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The recombination rate coefficients (RRCs) A, B, and C in MOVPE‐grown single‐quantum‐well light emitting diodes spanning the entire blue‐green spectral range are determined by fitting efficiency curves and differential carrier lifetimes. The results show definite trends for each of the RRCs: A tendentially decreases with increasing wavelength, B definitely decreases, and C remains approximately constant. Therefore, the increase of the droop with increasing wavelength (the green gap problem) is rather due to the decrease of B than an increase of C. The determined values of C are shown to be similar to what has been predicted by others with first‐principles computer simulations accounting for phonon‐assisted Auger recombination. Samples grown on sapphire and silicon substrates are compared and show significant differences only for the RRC A, presumably due to the difference in threading dislocation density.

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.

Metastable GaAs1−ySby with 0.22<y<0.70 has been grown pseudomorphically strained on (001) InP substrates using metalorganic chemical vapor deposition. The Sb concentration and layer thicknesses, ranging from 24 to 136 nm, were determined by high resolution x-ray diffraction (HRXRD) measurements. Low-temperature photoluminescence (PL) spectroscopy revealed spatially indirect band-to-band emission of electrons localized in the InP and holes in the GaAs1−ySby. At increased excitation power densities samples with layer thicknesses above 65 nm showed, also, spatially direct PL across the band gap of the strained GaAs1−ySby. From the PL data the band gap energy and the band offsets of GaAs1–ySby relative to InP were derived and compared with the predictions of the Model Solid Theory.