Generating list of all binary strings of size 2n, where the number of 1s in the first n bits equals the number of 1s in the last n bits

Question

For example, given input n=2, I want the output to be [\'1111\', \'1001\', \'0110\', \'0000\', \'0101\', \'1010\']. Note that the order of the output does not matter.