Help: Silvaco atlas simulation question

[greenspring]

I am simulating the spectral responce of a SiC PN junction, the work is to illuminate light on the p-n bilayer. The result showed a peak on around 450 nm while I know in principle the peak should be at 350 nm. The material for the 2 layers is 4H-SiC, i'm using sopra=sic.nk for the refractive index. Can anybody give me any suggestion on where the mistake might be?

Thanks.