Injection current and temperature dependence of the optoelectronic properties for electrical-stressed InGaN based micro-LEDs

Abstract

InGaN-based micro-LEDs are promising for many applications, including visible light communication (VLC), micro-display, etc. However, to realize the above full potential, it is important to understand the degradation behaviors and physical mechanisms of micro-LEDs during operation. Here, the optoelectronic properties of InGaN-based blue micro-LEDs were investigated over a wide range of injection currents (1-100 mA) and temperatures (5-300 K) before and after stress. The results show that the optical power of the micro-LED degrades after stress, especially at lower current density, indicating that the Shockley-Read-Hall (SRH) nonradiative recombination increased for the stressed device. In addition, the slopes of log L-log I curves changes from 1.0 to 2.1 at low current density, and the ideality factor extracted from the I-V curves change from 1.9 to 3.4 after current stress, indicating there is an increase of the defects in the active layer after stress. The activation energy of defects evaluated from the temperature-dependent electroluminescence (EL) spectra is about 200 meV, which could be related to the N-vacancy related defects. Besides, the peak wavelength, peak energy and the full width at half maximum of the injection current- and temperature-dependent EL spectra were discussed. The electron-hole pair combines in the form of SRH nonradiative recombination, causing some carriers to redistribute and a state-filling effect in higher-energy states in multiple quantum wells (MQWs), resulting in the appearance of the shorter-wavelength luminescence in the EL spectra. These findings can help to further understand the degradation mechanisms of InGaN micro-LEDs operated under high current density.