Effect of the Thickness of 2D GaSe Crystals on Their Photoelectric Performance

Layered semiconductor crystals of gallium selenide (GaSe) have found various potential applications as nonlinear optical materials for terahertz or high-order harmonic generation. Today, many research efforts are focused on the fabrication of two-dimensional GaSe flakes for optoelectronic applications due to their low dark current values, high photosensitivity, and flexibility. In this study, we demonstrate the influence of thickness-related interference on the spectral dependence of photoconductivity of metal/p-GaSe/metal planar photodetector structures. The flakes were micromechanically exfoliated from bulk GaSe crystal obtained by simple melt of Ga and Se particles in an evacuated ampoule. It is shown that the curves of spectral responsivity of photodetectors for the 230-nm- thick GaSe flakes exhibit several extrema caused by the interference phenomenon on the thick GaSe layer. The detailed study of the Raman spectra for different thicknesses of GaSe flakes has proven the existence of the interference effect. This means that, in the case of photodetectors based on rather thick 2D GaSe nanocrystals, the thickness of the flake should be taken into account when estimating the photosensitivity, since interference effects may occur.