A highly ordered and damage-free Ge inverted pyramid array structure for broadband antireflection in the mid-infrared

Abstract

With increasing demand for infrared (IR) photonics and optoelectronics, germanium (Ge) has recently regained attention due to its outstanding optical properties in the near infrared (NIR) and mid infrared (MIR) ranges. Here we present a highly ordered and damage-free microscale Ge inverted pyramid array fabricated by HF-free metal-assisted chemical etching. The surface quality of the inverted pyramid is systematically investigated, demonstrating the good preservation of single crystallinity with a minimized amount of defects at etched surfaces. In addition, an outstanding antireflection performance of the Ge inverted pyramid is realized in a broadband MIR wavelength range up to 15 μm. The damage-free Ge inverted pyramid array, together with its strong antireflection capability in the MIR range, provides an outstanding platform for future MIR photonic and optoelectronic applications.