Numerical modeling of DBOM and conductance semiconductor tests
Abstract
Test methods, characterization, and modeling have been critical to semiconductor technology since its earliest development. This thesis discusses numerical modeling approaches to the analysis of solar cell semiconductor devices. As a part of the work in support of this thesis, the Purdue simulator ADEPT has been augmented with an AC small-signal analysis method. The ADEPT simulation analysis of the widely used DBOM method has shown that this method is not suitable for solar cell carrier lifetime measurement. The DBOM method was found to have a sensitivity to change in the majority carrier concentration at the edges of the depletion region that dominates the minority carrier sensitivity. A possible refinement of this method using a very high carrier injection regime, as well as other possible applications of DBOM for solar cell analysis, are also discussed. The AC conductance method as applied to the junction device is described. Several competing theories are compared and simulations are developed to demonstrate the validity of the Dhariwal theory as well as its applications beyond theoretical limits. The results are applied to the analysis of polycrystalline CdTe solar cells. It is shown that conductance data alone are not sufficient for full characterization of highly compensated polycrystalline material. Using the approach of the conductance method, together with capacitance frequency sweep, AC sweep at different temperatures, and DC current data, can lead to excellent characterization results. An innovative method, based on peak conductance response shift and simultaneous fitting of simulation results to the capacitance and conductance data with varying DC bias, reveals the nature of solar cell traps and their density profiles. Although this approach is tedious, the method does not require specialized equipment and in some cases produces better results than DLTS.
Degree
Ph.D.
Advisors
Gray, Purdue University.
Subject Area
Electrical engineering|Condensation
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