Theoretical investigation of carrier capture and escape processes in cylindrical quantum dots

Abstract

In order to optimize the design of various optoelectronic devices utilizing quantum dots (QD), we must better understand the properties of carrier capture and escape times in these systems. Some of the properties of cylindrical quantum dots were studied. The wavefunctions and eigenenergies of a cylindrical quantum dot were approximated by a product of solutions of an infinite cylinder and a quantum well. It was assumed that the majority of transitions are caused by absorption/emission of polar optical phonons, and Fermi's golden rule was applied to calculate the transition rates to and from the QD. We have restricted our calculations to one-phonon (first order) processes only. We determined the carrier capture and escape times as a function of the size of the QD and carrier density. We have shown that the smallest capture times are achieved if the QD has only one quantum level. A short capture time is also achieved for a low carrier density. Similarly, the capture time has the smallest value when the QD has only one quantum level. The dependence of the carrier escape time for a fixed dot dimension shows a minimum as a function of carrier density. For small QDs, the capture and escape times are approximately independent of carrier density.