Formation of microcrystalline silicon layer for thin films silicon solar cells on aluminium substrates

Abstract

We investigated the formation of microcrystalline silicon (μc-Si:H) epitaxially grown on the polysilicon seed layer on the aluminium(Al) substrate using Electron cyclotron resonance plasma enhanced chemical vapor deposition method (ECR-PECVD). The μc-Si:H film serves as an active intrinsic absorber layer for a PIN configuration solar cell. A seed polysilicon (P+) layer was created by depositing amorphous silicon by ECR-PECVD method (using SiH4/Ar gases) directly on Al substrate followed by thermal annealing at 550°C resulting in a layer exchange. The μc-Si:H films was then deposited using a SiH4/H2 gas mix employing the same reactor. The optimization of deposition parameters was carried out on mono crystalline-Si wafers. The parameters which allowed to reaching the highest crystalline fraction of ∼ 65% are obtained for SiH4=4 sccm, H2=40 sccm and a deposition temperature of 480°C. The Raman spectroscopy was carried out on the deposited films to determine the crystalline fraction while the spectroscopic ellipsometry measurements were applied to get an insight on the optical constants of the deposited layers as well as on their thickness. X-ray diffraction (XRD) measurements were taken to identify the crystalline phase of the deposited film and surface morphologies of films were observed by scanning electron microscopy (SEM).