Effect of annealing temperature on electrical and structural properties of transparent indium tin oxide electrode to n-type GaN

The effects of thermal annealing temperature on electrical, structural and surface morphology characteristics of transparent indium tin oxide (ITO) electrode to n-type gallium nitride (GaN) have been investigated. The Schottky barrier height of as-deposited ITO/n-GaN is found to be 0.61 eV (I-V) 0.64 eV (C-V). The extracted barrier heights of ITO/n-GaN annealed contacts are 0.67 eV (I-V) 0.71 eV (C-V) at 200 deg. C, 0.70 eV (I-V) 0.75 eV (C-V) at 300 deg. C, and 0.72 eV (I-V) 0.78 eV (C-V) at 400 deg. C, respectively. Annealing at 500 deg. C for 1 min in the nitrogen ambient, increases the barrier height and the corresponding values are 0.74 eV (I-V) 0.83 eV (C-V). The Norde method was also used to extract the barrier height of ITO/n-GaN Schottky contacts. From the above observations, it is clear that the electrical properties of annealed ITO contacts are improved compared to the as-deposited films. Based on the Auger electron spectroscopy and X-ray diffraction results, the formation of gallide phases at the ITO/n-GaN interface could be the reason for the improvement of electrical properties upon annealing at various temperatures. The measured transmittance of ITO films between 380 nm and 450 nm is above 90% for a sample annealed at 500 deg. C. Atomic force microscopy results showed that the surface morphology of a contact annealed at 500 deg. C is fairly smooth with a RMS roughness of 2.37 nm