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Magneto-optical study of InP/InGaAs/InP quantum well

Magneto-optical study of InP/InGaAs/InP quantum well B. Karmakar, A.P. Shah, M.R. Gokhale and B.M. Arora Tata Institute of Fundamental Research Mumbai, India. Plan of the talk:. 1. Introduction to surface photo voltage (SPV) spectroscopy 2. Experimental setup

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Magneto-optical study of InP/InGaAs/InP quantum well

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  1. Magneto-optical study of InP/InGaAs/InP quantum well B. Karmakar, A.P. Shah, M.R. Gokhale and B.M. Arora Tata Institute of Fundamental Research Mumbai, India

  2. Plan of the talk: 1. Introduction to surface photo voltage (SPV) spectroscopy 2. Experimental setup 3. Growth and characterization of sample 4. Experimental results 5. Summary

  3. Introduction to surface photo voltage (SPV) spectroscopy SPV: Optical + Transport Process a) Photon absorption and electron hole pair generation b) Charge separation due to surface field.

  4. Motivation: a) MQW studied by B. B. Goldberg et al [ PRL 63, 1102 (1989)] b) Growth of MQW is not possible in highly strained system c) Transport and SPV spectroscopy can be done on same single quantum well sample d) Quantitative measurement of join density of states and their evolution with magnetic field

  5. Ec e Eg EF SPV Ev h Wavelength SPV on bulk sample: Generation of SPV in bulk materials Schematic spectrum The wavelength scan gives band edge

  6. Eee2-Ehh2 EC e Eee1-Elh1 EF SPV Eee1-Ehh1 EV h Wavelength SPV in quantum well structure: Generation of SPV from a QW Schematic spectrum A single quantum well can be probed easily

  7. Advantage over absorption or transmission spectroscopy a) SPV is very sensitive to SQW b) In MQW energy levels are broader compared to SQW c) Electron density is not same in all well in MQW structure e) Local measurement is possible

  8. mj e states n = 0 -1/2 +1/2 +3/2 +1/2 hh states n = 0 -1/2 -3/2 SPV spectroscopy in the presence of magnetic field and selection rules Parity conservation in growth direction for sub-band transition n = 0, 2 etc Parity conservation of the LL n = 0 Spin conservation mj = 1 There are inter band transition between Landau levels

  9. Tunable Diode Laser Optical Switch ITO Coated glass Sample Optical Fiber Super conducting magnet Lock-in amp Buffer Amplifier Schematic diagram of measurement setup

  10. Tunable diode laser Tunable range: 1520-1570 nm & 1565-1625 nm

  11. Optical switch

  12. Power requirement Photo voltage saturates logarithmically with intensity Experiment is done in linear regime Illuminated power is sub-micro Watt

  13. 100 Å InP cap 200 Å Si doped InP 100 Å InP spacer 90 Å In0.64Ga0.36As QW 1500 Å InP buffer SI InP Substrate Structure of the system under study Modulation doped quantum well structure InP/InGaAs/InP is used for the study. The sample is grown by metalorganic vapor phase epitaxy (MOVPE) under optimized conditions . Sample structure

  14. EC EF EV Schematic band diagram

  15. Characterization of the sample: Pl measurement Photoluminescence spectrum of the sample X-ray diffraction Electrical measurement: ns = 1.4  1011/cm2; µ = 90,000 cm2/V-sec

  16. Experimental conditions 1. T << /k 2. Tunneling should be possible 3. There should not be any relative vibration between sample and electrode

  17. Experimental results Without magnetic field results Optical process enhances with the lowering of temperature A peak like features is seen. This is attribute to formation of exciton At high temperature exciton does not form due to low binding energy At low temperature exciton does not brake, therefore exciton peak vanishes At low temperature tunneling is the main mechanism of charge separation from the quantum well Zero field temperature dependence of SPV

  18. Shift of band edge The shift of band edge is due to increase of band gap with the lowering of temperature. Zero field temperature dependence of SPV

  19. A comparison between PL and SPV

  20. Finite field results SPV spectrum at finite field

  21. Magnetic field dependence of SPV spectrum Magnetic field dependence of SPV

  22. Evolution of energy levels with magnetic field SPV spectroscopy is suitable to detect inter band LL transition in single QW To characterized the transitions, QH experiment is necessary The width of join density of states can be measured J(h) = E gh(E)ge(E + h) dE Shift of peaks at higher energy with magnetic field

  23. Summary SPV is shown to be a suitable techniques to probe magneto-optics of single quantum well. SPV signal increases with the lowering of temperature and then decrease further lowering of temperature. The excitonic peak is observed , this feature disappear at low temperature. To characterized the transitions, quantum Hall experiment is necessary.

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