,c) and energy shift (b,d) of X⁰ (a,b) and X^– (c,d) emissions for different overall times of the gate voltage cycle before defect passivation. (e-h) Integrated intensity (e,g) and energy shift (f,h) of X⁰ (e,f) and X^– (g,h) emissions for different values of V_max. (i–l) Normalized integrated intensity (i,k) and energy shift (j,l) of X⁰ (i,j) and X^– (k,l) emissions for different excitation powers. For all graphs, green arrows indicate where the measurement initiates and orange arrows denote the direction of the voltage sweep. The energy shift ΔE is relative to the first emission energy measured at 0 V. The voltage sweeps consist of a single cycle as follows: 0 V → V_max → – V_max → 0 V. The acquisition time for each PL spectrum was maintained at 0.2 s, with the overall time varied by adjusting the delay time between each spectrum.

Figure 4

Electric hysteresis modeling of polarization and carrier population fluctuations in a 1L-TMD-based device. (a) Representation of a gated device composed by a 1L-TMD on a dielectric substrate. Polarization (δP) and charge carrier (δN) fluctuations occur in the substrate under an external electric field, impacting the optical properties of the TMD. Local field (F_TMD) hysteresis considering polarization leakage channels and (b) increasing voltage amplitudes and (c) increasing voltage sweep periods. (d) Charge carrier fluctuation (δN) hysteresis considering five trapping and release channels. (e) Charge carrier fluctuation hysteresis for different voltage amplitudes. The arrows in (b–e) denote the direction of the voltage sweep.