Abstract
External quantum efficiency of industrial-grade green InGaN light-emitting diodes (LEDs) has been measured in a wide range of operating currents at various temperatures from 13 K to 300 K. Unlike blue LEDs, the efficiency as a function of current is found to have a multi-peak character, which could not be fitted by a simple ABC-model. This observation correlated with splitting of LED emission spectra into two peaks at certain currents. The characterization data are interpreted in terms of non-uniformity of the LED active region, which is tentatively attributed to extended defects like V-pits. We suggest a new approach to evaluation of temperature-dependent light extraction and internal quantum efficiencies taking into account the active region non-uniformity. As a result, the temperature dependence of light extraction and internal quantum efficiencies have been evaluated in the temperature range mentioned above and compared with those of blue LEDs.
Highlights
Semiconductor light-emitting diodes (LEDs) invented almost 100 years ago [1] have become key components in numerous applications: solid-state lighting, traffic lights, brake lights, various indicators, and signs [2,3].For many cases and, especially, for phosphor-free solid state lighting, high-efficiency green LEDs are of primary importance
Since the measured two-peak external quantum efficiency (EQE) dependencies shown in Figures 4 and 5 could not be approximated with a simple ABC-model, a new approach was developed for evaluation of internal quantum efficiency (IQE) and light extraction efficiency (LEE) of the green LED
The observation could be interpreted in terms of the active region non-uniformity, assuming co-existence of at least two sub-regions emitting at different wavelengths and having different radiative efficiencies
Summary
Semiconductor LEDs invented almost 100 years ago [1] have become key components in numerous applications: solid-state lighting, traffic lights, brake lights, various indicators, and signs [2,3]. A new level of external quantum efficiency (EQE), is achieved from commercial green LEDs: ~34% for directly emitting devices and ~54% for those using internal down-conversion of emitted light, see for example [4] that gives an overview of the external efficiency of different LED material systems of Osram OS. EQEs of the green-emitting multiple quantum wells reported in [7,8] for a wide temperature range of 4–300 K did not exhibit a dome-like dependence on current, demonstrating more complex behavior that could not be fitted by a simple ABC-model. Our data obtained with commercial true-green LEDs demonstrate non-ordinary variation of the emission wavelength with current and considerable deviation of EQE from a simple ABC-model. The ABC-model modified for non-uniform QWs allow us to estimate the temperature-dependent LEE
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