Changes in activation energies of donors and carrier concentration in Si-doped n-type GaN due to (NH₄)₂S_x treatment

In this study, changes in the activation energy of donors and carrier concentration in n-type GaN (n-GaN) samples, due to (NH₄) ₂S_x treatment, were investigated. We find that the activation energy of Si in the n-GaN samples without or with (NH ₄)₂S_x treatment was determined to be 21 meV and a donor level was also present in (NH₄)₂S _x-treated n-GaN near the surface with an activation energy of 59 meV which is associated with sulfur donors substituting for nitrogen. By rearranging the well-known equations for the conductivity and mobility in two-layer systems, we find that the electron concentration within the thin sulfur-passivated layer in n-GaN near the surface at room temperature increased from its original value 6.9 × 10¹⁷ cm^-3 to 9.7 × 10¹⁹ cm^-3, resulting in the occurrence of the Burstein-Moss shift for optical band-gap observation.