Identification of a nitrogen vacancy in GaN by scanning probe microscopy

Gallium nitride (GaN) is a material with important applications in optoelectronics, wireless communications, and power electronics. Devices for such applications are normally made with GaN single-crystal wafers. Yet an infinitesimal amount of atomic defects in these single crystals considerably hinders the electronic performance of GaN. One kind of atomic defect in GaN crystals that has been theoretically predicted but eludes direct experimental observation is nitrogen (N) vacancies. Here, we unambiguously identify a single N vacancy on a cleaved m-plane surface of GaN by direct visualization in real space with scanning tunneling microscopy (STM) and atomic force microscopy (AFM). The presence of a vacancy is established by AFM imaging and force spectroscopy measurements. The identification is accomplished by the analysis of STM images, tunneling current spectroscopy, and comparison with the outcomes from the quantification of band bending near the surface, current calculations, and first-principles simulations. All this information provides insight into the electronic perturbation of a single N vacancy at the surface band structure of GaN. Our results provide further understanding of the effect that point defects have on GaN, and will hopefully contribute to tune the behavior of this technologically relevant material in electronic devices.