Femtosecond carrier dynamics and saturable absorption in few layer germanium sulfide

Abstract

The development of materials with large nonlinear response and ultra-fast response is the goal of the field of nonlinear optics. Here, we report the large nonlinear response (Imχ(3)=-8.54 × 10−11 esu; FOM = 4.03 × 10−11 esu cm) and femtosecond timescale carrier recovery time in few-layer germanium sulfide (GeS) with high crystal quality. The GeS exhibited a broad-band nonlinear optical absorption (400−800 nm) and large nonlinear optical response which is wavelength and excitation intensity dependent. The saturable absorption response with short wavelength excitation is stronger than that of the other two long excitation wavelengths. The carrier recovery times of the few layer GeS were determined to be hundreds of femtoseconds. Our results indicated that the few layer GeS is a promising candidate for the nanophotonic applications such as saturable absorber and optical diode.