electricity to pole barn

Longtime lurker, have learned TONS of information in this forum. Thank you. I will be installing underground elec. service from my house 200 amp panel to my polebarn 100 amp panel 170 Ft. away. Wiring will be in 2 inch Sched. 40 PVC conduit buried 24 inches deep under a gravel driveway.

My question is about what aluminum wiring to use. I know from the elec. calculators that I need 1/0 wire for the two hots and the neutral. What size alum. ground wire do I need?

Next question- I can get several different kinds of aluminum wire for underground use.They all cost about the same.

They are: XLP/USE-2/RHH-RHW2 (single conductor)
or
XHHW-2 (single conductor)
or
Quadruplex Underground Secondary Distribution Cable size 1/0, 1/0, 1/0, &#2 A #2 alum. ground wire for my setup seems to be too large according to the online elec. calculators

Which wire should I get?

For 100A the ground needs to be at least #6 AL. Don't use Quadruplex URD because it's only rated for outside use, it is not to be installed inside the structure. Stick with the XLP/USE/RHH-RHW or the XHHW.