ECE_220A_Lecture_20_Dec_1_2011_slides

ECE_220A_Lecture_20_Dec_1_2011_slides - Characterization...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Characterization How do we determine that each steps in a process has worked correctly? Optical Micrograph 204 GHz static frequency divider (ECL master-slave latch) Z. Griffith, TSC CSIC 2010 Rodwell lecture Scanning Electron Microscope Rodwell lecture Rodwell lecture SEM TEM Atomic Force Microscopy Annealing SrTiO3(001) to obtain a flat atomically stepped surface unannealed 850°C 1h 900°C 1h 950°C 1h Scanning Tunneling Microscopy (STM) Why use STM? •  in-situ STM studies of MBE grown materials •  High resolution of surface structures •  Examination of initial growth sequences at material interfaces In STM, a sharp metal tip is brought close enough to the surface so that the vacuum tunneling resistance between the tip and the surface is finite and measurable. STM Tip Schematic View It Bias It Schematic View STM STM Tip Bias Surface Profile Surface Profile V z It z z x Constant current mode x x Constant height mode x In-situ STM studies of Ga-rich surface preparation by MBE • In-situ prepared GaAs(001) “4×6” Ga-rich surface c(8x2) (‘n’x6) c(8x2) LEED pattern Single atomic layer steps (a0/4) (‘n’x6) STM of GaAs (001) “4×6” Ga terminated surface c(8x2) Bilayer atomic step (a0/2) GaAs(311)A surface Brian Schultz Coverage Dependence of ErSb on GaSb(100) at 500°C Deposition Amount vs. Surface Coverage [011] 0.5ML ErSb → 12% 1.0ML ErSb → 24% 1.5ML ErSb → 35% [011] Linear Increase constant island thickness of 4 atomic layers Embedded Growth Step Flow Regrowth of GaSb STM Image of 0.5ML of ErSb on GaSb [011] 11.9 sec 9.8 sec [011] 4 ML×(11.9 s/ML – 9.8 s/ML) ~ 0.8ML 9.8 s/ML RHEED along [010] GaSb regrowth ErSb layer-by-layer & ErSb embedded growth growth Tg = 350°C STM TIP Cleave wafer to expose clean (110) surface (001) Substrate (1 a )F 10 InGaSb AlSb InAs InAs InAs 6 12 6 14 ML ce Growth Direction Superlattice X-STM of IR Laser Major Issues Major • Contrast: structural vs. electronic • Quantifying interfacial roughnees Combine experiments with first-principles theory. Kim et al. PRB, 67, 121306 (2003) Kim et al. PRB, 67, 121306 (2003) Kim et al. PRB, 67, 121306 (2003) Atom Manipulation with an STM Don Eigler, IBM Quantum Coral Don Eigler (IBM) http://blogs.nature.com/from_the_lab_bench/2011/04/12/nanodays-visual-trivia-1 Review of X-ray Diffraction Bragg Conditions λ Bragg’s Law: θ Mn (004) GaAs (004) GaAs (002) θ d Basic XRD Apparatus x-r ay so u tor rce d Cu Kα θ θ c ete sample X-ray diffraction to determine crystallographic phases What oxygen pressure is needed to form PrNiO3? Ni k-cell LAO(001) LAO(002) Ni flux (counts) Ni 6 Ni 7 Ni 8 20 Intensity (a.u.) Ni e-gun Intensity (a.u.) XRD measurements on the LaNiO3 films 25 30 LAO(001) 35 LNO(001) 40 45 LNO(002) 2θ (°) 50 55 LAO(002) 60 Ni Deposition time Ni 6 s Ni 7 s Ni 7.5 s Ni 8 s Ni 10 s 20 25 30 35 40 45 2θ (°) 50 55 60 !  By using the k-cell, the crystal quality is improved dramatically. Cross-sectional TEM of 400°C Annealed Mn/GaAs MnGa (002) Mn2 As (003) (202) (203) (002) (001) (000) (000) (100) (200) (200) MnGa Mn0.6Ga0.2As0.2 Mn0.6Ga0.2As0.2 GaAs Mn2As MnGa Mn0.6Ga0.2As0.2 10 nm GaAs Mn2As-like GaAs How about composition and chemistry? SEM-EDS X-ray emission SEM-EDS \1'43(4"4$/3.&(4,%--%.& *//9ATT4&:L%V%947%#:.3'TL%V%T\1'43e4"4$/3.&e-94$/3.-$.9> \1'43(4"4$/3.& 6 _ c c6(/3#&-%/%.& 04K43#"(V4? 4"4$/3.& \1'43(4"4$/3.&-(*#K4(4&43'%4-(/*#/(#34($*#3#$/43%-/%$ .5(/*4(.32%/#"53.,(L*%$*(/*4>(.3%'%&#/4A(5.3,(#(5%&'4393%&/(5.3(/*4(,#/43%#" Derivative Spectrum of Al2O3 Auger Sensitivities Overview of X-ray Photoemission Spectroscopy (XPS) Physical Concept: Basic XPS Apparatus: X-ray Energy (hν) Kinetic Energy (KE) so Energy Analyzer ur ce hν Al or Mg Kα θ sample e− Electron Detector 3p 2s Fe (Al Kα) 1s KE = hν − BE Hybrid Materials Epitaxy Center University of Minnesota ay monochromator Vacuum Level Valance Band Binding Energy (BE) x-r Photoelectron Spectroscopy Spectrum qualitative analysis A sample spectrum IDENTIFY ALL THE PEAKS •Most common lines, and known elements: O-1s (530 eV) C-1s (284 eV). Refer to standard spectrum which can be found in handbooks. Spin-orbit splitting, for l >0, j = l ± s Intensity ratio 2:1 for 2ps, 3:2 for 3ds, 4:3 for 4fs etc. •Auger lines. kinetic energy independent from the photon energy. (KLL) •Satellite lines (Kα3,4), ghost lines: impurity in anode. •Plasmon energy loss: interaction between photoelectron and plasmon. •Shake-up and shake-off, initial state effect. XPS Peaks as a Function of Mn Coverage on GaAs(001) c(4×4) X-ray Photoemission Spectrocopy (XPS): Normalized Ga3d Peaks 95°C reacted bulk Peak Position => Chemistry 250°C Peak Attenuation => Depth Information reacted bulk 25 ML Mn Coverage 20 ML Growth Model 15 ML coverage of the surface 10 ML Surface As/Ga 5 ML 1 monolayer 2 ML M n monolayers 1 ML MxGayAsz m monolayers 0 ML GaAs 1 0 -1 BE (eV) 1 0 -1 BE (eV) Quantification of Interfacial Reactions by XPS Mn/GaAs(001) at 95°C Mn/GaAs(001) at 250°C 1.00 1.00 Intensity (I/I0) Intensity (I/I0) As3d total As3d total 0.10 Ga3d reacted Ga3d reacted 0.10 Ga3d total Ga3d total 0.01 0.01 0 10 20 30 40 50 0 40 60 80 Mn Coverage (ML) Mn Coverage (ML) 0.4 ML surface As Mn n monolayers Mn0.6Ga0.2As0.2 11 monolayers GaAs 20 0.4 ML surface As 0.2 ML surface Ga Mn n monolayers Mn0.6Ga0.2As0.2 70 monolayers GaAs In-situ XPS determination of optimum Al thickness for in-situ tunnel barrier formation Al2p after Oxidation AlOy FeOx Fe Intensity Over oxidized AlOx Al Fe2p after Oxidation Al FeOx FeOx Fe Fe 3Å Correct oxidization AlOx Intensity 740 735 730 725 720 715 710 705 700 4Å 740 735 730 725 720 715 710 705 700 Intensity Fe Under oxidized AlOx Al 78 76 74 72 70 Intensity 80 5Å 68 740 735 730 725 720 715 710 705 700 9Å Fe 80 78 76 74 72 70 Binding Energy (eV) 68 740 735 730 725 720 715 710 705 700 Binding energy (eV) Ga Fe As Ga As Cross-sectional Transmission Electron Microscopy xC 1x o 1x Al O x Fe Fe Al xC O ox GaAs 50 Å FexCo1-x Fe Al cap 100 Å Al(5Å)-Ox In-situ grown AlOx tunnel barrier Fe(001) GaAs(001) 50 Å HAADF-STEM Fe/GaAs (001) c(4×4) in-situ post growth anneal 200°C 1h Fe As Fe Ga LeBeau et al. APL, 93, 121909 (2008) Model of post growth annealed Fe/GaAs(001) interface 2.5Å As 1.2Å Ga Ga As • • • • [001] [001] __ [110] _ [110] _ [110] [110] Low density Fe interfacial layer: Fe-As bonding -Fe in ‘Ga-like’ sites Has not been predicted by theory Have seen evidence for intensity modulation in first ‘bulk Fe’ layer Very different from the model proposed by Zega et al.(PRL, 96, 196101 (2006)) LeBeau et al. APL, 93, 121909 (2008) Sputter away the surface - Depth Profiling with Auger Electron Spectroscopy X-ray Photoelectron Spectroscopy Secondary Ion Mass Spectrometry Sputtering plus mass spectrometry of sputtered ions C. J. Palmstrøm, et al., J. Appl. Phys. 67, 334 (1990) C. J. Palmstrøm, et al., J. Appl. Phys. 67, 334 (1990) C. J. Palmstrøm, et al., J. Appl. Phys. 67, 334 (1990) Review of Rutherford Backscattering Spectroscopy (RBS) Basic RBS Apparatus Nuclear Particle Detector Scattered Beam Scattering Angle, θ MeV He Ion Beam Collimators “Billiard Ball” Model Sample M1 , E1 Momentum and Energy Balances θ MeV He Ion M1 , E0 φ M2 M2 , E2 E1 = K E0 Chu, Mayer and Nicolet “Backscattering Spectrometry” Chu, Mayer and Nicolet “Backscattering Spectrometry” Chu, Mayer and Nicolet “Backscattering Spectrometry” RBS Spectra and Simulation of Unannealed Sample Mn Ga simulation ~500×10 15 atoms/ cm2 As Ga Mn As Quantification of Mn/GaAs Reactions at 300°C by RBS RBS: He+ 2.3 MeV, 165° scattering angle as-grown Mn 6000 8 hour anneal 1 hour anneal Ga As Ga As Mn 6000 4000 4000 Ga 1700 1800 As 5000 4000 simulation 3000 2000 simulation 3000 As 2000 Ga Mn 1000 0 1300 1400 1500 1700 Energy (keV) Mn 1800 1900 2000 Ga 0 1300 Ga Mn 1400 1500 1000 1600 1700 1800 Energy (keV) ~450×1015 atoms/cm2 GaAs simulation 3000 As As 1000 1600 Yield 5000 Yield 5000 Yield Mn 6000 1900 0 1300 Mn 1400 1500 1600 1900 Energy (keV) Mn Mn0.6Ga0.2As0.2 GaAs Mn ~1500×1015 atoms/cm2 Mn0.6Ga0.2As0.2 GaAs Interfacial reacted layer of approximately uniform composition increases in thickness with time Diffusion-Limited Reactions and Activation Energy Time (hr) 2 5 10 20 30 D D0e Q kT Q = 2.0 eV atoms 2 21 D0 = 1.1×10 cm4 s Fully reacted Mn film 2500 2000 325°C 300°C 5 10 1500 4 D (10 atoms /cm *s) 325°C 4 10 300°C 2 1000 275°C 500 reacted layer thickness Mn Mn0.6Ga0.2As0.2 30 Reacted layer thickness (1015 atoms/cm2) 1 3 10 275°C GaAs 0 2 0 10 20 30 Time (min1/2) 40 10 19 20 21 1/kT (1/eV) 22 What are the dominant diffusing species? RBS marker experiment 6000 5000 0.75 ML Er marker Yield 4000 Mn Mn0.6Ga0.2As0.2 3000 GaAs GaAs Er 2000 1000 0.75 ML Er marker Mn Mn is the dominant diffusing species 0 1300 1500 1700 1900 Energy (keV) Er peak movement 100 Yield 80 unannealed 3 hr 10 hr 60 40 20 0 1875 1895 1915 1935 1955 Energy (keV) 1975 1995 2015 ...
View Full Document

This note was uploaded on 01/16/2012 for the course ECE 220a taught by Professor Staff during the Spring '08 term at UCSB.

Ask a homework question - tutors are online