GaN surface sputter damage investigated using deep level transient spectroscopy

For nominally identical GaN Schottky diodes prepared by resistive thermal evaporation and plasma sputter deposition, diodes prepared by sputter deposition were found to exhibit a clear increase in the reverse leakage current, which is about two orders of magnitude higher than diodes prepared using thermal evaporation. Defects in n-type GaN Schottky diodes fabricated by plasma sputtering of gold were investigated using deep level transient spectroscopy and compared with those in similar structures fabricated by resistive thermal evaporation. From deep level transient spectroscopy two defects were identified in the sputtered diode with the activation energies for charge carrier emission of 0.26 +/- 0.01eV relative to the conduction band edge and 0.62 +/- 0.04eV relative to the valence band edge. Defect concentration profiles of sputtered diodes show the defect density reduces from the surface to deeper in the structure, indicating that they are introduced through sputtering. Since the sputter deposition technique is widely used in device fabrication, attention should be paid to the adverse effects due to the additional defect introduction such as the charge trapping in HEMTs and the non-radiative recombination in LEDs.