  Efficiency at maximum power (EMP) is a very important specification for a
heat engine to evaluate the capacity of outputting adequate power with high
efficiency. It has been proved theoretically that the limit EMP of
thermoelectric heat engine can be achieved with the hypothetical boxcar-shaped
electron transmission, which is realized here by the resonant tunneling in the
one-dimensional symmetric InP/InSe superlattice. It is found with the transfer
matrix method that a symmetric mode is robust that regardless of the
periodicity, and the obtained boxcar-like electron transmission stems from the
strong coupling between symmetric mode and Fabry-P\'erot modes inside the
allowed band. High uniformity of the boxcar-like transmission and the sharp
drop of the transmission edge are both beneficial to the maximum power and the
EMP, which are optimized by the bias voltage and the thicknesses of barrier and
well. The maximum power and EMP are extracted with the help of machine learning
technique, and more than 95% of their theoretical limits can both be achieved
for smaller temperature difference, smaller barrier width and larger well
width. We hope the obtain results could provide some basic guidance for the
future designs of high EMP thermoelectric heat engines.
