2007 Fiscal Year Final Research Report Summary
A Si-based Semiconductor Optical Amplifier Afforded by High-brightness Quantum Dots Embedded in Silicon
| Project/Area Number |
17360007
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Applied materials science/Crystal engineering
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| Research Institution | The University of Tokyo |
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Principal Investigator |
FUKATSU Susumu The University of Tokyo, Graduate School of Arts and Sciences, Associate Professor (60199164)
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| Co-Investigator(Kenkyū-buntansha) |
KAWAMOTO Kiyoshi The University of Tokyo, Graduate School of Arts and Sciences, Assistant Professor (40302822)
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| Project Period (FY) |
2005 – 2007
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| Keywords | Si-based semiconductor optical amplifier / group-IV photonics / GaSb quantum Dots / proximity effect / direct-gap / current injection / on-off gain / amplified spontaneous emission |
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| Research Abstract |
Creation of semiconductor optical amplifiers and lasers using the indirect-band-gap silicon has been challenged enthusiastically in materials science, which is even deemed as a second industrial revolution : these Si-based optical components endowed with the unparalleled capabilities in electronics, if ever achieved, will allow to promote post-arsenic movement in society and total replacement of the now-III-V-dominating optoelectronics, thereby creating potential seeds for industries as represented by group-IV photonics, which holds considerable promise. The emerging Si-male active optical devices are key to bringing electronics and photonics together onto the same chip.
To this end, we have developed the first Si-based semiconductor optical amplifier (SiSOA) operating at cryogenic temperature. The amplifier chip contains partially strain-relieved, self-organizing GaSb quantum dots embedded in Si grown by molecular beam epitaxy. Evanescent coupling of election wave function occurs from
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the delta valleys in silicon into the forbidden gap of the adjacent direct-gap GaSb across a type-II potential barrier established at the heterointerface. Such proximity effect allows an otherwise indirect-valley occupying election to behave more like one in a direct-gap valley, which accounts for population inversion in the interface-localized three-level election-hole system appropriate to GaSb-Si. On-off gain was measured on a pair of butt coupled edge-emitting SiSOA chips under either exclusive photo-or electrical pumping. Improved values of gain coefficient, 10-13dB/cm, were obtained eventually after optimizing the pumping geometry while an SOI waveguide SiSOA produced a record value 15dB/cm ever achieved. Gain saturation characteristic of the three-level system was observed with increasing pump fluence, which was to be defeated only by significant loss due to free carrier absorption at further increased current injection.
Amplified spontaneous emission (ASE), i.e., precursor to possible lasing, was observed by optically pumping (sub-ns pulses at 8kHz, 532nm) the amplifier chip lengthwise using a cylindrical lens. The threshold values for this and on-off gain agreed well with each other as expected. Fast initial decay was captured in time-domain over the entire broad spectrum, which is consistent with inverted population created in the relevant electronic system. Less
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