1. MIRTHE Summer Workshop 2014, 04-08 August Four-zone quantum well infrared photodetector with a confined state in the continuum G. M. Penello, A. P. Ravikumar, D. L. Sivco and C. Gmachl

2. 2 MIRTHE Summer Workshop 2014, 04-08 August Motivation –Explore electron confinement by using electronic Bragg mirrors –Extend the energy range of III-V QWIPs (InGaAs/InAlAs lattice matched to InP) –Mid-IR application –Gas sensing systems –Free space communication http://en.wikipedia.org/wiki/Dielectric_mirror P. Kluczynski et al., Appl. Phys. B: Lasers and Opt., 105, 2, 427–434 (2011). http://en.wikipedia.org/wiki/L_band

3. 3 MIRTHE Summer Workshop 2014, 04-08 August QWIP Continuum Bound to continuum Quantum Well Infrared Photodetector Bound to bound Bound to quasibound Continuum High selectivity (narrow absorption peak) Tunable for a fixed bandoffset Poor carrier extraction Easy carrier extraction Tunable for a fixed bandoffset Lower selectivity (broad absorption peak) Good selectivity (narrow absorption peak) Easy carrier extraction Limited tunability for a fixed bandoffset

4. 4 MIRTHE Summer Workshop 2014, 04-08 August Bragg mirror Refraction and reflectionBragg mirror for electrons Electron with energy higher than the barrier Electron with energy lower than the barrier reflection on the interface refraction on the interface reflection on a layered material Electron with energy satisfying the bragg condition How to confine an electron in the continuum?

5. 5 MIRTHE Summer Workshop 2014, 04-08 August Continuum-localized states “Defect” on the superlattice. “defect” Increase transition energy High selectivity Easy carrier extraction Tunability not limited by bandoffset Low thermal excitation E z Bragg mirror Miniband is not shown for clarity

6. 6 MIRTHE Summer Workshop 2014, 04-08 August Continuum-localized states E0E0 E1E1 E2E2 E 0 →E 1 E 0 →E 2 Photocurrent Increase transition energy High selectivity Easy carrier extraction Tunability not limited by bandoffset Low thermal excitation Central QW = 2.5 nm Lateral QWs = 2.0 nm Barriers = 7.0 nm Best fit CQW: 2.4 nm LQWs: 1.7 nm Barriers: 6 nm Work done in collaboration with M. H. Degani, M. Z. Maialle, R. M. S. Kawabata, D. N. Micha, M. P. Pires, and P. L. Souza.

7. 7 MIRTHE Summer Workshop 2014, 04-08 August Asymmetric QWIP with a confined state in the continuum Asymmetric structure to explore a photovoltaic QWIP and a bias dependence of the photocurrent. High selectivity Easier carrier extraction in one direction Low thermal excitation E z

8. 8 MIRTHE Summer Workshop 2014, 04-08 August Four-zone QWIP with a confined state in the continuum 1 – emission zone 2 – drift zone 3 – capture zone 4 – tunneling (repopulation) zone

9. 9 MIRTHE Summer Workshop 2014, 04-08 August Simulation Asymmetric sample Bound to continuum QWIP Bound to bound QWIP (confined state in the continuum) Reference sample 9 7 7 7 7 779 Monolayer = 0.29343 nm –LQW = 7 monolayers ~ –DQW = 9 monolayers ~ –Barriers = 24 monolayers ~ Absorption cross section –Transfer matrix method –FWHM = 30 meV  ~ 0.1 (Typical in bound to bound transition) 2.1 nm 2.6 nm 7.0 nm InGaAs / InAlAs lattice matched to InP

10. 10 MIRTHE Summer Workshop 2014, 04-08 August Samples MBE –InGaAs / InAlAs lattice matched to InP –n-doped (2x10 18 cm -3 ) –Active layers repeated 20x separated by 30 nm InAlAs –InGaAs contact layers n-doped (2x10 18 cm -3 ) Processing –Wet etch –Ti/Au metallization –45 o lapping –Au wire bond QWIP mesa n-doped Reference sample Asymmetric sample

11. 11 MIRTHE Summer Workshop 2014, 04-08 August Photocurrent Excellent agreement between theoretical and experimental results. Photocurrent observed without applied bias on the asymmetric sample –“Four zone” photovoltaic QWIP 80K 0V 80K -5V  Asymmetric sample Reference sample

12. 12 MIRTHE Summer Workshop 2014, 04-08 August Photocurrent “Leaky” localized state More extended states to couple Broad photocurrent peak Similar to the reference sample Localized state Less extended states to couple Narrow photocurrent peak

13. 13 MIRTHE Summer Workshop 2014, 04-08 August Conclusion and future steps Asymmetric heterostructure with a confined state in the continuum was designed Photocurrent measurements confirmed the confined state in the continuum Photocurrent signal at 0V - photovoltaic QWIP Bias dependent photocurrent was explained by the asymmetry of the sample Figures of merit to be measured (responsivity and detectivity) “Four zone” photovoltaic QWIP to be optimized in our structure New heterostructures using the confined states in the continuum to be explored

14. 14 MIRTHE Summer Workshop 2014, 04-08 August Acknowledges Qcllab Capes Foundation, Ministry of Education of Brazil. MIRTHE (NSF-ERC)