## 1 Introduction  
Large-scale and flexible electronic and optoelectronic devices have recently attracted much attention for use in wearable displays, solar cells, sensors, and biomedical devices [1; 2]. For flexible, bendable, and wearable devices, organic films have been widely employed because of their excellent scalability and flexibility. Compared to inorganic materials, however, organic films have drawbacks such as a short lifetime, low efficiency, low brightness, difficulty in enlarging, and low stability in humid environments. Gallium nitride (GaN)-based microscale light-emitting diodes (microLEDs) have attracted substantial attention in recent years as they have the potential to replace conventional organic light-emitting diodes (OLEDs) for flexible and bendable displays [3; 4]. Conventional routes to these devices involve epitaxial growth of active materials followed by chip fabrication, wafer dicing, and pick-and-place robotic manipulation into individually packaged components for interconnection by bulk wire-bonding. However, dicing becomes more difficult as the chip size decreases beyond \(100\)\(\upmu\times 100\)\(\upmu\)m, and integrating them on flexible and bendable substrates also becomes a challenge. Therefore, another route has been suggested for the manufacture of electronic devices, and it involves chip fabrication, the separation of chips from the mother substrate, and transfer of separated chips to devices. There are two ways to separate chips from a substrate, namely laser lift off (LLO) and chemical lift off (CLO) [5]. Generally, separating GaN LEDs from a sapphire substrate by LLO is an expensive process because it requires the use of a deep ultraviolet excimer laser [6; 7; 8]. In addition, the current LLO process requires a series of complicated steps to transfer-print the GaNLED structure onto a flexible substrate, including bonding the structure to a hard substrate before LLO, selective removal of the bonding layer after LLO, transferring the flexible substrate using an elastomeric stamp, another round of transfer-printing if a flip transfer is necessary, and a long process time [5; 9]. The transfer of GaN films to receptor substrates results in a considerable release of stresses, which originate from the large lattice and thermal mismatch between the GaN-based layers and sapphire substrate. The released stresses may result in structural defects and even cracks in the epitaxial layers that degrade device performance [10]. Therefore, there is a strong need to develop a simplified method for higher-yield transfer while preserving the original layout of the GaN LEDs. Recently, [PERSON] et al. reported the scalable pick-and-place transfer-printing of GaN LEDs fabricated on silicon onto a mechanically flexible substrate through CLO, using a horizontal tether as the sacrificial layer and anchor to hold the isolated LED chips [11]. For thin-film LEDs, the device-processing steps for GaN LEDs fabricated on a Si substrate are almost identical to those for GaN LEDs on a sapphire substrate, except that the former requires the host substrate to be removed in a simple chemical mechanical process, while the latter uses an LLO process. Therefore, this method has the advantage of a short process time, simple steps, and low damage of the epilayer without using a high-power UV laser during the LLO process. In addition, with the significant improvements in growth and fabrication techniques, the current external quantum efficiency of GaN LEDs on a silicon substrate represents an improvement of 65% and is comparable to that of GaN LEDs on sapphire [12]. GaN LEDs can be grown on large-scale Si wafers, e.g., Si(111) substrates with diameters of up to 200 mm, which are cheaper than sapphire wafers. The GaN-on-silicon approach also benefits from the use of existing equipment for silicon manufacturing [13]. However, the pick-and-place transfer-printing method requires expensive equipment, a long process time, and a sacrificial layer.