All-electronic Nanosecond-resolved Scanning Tunneling Microscopy: Facilitating the Investigation of Single Dopant Charge Dynamics

Summary

We demonstrate an all-electronic method to observe nanosecond-resolved charge dynamics of dopant atoms in silicon with a scanning tunneling microscope.

Abstract

The miniaturization of semiconductor devices to scales where small numbers of dopants can control device properties requires the development of new techniques capable of characterizing their dynamics. Investigating single dopants requires sub-nanometer spatial resolution, which motivates the use of scanning tunneling microscopy (STM). However, conventional STM is limited to millisecond temporal resolution. Several methods have been developed to overcome this shortcoming, including all-electronic time-resolved STM, which is used in this study to examine dopant dynamics in silicon with nanosecond resolution. The methods presented here are widely accessible and allow for local measurement of a wide variety of dynamics at the atomic scale. A novel time-resolved scanning tunneling spectroscopy technique is presented and used to efficiently search for dynamics.

Introduction

Scanning tunneling microscopy (STM) has become the premier tool in nanoscience for its ability to resolve atomic-scale topography and electronic structure. One limitation of conventional STM, however, is that its temporal resolution is restricted to the millisecond timescale because of the limited bandwidth of the current preamplifier¹. It has long been a goal to extend STM's temporal resolution to the scales on which atomic processes commonly occur. The pioneering work in time-resolved scanning tunneling microscopy (TR-STM) by Freeman et. al.¹ utilized photoconductive switches and microstrip transmission li....

Protocol

1. Initial Setup of Microscope and Experiments

1. Begin with an ultrahigh vacuum cryogenic-capable STM and associated control software. Cool the STM to cryogenic temperatures.
   NOTE: Throughout this report, ultrahigh vacuum refers to systems that achieve <10 x 10^-10 Torr. The STM should be cooled to cryogenic temperatures; this is especially important when investigating the charge dynamics of dopants, which are thermally activated at modest temperatures. Other chambers may be at room temperature.
2. Ensure that the STM tip is equipped with high-frequency wiring (~500 MHz).
   NOTE: By using pulse shaping methods, a great increa....

Results

The results presented in this section of the text have been previously published^15,16. Figure 3 illustrates the behavior of an example selected DB with conventional STM. A conventional I(V) measurement (Figure 3A) clearly depicts a sharp change in the conductance of the DB at V_thr = -2.0 V. This behavior is also observed in STM images taken at -2.1 V (.......

Discussion

The variant of TR-STS in which the pump pulse is not applied is comparable to conventional STS, except that the system is being sampled at a high frequency rather than continuously. If the durations of the probe pulses are appropriate (>Γ_LH), the TR-STS signal acquired without the pump pulse can be multiplied by a constant proportional to the experiment's duty cycle to coincide exactly with a conventional STS measurement. This is only possible because the measurements are made without the.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Low Temperature Scanning Tunneling Microscope	Scientaomicron		Custom-made with 500MHz bandwidth wiring
Arbitarary Function Genorator	Tektronix	AFG3252C
RF Power Splitter/ Combiner	Mini-Circuits	ZFRSC-42-S +
RF Switch	Mini-Circuits	X80-DR230-S +
Non-Contact Infrared Pyrometers	Micron Infrared	MI 140