Local defects in two-dimensional gallium sulfide, as single-photon emitters: first-principle evaluation.

The single photon emitters (SPE), especially those in the near-infrared (NIR) range, are the critical means for emerging quantum communication technology. In this work, the local defects in 2D GaS are evaluated in terms of the single photon emission. Based on educated guess, twelve doping-substitution defects in GaS were selected for consideration. The defects were Y_X, where X = Ga or S, and Y = C, Si, Ge, N, P, As (X stands for a substituted element and Y for a dopant). To evaluate stability of the defects, their formation energy and phonon spectra were calculated. For the stable defected structures, the linear response GW and the Bethe-Salpeter equation (BSE) methods were used to obtain their electronic structure and optical excitation spectra. The calculation results indicate that GaS with the C_S-, N_S-, and P_S-defects have intense sharp excitation peaks in NIR region. The analysis of the contributions of the GW eigen states to the corresponding BSE eigen states concludes that these excitations can result in the emission with dominating narrow zero-phonon lines in the NIR region. I thus propose here the C_S-, N_S-, and P_S-defects in the two-dimensional GaS as promising candidates for the SPE in near-infrared emission region.