Is LDR as a semiconductor device?

Yup, semiconductors are perfect for this kind of application.

Is that made Intrinsic semiconductors or extrinsic (Impure) semiconductor?
I thing Intrinsic semiconductors.

Either will do the job. Extrinsic semiconductors will generally have a lower bandgap, and so will respond to light of a lower energy. Whereas intrinsic semiconductors will not respond until the photons reach a specific energy to excite electrons across the bandgap.

Thanks