Berlin 2018 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 24: Poster Session II
HL 24.37: Poster
Tuesday, March 13, 2018, 18:30–20:30, Poster F
Lift-off of GaN LEDs with ultrashort laser pulses — •Steffen Bornemann1,2, Nursidik Yulianto1,2, Andreas Waag1,2, and Hutomo Suryo Wasisto1,2 — 1Institut für Halbleitertechnik (IHT), Technische Universität Braunschweig, Hans-Sommer-Str. 66, 38106 Braunschweig — 2Laboratory for Emerging Nanometrology (LENA), Technische Universität Braunschweig, Langer Kamp 6a, 38106 Braunschweig
Due to their high efficiency and compact design, GaN-based LEDs are nowadays the light source of choice for many applications. Sapphire is usually taken as a low-cost substrate for epitaxial growth of the InGaN/GaN heterostructure. However, it provides poor electrical and thermal conductivity, limiting its practicability for commercial high-power LEDs as well as for structured light sources. Therefore, a transfer of thin LED structures to more suitable substrates, e.g. rigid silicon or flexible polyimide, is applied. The detachment from sapphire is normally realized with a UV excimer laser, leading to linear absorption in the first layers of GaN.
In this project, we present the successful implementation of a lift-off process based on a versatile femtosecond laser system operating at a wavelength of 520 nm. The corresponding photon energy is too low for direct absorption, but non-linear processes during the high-energy pulses enable separation of the LED from the original substrate. Luminescence experiments prove the functionality of the lifted chip, whereas SEM measurements reveal local laser induced damage on the surface. Possible mechanisms for these phenomena are discussed.