Abstract: nterest in gallium chalcogenides, i.e., gallium sulfide (GaS) and gallium selenide (GaSe), is growing rapidly due to its layered structure compatible with the fabrication of very thin layers by mechanical exfoliation and its wide band gap desirable for the design and fabrication of visible-UV optoelectronic devices. It is well known that the properties of these materials depend on their thickness; therefore, a facile and fast method is needed to infer the thickness of layered GaS and GaSe. Here, we report and validate a colorimetric method based on optical imaging for the quick and reliable quantitative determination of the thickness of exfoliated GaS and GaSe layers although it can be extended to other layered systems. For the validation of the method, the colorimetric computational estimate of the thickness is compared to the value obtained by atomic force microscopy. Further simulation of GaS and GaSe layers on different substrates of interest for different technological applications is provided as a quick guide for the rapid and reliable thickness determination of GaS and GaSe layers on various substrates.

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