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