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

2. Contents 1.Abstract 2.Introduction 3.Conduction mechanisms and power efficiency 4.Inverted fraction of Er ions 5.Conclusion High-Speed Circuits and Systems LAB.2 2011-1 Special Topics in Optical Communications

3. 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.3 2011-1 Special Topics in Optical Communications

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

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

6. 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: 1)Broadband absorption spectrum of the Si-ncl 2)The effective cross section of the system is increased three or four orders of magnitude High-Speed Circuits and Systems LAB.6 2011-1 Special Topics in Optical Communications

7. Introduction  A principal limitation of the material: 1)A small proportion of Er ions are coupled to Si-ncls 2)Optical pumping: high fluxes are required to achieve population inversion  Pumping the Si-ncl electrically 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: 1)Magnetron co-sputtering of three confocal cathodes, SiO 2, Er 2 O 3 and Si, under a pure Ar plasma 2)Annealing at 900°C for 30 minutes 3)Electroluminescence was measured using conventional MOS structure 4)Gate electrode: n-type polycrystalline silicon, thickness(200nm), area(2.56x10 -4 cm 2 ) High-Speed Circuits and Systems LAB.7 2011-1 Special Topics in Optical Communications

8. Conduction mechanism and power efficient  Current density-electric field characteristics: High-Speed Circuits and Systems LAB.8 The current on applied voltage is dependant on characteristic of dielectrics Poole-Frenkel-type mechanism: Material Si excess (%) Er concentration (at.cm -3 ) Thickness (nm) C35089.0x10 19 52 C352184.8x10 20 45 2011-1 Special Topics in Optical Communications

9. Conduction mechanism and power efficient High-Speed Circuits and Systems LAB.9 Electroluminescence at 1.54 μm was observed for both devices Applied Voltage: -30 V Carrier flux: 3.4x10 16 q.cm -2 s -1 PL was pumped with the 476 nm line of Ar laser η PE : The ratio between emitted optical power and electrical power input  1.3x10 -2 % η EQE =η PE x eV/ћω : The external quantum efficiency  0.4 %  Electroluminescence spectra of layer C352: 2011-1 Special Topics in Optical Communications

10. 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: Τ rad : the Er radiative life time S: the emission area d: the thickness of the active layer  Difficult to estimate the radiative time: 1)Presence of the Si-ncl due to the Purcell effect 2)Nanocluster size 3)Er-to-nanocluster separation High-Speed Circuits and Systems LAB.10 2011-1 Special Topics in Optical Communications

11. Inverted fraction of Er ions Τ rad (ms) C35010 C3525 High-Speed Circuits and Systems LAB.11  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 2011-1 Special Topics in Optical Communications

12. 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.12 Er population (%) C35020 C3523 2011-1 Special Topics in Optical Communications

13. 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 High-Speed Circuits and Systems LAB.13  Further works: 1)Optimize thin layers for electrical pumping 2)Analysis of the dynamics of the system is underway 2011-1 Special Topics in Optical Communications

14. Inverted fraction of Er ions EL rise and decay time are observed to be non-exponential High-Speed Circuits and Systems LAB.14  Time-resolved EL for C352 with increasing charge flux: Decay time (us) C350870 C352470 2011-1 Special Topics in Optical Communications

15. 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(η PE ) of 10 −2 % is reported, corresponding to an external quantum efficiency(η EQE ) of 0.4% High-Speed Circuits and Systems LAB.15 2011-1 Special Topics in Optical Communications

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