Synchrotron Radiation Spectroscopic Study of Surface and Bulk Electronic Structure of Wide Band Gap Semiconductors

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Wide band gap nitride semiconductors are the focus of intense scrutiny due to their potential applications in optoelectronic, high temperature, and spintronic devices. However, our understanding of the basic physics of these materials lags behind our ability to make electronic devices from them. This individual investigator award supports a project to investigate the electronic structure of clean and adsorbate-covered nitride semiconductors. The goals are to study the bulk and surface electronic structure of nitride semiconductor alloys in order to understand their fundamental electronic properties; to study gas adsorption on well characterized nitride surfaces in order to understand their chemical reactivity, their passivation, and the growth and stability of inorganic and organic overlayers; and finally to study the electronic structure of model magnetic semiconductors such as GaMnN. This project will have a significant impact on the education of students and postdoctoral research associates by exposing them to a highly collaborative research environment at national user facilities. They will be educated in the physics of novel semiconductor materials, and in the application of synchrotron radiation spectroscopies in their study. This is an ambitious program that aims to produce definitive measurements of surface and bulk electronic structure in wide band gap semiconductors. The project is co-funded by the Division of Materials Research at NSF and the Physics Division at the Army Research Organization.An important new class of semiconductors based on nitrogen compounds are the focus of intense scrutiny due to their potential applications in lasers and other optical devices that operate in the blue/UV portion of the spectrum. These materials, know as wide band gap nitride semiconductors, also hold the promise of being used in electronic devices operating at much higher temperatures than conventional materials. While many simple devices have been fabricated from these materials, there remains an acute lack of knowledge about their fundamental electronic and chemical properties. It is of vital importance for the full commercial exploitation of these materials to understand their basic properties since, for example, the behavior of electrons near the nitride surface controls their chemical reactivity, their structural stability, and how other materials are bonded to them. This individual investigator project will study the basic electronic properties of these materials using two probes: photoemission spectroscopy and x-ray emission spectroscopy. These probes involve providing the electrons in the material with additional energy by illuminating them with intense x-rays and measuring their response. This combination of spectroscopies will provide a comprehensive understanding of the electronic and chemical properties of these semiconductors. This program will also educate postdoctoral research associates, graduate and undergraduate students in the physics and chemistry of semiconductor materials, and the application of state of the art spectroscopic probes in their study. The project is co-funded by the Division of Materials Research at NSF and the Physics Division at the Army Research Organization.