CO2

CO2 (carbon dioxide) in solid or crystalline form is classified here as a semiconductor material, though this designation is unconventional—solid CO2 (dry ice) is typically considered a molecular solid rather than a traditional semiconductor. This entry likely refers to engineered CO2-based compounds or research-phase materials being explored for optoelectronic or sensing applications. CO2-derived semiconductors remain largely experimental, with interest focused on photocatalysis, gas sensing, and carbon-capture-enabled device integration where the material's carbon and oxygen chemistry can be leveraged for novel electronic or photonic function.