Temperature effects on optical properties and efficiency of red AlGaInP-based light emitting diodes under high current pulse pumping

In this paper, current-dependent emission spectra and efficiency measured on the same AlGaInP red light-emitting diode (LED) pumped with the current pulses of very different durations are recorded. This enabled for the first time distinguishing between high-carrier concentration and self-heating effects on the efficiency decline at high current magnitudes. The electron leakage to the p-side of the LED structure, which is the major mechanism of the efficiency reduction, is found to rise substantially when the device self-heating starts to develop. As a result, in comparison to continuous-wave excitation, driving the LED with sub-microsecond current pulses allows suppressing the device self-heating and, eventually, increasing the operating current by an order of magnitude without noticeable efficiency losses. Based on the reduced ABC-model, neglecting Auger recombination, the light extraction efficiency, injection efficiency, and internal quantum efficiency of the LED are estimated, suggesting light extraction to be the most critical factor for the overall efficiency of the LED. The coupled spectral/power LED characterization using the variable-duration current pulse pumping is found to be an effective approach for analyzing mechanisms of the device operation

AlGaInP red-emitting light emitting diode under extremely high pulsed pumping

Efficiency of commercial 620 nm InAlGaP Golden Dragon-cased high-power LEDs has been studied under extremely high pump current density up to 4.5 kA/cm2 and pulse duration from microsecond down to sub-nanosecond range. No efficiency decrease and negligible red shift of the emission wavelength is observed in the whole range of drive currents at nanosecond-range pulses with duty cycles well below 1%. Analysis of the pulse-duration dependence of the LED efficiency and emission spectrum suggests the active region overheating to be the major mechanism of the LED efficiency reduction at higher pumping, dominating over the electron overflow and Auger recombination