how to test p-type Gallium nitride, GaN, resistivity

[nanoou]

I am wondering if anyone can give me any suggestions on how to test a GaN structure. The structure is composed of a 100nm p-type GaN layer, larger 1 micron p-type GaN layer, then buffer layer, then substrate. The first layer, 100nm, and the second layer, 1 micron, are both GaN but have different dopent levels and as such different resistivity. I am looking to measure the resistivity of the 100nm layer only. I am aware I can do this with hall effect or differential hall effect. However I am a student and trying to expand me knowledge. I have seen other semiconductor resistivity measured by C-V techniques, mostly n-type, but none have mentioned p-type GaN(Is this possible??). However, I would love to hear other techniques or suggestions. I dont need a full explanation just a point in the right direction. Thank you all in advance for your time and help.