O. Jambois, Optics Express, 2010 Towards population inversion of electrically pumped Er ions sensitized by Si nanoclusters Jeong-Min Lee High-Speed Circuits and Systems LAB Special Topics in Optical Communications

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 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: %  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 Special Topics in Optical Communications

Si nanocrystal High-Speed Circuits and Systems LAB Special Topics in Optical Communications

Si nanocrystal and Erbium ion High-Speed Circuits and Systems LAB 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: 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 Special Topics in Optical Communications

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 Special Topics in Optical Communications

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) C x C x Special Topics in Optical Communications

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: 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: 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 Special Topics in Optical Communications

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 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.12 Er population (%) C35020 C 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 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 Special Topics in Optical Communications

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

Thank you for listening Jeong-Min Lee High-Speed Circuits and Systems Special Topics in Optical Communications