Mid-infrared Electro-Optic Modulation in Few-layer Black Phosphorus

TL;DR

This paper demonstrates mid-infrared electro-optic modulation in few-layer black phosphorus, revealing its potential as an efficient material for mid-IR modulators due to its layer-dependent properties and quantum confined Franz-Keldysh effect.

Contribution

The study provides the first experimental and theoretical analysis of mid-IR electro-optic modulation in black phosphorus, highlighting its layer-dependent optoelectronic properties.

Findings

Electro-optic modulation achieved in black phosphorus via electrostatic gating.

Quantum confined Franz-Keldysh effect identified as the dominant mechanism.

Strong layer dependence observed in inter-band transitions.

Abstract

Black phosphorus stands out from the family of two-dimensional materials as a semiconductor with a direct, layer-dependent bandgap in energy corresponding to the spectral range from the visible to the mid-infrared (mid-IR), as well as many other attractive optoelectronic attributes. It is, therefore, a very promising material for various optoelectronic applications, particularly in the important mid-IR range. While mid-IR technology has been advancing rapidly, both photodetection and electro-optic modulation in the mid-IR rely on narrow-band compound semiconductors, which are difficult and expensive to integrate with the ubiquitous silicon photonics. For mid-IR photodetection, black phosphorus has been proven to be a viable alternative. Here, we demonstrate electro-optic modulation of mid-IR absorption in few-layer black phosphorus under field applied by an electrostatic gate. Our experimental and theoretical results find that, within the doping range obtainable in our samples, the quantum confined Franz-Keldysh effect is the dominant mechanism of electro-optic modulation. Spectroscopic study on samples with varying thickness reveals strong layer-dependence in the inter-band transition between different sub-bands. Our results show black phosphorus is a very promising material to realizing efficient mid-IR modulators.