High Resolution Phonon-assisted Quasi-resonance Fluorescence Spectroscopy

Summary

The manuscript describes a method of phonon-assisted quasi-resonant fluorescence spectroscopy that incorporates both laser-limited resolution and photoluminescence (PL) spectroscopy. This method utilizes optical phonons to provide linewidth-limited resolution spectra of atom-like semiconductor structures in the energy domain. The method is also easily realized with a single spectrometer optical spectroscopy setup.

Abstract

High resolution optical spectroscopy methods are demanding in terms of either technology, equipment, complexity, time or a combination of these. Here we demonstrate an optical spectroscopy method that is capable of resolving spectral features beyond that of the spin fine structure and homogeneous linewidth of single quantum dots (QDs) using a standard, easy-to-use spectrometer setup. This method incorporates both laser and photoluminescence spectroscopy, combining the advantage of laser line-width limited resolution with multi-channel photoluminescence detection. Such a scheme allows for considerable improvement of resolution over that of a common single-stage spectrometer. The method uses phonons to assist in the measurement of the photoluminescence of a single quantum dot after resonant excitation of its ground state transition. The phonon's energy difference allows one to separate and filter out the laser light exciting the quantum dot. An advantageous feature of this method is its straight forward integration into standard spectroscopy setups, which are accessible to most researchers.

Introduction

High resolution is the key to unlocking new knowledge. With this knowledge, new technologies can be developed such as better sensors, more precise manufacturing tools, and more efficient computational devices. Generating this key, however, often comes at a high cost of resources, time or both. This issue is omnipresent across all scales from the atomic physics of resolving the lifted degeneracies of electron spins to astronomy where a small spectral shift can lead to detection of planets next to distant stars.^1,2,3

The focus of this work is on using a standard spectrometer setup and showing how it can resolve spectral features b....

Protocol

Note: The methodology described is specific to a particular software, although other software packages may be used instead.

1. Sample Preparation and Cool Down

1. Fabricate the sample.
   1. Grow the sample, using the Stranski-Krastanov growth method via molecular beam epitaxy creating two vertically-stacked self-assembled InAs/GaAs QDs that are separated by a 4 nm tunnel barrier as previously described.¹⁶ Embed the QDs in an electric field effect structure (i.e., Schottky diode) allowing for an electric field to be applied to the QDMs.¹⁷
      Note: The use of QDMs is not a requirement for th....

Results

The results presented in the figures show the high resolution capabilities of using phonons to assist in the PL measurement. The schematic (Figure 2) shows that, with the exception of the edge pass filters on both excitation and detection, the experimental setup remains a standard spectroscopy setup, with the optional addition of polarization control. Comparison with a single and triple spectrometer (Figure. 3) portrays the phonon-assisted method's great .......

Discussion

The above instructions demonstrate the phonon-assisted quasi-resonance spectroscopy method. By exciting into a QD discrete state, one can monitor the phonon emission line, achieving high resolutions. In the example provided, by using phonons it is even possible to resolve the lifetime-limited linewidth of the neutral exciton visible in experiments. The method is easy to incorporate into existing PL spectroscopy setups. As mentioned, once the energy of the desired transition line is identified via non-resonant spectroscop.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Tunable Diode Laser DL pro	Toptica Photonics	DL Pro
Closed Cycle Cryogen Free Refrigerator System for Microscopy	Cryo Industries of America Inc.	Cryocool G2
Sourcemeter	Keithley	2611a
50X Mitutoyo Plan Apo NIR Infinity-Corrected Objective	Mitutoyo America Corporation	378-825-5
Turbo pump	Pfeiffer Vacuum	HiPace 80
NIR coated Mirrors	Thor labs	BB1-E03
Polarizers	Thorlabs	LPNIR050-MP
200 mm AR coated Achromatic lens	Thorlabs	AC254-200-B-ML
100 mm AR coated Achromatic lens	Thorlabs	AC254-100-B-ML
960 Long pass filter	Thorlabs	960aelp
960 Short pass filter	Thorlabs	960aesp
Liquid Crystal Variable Retarder	Meadowlark Optics	LVR-100
0.75 m Spectrometer Acton SpectraPro	Princeton Instruments	Trivista
Liquid Nitrogen Cooled Camera	Princeton Instruments	7508-0002
External Camera	Watec	Wat-902H Ultimate	Optional
Ostoalloy	Lake Shore Cryotronics	Ostalloy 158
Gold wire (40 gauge)	Surepure Chemetals	Au-Wire-03-02
Silver Epoxy	A.I. Technology	Prima-Solder EG8020
Program Software	National Instruments	LabView