Title: Photoconductive laser spectroscopy and sub-bandgap defects in the metal-oxide semiconductors

Abstract

The emergence of high performance large-area electronic materials enabled the display technologies, which have transformed the way people interact with mobile devices such as smartphones and tablets. The most promising family of materials for this application are the metal-oxide semiconductors (MOS). Properties, which make MOS desirable, include their optical transparency, bandgap modulation, and high electron mobility. The journey from lab curiosity to market for MOS has taken place in a short time span, and current applications of the technology include flat panel displays, sensors, and logic devices. One of the chief problems of MOS is the tendency to form sub-bandgap defects, which can have a detrimental effect on device performance. Gaining an in-depth understanding of the behavior of these sub-bandgap defects will be key to unlocking better device performance or perhaps even discovering beneficial applications for sub-bandgap defects. We developed an alternative spectroscopic technique, the photoconductive laser spectroscopy that is able to identify distinct spectral signatures of sub-bandgap defects in MOS used in thinfilm transistors (TFTs). These sub-bandgap peaks are not normally visible in previously reported spectra measured by using available spectroscopic techniques. Negative bias illumination stress (NBIS) has a strong effect on the stability of the TFT performance. It is assumed that during NBIS, the deep neutral sub-bandgap defects in the MOS activated and modulate the threshold voltage of the TFT. I will talk about the photoconductive laser spectroscopy technique, which we developed, its sensitivity and effectiveness to identify and study, the modulation of sub-bandgap defects in the metal-oxide semiconductors.