Scanning Probe Microscopy of InAs/InP Nanowires

Table of Contents

1 Introduction

2 Theory

2.1 Scanning Tunneling Microscopy

2.2 Scanning Tunneling Spectroscopy

2.3 Nanowires

2.4 Quantum dots

3 Experimental background

3.1 Setup

3.2 Sample preparation

3.3 Tip production

3.4 Vacuum conditions

4 Results and Discussion

4.1 Cleaning

4.1.1 Surface

4.1.2 Nanowires

4.2 Imaging

4.2.1 InAs(111)B surface

4.2.2 InAs nanowires grown without gold particle

4.2.3 InP with InAs quantum well nanowires

4.2.4 InP with InAs quantum dots nanowires

4.3 Spectroscopy

4.3.1 InAs(111)B surface

4.3.2 Defect induced influence on spectra

5 Conclusion and Outlook

Objectives and Topics

This thesis aims to investigate the surface morphology and electronic properties of III-V semiconductor nanowires and the InAs(111)B substrate using scanning tunneling microscopy (STM) and spectroscopy (STS). The research focuses on the characterization of heterostructures, specifically evaluating radial heterostructures like InP cores with InAs shells and those containing quantum dots, to understand their potential for future optoelectronic applications.

• Scanning Tunneling Microscopy (STM) principles and tip preparation.
• Surface cleaning procedures for semiconductor nanowires in ultra-high vacuum.
• Morphological analysis of InAs and InP/InAs heterostructure nanowires.
• Investigation of electronic density of states via Scanning Tunneling Spectroscopy.
• Characterization of defects and their influence on surface properties.

Excerpt from the Book

Summary of Chapters

1 Introduction: Provides an overview of the significance of III-V semiconductor nanowires and outlines the experimental scope of the thesis.

2 Theory: Covers the physical principles of STM and STS, as well as the fundamental concepts regarding nanowire growth and quantum dot formation.

3 Experimental background: Describes the technical setup, sample preparation methods, tip production, and the vacuum conditions required for STM experiments.

4 Results and Discussion: Details the cleaning procedures, imaging results of surfaces and nanowires, and spectroscopic analysis of electronic states and defects.

5 Conclusion and Outlook: Summarizes the findings regarding morphology and electronic properties, and suggests future improvements for cleaning and identification of quantum dot regions.

Keywords

Scanning Tunneling Microscopy, Scanning Tunneling Spectroscopy, Nanowires, InAs, InP, Heterostructures, Quantum Dots, Surface Morphology, Ultra High Vacuum, Semiconductor, Band Gaps, Stacking Faults, Crystal Structure, Epitaxy, Atomic Resolution.

Frequently Asked Questions

What is the primary focus of this research?

The research focuses on the growth, morphology, and electronic characterization of III-V semiconductor nanowires, specifically examining InAs and InP/InAs heterostructures using STM and STS.

What are the central thematic areas?

The work covers experimental surface science, including vacuum techniques, surface cleaning, scanning probe microscopy imaging, and tunneling spectroscopy analysis.

What is the primary goal of this study?

The goal is to determine the morphology and electronic surface properties of different nanowire heterostructures to assess their suitability for future optoelectronic devices.

Which scientific method is employed?

The thesis utilizes Scanning Tunneling Microscopy (STM) for topographic imaging and Scanning Tunneling Spectroscopy (STS) for investigating the local density of electronic states.

What is covered in the main section?

The main section details the cleaning processes for different nanowire samples, the imaging of specific facets, and the analysis of spectroscopic data collected from surfaces and defect regions.

Which keywords characterize the work?

Key terms include Scanning Tunneling Microscopy, InAs/InP nanowires, heterostructures, quantum dots, and surface cleaning.

How do defects influence the electronic structure?

The thesis concludes that the observed surface defects (attributed to missing Indium atoms) do not show a significant influence on the local electronic structure based on the spectroscopic data.

Why are InP/InAs heterostructures investigated?

They are studied because the modulation of materials allows for the confinement of electrons and holes, potentially creating quantum dots which are essential for lasers and quantum information processing.

What role does the tip quality play in these experiments?

Tip quality is critical because atomic resolution imaging is sensitive to tip geometry; blunt or multiple tips can cause artifacts that obscure the true surface morphology.

What challenges were encountered during cleaning?

Cleaning nanowires proved to be more difficult than cleaning bulk surfaces, as excessive annealing can destroy the top facets or the InAs shell of the nanowires.