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Keywords:

  • doping concentration;
  • mobility;
  • photovoltaics;
  • Si quantum dots

Abstract

This article analyses silicon quantum dots based materials which could be used in all-silicon tandem solar cells. The contact properties of aluminium and nickel on this material are obtained by circular transmission line measurements (TLM). Both metals make ohmic contacts with the material and the contact resistance is also similar for both metals, indicating that either the material is very heavily doped or the surface defect density is very high. Doping by diffusion is demonstrated for the first time on this material and a MOS structure is fabricated in order to extract doping type, doping concentration and mobility. A simple model is established for the MOS structure. Using capacitance versus voltage (CV) measurements, we are able to extract doping concentration, mobility and surface charge by curve fitting. Using this fitting method, the relative permittivity of our material is estimated and an effective gate contact area is calculated for different frequencies, doping types and gate voltages. The doping concentration extracted is in the order of 1017 cm−3 and the mobility is two to three orders of magnitude lower compared to that of crystalline silicon with a similar doping level. Based on the CV curves we can demonstrate that B behaves like a p-type dopant and P as an n-type dopant in our material.