Modeling the effect of spatial position and concentration of defects on optical degradation of InGaN/GaN multi quantum well light emitting diodes

This paper investigates the effect of the properties and position of defects on the performance and reliability of InGaN/GaN Multi Quantum Well (MQW) LED. To this aim, we analyzed color-coded structures featuring two quantum wells, emitting respectively at 405 nm and 495 nm.In order to evaluate the mechanisms that limit the reliability of the devices, a constant current stress at I=80 A/cm(2) and T=350K was carried out. From the degradation results, the electrical characteristics show an increment in the leakage current in the sub-turn on forward voltage regime compatible with a diffusion process. To interpret the measurement results, we implemented a simulation deck through Apsys Crosslight software, in order to model the effect that different trap concentrations and spatial locations have on the optical characteristics. The energy of the involved traps was derived by deep level optical spectroscopy analysis (DLOS). By comparing the simulation results with the experimental data, we observed that optical degradation is compatible with an increment of defect density in specific layers of the active region. Moreover, we found that the position of the traps (i.e. their proximity to the quantum wells or the EBL), modifies the band bending and influences the carrier density inside the wells, thus affecting the recombination rate and the peak emission wavelength. Therefore, we suggest that the optical degradation in MQW LED can be ascribed to a combined effect of defects with different spatial location.