Show simple item record

dc.rights.licenseRestricted to current Rensselaer faculty, staff and students. Access inquiries may be directed to the Rensselaer Libraries.
dc.contributorWetzel, Christian
dc.contributorTerrones, H. (Humberto)
dc.contributorShur, Michael
dc.contributorPersans, Peter D., 1953-
dc.contributor.authorElsaesser, David Richard
dc.date.accessioned2021-11-03T09:05:18Z
dc.date.available2021-11-03T09:05:18Z
dc.date.created2018-10-24T13:39:58Z
dc.date.issued2017-05
dc.identifier.urihttps://hdl.handle.net/20.500.13015/2281
dc.descriptionMay 2017
dc.descriptionSchool of Science
dc.description.abstractThe role of piezoelectric polarization in a wide variety of polar and non-polar light emitting diode (LED) structures was analyzed by self-consistent Schrödinger-Poisson and carrier drift-diffusion simulations. I first reevaluate various sets of piezoelectric coeffi-cients by comparing to experimental spectroscopy results and then apply a set of choice to LED structures under current injection operation conditions in wurtzite c-plane, a-plane, semi-polar (11-22) crystal orientations and in cubic (001) growth orientation as well strain-reduced systems. For the non-polar and cubic systems I find a 22% increase of the electron-hole overlap, and a 18.3% for the c-plane strain reduced system at an InN fraction of x = 0.30 when compared to standard c-plane structures. The strain-reduced systems also exhibited a longer emission wavelength due to a lower degree of confine-ment in the quantum wells. Internal quantum efficiencies (IQEs) were determined for all LEDs. For the strain-reduced a-plane and c-plane LEDs, IQEs of 62.4% and 59.4%, respectively, I found for LEDs with an InN fraction of x = 0.30. While for cubic GaN, an LED with an InN fraction of x = 0.30 exhibited an IQE of 99.1%. Both the strain-reduced and cubic GaN LEDs offer exceptional improvements over a standard c-plane LED, which was found to have an IQE of 50.3% for the same InN fraction.
dc.description.abstractIn addition to the modeling I investigate the two-dimensional transition metal dichalcogenide material MoS2 as a buffer layer for the growth of GaN and GaInN structures in metal-organic vapor phase epitaxy (MOVPE). I confirmed growth of low-temperature GaN (LT-GaN) on MoS2 through Raman spectroscopy and XRD. In Raman spectroscopy and photo-luminescence (PL), evidence of sulfur possibly incorporating into GaN, and acting as a donor, was observed. XRD 2-theta scans indicate that for multiple quantum well (MQW) GaInN growth processes the MoS2 buffer layer degrades. I ob-served strong PL emission from green MQW structures, however, no MQW emission from blue MQWs was found, indicating that MoS2 affects the indium uptake of the quantum wells.
dc.description.abstractEnhancement factors in external quantum efficiency (EQE) of the cubic and strain-reduced LEDs were calculated through combining the optical and electrical model-ing. With the strain-reduced LEDs on nanopatterned templates, EQE enhancements of 1.65 (for the strain-reduced structure on c-plane) and 1.76 (for the strain-reduce structure a-plane) were found when compared to a standard planar LED. V-stripe cubic GaN LEDs offer a significant improvement in EQE, with enhancement factors ranging from 3.74 to 6.04, when compared to a planar wurtzite LED. Simulations of cubic GaN and strain reduced LED systems indicate that these structures should provide for improvements in long wavelength light emitters compared to conventional structures.
dc.description.abstractThrough wave propagation modeling, based on a finite-difference time-domain (FDTD) method, I investigated the optical effects of structures necessary for the for-mation of strain-reduced and cubic GaN LEDs. With the cubic GaN LED I investigated the effect on light extraction efficiency (LEE) due to a triangular-stripe shape that cubic GaN forms in, a result of our growth process for cubic GaN. Comparing the v-stripe cubic GaN to a planar wurtzite LED, I find that the cubic triangular-stripe cubic GaN structure increases the LEE by a factor of 1.9. In addition, I model ways to further enhance the LEE of v-stripe cubic GaN LEDs; namely, a removal of the v-stripe Si substrate, and implementation of a flip-chip LED design. By removing the Si substrate I find a 20% increase in LEE as compared to the cubic GaN LED still on the substrate. Through using a flip-chip design with the triangular-striped cubic GaN it was possible to enhance the LEE by a factor of 1.62 over the cubic GaN LED on a Si substrate. For the strain-reduced LEDs I simulated a nanopatterned GaN/GaInN template. The nanopatterned template was found to exhibit a 40% increase in LEE when compared to a planar GaN templated.
dc.description.abstractLight-emitting diodes based on piezoelectric GaN hold latent potential in terms of their radiative efficiencies. As such, much effort is being conducted to implement new LED structures to unlock this potential. In polar (0001) wurtzite LEDs a large internal polari-zation field separate electrons and holes resulting in a decrease in radiative efficiency. To reduce the polarization, strain-reduced structures are implemented, bringing electrons and holes together. Additionally, nonpolar LEDs using the a-plane of wurtzite GaN or the (001) plane of cubic GaN are able to eliminate the polarization field. In this thesis I focus on the understanding of changes that occur when implementing three systems for long-wavelength LEDs: strain-reduced LED structures, nonpolar cubic GaN, and GaInN systems on a strain-reducing buffer layer.
dc.language.isoENG
dc.publisherRensselaer Polytechnic Institute, Troy, NY
dc.relation.ispartofRensselaer Theses and Dissertations Online Collection
dc.subjectPhysics
dc.titleSimulation of light emitting diodes under piezoelectric polarization
dc.typeElectronic thesis
dc.typeThesis
dc.digitool.pid179292
dc.digitool.pid179293
dc.digitool.pid179294
dc.rights.holderThis electronic version is a licensed copy owned by Rensselaer Polytechnic Institute, Troy, NY. Copyright of original work retained by author.
dc.description.degreePhD
dc.relation.departmentDept. of Physics, Applied Physics, and Astronomy


Files in this item

Thumbnail

This item appears in the following Collection(s)

Show simple item record