Hi Melanie,
Thank you for posting your question. Would you mind sharing more info about your project (unfortunately uploading the file itself is not an option)? Specifically, the objects tree, materials used, mesh settings (in solver and/or any local added mesh objects), and the advanced settings in the solver. Also, what version of Lumerical are you using?
Obtaining convergence for large band-gap "semiconductor" materials is certainly more challenging. I would do my best to provide suggestions based on the information you can share.
Best regards,
Khash
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