Long mean free path of hot electrons selectively injected to higher subbands

The long hot-electron mean free path observed by Sivan, Heiblum, and Umbach in high-mobility 2D electron-gas heterostructures is explained by electron transport in the second subband. Our estimates show that the mean free path in the second subband is longer by 2 orders of magnitude than that in the first subband. New magnetic-focusing measurements reveal hot-electron velocities lower than the Fermi velocity, as expected for a higher-subband transport. The electrostatic potential near a biased constriction used as the hot-electron injector is shown to induce nonadiabatic intersubband transfer.