Electronic Noise Spectroscopy of InGaAs QDs

1. Electronic Noise Spectroscopy of InGaAs QDs Tim Morgan

2. Outline Motivation Noise Theory Discussion & Results Conclusions Future Work Noise Spectroscopy in QDs

3. Quantum Dot Devices QD Laser Infrared Detectors Single Photon Emitter byz.org cqd.eecs.northwestern.edu Biosensors Igor L. Medintz, et. al. Nature Materials 2003 Noise Spectroscopy in QDs

4. Quantum Dot Devices Infrared Photodetectors Passmore, B.S.; Jiang Wu; Manasreh, M.O.; Kunets, V.P.; Lytvyn, P.M.; Salamo, G.J.; Electron Device Letters, IEEE Volume 29, Issue 3, March 2008 Page(s):224 - 227 cqd.eecs.northwestern.edu Noise Spectroscopy in QDs

5. The Nature of Noise in QDs What is the source of noise in QDs? Does noise in QDs differ from bulk? Can noise be lowered by optimization of QDs? Noise Spectroscopy in QDs

6. The Plan Noise Spectroscopy:Noise Measurements & Analysis Hall Effect: How does Noise depend on Carrier Conc. & Mobility? Photoluminescence: How noise depend onElectronic structure? AFM: How does noise depend on morphology? MBE: GrowIn0.35Ga0.65As QDs Noise Spectroscopy in QDs

7. Noise Spectroscopy Noise Spectroscopy in QDs

8. Thermal Noise No Bias Due to random fluctuations of electron motion from lattice vibrations. SV,thermal Noise Spectroscopy in QDs

9. 1/f noise Bias Added Arises from both carrier and mobility fluctuations in the conductivity. 1/f The Hooge Parameter (α) is an indicator of crystal quality. Noise Spectroscopy in QDs

10. Generation-Recombination Noise Bias Added g-r, τ1 g-r, τ2 Noise Spectroscopy in QDs

11. Total Noise Noise Spectroscopy in QDs

12. The Plan MBE: GrowIn0.35Ga0.65As QDs Noise Spectroscopy in QDs

13. Sample Creation MBE Growth Solid Source Riber 32 P RHEED monitoring Noise Spectroscopy in QDs

14. The Structure 1500 Å GaAs: Si ND = 6 × 1016 200 Å GaAs: undoped InGaAs QD layer 200 Å GaAs: undoped 5000 Å GaAs: Si ND = 6 × 1016 5000 Å GaAs buffer GaAs (001) SI RHEED Sample # MLs Bulk S1 0 QW S2 6 QDs S3 9 QDs S4 11 QDs S5 13 Noise Spectroscopy in QDs

15. The Plan AFM: How does noise depend on morphology? MBE: GrowIn0.35Ga0.65As QDs Noise Spectroscopy in QDs

16. Morphology 9 ML Height: 33 ± 2.8 Å Density: 3.8 × 1010 cm-2 11 ML Height: 47 ± 2.8 Å Density: 8.4 × 1010 cm-2 13 ML Height: 53 ± 2.8 Å Density: 7.2 × 1010 cm-2 Noise Spectroscopy in QDs

17. AFM Trends QD Height increases with number of monolayers. QD Density increases with number of monolayers. Noise Spectroscopy in QDs

18. The Plan Photoluminescence: How noise depend onelectronic structure? AFM: How does noise depend on morphology? MBE: GrowIn0.35Ga0.65As QDs Noise Spectroscopy in QDs

19. Photoluminescence Width of energy well is the height of the QD. Noise Spectroscopy in QDs

20. PL Trends 9 ML 11 ML 9 ML 11 ML 13 ML 11 ML 13 ML 9 ML 13 ML • Peak position decreases in energy with increase in height. • FWHM shows increase • Integral Intensity shows decrease with increase in height Noise Spectroscopy in QDs

21. The Plan Hall Effect: How does Noise depend on carrier conc. & mobility? Photoluminescence: How noise depend onelectronic structure? AFM: How does noise depend on morphology? MBE: GrowIn0.35Ga0.65As QDs Noise Spectroscopy in QDs

22. Sample Preparation 270 nm Au 20 nm Ni 75 nm AuGe 20 µm Greek Cross Noise Spectroscopy in QDs

23. Finished Structures 13 ML All samples meet Noise Spectroscopy in QDs

24. Mobility +++ +++ - - - - - Noise Spectroscopy in QDs

25. Carrier Concentration Noise Spectroscopy in QDs

26. The Plan Noise Spectroscopy:Noise Measurements & Analysis Hall Effect: How does Noise depend on carrier conc. & mobility? Photoluminescence: How noise depend onelectronic structure? AFM: How does noise depend on morphology? MBE: GrowIn0.35Ga0.65As QDs Noise Spectroscopy in QDs

27. DLNS: Setup & Experiments • Setup • Shielded sample • Power supply: battery pack and series of resistors • Low noise preamplifier with band filter • Noise spectrum analyzer • Experiments • Temperature dependence: 82 K – 390 K, fixed bias • Room temperature: several biases • Low temperature (82 K): several biases Noise Spectroscopy in QDs

28. Noise Curves 0 ML 300 K • Series of spectra at fixed temperatures and various biases • Fit each specturm with all components of noise • Extract fit parameters for component breakdown analysis Noise Spectroscopy in QDs

29. Curve Fittings Noise Spectroscopy in QDs

30. Flicker Noise 0 ML Sample at 300 K • Fit Parameter: • Determine the Hooge Parameter at 300 K and 82 K Noise Spectroscopy in QDs

31. Hooge Comparison 300 K Noise Spectroscopy in QDs

32. QD Comparisons 300 K 9 ML 9 ML 13 ML 13 ML 11 ML 11 ML Noise Spectroscopy in QDs

33. Two Views 0 ML Shoulders Peaks Noise Spectroscopy in QDs

34. Bulk to QDs Noise Spectroscopy in QDs

35. GR Analysis • A different expression: • Peaks reveal the activation and ionization energy • ln Smax vs ln ω ionization energy • 1/kBTmax vs ln ω activation energy • Capture cross section: • Trap density: Noise Spectroscopy in QDs

36. Analysis Plots 11 ML 11 ML Position of Fermi Energy compared to Trap Position Activation Energy Noise Spectroscopy in QDs

37. GR Summary Noise Spectroscopy in QDs

38. Conclusions Sources of Noise in QDs GR Traps with activation energies of 0.74, 0.49, 0.34, 0.18 and 0.1 eV Noise in QDs does differ from bulk Flicker noise decreases with the insertion of In0.35Ga0.65As and the formation of QDs Optimization of QDs to lower noise Increase in height and density lowers flicker noise QDs do have an additional trap associated with them Noise Spectroscopy in QDs

39. Impact Reveal additional unknown defect associated with QDs QDs leads to lower flicker noise Lateral noise technique is sensitive tool to feel nanoscale objects • MRS Fall 08: “Low-frequency noise and lateral transport studies of In0.35Ga0.65As/GaAs quantum dot heterostructures” • Pending Publication: “Noise spectroscopy of deep traps in GaAs/InGaAsheterostructures: transition from quantum well to quantum dots.” Noise Spectroscopy in QDs

40. Future Work Study Gated QD samples Change where current flows to determine which layer noise arises from 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 limitations because of the noise Noise Spectroscopy in QDs

41. Thanks Dr. Greg Salamo Dr. VasylKunets Professor Ken Vickers Dr. Bill Brown Dr. Huaxing Fu Rob Sleezer Noise Spectroscopy in QDs

42. Noise Spectroscopy in QDs

43. What is a Quantum Dot? Single Atom Many Atoms A Few Atoms Confined • Single atom: Discrete energy level transitions • Many atoms: continuum of energy levels • A Few Atoms Confined: lower energy levels discrete because of confinement ~30 nm Noise Spectroscopy in QDs

44. QD Formation InGaAs fluxes When critical thickness is reached, the strain is relaxed and thus 3D islands (quantum dots) are formed. - I’m now happy!! Strain has built up! - I’m very uncomfortable!! 2D InGaAs wetting layer GaAs substrate Used with permission of Jihoon Lee Noise Spectroscopy in QDs

45. Atomic Force Microscopy Surface data • Height • Diameter • Density Noise Spectroscopy in QDs

46. Photoluminescence Noise Spectroscopy in QDs

47. Hall Effect • Transport Info • Mobility • Carrier • Concentration • Hall Coefficient • Conductivity • Primary Carrier Noise Spectroscopy in QDs

48. Contact Optimization lT c c AuGe/Ni/Au d rs Rs Rs dx Dopant 0 -l x • Annealing: minimize barrier to create Ohmic contacts • IV Testing: Verify Ohmic contacts made • TLM Measurements: determine contact resistance Noise Spectroscopy in QDs

49. Hall Measurements Hall Measurements Mobility Carrier concentration Resistance measurements Noise Spectroscopy in QDs

50. Noise Spectroscopy Vnoise Vbias SV is the average change in voltage squared in a bandwidth of 1 Hz. Noise Spectroscopy in QDs