Origin of the Inhomogeneous Electroluminescence of GaN-Based Green Mini-LEDs Unveiled by Microscopic Hyperspectral Imaging

Abstract

Although high quantum efficiency has been achieved in large-sized InGaN/GaN LEDs operating at relatively high current densities (above 35 A/cm 2 ), the operating current density of mini-LEDs (around 1 A/cm 2 ) is far less than that of traditional large-sized LEDs. The low external quantum efficiency (EQE) of mini-LEDs at small current densities seriously hinders their practical applications, highlighting the importance of investigating the radiative recombination mechanisms of mini-LEDs at small current densities. By using microscopic hyperspectral imaging, the cryogenic electroluminescence (EL) of GaN-based green mini-LEDs mainly originating from localized excitons was demonstrated experimentally. Based on the dependence of electron−phonon coupling on current and temperature, Coulomb screening of the polarization field weakens the electron−phonon coupling, whereas the band-filling effect enhances the coupling. Coulomb screening of the polarization field can also reduce the deviation of the localization. The EL from edge regions of the mesa adjacent to the sidewall possesses relatively higher peak energy due to the strain relaxation. Results of this work also suggest that optimization of the chromatic characteristics and efficiency can be achieved by strain engineering of GaN-based green mini-LEDs.

Impact of Localization on the Optical Properties of InGaN-Based Red Light-Emitting Diodes Grown on a Silicon Substrate

“…According to the classic ABC model, the current density corresponding to the EQE max is proportional to the ratio of A to C , where A and C denote the coefficient of SRH recombination and Auger recombination, respectively. As the temperature decreases from 300 to 80 K, the current density corresponding to the EQE max drops significantly with decreasing temperature, which can be ascribed to the reduction of SRH nonradiative recombination . However, the current density corresponding to the EQE max remains at 10 –4 A/cm 2 below 80 K.…”

“…As the temperature decreases from 300 to 80 K, the current density corresponding to the EQE max drops significantly with decreasing temperature, 32 which can be ascribed to the reduction of SRH nonradiative recombination. 33 However, the current density corresponding to the EQE max remains at 10 −4 A/cm 2 below 80 K.…”

Power-Dependent Optical Characterization of the InGaN/GaN-Based Micro-Light-Emitting-Diode (LED) in High Spatial Resolution

“…The current in small mesa could easily diffuse to the edge; thus, the luminescence was enhanced near the sidewall of micro-LEDs with smaller sizes. Such two contradictory observations are not unique, but seem to appear repeatedly other the studies [13][14][15][16][17][18][19][20]. However, these studies did not give an explanation for this non-uniform luminescence under uniform injection of carriers (PL), and whether it was related to the excitation power density.…”

Single-Photon-Camera-Based Time and Spatially Resolved Electroluminescence Spectroscopy for Micro-LED Analysis

“…7,8 The decrease in device efficiency and nonuniformity of electroluminescence (EL) caused by size reduction and other effects are obstacles before industrialization. 9,10 To address these challenges, it has been much aspired to thoroughly characterize the performance of micro-LEDs in the time and spatial scales.…”

“…For the micro-OLED display panel, the degradation of organic emitters strongly affects the device performance, which is of great importance to improve the operational lifetime . Very recently, micro-QLED devices were also fabricated by applying the inkjet printing or photolithography process. , The decrease in device efficiency and nonuniformity of electroluminescence (EL) caused by size reduction and other effects are obstacles before industrialization. , To address these challenges, it has been much aspired to thoroughly characterize the performance of micro-LEDs in the time and spatial scales.…”