iPhone external compact microphone?

I am looking for an iPhone external compact microphone to record my instructor lectures for during class. I would like to find one that would work well with my iPad as well. Do they make this accessory? I can not seem to find it. If so could you give me some links?

I would prefer to find a wireless bluetooth microphone that was sensitive enough to lay on the lecture table near the instructor if they make something like this!

Thanks

I've recorded lectures just with the microphone on my iphone and it worked fine. I just left the phone on my desk.