Room-Temperature Bound Exciton with Long Lifetime in Monolayer GaN

The synthesis of two-dimensional GaN offers new opportunities for this important commercial semiconductor in optoelectronic devices because the extreme quantum confinement enables additional control of its optical properties. Using first-principles calculations based on many-body Green's function theory, we demonstrate that in monolayer GaN, a large band gap of 5.387 eV is governed by enhanced electron-electron correlations. Strong electron-hole interactions due to weak screening lead to strongly bound excitons with a large binding energy of 1.272 eV. These tightly bound excitons result in strong absorption peaks in the middle ultraviolet region. The dynamical screening between electron-hole pairs is totally different from bare Coulomb interaction. Long quasiparticle (quasielectron, quasihole, and exciton) lifetimes are observed as a result of the many-body interactions. Because of the large binding energies, long exciton lifetimes, and large quantum degeneracy, an excitonic Bose-Einstein condensate can be observed experimentally. Our results indicate the importance of many-body effects in exploring the optical performance of novel GaN optoelectronic nanodevices.