Thermodynamic analysis of GaInN-based light-emitting diodes operated by quasi-resonant optical excitation

Abstract

In this study, we aim to understand the thermodynamics inside the junctions of GaInN-based LEDs through optical operation of the device (the wavelength of the pumping laser is 405 nm for quasi-resonant optical excitation). First, to achieve this goal, the short-circuit current vs the open-circuit voltage curve and photoluminescence spectrum are carefully analyzed and compared with the current–voltage curve and electroluminescence spectrum. By this comparative study, we experimentally demonstrate the electrical–optical energy conversion efficiency (ECE) > 100% under optical excitation. Second, the intra-band phonon absorption and emission inside and/or outside the junction (PPeltier and PHC) are investigated through the power-loss analysis. In so doing, we ascertain that the carriers in the multiple quantum wells are energized by phonons, which introduces the ECE > 100%. Specifically, after the energization, the Boltzmann carrier distribution is no longer controlled by the ambient lattice temperature but by higher temperature, namely, that of the carriers themselves. Based on the analysis, we propose a thermally enhanced effective temperature for the Boltzmann distribution. Finally, we compare the junction efficiency by photoluminescence (PL), composed of the internal quantum efficiency by PL and the ECE by PL, of the sample at various temperatures to investigate the effect of PHC on the overall PL efficiency.