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Defect analysis of GaAs/InGaAs heterostructures

Defect analysis of GaAs/InGaAs heterostructures. Tim Morgan. Outline. Introduction to Quantum Structures Theory of Electrical Transport and Noise Experimental Techniques Discussion & Results Conclusions. Introduction. Short History of QDs Types of QDs Uses of QDs

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Defect analysis of GaAs/InGaAs heterostructures

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  1. Defect analysis of GaAs/InGaAs heterostructures Tim Morgan

  2. Outline • Introduction to Quantum Structures • Theory of Electrical Transport and Noise • Experimental Techniques • Discussion & Results • Conclusions QDs & Noise 6.27.08

  3. Introduction • Short History of QDs • Types of QDs • Uses of QDs • Motivation for Noise Study of QDs QDs & Noise 6.27.08

  4. Theory • QD Formation • SK growth • RHEED studies • AFM • Other techniques • Photoluminescence • Physical understanding of what happens • Peak Position • Integral Intensity • Spectral Shape QDs & Noise 6.27.08

  5. Theory • Hall Measurements • Brief description of scenario • Mobility • Electron Concentration • Deep Level Noise Spectroscopy • Types of Noise • Thermal • Flicker • Generation-Recombination • QD contributions to noise • Our experiment QDs & Noise 6.27.08

  6. Experimental Techniques • MBE Growth • Structure design • Growth conditions • Preparing & Processing Samples • Van der Paaw Measurements • AFM • Photolithography • IV Testing • TLM Measurements • Packaging QDs & Noise 6.27.08

  7. Experimental Techniques • PL • Hall Measurements • Temperature dependent measurements • Mobility • Carrier concentration • Resistance measurements QDs & Noise 6.27.08

  8. Experimental Techniques • Deep Level Noise Spectroscopy • Understand measurement • Describe setup & equipment • Room temperature @ different biases • 82K with different biases • Temperature dependence from 82-390K QDs & Noise 6.27.08

  9. Discussion & Results • AFM shows QDs for 9, 11 & 13 ML samples • Anisotropy • Elongation in [01-1] • Shape • Height increases from 9 to 11 to 13 ML samples • Histograms of Height & diameter • PL • Red shift in energy from 9 to 11 to 13 ML samples • Single size distribution for all QD samples • Decrease in integral intensity from 9 to 11 to 13 ML • All results correlate well with AFM data QDs & Noise 6.27.08

  10. Discussion & Results • IV & TLM • Ohmic contacts • Contact resistance much lower than sample • Hall Measurements • Mobility • 6ML behaves like QW • QD samples slightly lower at lower temperatures • Carrier concentration • More ionization at higher temperatures • Small bumps indicate defects QDs & Noise 6.27.08

  11. Discussion & Results • DLNS • Room temperature • Hooge parameter doesn’t indicate change in flicker noise between samples • G-R defects visible in spectra • Low temperature (82K) • Hooge parameter doesn’t indicate change in flicker noise between samples • Temperature dependence • G-R peaks move QDs & Noise 6.27.08

  12. Discussion & Results • Defect Analysis • 3 defects in all 5 samples • Defect D in just QD samples • 2 different activation energies: 0.18 eV for 9 & 11 ML, 0.1 eV for 13 ML • 0.18 eV defect known as M1 in GaAs; other is suspected to be associated just with QD samples • Defect characteristics • Capture cross sections determined • Trap density • Energy level below conduction band for defect A only QDs & Noise 6.27.08

  13. Conclusions • Additional defect found due to QDs • Flicker noise doesn’t appear to change with the addition of QDs • Good news for QD devices as it is the main component of noise, especially at lower frequencies where it dominates over thermal noise • Proved that DLNS is a viable technique for defect detection in nanostructures as results agree with other well established techniques (e.g. DLTS) • Lateral technique versus vertical QDs & Noise 6.27.08

  14. Future Work • Study Gated QD samples • Change where current flows to determine which layer noise arises from • Study QDs with vertical biasing • Vary doping to change Fermi level • Enhance noise when in resonance with traps • Inject minority carriers with light into QD samples • Determine energy positions relative to conduction band • QDIPs • Look at noise in a QD device and show its detection limit because of the noise QDs & Noise 6.27.08

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