@ahmeddabak - Or instead of using DB, you could just the the eloquent model to begin with, that way created_at is already casted to Carbon. Why have the model if you're not even going to use it?
There is probably an underlying reason why the OP wants to use the query builder in preference to Eloquent, and why the OP needs the dates as Carbon instances. Maybe, if we knew these reasons, we could better suggest a solution.
I feel like sometimes i reach the limit of Eloquent and im just better of going DB way.
Like doing more complex joins also aliasing tables. Filtering data on joined tables so on.
As my query is behinde a Repository layer i can parse all my data fileds in the all() or paginate() function of my Repo.