Modulating Charge Separation with Hexagonal Boron Nitride Mediation in Vertical Van der Waals Heterostructures

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Stacking two-dimensional (2D) materials creates van der Waals heterojunctions with tunable optical and electrical properties.
• Type-II band alignment in heterojunctions can lead to efficient charge separation, but strong interlayer coupling can cause recombination.

Purpose of the Study:

• To demonstrate an alternative approach for enhancing charge separation in type-II van der Waals heterojunctions using thin dielectric spacers.
• To investigate the effect of hexagonal boron nitride (h-BN) as a sieve layer on the optical and electrical properties of InSe/GeS heterojunctions.

Main Methods:

• Fabrication of InSe/GeS heterojunctions with and without an h-BN interlayer.
• Characterization using photoluminescence, ultrafast pump-probe spectroscopy, and Raman spectroscopy.
• Two-terminal photoresponse measurements to evaluate device performance.

Main Results:

• Without h-BN, strong interlayer coupling led to emission quenching due to indirect recombination.
• The presence of h-BN significantly enhanced emission and suppressed interlayer charge recombination.
• The InSe/h-BN/GeS device exhibited a large photocurrent density, high photoresponsivity (9 × 10^2 A W^-1), detectivity (3.4 × 10^14 Jones), and photogain (1.7 × 10^3).
• Photovoltaic parameters, including short-circuit current and open-circuit voltage, showed distinct switching behavior with the h-BN interlayer.

Conclusions:

• Thin dielectric spacers, specifically h-BN, effectively mediate charge separation in 2D heterostructures.
• This approach provides a new degree of freedom for tuning heterojunction properties.
• The findings offer a promising route for developing high-performance optoelectronic devices.