Remarkably reduced efficiency droop by using staircase thin InGaN quantum barriers in InGaN based blue light emitting diodes

Journal of Applied Physics

Ikeda

Zhou

et al. 2015

Self Cite

Articles you may be interested inStrain reduction and crystal improvement of an InGaN/GaN quantum-well light-emitting diode on patterned Si (110) substrate Appl.Three dimensional numerical study on the efficiency of a core-shell InGaN/GaN multiple quantum well nanowire light-emitting diodes Effect of an electron blocking layer on the piezoelectric field in InGaN/GaN multiple quantum well light-emitting diodes Appl.Injection current dependences of electroluminescence transition energy in blue InGaN/GaN multiple quantum wells light emitting diodes (LEDs) with different quantum barrier thicknesses under pulsed current conditions have been analyzed taking into account the related effects including deformation caused by lattice strain, quantum confined Stark effects due to polarization field partly screened by carriers, band gap renormalization, Stokes-like shift due to compositional fluctuations which are supposed to be random alloy fluctuations in the sub-nanometer scale, band filling effect (Burstein-Moss shift), and quantum levels in finite triangular wells. The bandgap renormalization and band filling effect occurring at high concentrations oppose one another, however, the renormalization effect dominates in the concentration range studied, since the band filling effect arising from the filling in the tail states in the valence band of quantum wells is much smaller than the case in the bulk materials. In order to correlate the carrier densities with current densities, the nonradiative recombination rates were deduced experimentally by curve-fitting to the external quantum efficiencies. The transition energies in LEDs both with 15 nm quantum barriers and 5 nm quantum barriers, calculated using full strengths of theoretical macroscopic polarization given by Barnardini and Fiorentini [Phys. Status Solidi B 216, 391 (1999)] are in excellent accordance with experimental results. The LED with 5 nm barriers has been shown to exhibit a higher transition energy and a smaller blue shift than those of LED with 15 nm barriers, which is mainly caused by the smaller internal polarization field in the quantum wells. V C 2015 AIP Publishing LLC. [http://dx.

Section: Correlation Between Carrier Density and Current Densitymentioning

confidence: 99%

Injection current dependences of electroluminescence transition energy in InGaN/GaN multiple quantum wells light emitting diodes under pulsed current conditions

Journal of Applied Physics

Ikeda

Zhou

et al. 2015

Self Cite

“…[9][10][11] The hole injection can also be favored by modifying the active region. For example, researchers have suggested reducing the quantum barrier thickness, 12,13 increasing the quantum well thickness along the growth orientation, 14 using InGaN as quantum barriers, 15 and/or using Mg-doped quantum barriers. [16][17][18][19] The significance of using the GaN/InGaN structure as the last quantum barrier to enhance the hole injection has also been presented by several groups.…”

mentioning

confidence: 99%

On the hole accelerator for III-nitride light-emitting diodes

Applied Physics Letters

et al. 2016

In this work, we systematically conduct parametric studies revealing the sensitivity of the hole injection on the hole accelerator (a hole accelerator is made of the polarization mismatched p-electron blocking layer (EBL)/p-GaN/p-AlxGa1−xN heterojunction) with different designs, including the AlN composition in the p-AlxGa1−xN layer, and the thickness for the p-GaN layer and the p-AlxGa1−xN layer. According to our findings, the energy that the holes obtain does not monotonically increase as the AlN incorporation in the p-AlxGa1−xN layer increases. Meanwhile, with p-GaN layer or p-AlxGa1−xN layer thickening, the energy that the holes gain increases and then reaches a saturation level. Thus, the hole injection efficiency and the device efficiency are very sensitive to the p-EBL/p-GaN/p-AlxGa1−xN design, and the hole accelerator can effectively increase the hole injection if properly designed.

“…The non-uniform hole distribution that often takes place in the MQWs leads to a strong hole accumulation in the quantum wells close to the p-GaN side. 3 The hole injection can be homogenized by doping the quantum barriers with Mg acceptors, 4,5 using the InGaN instead of the GaN as the quantum barriers, 6 properly reducing the quantum barrier thickness, 7 increasing the thickness of the quantum well close to the p-GaN layer 8 and/or employing the cascaded active region. 9 As is well known, the p-EBL is adopted in the III-nitride LEDs to reduce the electron leakage, which nevertheless also blocks the hole injection due to the band offset between the p-EBL and the subsequent p-GaN layer.…”

mentioning

confidence: 99%

“…The holes in the quantum barriers can be more homogeneously distributed by, e.g., employing the InGaN as the quantum barriers. 6 The impact of the charge inverter is justified by measuring the optical performance for devices A and B as shown in Figs. 6(a) and 6(b), respectively.…”

mentioning

confidence: 99%

A charge inverter for III-nitride light-emitting diodes

Applied Physics Letters

et al. 2016

In this work, we propose a charge inverter that substantially increases the hole injection efficiency for InGaN/GaN light-emitting diodes (LEDs). The charge inverter consists of a metal/electrode, an insulator, and a semiconductor, making an Electrode-Insulator-Semiconductor (EIS) structure, which is formed by depositing an extremely thin SiO2 insulator layer on the p+-GaN surface of a LED structure before growing the p-electrode. When the LED is forward-biased, a weak inversion layer can be obtained at the interface between the p+-GaN and SiO2 insulator. The weak inversion region can shorten the carrier tunnel distance. Meanwhile, the smaller dielectric constant of the thin SiO2 layer increases the local electric field within the tunnel region, and this is effective in promoting the hole transport from the p-electrode into the p+-GaN layer. Due to the improved hole injection, the external quantum efficiency is increased by 20% at 20 mA for the 350 × 350 μm2 LED chip. Thus, the proposed EIS holds great promise for high efficiency LEDs.