Enhancement of thermopower in GaN by ion irradiation and possible mechanisms

摘要

A detailed analysis of defect assisted transport properties of GaN after irradiation is carried out. Unintentionally doped GaN samples were irradiated by a 100MeV oxygen ion beam and a 200 MeV silver ion beam at various fluences between 1 × 10~(10) ions/cm~2 and 5 × 10~(11) ions/cm~2. Thermopower and Hall effect measurements were done on pristine and irradiated GaN samples at variable temperatures. An increase in the thermopower with temperature as well as on irradiation (with respect to pristine GaN) was observed. Electrical conductivity and Hall mobility decreased on irradiation, suggesting scattering of charge carriers due to the formation of defects. A qualitative study of activation energy due to thermopower and conductivity is done by the scattering mechanism using different theoretical models to determine the transport path of the carriers. The observed increase in thermopower of GaN after irradiation suggests a probable hopping mechanism due to the presence of energy levels in the bandgap.