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1. About Omics Group OMICS Group International through its Open Access Initiative is committed to make genuine and reliable contributions to the scientific community. OMICS Group hosts over 400 leading-edge peer reviewed Open Access Journals and organize over 300 International Conferences annually all over the world. OMICS Publishing Group journals have over 3 million readers and the fame and success of the same can be attributed to the strong editorial board which contains over 30000 eminent personalities that ensure a rapid, quality and quick review process. 

2. About Omics Group conferences • OMICS Group signed an agreement with more than 1000 International Societies to make healthcare information Open Access. OMICS Group Conferences make the perfect platform for global networking as it brings together renowned speakers and scientists across the globe to a most exciting and memorable scientific event filled with much enlightening interactive sessions, world class exhibitions and poster presentations • Omics group has organised 500 conferences, workshops and national symposium across the major cities including SanFrancisco,Omaha,Orlado,Rayleigh,SantaClara,Chicago,Philadelphia,Unitedkingdom,Baltimore,SanAntanio,Dubai,Hyderabad,Bangaluru and Mumbai.

3. Growth and Operation Tolerances for Sb-based Mid-Infrared Lasers C.H. Grein University of Illinois at Chicago Collaborators: M.E. Flatté and T.F. Boggess (University of Iowa)

4. Background on Sb-based superlattice mid-infrared lasers Sensitivity of optimization of mid-infrared InAs/GaInSb superlattice laser active regions to Temperature Superlattice layer thicknesses Structure of intersubband absorption spectrum Initial/final state optimization in four-layer superlattices Outline

5. Band edge optimization reduce valence band density of states strained layer superlattices: heavy hole becomes lighter in in-plane direction Intersubband absorption reduction engineering bands which would otherwise provide initial or final states for intervalence or interconduction transitions at the lasing energy Auger final state optimization band structure engineering to reduce the number of final states in Auger transitions Optimization Strategies

6. Superlattice Band Structure Engineering • Responsible for order of magnitude or greater reductions of Auger rates • LWIR • Good agreement between theory and expt. for n>1017 cm-3 • Shockley-Read-Hall dominates for n<1017 cm-3 • Youngdale et al., APL 64, 3160 (1994) • MWIR • Auger coefficient=3 • R=1+ 2n+ 3n2 • W.W. Bewley et al., APL 93, 041118 (2008)

7. Observed Strained Layer Superlattice and Bulk Auger Coefficients R=1+ 2n+ 3n2 • Roughly two orders of magnitude slower Auger recombination in LWIR SLs than in bulk • Roughly one order of magnitude slower in MWIR

8. K.p Electronic Band Structure Model • Expansion in zone-center basis (emphasizing zone-center accuracy) • k typically less than 0.2Å-1 • Spherical (8-band) or cubic (14-band) symmetry • Relevant region of bulk band structure for optical and recombination properties SUCCESSES Simplicity Parameters connected 1-1 with experiments Energy levels and masses ~5-10 meV Absorption/gain spectra ~10% fundamental absorption (inc. excitons) ~20% differential transmission in SLMQW Auger/radiative rates Within factor of 2 for several material systems CHALLENGES Indirect constituents e.g. AlSb Defects Sometimes require full Brillouin zone Interface roughness For islands of diameter less than 15Å

9. InAs/GaSb: A Type II Broken Gap Superlattice With Controllable Interface Bonds

10. Carrier Recombination Calculations • Auger recombination • three dimensional formalism • non-parabolic bands splined from Kp • dispersion in matrix elements, splined from Kp • possible degenerate carrier statistics • modified version of well-tested superlattice code • typical factor of 2 agreement with experiment • Radiative recombination • excludes photon recycling • based on van Roosbroeck- Shockley • Impurity and defect mediated recombination • Neglected theoretical upper bounds to carrier lifetimes

11. Auger Recombination Formalism Rate for band-to-band transitions (Fermi’s Golden Rule): Matrix element is Common approximations (not employed here): -parabolic and isotropic bands -constant matrix elements -Boltzmann statistics -limitations to i, f -neglect Umklapp-neglect T-dependence of bands -neglect dopant/phonon/defect-assisted Auger 49.7Å InAs/57Å Ga0.9In0.1Sb Auger-1 most probable carriers at 40 K (electrons-solid circles; holes and empty states-hollow circles)

12. Experiment vs. Theory: Auger Recombination Rates

13. 49.7Å InAs/57Å Ga0.9In0.1Sb (10% In) 47Å InAs/21.5Å Ga0.75In0.25Sb (25% In) Vary In % but keep band gap fixed Test effects of band structure on Auger recombination Importance of Strain Case Study: 15 Micron Cutoff SLs and In %

14. Hole-Hole Auger Transitions: =15 m, T=40 K 49.7Å InAs/57Å Ga0.9In0.1Sb (10% In) A7=5.2x10-9 s 47Å InAs/21.5Å Ga0.75In0.25Sb (25% In) A7 > 1 s

15. Valence bands approximately one energy gap below top of valence band provide initial states for intersubband absorption final states for dominant Auger processes at room temperature (AM-7) Temperature changes move valence bands through “resonance region” Two-layer MWIR superlattices: 16.7Å InAs/35Å In0.25Ga0.75Sb-optimization ceases above 150 K; To good figure of merit 12.5Å InAs/39Å In0.25Ga0.75Sb- optimized from 250 K to 350 K; To figure of merit inapplicable Temperature Sensitivity of Optimization

16. Temperature Sensitivity of Electronic Band Structure

17. Valence Intersubband Absorption 12.5Å InAs/39Å In0.25Ga0.75Sb

18. Intersubband Absorption, Threshold Carrier and Threshold Current Densities

19. Layer Thickness Sensitivity of Optimization • Band structures for superlattices with same energy gap but different In0.25Ga0.75Sb layer thicknesses (300 K)

20. Intersubband Absorption, Threshold Carrier and Current Densities Require growth accuracy ±3.5 Å for InGaSb, ±0.25 Å for InAs

21. MWIR Four-Layer Superlattice • Incorporate strain-compensating quintarnary layer: InAs/In0.25Ga0.75Sb/InAs/Al0.30Ga0.42In0.28A0.50Sb0.50 • strain compensation occurs over ~100 Å SL period • provides Auger recombination and intersubband absorption optimization • 3.7 µm wavelength at 300 K

22. Importance of Umklapp and Saturation

23. Temperature Sensitivity of Auger Final State Optimization Blue: valence subbands 4, 5, 6

24. Artificially Shift Valence Subbands 4, 5, 6 • Increasing temperature has a profound impact on final-state optimization for Auger suppression • At 77 K the final-state optimization is very important • At 300 K the final-state optimization has just ceased to be of any importance • -this structure it may still be important at temperatures just slightly lower

25. SUMMARY • Details of temperature dependent valence band structure particularly important for optimizing design of Sb-based MWIR active regions • Strong intersubband absorption structure can make To parameterization inapplicable • Observe saturation of Auger recombination at high carrier densities • Occurs when holes become degeneratehh Auger dominant • Superlattice Umklapp processes provide about half of total Auger rate

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