Dissertation
Ultrafast pump-probe spectroscopic investigations of mid-IR superlattices and creation of metamaterial lenses for more efficient LEDs
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Autumn 2021
DOI: 10.17077/etd.006332
Abstract
Mid-wave infrared (MWIR) LEDs based on 6.1Å III/V semiconductors have trailed behind LEDs of other wavelength regimes in their wallplug efficiency. One contributing inefficiency is the low internal quantum efficiencies (IQE) of such materials which are often attributed to a limiting Auger recombination rate. However, recent work within this group has identified a four-layer superlattice (SL) based on 6.1Å III/V semiconductors with a remarkably high IQE of 77% at 77K (Muhowski 2020). We present in this work two-color, pump-probe, differential transmission measurements to interrogate the carrier dynamics of this SL. The W-superlattice (W-SL), consisting of InAs/GaInSb/InAs/AlAsSb layers, has a higher radiative rate than the standard InAs/GaSb superlattice and an improvement in the Shockley-Read-Hall lifetime which both contribute to this remarkably high IQE. Another contributing inefficiency is the low light extraction efficiency (LEE) of the LED device due to the small critical angle at the GaSb/air interface imposed by Snell’s Law. Research into metasurfaces and the advance of methods used to fabricate these planar structures has made it possible to realize a metalens tailored to increasing the radial output of geometrically constrained superlattice light emitting diodes (SLEDs). The metalens presented here, which allows for unprecedented control over optical wavefronts on a subwavelength scale, was designed to promote the extraction for an emitter of a specific mid-wave infrared wavelength, dielectric material, and unpolarized, Lambertian output. Results from a representative optical sample showed an enhanced output of 3.2x of the metalens design when compared to a planar surface.
Details
- Title: Subtitle
- Ultrafast pump-probe spectroscopic investigations of mid-IR superlattices and creation of metamaterial lenses for more efficient LEDs
- Creators
- Cassandra Lynne Bogh
- Contributors
- John P Prineas (Advisor)Vincent G Rodgers (Advisor)Christopher M Cheatum (Committee Member)Fatima Toor (Committee Member)Craig E Pryor (Committee Member)David R Andersen (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Physics
- Date degree season
- Autumn 2021
- Publisher
- University of Iowa
- DOI
- 10.17077/etd.006332
- Number of pages
- xv, 133 pages
- Copyright
- Copyright 2021 Cassandra Lynne Bogh
- Language
- English
- Description illustrations
- color illustrations
- Description bibliographic
- Includes bibliographical references (pages 109-124).
- Public Abstract (ETD)
High-efficiency semiconductor materials which emit in the infrared (IR) spectrum (0.7 μm – 25 μm) are important for advanced electro-optical devices such as superlattice light emitting diodes (SLEDs). IR SLEDs, like the visible LED bulbs in any home goods store, offer longer lifetimes, lower current, and voltage requirements, and don’t heat up as much as the thermal pixel arrays (TPAs). This is because SLEDs take advantage of a quantum electronic transition within the semiconductor material rather than heating the material up to produce the infrared light.
Here, we present three projects which all seek to improve the functionality and efficiency of IR SLEDs projectors. Projectors are composed of an array of IR SLEDs (1000 x 1000 pixels) mounted to a control circuit.
The first project demonstrates the successful light up of a projector based on a new base material (GaAs instead of GaSb and Si) on both the SLED and circuit side providing a potential alternative for joining the two together which is less time consuming and more cost effective.
The second project demonstrates the design, creation, and characterization of an optical structure known as a metalens which increased the IR light output from a flat surface by 3.2x.
The third project investigates the movement of electrons and holes in a new semiconductor material which had previously demonstrated a high internal quantum efficiency. The efficiency was high because the material was found to have a higher radiative (photon-producing) rate than the current material.
- Academic Unit
- Physics and Astronomy
- Record Identifier
- 9984210528402771
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