Electronic structure and optical properties of native point defects on Si-doped GaN (0001) surface

This paper investigates the formation energy, atomic structure, electronic structure and optical properties of native point defects on n-GaN (0001) surface based on the first-principles of the density functional theory. The results find that the 𝑉𝑁 is not easy to exist and the 𝑉𝐺𝑎, 𝑁𝐺𝑎 or 𝑁𝑖 defects are most likely to appear on the n-type GaN surface. The substitutional defect 𝑁𝐺𝑎 , the interstitial defect 𝑁𝑖 and the single Ga vacancy cause the conduction band to drop and the Fermi level to enter the conduction band in a deeper extent. However, both the valence band and the conduction band move up at the same time with the increase of Ga vacancies, exhibiting p-type characteristics and reducing the n-type conductivity of the surface. The N-vacancy makes the conduction band shift upwards, which reduces the n-type metal conductivity. It is also found that the reduction of photon adsorption on the surface affects the photo-emission of the surface, which is detrimental to the optoelectronic devices with n-GaN and metal contacts. This study shows that 𝑉𝐺𝑎, 𝑁𝐺𝑎 and 𝑁𝑖 native point defects all increase the doping difficulty of n-type GaN films and have a certain value for the fabrication of high-performance optoelectronic devices with n-GaN and metal contacts.