Electrical properties and microstructure formation of V/Al-based n-contacts on high Al mole fraction n-AlGaN layers

L. Sulmoni1, F. Mehnke1, A. Mogilatenko2,3, M. Guttmann1, T. Wernicke1, and M. Kneissl1,2

Published in:

Photonics Res., vol. 8, no. 8, pp. 1381-1387 (2020).

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Abstract:

The electrical and structural properties of V/Al-based n-contacts on n-AlxGa1-xN with an Al mole fraction x ranging from x=0.75 to x=0.95 are investigated. Ohmic n-contacts are obtained up to x=0.75 with a contact resistivity of 5.7×10-4Ω·cm2 whereas for higher Al mole fraction the IV characteristics are rectifying. Transmission electron microscopy reveals a thin crystalline AlN layer formed at the metal/semiconductor interface upon thermal annealing. Compositional analysis confirmed an Al enrichment at the interface. The interfacial nitride-based layer in n-contacts on n-Al0.9Ga0.1N is partly amorphous and heavily contaminated by oxygen. The role and resulting limitations of Al in the metal stack for n-contacts on n-AlGaN with very high Al mole fraction are discussed. Finally, ultraviolet C (UVC) LEDs grown on n-Al0.87Ga0.13N and emitting at 232 nm are fabricated with an operating voltage of 7.3 V and an emission power of 120 µW at 20 mA in cw operation.

1 Institut für Festkörperphysik, Technische Universität Berlin, 10623 Berlin, Germany
2 Ferdinand-Braun-Institut, Leibnitz-Institut für Höchstfrequenztechnik, 12489 Berlin, Germany
3 Institut für Physik, Humboldt Universität zu Berlin, 12489 Berlin, Germany