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.

Self-heating degrades the performance of devices in advanced technology nodes. Understanding of self-heating effects is necessary to improve device performance. Heat generation in these devices occurs at nanometer scales but heat transfer is a microscopic phenomena. Hence a multi-scale modeling approach is required to study the self-heating effects. A state of the art Monte Carlo device simulator and the commercially available Giga 3D tool from Silvaco are used in our study to understand the self heating effects. The Monte Carlo device simulator solves the electrical transport and heat generation for nanometer length scales accurately while the Giga 3D tool solves for thermal transport over micrometer length scales. The approach used is to understand the self-heating effects in a test device structure, composed of a heater and a sensor, fabricated and characterized by IMEC. The heater is the Device Under Test(DUT) and the sensor is used as a probe. Therefore, the heater is biased in the saturation region and the sensor is biased in the sub-threshold regime. Both are planar MOSFETs of gate length equal to 22 nm. The simulated I-V characteristics of the sensor match with the experimental behavior at lower applied drain voltages but differ at higher applied biases.

The self-heating model assumes that the heat transport within the device follows Energy Balance model which may not be accurate. To properly study heat transport within the device, a state of the art Monte Carlo device simulator is necessary. In this regard, the Phonon Monte Carlo(PMC) simulator is developed. Phonons are treated as quasi particles that carry heat energy. Like electrons, phonons obey a corresponding Boltzmann Transport Equation(BTE) which can be used to study their transport. The direct solution of the BTE for phonons is possible, but it is difficult to incorporate all scattering mechanisms. In the Monte Carlo based solution method, it is easier to incorporate different relevant scattering mechanisms. Although the Monte Carlo method is computationally intensive, it provides good insight into the physical nature of the transport problem. Hence Monte Carlo based techniques are used in the present work for studying phonon transport. Monte Carlo simulations require calculating the scattering rates for different scattering processes. In the present work, scattering rates for three phonon interactions are calculated from different approaches presented in the literature. Optical phonons are also included in the transport problem. Finally, the temperature dependence of thermal conductivity for silicon is calculated in the range from 100K to 900K and is compared to available experimental data.