Energy relaxation process in a quantum dot studied by DC current and pulse-excited current measurements

Energy relaxation from an excited to a ground state in a quantum dot is stu died by DC current and pulse-excited current measurements. We find that all the excited states can be classified as short-lived or long-lived excited states, although they are too short or too long for us to determine the act ual lifetime with our method. The relaxation time is short (less than a few ns) if the transition takes place by means of electron-phonon interaction, while it is very long (more than a few mus) if the transition involves a s pin-flip. The crossover between long and short relaxation time is studied a t a particular level crossing. (C) 2001 Elsevier Science B.V. All rights re served.