Observation of in-plane polarized intersublevel absorption in strongly coupled InGaAs/GaAs self assembled quantum dots

We present a mid-infrared absorption study of an n-i-n structure containing two planes of strongly coupled Ln_0.5Ga_0.5As self assembled quantum dots. We find that the dominant absorption occurs for light polarized in the growth plane (TE-polarized), contrasting with uncoupled dots which exhibit predominantly TM-polarized absorption in the same energy range. Our measurements suggest that uncoupled dots grown under the same conditions as the coupled dots contain one bound (s-like) electron level. By coupling the dots the confinement length in the growth direction (z) is increased, lowering the energy of the s-like ground state and binding additional p_x,y-like excited states. A significantly increased normal incidence photocurrent sinal is measured for the sample containing coupled dots, relative to samples containing up to 30 layers of uncoupled dots, confirming the enhancement of the normal incidence absorption.