專題演講 Seminar

2016/11/03(Thu)     10:00 -11:00    五樓第一會議室 5F, 1st Meeting Room

Title

Interplay of Native Point Defects with ZnO Schottky Barriers and Doping – From Bulk Crystals to Nanowires

Speaker

Prof. Leonard J. Brillson (Department of Electrical & Computer Engineering and Department of Physics, the Ohio State University)

Abstract

A combination of depth-resolved electronic and structural techniques now reveals that native point defects can play a major role in ZnO Schottky barrier formation and free carrier doping. Previous work has ignored these lattice defects at metal-ZnO interfaces due to the relatively low point defect densities in the bulk. Similarly, efforts to control doping type and density usually treat native defects as passive, compensating donors or acceptors. Recent advances provide a deeper understanding of the interplay between native point defects and electronic properties at ZnO surfaces, interfaces, and epitaxial films – from bulk crystals down to micro- and nanowires. Key to ZnO Schottky barrier formation is a massive redistribution of native point defects near its surfaces and interfaces. It is now possible to measure the energies, densities and in many cases the type of point defects below the semiconductor free surface and its metal interface with nanoscale precision. Using spatially-resolved cathodoluminescence spectroscopy (DRCLS) of deep level emissions in three dimensions calibrated with electrical techniques, we find that native point defects can (i) increase by orders-of-magnitude in densities within tens of nanometers of the semiconductor surface, (ii) alter free carrier concentrations and band profiles within the surface space charge region, (iii) dominate the Schottky barrier formation for metal contacts to ZnO, and (iv) play an active role in semiconductor doping. These results reveal the interplay between ZnO electronic defects, dopants, polarity, and surface nanostructure, and they highlight new ways to control ZnO Schottky barriers and doping.

Language

演講語言 (Language): in English