O. Jambois, Optics Express, 2010

Towards population inversion of electrically pumped Er ions sensi-

tized by Si nanoclusters

Jeong-Min Lee(minlj@tera.yonsei.ac.kr)

High-Speed Circuits and Systems LAB.

2011-1 Special Topics in Optical Communications

High-Speed Circuits and Systems LAB. 2

Contents

1. Abstract

2. Introduction

3. Conduction mechanisms and power efficiency

4. Inverted fraction of Er ions

5. Conclusion

2011-1 Special Topics in Optical Communications

High-Speed Circuits and Systems LAB. 3

Abstract

The estimation of the inverted Er fraction in a system of Er doped sil-icon oxide sensitized by Si nanoclusters

Electroluminescence: obtained from the sensitized Er with power ef-ficiency: 10-2 %

20 % of the total Er concentration: inverted in the best device(one order of mag. higher than optical pumping)

2011-1 Special Topics in Optical Communications

High-Speed Circuits and Systems LAB. 4

Si nanocrystal

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High-Speed Circuits and Systems LAB. 5

Si nanocrystal and Erbium ion

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High-Speed Circuits and Systems LAB. 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-ncl2) The effective cross section of the system is increased three or four or-

ders of magnitude

2011-1 Special Topics in Optical Communications

High-Speed Circuits and Systems LAB. 7

Introduction

A principal limitation of the material:1) A small proportion of Er ions are coupled to Si-ncls2) Optical pumping: high fluxes are required to achieve population inversion Pumping the Si-ncl electrically the excitation cross section is in-creased 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, SiO2, Er2O3 and Si,

under a pure Ar plasma2) Annealing at 900°C for 30 minutes3) Electroluminescence was measured using conventional MOS structure4) Gate electrode: n-type polycrystalline silicon , thickness(200nm),

area(2.56x10-4cm2)

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High-Speed Circuits and Systems LAB. 8

Conduction mechanism and power efficient

Current density-electric field characteristics:

The current on applied voltage is dependant on characteristic of di-electrics

Poole-Frenkel-type mechanism:

Material Si excess (%)

Er concentration (at.cm-3)

Thickness (nm)

C350 8 9.0x1019 52

C352 18 4.8x1020 45

( /exp( )B

B

q qEJ E

K T

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High-Speed Circuits and Systems LAB. 9

Conduction mechanism and power efficient

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 effi-ciency 0.4 %

Electroluminescence spectra of layer C352:

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High-Speed Circuits and Systems LAB. 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:

Τrad: 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 effect2) Nanocluster size3) Er-to-nanocluster separation

2opt radW

NS d

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High-Speed Circuits and Systems LAB. 11

Inverted fraction of Er ions

Τrad (ms)C350 10

C352 5

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

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High-Speed Circuits and Systems LAB. 12

Inverted fraction of Er ions At low flux: the population of

the first excited state in-crease linearly with electron flux

At higher flux: saturation is observed for both devices

The first time that the inver-sion level has been esti-mated for electrical pumping

For optical pumping, high fluxes are necessary to reach

Flux increases rise time decreases

Er population (%)

C350 20

C352 3

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High-Speed Circuits and Systems LAB. 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

Further works:1) Optimize thin layers for electrical pumping2) Analysis of the dynamics of the system is underway

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High-Speed Circuits and Systems LAB. 14

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:

Decay time (us)C350 870

C352 470

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High-Speed Circuits and Systems LAB. 15

Conclusion

Significant development in Si photonics for the realization of a Si-based optical source by demonstrating an increased fraction of in-verted Er ions

The benefits of using electrical pumping to reach high values of in-version

A power efficiency(ηPE) of 10−2% is reported, corresponding to an ex-ternal quantum efficiency(ηEQE) of 0.4%

2011-1 Special Topics in Optical Communications

Thank you for listening

Jeong-Min Lee(minlj@tera.yonsei.ac.kr)

High-Speed Circuits and Systems

2011-1 Special Topics in Optical Communications