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Description
HgCdTe is currently the dominant material for infrared sensing and imaging, and is usually grown on lattice-matched bulk CdZnTe (CZT) substrates. There have been significant recent efforts to identify alternative substrates to CZT as well as alternative detector materials to HgCdTe. In this dissertation research, a wide range of transmission electron microscopy (TEM) imaging and analytical techniques was used in the characterization of epitaxial HgCdTe and related materials and substrates for third generation IR detectors. ZnTe layers grown on Si substrates are considered to be promising candidates for lattice-matched, large-area, and low-cost composite substrates for deposition of II-VI and III-V compound semiconductors with lattice constants near 6.1 Å. After optimizing MBE growth conditions including substrate pretreatment prior to film growth, as well as nucleation and growth temperatures, thick ZnTe/Si films with high crystallinity, low defect density, and excellent surface morphology were achieved. Changes in the Zn/Te flux ratio used during growth were also investigated. Small-probe microanalysis confirmed that a small amount of As was present at the ZnTe/Si interface. A microstructural study of HgCdTe/CdTe/GaAs (211)B and CdTe/GaAs (211)B heterostructures grown using MBE was carried out. High quality MBE-grown CdTe on GaAs(211)B substrates was demonstrated to be a viable composite substrate platform for HgCdTe growth. In addition, analysis of interfacial misfit dislocations and residual strain showed that the CdTe/GaAs interface was fully relaxed. In the case of HgCdTe/CdTe/ GaAs(211)B, thin HgTe buffer layers between HgCdTe and CdTe were also investigated for improving the HgCdTe crystal quality. A set of ZnTe layers epitaxially grown on GaSb(211)B substrates using MBE was studied using high resolution X-ray diffraction (HRXRD) measurements and TEM characterization in order to investigate conditions for defect-free growth. HRXRD results gave critical thickness estimates between 350 nm and 375 nm, in good agreement with theoretical predictions. Moreover, TEM results confirmed that ZnTe layers with thicknesses of 350 nm had highly coherent interfaces and very low dislocation densities, unlike samples with the thicker ZnTe layers.
ContributorsKim, Jae Jin (Author) / Smith, David J. (Thesis advisor) / McCartney, Martha R. (Committee member) / Alford, Terry L. (Committee member) / Crozier, Peter A. (Committee member) / Arizona State University (Publisher)
Created2012
Description
Fluctuation Electron Microscopy (FEM) has become an effective materials' structure characterization technique, capable of probing medium-range order (MRO) that may be present in amorphous materials. Although its sensitivity to MRO has been exercised in numerous studies, FEM is not yet a quantitative technique. The holdup has been the discrepancy between the computed kinematical variance and the experimental variance, which previously was attributed to source incoherence. Although high-brightness, high coherence, electron guns are now routinely available in modern electron microscopes, they have not eliminated this discrepancy between theory and experiment. The main objective of this thesis was to explore, and to reveal, the reasons behind this conundrum.
The study was started with an analysis of the speckle statistics of tilted dark-field TEM images obtained from an amorphous carbon sample, which confirmed that the structural ordering is sensitively detected by FEM. This analysis also revealed the inconsistency between predictions of the source incoherence model and the experimentally observed variance.
FEM of amorphous carbon, amorphous silicon and ultra nanocrystalline diamond samples was carried out in an attempt to explore the conundrum. Electron probe and sample parameters were varied to observe the scattering intensity variance behavior. Results were compared to models of probe incoherence, diffuse scattering, atom displacement damage, energy loss events and multiple scattering. Models of displacement decoherence matched the experimental results best.
Decoherence was also explored by an interferometric diffraction method using bilayer amorphous samples, and results are consistent with strong displacement decoherence in addition to temporal decoherence arising from the electron source energy spread and energy loss events in thick samples.
It is clear that decoherence plays an important role in the long-standing discrepancy between experimental FEM and its theoretical predictions.
The study was started with an analysis of the speckle statistics of tilted dark-field TEM images obtained from an amorphous carbon sample, which confirmed that the structural ordering is sensitively detected by FEM. This analysis also revealed the inconsistency between predictions of the source incoherence model and the experimentally observed variance.
FEM of amorphous carbon, amorphous silicon and ultra nanocrystalline diamond samples was carried out in an attempt to explore the conundrum. Electron probe and sample parameters were varied to observe the scattering intensity variance behavior. Results were compared to models of probe incoherence, diffuse scattering, atom displacement damage, energy loss events and multiple scattering. Models of displacement decoherence matched the experimental results best.
Decoherence was also explored by an interferometric diffraction method using bilayer amorphous samples, and results are consistent with strong displacement decoherence in addition to temporal decoherence arising from the electron source energy spread and energy loss events in thick samples.
It is clear that decoherence plays an important role in the long-standing discrepancy between experimental FEM and its theoretical predictions.
ContributorsRezikyan, Aram (Author) / Treacy, Michael M.J. (Thesis advisor) / Smith, David J. (Committee member) / McCartney, Martha R. (Committee member) / Rez, Peter (Committee member) / Arizona State University (Publisher)
Created2015
Description
The two-dimensional electron gas (2DEG) at SrTiO3-based oxide interfaces has been extensively studied recently for its high carrier density, high electron mobility, superconducting, ferromagnetic, ferrroelectric and magnetoresistance properties, with possible application for all-oxide devices. Understanding the mechanisms behind the 2DEG formation and factors affecting its properties is the primary objective of this dissertation.
Advanced electron microscopy techniques, including aberration-corrected electron microscopy and electron energy-loss spectroscopy (EELS) with energy-loss near-edge structure (ELNES) analysis, were used to characterize the interfaces. Image and spectrum data-processing algorithms, including subpixel atomic position measurement, and novel outlier detection by oversampling, subspace division based EELS background removal and bias-free endmember extraction algorithms for hyperspectral unmixing and mapping were heavily used. Results were compared with density functional theory (DFT) calculations for theoretical explanation.
For the γ-Al2O3/SrTiO3 system, negative-Cs imaging confirmed the formation of crystalline γ-Al2O3. ELNES hyperspectral unmixing combined with DFT calculations revealed that oxygen vacancies, rather than polar discontinuity, were the key to the 2DEG formation. The critical thickness can be explained by shift of the Fermi level due to Ti out diffusion from the substrate to the film.
At the LaTiO3/SrTiO3 interface, aberration-corrected imaging showed crystallinity deterioration in LaTiO3 films a few unit cells away from the interface. ELNES showed that oxygen annealing did not alter the crystallinity but converted Ti3+ near the interface into Ti4+, which explained disappearance of the conductivity.
At the EuO/SrTiO3 interface, both high-resolution imaging and ELNES confirmed EuO formation. ELNES hyperspectral unmixing showed a Ti3+ layer confined to within several unit cells of the interface on the SrTiO3 side, confirming the presence of oxygen vacancies.
At the BaTiO3/SrTiO3 interface, spontaneous polarization and local lattice parameters were measured directly in each unit cell column and compared with oxidation state mapping using ELNES with unit-cell resolution. The unusually large polarization near the interface and the polarization gradient were explained by oxygen vacancies and the piezoelectric effect due to epitaxial strain and strain gradient from relaxation.
Advanced electron microscopy techniques, including aberration-corrected electron microscopy and electron energy-loss spectroscopy (EELS) with energy-loss near-edge structure (ELNES) analysis, were used to characterize the interfaces. Image and spectrum data-processing algorithms, including subpixel atomic position measurement, and novel outlier detection by oversampling, subspace division based EELS background removal and bias-free endmember extraction algorithms for hyperspectral unmixing and mapping were heavily used. Results were compared with density functional theory (DFT) calculations for theoretical explanation.
For the γ-Al2O3/SrTiO3 system, negative-Cs imaging confirmed the formation of crystalline γ-Al2O3. ELNES hyperspectral unmixing combined with DFT calculations revealed that oxygen vacancies, rather than polar discontinuity, were the key to the 2DEG formation. The critical thickness can be explained by shift of the Fermi level due to Ti out diffusion from the substrate to the film.
At the LaTiO3/SrTiO3 interface, aberration-corrected imaging showed crystallinity deterioration in LaTiO3 films a few unit cells away from the interface. ELNES showed that oxygen annealing did not alter the crystallinity but converted Ti3+ near the interface into Ti4+, which explained disappearance of the conductivity.
At the EuO/SrTiO3 interface, both high-resolution imaging and ELNES confirmed EuO formation. ELNES hyperspectral unmixing showed a Ti3+ layer confined to within several unit cells of the interface on the SrTiO3 side, confirming the presence of oxygen vacancies.
At the BaTiO3/SrTiO3 interface, spontaneous polarization and local lattice parameters were measured directly in each unit cell column and compared with oxidation state mapping using ELNES with unit-cell resolution. The unusually large polarization near the interface and the polarization gradient were explained by oxygen vacancies and the piezoelectric effect due to epitaxial strain and strain gradient from relaxation.
ContributorsLu, Sirong (Author) / Smith, David J. (Thesis advisor) / McCartney, Martha R. (Thesis advisor) / Chizmeshya, Andrew (Committee member) / Crozier, Peter A. (Committee member) / Arizona State University (Publisher)
Created2018
Description
In this dissertation research, conventional and aberration-corrected (AC) transmission electron microscopy (TEM) techniques were used to evaluate the structural and compositional properties of thin-film semiconductor compounds/alloys grown by molecular beam epitaxy for infrared photo-detection. Imaging, diffraction and spectroscopy techniques were applied to TEM specimens in cross-section geometry to extract information about extended structural defects, chemical homogeneity and interface abruptness. The materials investigated included InAs1-xBix alloys grown on GaSb (001) substrates, InAs/InAs1-xSbx type-II superlattices grown on GaSb (001) substrates, and CdTe-based thin-film structures grown on InSb (001) substrates.
The InAsBi dilute-bismide epitaxial films were grown on GaSb (001) substrates at relatively low growth temperatures. The films were mostly free of extended defects, as observed in diffraction-contrast images, but the incorporation of bismuth was not homogeneous, as manifested by the lateral Bi-composition modulation and Bi-rich surface droplets. Successful Bi incorporation into the InAs matrix was confirmed using lattice expansion measurements obtained from misfit strain analysis of high-resolution TEM (HREM) images.
Analysis of averaged intensity line profiles in HREM and scanning TEM (STEM) images of the Ga-free InAs/InAs1-xSbx type-II strained superlattices indicated slight variations in layer thickness across the superlattice stack. The interface abruptness was evaluated using misfit strain analysis of AC-STEM images, electron energy-loss spectroscopy and 002 dark-field imaging. The compositional profiles of antimony across the superlattices were fitted to a segregation model and revealed a strong antimony segregation probability.
The CdTe/MgxCd1-xTe double-heterostructures were grown with Cd overflux in a dual-chamber molecular beam epitaxy with an ultra-high vacuum transfer loadlock. Diffraction-contrast images showed that the growth temperature had a strong impact on the structural quality of the epilayers. Very abrupt CdTe/InSb interfaces were obtained for epilayers grown at the optimum temperature of 265 °C, and high-resolution imaging using AC-STEM revealed an interfacial transition region with a width of a few monolayers and smaller lattice spacing than either CdTe or InSb.
The InAsBi dilute-bismide epitaxial films were grown on GaSb (001) substrates at relatively low growth temperatures. The films were mostly free of extended defects, as observed in diffraction-contrast images, but the incorporation of bismuth was not homogeneous, as manifested by the lateral Bi-composition modulation and Bi-rich surface droplets. Successful Bi incorporation into the InAs matrix was confirmed using lattice expansion measurements obtained from misfit strain analysis of high-resolution TEM (HREM) images.
Analysis of averaged intensity line profiles in HREM and scanning TEM (STEM) images of the Ga-free InAs/InAs1-xSbx type-II strained superlattices indicated slight variations in layer thickness across the superlattice stack. The interface abruptness was evaluated using misfit strain analysis of AC-STEM images, electron energy-loss spectroscopy and 002 dark-field imaging. The compositional profiles of antimony across the superlattices were fitted to a segregation model and revealed a strong antimony segregation probability.
The CdTe/MgxCd1-xTe double-heterostructures were grown with Cd overflux in a dual-chamber molecular beam epitaxy with an ultra-high vacuum transfer loadlock. Diffraction-contrast images showed that the growth temperature had a strong impact on the structural quality of the epilayers. Very abrupt CdTe/InSb interfaces were obtained for epilayers grown at the optimum temperature of 265 °C, and high-resolution imaging using AC-STEM revealed an interfacial transition region with a width of a few monolayers and smaller lattice spacing than either CdTe or InSb.
ContributorsLu, Jing (Author) / Smith, David J. (Thesis advisor) / Alford, Terry L. (Committee member) / Crozier, Peter A. (Committee member) / McCartney, Martha R. (Committee member) / Zhang, Yong-Hang (Committee member) / Arizona State University (Publisher)
Created2017
Description
The research of this dissertation has involved the nanoscale quantitative characterization of patterned magnetic nanostructures and devices using off-axis electron holography and Lorentz microscopy. The investigation focused on different materials of interest, including monolayer Co nanorings, multilayer Co/Cu/Py (Permalloy, Ni81Fe19) spin-valve nanorings, and notched Py nanowires, which were fabricated via a standard electron-beam lithography (EBL) and lift-off process. Magnetization configurations and reversal processes of Co nanorings, with and without slots, were observed. Vortex-controlled switching behavior with stepped hysteresis loops was identified, with clearly defined onion states, vortex states, flux-closure (FC) states, and Omega states. Two distinct switching mechanisms for the slotted nanorings, depending on applied field directions relative to the slot orientations, were attributed to the vortex chirality and shape anisotropy. Micromagnetic simulations were in good agreement with electron holography observations of the Co nanorings, also confirming the switching field of 700-800 Oe. Co/Cu/Py spin-valve slotted nanorings exhibited different remanent states and switching behavior as a function of the different directions of the applied field relative to the slots. At remanent state, the magnetizations of Co and Py layers were preferentially aligned in antiparallel coupled configuration, with predominant configurations in FC or onion states. Two-step and three-step hysteresis loops were quantitatively determined for nanorings with slots perpendicular, or parallel to the applied field direction, respectively, due to the intrinsic coercivity difference and interlayer magnetic coupling between Co and Py layers. The field to reverse both layers was on the order of ~800 Oe. Domain-wall (DW) motion within Py nanowires (NWs) driven by an in situ magnetic field was visualized and quantified. Different aspects of DW behavior, including nucleation, injection, pinning, depinning, relaxation, and annihilation, occurred depending on applied field strength. A unique asymmetrical DW pinning behavior was recognized, depending on DW chirality relative to the sense of rotation around the notch. The transverse DWs relaxed into vortex DWs, followed by annihilation in a reversed field, which was in agreement with micromagnetic simulations. Overall, the success of these studies demonstrated the capability of off-axis electron holography to provide valuable insights for understanding magnetic behavior on the nanoscale.
ContributorsHe, Kai (Author) / McCartney, Martha R. (Thesis advisor) / Smith, David J. (Thesis advisor) / Chamberlin, Ralph V. (Committee member) / Crozier, Peter A. (Committee member) / Drucker, Jeff (Committee member) / Arizona State University (Publisher)
Created2010
Description
Multifunctional oxide thin-films grown on silicon and several oxide substrates have been characterized using High Resolution (Scanning) Transmission Electron Microscopy (HRTEM), Energy-Dispersive X-ray Spectroscopy (EDX), and Electron Energy-Loss Spectroscopy (EELS). Oxide thin films grown on SrTiO3/Si pseudo-substrate showed the presence of amorphised SrTiO3 (STO) at the STO/Si interface. Oxide/oxide interfaces were observed to be atomically clean with very few defects.
Al-doped SrTiO3 thin films grown on Si were of high crystalline quality. The Ti/O ratio estimated from EELS line scans revealed that substitution of Ti by Al created associated O vacancies. The strength of the crystal field in STO was measured using EELS, and decreased by ~1.0 eV as Ti4+ was substituted by Al3+. The damping of O-K EELS peaks confirmed the rise in oxygen vacancies. For Co-substituted STO films grown on Si, the EDS and EELS spectra across samples showed Co doping was quite random. The substitution of Ti4+ with Co3+ or Co2+ created associated oxygen vacancies for charge balance. Presence of oxygen vacancies was also confirmed by shift of Ti-L EELS peaks towards lower energy by ~0.4 eV. The crystal-field strength decreased by ~0.6 eV as Ti4+ was partially substituted by Co3+ or Co2+.
Spinel Co3O4 thin films grown on MgAl2O4 (110) were observed to have excellent crystalline quality. The structure of the Co3O4/MgAl2O4 interface was determined using HRTEM and image simulations. It was found that MgAl2O4 substrate is terminated with Al and oxygen. Stacking faults and associated strain fields in spinel Co3O4 were found along [111], [001], and [113] using Geometrical Phase Analysis.
NbO2 films on STO (111) were observed to be tetragonal with lattice parameter of 13.8 Å and NbO films on LSAT (111) were observed to be cubic with lattice parameter of 4.26 Å. HRTEM showed formation of high quality NbOx films and excellent coherent interface. HRTEM of SrAl4 on LAO (001) confirmed an island growth mode. The SrAl4 islands were highly crystalline with excellent epitaxial registry with LAO. By comparing HRTEM images with image simulations, the interface structure was determined to consist of Sr-terminated SrAl4 (001) on AlO2-terminated LAO (001).
Al-doped SrTiO3 thin films grown on Si were of high crystalline quality. The Ti/O ratio estimated from EELS line scans revealed that substitution of Ti by Al created associated O vacancies. The strength of the crystal field in STO was measured using EELS, and decreased by ~1.0 eV as Ti4+ was substituted by Al3+. The damping of O-K EELS peaks confirmed the rise in oxygen vacancies. For Co-substituted STO films grown on Si, the EDS and EELS spectra across samples showed Co doping was quite random. The substitution of Ti4+ with Co3+ or Co2+ created associated oxygen vacancies for charge balance. Presence of oxygen vacancies was also confirmed by shift of Ti-L EELS peaks towards lower energy by ~0.4 eV. The crystal-field strength decreased by ~0.6 eV as Ti4+ was partially substituted by Co3+ or Co2+.
Spinel Co3O4 thin films grown on MgAl2O4 (110) were observed to have excellent crystalline quality. The structure of the Co3O4/MgAl2O4 interface was determined using HRTEM and image simulations. It was found that MgAl2O4 substrate is terminated with Al and oxygen. Stacking faults and associated strain fields in spinel Co3O4 were found along [111], [001], and [113] using Geometrical Phase Analysis.
NbO2 films on STO (111) were observed to be tetragonal with lattice parameter of 13.8 Å and NbO films on LSAT (111) were observed to be cubic with lattice parameter of 4.26 Å. HRTEM showed formation of high quality NbOx films and excellent coherent interface. HRTEM of SrAl4 on LAO (001) confirmed an island growth mode. The SrAl4 islands were highly crystalline with excellent epitaxial registry with LAO. By comparing HRTEM images with image simulations, the interface structure was determined to consist of Sr-terminated SrAl4 (001) on AlO2-terminated LAO (001).
ContributorsDhamdhere, Ajit (Author) / Smith, David J. (Thesis advisor) / McCartney, Martha R. (Committee member) / Chamberlin, Ralph (Committee member) / Ponce, Fernando (Committee member) / Arizona State University (Publisher)
Created2015
Description
Extended crystal defects often play a critical role in determining semiconductor device performance. This dissertation describes the application of transmission electron microscopy (TEM) and aberration-corrected scanning TEM (AC-STEM) to study defect clusters and the atomic-scale structure of defects in compound semiconductors.
An extensive effort was made to identify specific locations of crystal defects in epitaxial CdTe that might contribute to degraded light-conversion efficiency. Electroluminescence (EL) mapping and the creation of surface etch pits through chemical treatment were combined in attempts to identify specific structural defects for subsequent TEM examination. Observations of these specimens revealed only surface etch pits, without any visible indication of extended defects near their base. While chemical etch pits could be helpful for precisely locating extended defects that intersect with the treated surface, this study concluded that surface roughness surrounding etch pits would likely mitigate against their usefulness.
Defect locations in GaAs solar-cell devices were identified using combinations of EL, photoluminescence, and Raman scattering, and then studied more closely using TEM. Observations showed that device degradation was invariably associated with a cluster of extended defects, rather than a single defect, as previously assumed. AC-STEM observations revealed that individual defects within each cluster consisted primarily of intrinsic stacking faults terminated by 30° and 90° partial dislocations, although other defect structures were also identified. Lomer dislocations were identified near locations where two lines of strain contrast intersected in a large cluster, and a comparatively shallow cluster, largely constrained to the GaAs emitter layer, contained 60° perfect dislocations associated with localized strain contrast.
In another study, misfit dislocations at II-VI/III-V heterovalent interfaces were investigated and characterized using AC-STEM. Misfit strain at ZnTe/GaAs interfaces, which have relatively high lattice mismatch (7.38%), was relieved primarily through Lomer dislocations, while ZnTe/InP interfaces, with only 3.85% lattice mismatch, were relaxed by a mixture of 60° perfect dislocations, 30° partial dislocations, and Lomer dislocations. These results were consistent with the previous findings that misfit strain was relaxed primarily through 60° perfect dislocations that had either dissociated into partial dislocations or interacted to form Lomer dislocations as the amount of misfit strain increased.
An extensive effort was made to identify specific locations of crystal defects in epitaxial CdTe that might contribute to degraded light-conversion efficiency. Electroluminescence (EL) mapping and the creation of surface etch pits through chemical treatment were combined in attempts to identify specific structural defects for subsequent TEM examination. Observations of these specimens revealed only surface etch pits, without any visible indication of extended defects near their base. While chemical etch pits could be helpful for precisely locating extended defects that intersect with the treated surface, this study concluded that surface roughness surrounding etch pits would likely mitigate against their usefulness.
Defect locations in GaAs solar-cell devices were identified using combinations of EL, photoluminescence, and Raman scattering, and then studied more closely using TEM. Observations showed that device degradation was invariably associated with a cluster of extended defects, rather than a single defect, as previously assumed. AC-STEM observations revealed that individual defects within each cluster consisted primarily of intrinsic stacking faults terminated by 30° and 90° partial dislocations, although other defect structures were also identified. Lomer dislocations were identified near locations where two lines of strain contrast intersected in a large cluster, and a comparatively shallow cluster, largely constrained to the GaAs emitter layer, contained 60° perfect dislocations associated with localized strain contrast.
In another study, misfit dislocations at II-VI/III-V heterovalent interfaces were investigated and characterized using AC-STEM. Misfit strain at ZnTe/GaAs interfaces, which have relatively high lattice mismatch (7.38%), was relieved primarily through Lomer dislocations, while ZnTe/InP interfaces, with only 3.85% lattice mismatch, were relaxed by a mixture of 60° perfect dislocations, 30° partial dislocations, and Lomer dislocations. These results were consistent with the previous findings that misfit strain was relaxed primarily through 60° perfect dislocations that had either dissociated into partial dislocations or interacted to form Lomer dislocations as the amount of misfit strain increased.
ContributorsMcKeon, Brandon (Author) / Smith, David J. (Thesis advisor) / McCartney, Martha R. (Thesis advisor) / Liu, Jingyue (Committee member) / Zhang, Yong-Hang (Committee member) / Arizona State University (Publisher)
Created2020
Description
The evolution of defects at different stages of strain relaxation in low-mismatched GaAs/GaAs1-xSbx/GaAs(001) (x ~ 0.08) heterostructures, and the underlying relaxation mechanisms, have been comprehensively studied primarily using transmission electron microscopy (TEM). Aberration-corrected scanning transmission electron microscopy (STEM) has been used for atomic-scale study of interfacial defects in low-mismatched GaAs(001)-based and high-mismatched GaSb/GaAs(001) heterostructures.Three distinct stages of strain relaxation were identified in GaAs/GaAs1-xSbx/GaAs(001) (x ~ 0.08) heterostructures with GaAsSb film thicknesses in the range of 50 to 4000 nm capped with 50-nm-thick GaAs layers. Diffraction contrast analysis with conventional TEM revealed that although 60° dislocations were primarily formed during the initial sluggish Stage-I relaxation, 90° dislocations were also created. Many curved dislocations, the majority of which extended into the substrate, were formed during Stage-II and Stage-III relaxation. The capping layers of heterostructures with larger film thickness (500 nm onwards) exhibited only Stage-I relaxation. A decrease in dislocation density was observed at the cap/film interface of the heterostructure with 4000-nm-thick film compared to that with 2000-nm-thick film, which correlated with smoothening of surface cross-hatch morphology. Detailed consideration of plausible dislocation sources for the capping layer led to the conclusion that dislocation half-loops nucleated at surface troughs were the main source of threading dislocations in these heterostructures.
Aberration-corrected STEM imaging revealed that interfacial 60° dislocations in GaAs/GaAsSb/GaAs(001) and GaAs/GaAsP/GaAs(001) heterostructures were dissociated to form intrinsic stacking faults bounded by 90° and 30° Shockley partial dislocations. The cores of the 30° partials contained single atomic columns indicating that these dislocations primarily belonged to glide set. Apart from isolated dissociated 60° dislocations, Lomer-Cottrell locks, Lomer dislocations and a novel type of dissociated 90° dislocation were observed in GaAs/GaAsSb/GaAs heterostructures.
The core structure of interfacial defects in GaSb/GaAs(001) heterostructure was also investigated using aberration-corrected STEM. 90° Lomer dislocations were primarily formed; however, glide-set perfect 60° and dissociated 60° dislocations were also observed. The 5-7 atomic-ring shuffle-set dislocation, the left-displaced 6-8 atomic-ring glide-set and the right-displaced 6-8 atomic-ring glide-set dislocations were three types of Lomer dislocations that were identified, among which the shuffle-set type was most common.
ContributorsGangopadhyay, Abhinandan (Author) / Smith, David J. (Thesis advisor) / Bertoni, Mariana (Committee member) / Crozier, Peter A. (Committee member) / King, Richard R. (Committee member) / McCartney, Martha R. (Committee member) / Arizona State University (Publisher)
Created2021