Verification of a generalised Planck law by investigation of the emission from GaAs luminescent diodes

A generalisation of Planck's law for the spontaneous emission from light emitting diodes with direct band gaps allows a calculation of the absolute spectral emission intensity to be performed when the applied voltage, temperature, and absorption coefficient of the light emitting region are known. For given values of these parameters the emission intensity is independent of the diode current and the quantum efficiency of the recombination process. GaAs LED spectra calculated on this basis are compared with measurements at 82 K and at 296 K, and are found to agree quite well. Differences are attributed to the uncertain knowledge of the absorption coefficient of the diode material.