Sidewall damage repair of GaN-based Micro-LED by combination of atomic layer etching and atomic layer deposition

To address the issue of sidewall damage caused by inductively coupled plasma (ICP) etching during the mesa etching process of GaN-based micro-light-emitting diodes (Micro-LEDs), this paper proposes a composite sidewall repair process combining atomic layer etching (ALE) and atomic layer deposition technology based on the traditional ICP etching technique. Firstly, ICP is used to quickly define the original Micro-LED mesa (with a mesa size of 20 μm and a depth of 1.4 μm. Subsequently, ALE is employed to etch the mesa (with a depth of 8 nm), which repairs the amorphization of GaN on the sidewalls caused by ICP etching damage with high precision and high selectivity. Furthermore, atomic layer deposition (ALD) is utilized to grow a SiO₂ passivation layer with high density and excellent interface properties. Through chemical bonding and physical coating, the dangling bonds of GaN at the sidewalls are reduced, the carrier transport path at the defects is blocked, and non-radiative recombination is decreased. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive spectroscopy (EDS) are used to characterize the surface morphology, interface properties, and sidewall damage of the samples. The results show that the sidewall damage depth of Micro-LEDs prepared by the ALE+ALD process is reduced from 9 nm (by the traditional etching method) to 6 nm, a decrease of 1.3 times. Moreover, the GaN/SiO2 interface is clearer and more regular, with fewer dangling bonds. In addition, potassium hydroxide (KOH) wet etching forms a 90° vertical mesa due to the selective etching of the C-plane, while the ALE repair process does not damage the original 70° sidewall angle formed by ICP etching, which can further improve the light extraction efficiency (LEE) and top surface light extraction efficiency (LSE). The mesa simulation results show that the LEE and LSE of the sample with a 70° sidewall angle are 41.1% and 25.4%, respectively, which are 33.3% and 113% higher than those of the sample with a 90° vertical mesa. This study confirms that the repair process combining ALE etching and ALD passivation can effectively reduce sidewall damage and optimize light extraction performance, providing a feasible technical route for the preparation of high-performance GaN-based Micro-LEDs.