Improvement of Ti/Al ohmic contacts on N-face n-type GaN by using O2 plasma treatment

Abstract

The effect of O2 plasma treatment on the electrical properties of Ti/Al (20/200 nm) contact to N (Nitrogen)-face n-GaN of vertical light-emitting diodes (VLEDs) has been investigated by varying the O2 plasma treatment power and time. Both photolithography and chemical lift-off methods are used to prepare the circular transfer length method (CTLM) patterns on the N-face n-GaN for measuring the contact and sheet resistances. Both total and sheet resistances are decreased with the increase in plasma treatment power up to 250 W. It is found that the Ti/Al-based Schottky contact layer transforms to ohmic characteristics after plasma treatment. GaN chemical bonds on the n-GaN surface are broken due to O2 plasma treatment; thus, resulting in formed GaO bonds which are interactively understood by using X-ray photoelectron spectroscopy characteristics. After plasma treatment, the forward voltage of VLED is not only reduced owing to decrease in total resistance but also both the light intensity distribution and the light-output-power are improved because of increase in current spreading through the contact layer.