The new google dev policy says this is not a legit way to get downloads.
Source
https://play.google.com/about/developer-content-policy.html See under "App Promotion".
There are few ad networks that has these type of ads(popup, popunder redirect) which I won't mention(sorry) cuz there are not many.
I've already given you a clue so you may be able to find it now.
I am currently using this method to drive traffic to app install offers so you can ask questions if any.
Also one of the good converting offer was taken down as someone was caught using promoting using this method so CPA networks are really following the new G Play policies and banning the ones that are promoting using this.