Development of blue-light GaN based micro light-emitting diodes using ion implantation technology

Discover Nano Research Development of blue‑light GaN based micro light‑emitting diodes using ion implantation technology Yu‑Hsuan Hsu1,2 · Shao‑Hua Lin1 · Dong‑Sing Wuu3 · Ray‑Hua Horng2 Received: 21 September 2024 / Accepted: 9 December 2024 © The Author(s) 2024  OPEN Abstract This study fabricated 10 μm chip size μLEDs of blue-light GaN based epilayers structure with different mesa processes using dry etching and ion implantation technology. Two ion sources, As and Ar, were applied to implant into the LED structure to achieve material isolation and avoid defects on the mesa sidewall caused by the plasma process. Excellent turn-on behavior was obtained in both ion-implanted samples, which also exhibited lower leakage current compared to the sample fabricated by the dry etching process. Additionally, lower dynamic resistance (Rd) and series resistance (Rs) were obtained with Ar implantation, leading to a better wall-plug efficiency of 10.66% in this sample. Consequently, outstanding external quantum efficiency (EQE) values were also present in both implant samples, particularly in the sample implanted with Ar ions. This study proves that reducing defects on the mesa sidewall can further enhance device properties by suppressing non-radiative recombination behavior in small chip size devices. Overall, if implantation is used to replace the traditional dry etching process for mesa fabrication, the ideality factor can decrease from 11.89 to 2.2, and EQE can improve from 8.67 to 11.03%. Keywords Micro-LED · Dry etching · Ion implantation · Wall-plug efficiency 1 Introduction In recent years, the field of optoelectronics has witnessed a remarkable surge in interest and innovation, driven by the quest for more efficient, compact, and versatile lighting and display technologies. Among these, micro light emitting diodes (μLEDs) have emerged as a promising solution, offering unprecedented levels of miniaturization, energy efficiency, and performance. μLEDs have garnered significant interest due to their numerous advantages, including high luminous intensity, resolution, contrast, response speed, lifespan, and energy efficiency [1–4]. Recognized for these exceptional performance characteristics, μLEDs are considered at the forefront of next-generation display technology. They find applications across various domains, from wearable devices like wristbands and watches to large-scale commercial billboards, public displays, and immersive technologies such as virtual reality (VR) or augmented reality (AR) devices [5–7]. However, as device dimensions shrink to the microscale, the influence of sidewall effects and non-radiative recombination becomes increasingly pronounced [8, 9]. Sidewall effects refer to the interaction between carriers and sidewall surfaces in μLEDs, leading to non-uniform carrier distribution, enhanced surface recombination, and reduced device efficiency. Non-radiative recombination processes involve the generation of electron–hole pairs that do not contribute * Ray‑Hua Horng, | 1Institute of Electronics, National Yang Ming Chiao Tung University, Hsinchu 30010, Taiwan, ROC. 2Department of Photonics, National Yang Ming Chiao Tung University, Hsinchu 30010, Taiwan, ROC. 3Department of Applied Materials and Optoelectronic Engineering, National Chi Nan University, Nantou 54561, Taiwan, ROC. Discover Nano (2024) 19:209 | https://doi.org/10.1186/s11671-024-04169-4 Vol.:(0123456789) Research Discover Nano (2024) 19:209 | https://doi.org/10.1186/s11671-024-04169-4 to light emission, leading to wasted energy and decreased quantum efficiency [10]. Understanding and mitigating these phenomena are critical for optimizing the performance and reliability of μLED devices. In μLEDs, the high surface-tovolume ratio exacerbates sidewall effects, causing deviations from ideal device behavior [11, 12]. As carriers approach the sidewall surfaces, they experience surface recombination and scattering, leading to non-uniform carrier distribution and reduced injection efficiency. Moreover, sidewall roughness and defects can trap carriers, increasing the likelihood of non-radiative recombination and reducing light output [7, 8, 13]. Experimental studies have revealed the detrimental impact of sidewall effects on device performance, highlighting the need for strategies to minimize sidewall-related losses. Suppressing sidewall damage is a critical challenge in μLEDs fabrication, as defects introduced during the etching process can lead to leakage currents, reduced efficiency, and poor device reliability. Various methods have been developed to address this issue, such as plasma treatments using gases such as oxygen, hydrogen, and nitrogen form protective passivation layers, wet chemical treatments like KOH etching or sulfur passivation remove damage layers and improve surface quality [14, 15]. Atomic layer deposition (ALD) further contributes by depositing conformal passivation layers, such as Al2O3, which protect against leakage currents and enhance optical performance [8]. Novel etching technique, such as neutral beam etching, minimized defect generation during fabrication [16]. Furthermore, ion implantation, particularly with the careful selection of ion implantation elements, researchers can effectively suppress sidewall damage and improve the performance and reliability of microLED devices. Ion implantation is a crucial process used in semiconductor manufacturing to introduce impurities into a substrate, altering its electrical properties. In microLED fabrication, ion implantation is a critical process for passivating defects and mitigating sidewall damage, improving device efficiency and reliability [17–25]. Various elements have been employed, each offering unique advantages. Fluorine is widely used for its ability to effectively passivate dangling bonds, reducing non-radiative recombination and leakage currents [22]. Nitrogen is particularly effective in GaN-based microLEDs, where it chemically bonds with the material to stabilize the surface and suppress recombination. Hydrogen is highly effective in forming stable complexes with defects, significantly reducing non-radiative recombination, although its thermal stability requires careful management [19]. The heavy ions, such as Ar, Kr, Xe, and As of different implantation energies and dosages have be demonstrated to play the isolation function and confine non-radiative regions to produce relatively invariant luminance in μLEDs display [19]. By carefully selecting these elements based on specific fabrication needs, ion implantation can significantly enhance the performance and reliability of microLED devices. A study to optimize implant energy for the mesa process in μLED fabrication, specifically targeting a 50 μm chip size has been studied using heavy ion 75 As in our group [26]. The heavy ion 75As was employed to disrupt the crystal structure in the LED epilayer, facilitating isolation. Through electrical measurements, w (...truncated)