Claremont Colleges Scholarship @ Claremont Pomona Senior Theses Pomona Student Scholarship 2005 Deep-UV Light Emitting Diodes: An Experimental Investigation of Characterization and Optimization Techniques Eric M. Fraser Pomona College Recommended Citation Fraser, Eric M., "Deep-UV Light Emitting Diodes: An Experimental Investigation of Characterization and Optimization Techniques" (2005). Pomona Senior Theses. Paper 11. http://scholarship.claremont.edu/pomona_theses/11 This Open Access Senior Thesis is brought to you for free and open access by the Pomona Student Scholarship at Scholarship @ Claremont. It has been accepted for inclusion in Pomona Senior Theses by an authorized administrator of Scholarship @ Claremont. For more information, please contact [email protected]. Deep-UV Light Emitting Diodes: An Experimental Investigation of Characterization and Optimization Techniques A thesis submitted in partial satisfaction of the requirements for the degree of Bachelor of Arts in Physics by Eric M. Fraser Advised by: Richard Mawhorter, Physics, Pomona College David Tanenbaum, Physics, Pomona College Charles Taylor, Chemistry, Pomona College John Kaeding, Materials, University of California at Santa Barbara Shuji Nakamura, Materials, University of California at Santa Barbara May 2005 Fraser 2 Table of Contents List of Figures and Tables .....................................................................................................................................3 1 Abstract............................................................................................................................................................4 2 Introduction .....................................................................................................................................................6 2.1 Background .............................................................................................................................................6 2.2 Motivation: ultraviolet applications.......................................................................................................6 2.2.1 Biological agent detection ..............................................................................................................8 2.2.2 Communication...............................................................................................................................8 2.2.3 Lighting ...........................................................................................................................................9 2.2.4 Optical storage ..............................................................................................................................13 2.3 Project overview ...................................................................................................................................15 2.3.1 Material choices ............................................................................................................................15 2.3.2 Fabrication method .......................................................................................................................18 2.3.3 Characterization techniques .........................................................................................................18 2.3.4 Research goal ................................................................................................................................20 2.4 Document overview..............................................................................................................................20 3 Theory............................................................................................................................................................21 3.1 Background theory................................................................................................................................21 3.1.1 Light emitting diodes....................................................................................................................21 3.1.2 Crystallography.............................................................................................................................23 3.2 Lattice mismatch ...................................................................................................................................30 3.2.1 Mismatch problem ........................................................................................................................31 3.2.2 Buffer layer....................................................................................................................................33 3.3 Crystal defects and dislocations...........................................................................................................35 3.3.1 Threading dislocations (edge, screw) ..........................................................................................36 3.3.2 Point defects (vacancy, interstitial, substitution) ........................................................................41 3.3.3 Other types of defects ...................................................................................................................41 3.3.4 Sources of defects .........................................................................................................................42 3.3.5 Effects of defects...........................................................................................................................43 3.4 X-ray methods.......................................................................................................................................44 3.4.1 On-axis measurements..................................................................................................................46 3.4.2 Off-axis measurements.................................................................................................................47 3.4.3 Device layer characterization .......................................................................................................47 4 Equipment......................................................................................................................................................52 4.1 Deposition reactor.................................................................................................................................52 4.2 Characterization equipment..................................................................................................................53 4.2.1 X-ray diffractometer .....................................................................................................................53 4.2.2 Optical microscope .......................................................................................................................55 4.2.3 Scanning electron microscope......................................................................................................55 4.2.4 Atomic force microscope .............................................................................................................55 5 Procedure .......................................................................................................................................................57 5.1 Deposition .............................................................................................................................................57 5.2 Characterization ....................................................................................................................................58 5.2.1 X-ray diffraction ...........................................................................................................................58 5.2.2 Scanning electron microscopy .....................................................................................................62 6 Analysis .........................................................................................................................................................63 7 Conclusions ...................................................................................................................................................72 8 References .....................................................................................................................................................73 9 Acknowledgements.......................................................................................................................................78 Fraser 3 List of Figures and Tables FIGURE 1: SOLAR IRRADIANCE BELOW EARTH'S SURFACE....................................................................................9 FIGURE 2: CHROMATICITY ...................................................................................................................................10 FIGURE 3: SPECTRA OF WHITE LIGHTS .................................................................................................................12 FIGURE 4: SEM IMAGE OF CD SURFACE .............................................................................................................14 FIGURE 5: PERIODIC TABLE WITH RELEVANT ELEMENTS HIGHLIGHTED ............................................................15 FIGURE 6: SAPPHIRE SUBSTRATE (A) DIAGRAM, (B) PHOTO ...............................................................................18 FIGURE 7: A P-N JUNCTION WITH (A) NO POTENTIAL, (B) FORWARD BIAS .........................................................22