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MBE GROWTH AND INSTRUMENTATION

MBE GROWTH AND INSTRUMENTATION. Thesis Proposal Outline for the Degree of Master of Science Dr. Roman Stemprok, Major Professor Dr. Terry Golding, Supervisor /Committee Member Dr. Vijay Vaidyanathan, Committee Member Dr. Albert B. Grubbs, Jr., Chair of the

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MBE GROWTH AND INSTRUMENTATION

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  1. MBE GROWTH AND INSTRUMENTATION Thesis Proposal Outline for the Degree of Master of Science Dr. Roman Stemprok, Major Professor Dr. Terry Golding, Supervisor /Committee Member Dr. Vijay Vaidyanathan, Committee Member Dr. Albert B. Grubbs, Jr., Chair of the Department Of Engineering technology University of North Texas

  2. MBE GROWTH AND INSTRUMENTATION • Problem Statement • Purpose of Research • Research Question • Statement of Need • Research Plan • Assumptions • Limitations • Review of Literature • Methodology • Summary • Timeline • References

  3. MBE GROWTH AND INSTRUMENTATION Problem Statement • Molecular Beam Epitaxy • Reflection High Energy Electron Diffraction (RHEED) RHEED Gun setup for MBE growth [1]

  4. MBE GROWTH AND INSTRUMENTATION Purpose of Research • MBE source maintenance • UHV basics and maintenance • MBE sample loading and preperation • Operating softwares such as SpecVIEW, Video RHEED Intensity Measurement Program, Spectramass 2000 software. • Developing a LabVIEW program for the acquisition of images and calculating the sample growth rate. • Using the program to study the growth of GaP using atomic phosphorus.

  5. MBE GROWTH AND INSTRUMENTATION Research Question • Identifying and overcoming the various limitations during MBE growth process • To write a LabVIEW program to acquire and analyze images using existing devices in the market at a minimum cost • Set up the III/V MBE system for growth of GaP samples through the use of a phosphorous cracker

  6. MBE Growth and Instrumentation/ Statement of Need • Molecular Beam Epitaxy • Slow growth rate of ~1μm/hr. • Reduced temperatures. For example about 500-600oC for GaAs. • Reduced handling requirements of toxic materials such as As. • The ability to abruptly cease or initiate molecular beams producing hyperabrupt surfaces. • Facility of in situ analysis during growth. • Growth of electronic and photonic devices such as solar cells, diode lasers, LEDs and bi-polar junction transistor.

  7. MBE Growth and Instrumentation/ Statement of Need • Electron Diffraction • Lattice + Basis = Crystal Structure

  8. Crystal Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Space Lattice Basis, containing two different ions

  9. MBE Growth and Instrumentation/ Statement of Need • Electron DiffractionBragg’s Law

  10. MBE Growth and Instrumentation/ Statement of Need • Electron diffraction: • The electron density of a crystal can be represented in Fourier series in single dimension as where, n(x) is the electron density and is a point in Fourier space or reciprocal lattice space, n(x) has a period of a and the sum is over all integers p : positive, negative and zero.

  11. MBE Growth and Instrumentation / Statement of Need • Extending the analysis to three dimensional lattice structures, where is called the reciprocal lattice vector and is given by where, h,k,l are integers, a, b, c are the crystal axes of the original crystal structure and A,B,C are the axes for the reciprocal lattice space.

  12. MBE Growth and Instrumentation / Statement of Need Ewald’s Sphere for construction of diffraction pattern in reciprocal lattice space, where,

  13. MBE Growth and Instrumentation / Statement of Need Fig (6.a) RHEED patterns and the corresponding electron micrographs of GaAs grown using MBE GaAs heated in vacuum to 580oC for 5min. RHEED Patterns RHEED patterns and the corresponding electron micrographs of Fig (6.a) after 1µm of GaAs deposited on surface of (6.a).

  14. MBE Growth and Instrumentation / Statement of Need RHEED OSCILLATIONS Ilustration of RHEED spot oscillations during the growth of a monolayer [7]

  15. MBE Growth and Instrumentation / Research Plan • LabVIEW • Preparing the III/V MBE chamber for the growth of GaP crystals using atomic phosphorous cracker.

  16. MBE Growth and Instrumentation / Research Plan LabVIEW • A subVI to store the images. • A subVI to mesaure the intensity of images at a particular region of interest, continuously in time. • A subVI to plot the Intensity vs Time graph of the measured intensity. • A subVI to calculate the growth rate of the sample.

  17. MBE Growth and Instrumentation / Research Plan Preparing the III/V Chamber • Cleaning the view ports: in the ratio of 1:2:10 • Checking the crucibles. • Clearing the molybdenum blocks: in a ratio of 1:2:1. • Aligning the linear transfer rod. • Venting the chamber. • Degassing and deoxidizing the samples.

  18. MBE Growth and Instrumentation / Assumptions • The terms and formulas used will require a basic knowledge of mathematics, engineering and physics. • The software implementation will require knowledge of LabVIEW, DOS and Windows Operating environment. • The experiments will be carried out based on the evidence available through prior research in this field. It will be assumed that similar or required growth environments have been established and the results will be analyzed accordingly. • The system is basically an III/V growth chamber and is assumed to work well at different temperatures and pressures with the materials not used previously within the chamber. • The LabVIEW program that is to be written is assumed to work on the similar guidelines of the existing software and yield compatible results. The depth and extension of the research mainly depends on the timeline and the cost constraints. • It is assumed that all samples are doped with the said percentages of constituent materials. • The RHEED is assumed to be fully functional as per the given specifications.

  19. MBE Growth and Instrumentation / Limitations • This research is limited only to get acquainted with the MBE growth process and instrumentation. • The proposed LabVIEW program shall be written for implementation only with the III/V MBE system. • The LabVIEW program is aimed only at displaying the intensity vs time graph and calculating the growth rate of the sample. • The measurements shall be taken on 4-6 samples. • The project is bound by the cost ( The frame grabber card and the Vision Development module cost $2100) and the timeline (6 months) constraints. • The study shall be concentrated mainly on the growth of GaP samples using an atomic phosphorous cracker.

  20. MBE Growth and Instrumentation / Review of Literature • Proposed by Gunther in 1958. Schematic illustration of basic evaporation process for molecular beam epitaxy .

  21. MBE Growth and Instrumentation / Review of Literature Schematic cross section of an advanced three- chamber UHV system designed for MBE growth and detailed surface studies [10].

  22. MBE Growth and Instrumentation / Methodology Introduction Varian 360, III/V MBE chamber at UNT

  23. MBE Growth and Instrumentation / Methodology Load-lock chamber of the III/V MBE system

  24. MBE Growth and Instrumentation / Methodology View port of the load-lock chamber showing the molybdenum blocks and samples.

  25. MBE Growth and Instrumentation / Methodology Preparation chamber of the III/V MBE system

  26. MBE Growth and Instrumentation / Methodology Top view of a typical standard MBE system growth chamber [13].

  27. MBE Growth and Instrumentation / Methodology Growth chamber of III/V MBE system.

  28. MBE Growth and Instrumentation / Methodology • Spectramass PC2000 mass spectrometer software. • SpecView Plus software. • Video RHEED Intensity Measurement System, Program RHEED. • Vacuum pumps: • Mechanical pump – (2) • Turbo pump – (1) • Ion pump – (3) • Cryo pump – (1)

  29. MBE Growth and Instrumentation/ Methodology Vacuum Pumps Vacuum pumps on the III/V MBE system

  30. Control Equipment MBE Growth and Instrumentation / Methodology RHEED control Equipment housing rack Furnace control unit housing rack Ion pump control unit housing rack

  31. MBE Growth and Instrumentation / Summary • Summary of the study. • Answer to research questions. • Conclusions based on the results and analysis of the study. • Strengths of the study. • Weakness of the study.

  32. Timeline in Months 1 2 3 4 5 6 7 8 9 10 11 12 Activity Review of Literature Working with MBE Acquire FG Card LabVIEW setup For MBE MBE setup for GaP Thesis write up MBE Growth and Instrumentation / Timeline

  33. MBE Growth and Instrumentation / References • http://mrlxp2.mrl.uiuc.edu/~rheed/index.html • Oscillations in the Surface Structure of Sn-doped GaAs during growth by MBE [Surf. Sci. 103, L90 (1981)] by J.J.Harris, B.A.Joyce and P.J.Dobson. • K.G. Gunther, Z.Naturforsch. 13A (1958) 1801; W. Hanlein, K.G. Gunther, in Advances in Vaccum Science & Technology (Proc. 1st Int. Congr. on Vacuum Techiques, Namur 1958) 727. • J.R.Arthur, J.Appl. Phys. 39 (1968) 4032. • C.Kittel, Introduction to Solid State Physics.

  34. MBE Growth and Instrumentation / References • A.Y.Cho, J. Vac. Sci. Technol. 8, S31 (1971). • http://www.ece.utexas.edu/projects/ece/mrc/groups/street_mbe/mbechapter • http://sine.ni.com/apps/we/nioc.vp?cid=11407&lang=US • Gunther, K.G. 1958. Z. Naturforsch. Teil A 13:1801-89. • Davey, J.E. Pankey, T. 1968. J. Appl. Phys, 39: 1941-48. • Molecular Beam Epitaxy of III-V Compounds: Technology and Growth Process, by Klaus Proog. Ann. Rev. Material Sci. 1981. 11-171-210.

  35. MBE Growth and Instrumentation / References • MBE Varian 360 manual, Operations and Routine Maintenance, Varian Industrial Equipment Group,1978. • W.Braun. Applied RHEED. Reflection High-energy Electron Diffraction during Crystal Growth. 1999. Springer Tracts in Modern Physics, 154. 2. The Spectramass PC 2000 mass spectrometer manual, Kurt J.Lesker Co. • The Spectramass PC 2000 mass spectrometer manual, Kurt J.Lesker Co. • Spec View Plus software – User Guide, Spec View LLC, February 1, 2000. • Varian System Instruction manual, Volume 1 & 2, Varian Industrial Equipment Group.

  36. QUESTIONS????

  37. Thank you……

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