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University of California, San Diego UNIVERSITY OF CALIFORNIA, SAN DIEGO Scanning Probe Characterization of Novel Semiconductor Materials and Devices A dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Materials Science and Engineering by Xiaotian Zhou Committee in charge: Professor Edward T. Yu, Chair Professor Prab Bandaru Professor Andy Kummel Professor Silvanus S. Lau Professor Deli Wang 2007 Copyright Xiaotian Zhou, 2007 All rights reserved. Signature Page The dissertation of Xiaotian Zhou is approved, and it is acceptable in quality and form for publication on microfilm: Chair University of California, San Diego 2007 iii Dedication To my parents and grandparents iv Table of Contents Signature Page..................................................................................................................iii Dedication ......................................................................................................................... iv Table of Contents .............................................................................................................. v List of Figures and Tables............................................................................................... ix List of Abbreviations and Symbols .............................................................................. xiv Acknowledgement........................................................................................................... xv Vita ................................................................................................................................. xvii ABSTRACT OF THE DISSERTATION .................................................................... xix 1. INTRODUCTION......................................................................................................... 1 1.1. Introduction to Atomic Force Microscopy (AFM) ...................................................... 1 1.1.1. Application of AFM in Semiconductor Devices ...................................................... 1 1.1.2. General Introduction to AFM Theory....................................................................... 3 1.2. Thesis Outline .............................................................................................................. 5 2. IMAGING OF THICKNESS AND COMPOSITIONAL FLUCTUATIONS IN INGAN/GAN QUANTUM WELL LED STRUCTURES BY SCANNING CAPACITANCE MICROSCOPY ................................................................................ 10 2.1. Introduction................................................................................................................ 10 2.2. Samples and Experiment Setup ................................................................................. 12 2.2.1. Sample Growth and Device Fabrication................................................................. 12 v 2.2.2. Scanning Capacitance Microscopy Details............................................................. 15 2.3. Numerical Simulations............................................................................................... 18 2.4. Imaging of Monolayer Thickness Fluctuations in InGaN Quantum Well................. 20 2.4.1. SCM Measurement Results and Analysis............................................................... 20 2.4.2. Numerical Simulations............................................................................................ 23 2.4.3. Scanning Capacitance Spectroscopy Data and Analysis ........................................ 25 2.5. Imaging of Nanoscale In Concentration Fluctuations in InGaN Quantum Well....... 28 2.5.1. Numerical Simulations............................................................................................ 29 2.5.2. In Clustering Induced Photoluminescence Enhancement....................................... 33 2.6. Conclusion .................................................................................................................35 Reference .......................................................................................................................... 37 3. SCANNING CAPACITANCE MICROSCOPY CHARACTERIZATION OF DEPENDENCE OF MG ACCEPTOR INCORPORATION IN P-TYPE GAN ON CRYSTAL POLARITY ................................................................................................. 40 3.1. Introduction................................................................................................................ 40 3.2. Experimental Techniques........................................................................................... 42 3.2.1. Samples and Device Fabrication............................................................................. 42 3.2.2. Scanning Kevin Probe Microscopy ........................................................................ 45 3.3. Results and Discussion .............................................................................................. 48 3.3.1. SCM Measurement Results and Analysis............................................................... 48 vi 3.3.2. Scanning Capacitance Spectroscopy and Numerical Simulation ........................... 51 3.4. Conclusion .................................................................................................................54 Reference .......................................................................................................................... 56 4. SCANNED ELECTRICAL PROBE CHARACTERIZATION OF CARRIER TRANSPORT BEHAVIOR IN INAS NANOWIRES................................................. 58 4.1. Introduction................................................................................................................ 58 4.2. Experiment.................................................................................................................60 4.2.1. Nanowire Growth.................................................................................................... 60 4.2.2. Device Fabrication.................................................................................................. 62 4.2.3. Measurement Setup................................................................................................. 65 4.3. Results and Data Analysis ......................................................................................... 67 4.3.1. Resistance vs Channel Length Data........................................................................ 67 4.3.2. Numerical Calculations........................................................................................... 72 4.4. Conclusions................................................................................................................78 Reference .......................................................................................................................... 79 5. ANALYSIS OF CARRIER MODULATION IN INAS NANOWIRES BY SCANNIN GATE MICROSCOPY ............................................................................... 82 5.1. Introduction................................................................................................................ 82 5.2. Measurement Setup.................................................................................................... 83 5.3. Results and Data Analysis ......................................................................................... 85 vii 5.3.1. Scanning Gate Microscopy Results ........................................................................ 85 5.3.2. Tip Sample Capacitance Model.............................................................................. 88 5.3.3. Numerical Calculations Using ISE ......................................................................... 89 5.4. Conclusions................................................................................................................92 Reference .......................................................................................................................... 94 APPENDIX...................................................................................................................... 96 A1. SCANNING KELVIN PROBE MICROSCOPY STUDY OF TRANSPORT PROPERTIES IN CUPC ORGANIC THIN FILM TRANSISTORS ....................... 96 A1.1. Introduction............................................................................................................. 96 A.2. Space Charge Limited Conduction Theory............................................................... 98 A.3. Measurement Setup................................................................................................... 99 A.4. Results and Data Analysis....................................................................................... 100 A.4.1. Macroscopic Current-Voltage Measurement....................................................... 100 A.4.2. Microscopic Potential Measurement.................................................................... 102 A.5. Conclusions............................................................................................................. 106 Reference ........................................................................................................................ 107 viii List of Figures and Tables Figure 1.1. Schematic setup of an atomic force microscope. Scanning probe tip is placed over the sample surface with position monitored by deflected laser....................... 4 Figure 2.1. (a) Schematic diagram of a representative InxGa1-xN/GaN quantum-well structure with the top GaN
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