Abstract

Scanning probe microscopy (SPM) techniques, principally atomic force microscopy (AFM), provide a relatively simple, fast-turnaround way to assess the surface morphology of many materials. Interesting and attractive images are frequently obtained. However, AFM sometimes seem to be a victim of its own success and simplicity, with morphological data being published with little by way of analysis or interpretation.

In the Cambridge GaN centre, various attempts have been made to take the use of SPM beyond this “pretty pictures” level. I will describe two examples of the use of topographical AFM data and its analysis in this context: (1) the development of a surface treatment which allows straightforward imaging of threading dislocations at GaN surfaces, and its application in a study of the origins of threading dislocations, and (2) the application of spectral analysis of AFM images to understanding the mechanisms of roughening and smoothing in InGaN films during annealing.

Currently available SPM techniques, however, extend the capability of the instrument far beyond the topographic realm. As examples of these more recently developed techniques, I will present: (1) the use of scanning capacitance microscopy for the quantification of carrier concentrations in n-type GaN and (2) the development of scanning spreading resistance microscopy as a composition-sensitive tool for the imaging of AlGaN samples.

Together, these four case studies may illustrate the broad applicability of SPM to understanding the structure and properties of materials.