%0 Journal Article
%T PECVD Silicon Nitride Passivation on Boron Emitter: The Analysis of Electrostatic Charge on the Interface Properties
%A Natalita M. Nursam
%A Yongling Ren
%A Klaus J. Weber
%J Advances in OptoElectronics
%D 2010
%I Hindawi Publishing Corporation
%R 10.1155/2010/487406
%X The dependence of surface recombination of boron diffused and undiffused silicon surfaces passivated with a-Si :H on the net charge density is investigated in detail. The films are deposited by plasma-enhanced chemical vapour deposition using a 2.45£¿GHz microwave remote plasma system. The surface charge density on the samples is varied by depositing charge using a corona discharge chamber. Excess carrier lifetime, capacitance-voltage, and Kelvin probe measurements are combined to determine the surface recombination velocity and emitter saturation current density as a function of net charge density. Our results show that the application of negative charge causes a substantial reduction in the surface recombination of samples with boron diffused emitters, even for high boron surface concentrations of £¿ . The significant difference observed in surface recombination between boron diffused and undiffused sample under accumulation implies that the presence of boron diffusion has results in some degradation of the Si-Si interface. Further, (111) oriented surfaces appear more sensitive to the boron surface concentration than (100) oriented surfaces. 1. Introduction The incorporation of silicon nitride (SiNx) films into semiconductor devices, and in particularly solar cells, has become an increasingly important topic. This is partly due to their favorable characteristics, which allow them to act as antireflection coatings as well as passivation layers. For the case of PECVD deposited nitride, the film properties can be varied over a broad range, and the films contain a high concentration of hydrogen atoms that can be used-to-passivate bulk defects. Given the growing interest in solar cells based on n-type silicon substrates [1], the passivation of p-type emitters has become more important and, therefore, the application of PECVD SiNx films on this type of emitter has emerged as a topic of interest as well. PECVD SiNx generally contains a moderate to high density of positive fixed charge located at or near the Si-SiNx interface. This positive charge is beneficial for the passivation of lowly doped or n doped surfaces but is generally undesirable on heavily doped p type surfaces, such as boron diffused emitters, as the positive charge results in a reduction in hole concentration at the Si surface and consequently an increase in surface recombination velocity. While recent studies have demonstrated that PECVD nitride could actually provide excellent passivation of diffused emitter structures when an appropriate postannealing process was carried out [2], the paper
%U http://www.hindawi.com/journals/aoe/2010/487406/