As already explained by @ Rayees, Doping leads to the change in lattice parameter which cause a shift in the peak positions. But more important thing to notice is which element you are adding and in how much amount. Because I don't think that a few ppm of doping element (of almost same atomic size) will make a detectable change in the peak positions. For reliable measurements the change caused by the doping must be sufficiently larger than the measurement errors of your instruments.

As explained well by both Rather and Yadav, doping effects only on physical properties in materials, semiconductors in particular such as optical and electrical properties. Doping have a very low concentration in the materal which doesn’t have any effect to show in the X-ray data

Successful incorporation of the dopant in the host lattice may cause lattice strain. This strain may cause shifting towards higher or lower 2 theta of the doped sample as compared to the un-doped one. Therefore, peak shifting can be used as a good indicator to confirm the successful incorporation of the dopant in the host lattice (up to its solubility limit). Please, check out my recent published paper for more detail information.

With the displacement of the peaks compared to undoped material peaks.

You can compare the shift in peak positions of doped samples with the undoped one. If the doping is with low wt% of materials say noble metals then you can not observe any peak shift.