Influence of laser lift-off on optical and structural properties of InGaN/GaN vertical blue light emitting diodes

Abstract

The influences of the laser lift-off (LLO) process on the InGaN/GaN blue light emitting diode (LED) structures, grown on sapphire substrates by low-pressure metalorganic chemical vapor deposition, have been comprehensively investigated. The vertical LED structures on Cu carriers are fabricated using electroplating, LLO, and inductively coupled plasma etching processes sequentially. A detailed study is performed on the variation of defect concentration and optical properties, before and after the LLO process, employing high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM) observations, cathodoluminescence (CL), photoluminescence (PL), and high-resolution X-ray diffraction (HRXRD) measurements. The SEM observations on the distribution of dislocations after the LLO show well that even the GaN layer near to the multiple quantum wells (MQWs) is damaged. The CL measurements reveal that the peak energy of the InGaN/GaN MQW emission exhibits a blue-shift after the LLO process in addition to a reduced intensity. These behaviors are attributed to a diffusion of indium through the defects created by the LLO and creation of non-radiative recombination centers. The observed phenomena thus suggest that the MQWs, the active region of the InGaN/GaN light emitting diodes, may be damaged by the LLO process when thickness of the GaN layer below the MQW is made to be 5 μm, a conventional thickness. The CL images on the boundary between the KrF irradiated and non-irradiated regions suggest that the propagation of the KrF laser beam and an accompanied recombination enhanced defect reaction, rather than the propagation of a thermal shock wave, are the main origin of the damage effects of the LLO process on the InGaN/GaN MQWs and the n-GaN layer as well

18‐2: Ultra‐Fine High Efficiency MicroLEDs with Testability and Transferability Using Layer‐Transfer Technology

“…In addition to releasing an LED die, LLO processing must not damage the dies by energy or thermal shock during mass-transfer. Direct decomposition LLO has been studied for die damage [8]. Data shows active layer damage in standard vertical LED.…”

52‐3: Invited Paper: Combining Engineered EPI Growth Substrate Materials with Novel Test and Mass‐Transfer Equipment to Enable MicroLED Mass‐Production

“…A key feature is an integrated "Laser Lift-Off" or LLO layer between the sapphire substrate and the thin EPI-ready GaN surface. The unique "soft" LLO release function of the QMAT EPI substrate avoids damage (higher A parameter) to the microLED chips by separating the LLO process layer from the microLED material layer [3].…”

Design and comparative study of lateral and vertical LEDs with graphene as current spreading layer

“…These problems can be attributed to the low mobility and high activation energy of the p-GaN layer [11][12][13]. In recent years, the V-LEDs have gained a lot of consideration by using laser lift-off technique [14][15]. Reasons for this increased attention include better turn-on behaviour and smaller series resistance due to the vertical injection of current.…”