BiasMDP

The Quality of the dielectric surface passivation is gaining in importance especially in photovoltaics. Because of novel solar cell concepts as PERC or IBC solar cells and the growing need for solar cells with high efficiencies a tool for a fast characterization of the passivation layers is needed. The MDPmap together with the BiasMDP option satisfies this need.

Dielectric surface passivation layers are producing a chemical and a field effect passivation. These both mechanism can be described via the parameters Dit (density of interface traps) and Qfix (density of fixed charges), which can both be determined with the BiasMDP. A bias voltage is applied, which compensates the fixed charges and ultimately leads to a strong inversion. The minority carrier lifetime is measured for different bias voltages and a lifetime curve as shown in figure 1 results. An explanation for this behavior is given in figure 1. By additionally measuring with a variable injection Qfix and Dit can be determined from this lifetime curve.

Fig. 1: typical effective lifetime curve as a function of the applied bias voltage; at the right side short explanations for the lifetime behavior are given

1

  • Low recombination due to field effect passivation (Qfix) and chemical passivation (Dit)
  • accumulation → τ0

2

  • Compensation of Qfix
    • → only chemical passivation
    • → recombination at interface defects
    • → SRH model can be applied

3

  • Strong inversion

First results show a very good correlation between BiasMDP and the standard method C(V). Comparable flat band voltages, also in dependence of different oxide thicknesses were measured.


For more information about BiasMDP please read:

[1] P. M. Jordan, D. K. Simon, T. Mikolajick, I. Dirnstorfer, Appl. Phys. Lett. 106, 061602 (2015)