# Observation of Complete Photonic Bandgap in Low Refractive Index Contrast Inverse Rod-Connected Diamond Structured Chalcogenides

## TL;DR

This study demonstrates the realization of a complete photonic bandgap in inverse rod-connected diamond structures made from low refractive index contrast materials, confirmed through infrared measurements, and introduces a reliable fabrication method.

## Contribution

It reports the first observation of a complete photonic bandgap in low contrast inverse rod-connected diamond structures using a new fabrication process.

## Key findings

- Complete photonic bandgap observed at n~1.9
- Fabrication achieved via low-temperature chemical vapor deposition
- Expands material options for photonic crystal applications

## Abstract

Three-dimensional complete photonic bandgap materials or photonic crystals block light propagation in all directions. The rod-connected diamond structure exhibits the largest photonic bandgap known to date and supports a complete bandgap for the lowest refractive index contrast ratio down to $n_{high}/n_{low} \sim 1.9$. We confirm this threshold by measuring a complete photonic bandgap in the infrared region in Sn--S--O $(n\sim1.9)$ and Ge--Sb--S--O $(n\sim2)$ inverse rod-connected diamond structures. The structures were fabricated using a low-temperature chemical vapor deposition process via a single-inversion technique. This provides a reliable fabrication technique of complete photonic bandgap materials and expands the library of backfilling materials, leading to a wide range of future photonic applications.