Hello, I am a new learner of Silvaco Atlas. I am currently conducting a simulation to study the effect of fixed charges in the passivation layer while working with AlGaN/GaN HEMTs. However, even after studying the Atlas manual, I couldn’t find a way to define fixed charges throughout the entire passivation layer—only options to define them at interfaces. How can I assign fixed charges to the entire passivation layer itself? Or is it acceptable to define them at the interface instead? I would greatly appreciate your guidance on this question.