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InP overgrowth on SiO2 for active photonic devices on silicon
KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.ORCID iD: 0000-0001-5967-2651
KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.ORCID iD: 0000-0002-0977-2598
2010 (English)In: Proceedings of SPIE - The International Society for Optical Engineering, SPIE - International Society for Optical Engineering, 2010, Vol. 7606Conference paper, Published paper (Refereed)
Abstract [en]

ntegrationof III-V materials on silicon wafer for active photonic deviceshave previously been achieved by growing thick III-V layers ontop of silicon or by bonding the III-V stack layersonto a silicon wafer. Another way is the epitaxial lateralovergrowth (ELOG) of a thin III-V material from a seedlayer directly on the silicon wafer, which can be usedas a platform for the growth of active devices. Asa prestudy, we have investigated lateral overgrowth of InP byHydride Vapor Phase Epitaxy (HVPE) over SiO2 masks of differentthickness on InP substrates from openings in the mask. Openingswhich varied in direction, width and separation were made withE-beam lithography allowing a good dimension control even for nano-sizedopenings (down to 100 nm wide). This mimics overgrowth ofInP on top of SiO2/Si waveguides. By optimizing the growthconditions in terms of growth temperature and partial pressure ofthe source gases with respect to the opening direction, separationand width, we show that a thin (~200 nm) layerof InP with good morphology and crystalline quality can begrown laterally on top of SiO2. Due to the thingrown InP layer, amplification structures on top of it canbe well integrated with the underlying silicon waveguides. The proposedELOG technology provides a promising integration platform for hybrid InP/siliconactive devices.

Place, publisher, year, edition, pages
SPIE - International Society for Optical Engineering, 2010. Vol. 7606
Series
Proceedings of SPIE-The International Society for Optical Engineering, ISSN 0277-786X
National Category
Nano Technology Nano Technology
Identifiers
URN: urn:nbn:se:kth:diva-13936DOI: 10.1117/12.841181ISI: 000285576100002Scopus ID: 2-s2.0-77951686688OAI: oai:DiVA.org:kth-13936DiVA: diva2:328456
Conference
SPIE Photonics West 2010 Conference on Silicon Photonics V, San Francisco, CA, JAN 24-27, 2010
Note

QC 20100705

Available from: 2010-07-05 Created: 2010-07-05 Last updated: 2016-05-02Bibliographically approved
In thesis
1. Investigation of New Concepts and Solutions for Silicon Nanophotonics
Open this publication in new window or tab >>Investigation of New Concepts and Solutions for Silicon Nanophotonics
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Nowadays, silicon photonics is a widely studied research topic. Its high-index-contrast and compatibility with the complementary metal-oxide-semiconductor technology make it a promising platform for low cost high density integration. Several general problems have been brought up, including the lack of silicon active devices, the difficulty of light coupling, the polarization dependence, etc. This thesis aims to give new attempts to novel solutions for some of these problems. Both theoretical modeling and experimental work have been done.

Several numerical methods are reviewed first. The semi-vectorial finite-difference mode solver in cylindrical coordinate system is developed and it is mainly used for calculating the eigenmodes of the waveguide structures employed in this thesis. The finite-difference time-domain method and beam propagation method are also used to analyze the light propagation in complex structures.

The fabrication and characterization technologies are studied. The fabrication is mainly based on clean room facilities, including plasma assisted film deposition, electron beam lithography and dry etching. The vertical coupling system is mainly used for characterization in this thesis. Compared with conventional butt-coupling system, it can provide much higher coupling efficiency and larger alignment tolerance.

Two novel couplers related to silicon photonic wires are studied. In order to improve the coupling efficiency of a grating coupler, a nonuniform grating is theoretically designed to maximize the overlap between the radiated light profile and the optical fiber mode. Over 60% coupling efficiency is obtained experimentally. Another coupler facilitating the light coupling between silicon photonic wires and slot waveguides is demonstrated, both theoretically and experimentally. Almost lossless coupling is achieved in experiments.

Two approaches are studied to realize polarization insensitive devices based on silicon photonic wires. The first one is the use of a sandwich waveguide structure to eliminate the polarization dependent wavelength of a microring resonator. By optimizing the multilayer structure, we successfully eliminate the large birefringence in an ultrasmall ring resonator. Another approach is to use polarization diversity scheme. Two key components of the scheme are studied. An efficient polarization beam splitter based on a one-dimensional grating coupler is theoretically designed and experimentally demonstrated. This polarization beam splitter can also serve as an efficient light coupler between silicon-on-insulator waveguides and optical fibers. Over 50% coupling efficiency for both polarizations and -20dB extinction ratio between them are experimentally obtained. A compact polarization rotator based on silicon photonic wire is theoretically analyzed. 100% polarization conversion is achievable and the fabrication tolerance is relatively large by using a compensation method.

A novel integration platform based on nano-epitaxial lateral overgrowth technology is investigated to realize monolithic integration of III-V materials on silicon. A silica mask is used to block the threading dislocations from the InP seed layer on silicon. Technologies such as hydride vapor phase epitaxy and chemical-mechanical polishing are developed. A thin dislocation free InP layer on silicon is obtained experimentally.

Place, publisher, year, edition, pages
Stockholm: KTH, 2010. xii, 79 p.
Series
Trita-ICT/MAP AVH, ISSN 1653-7610 ; 2010:4
Keyword
Planar integrated circuit, silicon photonics, slot waveguide, finite-difference time-domain, waveguide grating coupler, ring resonator, polarization diversity scheme, polarization beam splitter, polarization rotator, hybrid silicon laser, epitaxial lateral overgrowth, chemical-mechanical polishing.
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-13029 (URN)
Public defence
2010-06-11, C1, Electrum 1, Isafjordsgatan 26, Kista, 13:47 (English)
Opponent
Supervisors
Note
QC20100705Available from: 2010-05-26 Created: 2010-05-24 Last updated: 2011-08-30Bibliographically approved
2. High-quality InP on Si and concepts for monolithic photonic integration
Open this publication in new window or tab >>High-quality InP on Si and concepts for monolithic photonic integration
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

As the age of Moore’s law is drawing to a close, continuing increase in computing performance is becoming increasingly hard‐earned, while demand for bandwidth is insatiable. One way of dealing with this challenge is the integration of active photonic material with Si, allowing high‐speed optical inter‐ and intra‐chip connects on one hand, and the economies of scale of the CMOS industry in optical communications on the other. One of the most essential active photonic materials is InP, stemming from its capability in combination with its related materials to produce lasers, emitting at wavelengths of 1300 and 1550 nm, the two most important wavelengths in data‐ and telecom.

However, integrating InP with Si remains a challenging subject. Defects arise due to differences in lattice constants, differences in thermal expansion coefficients, polarity and island‐like growth behavior. Approaches to counter these problems include epitaxial lateral overgrowth (ELOG), which involves growing InP laterally from openings in a mask deposited on a defective InP/Si substrate. This approach solves some of these problems by filtering out the previously mentioned defects. However, filtering may not be complete and the ELOG and mask themselves may introduce new sources for formation of defects such as dislocations and stacking faults.

In this work, the various kinds of defects present in InP ELOG layers grown by hydride vapor phase epitaxy on Si, and the reason for their presence, as well as strategies for counteracting them, are investigated. The findings reveal that whereas dislocations appear in coalesced ELOG layers both on InP and InP/Si, albeit to varying extents, uncoalesced ELOG layers on both substrate types are completely free of threading dislocations. Thus, coalescence is a critical aspect in the formation of dislocations. It is shown that a rough surface of the InP/Si substrate is detrimental to defect‐free coalescence. Chemical‐mechanical polishing of this surface improves the coalescence in subsequent ELOG leading to fewer defects.

Furthermore, ELOG on InP substrate is consistently free of stacking faults. This is not the case for ELOG on InP/Si, where stacking faults are to some extent propagating from the defective substrate, and are possibly also forming during ELOG. A model describing the conditions for their propagation is devised; it shows that under certain conditions, a mask height to opening width aspect ratio of 3.9 should result in their complete blocking. As to the potential formation of new stacking faults, the formation mechanism is not entirely clear, but neither coalescence nor random deposition errors on low energy facets are the main reasons for their formation. It is hypothesized that the stacking faults can be removed by thermal annealing of the seed and ELOG layers.

Furthermore, concepts for integrating an active photonic device with passive Si components are elucidated by combining Si/SiO2 waveguides used as the mask in ELOG and multi‐quantum well (MQW) lasers grown on ELOG InP. Such a device is found to have favorable thermal dissipation, which is an added advantage in an integrated photonic CMOS device.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. 85 p.
Series
Trita-ICT/MAP AVH, ISSN 1653-7610 ; 2013:05
National Category
Nano Technology
Identifiers
urn:nbn:se:kth:diva-127837 (URN)
Public defence
2013-09-27, Sal/Hall E, Forum, KTH-ITC, Isafjordsgatan 39, Kista, 10:00 (English)
Opponent
Supervisors
Note

QC 20130909

Available from: 2013-09-09 Created: 2013-09-09 Last updated: 2013-09-09Bibliographically approved

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Wosinski, LechLourdudoss, Sebastian

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