Theoretical Insights into Band Gap Tuning Through Cu Doping and Ga Vacancy in GaSe Monolayer: A First-Principles Perspective

Gallium selenide (GaSe) has become increasingly popular in the field of optoelectronics due to its suitable band gap. The layered structure of bulk crystal GaSe makes it easy to create a monolayer of GaSe. However, this also results in an increase in the band gap. In this paper, we used the full-potential periodic density functional theory (DFT) method to examine the electronic structure of both pure and Cu-doped GaSe. We modeled Ga_1-xCu_xSe with x = 0.02, 0.03, 0.056, and 0.125 with and without Ga vacancy. We compared the structure, electronic properties, and magnetic properties of the pure bulk and monolayer with those of the Cu-doped samples. The density of state graphs clearly demonstrate that Ga-defected and Cu-doped GaSe have p-type characteristics. The presence of a Ga vacancy causes the GaSe monolayer to become half-metallic, which has potential applications in spintronics. When the Cu concentration reaches approximately 3%, there is a 20% reduction in the band gap. Both the Ga vacancy and Cu doping create deep defect levels that lead to carrier recombination. The position of these levels is highly dependent on the concentration of Cu. Increasing the Cu concentration from% 1 to 2.78% results in a decrease in recombination.