Efficiency enhancement of InGaN/GaN blue light-emitting diodes with top surface deposition of AlN/Al2O3

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/Al2O3 layers on top of p-type GaN (i.e., GaN:Mg) using remote plasma pretreatment and plasma-enhanced atomic-layer deposition (PEALD). The AlN/Al2O3 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/Al2O3 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/Al2O3 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.