Thanks for your answer. I usually use Hall measurements for GaN thinfim but for GaN nanowires it is not easy to do Hall measurements. Is there any technique developed for nanowires Hall measurements? Will you please guide me about that?

Thanks alot sir for your great answer 

I can also add to the suggestions, donor acceptor pair (DAP) recombination and acceptor bound exciton PL emission lines are affected by the p-type doping of the layer and so could be a good measure of whether your layer is p-type doped. 

Thanks for your answer sir. Here i would like to add a comment, Is this phenomena same even nanowires having diameter less than 30 nm?

Sure. I don't think that this will depend on size of your nanostructure (assuming you have similar doping concentrations) unless you have very low density of nanowires which could reduce the total PL intensity for a given laser spot size. This, which depends on your pitch size, may affect the intensity of all your emission lines including ABE and DAP