Interband vs Intersubband Optics: Fundamentals and Applications M.F. Pereira

1. Interband vs Intersubband Optics: Fundamentals and ApplicationsM.F. Pereira Theory of Semiconductor Materials and Optics Materials and Engineering Research Institute Sheffield Hallam University S1 1WB Sheffield, United Kingdom M.Pereira@shu.ac.uk

2. Outline • Motivation/Technological Applications • Highlights of Nonequilibrium Many Body Methods Applied to Quantum Cascade Lasers • Summary

3. Relevance of Intersubband Devices for THz and MIR Intersubband-based devices allow the generation of long wavelengths not possible with conventional interband optics!!!

4. Tricorder: 23rd Century End Users Keldysh Nonequilibrium Green's Functions are required to design new materials and custom-designed effects for those devices!!

5. Disease detection by breath analysis? Courtesy of F.K. Tittel

6. Possible with off-axis integrated cavity output spectroscopy (ICOS) based gas sensing using a QCL mid-IR source Courtesy of F.K. Tittel, Rice University

7. Wide Range of Gas Sensing Applications for mid-IR QCLs • Urban and Industrial Emission Measurements • Industrial Plants • Combustion Sources and Processes (eg. early fire detection) • Automobile and Aircraft Emissions • Rural Emission Measurements • Agriculture and Animal Facilities • Environmental, Spacecraft and Planetary Surface Monitoring (NH3, CO, CH4, C2H4, N2O, CO2 and H2CO) • Crew Health Maintenance & Advanced Human Life Support Technology • Atmospheric Chemistry (eg ecosystems and airborne) • Volcanic Emissions • Chemical Analysis and Industrial Process Control (NO, NH3, H2O) • Chemical, Pharmaceutical, Food & Semiconductor Industry • Toxic Industrial Chemical Detection • Biomedical and Clinical Diagnostics (eg. breath analysis) (NO, CO, COS, CO2, NH3, C2H4) • Forensic Science and Security • Fundamental and Life Sciences

8. Security Scanning (THz) • discriminate different types of drugs, explosives and automated identification of toxins such as nerve and mustard gas, anthrax.

9. Would you like to detect an otherwise undetectable cancer under the skin??

10. Medical Imaging and Diagnostics (THz) diseased tissue healthy tissue

11. Wide Range of Gas Sensing Applications for THz QCLs • IR astronomy • Space Missions • Dental Imaging • Pharmaceutical applications • Proteomics • Postal scanning • Plastic Landmine detection • Semiconductor imaging • Environmental sensing and monitoring • Point sensors • Last mile high bandwidth (Telecoms) • Collision avoidance radar, remote sensing, telemetry, physics, isotope ratios, industrial process control

12. Limitations of Current THz Sources

13. Teraview Scanner ~ £250K

14. Physical Principle Behind the Teraview Scanner

15. The Challenge: Intersubband Lasing It took 23 years to achieve this laser!

16. The Quantum Cascade Laser

17. Outline • Current THz sources: why quantum cascade lasers? • Details of the theory. • Current challenges for further THz QCL development: how can the theory help address them? • Summary

18. Self-Consistent Solution of the Dyson Equations

19. Energy and Spatially Resolved Populations Courtesy of S.-C. Lee

20. Voltage-Current Characteristics of a THz QCL Operating at 77 K

21. Importance of Quantum Transport

22. Light Generation and Amplification

23. Light Generation and Amplification

24. Light Generation and Amplification

25. Light Generation and Amplification

26. Light Generation and Amplification

27. Light Generation and Amplification

28. Light Generation and Amplification

29. Light Generation and Amplification

30. Light Generation and Amplification

31. Light Generation and Amplification

32. Light Generation and Amplification M.F. Pereira Jr. and A. Wacker, phys. stat. sol. (c) 4, 356 (2007).

33. Many-body effects are stronger at THz than at midIR

34. Many-body effects are stronger at THz than at midIR M.F. Pereira Jr, S.-C. Lee, and A. Wacker., Phys. Rev. B69, 205310 (2004).

35. Many-body effects are stronger at THz than at midIR . 10 x less doping than in typical mid-IR designs. M.F. Pereira, et al IEEE Conference Proceedings, pp. 94-96. ISBN - 0 -7 803 - 8530 – 6 Based on the structure introduced by B. Williams et al, APL 82, 1015 (2003).

36. Importance of Many-Body Effects in Absorption and Gain • Coulomb enhanced cross absorption can even eliminate the gain. • Coulomb-induced shift of the same order of magnitude of the transition energies in the THz domain. • Carrier-carrier scattering may dominate the broadening in THz QCLs. • Strong interplay of bandstructure and Coulomb effects leading to extra features in the absorption spectra.

37. QCL ridge Micro-Transmission Experimental Set Up D.G. Revin, L.R. Wilson, J. Cockbun, A.B. Krysa, J.S. Roberts, and R. Airey. Appl. Phys. Lett. 88, 131105 (2006). • Measurements in very broad mid-IR range • Diameter of focused spot ~ 50µm • CW operation in the cryostat (T=7-300K) • TE, TM polarization • Reflecting optics; better than 100:1 signal to noise contrast MCT Detector λ ~ 1.5 – 12.5 µm (100 – 800 meV) Broad band globar light from FTIR spectrometer

38. MidIR QCL Spectroscopy: Theory vs. Experiments Lattice-matched InGaAs/InAlAs/InP operating around λ≈7.7 μm.

39. Theory vs Experiments (10K) Theory Experiments

40. Theory vs Experiments (78K) M.F. Pereira Jr, R. Nelander, A. Wacker, D.G. Revin, M.R.Soulby, L.R. Wilson, J.W. Cockburn, A.B. Krysa, J.S. Roberts, and R.J. Airey, Journal of Materials Sience: Materials in Electronics 18, 689 (2007).

41. Fingerprints of charge transfer between injectors and active regions R.Nelander et. al., to appear in JAP.

42. Summary • Leading edge nonequilibrium many body theory applied to semiconductor materials. • Software development. • MidIR laser development for medical applications. • THz laser development for security applications.