Time-periodic flows of electrons and holes in semiconductor devices

The main purpose of this paper is mathematical analysis on time-periodic flows of electrons and holes in semiconductors. The flows appear in a situation that alternating-current voltages are applied to devices. In this paper, we study the drift-diffusion model for semiconductors in a three-dimensional bounded domain and investigate the existence and stability of time-periodic solutions. We first derive uniform-in-time estimates of time-global solutions and then prove by the relative entropy method that the difference of any two solutions decays exponentially fast as time tends to infinity. These facts enable us to show the unique existence and global stability of time-periodic solutions.