Intraband absorption in finite, inhomogeneous quantum dot stacks for intermediate band solar cells: limitations and optimization

摘要

We present a theoretical analysis of intraband optical transitions from theintermediate pseudo-band of confined states to the conduction band in a finite,inhomogeneous stack of self-assembled semiconductor quantum dots. The chain ismodeled with an effective Hamiltonian including nearest-neighbor tunnelcouplings and the absorption under illumination with both coherent (laser) andthermal radiation is discussed. We show that the absorption spectrum alreadyfor a few coupled dots differs from that of a single dot and develops astructure with additional maxima at higher energies. We find out that thisleads to an enhancement of the overall transition rate under solar illuminationby up to several per cent which grows with the number of QDs but saturatesalready for a few QDs in the chain. The decisive role of the strength ofinter-dot coupling for the stability of this enhancement against QD stackinhomogeneity and temperature is revealed.