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Title:Molecular beam epitaxy of InAsP graded buffers: From mid-infrared quantum wells to InAs virtual substrates with low threading dislocation density
Author(s):Eng, Brendan Chee-Ming
Advisor(s):Lee, Minjoo L
Department / Program:Electrical & Computer Eng
Discipline:Electrical & Computer Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Molecular Beam Epitaxy
Quantum Well
Abstract:The mid-infrared (MIR) wavelength regime is an area rich for industrial and scientific applications like gas sensing, remote sensing, environmental monitoring, and thermal imaging. While III-V compound semiconductors enable compact, high-efficiency MIR optoelectronic devices, lattice matching constraints limit the wavelength coverage on industrially favorable III-V substrates. Metamorphic growth can be used to overcome the lattice mismatch between low bandgap III-V materials and conventional III-V substrates like GaAs and InP. While metamorphic growth offers the opportunity to engineer III-V materials with novel functionality on GaAs or InP substrates, defects like threading dislocations and misfit dislocations harm the performance of these metamorphic structures. This thesis explores metamorphic growth on InP using InAsP graded buffers grown with molecular beam epitaxy. The first part of this thesis analyzes the relationship between growth design, defects, and optical properties of highly strained InAs quantum wells emitting at 2.6-2.7 um on InP. The second part of the thesis addresses the effects of growth temperature, terminal composition, and grading rate for InAsP graded buffers to demonstrate metamorphic InAs on InP with a threading dislocation density as low as 3.88x106 cm-2. Lattice matching constraints coupled with the compromised short-wavelength performance of InP-based quantum cascade lasers lead to a wavelength gap between 2.3 and 3.0 um for lasers on InP. To overcome this challenge, InAsP graded buffers are used to extend the emission wavelength of InAs quantum wells on InP. The first part of this thesis investigates the effects of growth design on the structural and optical properties of InAs quantum wells grown on InAsP graded buffers. Strain-balanced multiple quantum well (MQW) structures grown with In0.54Ga0.46 barriers demonstrated much higher photoluminescence intensity than structures with InAs0.25P0.75 barriers. Both structures showed reduced misfit dislocation density in comparison to MQW structures grown without strain-balancing. Misfit and threading dislocations were surprisingly still present within structures with In0.54Ga0.46As barriers that were slightly off the strain-balancing condition along with structures with InAs0.25P0.75 barriers, which showed great agreement with the strain-balancing design. For single quantum well structures, reducing pauses in the active region growth improved photoluminescence intensity by 2.62 times. Additionally, an InAs0.56P0.44 overshoot layer reduced the defect line density by 26.3 times coupled with an additional 1.51 times improvement in photoluminescence intensity. In the second part of this thesis, molecular beam epitaxy growth parameters are analyzed for InAsP graded buffers. For InAs0.5P0.5, 450 °C growth temperature led to optimally low threading dislocation density and surface roughness in comparison to 420 °C and 480 °C growth. As terminal As composition was increased from 50% to 100%, threading dislocation density increased, even with similar grading rates. Additionally, surface roughness increased as composition was increased from 25 to 80%, but decreased when As composition was increased to 100%. Metamorphic InAs grown on InAsP graded buffers with a grading rate of 0.51-4.00%/um demonstrated a linear trend between threading dislocation density and grading rate, indicating that InAsP is an ideal grading system even for high As compositions. All metamorphic InAs samples showed room temperature photoluminescence with a peak emission wavelength around 3.3 um along with smooth crosshatch morphology. Metamorphic InAs grown with a grading rate of 0.51%/um demonstrated a threading dislocation density as low as 3.88x106 cm-2, showing that InAsP can be used to develop high-quality InAs virtual substrates on InP with low threading dislocation density.
Issue Date:2020-04-03
Rights Information:Copyright 2020 Brendan Eng
Date Available in IDEALS:2020-08-27
Date Deposited:2020-05

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