Weak and strong localization in low-dimensional semiconductor structures.

The dependence of the localization length on the number of occupied subbands $N$ in low-dimensional semiconductors is investigated. The localization length is shown to be proportional to the number of occupied subbands in quasi-one-dimensional quantum wires while it grows exponentially with $N$ in quasi-two-dimensional systems. Also a weak localization theory is developed for large N with a well-defined small expansion parameter $1/N$. The temperature dependence of the conductivity deduced using this perturbation theory agrees with the experimentally observed dependence.