Self-heating and athermal effects on the electroluminescence spectral modulation of an AlGaInP light-emitting diode

We report on the investigation of electroluminescence (EL) modulation depth as a function of photon energy in a high-power double-heterojunction AlGaInP light-emitting diode (LED). At low frequencies, the modulation spectrum exhibits the features as follows: (i) a dip at the photon energy close to the EL spectrum peak; (ii) an almost wavelength-independent modulation enhancement in the long-wavelength wing of the EL spectrum; and (iii) a linear increase of the modulation depth with photon energy in the short-wavelength wing of the EL spectrum. With increasing modulation frequency, these features diminish but do not disappear. A model, which quantitatively accounts for the experimental data has been introduced. At low frequencies, the spectral modulation features are due mainly to the modulation of EL efficiency, bandgap energy and the carrier distribution function caused by the oscillation of junction temperature. In the high-frequency limit when the oscillation of junction temperature fades, the spectral modulation features can be understood in terms of asymmetrical EL band broadening due to athermal many-body effects. The investigation of spectrally resolved EL modulation was shown to be applicable for the estimation of small (similar to 0.1 K) junction temperature oscillation and thermal relaxation time constants of LEDs emitting due to band-to-band recombination of free carriers. (C) 2011 American Institute of Physics. [doi:10.1063/1.3643005]