Enhanced Light Emission from the Ridge of Two-dimensional InSe Flakes

TL;DR

This paper demonstrates enhanced light absorption and tunable photoluminescence in 2D InSe flakes with a ridge geometry, revealing new opportunities for optoelectronic device engineering.

Contribution

It introduces a novel ridge structure in 2D InSe flakes that significantly boosts absorption and enables defect PL tuning via electric fields.

Findings

Enhanced broad-range absorption at the ridge

Discovery of defect-related PL peaks up to 60 times stronger

PL tunability through external electric fields

Abstract

InSe, a newly rediscovered two-dimensional (2D) semiconductor, possesses superior electrical and optical properties as a direct bandgap semiconductor with high mobility from bulk to atomically thin layers, drastically different from transition metal dichalcogenides (TMDCs) in which the direct bandgap only exists at the single layer limit. However, absorption in InSe is mostly dominated by an out-of-plane dipole contribution which results in the limited absorption of normally incident light which can only excite the in-plane dipole at resonance. To address this challenge, we have explored a unique geometric ridge state of the 2D flake without compromising the sample quality. We observed the enhanced absorption at the ridge over a broad range of excitation frequencies from photocurrent and photoluminescence (PL) measurements. In addition, we have discovered new PL peaks at low temperature due to defect states on the ridge, which can be as much as ~ 60 times stronger than the intrinsic PL peak of InSe. Interestingly, the PL of the defects is highly tunable through an external electrical field, which can be attributed to the Stark effect of the localized defects. InSe ridges thus provide new avenues for manipulating light-matter interaction and defect-engineering which are vitally crucial for novel optoelectronic devices based on 2D semiconductors.