The depth-profiled carrier concentration and scattering mechanism in undoped GaN film grown on sapphire

Temperature-dependent Hall (TDH) measurements and confocal micro-Raman spectroscopy have been used to study the free carrier spatial distribution and scattering mechanism in unintentionally doped GaN film grown on the sapphire substrate with the method of metalorganic chemical vapor deposition. Both the TDH data and the depth-profiled Raman spectra agreed with the existence of a nonuniform spatial distribution of free carriers in the GaN film with a highly conductive layer of ∼1 μm thickness near the GaN sapphire boundary. With the consideration of this parallel conduction channel adjacent to GaN sapphire boundary, detailed analysis of the TDH mobility data suggests that a relatively high concentration of nitrogen vacancies exists and nitrogen vacancy scattering has an important influence on limiting the electron mobility in the bulk film of the present GaN sample.