Ultrashort Pulse Laser Lift-Off Processing of InGaN/GaN Light-Emitting Diode Chips

Abstract

Gallium nitride (GaN) film delamination is an important process during the fabrication of GaN light-emitting diodes (LEDs) and laser diodes. Here, we utilize 520 nm femtosecond laser pulses, exploiting nonlinear absorption rather than single-photon absorption such as in conventional laser lift-off (LLO) employing excimer or Q-switched laser sources. The focus of this study is to investigate the influence of laser scanning speed and integrated fluence corresponding to laser energy per area during the LLO processing of GaN LED chips and their resulting structural properties. Because both the sapphire substrate and InGaN/GaN heterostructures are fully transparent to the emission of the laser system, a key question is related to the impact of laser pulses on the quality of a thin film structure. Therefore, several characterization methods (i.e., scanning electron microscopy, atomic force microscopy, X-ray diffraction, Raman spectroscopy, and electroluminescence spectroscopy) were employed to understand the material modifications made by femtosecond LLO (fs-LLO). We demonstrated that by adjusting the laser scanning speed, smooth GaN surfaces and good crystal quality could be obtained regardless of the existing delamination of metal contact, which then slightly downgraded the LED performance. Here, the integrated fluence level was set in the range of 2.6–4.4 J/cm2 to enable the fs-LLO process. Moreover, two mitigation strategies were developed and proven to improve the optoelectrical characteristics of the lifted-off LEDs (i.e., modification of the processing step related to the metal creation and reduction of laser energy).

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

“…reported that the scheme of multi‐photons absorption to induce GaN layer separation based on nonlinear effects normally required a much higher laser fluence than conventional approaches, and it increased the energy consumption and the production cost in the actual production of GaN‐based devices. [ 28 ] More importantly, they found that the nonlinear absorption process resulted in deeper laser penetration depths, which led to the uncontrollability of the delamination region and increased the risk of functional layer damage. Additionally, the surface root mean square (r.m.s.)…”

“…Additionally, the surface root mean square (r.m.s.) roughness of the separated GaN layer with this scheme was also unsatisfactory (≈68 nm) [ 25,26,28,29 ] and even inferior to that of the GaN surface separated by conventional approaches (≈50 nm). [ 30–32 ] It means the using of multi‐photons absorption in LLO was unfavorable for bonding prefabricated GaN‐based devices to foreign substrates or electrodes.…”

Integration of Multifocal Microlens Array on Silicon Microcantilever via Femtosecond-Laser-Assisted Etching Technology

“…The femtosecond laser (343 nm, 200 kHz, 280 fs (Light Conversion Pharos, Vilnius, Lithuania)) is tightly focused through a high numerical aperture objective lens (NA = 0.95, 40×) and matched with a three-dimensional piezoelectric platform (the strokes of the xand y-axes are 1.5 mm, that of the z-axis is 100 µm, and accuracy is 1 nm) to realize the preparation of micro/nanostructures on the silicon surface [24][25][26][27][28][29]. In addition, the femtosecond laser can also be used to process other materials via multi-photon absorption, for example, lift off GaN [30,31]. After femtosecond laser treatment, a laser-modified region was formed on the silicon surface, changing its physical and chemical properties.…”

Transparent porous polymer sheets for efficient product separation in solar water splitting

“…29,30 Similar to the underlying mechanism for femtosecond laser li-off of semitransparent semiconductor materials (e.g., InGaN/GaN LEDs), the use of laser enables the processing of transparent polymers via nonlinear optical interaction, which prevents heating effect surrounding the microholes during the laser ablation process. [31][32][33] The ultra-fast laser system based on an Yb-based commercial femtosecond laser source (SPIRIT-1040, Newport Spectra-Physics GmbH, Germany) was used in this study. This laser has constant parameters, i.e., a center wavelength of 520 nm, a pulse width of 350 fs, and a repetition rate of 200 kHz.…”