What to write in the email for sending PhD application to a research group's head? I am applying for a Ph.D. position in a research group. On the group's webpage, the leader of the group has asked to send him CV and Motivation Letter if someone is interested in a Ph.D. position.

I have prepared the documents, but I am wondering that what should I write in the email by which I will send him the documents? 

Should I write about why am I interested in his work?

Should I talk about my educational background?

Or just simply say "Dear Professor, Attachment is my application for Ph.D. position in your group?"
Your CV has your background. Hopefully you have written an SOP (Statement of purpose) giving your goals for grad study and beyond. In the email you can probably best help yourself writing about why you want to work with him, but make it honest and not too "over the top". But a bit more than just your last suggestion. How does this group fit your SOP? 

If he gets a lot of applications he will quickly sort them into two piles. You want to be in the pile for "further consideration".