Looking for quick growing trees or hedges for privacy?

You can use bamboo but you had better put it in some kind of raised bed with a defined border that its roots can't cross. It will take over.

What is your location and lighting?

Clumping bamboo doesn't produce runners and so is not very invasive. It was my choice when deciding on a quick growing outdoor privacy screen.

I planted Privet a couple of years ago along our fence about every two feet. It has grown to about 10 feet tall and is evergreen so we have privacy and shade. I keep the bushes trimmed so they don't encroach into the yard thereby growing taller not wider.

Knock out roses will make a very pleasant hedge.