Seite - 187 - in Photovoltaic Materials and Electronic Devices

TowardsInAs/InGaAs/GaAsQuantumDot SolarCellsDirectlyGrownonSiSubstrate BilelAzeza,MohamedHelmiHadjAlouane,BouraouiIlahi,GillesPatriarche, LarbiSfaxi,AfifFouzri,HassenMaarefandRidhaM’ghaieth Abstract: This paper reports on an initial assessment of the direct growth of In(Ga)As/GaAs quantum dots (QDs) solar cells on nanostructured surface Si substrate by molecular beam epitaxy (MBE). The effect of inserting 40 InAs/InGaAs/GaAs QDs layers in the intrinsic region of the heterojunction pin-GaAs/n+-Si was evaluated using photocurrent spectroscopy in comparison with pin-GaAs/n+-Si and pin-GaAs/GaAs without QDs. The results reveal the clear contribution of the QDs layers to the improvement of the spectral response up to 1200 nm. The novel structure has been studied by X ray diffraction (XRD), photoluminescencespectroscopy(PL)andtransmissionelectronmicroscopy(TEM). These results provide considerable insights into low cost III-V material-based solarcells. ReprintedfromMaterials. Citeas: Azeza,B.;Alouane,M.H.H.; Ilahi,B.;Patriarche,G.; Sfaxi, L.; Fouzri, A.; Maaref, H.; M’ghaieth, R. Towards InAs/InGaAs/GaAs QuantumDotSolarCellsDirectlyGrownonSiSubstrate.Materials2015,8,4544–4552. 1. Introduction Recentattemptshavebeenmadeto increasesolarcell efficiencybyexploiting the below band gap photon energies. This approach is often termed as impurity bandsolarcellsor intermediatebandsolarcells (IBSC) [1–4]. This typeofstructure demonstrates an enhancement of the spectral response towards lower photon energies with promising possibilities to improve the solar cell’s efficiency up to 63% according to theoretical expectation [5–8]. However, the main problem encountered for III-V element-based solar cells mainly lies in the development of large surface photovoltaic structures due to their high cost, making the employment of low cost substrates highly desirable. Accordingly, the epitaxial growth of the GaAs layer on Si substrate has attracted considerable attention owing to their large area availability, low cost and high mechanical strength [9–14]. Promising InAs/GaAs QD-based optoelectronicdevices, directly grownon Si substrate,have already been reported [15–20]. In the meantime, with the exception of the employment of the bonding technique[21], the feasibilityof the direct growth of InAs/GaAs QDssolar cellsonSi substratehasnotyetbeenexplored. In this context, this paper reports, for the first time, on the effect of inserting InAs/InGaAs/GaAs multiple QDs layers within the pin-GaAs structure directly 187