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Highly reliable Ti-based ohmic contact to N-polar n-type GaN for vertical-geometry light-emitting diodes by using a Ta barrier layer

Jae-Seong Park, Jaecheon Han, and Tae-Yeon Seong

Open Access Open Access

Abstract

The formation of thermally stable and low resistance Ti/Al-based ohmic contacts to N-polar n-GaN for high-power vertical light-emitting diodes (VLEDs) using a Ta diffusion barrier is presented. Before annealing, both Ti/Al/Au and Ti/Ta/Al/Au contacts reveal ohmic behavior with specific contact resistances of 2.4 × 10−4 and 1.2 × 10−4 Ωcm2, respectively. However, unlike the Ti/Al/Au samples that are electrically degraded with increasing annealing time at 250 °C, the Ti/Ta/Al/Au samples remain thermally stable even after annealing for 600 min. LEDs fabricated with the Ti/Ta/Al/Au contacts yield 8.3% higher output power (at 300 mA) than LEDs with the Ti/Al/Au contact. X-ray photoemission spectroscopy results show that the Ta layer serves as an efficient barrier to the indiffusion of oxygen toward the GaN. On the basis of the XPS and electrical results, the annealing dependence of the electrical characteristics of Ti/Al-based contacts are described and discussed.

© 2014 Optical Society of America

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Figures (4)
Fig. 1
Fig. 1 The typical I-V characteristics of Ti(10 nm)/Al(150 nm)/Au(30 nm) and Ti(10 nm)/Ta(10 nm)/Al(150 nm)/Au(30 nm) contacts on N-polar n-GaN as a function of annealing time at 250 °C.

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Fig. 2
Fig. 2 The light output of LEDs fabricated with Ti/Al/Au and Ti/Ta/Al/Au contacts as a function of the forward current.

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Fig. 3
Fig. 3 The Ga 2p core levels taken from the contact/GaN interface regions of (a) Ti/Al/Au and (b) Ti/Ta/Al/Au samples before and after annealing at 250 °C for 600 min.

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Fig. 4
Fig. 4 XPS depth profiles obtained from (a) and (b) Ti/Al/Au, and (c) and (d) Ti/Ta/Al/Au samples on GaN before and after annealing at 250 °C for 600 min, respectively.

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