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Current density impact on the emission behavior of GaN-based blue emitting LEDs in the temperature range of 4.2–400 K



Blue emitting GaN-based light emitting diodes (LEDs) show a distinct spectral behavior with respect to temperature and injection current density. Operating LEDs with short current pulses of 500 ns provides a steady state situation, which allows investigating the emission behavior of LEDs at a certain device temperature thereby maintaining thermal equilibrium. The LEDs were examined in a temperature range between 4.2 and 400 K and in a current density range between 2 and 50 A cm−2. Low temperature investigations showed a blue shift of the electroluminescence spectra (EL) with respect to junction temperature, which is assigned to the radiative recombination of localized excitons. In the elevated temperature region a distinct red shift due to energy gap shrinkage was observed. Further, we expect an exciton lifetime reduction at 4.2 K. Additionally, the influence of the driving parameters (pulse injection current or direct current (DC)) in the presence of piezoelectric fields is discussed and separated into band filling effect and occurrence of fields, which screen the quantum confined Stark effect. Low temperature investigations indicate that band filling is mainly responsible for the blue shift of the EL spectra with respect to the injection current.