Differential etching of chalcogenides for infrared photonic waveguide structures

Chemical etching rates for two different chalcogenide glass compositions (As2S3 and As24S38Se38) were studied using sodium hydroxide based etchant solutions. Etching was performed using a variation of standard photolithographic masking and wet-etching techniques. Variations in etch rate with NaOH concentration and glass composition were observed. The depth of etch was characterized using an optical profilometer. Etch rate differences as large as three orders of magnitude between these two glasses were observed at low NaOH concentration (0.053 M). We present a single variable etch rate curve of etch depth per time (nm/s) versus NaOH overall solution concentration (in M) for these two different chalcogenide glasses (As2S3 and As24S38Se38). This technology shows promise for fabricating highly asymmetrical photonic structures and has potential applications in fabricating novel photonic bandgap (PBG) structures that will function in the long-wave infrared (LWIR) regime.