ROLE OF INTERFACES AND HYDROGEN SUBSURFACE REACTIONS IN THE MICROSTRUCTURAL AND OPTICAL MODIFICATIONS OF CRYSTALLINE SILICON BASED HETEROJUNCTIONS BY SPECTROSCOPIC ELLIPSOMETRY

摘要

In this work, we discuss the use of spectroscopic ellipsometry,which is a non-invasive and non-destructive technique with a sub-monolayer resolution, to study the structural modifications induced by hydrogen subsurface reactions in c-Si/a-Si:H/ITO heterostructures for solar cells. The samples have been prepared by e-beam deposition of an indium tin oxide (ITO) film on PECVD grown c-Si/a-Si:H heterojunctions. In this process, the c-Si/a-Si:H interface can be modified by hydrogen subsurface reactions during the initial stage of the a-Si:H film deposition, and the structural damage of this interface is enhanced during the post-annealing treatment of devices, which activates the out-diffusion of hydrogen from the a-Si:H layer into the underlying c-Si substrate. The hydrogen diffusion also causes a roughening of the a-Si/ITO interface and a decrease of the transparency and conductivity of the ITO film itself.