Resonance effect in inter-sub-band transitions of single quantum wells

Inter-sub-band transitions between electronic states of a single quantum well are considered. In such a double heterostructure a longitudinal polar optical mode emitted or absorbed in any transition can belong to one of a finite number of distinct branches. The transition rate is calculated here using fully quantum mechanical methods and its variation with the width of the well is explored. It is found that besides the familiar increase with increasing width of the well, the rate exhibits periodic peaks. These constitute a resonance effect which arises whenever the conditions of incorporating a new polar branch are satisfied. Illustrations are given specifically for GaAs/Ga 0.7 Al 0.3 As single quantum wells.