Preface to Special Issues on Recent Progress on Optical Functional Semiconductors Based on Group 14 Elements

This paper describes the overview of special issues on recent progress on optical functional semiconductors based on group 14 elements.Currently, silicon (Si) is mainly used in solar cells and optical sensors that are indispensable in the IOT society.In order to advance the performance of these devices, it is essential to improve the materials that compose the devices.New compounds of group 14 elements and metals are attracting attention as new optical functional materials.The recent research on the compounds was summarized.