Improving carrier transport in AlGaN deep-ultraviolet light-emitting diodes using a strip-in-a-barrier structure

Abstract

This paper reports the illustration of electron blocking layer (EBL)-free AlGaN light-emitting diodes (LEDs) operating in the deep-ultraviolet (DUV) wavelength at ∼ 270 n m . In this work, we demonstrated that the integration of an optimized thin undoped AlGaN strip layer in the middle of the last quantum barrier (LQB) could generate enough conduction band barrier height for the effectively reduced electron overflow into the p - G a N region. Moreover, the hole injection into the multi-quantum-well active region is significantly increased due to a large hole accumulation at the interface of the AlGaN strip and the LQB. As a result, the internal quantum efficiency and output power of the proposed LED structure has been enhanced tremendously compared to that of the conventional p - t y p e EBL-based LED structure.

Enhancing Efficiency of AlGaN Ultraviolet‐B Light‐Emitting Diodes with Graded p‐AlGaN Hole Injection Layer

“…[ 10,29 ] It is also evident that negative sheet polarization charges support the electron depletion at the conduction band, while allowing hole accumulation at the valence band. [ 7,30 ] The continuous formation of the negative sheet polarization charge region does not appear in LED2 due to the absence of the LGL in the HIL. Although there is a negative sheet polarization charge at the interface of the EBL and the HIL in LED2, it is limited to that particular interface.…”

“…This is due to a high valence band offset at the last abrupt barrier/EBL heterointerface and positive polarization‐induced sheet charge density. [ 7,8 ] Moreover, inefficient hole injection, associated with low‐Mg doping efficiency [ 9 ] and high‐Mg activation energy requirement [ 10 ] for the Al‐rich AlGaN layers, are other problems for the low IQE.…”

Improved Performance of Electron Blocking Layer Free AlGaN Deep Ultraviolet Light-Emitting Diodes Using Graded Staircase Barriers

“…This area accumulates a large number of electrons i.e., 3.66 × 10 16 cm −3 , which eventually contributes to non-radiative recombination [30]. In addition, due to this induced positive polarization sheet charges in LED 1, a hole depletion region is formed at the heterointerface of the last QB and EBL, as shown in Figure 3a, which reduces the hole injection efficiency [5]. The formation of the hole depletion region problem is eliminated in the case of LED 2 and LED 3 by removing the EBL.…”

“…Further, the values of ℏꞷLO in each step of GSQBs for LED3 are calculated [32] and presented in Figure 7. From Equations (4) and (5), it is understood that (E + ΔEc1 + qV2−ΔEc2−ℏꞷLO) < (E + qV1). Consequently, vth for LED3 would be less as compared to LED1.…”

“…This could mitigate the electron leakage to only an extent. However, hole injection efficiency is affected owing to the formation of positive polarization sheet charges at the interface of the last quantum barrier and EBL [5]. Moreover, as the EBL is Al-rich, Mg doping efficiency gets affected because of high acceptor activation energy, compensation by nitrogen vacancies, increased hole scattering, and limited acceptor solubility [6].…”