CMS: Research Projects

Research Topics

1. "Fundamental Physics of Photovoltaic Materials." Principal Investigators: S.-H. Wei and S.B. Zhang (funded by DOE Office of Energy Efficiency and Renewable Energy).

This project performs fundamental research to establish the basic knowledge infrastructure of photovoltaic materials using state-of-the-art computational tools. Our study is aimed at (1) predicting physical properties of new PV materials that are potential candidates for future PV applications, and (2) explaining new experimental results and providing guidelines for future experimental investigations.

Our current research activities are focused on the following areas:

Materials properties and defect physics of II-VI and chalcopyrite compounds
Reconstruction and defect formation on semiconductor surfaces
Electronic and transport properties of transparent conductive oxides
Hydrogen interaction in the stability of a-Si solar cells
Nitrides alloys and related materials for high-efficiency solar cells.

exploring the fundamental physics of photovoltaics materials

Using first-principles, total-energy calculation, we explained why [N] in GaAs can be significantly increased in epitaxial growth. We also identified that in high [N] sample, the N split interstitials [see (b) above] are the dominant defects that are detrimental to minority-carrier lifetimes.

2. "Overcoming Doping Bottlenecks in Semiconductors and Wide Gap Materials." Principal Investigators: S. Zhang and S.-H. Wei (funded by DOE Office of Sciences).

Doping semiconductors and wide-bandgap materials are essential for device applications. Yet, there are strong doping bottlenecks that may severely restrict potential applications of semiconductors, especially in wide-bandgap materials in which bipolar doping is very difficult. In this project we study what causes the doping bottlenecks by first-principles, total-energy calculations. We test systematically the various existing microscopic defect models and develop new models to understand the physics of doping. New strategies for overcoming the equilibrium doping bottlenecks are also proposed.

microscopic origin of the doping limit rule in n-type III-V semiconductors

First-principles, total-energy calculations reveal that equilibrium n-type doping is limited by the spontaneous formation of closed-shell defects: the (3-) charged cation vacancy in III-V semiconductors.

3. "Electronic Structure and Stability of Ordered Semiconductors." Principal Investigator: S.-H. Wei. (funded by DOE/Office of Sciences. Co-PI: A. Mascarenhas and J. Olson)

The phenomenon of the spontaneous ordering in semiconductors alloys has significant effects on the material properties of the alloys. As such, it has great impacts on semiconductor sciences and technological applications. In this project, we perform first-principles theoretical study to understand the mechanism of spontaneous long-range order in semiconductor alloys and ordering-induced changes in materials' optical, electrical, magnetic and structural properties.

First-principles theoretical calculations allow to understand and predict the mechanism of spontaneous long-range order in semiconductor alloys and ordering-induced changes in materials' optical, electrical, magnetic and structural properties.