The improvement of the luminous efficacy of LED chips by a pre-treatment process before annealing process on ITO films deposited by magnetron sputtering

Indium Tin Oxide (ITO) films deposited by magnetron sputtering are widely used as transparent conducting layers for InGaN based light-emitting diodes (LEDs). Compared to ITO films deposited by electron beam evaporation, tthe ITO films deposited by magnetron sputtering typically have higher optical transmittance and greater electrical conductivities, which can result in higher efficiency for LEDs. However, the surface of LEDs could be damaged due to bombarding of highly energetic ITO particles during magnetron sputtering, which can cause a higher ITO/p-GaN contact resistance. In addition, the n-electrode/n-GaN contact can also be affected by different ITO treatment processes. Therefore, there is still a need to optimize the ITO deposition and treatment processes to minimize the working voltage In this work, the relationship of the ohmic contacts of ITO/p-GaN and n-electrode/n-GaN with ITO deposition and treatment process have been investigated in details, by Circle Transport Line method (CTLM) and Transport Line method (TLM). It is found that a special pre-treatment process for magnetron sputtering ITO films can reduce the working voltage by 0.1V compared to the conventional processes by further lowering the n-electrode/n-GaN contact resistivity. This work can help further improve the luminous efficacy of white LEDs especially in the high power working conditions.