Time response in tunneling to a pn junction

Abstract

We report on the variation in the response time in scanning tunneling microscopy (STM) measurements across a Si pn junction, and its effect on STM images of such devices. The response time of the tip height subsequent to a stepwise change in the voltage at a fixed demanded current varies by almost two orders of magnitude across the junction, with the slowest response of nearly 80 ms corresponding to the tip–sample junction in strong inversion. Measurements at decreasing separation show an increase in response time up to a saturation point, consistent with screening due to the inversion charge. The slow response in regions where the tip–sample junction is in inversion explains observations of anomalously deep features in STM topography images and scan direction-dependent features in STM conductance maps.