Khashayar Ghaffari
Ansys Employee

Hi, 

Thank you for reaching out. The error will happen if the carrier density in the quantum wells is above certain level. The assumption is that the coupled mode will be used only for EAM application where device is reverse biased so the density in quantum wells is very small. There could be doping, but if it is too close to the wells or if the device operates in forward bias there could be the error. We will keep you updated for any future updates for forward bias operations e.g. for lasers or LEDs.