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Intrinsic Electric Field Driven High Sensitive Photodetection in Alloy TMDC MoSSe

Chumki Nayak, Suvadip Masanta, Shubhadip Moulick, Manotosh Pramanik, Atanu Kabiraj, Satchidananda Rath, Sukanya Ghosh, Atindra Nath Pal, Bipul Pal, Achintya Singha

Abstract

Alloying offers an effective way to improve the functionality of transition metal dichalcogenides (TMDCs) in both fundamental research and optoelectronic applications, as it allows for engineering their electronic and optical properties. This study investigates the optoelectronic properties of CVD-synthesized alloy MoSSe, which exhibits an inherent out-of-plane dipole moment, arising from asymmetry in S and Se atoms on either side of the Mo layer, as confirmed by piezoelectric force microscopy, polarization-resolved second harmonic generation studies and theoretical first-principles calculations. Time-resolved photoluminescence measurements reveal an extended exciton radiative recombination lifetime in MoSSe, attributed to electron-hole wavefunction separation by the dipole moment, which improves photodetection by facilitating enhanced electron-hole separation before recombination. The device demonstrates significant responsivity over broad spectral range. By employing the photogating effect, the device response can be switched from slow to fast modes. These findings are further supported by illumination intensity-dependent photoluminescence and Raman measurements, underscoring the potential of polar TMDCs in future optoelectronic devices.

Intrinsic Electric Field Driven High Sensitive Photodetection in Alloy TMDC MoSSe

Abstract

Alloying offers an effective way to improve the functionality of transition metal dichalcogenides (TMDCs) in both fundamental research and optoelectronic applications, as it allows for engineering their electronic and optical properties. This study investigates the optoelectronic properties of CVD-synthesized alloy MoSSe, which exhibits an inherent out-of-plane dipole moment, arising from asymmetry in S and Se atoms on either side of the Mo layer, as confirmed by piezoelectric force microscopy, polarization-resolved second harmonic generation studies and theoretical first-principles calculations. Time-resolved photoluminescence measurements reveal an extended exciton radiative recombination lifetime in MoSSe, attributed to electron-hole wavefunction separation by the dipole moment, which improves photodetection by facilitating enhanced electron-hole separation before recombination. The device demonstrates significant responsivity over broad spectral range. By employing the photogating effect, the device response can be switched from slow to fast modes. These findings are further supported by illumination intensity-dependent photoluminescence and Raman measurements, underscoring the potential of polar TMDCs in future optoelectronic devices.
Paper Structure (3 sections, 9 equations, 18 figures, 1 table)

This paper contains 3 sections, 9 equations, 18 figures, 1 table.

Table of Contents

  1. Introduction
  2. Results and Discussion
  3. Conclusion

Figures (18)

  • Figure 1: Primary characterizations of as-synthesized MoSSe sample. (a) Optical image (top) and top view of the atomic structure (bottom), (b) AFM topography, (c) PL spectrum of MoSSe. (d) Normalized SHG along with corresponding input laser spectra. (e) Polar plots of the polarization-resolved SHG intensity, measured with the detection polarizer maintained parallel to the input laser polarization (0 degree corresponds to S polarized input). (f) PFM amplitude image, (g) and (h) PFM amplitude and phase as a function of DC bias voltage of the monolayer MoSSe, respectively. Inset of Figure (g) shows the appearance of butterfly-shaped feature within the DC voltage range of -0.5 V to +1 V
  • Figure 2: Effect of out-of-plane electric field in TMDCs. Electrostatic potential with respect to the vacuum level is plotted along the direction perpendicular to the plane of (a) monolayer MoSSe, (inset shows the zoom view of the vacuum potential between the two terminal chalcogen layers). The red dashed lines show the vacuum potential between the two terminal chalcogen layers. (b) Partial charge density difference for monolayer MoSSe (top) and MoS$_2$ (bottom), respectively. The red and blue isosurfaces show electron accumulation and depletion, respectively, drawn at = 0.01 e/bohr$^3$. The purple, yellow and green atoms show Mo, S and Se, respectively. (c) Schematic representation of out-of-plane wavefunctions for MoSSe (top) and MoS$_2$ (bottom). The presence of built-in electric field ($E_{int}$) in MoSSe significantly reduces the overlap and separates the center of the out-of-plane wavefunctions of electrons and holes and (d) TRPL spectrum of A exciton of the MoSSe.
  • Figure 3: Photosensing behavior of MoSSe photodetector.(a) Schematic representation of MoSSe FET device structure. Inset shows optical image of as synthesized device. (b) I-V characteristics of the device under dark (black line) an illumination (633 nm) conditions (red line) at V$_{ds} =$ 0 V to 2 V. (c) Responsivity (pink curve), detectivity (blue curve) and (d) external quantum efficiency ($\eta_{ext}$) at V$_{ds} =$ 2 V over the broad spectral region (400-1100 nm). (e) Transfer characteristics of the device under dark (inset) and illumination conditions with V$_{ds} =$1 V and (f) logarithmic representation of photocurrent as a function of power density.
  • Figure 4: Temporal response of MoSSe photodetector. (a) Rise (b) decay response at two illumination intensities (159 and 0.01 $\mu W/\mu m^2$) and (c) semi-logarithmic representation of extracted rise and decay times as a function of illumination intensity.
  • Figure 5: Optical study of MoSSe. (a) PL spectra at different illumination intensities. (b) Calculated carrier density as a function of illumination intensity and (c) schematic representation of photodetection mechanism at low and high power density region.
  • ...and 13 more figures