A Unified 2D Solver for Modeling Carrier and Defect Dynamics in Electronic and Photovoltaic Devices

Semiconductor devices often face reliability issues due to their operational con-

ditions causing performance degradation over time. One of the root causes of such

degradation is due to point defect dynamics and time dependent changes in their

chemical nature. Previously developed Unified Solver was successful in explaining

the copper (Cu) metastability issues in cadmium telluride (CdTe) solar cells. The

point defect formalism employed there could not be extended to chlorine or arsenic

due to numerical instabilities with the dopant chemical reactions. To overcome these

shortcomings, an advanced version of the Unified Solver called PVRD-FASP tool was

developed. This dissertation presents details about PVRD-FASP tool, the theoretical

framework for point defect chemical formalism, challenges faced with numerical al-

gorithms, improvements for the user interface, application and/or validation of the

tool with carefully chosen simulations, and open source availability of the tool for the

scientific community.

Treating point defects and charge carriers on an equal footing in the new formalism

allows to incorporate chemical reaction rate term as generation-recombination(G-R)

term in continuity equation. Due to the stiff differential equations involved, a reaction

solver based on forward Euler method with Newton step is proposed in this work.

The Jacobian required for Newton step is analytically calculated in an elegant way

improving speed, stability and accuracy of the tool. A novel non-linear correction

scheme is proposed and implemented to resolve charge conservation issue.

The proposed formalism is validated in 0-D with time evolution of free carriers

simulation and with doping limits of Cu in CdTe simulation. Excellent agreement of

light JV curves calculated with PVRD-FASP and Silvaco Atlas tool for a 1-D CdTe

solar cell validates reaction formalism and tool accuracy. A closer match with the Cu

SIMS profiles of Cu activated CdTe samples at four different anneal recipes to the

simulation results show practical applicability. A 1D simulation of full stack CdTe

device with Cu activation at 350C 3min anneal recipe and light JV curve simulation

demonstrates the tool capabilities in performing process and device simulations. CdTe

device simulation for understanding differences between traps and recombination

centers in grain boundaries demonstrate 2D capabilities.