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HL: Fachverband Halbleiterphysik

HL 33: Poster Session III

HL 33.15: Poster

Mittwoch, 14. März 2018, 17:30–19:30, Poster F

Sub 240 nm UVC LEDs featuring low contact resistance V-based electrodes on n-Al_0.9Ga_0.1N — •Luca Sulmoni¹, Frank Mehnke¹, Martin Guttmann¹, Christian Kuhn¹, Tim Wernicke¹, and Michael Kneissl^1,2 — ¹Technische Universität Berlin, Institute of Solid State Physics — ²Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, Berlin

The design and fabrication of III-nitride-based heterostructures is particularly demanding for deep UV LEDs emitting below 240 nm as the external quantum efficiency drastically decreases with decreasing wavelength. In addition, ohmic contacts to n-Al_xGa_1−xN are extremely challenging for very high Al mole fractions mainly due to the low electron affinity and to limitations in the ionized donor concentration. This results in high operating voltages and resistive heating.

Al_0.9Ga_0.1N:Si layers were grown on low defect density AlN by MOVPE with a specific sheet resistivity of 0.3 Ω cm. In this study, we achieved ohmic contacts on n-Al_0.8Ga_0.2N with estimated specific contact resistivities of 9·10⁻⁴ Ω cm². By further optimizing the four-metal electrode V/Al/Ni/Au configuration and the rapid thermal annealing procedure, we were able to sensibly reduce also the contact resistivities as well as the Schottky behavior of our n-contacts on n-Al_0.9Ga_0.1N. The V/Al/Ni/Au n-contacts on n-Al_0.9Ga_0.1N annealed at 750^∘C exhibited moderate rectifying characteristics with estimated specific contact resistivities as low as 3·10⁻³ Ω cm² at a current density of 0.1 kA/cm². Finally, we fabricated UVC LEDs emitting at 234 nm with output power of 40 µW at 20 mA and 12.5 V in cw operation.