Towards population inversion of electrically pumped Er ions sensitized by Si nanoclusters

1. 2011-1 Special Topics in Optical Communications Towards population inversion of electrically pumped Er ions sensitized by Si nanoclusters O. Jambois, Optics Express, 2010 Jeong-Min Lee (minlj@tera.yonsei.ac.kr) High-Speed Circuits and Systems LAB.

2. 2011-1 Special Topics in Optical Communications Contents • Abstract • Introduction • Conduction mechanisms and power efficiency • Inverted fraction of Er ions • Conclusion High-Speed Circuits and Systems LAB.

3. 2011-1 Special Topics in Optical Communications Abstract • The estimation of the inverted Er fraction in a system of Er doped silicon oxide sensitized by Si nanoclusters • Electroluminescence: obtained from the sensitized Er with power efficiency: 10-2 % • 20 % of the total Er concentration: inverted in the best device(one order of mag. higher than optical pumping) High-Speed Circuits and Systems LAB.

4. 2011-1 Special Topics in Optical Communications Si nanocrystal High-Speed Circuits and Systems LAB.

5. 2011-1 Special Topics in Optical Communications Si nanocrystal and Erbium ion High-Speed Circuits and Systems LAB.

6. 2011-1 Special Topics in Optical Communications Introduction • Key challenges of Si photonics: • Realization of an efficient Si-based light source • Various Si nanocluster (Si-ncl)-based materials using quantum confinement effects in Si  Light emitting diode • Realization of a Si-based injection laser • The system of Er-doped silica sensitized by Si-ncl (1.55um is important for telecom applications and absorption minimum) • The improvement in Er excitation thanks to Si-ncl sensitization: • Broadband absorption spectrum of the Si-ncl • The effective cross section of the system is increased three or four orders of magnitude High-Speed Circuits and Systems LAB.

7. 2011-1 Special Topics in Optical Communications Introduction • A principal limitation of the material: • A small proportion of Er ions are coupled to Si-ncls • Optical pumping: high fluxes are required to achieve population inversion  Pumping the Si-nclelectrically the excitation cross section is increased by two orders of magnitude from that achieved using optical pumping • Preparation of active layers of Er-doped SRSO: • Magnetron co-sputtering of three confocal cathodes, SiO2, Er2O3 and Si, under a pure Ar plasma • Annealing at 900°C for 30 minutes • Electroluminescence was measured using conventional MOS structure • Gate electrode: n-type polycrystalline silicon , thickness(200nm), area(2.56x10-4cm2) High-Speed Circuits and Systems LAB.

8. 2011-1 Special Topics in Optical Communications Conduction mechanism and power efficient • Current density-electric field characteristics: • The current on applied voltage is dependant on characteristic of dielectrics • Poole-Frenkel-type mechanism: High-Speed Circuits and Systems LAB.

9. 2011-1 Special Topics in Optical Communications Conduction mechanism and power efficient • Electroluminescence spectra of layer C352: • Electroluminescence at 1.54 μm was observed for both devices • Applied Voltage: -30 V • Carrier flux: 3.4x1016 q.cm-2s-1 • PL was pumped with the 476 nm line of Ar laser • ηPE: The ratio between emitted optical power and electrical power input  1.3x10-2 % • ηEQE=ηPE x eV/ћω : The external quantum efficiency  0.4 % High-Speed Circuits and Systems LAB.

10. 2011-1 Special Topics in Optical Communications Inverted fraction of Er ions • From the estimation of the optical power  Estimate the number of Er ions in the first excited state  The number of Er ions in the first excited state: • Τrad: the Er radiative life time • S: the emission area • d: the thickness of the active layer • Difficult to estimate the radiative time: • Presence of the Si-ncl due to the Purcell effect • Nanocluster size • Er-to-nanocluster separation High-Speed Circuits and Systems LAB.

11. 2011-1 Special Topics in Optical Communications Inverted fraction of Er ions • Si-ncl size and/or density are higher  shorter-radiative time • Estimate fraction of the light • Total internal reflection inside the active layer • Back reflection from the back electrode • 12 % of the emitted light is able to leave the top electrode High-Speed Circuits and Systems LAB.

12. 2011-1 Special Topics in Optical Communications Inverted fraction of Er ions • At low flux: the population of the first excited state increase linearly with electron flux • At higher flux: saturation is observed for both devices • The first time that the inversion level has been estimated for electrical pumping • For optical pumping, high fluxes are necessary to reach • Flux increases  rise time decreases High-Speed Circuits and Systems LAB.

13. 2011-1 Special Topics in Optical Communications Inverted fraction of Er ions • Observe a sublinear evolution of the reciprocal rise time with flux  main mechanism for Er excitation is through Si-ncl • Conduction mechanism: Si-ncl play a dominant role in charge transport • Electrical pumping: excitation of almost all the coupled Er • Further works: • Optimize thin layers for electrical pumping • Analysis of the dynamics of the system is underway High-Speed Circuits and Systems LAB.

14. 2011-1 Special Topics in Optical Communications Inverted fraction of Er ions • EL rise and decay time are observed to be non-exponential • Time-resolved EL for C352 with increasing charge flux: High-Speed Circuits and Systems LAB.

15. 2011-1 Special Topics in Optical Communications Conclusion • Significant development in Si photonics for the realization of a Si-based optical source by demonstrating an increased fraction of inverted Er ions • The benefits of using electrical pumping to reach high values of inversion • A power efficiency(ηPE) of 10−2% is reported, corresponding to an external quantum efficiency(ηEQE) of 0.4% High-Speed Circuits and Systems LAB.

16. 2011-1 Special Topics in Optical Communications Thank you for listening Jeong-Min Lee (minlj@tera.yonsei.ac.kr) High-Speed Circuits and Systems