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InP-based photonic crystals: Processing, Material properties and Dispersion effects
KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Photonic crystals (PhCs) are periodic dielectric structures that exhibit a photonic bandgap, i.e., a range of wavelength for which light propagation is forbidden. The special band structure related dispersion properties offer a realm of novel functionalities and interesting physical phenomena. PhCs have been manufactured using semiconductors and other material technologies. However, InP-based materials are the main choice for active devices at optical communication wavelengths. This thesis focuses on two-dimensional PhCs in the InP/GaInAsP/InP material system and addresses their fabrication technology and their physical properties covering both material issues and light propagation aspects.

Ar/Cl2 chemically assisted ion beam etching was used to etch the photonic crystals. The etching characteristics including feature size dependent etching phenomena were experimentally determined and the underlying etching mechanisms are explained. For the etched PhC holes, aspect ratios around 20 were achieved, with a maximum etch depth of 5 microns for a hole diameter of 300 nm. Optical losses in photonic crystal devices were addressed both in terms of vertical confinement and hole shape and depth. The work also demonstrated that dry etching has a major impact on the properties of the photonic crystal material. The surface Fermi level at the etched hole sidewalls was found to be pinned at 0.12 eV below the conduction band minimum. This is shown to have important consequences on carrier transport. It is also found that, for an InGaAsP quantum well, the surface recombination velocity increases (non-linearly) by more than one order of magnitude as the etch duration is increased, providing evidence for accumulation of sidewall damage. A model based on sputtering theory is developed to qualitatively explain the development of damage.

The physics of dispersive phenomena in PhC structures is investigated experimentally and theoretically. Negative refraction was experimentally demonstrated at optical wavelengths, and applied for light focusing. Fourier optics was used to experimentally explore the issue of coupling to Bloch modes inside the PhC slab and to experimentally determine the curvature of the band structure. Finally, dispersive phenomena were used in coupled-cavity waveguides to achieve a slow light regime with a group index of more than 180 and a group velocity dispersion up to 10^7 times that of a conventional fiber.

Place, publisher, year, edition, pages
Stockholm: KTH , 2008. , xv, 115 p.
Series
Trita-ICT/MAP AVH, ISSN 1653-7610 ; 2008:7
Keyword [en]
Photonic crystals, indium phosphide, photonic bandgap, Bloch modes, slow light, dispersion, coupled cavity waveguides, chemically assisted ion beam etching, lag effect, cavities, optical losses, carrier transport, carrier lifetimes, negative refraction, photonic bandstructure
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-4734ISBN: 978-91-7178-969-3 (print)OAI: oai:DiVA.org:kth-4734DiVA: diva2:13689
Public defence
2008-05-30, N1, Electrum 3, Kista, 10:00
Opponent
Supervisors
Note
QC 20100712Available from: 2008-05-08 Created: 2008-05-08 Last updated: 2010-07-12Bibliographically approved
List of papers
1. Characterization of the feature-size dependence in Ar/Cl2 chemically assisted ion beam etching of InP-based photonic crystal devices
Open this publication in new window or tab >>Characterization of the feature-size dependence in Ar/Cl2 chemically assisted ion beam etching of InP-based photonic crystal devices
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2007 (English)In: Journal of Vacuum Science & Technology B, ISSN 1071-1023, E-ISSN 1520-8567, Vol. 25, no 1, 1-10 p.Article in journal (Refereed) Published
Abstract [en]

The authors address feature-size dependence in Ar/Cl-2, chemically assisted ion beam etching (CAIBE) in the context of the fabrication of photonic crystal (PhC) structures. They systematically investigate the influence of various parameters such as hole diameter (115-600 nm), etch duration (10-60 min), and ion beam energy (300-600 eV) on PhC etching in InP with Ar/Cl-2, CAIBE. For a 60 min etching at an Ar-ion energy of 400 eV, the authors report an etch depth of 5 mu m for hole diameters d larger than 300 nm; the etch depth is in excess of 3 mu m for d larger than 200 nm. The evolution of roughness at the bottom of the etched holes and its dependence on hole size and etching conditions,is discussed. The physical mechanism of the observed feature-size dependent etching (FSDE) is then discussed and the effect of the process parameters is qualitatively understood using a model combining the effect of ion sputtering and surface chemical reactions. Finally, the effect of FSDE on the PhC optical properties is assessed by measuring the quality factor of one-dimensional Fabry-Perot PhC cavities. The measured quality factors show a clear trend with the etch depth: the cavity Q increases as the etch depth increases.

Keyword
WAVE-GUIDES; FABRICATION; GAAS; MODE; SEMICONDUCTOR; CHLORINE; CAVITY; RATIO; CL2
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-8375 (URN)10.1116/1.2402142 (DOI)000244512400003 ()2-s2.0-34047147995 (Scopus ID)
Note
QC 20100707Available from: 2008-05-08 Created: 2008-05-08 Last updated: 2010-07-07Bibliographically approved
2. Minimization of out-of-plane losses in planar photonic crystals by optimizing the vertical waveguide
Open this publication in new window or tab >>Minimization of out-of-plane losses in planar photonic crystals by optimizing the vertical waveguide
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2004 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 85, no 18, 3998-4000 p.Article in journal (Refereed) Published
Abstract [en]

A two-dimensional phenomenological approach previously developed for the modeling of out-of-plane losses in low refractive index contrast planar photonic crystals (PPhCs) is used to study the dependence of the different loss terms on the planar waveguide parameters. It is demonstrated that: (i) Losses can be minimized by designing vertical heterostructures optimized for a given technological process and/or for a given hole shape; and (ii) any small reduction of the loss value has a strong impact on the optical performances of PPhC structures.

Keyword
RADIATION LOSSES; HOLE DEPTH; INP; FABRICATION; SHAPE
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-8376 (URN)10.1063/1.1813634 (DOI)000224894900014 ()2-s2.0-10044266687 (Scopus ID)
Note
QC 20100707 QC 20110915Available from: 2008-05-08 Created: 2008-05-08 Last updated: 2011-09-15Bibliographically approved
3. Impact of feature-size dependent etching on the optical properties of photonic crystal devices
Open this publication in new window or tab >>Impact of feature-size dependent etching on the optical properties of photonic crystal devices
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2008 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 103, no 9, 096106-1-096106-3 p.Article in journal (Refereed) Published
Abstract [en]

Feature size dependence in Ar/Cl-2 chemically assisted ion beam etching of InP-based photonic crystals (PhCs) and its influence on the optical properties of PhC devices operating in the band gap are investigated. The analysis of the measured quality factors, the determined mirror reflectivities, and losses of one-dimensional Fabry-Perot cavities clearly demonstrates the importance of feature-size dependent etching. The optical properties show a dramatic improvement up to a hole depth of about 3.5 mu m that is primarily due to a significant reduction in extrinsic losses. However, beyond this hole depth, the improvement is at a lower rate, which suggests that extrinsic losses, although present, are not dominant.

Keyword
WAVE-GUIDE; LOSSES; FABRICATION
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-8377 (URN)10.1063/1.2913168 (DOI)000255983200189 ()2-s2.0-43949097571 (Scopus ID)
Note
QC 20100707. Uppdaterad från in press till published (20100707). Tidigare titel: Impact of feature size dependence on the optical properties of two-dimensional photonic crystal devices.Available from: 2008-05-08 Created: 2008-05-08 Last updated: 2010-07-07Bibliographically approved
4. Evidence for accumulated sidewall damage in dry etched photonic crystals
Open this publication in new window or tab >>Evidence for accumulated sidewall damage in dry etched photonic crystals
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2008 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118Article in journal (Other academic) Submitted
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-8378 (URN)
Note
QS 20120314Available from: 2008-05-08 Created: 2008-05-08 Last updated: 2013-11-19Bibliographically approved
5. Development of damage and its impact on surface recombination velocities in dry-etched InP-based photonic crystals
Open this publication in new window or tab >>Development of damage and its impact on surface recombination velocities in dry-etched InP-based photonic crystals
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(English)Manuscript (Other academic)
Identifiers
urn:nbn:se:kth:diva-8379 (URN)
Note
QC 20100709Available from: 2008-05-08 Created: 2008-05-08 Last updated: 2013-11-19Bibliographically approved
6. Carrier transport through a dry-etched InP-based two-dimensional photonic crystal
Open this publication in new window or tab >>Carrier transport through a dry-etched InP-based two-dimensional photonic crystal
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2007 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 101, no 12, 123101-1-123101-6 p.Article in journal (Refereed) Published
Abstract [en]

The electrical conduction across a two-dimensional photonic crystal (PhC) fabricated by Ar/Cl-2 chemically assisted ion beam etching in n-doped InP is influenced by the surface potential of the hole sidewalls, modified by dry etching. Carrier transport across photonic crystal fields with different lattice parameters is investigated. For a given lattice period the PhC resistivity increases with the air fill factor and for a given air fill factor it increases as the lattice period is reduced. The measured current-voltage characteristics show clear ohmic behavior at lower voltages followed by current saturation at higher voltages. This behavior is confirmed by finite element ISE TCAD (TM) simulations. The observed current saturation is attributed to electric-field-induced saturation of the electron drift velocity. From the measured and simulated conductance for the different PhC fields we show that it is possible to determine the sidewall depletion region width and hence the surface potential. We find that at the hole sidewalls the etching induces a Fermi level pinning at about 0.12 eV below the conduction band edge, a value much lower than the bare InP surface potential. The results indicate that for n-InP the volume available for conduction in the etched PhCs approaches the geometrically defined volume as the doping is increased.

Keyword
WAVE-GUIDES; SIDEWALL RECOMBINATION; SURFACE; DAMAGE; DEPENDENCE; WIRES; MODEL
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-8380 (URN)10.1063/1.2747222 (DOI)000247625700002 ()2-s2.0-34547493266 (Scopus ID)
Note
QC 20100707Available from: 2008-05-08 Created: 2008-05-08 Last updated: 2010-07-07Bibliographically approved
7. Negative Refraction at Infrared Wavelengths in a Two-Dimensional Photonic Crystal
Open this publication in new window or tab >>Negative Refraction at Infrared Wavelengths in a Two-Dimensional Photonic Crystal
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2004 (English)In: Physical Review Letters, ISSN 0031-9007, Vol. 93, no 073902Article in journal (Refereed) Published
Abstract [en]

We report on the first experimental evidence of negative refraction at telecommunication wavelengths by a two-dimensional photonic crystal field. Samples were fabricated by chemically assisted ion beam etching in the InP-based low-index constrast system. Experiments of beam imaging and light collection show light focusing by the photonic crystal field. Finite-difference time-domain simulations confirm that the observed focusing is due to negative refraction in the photonic crystal area.

Keyword
BAND-GAP; INDEX; PROPAGATION; LENS
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-8381 (URN)10.1103/PhysRevLett.93.073902 (DOI)000223273300023 ()2-s2.0-19444373513 (Scopus ID)
Note
QC 20100707 QC 20110923Available from: 2008-05-08 Created: 2008-05-08 Last updated: 2011-09-23Bibliographically approved
8. Bloch mode excitation in two-dimensional photonic crystals imaged by Fourier optics
Open this publication in new window or tab >>Bloch mode excitation in two-dimensional photonic crystals imaged by Fourier optics
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2009 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, no 16, 165116-1-165116-6 p.Article in journal (Refereed) Published
Abstract [en]

Coupling into the Bloch modes of a two-dimensional photonic crystal (PhC) field is investigated by Fourier optics. The PhC was designed to operate in the second band above the air-light line, close to the autocollimation regime for TE polarization. The sample was fabricated in an InP-based heterostructure and an access ridge waveguide provides in-plane excitation of the PhC. The spatial Fourier transform of the field maps obtained from finite-difference time-domain simulations and those calculated by plane-wave expansion are compared to the experimentally obtained equifrequency surfaces (EFS). The shape of the imaged EFS and its variation with the excitation wavelength is shown to be consistent with the theoretical simulations. Finally, the results indicate that if combined with different excitation geometries, Fourier optics can be a powerful technique to assess photonic crystal devices and to design efficient structures.

Keyword
excited states; finite difference time-domain analysis; Fourier transform optics; Fourier transforms; indium compounds; photonic crystals; LIGHT-PROPAGATION; GAP
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-8382 (URN)10.1103/PhysRevB.79.165116 (DOI)000265945200038 ()2-s2.0-66149179252 (Scopus ID)
Note
QC 20100707. Uppdaterad från manuskript till artikel i tidskrift (20100707).Available from: 2008-05-08 Created: 2008-05-08 Last updated: 2010-07-12Bibliographically approved
9. Highly dispersive photonic crystal-based coupled-cavity structures
Open this publication in new window or tab >>Highly dispersive photonic crystal-based coupled-cavity structures
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2006 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 88, no 20, 201106-1-201106-3 p.Article in journal (Refereed) Published
Abstract [en]

We measured the wavelength dependence of the group velocity dispersion (GVD) for different photonic-crystal coupled-cavity structures through a phase analysis of the transmitted modulated signal. GVD values as large as 10(6)-10(7) times the dispersion of a standard single mode fiber are obtained when operating close to the band edge of the miniband, in agreement with the calculated group index. The GVD is found to be smaller for the structure based on more open cavities.

Keyword
SLAB-WAVE-GUIDE; RESONATOR
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-8383 (URN)10.1063/1.2203955 (DOI)000237682100006 ()2-s2.0-33646866746 (Scopus ID)
Note
QC 20100707Available from: 2008-05-08 Created: 2008-05-08 Last updated: 2010-07-07Bibliographically approved

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