To cite caret in publications use:

  Kuhn, M. (2008). Building Predictive Models in R Using the caret
  Package. Journal of Statistical Software, 28(5), 1–26.
  https://doi.org/10.18637/jss.v028.i05

A BibTeX entry for LaTeX users is

  @Article{,
    title = {Building Predictive Models in R Using the caret Package},
    volume = {28},
    url = {https://www.jstatsoft.org/index.php/jss/article/view/v028i05},
    doi = {10.18637/jss.v028.i05},
    number = {5},
    journal = {Journal of Statistical Software},
    author = {{Kuhn} and {Max}},
    year = {2008},
    pages = {1–26},
  }