2 0 1 2 / 1 6 / 1 2

H a m i d r e z a K h a s h e iC l a s s P r e s e n t a t i o n o n S e m i c o n d u c t o r D e v i c e s 1L i g h t E m i s s i o n F r o m S i l i c o n

Light Emission From Silicon

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Introduction Some background Information

Why Silicon? Introduce a structure Ge-on-Si Light-Emitting Materials and Devices for

Silicon Photonics References

Outline

3H a m i d r e z a K h a s h e iC l a s s P r e s e n t a t i o n o n S e m i c o n d u c t o r D e v i c e s 1L i g h t E m i s s i o n F r o m S i l i c o n 2 0 1 2 / 1 6 / 1 2

Introduction What is Band gap? What is direct and indirect Band gap ?

Material Symbol Band gap (ev) @ 302k

Silicon Si 1.12

Germanium Ge 0.67

Gallium Arsenide

GaAs 1.424

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Introduction

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Using silicon allows us to Integrate photonics and microelectronics , and to exploit existing processing technology and

know-how . Most of the components required for silicon photonics exist, but the missing link is a silicon-based optical source. Our work focuses on filling this gap. Silicon is a very inefficient light emitter, thanks to its indirect band gap. This requires us to develop techniques to modify its optical and electronic properties.

Why Silicon?

6H a m i d r e z a K h a s h e iC l a s s P r e s e n t a t i o n o n S e m i c o n d u c t o r D e v i c e s 1L i g h t E m i s s i o n F r o m S i l i c o n 2 0 1 2 / 1 6 / 1 2

Impurity ColorSamarium RedTerbium GreenCerium BlueErbium IR

Quantum Confinement

Efficiency > 10 %

Introduce a structure

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Theory Ge-on-Si is a particularly interesting candidate due to its pseudo direct band gap behavior

and its compatibility with advanced electronics on Si. The direct band gap of Ge is 0.8 eV, corresponding exactly to 1550 nm. Tensile strain further decreases the energy difference between Γ and L valleys so that Ge

becomes closer to a direct band gap material (Fig. 1b)

Ge-on-Si Light-Emitting Materials and Devices for Silicon Photonics

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Tensile strained epitaxial Ge was grown on Si by ultra-high vacuum chemical vapor deposition (UHVCVD) .

Ge-on-Si Light-Emitting Materials and Devices for Silicon Photonics

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Although theory predicts that Ge becomes a direct band gap material under 2% tensile strain, the band gap shrinks to only 0.5 eV and the emission wavelength shifts to 2500 nm.

To obtain direct band gap emission while still keeping the wavelength around 1550 nm, we proposed a combination of two approaches, as shown in Fig. 1c.

1. introducing 0.25% tensile strain to decrease the difference between the direct and indirect gaps of Ge .

2. compensating the remaining energy difference between Γ and L valleys by n-type doping such that the Fermi level reaches the Γ valley .

Ge-on-Si Light-Emitting Materials and Devices for Silicon Photonics

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[1] : Dr.hasan katuzian, Photonic Vol-1[2] : Dr.hasan katuzian, Photonic Vol-2[3] : Jifeng Liu , Towards a Ge-based Laser for CMOS Applications[4] : Xiaochen Sun , Ge-on-Si Light-Emitting Materials and Devices for Silicon

Photonics

References

11H a m i d r e z a K h a s h e iC l a s s P r e s e n t a t i o n o n S e m i c o n d u c t o r D e v i c e s 1L i g h t E m i s s i o n F r o m S i l i c o n 2 0 1 2 / 1 6 / 1 2

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