Voltage-tunable group delay of an electron wave packet through a single quantum potential well

It is shown that the group delay of an electron wave packet through a potential well can be either negative or positive and is tunable by finite electric fields. The group delay depends not only on the width of potential well and the incident energy, but also on the electric field strength. It is also proved that the transmission time and reflection time for two propagation directions satisfy reciprocal relation, resulting from the time reversal invariance in quantum mechanism.