A Unified Pervasive Linebroadening Function for Quantum Wells in Light Emitting Diodes

The broadening functions for quantum wells in LEDs and laser diodes below the lasing threshold are examined. Inhomogeneous and homogeneous broadening mechanisms are included. Hydrogen-atom-like exciton and the electron-hole plasma recombination models are considered. Material disorder and the Urbach tail are reviewed as the main reasons for the inhomogeneous broadening. Charge carrier scattering and relaxation times in the conduction and valence bands are examined as the origin for the homogeneous lifetime broadening. Two homogeneous lineshapes are compared using the momentum relaxation times obtained from the electron and hole mobilities available for GaAs. In addition to crystal disorder, the mutual collision of charge carriers in the quantum wells is examined as the reason for the relaxation time shortening. The analogy to pressure broadening in gases is used to combine the proper homogeneous and inhomogeneous broadening functions to a unified quantum well lineshape.

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Effect of Inhomogeneous Broadening in Ultraviolet III-Nitride Light-Emitting Diodes

Materials ◽

10.3390/ma14247890 ◽

2021 ◽

Vol 14 (24) ◽

pp. 7890

Author(s):

Friedhard Römer ◽

Martin Guttmann ◽

Tim Wernicke ◽

Michael Kneissl ◽

Bernd Witzigmann

Keyword(s):

Active Region ◽

Quantum Wells ◽

High Efficiency ◽

Light Emitting Diodes ◽

Inhomogeneous Broadening ◽

Aluminium Content ◽

Hole Density ◽

Free Hole ◽

Light Emitting ◽

The Impact

In the past years, light-emitting diodes (LED) made of GaN and its related ternary compounds with indium and aluminium have become an enabling technology in all areas of lighting. Visible LEDs have yet matured, but research on deep ultraviolet (UV) LEDs is still in progress. The polarisation in the anisotropic wurtzite lattice and the low free hole density in p-doped III-nitride compounds with high aluminium content make the design for high efficiency a critical step. The growth kinetics of the rather thin active quantum wells in III-nitride LEDs makes them prone to inhomogeneous broadening (IHB). Physical modelling of the active region of III-nitride LEDs supports the optimisation by revealing the opaque active region physics. In this work, we analyse the impact of the IHB on the luminescence and carrier transport III-nitride LEDs with multi-quantum well (MQW) active regions by numerical simulations comparing them to experimental results. The IHB is modelled with a statistical model that enables efficient and deterministic simulations. We analyse how the lumped electronic characteristics including the quantum efficiency and the diode ideality factor are related to the IHB and discuss how they can be used in the optimisation process.

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Understanding the Luminescence Characteristics of Ultraviolet InGaN/AlGaN Multiple Quantum Wells with Different In Gradients

Crystals ◽

10.3390/cryst11111390 ◽

2021 ◽

Vol 11 (11) ◽

pp. 1390

Author(s):

Jie Zhang ◽

Wei Liu ◽

Shuyuan Zhang

Keyword(s):

Quantum Wells ◽

Growth Direction ◽

Multiple Quantum Wells ◽

Multiple Quantum ◽

Peak Wavelength ◽

Electron Hole ◽

Light Emitting ◽

Luminescence Efficiency ◽

Valence Bands ◽

Luminescence Characteristics

The electroluminescence (EL) properties of InGaN/AlGaN ultraviolet light-emitting multiple quantum wells (MQWs) with identical average In content but different In gradients (In content increases linearly, along the growth direction) are investigated numerically. It is found that the luminescence efficiency is improved, and the EL spectral peak wavelength becomes longer for the MQW sample with a larger In gradient. Since the influence of In gradient is different for the conduction and valence bands in InGaN layers, the distribution of electrons and holes in QWs may be changed, leading to a redshift of EL spectra. In particular, when the In gradient increases, the overlap integral of electron-hole wavefunction in InGaN QWs increases, resulting in a higher radiative recombination rate and an enhanced EL intensity.

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