Electrostatic force spectroscopy of near-surface localized states

TL;DR

This paper demonstrates a cryogenic electrostatic force microscopy technique to detect and analyze localized electronic states in semiconductors, revealing discrete charge filling events and providing spectroscopic insights.

Contribution

It introduces a method to measure localized states' energies and tunneling times via cantilever frequency shifts, advancing nanoscale electronic state spectroscopy.

Findings

Discrete peaks in frequency shift indicate individual charge trapping events.

The technique allows extraction of energy levels and tunneling times of localized states.

Application to InAs quantum dots confirms the method's effectiveness.

Abstract

Electrostatic force microscopy at cryogenic temperatures is used to probe the electrostatic interaction of a conductive atomic force microscopy tip and electronic charges trapped in localized states in an insulating layer on a semiconductor. Measurement of the frequency shift of the cantilever as a function of tip-sample shows discrete peaks at certain voltages when the tip is located near trap centers. These discrete changes in frequency is attributed to one by one filling of individual electronic states when the quantized energies traverses the substrate conduction band fermi energy as tip-sample voltage is increased. Theoretical analysis of the experiment suggests that such measurement of the cantilever frequency shift as a function of bias voltage can be interpreted as an AC force measurement, from which spectroscopic information about the location, energy and tunneling times of localized states can be deduced. Experimental results from study of a sample with InAs quantum dots as trap centers is presented.