Colloidal quantum dot emitters and detectors

Abstract

The integrated optoelectronic device (100, 200, 300) comprises a substrate (30) supporting a passive waveguide (31) for providing refractive index confinement in two short directions and guidance along a long direction in at least one optical mode. The device further comprises a first charge transport layer (11) for transporting charge carriers of a first conductivity type, a second charge transport layer (12) for transporting charge carriers of a second conductivity type opposite the first conductivity type, and an active layer (20) comprising a particulate film of solution-processable semiconductor nanocrystals. The active layer is disposed relative to the charge transport layer to form a diode junction. The active layer, and the first and second charge transport layers are further formed on the substrate such that each overlaps at least a portion of the waveguide in a cross section perpendicular to the long direction. The active layer is evanescently coupled to the waveguide.

Description

[Technical field]

[0001] The present invention relates to the field of light emitting and detecting devices, and in particular to light emitters and photodetectors for photonic integrated circuits based on solution processable semiconductor materials such as colloidal quantum dots. [Background technology]

[0002] Due to their simplified and inexpensive fabrication, optoelectronic devices based on solution-processable active materials such as colloidal quantum dots (QDs) have the potential to replace their epitaxially grown counterparts commonly used today. The feasibility of electrically pumped laser diodes using colloidal quantum dot layers as gain materials has long been questioned, but recent research efforts have led to the development of specially designed colloidal QDs that exhibit reduced Auger recombination rates and thus become promising candidates for the realization of the long-awaited quantum dot (QD) laser diodes.

[0003] Lim, J., et al. “Optical gain in colloidal quantum dots achieved with direct-current electrical pumping”, Nature Mater. 17, 42-49 (2018) propose that chemically synthesized semiconductor QDs can enable solution-processable laser diodes. In electroluminescent devices with pin architecture, continuously graded QDs were used to achieve population inversion and optical gain by direct-current electrical pumping. A thin active QD layer was sandwiched between an electron transport layer and a hole transport layer, and a specially shaped dielectric LiF spacer served as a template for the fabrication of a tapered hole injection layer. A narrow (70-100 μm wide) contact area with the QD emission layer is obtained with such a current focusing architecture. Currents up to about 18 A cm -2 Current densities of up to 1000 nm were measured without damaging either the QDs or the injection layer.

[0004] The drawback to this approach is the lack of a sufficient optical cavity for electrically pumped lasing, and the need for additional spacers to shape the hole injection layer contact to the small contact area.

[0005] In Roh, J. et al. “Optically pumped colloidal-quantum-dot lasing in LED-like devices with an integrated optical cavity”, Nat. Commun. 11, 271 (2020), such specially designed QDs are used to implement multilayer p-n structures with dual functionality, operating as light-emitting diodes (LEDs) if an additional p-contact is provided on the p-n structure, or as optically pumped lasers if the p-contact is removed. They propose an optical cavity in which a distributed feedback resonator is directly integrated into the bottom low-index ITO (L-ITO) cathode of the multilayer stack. The optical mode is weakly confined by the ultrathin quantum dots with active layer.

[0006] A drawback of this approach is that it requires careful engineering of the refractive index profile throughout the device to obtain weak optical confinement of the guided modes in the QD medium. A non-standard mixture of ITO and silica is required to ensure sufficiently stable mode guidance in the very thin active layers that are essential for electrically pumped lasing. The maximum current density demonstrated in these devices is 0.2 A cm. -2 , which is too small to achieve lasing threshold by electrical injection.

[0007] Thus, there remains a need for efficient optoelectronic devices, specifically laser diodes, that are fabricated from solution processable active materials. Summary of the Invention

[0008] It is an object of embodiments of the present invention to provide an efficient optoelectronic device structure that supports high injection current densities in active layers comprising solution-processable semiconductor nanocrystal materials, and also supports low-loss optical mode guidance.

[0009] It is a further object of embodiments of the present invention to provide an optoelectronic device structure that induces and confines optical modes in a robust and reliable manner that is independent of the thickness of an active layer comprising solution-processable semiconductor nanocrystal material, in particular the thickness of a thin-film active layer that is reversible under a DC bias current.

[0010] The above object is achieved by a method and device according to the present invention.

[0011] The present invention relates to an integrated optoelectronic device comprising a substrate, a first charge transport layer for transporting charge carriers of a first conductivity type, a second charge transport layer for transporting charge carriers of a second conductivity type opposite to the first conductivity type, and an active layer comprising a particulate thin film of solution processable semiconductor nanocrystals, e.g., a particulate film (single layer, double layer, multilayer) of colloidal quantum dots. The substrate supports passive waveguides for guiding light along the long dimension (optical axis) of the device and index confining the guided light to at least one optical mode in each of the short dimensions of the device. The active layer is positioned relative to the charge transport layer to form a diode junction. The active layer and the first and second charge transport layers are formed on the substrate and each overlaps at least a portion of the waveguide in a cross section perpendicular to the direction of propagation of at least one optical mode in the waveguide. The active layer is optically coupled to the waveguide. The waveguide is typically a non-planar waveguide, e.g., a non-slab, which means that the refractive index confinement in the short dimension available in the waveguide is two-dimensional, allowing the optical axis of the waveguide to bend, i.e., the long dimension of the waveguide can change with respect to the substrate supporting the waveguide. In any case, the two short dimensions of the waveguide correspond to the two smaller dimensions of the waveguide, typically characterized by a submicron length scale, while the long dimension of the waveguide corresponds to the optical axis of the waveguide and extends over a distance much larger than the two short dimensions of the waveguide. That is, the waveguide realizes the refractive index confinement of at least one optical mode in a first short dimension parallel to the charge transport layer and the active layer, and in a second short dimension perpendicular to the charge transport layer and the active layer. Then, both the first short dimension and the second short dimension are perpendicular to the long dimension.

[0012] In contrast to conventional III / V semiconductor devices such as laser diodes, where low bandgap materials have a higher refractive index to enable optical mode confinement within the active region, and where the bandgap and refractive index are routinely tuned by modifying the composition, active layers based on solution-processed semiconductor nanocrystal materials are not compatible with these established design principles. The main reason is that the various commonly available organic and inorganic charge transport layers limit the available current density that can be injected into the active layer, and therefore it is not possible to invert thick active layers based on solution-processed semiconductor nanocrystal materials that would enable sufficient mode confinement. The present invention provides a solution to these problems by providing index confinement to the optical mode by a waveguide and overlapping the mode with the active layer.

[0013] In embodiments of the invention, the average interparticle distance between adjacent particles in the active layer particulate film may be less than 10 nm, e.g., 5 nm or less, resulting in a close-packed assembly of particles (e.g., closely packed) within the active layer particulate film. The active layer particulate film is typically discontinuous, i.e., does not include a continuous phase host material in which the semiconductor nanocrystal particles are embedded. Preferably, the nanoparticle surface density in the active layer particulate film is less than 1.0*10 11 cm -2 greater than, for example, 1.0*10 12 cm -2 Greater than, for example, 5.0*10 12 cm -2 That's all.

[0014] In embodiments of the present invention, the optoelectronic device may be configured to operate as a light emitting device (e.g., a laser diode, an LED, or a semiconductor optical amplifier), a light detecting device (e.g., a photodetector), or a light modulating device (e.g., an electro-optical modulator).

[0015] In an embodiment of the present invention, the optoelectronic devices may be provided as photonic integrated circuits (PICs). They therefore have the advantage of being small devices, mass producible, wafer-scale and low cost. The solution-processed semiconductor nanocrystal materials are compatible with a wide variety of passive waveguide platforms. In contrast to conventional III / V semiconductor active devices, the solution-processed materials of the active layers do not rely on expensive and complex epitaxial growth environments and can be obtained at lower temperatures.

[0016] In an embodiment of the invention, the solution processable semiconductor nanocrystal material of the active layer comprises one or more of the group of colloidal quantum dots, nanocrystalline perovskite-based materials, bulk semiconductor crystals, and nanoplatelets. Semiconductor nanocrystal materials such as colloidal quantum dots are attractive for their large material gain and wavelength tunability.

[0017] In embodiments of the present invention, the current path through the first charge transport layer, the active layer, and the second charge transport layer may not extend into the waveguide, which has the advantage that free carrier induced absorption modal losses can be reduced.

[0018] In an embodiment of the present invention, the active layer can be optically evanescently coupled to the waveguide by the modal overlap between at least one guided optical mode confined in the waveguide and the active layer. The confinement factor of at least one guided mode in the active layer can be designed as a function of the geometry and material of the waveguide and the active layer distance. This has the advantage that the saturation output of the optoelectronic device can be controlled.

[0019] In an embodiment of the invention, the waveguide is configured to confine and guide the at least one guided optical mode independently of the active layer. The confinement of the at least one optical mode is index confinement governed by the waveguide. Thus, thickness and / or distance variations of the active layer relative to the waveguide do not result in loss of optical confinement and guiding in the device. The optical waveguide is typically a non-planar waveguide, e.g., a rib waveguide or a ridge waveguide. Furthermore, optical waveguides supporting only a single guided mode or only a small number of guided optical modes (e.g., three or fewer guided optical modes) are preferred.

[0020] In embodiments of the invention, the contacts of the active layer may overlap the waveguide in the cross section, which is an additional advantage since electrical confinement and charge carrier recombination may occur in close proximity to the location of the peak intensity of at least one guided optical mode, thereby improving the internal quantum efficiency of the device.

[0021] In an embodiment of the present invention, the first charge transport layer may be an organic semiconducting hole transport layer and the second charge transport layer may be an inorganic semiconducting electron transport layer. The first and second charge transport layers, the active layer and the waveguide may be stacked vertically in the cross section. This has the advantage that the second charge transport layer can also serve as the bottom contact of the diode junction. Therefore, no further bottom contact layer (cathode) is required, which allows for a reduction in carrier-induced modal losses. Furthermore, no additional layers, such as adhesion or bonding layers, are required for the vertical stacking between the waveguide and the active layer. This has the advantage that the optoelectronic device according to such an embodiment can be used to reduce the laser threshold current density in the laser diode, to reduce modal losses, and / or to obtain an improved modal overlap with the active layer.

[0022] In an embodiment of the present invention, the second charge transport layer may be a semiconducting electron transport layer provided between the active layer and the waveguide. The semiconducting electron transport layer may be optimized for good electron mobility, good conductivity, and reduced optical losses. This has the advantage that the modal losses of at least one guided mode occurring close to the waveguide are further reduced. This can be further improved by providing a thicker first charge transport layer such that the top contact electrode is located further away from the waveguide and the optical mode guided therein.

[0023] In an embodiment of the invention, the second charge transport layer may conform to the contours of the waveguide, which rises from the surface of the substrate. This has the advantage that the recombination or generation of charge carriers occurs in close proximity to the waveguide and the peak intensity of at least one guided optical mode. As a result, the internal quantum efficiency of the device can be increased. Furthermore, in such an embodiment, good current focusing is obtained in the active layer, allowing a larger current density to be injected or extracted from the active layer, and further allowing the inversion of thin film active layers comprising solution-processed semiconductor nanocrystal materials with DC current bias.

[0024] In an embodiment of the invention, the first and second charge transport layers may be coplanar and arranged to overlap different portions of the waveguide in the cross section such that adjacent edges of the first and second charge transport layers are separated by a gap and the active layer spans at least a portion of the first and second charge transport layers and extends into the gap. The waveguide may be a slotted waveguide such that the gap extends between two waveguide rails of the slotted waveguide. An advantage of such an embodiment is that an increased modal overlap with the active layer may be obtained and the electric field associated with at least one guided optical mode is relatively uniform in the gap.

[0025] In another aspect, the present invention relates to an integrated light emitting device, in particular an integrated light emitting diode (LED) or an integrated laser diode (LD), comprising an integrated optoelectronic device according to an embodiment of the previous aspect. In an embodiment of this aspect, an optical waveguide is evanescently coupled to the light emitting layer stack of the integrated light emitting device, for example, the light emitting layer stack of an LED or LD, comprising an active layer and a charge transport layer. This light emitting layer stack is typically oriented perpendicular to the waveguide-carrying substrate, i.e. perpendicular to the top surface of the waveguide and layers of the light emitting layer stack that are coplanar with the waveguide, including a plane (e.g., a substrate layer).

[0026] In a further aspect, the present invention may also relate to an integrated photodetector (PD) comprising an integrated optoelectronic device according to an embodiment of the first aspect. The photodetector further comprises a first electrode in electrical contact with the first charge transport layer and a second electrode in electrical contact with the second charge transport layer to induce a reverse bias condition across the diode junction, the active layer being adapted to generate charge carriers of opposite conductivity charge under the reverse bias condition, and the diode junction being adapted to separate and collect the generated charge carriers in the corresponding charge transport layer under the reverse bias condition. In an embodiment of this aspect, the optical waveguide is evanescently coupled to the light absorption layer stack of the integrated PD, comprising the active layer and the charge transport layer. This light absorption layer stack is typically oriented perpendicular to the waveguide-carrying substrate, i.e. perpendicular to the top surface of the waveguide and layers of the light emitting layer stack that are coplanar with the waveguide, including a plane (e.g., substrate layer).

[0027] In a further aspect, the invention relates to a method for separating charge current injection and index confinement of guided optical modes in an active layer of an integrated optoelectronic device, the integrated optoelectronic device comprising a first charge transport layer for transporting charge carriers of a first conductivity type, a second charge transport layer for transporting charge carriers of a second conductivity type opposite to the first conductivity type, and an active layer comprising a solution-processed semiconductor nanocrystal material, the active layer being positioned relative to the charge transport layer to form a diode junction. The method includes providing a substrate optically coupled to the active layer and supporting a passive waveguide for index confinement and guiding light in at least one optical mode. Index confinement is obtained in two short directions of the elongated waveguide body, e.g., the width and height of the waveguide, while the confined light in at least one optical mode is guided in a longitudinal direction, which corresponds to the preferred extension direction of the waveguide. The method further includes disposing the active layer and each of the first and second charge transport layers on the substrate such that they overlap at least a portion of the waveguide in a cross section perpendicular to the longitudinal direction of the confined light propagating along the waveguide.

[0028] The advantage of such a separation method is that low-loss passive waveguides can be combined with high material gain and thin active layers without compromising reliable light guiding in the waveguide. Moreover, it provides a more flexible design approach that helps to reduce mode overlap with or leakage into lossy contact layers. This is in contrast to prior art lasing devices based on solution-processable semiconductor nanomaterials, where a combination of index confinement and charge carrier injection is realized in a single active layer of the device stack. In such prior art devices, there are conflicting requirements for the thickness of the active layer. On the one hand, a relatively thin active layer is necessary to obtain efficient charge carrier injection at speeds that allow population inversion and lasing. On the other hand, a relatively thick active layer is preferred in view of better index confinement and modal gain properties of the guided optical modes. For example, light is guided more reliably without significant leakage into the surrounding layers, especially the metal contact layers and charge transport layers with high optical losses, thereby significantly increasing the lasing threshold, which cannot be obtained even by purely electrical pumping.

[0029] A final aspect of the invention relates to a method for manufacturing an integrated optoelectronic device according to any one of the embodiments of the first aspect, comprising providing a substrate with passive waveguides and forming a stack on said substrate by sequentially depositing in the following order: (i) a second charge transport layer for transporting charge carriers of a second conductivity type; (ii) an active layer comprising a particulate film of semiconductor nanocrystals, the semiconductor nanocrystals being deposited from solution; and (iii) a first charge transport layer of a first conductivity type opposite to the second conductivity type for transporting charge carriers.

[0030] According to the method of the present invention, the waveguide is configured to guide light along a longitudinal direction and to index confine the guided light in each transverse direction in at least one guided optical mode. Furthermore, the deposited active layer and each of the deposited first and second charge transport layers overlap at least a portion of the waveguide in a cross section perpendicular to the longitudinal direction (i.e., the direction of light propagation in the waveguide). The active layer is disposed relative to the two charge transport layers to form a diode junction, and the active layer is optically evanescently coupled to the waveguide.

[0031] According to a preferred embodiment, the deposited first charge transport layer is an organic layer and the deposited second charge transport layer is an inorganic layer. Depositing the first charge transport layer may include vacuum thermal evaporation or organic vapor phase deposition, and depositing the second charge transport layer may include thermally controlled atomic layer deposition (ALD) with or without the assistance of a reactive plasma (plasma-assisted ALD). In a particularly preferred embodiment, depositing the second charge transport layer includes depositing a nanometric layer of polycrystalline zinc oxide (ZnO) using atomic layer deposition at a substrate temperature between 60°C and 300°C, optionally with a subsequent annealing step at about 400°C. Annealing may be performed in a nitrogen or hydrogen atmosphere. Plasma-assisted or radical-assisted atomic layer deposition processes can be used with the additional advantages of reduced temperature treatment, greater process flexibility (e.g., regarding the choice of precursors and their reactivity), reduced purging times, removal of precursor ligands, improved film properties, and increased film growth per deposition cycle, among others.

[0032] According to a preferred embodiment, depositing the semiconductor nanocrystals of the active layer from solution comprises subjecting a dispersion of preformed semiconductor nanocrystals, e.g., presynthesized colloidal core-shell quantum dots, to a wet processing technique such as spin coating, dip coating, spray coating, Langmuir-Blodgett or Langmuir-Schäfer deposition, or inkjet printing.

[0033] According to some embodiments of the present invention, the second charge transport layer may be directly deposited on the waveguide to obtain an overcoated waveguide. Furthermore, the method may include depositing a cladding material on both sides of the overcoated waveguide, thereby passivating the second charge transport layer, and planarizing the deposited cladding material such that the top surface of the deposited cladding material is flush with the top surface of the overcoated waveguide. Moreover, one or more of the steps of contacting the first charge transport layer with a first metal electrode, contacting the second charge transport layer with a second metal electrode, and encapsulating the integrated optoelectronic device may be performed.

[0034] Embodiments of the present invention have the advantage that the semiconductor nanocrystals of the active layer particulate film can be obtained from solution, which is more versatile and less expensive compared to epitaxial growth methods, such as molecular beam epitaxy. For example, solution processing of semiconductor nanocrystals allows for monolayer or multilayer deposition not only on amorphous surfaces, but also on rough or patterned surfaces. Furthermore, compared to conventional epitaxial growth methods, denser particulate films can be obtained and no host material is required.

[0035] The embodiments of the present invention also have the advantage that integrated optoelectronic devices can be more easily manufactured without the need for additional intermediate layer bonding steps between two wafers or between a wafer and a die. As a result, intermediate bonding layers, e.g., adhesive layers, which are relatively thick relative to the waveguide dimensions (especially the height), can be avoided, thereby improving the mode overlap and evanescent coupling efficiency between the waveguide optical mode and the active layer. In the case of a conductive intermediate bonding layer, removing the intermediate bonding layer leads to a lower series resistance along the current path and increases the achievable current density of charge carriers upon injection into the active layer.

[0036] Fabrication of integrated optoelectronic devices without bonding is also favorable from the standpoint of alignment and overall device compactness, since bonding is not self-aligned and typically requires large design tolerances. Bonding of patterned mesas also often leads to larger overall devices, preventing high density integration of compact optoelectronic devices on a chip. Furthermore, epitaxial growth of bonded mesa materials typically entails higher costs compared to the solution-processed semiconductor nanocrystals of the present invention.

[0037] Particular and preferred aspects of the invention are set out in the accompanying independent and dependent claims. Features from the dependent claims may be combined with features from the independent claims and with features of other dependent claims as appropriate and not merely as explicitly set out in the claims.

[0038] Certain objects and advantages of the invention have been described above for purposes of summarizing the invention and the advantages achieved over the prior art. Of course, it is to be understood that not all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, one skilled in the art will recognize that the invention may be embodied in a manner that achieves or optimizes one or more advantages as taught herein without necessarily achieving other objects or advantages that may be taught or suggested herein.

[0039] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. [Brief description of the drawings]

[0040] The invention will now be further explained, by way of example only, with reference to the accompanying drawings in which:

[0041] [Figure 1] FIG. 2 is a cross-sectional view of an integrated optoelectronic device according to a first embodiment of the present invention comprising a vertical diode junction and a strip waveguide flush with the substrate. [Diagram 2]FIG. 4 is a cross-sectional view of an integrated optoelectronic device according to a second embodiment of the present invention comprising a horizontal diode junction and a slotted waveguide. [Diagram 3] FIG. 4 is a cross-sectional view of an integrated optoelectronic device according to a third embodiment of the present invention comprising a horizontal diode junction and a strip waveguide. [Figure 4] 4 is a cross-sectional view of an integrated optoelectronic device according to a fourth embodiment of the present invention comprising a vertical diode junction and a ridge waveguide rising from a substrate. [Diagram 5] FIG. 5 is a perspective view of the embodiment shown in FIG. [Figure 6] 1 illustrates an example of an optical feedback means that may be used in an integrated optoelectronic device according to an embodiment of the present invention. [Figure 7] 1 illustrates an example of an optical feedback means that may be used in an integrated optoelectronic device according to an embodiment of the present invention. [Figure 8] 1 illustrates an example of an optical feedback means that may be used in an integrated optoelectronic device according to an embodiment of the present invention. [Figure 9] 1 illustrates an example of an optical feedback means that may be used in an integrated optoelectronic device according to an embodiment of the present invention. [Figure 10] 1 illustrates an example of an optical feedback means that may be used in an integrated optoelectronic device according to an embodiment of the present invention. [Figure 11] 1 illustrates an example of an optical feedback means that may be used in an integrated optoelectronic device according to an embodiment of the present invention. [Figure 12] 5 shows a spatial mode profile of the fundamental guided mode in a cross-section of an integrated optoelectronic device according to the embodiment of FIG. 4. [Figure 13] 13 shows the spatial mode profile of the fundamental guided mode obtained from FIG. 12 by removing the active layer.

[0042] The drawings are only schematic and non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. The dimensions and relative dimensions do not necessarily correspond to actual reduction to practice of the invention.

[0043] Any reference signs in the claims should not be construed as limiting the scope.

[0044] In the different drawings, the same reference signs refer to the same or similar elements. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0045] The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims.

[0046] The terms first, second, and the like in this description and claims are used to distinguish between similar elements and are not necessarily used to describe an order, either temporally, spatially, sequentially, or in any other manner. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operating in orders other than those described or illustrated herein.

[0047] Furthermore, directional terms such as top, bottom, front, rear, under, above, etc. in this description and claims are used for descriptive purposes with reference to the orientation of the drawings being described and are not necessarily used to describe relative positions. Because components of embodiments of the present invention may be positioned in a number of different orientations, the directional terms are used for illustrative purposes only and are not intended to be limiting in any way unless otherwise indicated. It should therefore be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the present invention described herein are capable of operation in orientations other than those described or illustrated herein.

[0048] It should be noted that the term "comprising" used in the claims should not be interpreted as being limited to the means recited thereafter, and does not exclude other elements or steps. It is therefore interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not exclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression "a device comprising means A and means B" should not be limited to a device consisting of only components A and B. This means that in the context of the present invention, the only relevant components of the device are A and B.

[0049] References throughout this specification to "one embodiment" or "an embodiment" mean that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification do not necessarily all refer to the same embodiment, but may refer to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments.

[0050] Similarly, in describing exemplary embodiments of the present invention, it should be understood that various features of the present invention may be grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in understanding one or more of the various inventive aspects. However, this method of disclosure should not be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of the present invention.

[0051] Furthermore, although some embodiments described herein include some but not all features that are included in other embodiments, a combination of features from different embodiments is meant to be within the scope of the invention as would be understood by one of ordinary skill in the art to form different embodiments.

[0052] In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.

[0053] definition When referring to solution-processed materials, it is meant that the material is obtained from a wet chemical environment, e.g., from a solution, by any deposition technique that forms part of the art. Known deposition techniques from solutions include, but are not limited to, spin-coating, evaporation, centrifugation, sol-gel processing, inkjet printing, screen printing, spray coating, and precipitation. The ability of solution-processable materials to deposit at amorphous solid interfaces is a clear advantage over epitaxially grown materials.

[0054] When referring to nanocrystalline materials, it is meant that the material is composed of particles with all three dimensions less than 100 nm. Specifically, quantum dots typically refer to particles that are less than 20 nm in each spatial direction. More generally, quantum dots refer to nanometer-sized crystals that exhibit quantum confinement effects in all three spatial dimensions for charge carriers of at least one conductivity type.

[0055] In the context of the present invention, when a layer overlaps, or is said to overlap, a portion of a waveguide at a given cross-section, the plane of projection of that layer in a direction perpendicular to that layer includes the plane of projection of that portion of the waveguide along the same direction, which portion also includes the cross-section plane.

[0056] In a first aspect, the present invention relates to an integrated optoelectronic device. According to embodiments of the present invention, the optoelectronic device structure can be adapted to function primarily as a light emitting device (e.g., a semiconductor laser diode (LD) or a semiconductor light emitting diode (LED)), an optical amplification device (e.g., a semiconductor optical amplifier (SOA)), an optical detection device (e.g., a photodiode or a wavelength-resolving photodetector), or an optical modulation device (e.g., an electro-optic modulator based on the electroabsorption effect (e.g., the quantum confined Stark effect) or the electrorefractive effect (e.g., the Pockels effect)). The optoelectronic device according to embodiments of the present invention is an integrated device that can be fabricated as a wafer-scale photonic integrated circuit. Thus, an advantage of embodiments of the present invention is to provide a low-cost, mass-producible, compact optoelectronic device with various functions including light emission, lasing, optical amplification, and optical detection. The integrated optoelectronic devices according to embodiments can be combined on the same integrated photonic chip to provide a more versatile circuit, e.g., a lasing device coupled to a modulator, or a photodiode including a preamplification stage.

[0057] FIG. 1 is a cross-sectional view of an integrated optoelectronic device according to a first embodiment. The optoelectronic device 100 comprises a substrate 30 in which an optical waveguide 31 is formed such that the top surface of the waveguide is flush with the top surface of the substrate. The waveguide is configured to guide at least one optical mode in a direction perpendicular to the cross-section. A vertical layer stack is formed on the waveguide including a region of the substrate including, from the top to the bottom of the stack, a contact layer forming a first electrode 40, a first charge transport layer 11, an active layer 20 comprising a solution-processed semiconductor nanocrystal material, and a second charge transport layer 12. The second charge transport layer 12 and the substrate 30 are disposed in succession at least where the waveguide 31 is formed in the substrate 30, i.e. where the second charge transport layer is in physical contact with the top surface of the waveguide. A second electrode 50 is provided as a pair of electrodes in electrical contact with the second charge transport layer 12.

[0058] The vertical layer stack has the structure of a pin diode and operates according to a pin diode. As a result, the integrated optoelectronic device 100 can selectively operate as a light emitting device (e.g., a laser diode) or a light detecting device depending on the selected bias state of the diode structure constituted by the optoelectronic device. Applying a forward bias to the diode structure results in light emission, while applying a reverse or zero bias to the diode structure results in light absorption. More specifically, the active layer 20 is disposed between the first charge transport layer 11 and the second charge transport layer 12 such that under a forward bias condition, majority charge carriers pumped into and transported by each of the charge transport layers 11, 12 are efficiently injected into the active layer and recombine therein, thereby generating light. In contrast, under a reverse or zero bias condition, light is absorbed in the active layer 20, thereby generating electron-hole pairs, which are then split into majority carriers in the first charge transport layer 11 and the second charge transport layer 12. Those skilled in the art will understand that the layer thicknesses and the specific material selection of the active layer 20 and the two charge transport layers 11, 12 depend largely on the intended use of the optoelectronic device, and it is within the routine work of a skilled craftsman to select the materials and optimize the layer thicknesses according to the device function, for example to realize a light emitting or light amplifying device (LD, LED, SOA), a photodetector or an optical modulator.

[0059] Side contact of the vertical layer stack by a laterally offset electrode pair 50 is preferred, since the presence of the waveguide precludes the possibility of making a straight back contact to the vertical layer stack. This has the advantage that all electrical contacts are provided on the same device side, and furthermore the second electrode 50 can be made close to the diode structure of the vertical stack, thereby reducing resistive heating losses. In this embodiment, lateral charge transport towards the vertical layer stack is also achieved by the second charge transport layer 12. Therefore, no additional contact layer is required to electrically contact the bottom surface of the vertical layer stack. High current densities can be obtained in the active layer by limiting the lateral extent of the vertical layer stack, which is a prerequisite for reaching population inversion and lasing in a semiconductor laser diode with an optoelectronic device according to this embodiment. Furthermore, the laterally offset pair of conductive electrodes 50 also reduces the contribution of free carrier induced optical losses in the waveguide 31. Although the vertical layer stack is shown to be centrally located with respect to the waveguide 31 in FIG. 1, it may also be positioned asymmetrically with respect to the waveguide. Thus, the optoelectronic device 100 is robust against misalignments during fabrication, e.g., lithography. As an alternative to the first electrode 40 forming a flat top electrode layer, the first electrode 40 may be patterned, e.g., in the form of two parallel coplanar stripe electrodes. Despite the additional patterning step, such an electrode configuration has the advantage that metal-induced propagation losses for guided optical modes in the waveguide are further reduced.

[0060] Referring now to FIG. 2, a cross-sectional view of an integrated optoelectronic device 200 according to a second embodiment of the present invention is depicted. In this embodiment, the waveguide is arranged as a slotted waveguide, consisting of two waveguide rails 31a, 31b, separated by a gap 21. The first charge transport layer 1 1 is formed continuously on the substrate surface only on one side of the waveguide, e.g., where the first waveguide rail 3 1 a is located, and the second charge transport layer 1 2 is formed continuously on the substrate surface only on the other side of the waveguide, e.g., where the second waveguide rail 3 1 b is located. Both the first charge transport layer 1 1 and the second charge transport layer 1 2 extend into the gap 21, however, without contacting each other, such that the sidewalls facing the gap of each of the two waveguide rails 31a, 31b are covered by the first charge transport layer and the second charge transport layer, respectively. The remaining gap portion, not filled by the charge transport layer, comprises the active layer 20. The first electrode 40 and the second electrode 50 are provided away from the waveguides and are in electrical contact with the first charge transport layer 11 and the second charge transport layer 12, respectively. As shown in FIG. 2, the active layer 20 may have a gap-filling portion that is included in the gap 21 and an extension portion that is not included in the gap 21. Taken together, the extension and gap-filling portions of the active layer 20 have a T-shaped appearance in cross-section. An advantage of this embodiment is that the active layer has a gap-filling portion that extends into the gap between the slotted waveguides, which increases the mode overlap with the active layer. Furthermore, the electric field of the fundamental mode supported by the slotted waveguide is relatively uniform in the gap region, compared to, for example, the evanescent tail that is strongly reduced above the ridge waveguide. The extension may overlap the two charge transport layers 11, 12 to a lateral extent, for example corresponding to the lateral dimension of the waveguides 31a-b. The thickness (e.g., height) of the overgrown extension can be controlled. This has the advantage that contacts to the active layer can also be present outside the gap, whereby the unity gain or unity absorption coefficient can be increased modestly without a concomitant increase in the width of the active layer in the gap, i.e., without significantly changing the current density supported by the diode structure in the gap region.Furthermore, in this embodiment, the two charge transport layers 11, 12 and the active layer 20 sandwiched therebetween form a horizontal pin diode junction, e.g., a diode junction with a junction surface oriented perpendicular to the substrate, showing that the stacking is not limited to a vertical stacking configuration. Good electrical confinement for concentrated charge carrier recombination is automatically achieved by the gap, which can be shallow with respect to the longitudinal extent of the optoelectronic device. Thus, high current density in the narrow gap-fill of the active layer can be obtained as a prerequisite for reaching population inversion and lasing in a semiconductor laser diode with an optoelectronic device according to this embodiment.

[0061] FIG. 3 is a cross-sectional view of an integrated optoelectronic device 300 according to a third embodiment of the present invention, similar to the second embodiment of FIG. 2, but in which the waveguide 31 is provided as a strip waveguide. As a result, the gap 21 is not provided in a natural way by the structure of the waveguide itself. In this embodiment, the gap 21 is defined as a separation space (e.g., an elongated opening, a slit) extending between the first charge transport layer 11 and the second charge transport layer 12, each of which is formed successively on the substrate surface only on one side of the waveguide 31. The gap 21 is filled by an active layer 20, which extends over a portion of the first charge transport layer 11 and the second charge transport layer 12 on each side of the gap 21, e.g., over a portion of the first charge transport layer 11 and the second charge transport layer 12 covering the waveguide 31. The active layer 20 may therefore have a gap-filling portion included in the gap 21 and an extension portion not included in the gap 21. Taken together, the extension and gap-fill portions of the active layer 20 have the appearance of a T-shape in cross-section. Preferably, the gap 21 is centrally located with respect to the waveguide 31 so as to symmetrically couple light from the waveguide 31 into the active layer 20 or vice versa, e.g., from the active layer 20 into the waveguide 31.

[0062] FIG. 4 shows a cross-sectional view of an integrated optoelectronic device 400 according to a fourth embodiment of the present invention. It differs from the first embodiment of FIG. 1 in that the waveguide 31 is formed on the surface of the substrate 30 so that the waveguide protrudes from the substrate surface. The top surface of the waveguide is therefore not flush with the surface of the substrate. In conformity with the contours of the waveguide 31, the second charge transport layer 12 covers the top and side surfaces of the waveguide 31 with a substantially constant layer thickness, for example, the second charge transport layer 12 conformally coats the waveguide 31 rising from the substrate surface. The cladding material 32 may be provided on both sides of the waveguide 31 flush with the coated top surface of the waveguide. The cladding material 32 may act as an additional support member for the vertical layer stack provided on top of the waveguide that rises from the substrate and is coated. A further advantage of this embodiment is that the cladding layer 32 acts as a passivation layer for the second charge transport layer 12. An opening may be provided in the cladding layer 32 where the second electrode 50 is in electrical contact with the second charge transport layer 12, or the cladding 32 may be of limited lateral extent to achieve electrical contact between the second electrode 50 and the second charge transport layer 12. This embodiment is particularly suitable for achieving good current focusing and high current density in the active layer 20, since the contact of the active layer 20 by the second charge transport layer 12 is limited to the lateral size (width) of the waveguide 31. A further advantage is that the waveguide 31 is located adjacent to the current injection and recombination region of the active layer, thereby allowing efficient coupling of light generated or absorbed in the active layer into or out of the waveguide, respectively. As an alternative to the first electrode 40 forming a flat top electrode layer, the first electrode 40 may be patterned, for example, in the shape of two parallel coplanar stripe electrodes. Despite the additional patterning step, such an electrode configuration has the advantage that metal-induced propagation losses for guided optical modes in the waveguide are further reduced.

[0063] Figure 5 is a perspective view of the integrated optoelectronic device 400 of Figure 4. The waveguide 31 is provided as a straight waveguide, but may also have a different shape and / or a shape that varies in the longitudinal direction (e.g., the direction of light propagation in the waveguide). For example, the waveguide may be curved, S-shaped, or otherwise bent in the direction of light propagation along the waveguide. The electrodes 40, 50 may all extend longitudinally to allow current delivery or extraction along the vertical layer stack.

[0064] FIG. 12 shows the optical intensity distribution (mode profile) of the fundamental guided transverse electric (TE) mode of the waveguide 31 in the embodiment of FIGS. 4 and 5. This is compared to the optical mode profile of the same waveguide, and nearly identical vertical layer stack, as shown in FIG. 13, where only the active layer is omitted. From this comparison, it follows that the optical mode profile associated with the waveguide without the active layer is substantially unchanged when the active layer is included. That is, the general shape and optical properties of the waveguide and its associated optical mode, such as the 1 / e spatial extent and confinement factor, are not significantly affected by the presence of the active layer. The overlap of the fundamental guided mode with the active layer in FIG. 13 allows for some degree of evanescent wave coupling, e.g., the mode overlap ratio can be in the range of 0.1% to 10% of the effective mode area.

[0065] The substrate may be an insulating or semi-insulating substrate, for example a silicon substrate with a buried oxide between the bulk silicon and a layer of material for the formation and functionality of the photonic integrated circuit, for example a silicon nitride layer (visible and infrared) or a silicon layer (infrared).

[0066] The first charge transport layer 11 can be a hole transport layer, preferably implemented as an organic hole transport layer, although inorganic hole transport layers can also be used. Typical materials for the first charge transport layer can include semiconducting OLED materials, such as organic molecular semiconductors with large HUMO-LUMO energy gaps, such as triphenylamines, such as N,N'-Di(1-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine (NPD), tetraphenylaphthacene (rubrene), or carbazole derivatives, such as tris(4-carbazoyl-9-ylphenyl)amine (TCTA). Furthermore, the first charge transport layer can be a multilayer, including a transport layer, such as a hole transport layer, and an injection layer (e.g., a hole injection layer), and / or a layer for band alignment or charge generation. The multilayer first charge transport layer can also include at least one electron blocking layer. The layer thickness of the first charge transport layer 11 can vary from tens of nanometers to hundreds of nanometers, for example, 2 μm. A non-limiting example of the first charge transport layer includes a triple charge transport layer consisting of a charge generation layer (e.g., a layer of 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HATCN)), a hole transport layer (e.g., a layer of NPD), and a hole injection layer (e.g., a layer of TCTA).

[0067] The second charge transport layer 12 may be an electron transport layer. It may be provided as a thin layer of an organic or inorganic semiconductor material, for example a thin layer of polycrystalline zinc oxide, or a thin layer of zinc oxide nanocrystals. However, conductive polymers or electron-deficient molecular semiconductors may also be used. In some embodiments of the invention, when the first charge transport layer 11 is located close to the optical waveguide 31, this layer is preferably formed from a semiconductor material that combines good charge carrier mobility (e.g. low resistance) with low optical attenuation. This has the advantage of lowering the laser threshold current and power consumption. The embodiments of the invention are not limited to a first charge transport layer for holes and a second charge transport layer for electrons. For example, the first charge transport layer may be an electron transport layer and the second charge transport layer may be a hole transport layer.

[0068] In the above embodiments, the second charge transport layer has been described as being at least contiguous with the substrate when the waveguide is formed in the substrate, i.e., the second charge transport layer is in physical contact with the top surface of the waveguide, but this is not a limiting feature of the invention. In alternative embodiments, a low index intermediate layer having a low index of refraction compared to the waveguide may be interposed between the waveguide and the second charge transport layer, thus avoiding direct physical contact. An intermediate layer may be used, for example, in embodiments where it is beneficial to have a seed layer to initiate homogeneous growth of the second charge transport layer during device fabrication. Preferably, such an intermediate layer is kept thin to maintain good mode overlap with the active layer. Furthermore, in embodiments of the invention, the waveguide may extend longitudinally beyond the active device area, including the active layer. This may be an advantage, as it allows for shadow mask deposition of the organic hole transport layer 11 and the p-metal contact electrode 40 with very coarse overlay accuracy.

[0069] The semiconductor nanomaterials comprising the active layer 20 are disposed between the first charge transport layer 11 and the second charge transport layer 12 to form a diode junction, e.g., a planar pin junction lying parallel to the substrate 30. When this diode junction is positively biased (e.g., forward biased state), transported majority carriers, e.g., holes and electrons, are injected from each side into the active layer 20 and then recombine, thereby generating electroluminescence. When the diode junction is negatively biased (e.g., reverse biased state) or unbiased (e.g., zero bias state), majority carriers from the active layer 20, e.g., via light absorption and electron-hole pair generation, are separated into the respective charge transport layers under the influence of the built-in electric field present across the diode junction. The semiconductor nanocrystal materials may include colloidal quantum dots, nanoplatelets, nanorods, nanoflakes, or perovskite structure materials, such as cesium lead halide perovskite nanocrystals, and may be packed into single, bilayer, or multilayer thin films. Colloidal QDs may be of the core-shell type, with the core and shell diameters designed as a function of material gain and gain threshold, as described, for example, in Bisschop, S., et al. “The impact of Core / Shell Sizes on the Optical Gain Characteristics of CdSe / CdS Quantum Dots”, ACS Nano 12(9), 9011-9021 (2018). Another type of colloidal QD that can be used in embodiments of the present invention is a continuously graded core-shell QD, as described in the reference literature of Lim et al. Semiconductor nanocrystal materials such as colloidal QDs may be filled into the thin-film active layer with a filling factor of up to 50%, or even higher if the organic ligands on the QD shell are at least partially removed. The gaps in the thin-film active layer that are not filled with semiconductor nanocrystal materials such as colloidal QDs typically contain organic ligands and air. However, in certain embodiments, colloidal QDs may also be embedded in an inorganic or polymer matrix.The optical properties of active layers containing solution-processed semiconductor nanocrystal materials are well described by the effective medium approach, which accounts for their subwavelength inhomogeneity. As a result, the effective refractive index of active layers containing solution-processed semiconductor nanocrystal materials is relatively low compared to dense bulk materials (e.g., silicon nitride) used in integrated waveguides, which is also why robust refractive index confinement in such thin-film active layers is a challenging task. In contrast, thicker active layers containing solution-processed semiconductor nanocrystal materials generally cannot be inverted by a DC bias current and cannot be used as electrically pumped gain media.

[0070] In a further aspect, the present invention relates to an integrated light emitting device comprising or based on an integrated optoelectronic device according to an embodiment of the previous aspect. The light emitting device may be a light emitting diode (LED). In contrast to a laser diode, an LED emits an incoherent and spectrally broad light flux. The output spectrum of the LED is determined by the electroluminescence spectrum of the semiconductor nanocrystal material of the active layer. A portion of the spontaneously emitted photons is coupled into a waveguide of the optoelectronic device, for example a multimode waveguide for better photon collection efficiency. For use as an LED, a high light extraction efficiency from the waveguide is desirable to achieve good brightness levels. This may be achieved by further providing an anti-reflective coating on both end faces of the waveguide, or by providing a highly reflective element (for example a broadband mirror or a reflective coating) at one end of the waveguide and an anti-reflective coating at the other end of the waveguide. The light emitting device may also be a superluminescent light emitting diode (SLED) if the spontaneous emission of the active layer is coupled into the waveguide and then amplified by the active layer before being emitted from the device. Furthermore, light emitting devices based on integrated optoelectronic devices according to certain embodiments may be configured as white LEDs. To this end, multiple active device regions, each including an active layer including different semiconductor nanocrystal materials (e.g., QDs of different diameters emitting at different wavelengths) each arranged and solution processed according to the optoelectronic device embodiments described above, may be provided along and coupled to the same passive waveguide.

[0071] The integrated light emitting device may also be a semiconductor laser diode. To be capable of lasing, the optoelectronic device according to the embodiments of the present invention further comprises an optical feedback means, e.g. a reflector, arranged with respect to the active layer to form a high-quality optical cavity, including the active layer as a gain medium. The optical feedback means ensures many cavity round trips for the intracavity light generated by stimulated emission and repeatedly amplified, ultimately resulting in a highly coherent emission with high spectral intensity output by the laser diode. In its simplest form, the optical feedback means may be realized by cutting the waveguide end face. The achievable quality of the optical cavity formed by the cut waveguide is limited, but this may be sufficient for some applications. Various other optical feedback means may be used to envisage a high-quality optical cavity, which will be further described with reference to Figs. 6-11. Typically, the optical feedback means comprises a highly reflective first member on one side of the optical cavity and a slightly less reflective second member on the other side, i.e. the side where the light is coupled out of the cavity. The purpose of these figures is to illustrate the various optical feedback means and the associated optical cavities resulting from them. Thus, not all elements of the optoelectronic device are represented in these figures, but only the active layer 20 acting as the gain medium of the laser diode (LD), the waveguide 31 as part of the optical cavity, and the feedback means optically coupled to the waveguide to turn the cavity into a high quality optical cavity, e.g., an optical cavity with good finesse (F>>1) and / or good quality factor (Q factor) (e.g., Q>>1, e.g., Q>1000). Phase shifters, e.g., heaters, spatial mode filters and / or converters may be provided along the waveguide 31 to adjust, select and stabilize the output wavelength and / or spatial mode profile of the LD. A saturable absorber may be provided along the waveguide 31 to enable mode locking for a mode-locked laser diode. This saturable absorber may include, but is not limited to, the same solution-processed semiconductor nanocrystal material as the active layer of the optoelectronic device.

[0072] 6, a semiconductor LD 600 comprises a ring-shaped waveguide 31, e.g., a micro-ring resonator waveguide, which serves as the optical cavity of the LD and also provides optical feedback to the active layer 20. A coupling portion 601, e.g., a directional coupler, is provided along the ring-shaped waveguide 31 to couple light from the optical cavity to an output waveguide 602 of the LD. The output waveguide 602 may be provided with an anti-reflection coating on its end facet to prevent residual reflections from re-entering the optical cavity.

[0073] FIG. 7 is a variation of the embodiment shown in FIG. 6, in which the LD 700 includes a curved waveguide 31 that is not circular, e.g., is not implemented as a ring resonator waveguide, and therefore cannot provide optical feedback by itself. In this embodiment, an additional ring resonator 702, e.g., a micro-ring resonator, is provided. It performs the optical feedback function by receiving light from a first end of the waveguide 31 via a first coupling 701a and feeding back light to a second end of the waveguide 31 via a second coupling 701b. The additional ring resonator 702 has the advantage that it can be used as a wavelength filter integrated into the optical cavity, e.g., as a wavelength selection device to select a wavelength for lasing from multiple longitudinal cavity modes.

[0074] FIG. 8 shows a LD 800 configured as a distributed feedback laser (DFB). A distributed reflector, e.g., a pair of Bragg reflectors 801a-b, is placed inside or adjacent to the gain region of the LD 800, e.g., inside or adjacent to the active layer 20. The distributed reflector may be implemented as a diffractive waveguide grating or cladding layer corrugations, modulated doping concentration, etc. The pair of Bragg reflectors 801a, 801b may include phase shifting sections, e.g., π / 2 or ¼ Bragg wavelength shifting sections. The distributed reflector acts as a wavelength selective filter, maximizing optical feedback at a given wavelength for lasing, but suppressing optical feedback at other wavelengths, e.g., competing longitudinal cavity modes. 9 is configured as a distributed Bragg reflector laser (DBR) in which a distributed reflector, e.g., a pair of Bragg reflectors 901a-b, is located outside the gain region of the LD 900, e.g., outside the active layer 20. As a result, the DBR configuration is insensitive to changes in current density or current gain.

[0075] 10 shows an LD 1000 in which a waveguide 31 is terminated on one side by a waveguide loop mirror 1003 and on the other side by a reflector arrangement including a microring resonator 1002, two access waveguides to the microring resonator 1002, and a coupling element 1001. The two access waveguides are coupled to the microring resonator 1002 via respective couplings and correspond to two output branches of the coupling element 1001, e.g., a 1-2 directional coupler, or a multimode interferometer.

[0076] The LD 1100 shown in FIG. 11 comprises a ring-shaped waveguide 31 as an optical cavity. Compared with the LD 600 in FIG. 6, the active layer 20 of the present LD 1100 completely overlaps the waveguide 31. The output waveguide 602 is evanescently coupled to the optical cavity waveguide 31, for example by a coupling part 601, and may be provided with anti-reflection means to suppress external feedback re-entering the optical cavity. Alternatively, the output waveguide 602 may be used as an external cavity providing feedback to the ring-shaped cavity. In this case, the output waveguide 602 may comprise its own reflector.

[0077] In an integrated optoelectronic device according to an embodiment of the present invention, multiple gain sections may be disposed along the waveguide 31, each gain section having a cross-section as described above for embodiments of the present invention. The solution-processed semiconductor nanocrystal material in the active layer of each of the multiple gain sections may be selected such that the electrical emission spectrum corresponding to each overlaps with that of the other gain sections. This may be useful to extend the tunable operating wavelength of a light emitting device, e.g., a laser diode, or may be used to achieve independent gain or absorption modulation within the same optical cavity.

[0078] The light emitting diode or laser diode configurations may also be used as traveling wave or Fabry-Perot SOAs, respectively, when electrically biased below the lasing threshold. The waveguide may be tilted with respect to the cut surface to further reduce the effects of multiple reflections, for example, in addition to anti-reflection coatings on the waveguide surface.

[0079] In another aspect, the invention relates to an integrated photodetector. The photodetector comprises or uses any of the integrated optoelectronic devices related to the embodiments of the first aspect. The thickness and material selection of the individual layers of the optoelectronic device are preferably optimized for a targeted absorption wavelength region and detector responsivity under reverse bias conditions. It is possible to have a multi-sectioned photodetector, each section comprising a reverse biased optoelectronic device according to an embodiment of the invention. The individual sections may be designed to absorb light of different wavelengths or wavelength ranges, for example by adapting the diameter or composition of quantum dots in the active layer of each section. This type of multi-sectioned photodetector may be used in spectroscopic applications.

[0080] To operate the integrated optoelectronic device according to the preceding embodiment as a light emitting device, the electrodes 40, 50 are connected to a power supply that applies a forward bias across the diode junction. As a result, majority carriers of opposite charge polarity are injected into the active layer 20 via the respective charge transport layers 11, 12 and recombine with the semiconductor nanocrystal material, e.g. solution processed quantum dots, thereby generating light. The power supply may be a constant current source to control the current density injected into the active layer 20 and thus the output light intensity of the device. The current modulation means may provide current amplitude modulation during operation of the optoelectronic device, e.g. to obtain gain modulation in a semiconductor laser diode. The optoelectronic device may be mounted on a heat dissipation structure, e.g. a heat sink, to avoid significant temperature rise in the device, which often accompanies thermal drift of the device performance. A temperature controller, e.g. with a control unit and a thermoelectric cooling unit, may be provided to ensure stable temperature conditions when the device is in use.

[0081] To operate an integrated optoelectronic device according to the preceding embodiments as a photodetector device, the electrodes 40, 50 are connected to a power supply that applies a reverse bias across the diode junction. As a result, majority carriers of opposite charge polarity are collected by the respective charge transport layers 11, 12 from the active layer 20 where they arise as photogenerated electron-hole pairs and are then extracted from the electrodes 40, 50 of the device in the form of a photocurrent. The photocurrent may then be processed in the electrical domain, for example, amplified and / or quantized.

[0082] Integrated optoelectronic devices according to embodiments of the present invention may be further packaged according to techniques known in the art, for example by mounting the optoelectronic device on a device carrier and wire bonding in a hermetically sealed, externally accessible package, for example a butterfly package with pin connectors. EXAMPLES

[0083] An exemplary integrated optoelectronic device has a cross-section as shown in the embodiment associated with FIG. 4. For example, a silicon nitride strip waveguide 31, 300 nm high and 1000 nm wide, may be fabricated using standard SOI technology for PICs, rising from an insulator-on-silicon substrate 30. Silicon nitride based dielectric waveguides typically have very low optical propagation losses, e.g., only 1 dB / m, and transmit light within the visible and infrared spectrum. In this embodiment, the waveguide 31 is configured as a multimode waveguide, inducing a higher order TE1 mode in addition to the fundamental TE0 mode, with a good balance between coupling efficiency and excess loss to the active layer, although other embodiments of the invention may comprise single mode waveguides, particularly in embodiments intended to embed laser diodes, although wider multimode waveguides may also be beneficial for delivering increased output power in high power laser diodes. The second charge layer 12 corresponds to a thin layer of continuous semiconducting zinc oxide, an inorganic electron transport layer. This thin layer of native n-type zinc oxide, e.g. 10 nm thick, is provided on top of the waveguide 31, conformally covering its contours. A pair of Ti / Au / Ti (20 nm / 100 nm / 20 nm) metal n-contacts are formed on the zinc oxide layer, constituting the second electrode 50. Silicon oxide has been used as the side cladding material 32 for the overcoated waveguide. The top surface of the side cladding material 32 is flush with the top surface of the overcoated waveguide, e.g. the top surface of the second charge transport layer 12 covering the waveguide 31, providing a planar interface for uniform deposition of the active layer 20. In this example, the active layer 20 consists of a 20 nm thick film (e.g. corresponding to 2-3 layers) of solution-processed randomly oriented quantum dots, e.g. spherical colloidal CdSe / CdS core-shell quantum dots, or non-spherical nanocrystals with isotropic dipole orientation. Suitable values ​​for the core diameter and shell diameter are, for example, up to 2800 cm -1 high intrinsic material gain, and e.g. TIFF0007660859000001.tif840, may be 3.5 nm and 7.5 nm, respectively, to obtain both reasonably low injection current density thresholds for net stimulated emission in the active layer. Finally, the first charge transport layer 11 was implemented as a 600 nm thick organic hole transport layer with a 300 nm thick aluminum p-contact formed as the first electrode 40. More specifically, the first charge transport layer 11 consists of 70 nm of TCTA (hole injection layer), 500 nm of NPD (hole transport layer), and 30 nm of HTA-CN (band alignment layer for holes).

[0084] Finite element and finite difference time domain simulations have been performed to optimize the waveguide geometry (e.g., width and height) and the individual layer thicknesses of the vertical layer stack with the goal of achieving good LED performance. The simulations were performed for a wavelength of 650 nm, which was assumed to be the peak wavelength of the electroluminescence spectrum. Such simulations are based on the refractive indices of the charge transport layers 11, 12 and the silicon nitride waveguide 31, obtained from ellipsometry measurements. The metal induced propagation loss experienced by the fundamental guided mode (and all higher modes) in the presence of the first electrode 40 was found to decay exponentially fast as a function of the layer thickness of the first charge transport layer. For example, a metal induced propagation loss of 4 dB / cm was found by simulation for a 500 nm thick first charge transport layer and was also verified by cutback measurements, while a metal induced propagation loss of 2 dB / cm was estimated for the 600 nm thick first charge transport layer of this example. The imaginary part of the complex refractive index of the zinc oxide layer is k=2.5*10 by cutback measurement. -4The unavoidable overlap of the evanescent tail of the guided optical mode confined in the waveguide with the lossy zinc oxide layer results in further propagation losses. The dimensions of the silicon nitride waveguide are part of the simulation results and constitute a trade-off between the overall propagation losses on the one hand and a good spontaneous dipole emission coupling efficiency of the quantum dots of the active layer 20 to the waveguide 31 on the other hand. Based on the simulation results, the former is estimated as 12 dB / cm and the latter as 0.5%-1.0% (integrated over the waveguide width) for a mode overlap of about 3.6% with the active layer. The material gain required to overcome the propagation loss is about 880 cm -1 which is within the feasibility of gain-optimized core-shell quantum dots. Furthermore, if only coupling efficiency is considered for optimization, the optimal waveguide height for single-mode waveguides is found to be in the range of 100 nm to 150 nm.

[0085] In the following, the fabrication method of the integrated optoelectronic device of this example is briefly described. Starting with a bare silicon sample with a 1.0 μm thick thermal oxide layer, a 300 nm thick silicon nitride layer is deposited by plasma enhanced chemical vapor deposition. The waveguides are defined by patterning the silicon nitride layer using electron beam lithography and reactive ion etching. Alternatively, photonic integrated circuits with prefabricated waveguides can be provided, e.g. factory patterned silicon nitride on an insulator (e.g. silicon oxide insulating layer on a silicon substrate).

[0086] Next, a 10 nm thin zinc oxide (ZnO) (polycrystalline, continuous) layer is deposited via atomic layer deposition (ALD) that conformally covers the waveguide. The ZnO deposition is approximately 5*10 -6 It is carried out at a base pressure of 100 mbar and a temperature between 60°C and 300°C, preferably around 150°C, and may be assisted by reactive plasma (e.g. acid-rich plasma and / or ozone-rich plasma). The gas flow pressure of the precursor (e.g. diethylzinc for zinc) and reactant (e.g. distilled water vapor) is adjusted to 5*10 using needle valves. -3The pressure is adjusted to 1000 psi mbar. Alternative deposition techniques for the second charge transport layer, e.g. a ZnO layer, include a sol-gel deposition process or sputter deposition. A thin layer of ZnO nanocrystals may alternatively be deposited, e.g. using spin coating. A passivation and etch stop layer comprising 15 nm thick aluminum oxide is then applied by ALD (e.g. using trimethylaluminum as precursor and distilled water vapor as reactant), followed by an optional annealing step, e.g. annealing at a maximum temperature of 400° C. in N2 and H2 atmospheres. As a result, a zinc oxide layer with good performance is obtained in terms of resistance and optical losses, e.g. a sheet resistance of (1.2±0.1) kΩ / sq and free carrier absorption losses of about 10 dB / cm. Using diluted KOH, the passivation layer is locally removed on both sides of the waveguide to allow the formation of the metal contacts of the second electrode (e.g. 20 nm Ti / 100 nm Au / 20 nm Ti). Photolithography and lift-off processes may be performed for this step. In a further step, the zinc oxide layer beyond the device is removed using wet etching in diluted HCl, followed by chemical vapor deposition of a silicon oxide layer. This silicon oxide layer is opened again (e.g. via electron beam lithography, reactive ion etching, and KOH wet etching to remove the etch stop layer) to expose the zinc oxide layer in the areas where the waveguides are located and where the next layer of the vertical layer stack will be formed. As a result, a 20 nm thick active layer is deposited on the exposed parts of the zinc oxide layer by using lift-off of a layer of CdSe / CdS quantum dots (e.g. oleate capped) spin-coated from toluene. In a shadow mask evaporation step, the three organic layers (TCTA, NPD, HAT-CN) constituting the first charge transport layer are obtained under continuous rotation of the sample holder. As an alternative to vacuum thermal evaporation, organic vapor phase deposition with an inert carrier gas may be used to deposit the organic charge transport layer. Finally, a 300 nm thick aluminum layer is deposited from the vapor phase to form the first electrode.

[0087] Several prototype integrated optoelectronic devices, each with an active device area 2 mm long and a waveguide approximately 1 cm long, have been fabricated and tested in the manner described above. -2 A current density of 100 A cm was measured across the first device, where the highest optical output power was observed, at a forward bias voltage of 100 V. A second device, fabricated on the same chip as the first, exhibited a current density of 100 A cm at a forward bias voltage of 120 V. -2 A current density as high as 1000 uW was obtained, and higher voltages caused device failure. The measured turn-on voltage for observable optical output from the fabricated optoelectronic devices is about 3 V. However, these measurements are limited by the noise floor of the optical power meter used during testing, and true electrical turn-on is expected at a forward bias voltage of about 2 V. The emission peak of the acquired electroluminescence spectrum is located at 642 nm. A spectrally integrated optical output power of about 2.0 nW was obtained in the fundamental waveguide mode of the first tested device, with a current density of 47 A cm. -2 It is electrically pumped with a current density of 1.5 Wcm -2 This corresponds to an optical power density of 100 nm. Higher order modes can be efficiently filtered out by defining two single mode waveguide sections (e.g., 450 nm wide and 0.4 mm long each) simultaneously with the multimode waveguide 31, so that they are directly connected to the multimode waveguide 31 at either end. Based on measured device output power, the maximum internal quantum efficiency is estimated to be about 11%.

[0088] Further prototype optoelectronic devices (0.5 mm long) have been fabricated in the manner described above and tested for their photodetection performance. Although the prototypes are developed for use with LEDs, they operate as photodetectors under reverse bias conditions. For photodetector characterization of the exemplary optoelectronic device, light from an external LED (λ=635 nm) is coupled into the waveguide 31. At a reverse bias voltage of −7 V, the current is 1.5 μA / cm 2The dark current of the detector is measured and a suboptimal quantum efficiency of about 6% is extracted from the measured data. The quantum efficiency of the detector can be further improved by optimizing the band alignment and device processing.

[0089] In a further aspect, the invention relates to a method of decoupling an active layer width from an optically confined guided mode in an integrated optoelectronic device, such as an integrated light emitting or light detecting device. The integrated optoelectronic device comprises a substrate on which is formed a first charge transport layer for transporting charge carriers of a first conductivity type, a second charge transport layer for transporting charge carriers of a second conductivity type opposite the first conductivity type, and an active layer comprising a solution-processed semiconductor nanocrystal material. The active layer is positioned with respect to the first and second charge transport layers such that a diode junction is formed that is operable under forward bias conditions or under zero or reverse bias conditions. Under forward bias conditions, the active layer is configured to generate light upon recombination of charge carriers of the opposite conductivity type injected into the active layer by the respective charge transport layers. Under zero or reverse bias conditions, the active layer is configured to generate charge carriers of opposite conductivity type upon absorption of light incident on the diode junction, and the diode structure is further configured to separate the generated charge carriers into the first and second charge transport layers according to their conductivity types. The first and second charge transport layers are typically provided as n-type or p-type semiconductor layers. The separation method includes providing a passive waveguide on the substrate such that in a cross section perpendicular to the longitudinal direction of the optoelectronic device, e.g., in the direction of propagation of light in the waveguide, each of the first and second charge transport layers and the active layer overlaps a portion of the waveguide. The waveguide is then provided separately from the active layer. The waveguide is configured to confine and guide at least one optical waveguide mode, the confinement corresponding to the direction of the cross section. Furthermore, the position of the waveguide relative to the active layer is adapted for mutual evanescent coupling of light between them. Evanescent coupling between the active layer and the waveguide occurs, for example, when at least one guided optical mode supported by the waveguide extends into and overlaps the active layer. The waveguide may extend into the substrate from the substrate surface or may rise up from the substrate surface. The waveguide may support a single mode or multiple modes in cross section.The method may further include providing a current path to and through a diode junction formed by the first and second charge transport layers and the active layer that does not pass through the waveguide, which may be obtained by positioning the waveguide relative to the diode junction such that the waveguide does not form part of the diode junction.

[0090] While the present invention has been illustrated and described in detail in the drawings and the foregoing description, such illustration and description are to be considered as illustrative or exemplary and not restrictive. The foregoing description sets forth specific embodiments of the present invention in detail. However, no matter how detailed the above appears in the text, it will be understood that the invention can be practiced in many ways. The present invention is not limited to the disclosed embodiments.

Claims

1. An integrated optoelectronic device (100, 200, 300) comprising: a substrate (30) supporting a passive waveguide (31) configured to guide light along a longitudinal direction and to index confine the guided light in each of the transverse directions in at least one guided optical mode; a first charge transport layer (11) for transporting charge carriers of a first conductivity type; a second charge transport layer (12) for transporting charge carriers of a second conductivity type opposite to said first conductivity type; an active layer (20) comprising a particulate film of solution-processable semiconductor nanocrystals, the active layer being disposed relative to the charge transport layer to form a diode junction; the active layer, the first charge transport layer and the second charge transport layer are formed on the substrate, and each overlaps at least a portion of the waveguide in a cross section perpendicular to the longitudinal direction; the active layer is optically evanescently coupled to the waveguide; and An integrated optoelectronic device, wherein said first charge transport layer (11) is an organic semiconducting hole transport layer and said second charge transport layer (12) is an inorganic semiconducting electron transport layer.

2. the individual particles of the active layer particulate film are closely packed, whereby the average interparticle distance between adjacent particles of the active layer particulate film is less than 5 nanometers; and / or 10. The integrated optoelectronic device of claim 1, wherein particles of the active layer particulate film comprise one or more of the group consisting of colloidal quantum dots, nanocrystalline perovskite-based materials, bulk semiconductor nanocrystals, and nanoplatelets.

3. 2. The integrated optoelectronic device of claim 1, wherein a current path through said first charge transport layer, said active layer, and said second charge transport layer does not extend into said waveguide.

4. 2. The integrated optoelectronic device of claim 1, wherein the second charge transport layer (12) is in direct physical contact with the waveguide (31).

5. 2. The integrated optoelectronic device of claim 1, wherein an electrically contacted portion of said active layer overlaps said waveguide in said cross section.

6. the first charge transport layer (11), the second charge transport layer (12), the active layer (20), and the waveguide (31) are stacked vertically in the cross section; 2. The integrated optoelectronic device of claim 1, wherein the second charge transport layer is disposed between the active layer and the waveguide.

7. 2. The integrated optoelectronic device of claim 1, wherein the second charge transport layer (12) conforms to the contours of the waveguide (31), thereby providing a conformal coating to the waveguide.

8. 8. The integrated optoelectronic device of claim 7, further comprising a cladding material (32) on either side of the conformally coated waveguide and flush with the coated upper surface of the waveguide.

9. 2. The integrated optoelectronic device of claim 1, wherein the first charge transport layer (11) and the second charge transport layer (12) are coplanar and arranged to overlap different portions of the waveguide in the cross section, adjacent edges of the first charge transport layer and the second charge transport layer are separated by a gap (21), and the active layer (20) extends over at least a portion of the first charge transport layer and the second charge transport layer and into the gap (21).

10. 10. The integrated optoelectronic device of claim 9, wherein the waveguide is configured as a slotted waveguide having two waveguide rails rising from a surface of the substrate and separated by a slot, the first charge transport layer and the second charge transport layer extending into the slot.

11. 2. The integrated optoelectronic device of claim 1, wherein the integrated optoelectronic device is an integrated light emitting diode and further comprises a first electrode (40) in electrical contact with the first charge transport layer (11) and a second electrode (50) in electrical contact with the second charge transport layer (12) to induce a forward bias condition across the diode junction, the active layer being adapted to generate light upon recombination of charge carriers of opposite conductivity type injected into the active layer by the respective charge transport layers under the forward bias condition.

12. the integrated optoelectronic device is an integrated laser diode; a first electrode (40) in electrical contact with the first charge transport layer (11) and a second electrode (50) in electrical contact with the second charge transport layer (12) to induce a forward bias condition across the diode junction, the active layer being adapted to generate light upon recombination of charge carriers of opposite conductivity type injected into the active layer by the respective charge transport layers under the forward bias condition; 10. The integrated optoelectronic device of claim 1 further comprising optical feedback means optically coupled to said waveguide thereby forming an optical cavity.

13. 13. The integrated optoelectronic device of claim 11 or 12, wherein the diode is arranged to emit light horizontally, in a plane parallel to the substrate (30), or at an angle to the substrate (30), in an area of ​​the substrate not covered by the active layer and the first and second charge transport layers.

14. 1. A method for manufacturing an integrated optoelectronic device, the method comprising: providing a passive waveguide (31) in a substrate (30), the waveguide configured to guide light along a longitudinal direction and to provide index confinement of the guided light in each of its transverse directions in at least one guided optical mode; forming a stack of layers, a second charge transport layer (12) for transporting charge carriers of the second conductivity type; an active layer (20) comprising a particulate film of semiconductor nanocrystals, the semiconductor nanocrystals being deposited from a solution; a first charge transport layer (11) for transporting charge carriers of a first conductivity type opposite to said second conductivity type, on said substrate (30) by sequentially depositing in this order on said substrate (30); the deposited active layer (20) and each of the deposited first charge transport layer (11) and the deposited second charge transport layer (12) overlap at least a portion of the waveguide in a cross section perpendicular to the longitudinal direction, the active layer (20) is positioned relative to the charge transport layers (11, 12) to form a diode junction, the active layer (20) is optically evanescently coupled to the waveguide (31), and A method, wherein said deposited first charge transport layer (11) is an organic layer and said deposited second charge transport layer (12) is an inorganic layer.

15. 15. The method of claim 14, wherein depositing the first charge transport layer (11) comprises vacuum thermal evaporation or organic vapor phase deposition and / or depositing the second charge transport layer (12) comprises thermal controlled atomic layer deposition.

16. 15. The method of claim 14, wherein depositing the second charge transport layer (12) comprises depositing a nanometric layer of polycrystalline zinc oxide (ZnO) using atomic layer deposition at a substrate temperature between 60°C and 300°C.

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