Influence of GaAs Substrate Orientation and Multi-Stacking InAs/InGaAs Quantum-Dot Layers on Intermediate Band Solar Cells: An Optical Study

In this work we present an optical study of InAs/InGaAs quantum dots (QDs) solar cells (SCs) deposited by molecular beam epitaxy on GaAs substrates with (11N)A orientation. Five stacks of InAs/InGaAs/GaAs QDs heterostructures are inserted in the intermediate region to enhance the SC photoabsorption. InAs/InGaAs (11N)A QDs SCs were investigated by spectroscopic ellipsometry (SE). To compare results, a reference GaAs SC is deposited with similar structure as InAs QDs SCs but without intermediate QDs layers. From SE analysis, optical constants are extracted, and transition energies are computed and identified. The two mean peaks, that appeared in the SCs dielectric function spectra at ∼2.8 and ∼4.4 eV, are assigned to the E1 and E2 critical point of GaAs and InAs, respectively. Other optical parameters such as the surface energy, volume energy losses functions and reflection loss were also calculated. The losses functions and reflection loss factors of the two InAs QDs SCs show different behaviors when the photon energy varies. Both effects of substrate orientation and InAs/InGaAs QDs intermediate layers are investigated. The results demonstrate the impact of substrate surface orientation and staked InAs QDs layers in the SC intermediate region on the optical parameters which in turn affect the SC efficiency.