Optical generation of picosecond electrical pulses in asymmetric quantum well structures placed in transverse magnetic field

Abstract

It has been shown1 that when a magnetic field is applied to the asymmetric quantum well (QW) structure in a direction perpendicular to the direction of growth, the transverse dispersion curves of the energy subbands in the conduction and valence bands shift by an amount proportional to the field strength and to the displacement of the center of gravity of the subband envelope function. It is shown in this work that optically excited carriers have asymmetrical distribution in k vector space and therefore they have finite drift velocity in the direction perpendicular to both growth direction and field direction. Depending on whether the external circuit is open or closed, that results in either voltage along the QW plane or the current in that direction. When the optical pulse is off, the voltage (current) decays with the time constant equal to that of intraband relaxation time, i.e., of the order of 1 ps or less depending on temperature. This may serve as a basis for future ultrafast detectors or as a tool for generation and study of hot carriers. Current sensitivity of the proposed device has been evaluated as a function of material, geometry, field, and other factors and found to be of the order of a few μA/W at 10-T magnetic fields.