Efficiency enhancement of InGaN/GaN blue light-emitting diodes with top surface deposition of AlN/Al2O3. (January 2018)

• Record Type: Journal Article
• Authors: Kim, Kwangeun; Hua, Mengyuan; Liu, Dong; Kim, Jisoo; Chen, Kevin J.; Ma, Zhenqiang
• Is Part Of: Nano energy. Volume 43(2018)
• Page Start: 259
• Page End: 269
• Publication Date: 2018-01
• Subjects: Efficiency droop -- Light-emitting diodes -- AlN -- GaN -- Carrier injection -- Quantum-confined Stark effect; Nanoscience -- Periodicals; Nanotechnology -- Periodicals; Nanostructured materials -- Periodicals; Power resources -- Technological innovations -- Periodicals; Nanoscience; Nanostructured materials; Nanotechnology; Power resources -- Technological innovations; Periodicals; 621.042
• DOI: 10.1016/j.nanoen.2017.11.047
• Languages: English
• ISSNs: 2211-2855

Abstract

Abstract: Improving the energy conversion efficiency of light-emitting diodes (LEDs) for blue light emission has been a continuing pursuit for the past several decades. Here, we report InGaN/GaN LEDs with improved energy efficiency through the simple deposition of multifunctional ultrathin AlN/Al2 O3 layers on top of p-type GaN (i.e., GaN:Mg) using remote plasma pretreatment and plasma-enhanced atomic-layer deposition (PEALD). The AlN/Al2 O3 stacked layers played principal roles in improving the LED energy efficiency: 1) The surface defect states of p-type GaN were reduced to minimize leakage current and oxidation was prevented by passivating the GaN surface; 2) the net positive charges formed at the AlN/GaN interface enhanced the hole injection rate into the multi-quantum well (MQW) by formation of downward band bending with the increased surface potential; and 3) the increased hole injection rate induced the band-filling effect and screening of internal polarization fields in the MQW. The AlN/Al2 O3 stacked layers deposited on the GaN:Mg have overall improved the radiative recombination rate of the InGaN/GaN LEDs and thus light-emission efficiency. X-ray photoelectron spectroscopy was used to characterize the surface potential change of GaN. The peak efficiency values of wall-plug efficiency, the external-quantum efficiency, and the efficacy of the AlN/Al2 O3 coated InGaN/GaN LEDs were improved by 29%, 29%, and 30%, respectively. The corresponding efficiency droop rates were decreased by 13%, 6% and 3%, respectively, as compared to those of reference LEDs. Graphical abstract: Highlights: Enhancement in the energy conversion efficiency of InGaN/GaN blue LEDs with ultrathin AlN/Al2O3 stacked layers. Formation of AlN/Al2O3 top surface layers through in-situ RPP and PEALD. Enhanced radiative recombination rate in MQW due to the increased carrier injection. Improvements in WPE, EQE, and Efficacy, and their corresponding efficiency droop rates.