GB2507513A

GB2507513A - Semiconductor device with epitaxially grown active layer adjacent an optically passive region

Info

Publication number: GB2507513A
Application number: GB1219596.2A
Authority: GB
Inventors: Lukas Czornomaz; Jens Hofrichter; Mirja Richter; Heike E Riel
Original assignee: International Business Machines Corp
Current assignee: International Business Machines Corp
Priority date: 2012-10-31
Filing date: 2012-10-31
Publication date: 2014-05-07
Also published as: CN103794985A; GB201219596D0

Abstract

A semiconductor device 1 comprising an optically passive aspect 2, and an optically active material 6, wherein the optically passive aspect 2 is patterned to comprise a photonic crystal structure 4 with a predefined structure 5, and the optically active material 6 is grown in the predefined structure 5 with a layer 7 acting as a seed layer. Any material which exceeds predefined area 5 may be removed by etching or polishing. The optically active material 6 may be crystalline or amorphous and performs light generation, amplification, detection or modulation. The optically passive region 2 may form a wire waveguide 3. A VCSEL may be formed by the optically active material 6. The cross section of the optically passive region 2 may be smaller than or the same size as that of the predefined structure 5, there may be a tapered region between the optically passive region and the structure 5. The photonic crystal may be a 2D crystal.

Description

Semiconductor device

Field of the invention

S The present invention relates to a semiconductor device for use in an optical application and a method of fabrication therefor.

Background of the invention

In order to meet the requirements of future computing systems, higher speed and more energy efficient alternatives to electrical interconnects such as, for example, on-chip optical interconnects and chip-to-chip optical interconnects, may be needed.

Integrated optics, particularly silicon photonics, may suitably meet such needs. For the cost-effective, mass-fabrication of CMOS-based chips having a performance capability suitable for use in high-speed devices and/or applications, integrated optical interconnects with compatible light sources are to be provided. A problem in this regard is that, due to the indirect band-gap of silicon, no silicon-based light sources are available and/or may be used. This problem has been addressed by the use of Ill-V based semiconductor material systems typically being provided as light sources for use in conjunction with silicon photonics and, more generally, integrated optics based on a silicon platform. However, an associated problem in this regard is posed by the lattice mismatch between Ill-V compound semiconductors and silicon, making the direct, monolithic integration of Ill-V based light sources on a silicon platform non-trivial. In previously-proposed approaches for facilitating such integration, bonded Ill-V based light sources or blanket gain materials have been used. In this regard, it may be time-consuming and challenging to achieve relatively high-precision alignment when bonding a pre-processed Ill-V based light source to a given waveguide structure, particularly since the alignment precision may be further limited by the bonding process. For bonding a blanket Ill-V material on a pre-processed silicon-based waveguide, the alignment marks located on the silicon wafer that are provided for the lithography step involved in the patterning of the Ill-V layer may be used. Because the alignment accuracy of light sources based on compound semiconductor systems, such as, for example, Ill-V materials, with respect to optical structures, such as, for example, silicon waveguides and/or resonators, may be rather dependent on lithography accuracy, it may be insufficient for certain applications.

Reference is now made to the document titled, "Defect reduction of GaAs epitaxy on Si (001) using selective aspect ratio trapping", by Li et aL published in AppI. Phys. Lett., vol. 91, 021114, 2007, in which Ill-V epitaxy in oxide trenches on silicon has been reported using aspect ratio trapping. Reference is also made to the document S titled, Monolithic integration of GaAs/lnGaAs lasers on virtual Ge substrates via aspect-ratio trapping", by Li etal. published in J. Electrochem. Soc. 156, H574, 2009, in which the formation of GaAs/lnGaAs quantum well lasers, by metallorganic chemical vapour deposition, on virtual Ge substrates on silicon has been demonstrated via aspect ratio trapping and epitaxial lateral overgrowth. These documents are respectively concerned with addressing other known problems associated with the fabrication of structures comprising compound semiconductor material systems, such as Ill-V material systems, on silicon, which may cause performance deterioration of devices in which such structures are integrated. Such problems are related to the lattice mismatch and difference in thermal coefficients between Ill/V material systems and silicon. However, neither of these documents address the problems, as discussed hereinabove, associated with the alignment of compound semiconductor systems that are monolithically integrated and optically coupled with optical structures, for example, waveguides and, more generally, photonic structures.

In the document titled, "Si-InAs heterojunction Esaki tunnel diodes with high current densities", by Bjoerk etaL, published in AppI. Phys. Lett., vol. 97, 163501, 2010, Ill-V nanowire growth on silicon is discussed. The problems and/or issues associated with the alignment of compound semiconductor systems that are monolithically integrated and optically coupled with optical components such as waveguides and/or photonic structures are not addressed.

Reference is made to the documents titled, "Electrically pumped hybrid AlGalnAs-silicon evanescent laser", by Fang et aL, published in Optics Express, vol. 14, issue 20, pp. 9203 -9210, 2006, and Electrically pumped lnP-based microdisk lasers integrated with a nanophotonic silicon-on-insulator waveguide circuit", by Van Campenhout etal., published in Optics Express, vol. 15, issue 11, pp. 6744-6749, 2007. These documents generally disclose the alignment of an active lasing region towards a waveguide using contact lithography, with an alignment accuracy of better than 2 microns being achieved. Turning to the document titled, Metamorphic DBR and tunnel-junction injection: A CW RT monolithic long-wavelength VCSEL", by Boucart et aL, published in IEEE U. Sel. Topics Quantum Electron, vol. 5, issue 3, pp. 520-529, 1999, Ill-V light sources on silicon are described. This document publishes the fabrication of a long-wavelength, vertical-cavity, surface-emitting laser (VCSEL), which is monolithically integrated on an indium phosphide (lnP) wafer, capable of operating at room temperature, and has a tunnelling junction for reduced losses sustained during operation. This document does not address the issues/problems associated with the alignment of compound semiconductors that are optically coupled to optical structures such as waveguides, and more particularly those based on a silicon platform.

In each of the documents titled, Design and optical characterisation of photonic crystal lasers with organic gain material', published by Baumann et aL in Journal of Optics, vol. 12, 065003, 2010, and Organic mixed-order photonic crystal lasers with ultrasmall footprini', by Baumann et aL, published in AppI. Phys. Lett., vol. 91, 171108, 2007, spin-coating of an organic gain material onto a two-dimensional photonic crystal is reported. Whilst suitable for organic gain material, spin-coating is not compatible with respect to solid state gain materials, such as, for example, Ill-V material systems.

US 2008/0002929A1 describes an apparatus and a method for electrically pumping a hybrid evanescent laser. For one example, the apparatus includes an optical waveguide disposed in silicon. An active semiconductor material is disposed over the optical waveguide defining an evanescent coupling interface between the optical waveguide and the active semiconductor material such that an optical mode to be guided by the optical waveguide overlaps both the optical waveguide and the active semiconductor material. A current injection path is defined through the active semiconductor material and at least partially overlapping the optical mode such that light is generated in response to electrical pumping of the active semiconductor material in response to current injection along the current injection path at least partially overlapping the optical mode. In this document, the light generated by the active semiconductor material is evanescently coupled to a silicon waveguide that constitutes a passive aspect. Because the active semiconductor material is remotely positioned with respect to the silicon waveguide, it may be that the position of the generated light relative to passive aspect is relatively unchanged. Also, it may be that the overlap of the generated light with the active semiconductor material is relatively small, and so it may be expected that the teaching of the present document is based on a hybrid mode of operation, that is, a mainly passive mode with a relatively smaller active mode. Such a hybrid mode of operation may cause relatively higher threshold currents and lower optical output levels. Alignment issues may not be considered in the present document and, indeed are not addressed, since the position of the generated light is determined by the position of the underlying silicon waveguide. Positioning of the active semiconductor material relative to the underlying silicon waveguide may be facilitated by contact lithography with micron-scale precision in the present case.

US 2008/0198888 Al discloses a method of bonding a compound semiconductoi on a silicon waveguide for attaining a laser above a silicon substrate. This document is concerned with the heterogeneous integration, rather than the monolithic integration, of a light source based on a compound semiconductor material system with respect to a silicon substrate. Furthermore, such heterogeneous integration is achieved by optical contact-lithography, which has associated micron-range alignment tolerances.

US2009/0245298A1 discloses a silicon laser integrated device, comprising: a silicon-on-insulator substrate comprising at least one waveguide in a top surface, and a compound semiconductor substrate comprising a gain layer, the compound semiconductor substrate being subjected to a hybrid integration process, wherein the upper surface of the compound semiconductor substrate is bonded to the top surface of the silicon-on-insulator substrate. This document is concerned with the hybrid/heterogeneous integration, rather than the monolithic integration, of a surface of a compound semiconductor substrate with respect to a silicon-on-insulator substrate. Alignment between the compound semiconductor substrate and the silicon-on-insulator substrate is performed by optical contact-lithography, which has associated micron-range alignment tolerances. Based on the index contrasts of the fabricated structures, it may be that the light generated by the laser source/compound semiconductor aspect is mainly confined in the silicon with a relatively small proportion being confined within the compound semiconductor, which may serve to limit the efficiency of the laser and result in relatively increased power consumption.

US5703896 discloses an apparatus for eniitting varying colours of light comprising: a lasing layer formed of crystalline silicon quantum dots formed in an isolation matrix of hydrogenated silicon; said quantum dots being formed in three patches; each of said three patches having different sized quantum dots therein to thereby produce three different colours of light; a barrier layer of p-type semiconductor under said lasing layer, said p-type semiconductor being selected from the group GaP, SiC, GaN, ZnS; a substrate member under said barrier layer; an n-type semiconductor layer above said lasing layer, said n-type semiconductor layer being selected from the group GaP, SiC, CaN, ZnS; a positive potential contact beneath said substrate member, three negative potential contacts; each of said three contacts being above a different one of said three patches; each of said three contacts acting with said positive contact to selectively bias a different one of said three patches; three sectors of concentric grating surrounding said three patches; each of said sectors having a radial period corresponding to the colour of light produced by an adjacent one of said three patches; and each of said sectors resonating photons emitted by said adjacent patch to stimulate coherent light emission. This document is concerned with the fabrication of silicon quantum dots in silicon. It does not address the monolithic integration of a light/laser source based on a compound semiconductor such as, a Ill-V material system, with respect to an optical structure such as, a photonic structure and/or optical waveguide based on a silicon platform.

US2007/0105251 discloses a laser structure comprising: at least one active layer including doped Ge so as to produce light emissions at approximately 1550 nm from the direct band-gap of Ge; a first confinement structure being positioned on a top region of said at least one active layer; and a second confinement structure being positioned on a bottom region of said at least one active layer. This document generally seems to be concerned with a VOSEL device. It does not seem to address the challenges faced in achieving alignment, on a scale of nanometres, of a light source based on a compound semiconductor material system that is monolithically integrated and optically coupled with an optical structure such as a waveguide based on a silicon platform.

US2007/0104441 discloses an integrated photodetector apparatus comprising: (a) a substrate comprising a first cladding layer disposed over a base layer, the base layer comprising a first semiconducting material, the first cladding layer defining an opening extending to the base layer; (b) an optical waveguide comprising the first semiconductor material and disposed over the substrate; and (c) a photodetector comprising a second semiconductor material epitaxially grown over the base layer at least in the opening, the photodetector comprising an intrinsic region optically coupled to the waveguide, at least a portion of the intrinsic region extending above the first cladding layer and laterally aligned with the waveguide. The disclosed fabrication method is in relation to a germanium photodetector that is laterally coupled to a polycrystalline waveguide and is aligned relative thereto by way of a dedicated, multiple-step alignment procedure. This document does not address how a compound semiconductor based light source may be monolithically integrated and/or aligned, with an alignment tolerance on a scale of nanometres, with respect to integrated optics based on a silicon platform.

US5259049 discloses an electro-optical device comprising: a substrate; a laser grown on said substrate, and having an active region, an etched mirror, and a laser ridge thereon, wherein the shape of the laser ridge is transferred to said substrate so as to form a substrate ridge, said laser generating a beam; and an optical waveguide coupled to the mirror, and being deposited on said substrate ridge so as to be laterally aligned by said substrate ridge to said laser ridge, said optical waveguide effectively shaping the beam generated by said laser said optical waveguide comprising a lower cladding layer grown on top of said substrate ridge, a waveguide core disposed on top of said lower cladding layer, and an upper cladding layer disposed on top of said waveguide core, wherein said cladding layers and said waveguide core comprise material having refractive indices which match the refractive indices of the laser, wherein said upper and lower cladding layers have approximately the same refractive indices, and wherein the difference between the refractive index of the waveguide core and the refractive index of said upper cladding layer is equal to the difference between the refractive indices of the active layer of said laser and the upper cladding layer, respectively. This document discloses a device in which a pre-fabricated laser is coupled to a waveguide structure. The waveguide structure is arranged on top of the laser and is aligned thereto by way of a ridge feature associated with the laser.

US6163639 discloses a process for fitting connectors to optical elements to an integrated optical circuit consisting of connecting at least one optical element to this circuit such that the outputs and/or inputs of each element are located approximately in the same plane as the inputs and/or outputs of this circuit, also located in the same plane, characterised in that it comprises the following steps: the circuit is positioned on a template with patterns that enable subsequent precise alignment of optical elements with inputs and/or outputs of the circuit, at least one block capable of holding the optical element(s) is positioned on the template facing the inputs and/or outputs of the circuit and is fixed to this circuit; the template is removed, and the optical element(s) is (are) placed in each block, the blocks then being aligned with the inputs and/or outputs of the circuit. This document discloses a passive alignment method of an optically active photonic circuit towards a waveguide section.

Encompassed within the context of passive optical components in this document are waveguides or fibres and not cavities and/or nanophotonic on-chip waveguides.

Regarding the passive optical components, they are inserted into dedicated alignment marks provided on the host substrate. The alignment marks are v-grooves etched into the host substrate, which may mean that the alignment tolerances are S lithography dependent. Generally, this document does not address the monolithic integration of a light source based on a compound semiconductor material system with respect to integrated optics based on a silicon platform, and instead is concerned with providing hybrid integration of bulk photonic components with fibres.

The described approach may be considered to be analogous with a packaging method for coupling an active Ill-V based chip with silica glass fibres. Alignment tolerances with the described approach may be insufficient for relatively large index contrast integrated photonic components.

US2004/0218648A1 discloses a laser diode comprising: a substrate; a lower material layer formed on the substrate; a resonance layer formed on the lower material layer, an upper material layer formed on the resonance layer and having a ridge at the top, a buried layer having a contact hole corresponding to the ridge of the upper material layer; a protective layer formed of a material different from the material of the buried layer, and having an opening corresponding to the contact hole of the buried layer; and an upper electrode formed on the protective layer to contact an upper surface of the ridge through the contact hole. This document discloses a device architecture and fabrication method for a low-leakage laser diode. An alignment process is described which relates to only the electronic injection part of the laser diode and not in respect of the material used as light source/laser with respect to the material comprising the integrated optics. It is also not addressed how optical coupling between the laser and the surrounding optical medium/integrated optics may be achieved.

Reference is made to the document titled, Hybrid Ill-V semiconductor/silicon nanolaser", by Halioua et aL, published in Optics Express, vol. 19, 9221, 2011, in which an optically pumped one-dimensional photonic cavity laser is vertically coupled to a pre-structured straight silicon waveguide. Alignment of the laser with respect to the silicon waveguide is performed by electron-beam lithography using markers formed in the silicon waveguide, with an overlay accuracy of better than 50 nm potentially being achieved. Although the <5Onm alignment precision is by far better than what can be achieved with optical contact lithography, it may still not be considered suitable for high quality-factor, low modal-volume micro-resonators, for example. Furthermore, electron-beam lithography is labour intensive, time-consuming and expensive.

Accordingly, it is a challenge to monolithically integrate an optically active material, S having a relatively high non-linearity, optical gain, light emission, with respect to surrounding passive optical/photonic structures/components, for example, waveguides and cavities. It is also desirable that such a task is performed with an alignment tolerance that is on the scale of nanometres and with the alignment procedure being conducted without dedicated alignment steps/lithographic processes and so as to be compatible with mass-fabrication.

Summary of the invention

According to an embodiment of a first aspect of the present invention, there is provided a semiconductor device for use in at least an optical application comprising: at least an optically passive aspect that is operable in substantially an optically passive mode, and at least an optically active material comprising at least a material that is operable in substantially an optically active mode, wherein: the optically passive aspect is patterned to comprise at least a photonic structure with at least a predefined structure, and the optically active material is formed in the predefined structure so as to be substantially self-aligned in at least a lateral plane with the optically passive aspect. In an embodiment of the present invention, the optically active material is grown in a predefined structure of the photonic structure patterned in the optically passive aspect. In this way, the optically active material is substantially self-aligned in at least a lateral plane and optically coupled with respect to the optically passive aspect. The alignment of the optically active material with respect to the optically passive aspect and/or features thereof may be done without the need for dedicated alignment steps and/or equipment. Since the optically active material is formed in the predefined structure, which is a structural feature provided in respect of, and as inherent to, the photonic structure, a precision with which the optically active material is placed relative to the optically passive aspect and/or features thereof may depend on a respective etch process or mask accuracy that is used in patterning the optically passive aspect with the photonic structure and the features thereof. Thus, the optically active material may be laterally aligned with respect to the optically passive aspect with an accuracy of down to a few nanometres, for example, 5 nm, without the need for labour-intensive, time-consuming and expensive equipment such as electron-beam lithography whilst also being suitable for mass-fabrication. In an embodiment of the present invention, the photonic structure comprising the predefined structure is fabricated first and then the optically active material is formed in the predefined structure. Thus, the fabrication step by way of which the photonic structure is provided may be considered to perform a dual function. The basis of the dual function is the predefined structure of the photonic structure: firstly, it provides a growth location for the optically active material in order to facilitate optical coupling between the optically active material and the optically passive aspect and, secondly, it facilitates the self-alignment feature of an embodiment of the present invention. The optically passive aspect may also be denoted as an optically passive region of the semiconductor device.

Preferably, the optically active material is substantially selectively formed in the predefined structure. In an embodiment of the present invention, the optically active material is formed in the predefined structure, a structural feature that is provided in respect of, and inherent to, the photonic structure of an embodiment of the present invention. This feature may be considered to extend the advantage of facilitating monolithic integration of the optically active material with respect to the optically passive aspect with relative ease of implementation compared to previously-proposed techniques.

Alternatively, and desirably, the optically active material is formed relative to the optically passive aspect so as to exceed at least an area of the predefined structure.

This feature may provide the advantage of ease of formation of the optically active material since it need not be formed precisely in and/or with respect to the predefined structure. In this regard, and preferably, the excess optically active material is removed so that the optically active material is provided in at least the predefined structure. The excess optically active material is desirably removed by wet-chemical etching or chemical mechanical polishing.

Preferably, at least a structural characteristic of the predefined structure is chosen thereby to facilitate the optically active material to be substantially self-aligned with respect to the optically passive aspect. By making an appropriate selection of one or more structural characteristics of the predefined structure such as a width, height and/or a shape thereof, the self-alignment feature of an embodiment of the present invention may be further improved and/or provided to suit, for example, an application of an embodiment of the present invention. Furthermore, any lattice -10-mismatch between the respective materials/material systems used for the optically active material and the optically passive aspect may be addressed by way of such a selection.

Desirably, the predefined structure is a trench, a hole or a combination thereof. The predefined structure is a structural feature provided in respect of the photonic structure, and in an embodiment of the present invention is chosen to be a trench, a hole or a combination thereof. Since such features may be provided with relative ease and/or precision regarding location and/or structural characteristics, they extend to an embodiment of the present invention, the advantages of ease of implementation of the self-alignment feature and versatility since the shapes and/or sizes thereof may be adapted to target specific devices, typically in the range of 10 nanometres to 10 micrometres.

Preferably, the predefined structure is provided in a given location of the optically passive aspect. In respect of the self-alignment and optical coupling of the optically active material with the optically passive aspect, the optically active material is formed locally in the predefined structure provided in the photonic structure rather than over the whole surface of the optically passive aspect. For example, the predefined structure may be formed in the photonic structure where the integration of the laser/light source, by way of the optically active material, is anticipated. This feature of an embodiment of the present invention may extend the advantages of ease of design, fabrication and implementation of an embodiment of the present invention since the optically active material is provided relative to the optically passive aspect as desired rather than being provided generally, the latter necessitating further processing steps for the removal of the optically active material from those regions other than the predefined structure.

Desirably, the optically active material is operable to perform light generation, detection, modulation or a combination thereof. This feature may facilitate increased versatility and application of an embodiment of the present invention to different optical systems.

Preferably, the optically active material comprises at least one of: a Ill-V material system, a Il-VI material system, at least a silicon nanoparticle, at least a silicon quantum dot, germanium and heterostructures thereof comprising at least one of gallium arsenide, gallium antimonide, gallium nitride, indium phosphide, indium aluminium arsenide, indium arsenic phosphide, indium gallium phosphide, gallium phosphide, indium gallium arsenide, indium gallium arsenic phosphide, and an organic material system. Desirably, the optically active material comprises a crystalline, polycrystalline or amorphous material. An embodiment of the present invention is not limited to the use of a specific material/material system for the optically active material and, in fact, different and a broad range of materials may be used therefor, which feature may provide the advantages of increased versatility in terms of devices and/or optical systems/applications in which an embodiment of the present invention may be used. Appropriate material stacks and/or quantum dots are encompassed within the scope of the present invention for the optically active material.

Preferably, the optically passive aspect comprises a multilayer structure provided on at least a seed layer. In a preferred embodiment of the present invention, the multilayer structure comprises at least a silicon layer arranged on an insulator layer and the seed layer comprises bulk silicon. Other appropriate material stacks are also encompassed within the scope of the present invention for the optically passive aspect.

Desirably, the optically passive aspect comprises at least one of: silicon, a Ill-V compound semiconductor, germanium, gallium arsenide, gallium antimonide, gallium nitride, indium phosphide, indium aluminium arsenide, indium arsenic phosphide, indium gallium phosphide, gallium phosphide, indium gallium arsenide, indium gallium arsenic phosphide, aluminium oxide, tantalum pent-oxide, hafnium dioxide, titanium dioxide, silicon dioxide, silicon nitride and silicon oxi-nitride. An embodiment of the present invention is not limited to the use of a specific material/materials for the optically passive aspect and, in fact, different and a broad range of materials may be used therefor, which feature may provide the advantages of increased versatility in terms of devices and/or optical systems/applications in which an embodiment of the present invention may be used.

Preferably, the optically passive aspect comprises at least an optical waveguide and an optical cavity. In an embodiment of the present invention, the optically passive aspect may comprise an optical waveguide for the transmission and/or coupling of light from the predefined structure to a desired location and a cavity for the formation of a laser so as to allow the photons generated by the optically active material to travel the gain medium, thereby generating stimulated emission. -12-

Desirably, an embodiment of the present invention comprises at least a vertical-cavity surface-emitting laser implemented by way of alternating layers of the optically active material. This feature comprises a coupling scheme for optically coupling the S optically active material with the optically passive aspect by way of a vertical cavity feature. Specifically, a vertical cavity surface-emitting laser is proposed having alternating layers of optically active material that form the dielectric Bragg reflectors.

An advantage of this feature may be that the coupling properties may be tuned as desired by variation of the mirror reflectivity, that is, by using more or fewer of the alternating layers of the optically active material. A further advantage of this feature may be ease of integration/implementation of an embodiment of the present invention in optical systems/applications where space economy in a lateral plane is desired. In this regard, and preferably, at least an emission region of the vertical-cavity surface-emitting laser is positioned relative to the optically passive aspect such that light generated by the vertical-cavity surface-emitting laser is coupled substantially in at least one of: a vertical plane relative to a surface of the optically passive aspect and laterally in an in-plane direction of the optically passive aspect.

By way of this feature, light may be coupled from the vertical-cavity surface emitting laser in a desired plane or planes relative to the optically passive aspect and, thus, may extend the advantage of broadening a range of applications/optical systems in which an embodiment of the present invention may be used.

Desirably, at least a cross-section of the optically passive aspect in a longitudinal plane is smaller than a corresponding cross-section of the predefined structure, thereby facilitating light generated by the optically active material to be substantially coupled to the optically passive aspect. This feature is provided in relation to a first coupling scheme for optically coupling the optically active material with the optically passive aspect by way of a lateral cavity feature. Because the cross-section of the optically passive aspect in the longitudinal plane is chosen to be smaller than a corresponding cross-section of the predefined structure, light generated by the optically active material is better confined within the optically passive aspect. Thus, this feature may extend the advantages of improved optical coupling efficiency and improved device performance to an embodiment of the present invention. With respect to the afore-described feature, preferably, the optically passive aspect comprises a tapered region between the smaller cross-section thereof and the predefined structure. The taper feature may be used to advantage to match the respective modal sizes of a light source based on the optically active material and the -13-optically passive aspect, for example, where the light source is a Ill-V material system and the optically passive aspect comprises a silicon optical waveguide. In this way, a modal gain of an embodiment of the present invention may be further improved.

S

Desirably, in an alternative embodiment of the present invention, a cross-section of the optically passive aspect in a longitudinal plane is substantially of the same size as the corresponding cross-section of the predefined structure. Fewer processing resources may be needed to fabricate an embodiment of the present invention where the cross-section of the optically passive aspect and the predefined structure are substantially the same. Thus, this feature may extend the advantage of ease of fabrication and/or implementation to an embodiment of the present invention.

Preferably, and in relation to the first coupling scheme for optically coupling the optically active material and the optically passive aspect with a lateral cavity feature, the optically passive aspect comprises a wire waveguide. This feature may extend the advantages of ease of fabrication and/or integration since wire waveguides, particularly, silicon wire waveguides, may be fabricated with well-established complementary metal-oxide semiconductor (CMOS) processes.

In an alternative implementation of the lateral cavity feature, there is provided a second coupling scheme for optically coupling the optically active material with the optically passive aspect comprising at least a one-dimensional photonic crystal cavity in which periodic holes are formed in an in-plane direction of the photonic structure and in a region thereof where light generated by the optically active material is substantially coupled to the optically passive aspect. Because a modal volume and/or the quality factor of a lateral cavity implemented as a one-dimensional photonic crystal cavity may be better controlled, corresponding advantages are extended, by way of the afore-described feature, to an embodiment of the present invention. In a first implementation of the one-dimensional photonic crystal cavity, it may be formed as un-chirped and un-tapered in the optically passive aspect. In this case, the optically passive aspect may be implemented as having a smaller cross-section in the longitudinal plane than the predefined structure of an embodiment of the present invention with the optically passive aspect being linked to the predefined structure by a tapered width. Advantages associated with the aforementioned first implementation include: ease of implementation, better confinement of light in the optically passive aspect and facilitating matching of the respective modes of the optically active -14-material and the one-dimensional photonic crystal cavity. In a second implementation of the one-dimensional photonic crystal cavity, the optically passive aspect has a cross-section in a longitudinal plane that is substantially of the same size as the corresponding cross-section of the predefined structure. Such a second S implementation may provide the advantage that fewer processing resources may be facilitated to produce such a structure since the optically passive aspect and the predefined structure have substantially the same size in the longitudinal plane.

In an alternative implementation of the lateral cavity feature, there is provided a third coupling scheme for optically coupling the optically active material with the optically passive aspect comprising at least a two-dimensional photonic crystal cavity in which periodic holes are formed in two in-plane directions of the photonic structure. Even better control of a modal volume and/or the quality factor in both in-plane directions may be achieved with a lateral cavity implemented as a two-dimensional photonic crystal cavity and so corresponding advantages are extended to an embodiment of the present invention. In this regard, desirably, there is provided at least a photonic crystal waveguide configured to couple the light generated by the optically active material to at least a desired location, which feature may provide improved optical coupling of light generated by the optically active material to a desired location and so facilitate improved device performance of an embodiment of the present invention.

In relation to an embodiment of the present invention comprising a one-dimensional photonic cavity or a two-dimensional photonic cavity, preferably, the periodic holes are substantially of the same-size. This feature has the associated advantage of ease of fabrication and/or implementation and so imparts such corresponding advantages to an embodiment of the present invention.

In relation to an embodiment of the present invention comprising a one-dimensional photonic cavity, a hole-size of at least some of the periodic holes is desirably tapered to progressively increase to a given size in a direction away from the predefined structure. This feature may facilitate mode-shaping of the cavity mode and higher quality factor values.

In an alternative implementation of the lateral cavity feature, there is provided a fourth coupling scheme for optically coupling the optically active material with the optically passive aspect in which an embodiment of the present invention further comprises a circular grating of alternating layers of at least two materials, one of the -15-materials having a lower refractive index than the other of the two materials, the predefined structure being located within a defect in the circular grating. Such a lateral cavity design may offer azimuthal symmetry resulting in a band-gap for substantially all in-plane k-vectors. Furthermore, such a cavity design may facilitate higher quality factor values to be achieved, such as, for example, 106.

A corresponding method aspect is also provided, and so according to an embodiment of a second aspect of the present invention, theie is piovided a method for fabricating a semiconductor device for use in at least an optical application comprising: providing at least an optically passive aspect that is operable in substantially an optically passive mode, and providing at least an optically active material comprising at least a material that is operable in substantially an optically active mode, wherein: the optically passive aspect is patterned to comprise at least a photonic structure with at least a predefined structure, and forming the optically active material in the predefined structure so as to be substantially self-aligned in at least a lateral plane with the optically passive aspect.

Brief description of the drawings

Reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 shows a side-view of an embodiment of the present invention; Figures 2a to 2c show the stages of fabrication of an embodiment of the present invention; Figures 3a and 3b illustrate a first coupling scheme with a lateral cavity feature in an embodiment of the present invention; Figures 4a to 4e illustrate a second coupling scheme with a lateral cavity feature in an embodiment of the present invention; Figure 5 illustrates a third coupling scheme with a lateral cavity feature in an embodiment of the present invention; -16-Figure 6 illustrates a fourth coupling scheme with a lateral cavity feature in an embodiment of the present invention, and Figures 7a and 7b illustrate a coupling scheme with a vertical cavity feature.

S

Detailed description of the preferred embodiments of the present invention Within the description, the same reference numerals or signs have been used to denote the same parts or the like.

Reference is now made to Figure 1 showing a semiconductor device 1 according to an embodiment of a first aspect of the present invention comprising at least an optically passive aspect ore device region 2 that, when the semiconductor device 1 is in use, is operable in substantially an optically passive mode for the transmission and/or coupling of light from a given location to a desired location, rather than for the generation, amplification, detection and/or modulation of light. The optically passive aspect 2 is patterned to comprise at least a photonic structure 4 with at least a predefined structure 5. In a preferred embodiment of the present invention, the optically passive aspect 2 comprises at least an optical waveguide 3 and an optical cavity 4'. The optical cavity 4' may be: implemented by way of a reflector and/or a resonator in an embodiment of the present invention and formed as a constituent feature of the photonic structure 4.

There is also provided at least an optically active material 6 comprising at least a material that is operable in substantially an optically active mode. Regarding the optically active material 6, it is chosen to be suitable for light generation, amplification, detection and/or modulation. By optically active, it is meant that the optically active material 6 has a characteristic facilitating light emission, optical gain and/or a relatively high non-linearity, making it suitable for the fabrication of modulators, or having relatively high absorption properties for the fabrication of detectors. The optically active material 6 is formed in the predefined structure 5, and in this way, it is optically coupled and substantially self-aligned in at least a lateral plane with the optically passive aspect 2, particularly the features thereof such as the optical waveguide 3.

In an embodiment of the present invention, the predefined structure 5 is a photonic cavity in the photonic structure 4. It is preferably a trench, hole or a combination -17-thereof. At least a structural characteristic of the predefined structure 5 such as a width, height and/or a shape thereof, may be selected thereby to facilitate a desired tuning of the self-alignment of the optically active material 6 with respect to the optically passive aspect 2. In a preferred embodiment of the present invention, the aspect ratio of the predefined structure 5, that is, the ratio of its height to its width/diameter, is chosen to be greater than 1 and, more preferably, greater than 3.

In an embodiment of the present invention, the aspect ratio is broadly chosen so as to facilitate aspect ratio trapping of the defects that are due to the lattice mismatch between the respective materials/material systems used for the optically active material 6 and the optically passive aspect 2. In a preferred embodiment of the present invention, the height of the predefined structure 5 is chosen to be 1000 nm and its width/diameter is chosen to be 250 nm. An embodiment of the present invention is, of course, not limited to the given examples of the aspect ratio, height and/or width dimensions for the predefined structure 5, and in fact any other sizes falling within the scope of the present invention may be used therefor.

In an embodiment of the present invention, the predefined structure 5 is provided in a given location of the optically passive aspect 2. In respect of the self-alignment and optical coupling of the optically active material 6 with the optically passive aspect 2, the optically active material is formed locally in the predefined structure 5 provided in the photonic structure 4 rather than over the whole surface of the optically passive aspect 2. In this regard, the predefined structure 5 is formed in the photonic structure 4 where the integration of the laser/light source, by way of the optically active material 6, is anticipated.

In an embodiment of the present invention, the predefined structure 5 may be an aperture comprising an insulating material or a blocking p-n junction. The insulating material is formed on the outer walls of the predefined structure 5 and may be selected from one of: silicon, germanium, gallium arsenide, gallium antimonide, gallium nitride, indium phosphide, indium aluminium arsenide, indium arsenic phosphide, indium gallium phosphide, gallium phosphide, indium gallium arsenide, indium gallium arsenic phosphide, aluminium oxide, tantalum pent-oxide, hafnium dioxide, titanium dioxide, silicon dioxide, silicon nitride and silicon oxi-nitride. Of course, an embodiment of the present invention is not limited to the use of such materials and any other suitable materials for the blocking p-n junction or the insulating material for the predefined structure 5 are encompassed within the scope of the present invention. -18-

Regarding the formation of the optically active material 6 in the predefined structure 5, two methods are proposed in an embodiment of the present invention. In one method, selective epitaxial growth is done in which the optically active material 6 is S substantially selectively formed in the predefined structure 5. In another method, height selective epitaxial growth of the optically active material 6 is done in which it is formed relative to a surface of the optically passive aspect 2 in which the predefined structure 5 is formed so as to exceed at least an area of the predefined structure 5.

Thus, the optically active material 6 is formed relative to the optically passive aspect 2 so as to at least be formed in and around the predefined structure 5. The excess optically active material 6, which may be any of the optically active material 6 around the predefined structure 5 and/or on the optically passive aspect 2, is removed so that the optically active material 6 is provided in the predefined structure 5. Removal of the excess optically active material 6 may be done by wet-chemical etching, chemical mechanical polishing or any other suitable method for this purpose.

In an embodiment of the present invention, for the optically active material 6, a wide and diverse range of materials and/or material systems may be used, such as, for example, a Ill-V material system, a Il-VI material system, at least a silicon nanoparticle, at least a silicon quantum dot, germanium and heterostructures thereof comprising at least one of gallium arsenide, gallium antimonide, gallium nitride, indium phosphide, indium aluminium arsenide, indium arsenic phosphide, indium gallium phosphide, gallium phosphide, indium gallium arsenide, indium gallium arsenic phosphide, and an organic material system. Regarding the organic material system, laser dyes and/or other relatively highly non-linear polymers are encompassed within the scope of the present invention. In this regard, those polymers with a relatively low oscillator strength and large exciton radius may exhibit a relatively high non-linearity and so are considered to be encompassed within the scope of the present invention. For the optically active material 6, a crystalline material such as crystalline silicon, polycrystalline material such as polycrystalline silicon or amorphous material such as amorphous silicon, amorphous barium titanate, may be used in an embodiment of the present invention. The aforementioned materials/material systems have been given by way of example. An embodiment of the present invention is not limited to the use thereof and any other materials/material systems that may fall within the scope of the present invention for the optically active material 6 are considered to be included within the ambit of the present invention. Generally, for the optically active material 6, those -19-materials/material systems having a band-gap characteristic such that they exhibit a relatively high non-linearity, that is, a relatively high optical gain and high absorption, suited for a given application defined by a given target wavelength, may be used in an embodiment of the present invention.

With reference being made again to Figure 1, the optically passive aspect 2 may be implemented so as to comprise a multilayer structure 3', 3" provided on at least a seed layer 7. In a preferred embodiment of the present invention, the multilayer structure comprises at least a topmost silicon layer 3' arranged on an underlying insulator layer 3" and the seed layer 7 comprises bulk silicon. The optical waveguide aspect 3 of the optically passive aspect 2 is patterned substantially in the topmost silicon layer 3' of the multilayer structure 3', 3". By forming the optically active material 6 in the predefined structure 5, the optically active material 6 is substantially self-aligned laterally with the optically passive aspect 2, particularly the optical waveguide 3, as can be clearly seen from Figure 1.

In an embodiment of the present invention, the optically active material 6 may be selected so as to have an emission wavelength that is substantially matched with a transmission range of the optically passive aspect 2, and particularly of the optical waveguide 3. By way of example, if the optical waveguide 3 comprises a silicon waveguide, the optically active material 6 may be selected so as to have a transmission range larger than 1100 nm. In this regard, such a wavelength range may be obtained for the optically active material 6 being: InAs quantum dots capped with GaAs; (In, Ga)As, (In, Ga)(As, N) or (In, Ga)(As, N, Sb), (In, Ga)(As N) quantum wells; lnGaAsP quantum wells; lnAsP quantum wells; NAsP or other Ill-V compound materials.

Reference is now made to Figures 2a to 2c which illustrate the fabrication stages of an embodiment according to the first aspect of the present invention. As can be seen from Figure 2a, the photonic structure 4 comprising periodic holes 4' is formed in the optically passive aspect 2. The periodic holes 4' may comprise a material of lower refractive index than that used for the photonic structure 4, such as, for example, air.

The photonic structure 4 is also formed so as to comprise a predefined structure 5, which, in the present example, is shown as a hole 5 of larger diameter than the periodic holes 4'. In the present example, the optically passive aspect 2 comprises a multilayer structure 3', 3" provided on a seed layer 7 with the multilayer structure comprising a topmost silicon layer 3' provided on an underlying insulator/buried oxide layer 3" and the seed layer 7 being bulk silicon as hereinbefore described with -20 -reference to Figure 1. The photonic structure 4 is formed in the multilayer structure 3', 3" such that periodic holes 4' are formed in the topmost silicon layer 3' giving access to the underlying insulator/buried oxide layer 3". Then, and as illustrated by Figure 2b, a lithography step such as etching is performed at the location of the predefined structure 5 so as to open the insulator/buried oxide layer 3" and to give access to the seed layer 7, such selective etching being performed by covering substantially all but the predefined structure 5 of the optically passive aspect 2 with photoiesist, foi example. In this regaid, the alignment toleiances are relatively non-stringent due to the selectivity of the etching process not attacking the silicon 3', 7 but the insulator/buried oxide layer 3". As illustrated by Figure 2c, the optically active material 6, which in the present example is based on a Ill-V material system, is selectively grown in the predefined structure/oxide aperture 5. Alternatively, and with respect to Figure 2c, the optically active material 6 may also be grown on a larger area on the surface of the optically passive aspect 2 in which the predefined structure 5 is formed and then the excessive optically active material 6 is removed from everywhere but the predefined structure 5 using lithography and the non-stringent alignment tolerances as hereinbefore mentioned.

Generally, and with regard to an embodiment of the present invention, the light source may only be located in the optically active material 6 and exhibits optically or electrically pumped emission. While silicon does not exhibit sufficient photoluminescence efficiency due to its indirect band-gap, it offers relatively low- propagation loss and dispersion. Furthermore, it may be fabricated with well-established CMOS processes, which makes it attractive for use as wave-guiding material that may be integrated with ease and fabricated in a cost-effective manner.

Thus, in a preferred embodiment, the optically active material 6 is based on a Ill-V based material system and the optical waveguide 3 is implemented by way of a silicon waveguide. In this regard, light generated by the optically active material 6 has to be transferred to the silicon waveguide 3, which is done by different coupling schemes that are described hereinafter.

Reference is now made to Figures 3a and 3b which illustrate a first coupling scheme with a lateral cavity feature in an embodiment of the present invention. As shown in Figure 3a, a cross-section of the silicon waveguide 3 in a longitudinal plane is smaller than a corresponding cross-section of the predefined structure 5, which is shown as hole-shaped in the present example. This feature facilitates light generated by the Ill-V based light source 6 to be substantially coupled to and better confined within the -21 -silicon waveguide 3. In a modification made to an embodiment of the present invention as shown in Figure 3b, a tapered region B is provided between the smaller cross-section of the silicon waveguide 3 and the predefined structure 5. The taper feature 8 may be used to advantage to match the respective modal sizes of the Ill-V S based light source and the silicon waveguide 3, which adiabatically taper the modal size of the light.

Reference is now made to Figures 4a to 4e, which illustrate a second coupling scheme with a lateral cavity feature for optically coupling the Ill-V based light source 6 to the silicon waveguide 3. The second coupling scheme is based on the photonic structure 4 comprising at least a one-dimensional photonic crystal cavity 10 in which periodic holes 4' are formed in an in-plane direction of the photonic structure 4 and in a region thereof where light generated by the Ill-V based light source 6 is substantially coupled to the silicon waveguide 3. The use of relatively high-reflective materials such as silicon and Ill-V materials facilitates vertical and in-plane confinement by way of index-guiding. The second coupling scheme according to an embodiment of the present invention is not limited to the formation of the one-dimensional photonic cavity 10 in the silicon waveguide 3 as shown in any one of Figures 4a to 4e. Indeed, mixed cavities with the periodic holes/reflectors 4' being partially located in the Ill-V material system on which the light source 6 is based and in the silicon forming the basis of the waveguide 3 are also considered as encompassed within the scope of the present invention.

As can be clearly seen, Figure 4a and corresponding Figure 4b pertain to when the predefined structure 5 is implemented as a trench and Figure 4c and corresponding Figure 4d relate to where the predefined structure 5 is implemented as a hole. In Figures 4a to 4d, it can be seen that the silicon waveguide 3 is implemented as having a smaller cross-section in the longitudinal plane as compared to the corresponding dimension of the predefined structure 5 and it has a tapered width 8 where it is linked to the predefined structure 5. In Figures 4a and 4c, the periodic holes 4' are substantially of the same size. Advantages associated with the embodiments of the present invention as shown in Figures 4a and 4c include: ease of implementation since the periodic holes 4' are substantially of the same size, better confinement of light in the silicon waveguide 3 since it has a smaller cross-section in the longitudinal plane than the predefined structure 5 and facilitating matching of the respective modes of the Ill-V based light source 6 and the one-dimensional photonic crystal cavity 10 by way of the tapered region 8 of the silicon -22 -waveguide 3. In contrast to Figures 4a and 4c, in an embodiment of the present invention as shown in Figures 4b and 4d, the periodic holes 4' are implemented as progressively increasing to a given size in a direction away from the predefined structure 5, where the given size may be substantially compatible to a width of the S silicon waveguide 3 in the longitudinal plane, for example. Such an implementation has, in addition to the advantages afore-described with reference to Figures 4a and 4c, the advantage that the tapered holes facilitate mode-shaping of the cavity mode and higher quality-factor values.

Figure 4e shows a second implementation of the one-dimensional photonic crystal cavity 10 in which the silicon waveguide 3 has a cross-section in a longitudinal plane that is substantially of the same size as the corresponding cross-section of the predefined structure 5. Such a second implementation may provide the advantage that fewer processing resources may be facilitated to produce such a structure since the silicon waveguide 3 and the predefined structure 5 have substantially the same size in the longitudinal plane. Since the periodic holes 4' of the photonic structure 4 are implemented as progressively increasing to a given size in a direction away from the predefined structure 5, an embodiment of the present invention as shown in Figure 4e may provide the further advantage of mode-shaping of the cavity mode and higher quality-factor values.

In an alternative implementation of the lateral cavity feature and as shown in Figure 5, there is provided a third coupling scheme for optically coupling the Ill-V based light source 6 with the silicon waveguide 3 in which the photonic structure 4 comprises at a two-dimensional photonic crystal cavity 20 in which periodic holes 4' of substantially the same size are formed in two in-plane directions of the photonic structure 4. In this regard, within the two-dimensional photonic crystal cavity 20, a defect is formed, corresponding to where the Ill-V based light source 6 is implemented, by the Ill-V material being formed in the predefined structure 5. Light generated by the Ill-V based light source 6 is confined within the defect; it is coupled to a desired location by way of a photonic crystal waveguide 21.

In an alternative implementation of the lateral cavity feature as shown in Figure 6, there is provided a fourth coupling scheme for optically coupling the Ill-V based light source 6 with the silicon waveguide 3. As shown in one example of the fourth coupling scheme, the silicon waveguide 3 comprises at least a circular grating 30 of alternating layers 30', 30" of at least two materials, one of the materials having a -23 -lower refractive index than the other of the two materials, the predefined structure 5 being located within a defect in the circular grating 30. In an embodiment of the present invention as shown in Figure 6, the cavity mirrors 30', 30" may be entirely formed in the silicon/wave-guiding material 3 with the Ill-V material comprising the defect. The cavity mirrors 30', 30" may be formed with alternating layers of dielectric and/or non-Ill-V material systems, for example, silicon dioxide. The surrounding refractive index of silicon is about 3.48, whereas the defect preferably has a lower refractive index, most preferably lower than 3.4. Furthermore, the silicon waveguide 3 comprises a tapered region 8 that may facilitate matching of the respective cavity modes and the waveguide mode.

Reference is now made to Figures 7a and 7b, which illustrate a coupling scheme for optically coupling the Ill-V based light source 6 to the silicon waveguide 3 based on a vertical cavity feature 40. In an embodiment of the present invention, the vertical cavity feature 40 is implemented by way of a vertical-cavity, light-emitting structure such as a vertical-cavity, surface-emitting laser. The vertical-cavity, surface-emitting laser 40 is implemented by way of alternating layers 40', 40" of the Ill-V material, which form the dielectric Bragg reflectors/mirrors 41. The stacked multiple layers 40', 40" have alternating refractive indices and typically also differ in their band-gap, thus facilitating a Bragg reflector 41 having close to unity reflection. This facilitates relatively low-threshold, high-power vertically-emitting lasers and/or light-emitting diodes to be produced in an embodiment of the present invention.

Figure 7a shows an embodiment of the present invention where an emission region 42 of the vertical-cavity, surface-emitting laser 40 is such that the light it generates is coupled in substantially a vertical plane relative to a surface of the silicon waveguide 3. In this regard, and viewing Figure 7a in conjunction with Figure 1, the vertical-cavity, surface-emitting laser 40 is formed on the topmost silicon layer 3' of the multilayer structure 3', 3" of the optically passive aspect 2.

Figure 7b shows an embodiment of the present invention in which at least an emission region 42 of the vertical-cavity, surface-emitting laser is such that the light it generates is coupled substantially laterally in an in-plane direction of the silicon waveguide 3. In this regard, and viewing Figure 7b in conjunction with Figure 1, the vertical-cavity, surface-emitting laser 40 is formed on the seed/bulk silicon layer 7. An advantage associated with an embodiment of the present invention as shown in Figure 7b is that a top and bottom mirrors 41' are facilitated. In contrast, only a top -24 -mirror 41' is facilitated in an embodiment of the present invention as shown in Figure 7a.

The respective vertical cavity designs shown in Figures 7a and 7b may be S implemented in isolation or in combination with any one of the lateral cavity features described hereinabove with reference to Figures 3 to 6. Furthermore, the mirrors/reflectors in Figures 7a and 7b may be implemented by way of high contrast gratings rather than dielectric Bragg mirrors, which may facilitate more compact structures to be facilitated. The growth position of the Ill-V material/optically active material 6 is determined by the position of the predefined structure 5, which defines the access point of the gaseous and molecular precursors during metal organic chemical vapour deposition and molecular beam epitaxial growth, respectively.

Regarding optically coupling the Ill-V based light source 6 to the silicon waveguide 3, hybrid structures with Ill-V/silicon mixed resonators and/or three-dimensional cavities may be contemplated within the scope of an embodiment of the present invention.

The present invention has been described purely by way of example and modifications of detail may be made within the scope of the invention.

Each feature disclosed in the description, and where appropriate, the claims and the drawings, may be provided independently or in any appropriate combination.

Claims

-25 -Claims 1. A semiconductor device (1) for use in at least an optical application comprising: at least an optically passive aspect (2) that is operable in substantially an optically passive mode, and at least an optically active material (6) comprising at least a material that is operable in substantially an optically active mode, wherein: the optically passive aspect (2) is patterned to comprise at least a photonic structure (4) with at least a predefined structure (5), and the optically active material (6) is formed in the predefined structure (5) so as to be substantially self-aligned in at least a lateral plane with the optically passive aspect (2).
2. A semiconductor device (1) as claimed in claim 1 wherein the optically active material (6) is substantially selectively formed in the predetined structure (5).
3. A semiconductor device (1) as claimed in claim 1 wherein the optically active material (6) is formed relative to the optically passive aspect (2) so as to exceed at least an area of the predefined structure (5).
4. A semiconductor device (1) as claimed in claim 3 wherein excess optically active material (6) is removed so that the optically active material (6) is provided in at least the predefined structure (5).
5. A semiconductor device (1) as claimed in claim 4 wherein the excess optically active material (6) is removed by wet-chemical etching or chemical mechanical polishing.
6. A semiconductor device (1) as claimed in any preceding claim wherein at least a structural characteristic of the predefined structure (5) is chosen thereby to facilitate the optically active material (6) to be substantially self-aligned with respect to the optically passive aspect (2).
7. A semiconductor device (1) as claimed in any preceding claim wherein the predetined structure (5) is a trench, a hole or a combination thereof.

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8. A semiconductor device (1) as claimed in any preceding claim wherein the predefined structure (5) is provided in a given location of the optically passive aspect (2).
9. A semiconductor device (1) as claimed in any preceding claim wherein the optically active material (6) is operable to perform light generation, amplification, detection, modulation or a combination thereof.
10. A semiconductor device (1) as claimed in any preceding claim wherein the optically active material (6) comprises at least one of: a Ill-V material system, a Il-VI material system, at least a silicon nanoparticle, at least a silicon quantum dot, germanium and heterostructures thereof comprising at least one of gallium arsenide, gallium antimonide, gallium nitride, indium phosphide, indium aluminium arsenide, indium arsenic phosphide, indium gallium phosphide, gallium phosphide, indium gallium arsenide, indium gallium arsenic phosphide, and an organic material system.
11. A semiconductor device (1) as claimed in any preceding claim wherein the optically active material (6) comprises a crystalline, polycrystalline or amorphous material.
12. A semiconductor device (1) as claimed in any preceding claim wherein the optically passive aspect (2) comprises a multilayer structure (3', 3") provided on at least a seed layer (7).
13. A semiconductor device (1) as claimed in any preceding claim wherein the optically passive aspect (2) comprises at least one of: silicon, a Ill-V compound semiconductor, germanium, gallium arsenide, gallium antimonide, gallium nitride, indium phosphide, indium aluminium arsenide, indium arsenic phosphide, indium gallium phosphide, gallium phosphide, indium gallium arsenide, indium gallium arsenic phosphide, aluminium oxide, tantalum pent-oxide, hafnium dioxide, titanium dioxide, silicon dioxide, silicon nitride and silicon oxi-nitride.
14. A semiconductor device (1) as claimed in any preceding claim wherein the optically passive aspect (2) comprises at least an optical waveguide (3) and an optical cavity (4').

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15. A semiconductor device (1) as claimed in any one of claims 1 to 14 comprising at least a vertical-cavity surface-emitting laser (40) implemented by way of alternating layers (40', 40") of the optically active material (6).
16. A semiconductor device (1) as claimed in claim 15 wherein at least an emission region (42) of the vertical-cavity surface-emitting laser (40) is positioned relative to the optically passive aspect (2) such that light generated by the vertical-cavity surface-emitting laser (40) is coupled substantially in at least one of: a vertical plane relative to a surface of the optically passive aspect (2) and laterally in an in-plane direction of the optically passive aspect (2).
17. A semiconductor device (1) as claimed in any one of claims 1 to 16 wherein at least a cross-section of the optically passive aspect (2) in a longitudinal plane is smaller than a corresponding cross-section of the predefined structure (5), thereby facilitating light generated by the optically active material (6) to be substantially coupled to the optically passive aspect (2).
18. A semiconductor device (1) as claimed in claim 17 wherein the optically passive aspect (2) comprises a tapered region (8) between the smaller cross-section thereof and the predefined structure (5).
19. A semiconductor device (1) as claimed in any one of claims 1 to 16 wherein a cross-section of the optically passive aspect (2) in a longitudinal plane is substantially of the same size as the corresponding cross-section of the predefined structure (5).
20. A semiconductor device (1) as claimed in any one of claims 1 to 18 wherein the optically passive aspect (2) comprises a wire waveguide (3).
21. A semiconductor device (1) as claimed in claim 18 or claim 19 comprising at least a one-dimensional photonic crystal cavity (10) in which periodic holes (4') are formed in an in-plane direction of the photonic structure (4) and in a region thereof where light generated by the optically active material (6) is substantially coupled to the optically passive aspect (2).
22. A semiconductor device (1) as claimed in any one of claims 1 to 16 comprising at least a two-dimensional photonic crystal cavity (20) in which periodic holes (4') are formed in two in-plane directions of the photonic structure (4).

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23. A semiconductor device (1) as claimed in claim 22 comprising at least a photonic crystal waveguide (21) configured to couple the light generated by the optically active material (6) to at least a desired location.
24. A semiconductor device (1) as claimed in claim 21, 22 or 23 wherein the periodic holes (4') are substantially of the same-size.
25. A semiconductor device (1) as claimed in claim 21 wherein a hole-size of at least some of the periodic holes (4') is tapered to progressively increase to a given size in a direction away from the predefined structure (5).
26. A semiconductor device (1) as claimed in any one of claims 1 to 16 further comprising a circular grating (30) of alternating layers (30', 30") of at least two materials, one of the materials having a lower refractive index than the other of the two materials, the predefined structure (5) being located within a defect in the circular grating (30).
27. A method for fabricating a semiconductor device (1) for use in at least an optical application comprising: providing at least an optically passive aspect (2) that is operable in substantially an optically passive mode, and providing at least an optically active material (6) comprising at least a material that is operable in substantially an optically active mode, wherein: the optically passive aspect (2) is patterned to comprise at least a photonic structure (4) with at least a predefined structure (5), and forming the optically active material (6) in the predefined structure (5) so as to be substantially self-aligned in at least a lateral plane with the optically passive aspect (2).