Low‐Energy UV Ultrafast Laser Controlled Lift‐Off for High‐Quality Flexible GaN‐Based Device

Abstract

A one‐step laser lift‐off (LLO) for patterned gallium nitride (GaN) film and GaN‐based light‐emitting diode (LED) device is achieved using 355 nm picosecond laser irradiation in this research. The laser fluence required for separation is 0.09–0.13 J cm−2, which is much lower than that for the currently reported LLO methods. The separated GaN film is intact with only 0.04 GPa of residual stress. The ultra‐smooth separated surface with root mean square roughness of only 5.2 nm is attributed to the interconnection of microcrack‐free flat cavities formed by the combination of high photon energy‐induced intrinsic absorption and subsequent plasma generation. The flat cavity with a depth‐to‐width ratio of 1:4000 limits the delamination region to a few nanometers at the GaN/sapphire interface. GaN‐based LED is transferred with perfect electroluminescence (EL) by the strategy. The stable EL spectral peak positions and intensity independent of the bending state prove that the presented low‐energy ultrafast LLO technique ensured the flexibility of the separated LED device without affecting the performance. This research provides a promising strategy to achieve the LLO of GaN devices with low energy consumption, high controllability, and high efficiency, which is significant for the industrial fabrication of flexible GaN‐based electronics.

Laser-lift-off of GaN-based transistors with an ultra-short-pulsed deep UV laser

“…At first the metallic gallium formation threshold at the wavelength of 266 nm had to be determined. At a wavelength of λ= 355 nm separation threshold is found to be between 0.13 J/cm 2 and 0.18 J/cm 2 with an UV USP-laser 16 , assuming a slightly higher absorptance at shorter wavelengths at room and higher process temperature, similar values are expected. To determine the threshold, Sample 1 was exposed from the GaN-side with a sequence of spatially separated single pulses.…”

“…This results in higher laser fluences of delamination, lower efficiency, higher variability and longer interaction lengths, with larger residual roughness and deeper damage regions 15 . The delamination threshold as well as the unwanted damage was shown to be significantly reduced by using an ultra-short (~10ps) pulsed (USP) UV-laser with 355 nm wavelength 16 . Recently, new industrial-grade USP laser sources in the deep UV (DUV) regime for industrial usage e.g., at 266 nm have been introduced 17 .…”

Laser Lift‐Off Technologies for Ultra‐Thin Emerging Electronics: Mechanisms, Applications, and Progress

“…Compared with the UV nanosecond laser, the UV picosecond laser achieves one-step LLO of GaN-based light-emitting diode devices with smaller laser fluence (90-130 mJ cm −2 ). [60] This shows that shortening the laser pulse width can reduce the ablation threshold of the responsive material. Meanwhile, the reduction of the ablation threshold and the shortening of the pulse width further suppress the range of the HAZ of the GaN response layer.…”

Centimeter-Transferable III-Nitride Membrane Enabled by Interfacial Adhesion Control for a Flexible Photosensitive Device

“…Otherwise, the wet etching is usually time-consuming, and it potentially causes ionic pollution. The laser lift-off (LLO) technique offers a chance for the separation of III-nitride from the sapphire substrate, and it relies on the absorption of laser photon energy and decomposition at the epitaxial interface; thus, the laser photon energy should be larger than the band gap of III-nitride. , In addition, a laminate adhesion layer has to be designed on the III-nitride membrane to deal with the strain release after LLO . Apart from these requirements, the interfacial burning damage and difficulty in large-area separation uniformity for LLO needs to be given more attention before it achieving the high efficiency and yield for mass production.…”