APPLIED PHYSICS LETTERS 99, 202106 (2011) Indium as an efficient ohmic contact to N-face n-GaN of GaN-based vertical light-emitting diodes Seon Young Moon, Jun Ho Son, Kyung Jin Choi, Jong-Lam Lee, and Ho Won Jang APPLIED PHYSICS LETTERS 99, 202106 (2011) 報告者: C.C.Shan

Outline Introduction Band-diagram Experiment Conclusion

Introduction We propose indium (In), a low work function and nitride- forming element, as an efficient ohmic contact layer to N- face n-GaN. While conventional Al-based ohmic contacts show severe degradation after annealing at 300 C, In- based ohmic contacts display considerable improvement in contact resistivity. The annealing-induced enhancement of ohmic behavior in In-based contacts is attributed to the formation of an InN interfacial layer, which is supported by x-ray photoemission spectroscopy measurements. These results suggest that In is of particular importance for application as reliable ohmic contacts to n-GaN of GaN- based vertical light-emitting diodes.

Band-diagram 簡易結構及能帶圖 Schematic band diagrams for (a) Al/AlN/N-face n-GaN and (b) In/InN/N-face n-GaN structures. PS and PP denote spontaneous polarization and piezoelectric polarization, respectively. For an InN epilayer on N-face n-GaN, PS is calculated to be 0.032 C/m2 and PP is 0.241 C/m2.

Experiment I-V curve結果 (a) and (b) Typical IV curves of Al (200 nm) and In (200 nm) contacts to N-face n-GaN before and after annealing.

Experiment 接觸電阻實驗結果 Contact resistivities of the Al and In contacts as a function of annealing temperature.

Experiment XPS量測結果 XPS spectra of Ga2p3/2 (b) In 3d5/2 core levels for as-deposited and 300 C-annealed In (10A ° ) contacts on N-face n-GaN. All In3d5/2 peaks were fitted using a Shirley background and mixed Lorentzian–-Gaussian line shapes.

Experiment I-V curve 量測結果 Typical IV curves of Ti/Al (50/200 nm) and In/Ti/Al (200/50/200 nm) contacts to N-face n-GaN before and after annealing at 300 C and 450 C.

Conclusion We have demonstrated that low resistance ohmic contacts to N-face n-GaN are achieved using In. While conventional Al-based contacts showed severe degradation after annealing at 300 C, In-based contacts displayed considerably improved ohmic behaviors after annealing. The origin of the ohmic contact formation and the annealing induced improvement was discussed with the formation of an interfacial InN layer. Our results prove that In-based ohmic contacts can be utilized as reliable electrodes to N- face n-GaN of GaN-based vertical LEDs for solid-state lighting.

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