As thin Si quantum wells with oxide barriers have become an experimental reality in silicon-on-insulator technology, we discuss the feasibility of a terahertz laser based on an intersubband transition in such a Si quantum well. Electrons tunnel into an upper two-dimensional subband from a thin polysilicon gate through an ultrathin tunneling oxide and are extracted laterally from the Si well by diffusion. Population inversion arises because lateral diffusion to the contacts can be a faster process than intersubband relaxation and also because the in-plane diffusivity in the upper subband is suppressed by the interaction with a nearby subband characterized by a heavy in-plane mass. Thick oxide layers provide optical confinement and the main optical loss mechanism is the weak free-carrier absorption in thin doped regions in the polysilicon gate and substrate. A voltage on the substrate may provide some tunability of the gain peak.
ON THE POSSIBILITY OF AN INTERSUBBAND LASER IN SILICON-ON-INSULATOR
