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We identify a quantum well internal high density Augerlike loss process as the origin of the so called ‘droop’ of internal quantum efficiency (IQE) in InGaN based light emitters. The IQE of such a device peaks at small current densities and then monotonously decreases towards higher currents. The origin of this ‘droop’ has been widely discussed recently and many possible mechanisms have been proposed for explaining the effect. We compare temperature and carrier density dependent electroluminescence and photoluminescence measurements of a green emitting single quantum‐well (SQW) LED over a wide parameter range. The carrier‐density as well as temperature dependence of efficiency is identical in both measurements, indicating that the decrease is due to a high density quantum‐well internal loss process. The data can be accurately modeled assuming an Auger‐like loss process with C = 3.5 × 10–31 cm6s–1. We suggest phonon‐ or defect‐assisted Auger recombination as the origin of this loss‐channel. The high current performance can be improved if a thick InGaN SQW or a multi quantum‐well (MQW) is used. This is in very good agreement with theoretical simulations (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

1 Introduction The performance of commercial LEDs has improved tremendously over the past few years. Today commercial LEDs cover the entire spectral range from UV to IR. The brightness of InGaN-LEDs has been increased by more than an order of magnitude over the last 10 years. Internal Quantum Efficiencies (IQE) of 75% with corresponding wall plug efficiencies (WPE) above 50% have been demonstrated for blue LEDs [1]. The OSRAM Opto Semiconductors ThinGaN-technology has pushed the Light Extraction Efficiency (LEE) of LED chips beyond 80%. Thin GaN technology also provides scalability of LED chips: LED brightness and efficiencies can be scaled to larger chip areas without losses. However, the InGaN Internal Quantum Efficiency is neither independent of the energy gap (or emission wavelength) nor of the current density: while IQE of more than 75% can be achieved for blue InGaN LEDs (440 nm, 50 A/cm 2 ) the IQE drops to less than 40% for green InGaN LEDs (540 nm, 50 A/cm²). At high current densities this efficiency loss even worsens especially for long wavelengths ("droop"). Pushing InGaN-LEDs towards red emission, the IQE drops dramatically below 10%. For wavelength above 580 nm the InGaAlP material system provides very efficient yellow, amber and red LEDs. In the wavelength range between 500 nm and 580 nm, InGaAlP LEDs are not efficient anymore due to weak carrier confinement.

GaN ( 1 1 ¯ 00 ) cleavage surfaces were investigated by cross-sectional scanning tunneling microscopy and spectroscopy. It is found that both the N and Ga derived intrinsic dangling bond surface states are outside of the fundamental band gap. Their band edges are both located at the Γ¯ point of the surface Brillouin zone. The observed Fermi level pinning at 1.0 eV below the conduction band edge is attributed to the high step and defect density at the surface but not to intrinsic surface states.

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