Low resistance n-contact for UVC LEDs by a two-step plasma etching process

H.K. Cho1, J.H. Kang1, L. Sulmoni2, K. Kunkel1, J. Rass1, N. Susilo2, T. Wernicke2, S. Einfeldt1 and M. Kneissl1,2

Published in:

Semicond. Sci. Technol., vol. 35, no. 09, pp. 095019, DOI: 10.1088/1361-6641/ab9ea7 (2020).

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Abstract:

The impact of plasma etching on the formation of low-resistance n-contacts on the AlGaN:Si current spreading layer during the chip fabrication of ultraviolet light-emitting diodes (UV LEDs) emitting at 265 nm is investigated. A two-step plasma etching process with a first rapid etching using BCl3/Cl2 gas mixture and a second slow etching step using pure Cl2 gas has been developed. The etching sequence provides smooth mesa side-walls and an n-AlGaN surface with reduced surface damage. Ohmic n-contacts with a contact resistivity of 3.5 × 10-4 Ωcm2 are obtained on Si-doped Al0.65Ga0.35N layers and the operating voltages of the UVC LEDs were reduced by 2 V for a current of 20 mA.

1 Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, Gustav-Kirchhoff-Str. 4, 12489 Berlin, Germany
2 Technische Universität Berlin, Institute of Solid State Physics, Hardenbergstr. 36, EW 6-1, 10623 Berlin, Germany

Keywords:

light emitting diode, plasma etch, ohmic contact, low resistance n-contact, high Al mole fraction n-AlGaN, operating voltage