The left side of the junction is N type and the right side of the junction is P type.
Is the bold part an adjective phrase and optional?
For you to be able to omit the phrase, there has to be no chance the reader/writer could substitute anything else. This depends on the preceding sentences and context.
If you haven't written/spoken about anything else that can have N/P type on the left/right side in the last few sentences, omitting "of the junction" at that point should be OK, the user will asasume you are still talking about the "junction."
If there is any doubt and you are writing something for technical users, include it. You will never be incorrect by including it.