Radiative Recombination and Carrier Injection Efficiencies in 265 nm Deep Ultraviolet Light‐Emitting Diodes Grown on AlN/Sapphire Templates with Different Defect Densities

Abstract

The electro‐optical characteristics of deep ultraviolet light‐emitting diodes (DUV LEDs) emitting at 265 nm and grown on AlN/sapphire templates with different threading dislocation densities, i.e., high‐temperature annealed (HTA) AlN, epitaxially laterally overgrown (ELO) AlN, and HTA‐ELO AlN are analyzed. The external quantum efficiency of each individual device is separated into maximum radiative recombination efficiency, carrier injection efficiency, and light extraction efficiency. This is achieved by combining an ABC‐model‐based fit of the current‐dependent external quantum efficiency together with calibrated Monte Carlo ray‐tracing simulations. A maximum radiative recombination efficiency between 50% and 60% is estimated for DUV LEDs grown on ELO and HTA‐ELO AlN/sapphire, whereas the values for devices grown on HTA AlN/sapphire are around 45%. The extracted radiative recombination efficiency does not scale with the measured threading dislocation density (TDD), even when accounting for the inhomogeneous TDD in the AlN base layers. This discrepancy is attributed to the formation of dislocation half‐loops introduced by additional compressive strain caused by the HTA process and may result in the formation of additional nonradiative recombination centers in the AlGaN multi‐quantum well region. In addition, the carrier injection efficiency values ranging from 45% to 55% are determined for devices grown on all three templates.

Modeling of the Electrical Characteristics and Degradation Mechanisms of UV-C LEDs

“…All the details are reported in TABLE 1. The recombination coefficients of radiative, SRH and Auger-Meitner rates are set at 2 × 10 −10 cm 3 /s, 2 × 10 7 s -1 and 1 × 10 −30 cm 6 /s respectively, based on typical values found in the literature for similar devices [20][21][22][23]. An additional shunt resistance was added to the model to consider the impact of parasitic conduction paths at very low voltages [24], that show an ohmic behavior [25,26] whereas a discrete series resistance was added to reproduce additional nonidealities of the contact, buffer layers or partial activation of doping [30] not considered by our simulation framework.…”

Investigation of degradation dynamics of 265 nm LEDs assisted by EL measurements and numerical simulations

“…To support this hypothesis, we mathematically reproduced the EQE curves of the QW14 device from the L-I characterization , where q was the elementary charge, V the volume in the active region and I the current in the device. We chose the non-radiative (A), bimolecular (B) and Auger-Meitner (C) coefficients and the injection efficiency η inj by starting from typical values reported in the literature for similar devices [26][27][28] and by reasonably adjusting them to fit the curves. The fitted curves reported in figure 6(b) were obtained by fixing the B and C coefficient, finding the values of A and η inj that best fit the experimental curves at 0 min and by changing these latter two parameters to also fit the curve at 20 000 min.…”

Degradation of AlGaN-based SQW UV-C LEDs investigated by capacitance deep level transient spectroscopy

“…The devices under test are grown by metal organic vapor phase epitaxy (MOVPE) on epitaxially laterally overgrown (ELO) AlN/sapphire template with a threading dislocation density of 1.6x10 9 cm -2 [10]. Above this, after a series of adapting buffer layers [11], a 200 nm n-contact layer in Al0.65Ga0.35N Si-doped (Nd = 4E18 cm -3 ) was grown. It is followed by the first barrier layer in Al0.63Ga0.37N (Si: 5E18 cm -3 ), a 1.4 nm Al0.48Ga0.52N SQW, a 10 nm last barrier layer in Al0.62Ga0.38N (undoped), and a 10 nm undoped Al0.80Ga0.20N interlayer.…”