Electronic Structure of Technologically Important Interfaces and Heterostructures

Abstract

From thin film solar cells to metal-oxide-semiconductor devices in leading edge integrated circuits, the electronic structure at and near the interfaces between component materials determines the most important fundamental operating characteristics of those devices such as turn-on voltage, power dissipation and off-state current leakage. Fermi level location at buried interfaces, semiconductor band-bending, charge transfer, oxide defects and work functions of the constituent materials all contribute to device performance. In this talk I will describe how these important parameters can be determined by employing femtosecond photovoltage spectroscopy (FPS)[1], an extension of ultraviolet photoelectron spectroscopy (UPS) using ultrafast lasers. While UPS is fundamentally a surface sensitive spectroscopy, I will describe how pump/probe techniques add a new dimension to this venerable spectroscopy, permitting the accurate extraction of the underlying band bending in Si. When combined with valence band edge location of the semiconductor and oxide, and determination of the system Fermi level, full characterization of the electronic structure of an MOS stack can be obtained providing key insights on device operating properties. I will describe the use of FPS to investigate device stacks ranging from Si and III-V based MOS structures to thin film solar cells formed from earth-abundant elements. In each case surprising new details were uncovered that led to performance optimization of these technologically important devices. [1] Richard Haight and Adra V. Carr, "Industrial Applications of Ultrafast Lasers", World Scientific Press, 2018, ISBN:97898145690002