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Dislocation Formation and Glide in Atomically-Ordered Iii-V Semiconductors

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Dislocation Formation and Glide in Atomically-Ordered Iii-V Semiconductors DISLOCATION FORMATION AND GLIDE IN ATOMICALLY-ORDERED III-V SEMICONDUCTORS by Ryan Matthew France A thesis submitted to the Faculty and Board of Trustees of the Colorado School of Mines in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Materials Science). Golden, Colorado Date _______________________________________ Signed: _______________________________________ Ryan France Signed: _______________________________________ Dr. Brian Gorman Thesis Advisor Golden, Colorado Date _______________________________________ Signed: _______________________________________ Dr. Ryan Richards Director Materials Science Graduate Program ii ABSTRACT Strain relaxation of III-V materials is a complex process that can be heavily influenced by material microstructure. In this thesis, I investigate the effects of CuPt atomic ordering on dislocation formation and glide in III-V materials. CuPt atomic ordering has been observed in many ternary and quaternary III-V materials, and consists of alternating {111} planes of one or both of the mixed-group constituents. Most importantly, the ordered structure is induced by the surface reconstruction during epitaxy and is metastable in the bulk of the film. Glide through ordered planes disrupts the order pattern and reduces this metastability, and so is energetically favorable. This presents a unique situation where dislocations receive an additional driving force for glide. The additional glide force reduces the critical thickness of pseudomorphic material, but should also beneficially increase the glide length of metamorphic material. In addition, the distribution of dislocations is heavily skewed towards those that disrupt the order pattern. New dislocations can form upon order-disorder transitions in a metamorphic buffer as glide becomes more energetically favorable on different glide planes, necessitating redesign of the buffer structure. Further implications are discussed, as well as strategies to improve stability of pseudomorphic material and reduce the dislocation density of metamorphic material. iii TABLE OF CONTENTS ABSTRACT ……………………………………………………………………………… iii LIST OF FIGURES …………………………………………………………….….….…. vii LIST OF TABLES ……………………………………….….….….…………………….. ix ACKNOWLEDGEMENTS …………….….….….……………………………………… x CHAPTER 1 INTRODUCTION ….….….…………………………………………. 1 1.1 Thesis Organization ….….….………………………………………… 2 1.2 Motivation ….….….………………………………………………….. 4 1.2.1 Lattice-Mismatched Alloys ….….….………………………… 4 1.2.2 Lattice-Mismatched GaxIn1-xP for Metamorphic Solar Cells … 6 1.3 Strained-Layer Epitaxy Background ….….….……………………….. 7 1.3.1 Epitaxial Strain and Relaxation ….….….…………………….. 8 1.3.2 The Critical Thickness and Pseudomorphic Devices ………… 11 1.3.3 Dislocation Glide and Metamorphic Devices ………………… 14 1.4 Atomic Ordering ….….….……………………………………………. 18 1.4.1 CuPtB Ordering in III-V Materials ….….….………………….. 18 1.4.2 Dislocation Glide through Ordered Planes ….….….…………. 20 1.5 References ……………………………………………………………. 21 CHAPTER 2 CRITICAL THICKNESS OF ATOMICALLY ORDERED III-V ALLOYS ………………………………………….. 25 2.1 Abstract …………….….….….………………………………………. 25 2.2 Manuscript …………….….….….……………………………………. 25 2.3 Acknowledgements …………….….….….…………………………... 34 2.4 References …………….….….….……………………………………. 34 CHAPTER 3 CONTROL OF MISFIT DISLOCATION GLIDE PLANE DISTRIBUTION DURING STRAIN RELAXATION OF CUPT-ORDERED GAINAS AND GAINP …………….….….….….. 36 3.1 Abstract …………….….….….……………………………………….. 36 3.2 Introduction …………….….….….…………………………………… 36 3.3 Experimental Procedures …………….….….….……………………... 40 3.4 Results and Discussion …………….….….….……………………….. 42 iv 3.4.1 Effect of Miscut and Ordering on Glide Plane Distribution …. 42 3.4.2 Relationship between ordering parameter, glide plane distribution, and dislocation formation ………….…………… 45 3.4.3 Glide plane control …………….….….….…………………… 48 3.5 Summary …………….….….….……………………………………... 48 3.6 Acknowledgements …………….….….….…………………………... 49 3.7 References …………….….….….……………………………………. 49 CHAPTER 4 LATTICE-MISMATCHED 0.7-EV GAINAS SOLAR CELLS GROWN ON GAAS USING GAINP COMPOSITIONALLY GRADED BUFFERS …………….….….….………………………… 51 4.1 Abstract …………….….….….………………………………………. 51 4.2 Introduction …………….….….….…………………………………… 51 4.3 Experimental Details …………….….….….…………………………. 52 4.4 Measurement and Analysis of GaInP buffer …………….….….….…. 54 4.5 Reduction of Dislocation Density …………….….….….……………. 59 4.6 Solar Cell Results …………….….….….………………………….…. 60 4.7 Summary …………….….….….……………………………………… 62 4.8 Acknowledgements …………….….….….…………………………... 62 4.9 References …………….….….….……………………………………. 63 CHAPTER 5 IMPLICATIONS AND FUTURE WORK …………….….….….…... 65 5.1 Glide Enhancement in Metamorphic Buffers …………….….….…… 65 5.2 APB Interaction in Ordered Metamorphic Material …………….…… 67 5.3 Surface Energy and Nucleation …………….….….….……………… 68 5.4 Growth on Other Substrates …………….….….….………………….. 69 5.5 References …………….….….….……………………….….………... 70 CHAPTER 6 CONCLUSIONS …………….….….….……………………….….…. 71 6.1 Dislocation Glide Enhancement …………….….….….……………… 71 6.1.1 Critical Thickness of Pseudomorphic Material …………….… 71 6.1.2 Residual Strain of Metamorphic Material …………….……… 72 6.2 Burgers Vector Distribution of Active Dislocations …………………. 73 6.2.1 Glide-Plane Switching upon Order-Disorder Transition …….. 74 v 6.2.2 Control of Burgers Vector Distribution in Metamorphic Material …………….….….….……………….. 75 6.3 Dislocation Density Reduction in Ordered Buffers …………….….… 76 6.4 Final Conclusions …………….….….….……………………………. 77 6.5 References …………….….….….…………………………….……... 78 vi LIST OF FIGURES Figure 1.1 Illustrations of pseudomorphic and metamorphic material …………... 2 Figure 1.2 Bandgap vs lattice constant for common semiconductors, with optimal bandgap combination of 2-, 3-, and 4-junction devices overlaid …….. 5 Figure 1.3 Solar cell metrics as a function of dislocation density ……………….. 6 Figure 1.4 Modeled 2-junction solar cell efficiency for various bandgaps ……… 7 Figure 1.5 Illustration of dislocations in III-V materials ………………………… 10 Figure 1.6 Critical thickness of various III-V materials …………………………. 13 Figure 1.7 TEM of phase separation and dislocation pinning in GaInP graded buffers ………………………………………………………… 17 Figure 1.8 Illustration of dislocation glide through ordered planes of GaInP …… 20 Figure 2.1 Critical thickness of (a) arbitrary material with varied boundary energy and (b) GaInP and GaInAs with varied order parameter …….. 29 Figure 2.2 Strain relaxation throughout growth of GaInP with varied ordering … 31 Figure 2.3 Cathodoluminescence images of lattice-mismatched GaInP with varied thickness and order parameters ……………………………….. 32 Figure 3.1 (a) Illustration of dislocations in III-V materials (b) Illustration showing components of the Burgers vector for a/2<101>{111} dislocations on a miscut susbtrate (c) Illustration showing dislocation glide through ordered {111} planes in GaInP ………………………... 39 Figure 3.2 X-ray diffraction reciprocal space map (XRD RSM) of (004) planes from lattice-mismatched (a) GaInAs and (b) GaInP. (c) Illustration of compositionally graded buffers …………………………………… 43 Figure 3.3 XRD RSM and TED of mixed-material buffers, showing control over the distribution of dislocations ………………………………….. 44 Figure 3.4 Dark field TEM of (1/2)(113), showing sharp APBs in the ordering, produced by dislocation glide ……………………………………….. 46 Figure 3.5 XRD RSM of GaInP buffers with varying final composition ……….. 47 Figure 3.6 Control over the glide plane distribution in GaInP buffers using Sb surfactant ………………………………………………………….. 49 Figure 4.1 Illustration of a compositionally graded buffer and a lattice-mismatched GaInAs solar cell ………………………………… 53 Figure 4.2 Cathodoluminescence of the final layer of a GaxIn1-xP compositionally graded buffer, graded to InP ………………………………………….. 55 vii Figure 4.3 In situ stress-thickness product, from wafer curvature of a GaxIn1-xP compositionally graded buffer, graded to InP ……………………….. 56 Figure 4.4 AFM image of a GaxIn1-xP buffer, graded to InP …………………….. 56 Figure 4.5 TEM and TED of a GaInP buffer, graded to InP …………………….. 58 Figure 4.6 XRD RSM of (004) planes of a GaInP buffer, graded to InP ………… 58 Figure 4.7 (a) Residual TDD and (b) RMS roughness of a GaInP buffer, graded to InP, with varying total thickness …………………………… 59 Figure 4.8 (a) J-V and (b) IQE of GaInAs solar cells, grown on both InP substrates and GaInP graded buffers …………………………………. 61 Figure 5.1 Calculated APB energy for various APB spacings …………………… 68 Figure 5.2 TEM of GaInP graded buffers grown on (001) substrates miscut 6° towards {111}A …………………………………………….. 69 Figure 6.1 Glide plane distribution and dislocation density throughout a GaInP graded buffer, showing an increase at the glide-plane switch ………… 74 viii LIST OF TABLES Table 1.1 Anti-phase Boundary Energy created upon glide of 60° dislocations through various CuPt-ordered materials ………………………………. 21 ix ACKNOWLEDGEMENTS All research builds upon earlier work, and here the question of where to begin acknowledgements is near impossible to answer. First, I am greatly thankful for the MOVPE growth tutelage of John Geisz, Jerry Olson, and Dan Friedman, who were also responsible for making the research progress rapid through setting up an excellent lab. I am grateful to Waldo Olavarria, who regularly placed himself at risk as the main reactor operator (unloading my phosphine runs were always a potential fire hazard!). I was blessed to have access to the solar cell processing skills of Michelle Young, who managed to somehow be a perfectionist while still turning
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