What are the steps for the LQ decomposition of a tall matrix

Question

I need to write an R function that decomposes a rectangular $6 \times 4$ matrix into $6\times 4$ lower triangular L matrix and an orthogonal Q matrix, however I can't seem to find any information on the steps I need to apply. What I found is a work around, i.e apply a QR decomposition on the transpose of A, but in this case A will become a fat and I believe QR works for tall matrices. The function I try to mimic is the lq() function from the tensr package in R, but this function uses some C++ functions that are hidden and I need them to not be like that. Thanks in advance.