Micro-structure Engineering of InGaN/GaN Quantum Wells for High Brightness Light Emitting Devices

Handle URI:
http://hdl.handle.net/10754/293687
Title:
Micro-structure Engineering of InGaN/GaN Quantum Wells for High Brightness Light Emitting Devices
Authors:
Shen, Chao
Abstract:
With experimental realization of micro-structures, the feasibility of achieving high brightness, low efficiency droop blue LED was implemented based on InGaN/GaN micro-LED-pillar design. A significantly high current density of 492 A/cm2 in a 20 μm diameter (D) micro-LED-pillar was achieved, compared to that of a 200 μm diameter LED (20 A/cm2), both at 10 V bias voltage. In addition, an increase in sustained quantum efficiency from 70.2% to 83.7% at high injection current density (200 A/cm2) was observed in micro-LED-pillars in conjunction with size reduction from 80 μm to 20 μm. A correlation between the strain relief and the electrical performance improvement was established for micro-LED-pillars with D < 50 μm, apart from current spreading effect. The degree of strain relief and its distribution were further studied in micro-LED-pillars with D ranging from 1 μm to 15 μm. Significant wavenumbers down-shifts for E2 and A1 Raman peaks, together with the blue shifted PL peak emission, were observed in as-prepared pillars, reflecting the degree of strain relief. A sharp transition from strained to relaxed epitaxy region was discernible from the competing E2 phonon peaks at 572 cm-1 and 568 cm-1, which were attributed to strain residue and strain relief, respectively. A uniform strain relief at the center of micro-pillars was achieved, i.e. merging of the competing phonon peaks, after Rapid Thermal Annealing (RTA) at 950℃ for 20 seconds, phenomenon of which was observed for the first time. The transition from maximum strain relief to a uniform strain relief was found along the narrow circumference (< 2.5 μm) of the pillars from the line-map of Raman spectroscopy. The extent of strain relief is also examined considering the height (L) of micro-LED-pillars fabricated using FIB micro-machining technique. The significant strain relief of up to 70% (from -1.4 GPa to -0.37 GPa), with a 71 meV PL peak blue shift, suggested that micro-LED-pillar with D < 3 μm and L > 3 μm in the array configuration would allow the building of practical devices. Overall, this work demonstrated a novel top-down approach to manufacture large effective-area, high brightness emitters for solid-state lighting applications.
Advisors:
Ooi, Boon S. ( 0000-0001-9606-5578 )
Committee Member:
Bakr, Osman M.; Zhang, Xixiang ( 0000-0002-3478-6414 )
KAUST Department:
Physical Sciences and Engineering (PSE) Division
Program:
Materials Science and Engineering
Issue Date:
May-2013
Type:
Thesis
Appears in Collections:
Theses; Physical Sciences and Engineering (PSE) Division; Materials Science and Engineering Program

Full metadata record

DC FieldValue Language
dc.contributor.advisorOoi, Boon S.en
dc.contributor.authorShen, Chaoen
dc.date.accessioned2013-06-09T18:36:11Z-
dc.date.available2013-06-09T18:36:11Z-
dc.date.issued2013-05en
dc.identifier.urihttp://hdl.handle.net/10754/293687en
dc.description.abstractWith experimental realization of micro-structures, the feasibility of achieving high brightness, low efficiency droop blue LED was implemented based on InGaN/GaN micro-LED-pillar design. A significantly high current density of 492 A/cm2 in a 20 μm diameter (D) micro-LED-pillar was achieved, compared to that of a 200 μm diameter LED (20 A/cm2), both at 10 V bias voltage. In addition, an increase in sustained quantum efficiency from 70.2% to 83.7% at high injection current density (200 A/cm2) was observed in micro-LED-pillars in conjunction with size reduction from 80 μm to 20 μm. A correlation between the strain relief and the electrical performance improvement was established for micro-LED-pillars with D < 50 μm, apart from current spreading effect. The degree of strain relief and its distribution were further studied in micro-LED-pillars with D ranging from 1 μm to 15 μm. Significant wavenumbers down-shifts for E2 and A1 Raman peaks, together with the blue shifted PL peak emission, were observed in as-prepared pillars, reflecting the degree of strain relief. A sharp transition from strained to relaxed epitaxy region was discernible from the competing E2 phonon peaks at 572 cm-1 and 568 cm-1, which were attributed to strain residue and strain relief, respectively. A uniform strain relief at the center of micro-pillars was achieved, i.e. merging of the competing phonon peaks, after Rapid Thermal Annealing (RTA) at 950℃ for 20 seconds, phenomenon of which was observed for the first time. The transition from maximum strain relief to a uniform strain relief was found along the narrow circumference (< 2.5 μm) of the pillars from the line-map of Raman spectroscopy. The extent of strain relief is also examined considering the height (L) of micro-LED-pillars fabricated using FIB micro-machining technique. The significant strain relief of up to 70% (from -1.4 GPa to -0.37 GPa), with a 71 meV PL peak blue shift, suggested that micro-LED-pillar with D < 3 μm and L > 3 μm in the array configuration would allow the building of practical devices. Overall, this work demonstrated a novel top-down approach to manufacture large effective-area, high brightness emitters for solid-state lighting applications.en
dc.language.isoenen
dc.subjectgallium nitrideen
dc.subjectquantum wellen
dc.subjectstrain reliefen
dc.subjectLEDen
dc.subjectefficiency droopen
dc.titleMicro-structure Engineering of InGaN/GaN Quantum Wells for High Brightness Light Emitting Devicesen
dc.typeThesisen
dc.contributor.departmentPhysical Sciences and Engineering (PSE) Divisionen
thesis.degree.grantorKing Abdullah University of Science and Technologyen_GB
dc.contributor.committeememberBakr, Osman M.en
dc.contributor.committeememberZhang, Xixiangen
thesis.degree.disciplineMaterials Science and Engineeringen
thesis.degree.nameMaster of Scienceen
dc.person.id118525en
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