Mathieu Deflem has uploaded an interesting chapter on
"The Legal Theory of Jürgen Habermas"
Between the Philosophy and the Sociology of Law
The chapter is published in "Law and Social Theory", ed. by Reza Banakar and Max Travers (Hart Publishing, 2nd ed. 2013).
Mathieu Deflem is Professor of Sociology at the University of South Carolina. He is the editor of "Habermas, Modernity and Law" (Sage, 1996). Available as pdf copy here.