Modeling the spectral shape of InGaAIP-based red light-emitting diodes

摘要

We have developed a spectral model for describing the shape of the emission spectrum of InGaAIP-based red light-emitting diodes (LEDs) with quantum-well structure. The model is based on Maxwell-Boltzmann distribution with junction temperature T_j and an experimental two-dimensional joint density of states (DOS). We model the DOS with a sum of two exponentially broadened step functions describing the two lowest sub-bands in semiconductor quantum well. The relative locations ΔΕ_1 =0meV and ΔΕ_2 = 112.7meV above the band gap energy E_g= 1.983 eV and the ratio 2.13 of the step heights were fixed using an experimental DOS extracted from a LED spectrum measured at known T_j and driving current I. The model can then be fitted to other spectra of other LED samples at varied T_j and / by varying the fitting parameters E_g, T_j, and the broadening of the sub-band edges. The model was tested for three LED samples over I = 200-370 mA and T_j = 303-398 K. Junction temperatures obtained by modeling were compared with calibrated T_j obtained by the forward voltage method. The mean absolute difference was about 2.9 K (0.8%) over the whole region studied and the maximum difference was 8.5 K. The thermal coefficient measured for E_g was -0.509 meVK~(-1). For the first and second sub-band edges, the thermal broadening coefficients were 18 μeVK~(-1) and 37 μeVK~(-1) respectively.