Depth-resolved cathodoluminescence spectroscopy as a probe of defect structure in oxides

Abstract

Depth-resolved cathodoluminescence spectroscopy (DRCLS) is a powerful technique for probing the nature of defects in oxides, both electronically and spatially on a nanometer scales. The information derived from this technique provides a tool to guide the growth and processing of state-of-the-art semiconductors and dielectrics for micro- and opto-electronics. DRCLS is particularly effective in probing electronic and chemical structure within ultrathin films, beyond the capabilities of conventional techniques. This talk highlights the capabilities of DRCLS with recent results from conventional oxides such as ZnO, to complex oxides such as the perovskite titanates, and the high-K dielectric HfO 2 . These studies establish the physical nature of native point defects in these materials as well as their spatial distribution on a nanometer scale. Deep level transient and optical spectroscopies (DLTS and DLOS), capacitance-voltage, as well as atomic force microscopy (AFM) combined with Kelvin Force Probe Microscopy (KPFM) provide methods to calibrate the observed luminescence features in terms of defect densities and carrier concentrations in these materials. DRCLS combined with these calibration techniques reveal dramatic increases in defect densities within tens of nanometers of surfaces and interfaces. In turn, such defect segregation has major effects on metal-semiconductor Schottky barrier formation, dielectric loss in capacitance structures at RF frequencies, and interface trapping in metal-oxide-semiconductor structures. For all these electronically-active oxides, DRCLS provides a rapid, non-destructive and highly sensitive method to evaluate localized electronic states and guide the growth and processing of these materials to achieve state-of-the-art device structures.