On the origin of annealing-induced degradation in Al-based ohmic contacts to N-Face n-GaN
- On the origin of annealing-induced degradation in Al-based ohmic contacts to N-Face n-GaN
- 장호원; 이종람
- Issue Date
- International Conference on Electronic Materials and Nanotechnology for Green Environment 2010
- Thin-film vertical InGaN/GaN light-emitting diodes (LEDs) fabricated by the laser lift-off (LLO)
process1 have been demonstrated to be very effective for high power operations, which are required to
realize solid-state lighting. In the vertical LEDs, an ohmic contact should be formed on the laserirradiated
N-face n-GaN epilayer. However, achieving reliable ohmic contacts in the laser-irradiated
N-face n-GaN is very challenging due to thermal degradation at a wide range of temperatures (200–
700°C), whereas ohmic contacts to Ga-face GaN can be easily formed using conventional Al-based
metallization after annealing at temperatures over 400°C. Although the changes in surface states, point
defects, and interfacial compounds have been reported to cause the annealinginduced, degradation of
ohmic contacts to the N-face GaN, the exact origin is still unclear. Developing thermally stable
metallization on the laser-irradiated N-face n-GaN seems to be possible only on the basis of a precise
understanding of the band bending at the metal/GaN interface, but no work has been reported yet
about the change in the interfacial band bending with annealing in metal contacts to the N-face n-
GaN.In this work, we investigate band bendings in Al ohmic contacts to laser-irradiated Ga- and Nface
n-GaN as a function of annealing temperature using synchrotron radiation photoemission
spectroscopy (SRPES). The SRPES results are then compared with electrical properties of the contacts.
The origin of the different behaviors in band bendings between both samples is discussed in terms of
point defects and polarity-dependent polarization charges at the interfacial regions. Finally we propose
promising methods and metallization schemes by which reliable ohmic contacts on the N-face GaN
can be obtained.
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