## 3 Results and Discussion  
Figure 2 shows optical microscope images and field-emission scanning electron microscope (FE-SEM) images before and after the CLO process. To detach the LED arrays from the Si substrate, we used spontaneously formed vertical tethers during the CLO process. Supplementary Figure S1 shows that Si was etched anisotropically with increasing etching time, where the Si(110) plane is defined as the lateral direction. Figure 2a,b shows that the cross-sectional area of the spontaneously formed vertical Si tethers was \(52\times 21\)\(\upmu\)m\({}^{2}\) and the height was 710 nm before the deposition of PMMA. These vertical Si tethers were removed by additional etching with KOH. The PMMA stamp holding the microLED arrays was moved to the glass substrate, and the PMMA was removed by acetone to expose the microLED arrays. Figure 2c,d shows the PL mapping images of GaN LED before and after transfer to glass substrate. It clearly shows that there was no degradation of optical properties and a shift in spacing between the LEDs. These results demonstrate that, unlike LLO, CLO is a damage-free process. Figure 2e shows the emission images of GaN LEDs on various transparent, flexible, or rigid substrates. Figure 2f shows an area measuring \(3\times 3\) cm\({}^{2}\) that was transferred to a glass substrate. These results show that the CLO approach is not dependent on the size of the transfer area. Figure 1: Schematic illustrations and images corresponding to steps for the transfer of Gallium nitride (GaN) light emitting diodes (LEDs): (**a**) isolated microLED arrays, (**b**) Isolated GaN micro LED arrays with spontaneously formed vertical tether, (**c**) deposition of PMMA and removal of remaining pillars, and (**d**) transfer of microLED arrays to unusual substrate. (**e**) MicroLED arrays on an unusual substrate. Figure 3 shows Raman spectra of the three samples measured at room temperature. In the spectrum of the GaN LEDs before transfer, the peak at 565.4 cm\({}^{-1}\) corresponds to the E\({}_{2}\) mode of the GaN hexagonal phase. It has been previously shown that the E\({}_{2}\) mode Raman peak of unstrained hexagonal GaN is located at 567.4 cm\({}^{-1}\)[14]. The relationship between the E\({}_{2}\) mode Raman peak shift (\(\Delta\omega_{y}\)) and the in-plane biaxial stress (\(\sigma_{\chi\chi}\)) can be expressed as [14; 15]:  
\[\sigma_{\chi\chi}=\Delta\omega_{y}/\text{K}_{y} \tag{1}\]  
where \(\sigma_{\chi\chi}\) is the stress in GPa, \(\Delta\omega_{y}\) is the Raman peak shift in cm\({}^{-1}\), and K\({}_{y}\) is the stress coefficient (4.3 cm\({}^{-1}\) GPa\({}^{-1}\)). The stress on the GaN surface before transfer was estimated to be 0.465 GPa, which means that the GaN epilayer on the Si substrate had high tensile stress. The E\({}_{2}\) Raman peak in the spectra obtained for the GaN LEDs on Si, glass, and PET substrates after transfer is shifted to 567.1 cm\({}^{-1}\). The stress on the GaN surface was estimated to be 0.07 GPa after transfer, indicating that the tensile strain was fully released. Since tensile stress can blue shift an emission peak and reduce the efficiency  
Figure 2: (**a**) Optical microscope image of GaN LED array with vertical tethers. (**b**) FE-SEM image of a GaN LED with a spontaneously formed vertical tether. PL mapping image of GaN LED (**c**) before transfer and (**d**) after transfer (**e**) Images of light emission from GaN LEDs transferred onto various substrates. FE-SEM image of GaN LEDs on a silicon substrate after transfer. (**f**) Optical microscope image of a GaN LED array (3 × 3 cm\({}^{2}\)) on a glass substrate after transfer. of a device, a red-shift of the emission peak and improvement in the LED efficiency are expected in the spectrum obtained after transfer. The strain of the MQW layer is more effectively released after transfer to Si, which is proven by X-ray reciprocal space mapping (RSM) of the (105) reflector for the sample before and after transfer to Si (Supplementary Figure S2). The vertical solid line represents the fully strained axis.