Electrical and Optical Studies of Metal:Semiconductor Nanocomposites for Nanophotonics

1. Electrical and Optical Studies of Metal:SemiconductorNanocomposites for Nanophotonics Stephen March1 PI: Professor Seth Bank2 Mentors: Erica Krivoy2 and Rodolfo Salas2 1Iowa State University 2 University of Texas at Austin

2. Introduction Motivation • Explore optically tunable III-V materials • Applications: • IR and fiber optic sensors • Plasmonics Growth Technique • Molecular Beam Epitaxy (MBE) • Atomic control • Precise thin-film composition • Superlattices • Thin-film semiconductor As Er Ga Individual atoms Single Epilayer Substrate Wafer

3. Project Goals • Investigate the optical tunability of rare-earth monopnictide (RE-V) nanoparticle superlattices • Study the Burstein–Moss blueshift and electronic band structure in heavily-doped InAsmaterials as a function of MBE growth conditions and dopant type Blueshift = toward higher energy1 1 UVABC’s. Company Webpage. 2013.

4. Experimental Set-up Normalized Curves in MATLAB Final Output Curve Splice in MATLAB 3 Curve Collection in LabView Detector Source M1 Sample M2 M3

5. Results – RE-V • Er, LaLu • small ML • few periods ML thickness • Lu • large ML • many periods GaAs ErAs monolayer (ML) • Adjustable parameters • RE, # periods, period size, ML (nanoparticle) size • Dramatic absorption increase 0.8 eV – 0.9 eV • 0.8 eV=1550 nm • 1550 nm critical for fiber optic systems! Period TEM of GaAs + ErAssuperlattice2 2 A.M. Crook et al., Appl. Phys. Lett., 2011 1nm GaAs Spacer ErAs GaAs 5 nm

6. Discussion – RE-V • Sub-bandgap RE-V absorption • Engineered formation of intermediate states 3 Ec Ec hνsmall Transmission hνsmall EF Intermediate States Absorption EF Ev Ev GaAs + RE-V GaAs 3M.P. Hanson, et al. , AIP Conf. Proc. 772 2004

7. Results – Heavily-doped InAs Thin-film absorption expression α, Absorption Coefficient t, film thickness (~ 500 nm) T, Transmission R, Reflection α2 linear interpolation  Egap,eff4 Increased doping 4 J.Wu et al. Phys Rev. B 66, 2002 Non-parabolic Divergence Observed Egap,effblueshift • 0.64 – 1.16 eV tunable range • Intrinsic 0.33 eVEgap,eff • n-type more responsive than p-type • Non-Parabolic model divergence • Agrees with literature trends 5,6 • Extends non-parabolic model to unexplored high n values Tunable range 5 I.T. Ferguson et al., Semicond. Sci Technol. 8 ,19936W.G. Spitzer et al.,Phys Rev 106, 1957

8. Discussion – Heavily-doped InAs Non-parabolic Region E EC Unfilled k ΔE Filled Efilled Burstein – Moss Effect 7,8 EF hνlarge Egap,eff hνsmall Egap Absorption Transmission δE EV Heavily Doped Undoped 7 E. Burstein. Phys. Rev. 93, 19548 T. S. Moss., Proc. Phys. Soc. B 67, 1954

9. Conclusion • Explored 2 material systems • RE-V nanoparticle superlattices • Heavily-doped InAs • Demonstrated desirable and easy to engineer sub- and greater-than bandgap absorption • Achievable through precisely controlled MBE techniques • Communication and sensor technology relies on optical tunability of materials • Insight from this investigation may lead to enhanced performance of optical device technology

10. Acknowledgements • Professor Bank • Erica Krivoy, Rodolfo Salas, Scott Maddox • UT LASE Group: • Dan Ironside, Kyle McNicholas, Ann Kathryn Rockwell, Nate Sheehan, Scott Sifferman, Emily Walker, VaishnoDasika • UT MER staff • NNIN

11. Questions?

12. Complete References • UVABC’s http://www.uvabcs.com/uvlight-typical.php • A.M. Crook et al. Suppression of planar defects in the molecular beam epitaxy of GaAs/ErAs/GaAs herterostructures. Appl. PhysLett. 99, 2011 • M.P. Hanson, et al. Strong sub-bandgap absorption in GaSb/ErSbnancomposites attributes to plasma resonances of semimetallicErSb. AIP Conf. Proc. 772 2004 • J.Wuet al. Effects of the narrow band gap on the properties of InN. Phys Rev. B 66, 2002 • I.T. Ferguson et al. Infrared reflection and transmission of undopedand Si-doped InAs grown on GaAs by molecular beam epitaxy. Semicond. Sci Technol. 8 ,1993 • W.G. Spitzer and H. Y. Fan. Determination of Optical Constants and Carrier Effective Mass of Semiconductors. Phys Rev 106, 1957 • E. Burstein. Anomalous Optical Absorption Limit in InSb. Phys. Rev. 93, 1954 • T. S. Moss. The Interpretation of the Properties of Indium Antimonide. Proc. Phys. Soc. B 67, 1954

13. Analysis – Role of the Surfactant • Schwoebol barrier (SB) causes island growth • Surfactant (e.g. Bi) lowers barrier • Smoother layers Energy U(x) SB Source: D. Birnie, “MBE – Molecular Beam Epitaxial Growth of Semiconductors”, 2005. Emin x

14. Terahertz Photomixer 2 1 - 2 1 Telecom Lasers V+ V- Si Lens THz Radiation

15. Final Report Pictures – grey scale Non-parabolic E EC Unfilled Ec EFermi e- Filled EBM k Intermediate States e- hνlarge Egap Photoelectric Absorption EFermi Egap,eff hνsmall Photoelectric Absorption EV Ev Heavily Doped GaAs + RE-V