Tunable optoelectronic arrangement

Abstract

The invention concerns an optoelectronic arrangement based on a resonant cavity LED (RCLED) comprising a tunable optical cavity. The tuning of the cavity is achieved using microelectromechanical systems (MEMS)-based actuators. The resultant arrangement achieves improved linewidth and reliability of output characteristics under variable operating conditions.

Description

[0001] TUNABLE OPTOELECTRONIC ARRANGEMENT

[0002] The present application claims priority of German patent application DE 10 2024 115 883 . 2 dated June 6 , 2024 , the disclosure of which is incorporated herein by reference in its entirety .

[0003] The present invention concerns an optoelectronic arrangement comprising a tunable resonant optical cavity as well as a method for manufacturing such an optoelectronic arrangement .

[0004] BACKGROUND

[0005] Micro-LEDs have been employed in a large variety of applications . The output characteristics of micro-LED emissions are typically characterized by a wide , Lambertian emission angle profile , which is disadvantageous in applications requiring narrow emission angle profiles , such as augmented reality (AR) proj ection . This challenge has been conventionally addressed through incorporation of micro- optical elements or other beam-shaping devices , which are associated with increased production costs and manufacturing complexity .

[0006] It is an obj ect of the present application to provide an optoelectronic arrangement that maintains the desired emission characteristics of at least one RC-LED under a variety of operating conditions .

[0007] SUMMARY OF THE INVENTION

[0008] This and other obj ects are addressed by the subj ect matter of the independent claims . Features and further aspects of the proposed principles are outlined in the dependent claims .

[0009] An alternative to the above-mentioned approach is the use of Resonant Cavity ( RC ) LEDs . RC-LEDs are produced by arranging the active layer of an LED device into a resonant optical cavity defined by two mirrors with different reflectivity . However, the optical resonant modes of the cavity in RC-LEDs are dependent on the cavity length . It is therefore necessary to achieve precise control of cavity length to an accuracy within nanometer range , in particular, to an accuracy below 20 nm to ensure reliable performance of RC-LEDs . In applications with demanding temperature requirements , for instance , under working conditions from -40 ° C to +80 ° C, thermal expansion of the materials forming the cavity can nevertheless lead to substantial deviation of cavity dimensions from design values . The resultant detuning of the cavity is associated with loss of the desired emission profile and / or efficiency .

[0010] RC-LEDs comprise a light-emitting semiconductor stack whose active region is arranged within a resonant optical cavity . The optical cavity is defined by a first highly reflective mirror forming a bottom surface of the RC-LED and a second partially reflective mirror arranged on an opposite side of the active layer to the first reflective mirror . The emission characteristics of RC-LEDs are dependent on the design of the optical cavity, in particular , the cavity length, which corresponds to the distance between the two mirrors .

[0011] RC-LEDs with a suitably designed cavity length exhibit a more directed emission characteristic, and thus , a narrower emission angle profile is achievable . Placement of the active layer within a resonant optical cavity allows enhanced spontaneous emission from the LED device for on-resonance wavelengths . Furthermore , as the emission linewidth is proportional to the finesse of the optical cavity, improved spectral purity is achieved through appropriate cavity design .

[0012] The inventor proposes an optoelectronic arrangement featuring an RC- LED with variable cavity length . The variation of the cavity length is achieved by implementing one of the cavity-defining mirrors as a movable membrane such that the distance between the membrane and a second cavity-defining mirror , placed on the fixed semiconductor epi can be changed by microelectromechanical actuators attached to the movable membrane . The resultant microoptoelectromechanical system (MOEMS ) features an adj ustable optical cavity length, and hence , tunable resonance modes .

[0013] The ability to tune the resonance condition of the cavity can be used advantageously in different ways . The adj ustment of the position of the movable mirror membrane allows maintaining of a substantially constant cavity length despite thermal expansion of the semiconductor material arising from environmental or operation-related conditions . Thus , reliability and consistency of outcoupling efficiency as well as substantially constant linewidth, expressed by the full width at half maximum ( FWHM) , is achieved from the RC-LED under varying thermal conditions .

[0014] Furthermore , the movable mirror membrane may be used to slightly over- or undertune the cavity with respect to the emitter, thus allowing variation of emission characteristics . Overtuning of RC-LEDs , for instance , results in a wider emission angle range and / or sharp maxima in certain directions which is advantageous in beam steering application . Undertuning , on the other hand, allows concentration of the emission profile in a narrow angle window .

[0015] The proposed optoelectronic arrangement may be advantageously used in high-speed communication applications through alternating between resonant modes of the optical cavity, or alternatively, alternating between resonance and non-resonance .

[0016] The proposed optoelectronic arrangement comprises at least one light emitting device , in particular, a pLED . The light emitting device comprises a first doped semiconductor layer , an active layer arranged on a surface of the first doped semiconductor layer, a second doped semiconductor layer , a first reflective layer, and at least one first electrical contact surface arranged in contact with the first reflective layer , and electrically connected to at least one of the doped layers . The second doped semiconductor layer comprises a different dopant from the first doped semiconductor layer . The first doped layer is arranged on a surface of the first reflective layer, whereby the first reflective layer forms a backside mirror . A surface of the second doped semiconductor layer facing away from the active layer forms a light-emitting surface . The arrangement further comprises a second partially reflective layer and an actuator . The second partially reflective layer is arranged at a distance from the lightemitting surface , forming , together with the first reflective layer , a resonant optical cavity within which the active layer is positioned . The actuator is arranged in connection with the second partially reflective layer, such that a distance between the second partially reflective layer and the first reflective layer can be varied, thereby varying the length of the optical cavity formed between the reflective layers .

[0017] The at least one light-emitting device comprises any suitable semiconductor material , in particular, any II I / V group semiconductor compound . The choice of material is dependent on desired device characteristics , in particular , desired emission wavelength . Common material families for manufacture of pLEDs include nitrides , phosphides and arsenides , whereby the selected material may comprise binary, ternary and / or quaternary compounds .

[0018] Some aspects of the proposed invention feature doped semiconductor layers implemented as multiple sublayers , wherein the composition, thickness and structure of the sublayers is dependent on the desired functionality . Such sublayers may comprise different material composition, different dopant material , doping concentration, and may even be undoped in some instances . The sublayers provide dedicated functionality including but not limited to current spreading, current inj ection, current blocking, to mention a few . The dopant type and concentration may also be varied to achieve desired emission characteristics and device performance . In some aspects , the doped semiconductor layers comprises superlattice sublayers . In other aspects , the second doped semiconductor layer forming the lightemitting surface comprises a light conversion layer, allowing conversion of emitted light from a first wavelength to at least a second wavelength, wherein the second wavelength is different from the first wavelength . Some aspects of the proposed invention comprise a transparent conductive oxide sublayer which forms the light emitting surface .

[0019] In some aspects , active layer comprises a multi quantum well structure including a plurality of barrier and quantum well layers . The active layer may be undoped or may comprise small dopant concentration in some aspects . In some aspects , the active layer may comprise undoped cladding layers .

[0020] The pLED semiconductor layers may be structured to form at least one mesa structure , for instance , through a process of wet and / or dry etching , wherein boundaries of the pLED are defined by sidewalls .

[0021] In some aspects , a current blocking layer is arranged between the first doped layer and the active layer , said current blocking layer comprising at least one aperture . The current blocking layer directs current flow within the semiconductor layers through a narrow region defined by the at least one aperture . Such a current blocking layer may be formed, for example , by depositing an oxide and locally forming apertures . Alternatively, part of the first doped layer is locally passivated through introduction of hydrogen, or by destroying the doping via implant damage using a patterned implant . In some aspects of the invention comprising a current blocking layer, a dielectric layer is arranged within the semiconductor layers , extending through the first doped layer , the active layer and at least partially through the second doped layer .

[0022] The proposed invention comprises a resonant optical cavity defined by two reflective layers arranged facing each other . The first reflective layer is configured to be fixed and is arranged to form a backside of the at least one pLED device . The first reflective layer is characterized by a high reflectivity at the emission wavelength of the pLED, in particular , greater than 95% , and particularly, greater than 99% . Suitable materials for the first reflective layer include metals such as Ag, Au, Al , Ni and alloys thereof , or a suitably configured Distributed Bragg Reflector ( DBR) . Implementation of the first reflective layer as a DBR layer allows achievement of higher reflectivity, with reflectivity values up to 100% achievable for suitably configured DBR layers .

[0023] The second partially reflective layer defining the resonant optical cavity is arranged at a distance from the light-emitting surface of the pLED and is configured to have a lower reflectivity than the first reflective layer at the emission wavelength of the at least one optical device . The characteristics of the modes of the resonant cavity is a function of the length of the resonant cavity, that is , the distance between the second partially reflective layer and the first reflective layer . In some aspects , the second partially reflective layer comprises a DBR with layer thickness of X / 4 , where is the emission wavelength of the at least one optical device . The reflectivity of the second partially reflective layer is a function of the number of double layers , wherein a double layer comprises one layer each of two materials of different refractive indices . Any suitable material pairs may be chosen, with the number of double layers appropriately designed to achieve the desired reflectivity . The thickness of the second partially reflective layer is in some aspects less than 10pm, in particular, less than 5 pm, and may in some aspects be less than 2pm. An exemplary aspect comprises a second partially reflective layer implemented as a DBR comprising 10 double layers of SiCh and Nb2Os , with a resultant DBR layer thickness up to approximately 2pm for operation at wavelengths within the visible spectrum .

[0024] In some aspects , the second partially reflective layer comprises a light conversion sublayer which may be arranged on a surface facing the light emitting surface of the pLED, or alternatively may be arranged on a surface facing away from the light emitting surface . Locating the light conversion sublayer on the surface of the second partially reflective layer reduces thermal effects associated with light conversion as the conversion layer is in this case located at a distance from the active layer . Furthermore , combination of a light conversion sublayer and suitable configuration of the optical cavity by appropriately positioning the second partially reflective layer results in improved emission characteristics and reduction or elimination of thermal wavelength shift in the converted light .

[0025] According to the proposed invention, tuning of the resonant cavity is achieved through variation of the distance between the reflective layers by means of an actuator . The actuator is connected to the second partially reflective layer and is laterally adj acent to the lightemitting surface of the pLED . The actuator is , in particular , implemented as a microelectromechanical system (MEMS ) . MEMS actuators are characterized by at least one dimension in the micrometer range . Typical MEMS actuators may be implemented as electrostatic, piezoelectric , electromagnetic or electrothermal actuators . Electromagnetic and electrothermal actuators are however limited in terms of actuation speed and ease of manufacture and are therefore not commonly integrated into microoptoelectromechanical systems (MOEMS ) or applications requiring high speed actuation .

[0026] In some aspects of the proposed invention the actuator comprises a plurality of actuation elements which are in particular arranged to achieve desired characteristics such as uniformity of displacement and / or mechanical stability . Some aspects feature paired actuation elements arranged on opposite sides of the light-emitting surface . In some aspects , at least one first pair of actuation elements and at least one second pair of actuation elements are arranged laterally perpendicular to each other .

[0027] In some aspects , in particular, where the actuation principle involves actuation elements comprising at least two parallel plates , at least one first plate of each actuation element is arranged adj acent to the light emission surface , displaced vertically from the second partially reflective layer . At least one second plate of each actuation element is arranged on a surface of the second partially reflective layer . In some aspects , the at least one second plate is arranged on a surface of the second partially reflective layer facing towards the light emitting surface of the pLED . This is the case , for example , for electrostatic actuators and some implementations of electromagnetic actuators . In other aspects , the at least one second plate is arranged on a surface of the second partially reflective layer facing away from the light emitting surface of the pLED .

[0028] The proposed optoelectronic arrangement further comprises , in some aspects , a support arranged laterally displaced from the light emitting surface and connected to the second partially reflective layer . The upper surface of the support protrudes vertically above the lightemitting surface , such that a distance exists between the second partially reflective layer arranged thereupon and the light-emitting surface . In some aspects , the support laterally encloses the light emitting surface and the actuator . The support may thereby form a continuous boundary around the light emitting surface . In other aspects , the support may comprise a plurality of pillars , posts , noncontiguous wall-like structures or any suitable protruding structure arranged laterally adj acent the light emitting surface of the optoelectronic arrangement . In other aspects , the support comprises the actuator, with suitable positioning of the second partially reflective layer on surfaces of a plurality of actuation elements .

[0029] The connection between the second partially reflective layer and the support is achieved in some aspects through a connector coupling the support with a first region of the second partially reflective layer positioned vertically above the light emitting surface and forming a resonant optical cavity with the first reflective layer, said connector corresponding to a second region of the second partially reflective layer . In this regard, the connector in particular comprises a plurality of connecting elements distributed around the perimeter of the second partially reflective layer . In some aspects , the connector comprises at least one beam extending from a periphery of the first region of the second partially reflective layer to a surface of the support , wherein a beam is defined as a structure connecting two points along a substantially straight line . Alternative aspects comprise a connector implemented as a spring-like structure or a meandering structure . The connector may be monolithically integrated with the second partially reflective layer and formed by an etching process involving a patterned mask . Nonetheless , any alternative methods for forming a suitable connector between the first region of the second partially reflective layer and the support may be implemented, including but not limited to deposition processes .

[0030] Some aspects of the proposed invention further comprise at least one second light-emitting device , in particular, a plurality of light emitting devices . The plurality of light emitting devices is in some aspects arranged in an array comprising rows and columns . The at least one second light emitting device comprises the following layers arranged sequentially : a first reflective layer , a first doped semiconductor layer , an active layer and a second doped semiconductor layer . The at least one second light emitting device further comprises at least one first electrical contact surface electrically connected to at least one of the doped layers , wherein the electrical contact surface is in contact with the first reflective layer . The first reflective layer forms a backside surface of the light emitting device , and the second doped layer forms a light emitting surface . The second partially reflective layer is arranged to extend laterally above the first light emitting device and the at least one second light emitting devices and is positioned at a distance from the light emitting surfaces of the light emitting devices .

[0031] Further aspects of the optoelectronic arrangement , specifically, wherein the arrangement comprises a plurality of light-emitting devices , are configured for generation of multiple wavelengths either sequentially or simultaneously . A typical application of such an optoelectronic arrangement is in applications requiring RGB pixels , or for generation of white light . Other typical applications include where a combination of visible light and infrared or ultraviolet emissions is desired . In this regard, the first one light-emitting semiconductor device is configured to emit light at a first wavelength, and at least one second light-emitting semiconductor device is configured to emit light at a second wavelength, wherein the second wavelength is different from the first wavelength . Emission of a different wavelength may be achieved through configuration of the material forming the active layer of the light-emitting devices . Alternatively, some aspects comprise light-emitting devices wherein a light conversion sublayer is integrated into the second doped layer forming the light emission surface .

[0032] In some aspects , the at least one second light emitting device is characterized by similar or substantially identical material , structure and / or dimensions as the first light emitting device . The first and the at least one second light emitting device may therefore be monolithically integrated . In some aspects , the first and at least one second light emitting device are configured to be independently controllable . In other aspects , the at least one second light emitting device comprises different material , structure and / or dimensions from the first light emitting device . The light emitting devices in some such aspects are monolithically integrated . In other aspects , the light emitting devices are processed separately and transferred to a common carrier substrate .

[0033] Where the vertical dimensions of the light emitting devices differ, the light emitting surfaces of the light emitting devices are in some aspects configured to be substantially coplanar . In other aspects , the light emitting surface of at least one first light emitting device protrudes vertically with respect to the light emitting surface of at least one second light emitting device . Differences in the vertical position of the light emitting surface are included in some aspects to allow achievement of different cavity lengths for different light emitting devices , whereby the first reflective layer of the light emitting devices are appropriately positioned with respect to the second partially reflective layer . In other aspects , differences in the vertical position of the light emitting surface arise from variations in the composition and dimensions of the semiconductor layers in the light emitting devices , for instance through additional sublayers such as light conversion layers , transparent conductive oxide layers , and so on .

[0034] In some aspects wherein the optoelectronic arrangement comprises a plurality of light-emitting devices , the actuator comprises at least one actuating element positioned between at least two light-emitting devices . Such positioning allows larger arrays of light-emitting devices to be incorporated in the proposed optoelectronic arrangement while maintaining mechanical stability of the second partially reflective layer arranged connected to the actuating element , as well as improving uniformity of displacement of the second partially reflective layer, in particular , by controlling the actuating elements synchronously .

[0035] The actuator is in some aspects configured to produce a substantially uniform displacement of the second partially reflective layer with respect to the first reflective layer of the plurality of light emitting devices . Where light emitting devices of different dimensions are included in the optoelectronic arrangement , the first reflective layer of the light emitting devices is , for example , correspondingly positioned with respect to the second partially reflective layer, in particular, within a carrier substrate . This allows achievement of substantially equal cavity lengths through uniform operation of the actuation elements . In other aspects , the actuator is configured to produce a first displacement of the second partially reflective layer with respect to the first reflective layer of the first light emitting device and at least a second displacement of the second partially reflective layer with respect to the first reflective layer of the second light emitting device , wherein the second displacement is different from the first displacement . This can be achieved, for instance , by supplying different voltages to different actuation elements . This allows achievement of different cavity lengths simultaneously for different light emitting devices , in particular where the first reflective layers of the light emitting devices are positioned on a common horizontal plane . Differences in the cavity length may additionally be desirable in applications wherein undertuning or overtuning of one or a group of light emitting devices is desirable such that a specific emission spectrum is achieved for the optoelectronic arrangement , both in aspects comprising substantially identical light emitting devices , and in aspects comprising light emitting devices with different emission characteristics . Realization of different displacements of the second partially reflective surface is additionally advantageous in countering process variability within the optoelectronic arrangement .

[0036] The resonant optical cavity is in some aspects subdivided into two cavities , wherein a third partially reflective layer arranged on the light emitting surface forms a first fixed cavity, and the second partially reflective layer is arranged at a vertical distance from the third partially reflective layer, forming a second tunable cavity . Such a configuration has been published as RC2-LED and is typically associated with a lower overall extraction efficiency than a singlecavity RC-LED, but a significantly higher extraction efficiency inside a narrow angle range . The displacement of the second partially reflective layer with respect to the fixed first and third reflective layers allows for tuning the directionality of emitted light . The third partially reflective layer may comprise any suitable material , and is in some aspects implemented as a DBR layer . The third partially reflective layer is characterized by a reflectivity lower than the reflectivity of the first reflective layer and greater than the reflectivity of the second partially reflective layer .

[0037] Further aspects of the proposed invention relate to a method for processing an optoelectronic arrangement . In a first step, a carrier substrate comprising at least one light emitting device is provided . The at least one light emitting device comprises a first reflective layer arranged on a surface of the carrier substrate , a first doped layer arranged on a surface of the first reflective layer facing away from the carrier substrate , an active layer arranged on a surface of the first doped layer facing away from the carrier substrate , and a second doped layer arranged on a surface of the active layer forming a light emitting surface . At least one first electrical contact surface is arranged in contact with the first reflective layer and forms an electrical connection to at least one of the doped layers .

[0038] In some aspects , the at least one light emitting device is at least partially epitaxially grown on a growth substrate and bonded onto the carrier substrate , after which the growth substrate is removed . Thus , for example , some sublayers of the second doped layer are , in some aspects , epitaxially grown on the growth substrate in an initial step, and further sublayers , such as light conversion layers and transparent conductive oxide layers , are deposited on the surface of the second doped layer after removal of the growth substrate .

[0039] In a subsequent step, a second partially reflective layer arrangement is arranged on a surface of the carrier substrate . The second partially reflective layer arrangement comprises a second partially reflective layer , an actuator and, optionally, a support . The actuator, which optionally comprises a plurality of actuation elements , is connected to the second partially reflective layer and arranged on a surface of the carrier substrate such that the actuator is laterally adj acent to the light-emitting surface of the at least one light emitting device . The second reflective layer is positioned at a vertical distance above the light emitting surface , and optionally rests on a support positioned laterally adj acent to the actuator .

[0040] Arranging of the second partially reflective layer arrangement on the surface of the carrier substrate may be achieved in different ways . One method involves a first step of arranging the actuator on a surface of the carrier substrate such that the actuator is laterally adj acent to the light emitting surface . The actuator is connected to the surface of the carrier substrate using a suitable bonding process , in particular, using an appropriate adhesive . A subsequent step involves depositing a sacrificial layer on the surface of the carrier substrate such that the light emitting surface and the actuator are enclosed within the sacrificial layer .

[0041] The sacrificial layer is patterned and etched followed by depositing of a support . In some aspects , the support comprises a continuous structure laterally surrounding the light emission surface . In other aspects , the support structure comprises a plurality of protrusions which are optionally at least partially contiguous . Such protrusions may be characterized by any of a variety of cross-sections , including circular, elliptical , polygonal , spiral , and so on . The support comprises any suitable dielectric material , in particular , a compressible material . The support is deposited to protrude at least above the light emitting surface , with an overall height that is dependent on the maximum desired length of the resonant optical cavity . The sidewalls of the support are positioned laterally adj acent to the light-emitting surface . An upper surface of the support facing away from the carrier substrate is substantially coplanar with an upper surface of the sacrificial layer adj acent to and surrounding the support , and an upper surface of the actuator facing away from the carrier substrate . This may optionally be achieved through a planarization step subsequent to deposition of the support structure . In a subsequent step, a partially reflective layer is deposited on the upper surfaces of the sacrificial layer , the actuator and the support . In some aspects , an adhesive layer may be deposited on the surfaces of the support and the actuator to ensure a firm bond between the partially reflective layer and the surfaces of the support and the actuator . The partially reflective layer is patterned and etched such that a first region is formed vertically above the light emitting surface , and connectors are formed coupling the first region to the support . The sacrificial layer is thereafter removed, resulting in a mirror membrane suspended above the light emitting surface and resting on the upper surfaces of the support and the actuator .

[0042] An alternative method of arranging the second partially reflective layer arrangement on the surface of the carrier substrate involves a first step of arranging the actuator on the surface of the carrier substrate , followed by a subsequent step of depositing the support on the surface of the carrier substrate , such that the actuator is between the support and the light emitting surface . A sacrificial layer is then deposited on the surface of the carrier substrate such that the support structure and the actuator are enclosed within the sacrificial layer . The next step involves planarizing the upper surface of the sacrificial layer at least to a depth corresponding to upper surfaces of the support structure and the actuator , such that the upper surfaces of the support structure and the actuator are exposed . An optional adhesive layer may be deposited on the exposed upper surfaces of the support structure and / or the actuator . The second partially reflective layer is thereafter deposited on the surfaces of the sacrificial layer, the support structure and the actuator . In a subsequent step , the partially reflective layer is patterned and etched to form a first region vertically above the light-emitting surface and a connector coupling the first region to the support structure . The sacrificial layer is thereafter removed .

[0043] An alternative method of arranging the partially reflective layer arrangement on the surface of the carrier substrate involves a first step of arranging the actuator on the surface of the carrier substrate adj acent to the light emitting surface . The next step involves depositing a support structure on the surface of the carrier substrate . Optionally, a sacrificial layer may be deposited on the surface of the carrier substrate to enclose the actuator and the support , and subsequently planarized to expose upper surfaces of the support and the actuator . In a subsequent step , a growth substrate , such as Silicon, is provided . The second partially reflective layer is deposited on the growth substrate . Thereafter the second partially reflective layer is patterned and etched to form a first region correspondingly dimensioned to be positioned vertically above the light emitting surface and a connector dimensioned to couple the first region to the support . In a subsequent step , the second partially reflective layer is bonded to the surface of the support layer and the actuator through a wafer bonding process . The growth substrate and, where applicable , the optional sacrificial layer are thereafter removed .

[0044] In other aspects , the second partially reflective layer is deposited on a growth substrate as previously described . Subsequently the actuator is bonded to the surface of the second partially reflective layer . Thereafter the support is deposited on the surface of the second partially reflective layer such that the actuator is laterally positioned between the support and the light emitting surface . The upper surfaces of the support and the actuator are optionally planarized . Through a wafer bonding process , the second partially reflective layer arrangement is bonded to the surface of the carrier substrate , after which the growth substrate is removed . An optional additional step prior to wafer bonding involves depositing a sacrificial layer on the surface of the second partially reflective layer such that the support and the actuator are enclosed within the sacrificial layer and planarizing the sacrificial layer to expose surfaces of the support and the actuator . The second partially reflective layer is thus protected during the wafer bonding process . The sacrificial layer is subsequently removed .

[0045] In other aspects , the proposed method further comprises a step of depositing a third partially reflective layer on a surface of the carrier substrate corresponding to the light emitting surface to form a dual-cavity light emitting device , wherein a first fixed cavity is formed by the first reflective layer and the third partially reflective layer , and a second tunable cavity is formed between the second and third partially reflective layers .

[0046] SHORT DESCRIPTION OF THE DRAWINGS

[0047] Further aspects and embodiments in accordance with the proposed principle will become apparent in relation to the various embodiments and examples described in detail in connection with the accompanying drawings in which :

[0048] Figure 1 shows an optoelectronic arrangement according to the proposed principle ;

[0049] Figure 2 illustrates a detailed view of an optoelectronic arrangement in accordance with some aspects of the proposed principle ;

[0050] Figure 3 illustrates a step in a method of processing an optoelectronic arrangement in accordance with some aspects of the proposed principle ;

[0051] Figures 4A and 4B show plan views of some aspects of the proposed method;

[0052] Figures 5 to 7 illustrate some aspects of the proposed optoelectronic arrangement ;

[0053] Figures 8A and 8B illustrate an aspect related to provision of electrical contact to an optoelectronic arrangement in accordance with some aspects of the proposed principle .

[0054] DETAILED DESCRIPTION

[0055] The following embodiments and examples disclose various aspects and their combinations according to the proposed principle . The embodiments and examples are not always to scale . Likewise , different elements can be displayed enlarged or reduced in size to emphasize individual aspects . It goes without saying that the individual aspects of the embodiments and examples shown in the figures can be combined with each other without further ado , without this contradicting the principle according to the invention . Some aspects show a regular structure or form. It should be noted that in practice slight differences and deviations from the ideal form may occur without , however, contradicting the inventive idea .

[0056] In addition, the individual figures and aspects are not necessarily shown in the correct size , nor do the proportions between individual elements have to be essentially correct . Some aspects are highlighted by showing them enlarged . However , terms such as "above" , "over" , "below" , "under" "larger" , "smaller" and the like are correctly represented with regard to the elements in the figures . So it is possible to deduce such relations between the elements based on the figures .

[0057] Figure 1 illustrates an exemplary optoelectronic arrangement 1 according to the proposed principle . The optoelectronic arrangement 1 comprises a carrier substrate 10 within which an array 20 of light emitting devices 11 , in particular , pLEDs is arranged . A first reflective layer 13 is provided on the backside of each light emitting device , and a first contact surface 15 is connected to the first reflective layer , providing electrical connection to a first doped layer of the light emitting device . The optoelectronic arrangement further comprises a second partially reflective layer 12 arranged in connection with an actuator 16 , wherein an upper surface of the second partially reflective layer 12 rests on a surface of the support 17 . In some aspects , not illustrated herein, the upper surfaces of the actuators may serve as the support . A second contact surface 18 , arranged within the carrier substrate provides electrical contact to a second doped layer of the light emitting device . The first reflective layer 13 and the second reflective layer 12 are separated by a variable distance , said distance defining the length of a resonant optical cavity 14 . The actuator 16 is configured to vary the length of the resonant optical cavity 14 by vertically displacing the second partially reflective layer 12 . The support 17 may be compressible , in particular, where uniform movement of the second partially reflective layer is desired . A more detailed illustration of the features of the light emitting device is shown in Figure 2 . Each light emitting device 11 comprises a first doped layer 111 , an active layer 112 and a second doped layer 113 , wherein a light emitting surface 114 is formed by an upper surface of the second doped layer . In the illustrated embodiment , the second doped layer 113 further comprises a transparent conductive oxide sublayer 113a . A dielectric layer 115 is arranged along the bottom and sidewalls of the light emitting device , and is patterned to allow access to the first doped semiconductor layer 111 from a backside of the light emitting device . The first reflective layer 13 is arranged on a surface of the first doped layer 111 facing away from the active layer 112 to at least partially form the backside of the light emitting device . The first reflective layer comprises any suitably material with high reflectivity, in particular , greater than 95 % , or more particularly, greater than 97% . Examples of suitable materials for visible wavelengths include Ag, Au and Al . An electrical contact surface 15 is connected to the first reflective layer 13 , allowing electrical connection to the first doped layer 111 . A current spreading layer 151 is arranged in contact with the first reflective layer 13 and may optionally comprise the same material as the first reflective layer . The active layer 112 is arranged within a resonant optical cavity 14 defined by the first reflective layer 13 and the movable second partially reflective layer 12 . The second partially reflective layer 12 comprises a DBR layer formed from alternating layers of material 121 , 122 with differing refractive indices .

[0058] Figure 3 illustrates a step in a method for processing an optoelectronic arrangement according to the proposed principle . A carrier substrate 10 comprising an array 20 of light emitting devices 11 is provided . An actuator 16 is arranged on a surface of the carrier substrate adj acent to the light emitting surface 114 . A sacrificial layer 30 is subsequently deposited on the surface of the carrier substrate , enclosing the actuator 16 . The sacrificial layer is patterned and etched to partially expose the carrier substrate , following which the support 17 is deposited on the surface of the carrier substrate . The sacrificial layer is planarized to expose upper surfaces of the support 17 and the actuator 16 . Subsequently the second partially reflective layer 12 is deposited on the upper surface comprising surfaces of the sacrificial layer 30 , the actuator 16 and the support 17 .

[0059] The second partially reflective layer is patterned and etched to form a connector 123 coupling a first region 124 vertically above the light emitting surface to the support 17 , as illustrated in Figures 4A and 4B . The sacrificial layer 30 is thereafter removed, resulting in a suspended reflective membrane formed by the second partially reflective layer 12 , supported peripherally by the support 17 . In some aspects , not illustrated herein, the second partially reflective layer 12 is peripherally supported by the actuator 16 , whereby the step of patterning and etching the second partially reflective layer to form the connector 123 may be eliminated . The connector 123 may be in form of substantially straight , beam-like structures , as illustrated in Figure 4A. In some aspects , the connector is in form of meandering structures , as illustrated in Figure 4B . The connector may attach to the vertices or the sides of the first region 124 of the second reflective layer, as shown in Figures 4A and 4B respectively . The support 17 is shown as a continuous structure enclosing the light emitting surface of the light emitting devices 11 and the actuator 16 . In other aspects , the support comprises different structures , such as pillars , non-contiguous wall-like elements , and so on .

[0060] Figures 4A and 4B additionally illustrate the positioning of actuation elements forming the actuator in accordance with some aspects of the proposed invention . The illustrations show an actuator comprising paired elements 16a, 16b arranged in parallel to each other, wherein a first pair of parallel elements 16a is arranged perpendicular to a second pair of parallel elements 16b, forming a quadrilateral shape surrounding the light emitting devices 11 .

[0061] Additional aspects of the proposed optoelectronic arrangement are partially illustrated in Figures 5 and 6 . In Figure 5 , the light emitting device is configured to form an RC2-LED, characterized by a first cavity 41 and a second cavity 42 overlaid upon each other . The first cavity 41 is formed between the first reflective layer 13 and a third partially reflective layer 40 arranged on the light emitting surface 114 of the light emitting device 11 . The second cavity 42 is formed between the third partially reflective layer 40 and the second partially reflective layer 12 . The third partially reflective layer 40 in the illustrated aspect is implemented as a DBR, with the layer materials and thickness suitably selected depending on the desired emission characteristics . The reflective layer material is however not limited to a DBR, and any suitable partially reflective material may be used .

[0062] In some aspects , the first reflective layer is implemented as a DBR layer . Exemplary embodiments are illustrated in Figures 6 and 7 . In Figure 6 , the first contact surface 15 connected to the first reflective layer 130 and the first doped layer 111 is aligned to the sidewalls of the light emitting device . A passivation layer 115 isolates the first contact surface 15 from the active layer 112 and the second doped layer 113 . A current spreading layer 151 is connected to the first contact surface 151 . The passivation layer 115 additionally isolates the second contact surface 18 , which is connected to the second doped layer 113 through the transparent conductive oxide sublayer 113a .

[0063] Figure 7 illustrates an aspect of the proposed optoelectronic arrangement further comprising a current blocking layer 50 arranged between the first doped layer 111 of the light emitting device and the active layer 112 . The current blocking layer 50 comprises an aperture 51 through which current is channelled within the light-emitting device , thus isolating individual pixels within the semiconductor stack . Optional dielectric layers 115 may be arranged within the semiconductor stack extending from the first doped layer 111 , through the active layer 112 and partially through the second doped layer 113 . The contact surfaces 15 associated with the first doped layer are aligned to the sidewalls of the light emitting device . The second contact surface 18 is in this particular aspect arranged on the light emitting surface 114 of the light emitting device , which is formed by the transparent conductive oxide sublayer 113a .

[0064] Further aspects related to electrical connection of the proposed optoelectronic arrangement are illustrated in Figures 8A and 8B . Contact to the second doped semiconductor layer is achieved through a grid-like contact 180 arranged on the light emitting surface 114 . An access point 18 is located at a peripheral point , arranged in contact with the light emitting surface 114 , which comprises a transparent conductive oxide sublayer . The access point 18 is configured to contact the conductive oxide sublayer 113a from the top side of the carrier substrate , as illustrated by contact 18a , or may be configured to access the transparent conductive oxide sublayer 113a from the bottom side of the carrier substrate , as shown by contact 18b .

[0065] LIST OF REFERENCES

[0066] I optoelectronic arrangement

[0067] 10 carrier substrate

[0068] II light emitting device

[0069] III first doped semiconductor layer

[0070] 112 active layer

[0071] 113 second doped semiconductor layer

[0072] 113a transparent conductive oxide sublayer

[0073] 114 light emitting surface

[0074] 115 dielectric layer

[0075] 12 second partially reflective layer

[0076] 121 , 122 distributed Bragg reflector ( DBR) sublayers

[0077] 123 connector

[0078] 124 first region of second partially reflective layer

[0079] 13 , 130 first reflective layer

[0080] 14 optical cavity

[0081] 15 first contact surface

[0082] 151 current spreading layer

[0083] 16 actuator

[0084] 16a , 16b actuation elements

[0085] 17 support

[0086] 18 , 18a , 18b second contact surface

[0087] 180 contact grid

[0088] 20 pixel array

[0089] 30 sacrificial layer

[0090] 40 third partially reflective layer

[0091] 41 first optical cavity

[0092] 42 second optical cavity

[0093] 50 current blocking layer

[0094] 51 aperture

Claims

CLAIMS1 . Optoelectronic arrangement comprising : a first one light-emitting semiconductor device comprising : a first reflective layer; a first doped layer arranged on a surface of the first reflective layer; an active layer arranged on a surface of the first doped layer facing away from the first reflective layer; a second doped layer arranged on a surface of the active layer facing away from the active layer forming a light emitting surface ; at least one first electrical contact surface arranged in contact with the first reflective layer , and electrically connected to at least one of the doped layers ; a second partially reflective layer arranged at a distance from the light emitting surface ; an actuator in connection with the second partially reflective layer and configured to displace the second partially reflective layer with respect to the first reflective layer ; wherein the actuator comprises two substantially parallel plates , wherein a first one of the two substantially parallel plates is connected on one of :A surface of the second partially reflective second layer facing the light-emitting surfaceA surface of the second partially reflective second layer facing away from the light-emitting surface .2 . Arrangement according to claim 1 , wherein the actuator is a microelectromechanical actuator , in particular , wherein the actuator comprises at least one of : an electrostatic actuator a piezoelectric actuator an electromagnetic actuator an electrothermal actuator .3 . Arrangement according to any of the above claims , further comprising a support arranged laterally displaced from the light emitting surface and connected to the second partially reflective layer ; wherein the support optionally laterally encloses the light emitting surface .4 . Arrangement according to claim 3 , wherein the second partially reflective layer comprises a connector coupling a first region positioned above the light emitting surface with the support , and wherein the connector comprises at least one of :A beam;A spring;A meandering structure .5 . Arrangement according to claim 4 , wherein the connector is monolithically integrated with the second partially reflective layer .6 . Arrangement according to any of the above claims , further comprising a wavelength converter, wherein the wavelength converter is arranged on at least one of :A light emitting surface of the first one light-emitting device ; A surface of the second partially reflective layer .7 . Arrangement according to any of the preceding claims , wherein the actuator comprises at least one first pair of actuating elements and optionally at least one second pair of actuating elements arranged laterally perpendicular to the first pair of actuating elements , positioned such that the light-emitting surface is located between the actuating elements .8 . Arrangement according to any of the preceding claims , wherein the actuator is positioned laterally between the support and the light emitting surface .9 . Arrangement according to any of the preceding claims further comprising at least one second light-emitting device , the at least one second light-emitting device comprising : a first reflective layer; a first doped layer arranged on a surface of the first reflective layer; an active layer arranged on a surface of the first doped layer facing away from the first reflective layer; a second doped layer arranged on a surface of the active layer facing away from the active layer forming a light emitting surface ; at least one first electrical contact surface arranged in contact with the first reflective layer , and electrically connected to at least one of the doped layers ; wherein the second partially reflective layer is arranged to extend laterally above the first one light-emitting device and the at least one second light-emitting semiconductor devices .10 . Arrangement according to claim 9 , wherein the actuator comprises at least one actuating element positioned between at least two lightemitting devices .11 . Arrangement according to any of claims 9 or 10 , wherein the first one light-emitting semiconductor device is configured to emit light of a first wavelength, and wherein at least one second lightemitting semiconductor device is configured to emit light at a second wavelength, wherein the second wavelength is different from the first wavelength .12 . Arrangement according to any of claims 9 to 11 , wherein the at least one second light-emitting device comprises different material and / or a different structure and / or different physical dimensions from the first light-emitting device .13 . Arrangement according to any of claims 9 to 12 , wherein the first one light-emitting device and the at least one second light-emitting device are monolithically integrated, andwherein the first light-emitting device and the at least one second light-emitting device are configured to be independently electrically controllable .14 . Arrangement according to any of claims 9 to 13 , wherein the actuator is configured to produce a substantially uniform displacement of the second partially reflective layer with respect to the first reflective layer of the first light-emitting device and the at least one second light-emitting device .15 . Arrangement according to any of claims 9 to 13 , wherein the actuator is configured to produce a first displacement of the second partially reflective layer with respect to the first reflective layer of the first light-emitting device and at least a second displacement of the second partially reflective layer with respect to the first reflective layer of at least one second light-emitting devices , wherein the first displacement is different from the second displacement .16 . Arrangement according to any of the preceding claims , further comprising a third partially reflective layer arranged on the lightemitting surface , wherein the second partially reflective layer is arranged at a distance from the third partially reflective layer .17 . Arrangement according to any of the preceding claims , wherein at least one of the first reflective layer and / or the second partially reflective layer and / or the third partially reflective layer comprises a distributed Bragg reflector ( DBR) .18 . Arrangement according to any of the preceding claims , wherein the second partially reflective layer comprises a thickness less than 50 pm, in particular , less than 20 pm, in particular less than 5 pm.19 . Method of processing an optoelectronic arrangement , comprising the steps :Providing a carrier substrate comprising at least one lightemitting device , wherein the at least one light-emitting device comprises :a first doped layer; an active layer arranged on a surface of the first doped layer facing away from the carrier substrate ; a second doped layer arranged on a surface of the active layer facing away from the active layer forming a light emitting surface ; a first reflective layer in contact with a surface of the first doped layer of the light-emitting device , said surface of the first doped layer facing away from the light-emitting surface of the light-emitting device ; at least one first electrical contact surface arranged in contact with the first reflective layer , and electrically connected to at least one of the doped layers ;Arranging a second partially reflective layer arrangement on a surface of the carrier substrate , said second partially reflective layer arrangement comprising : a second partially reflective layer configured to be located at a variable vertical distance from the lightemitting surface ; an actuator configured to displace the second partially reflective layer with respect to the first reflective layer of the at least one light-emitting device , wherein the actuator is in contact with the second partially reflective layer .20 . Method according to claim 19 , wherein the step of arranging the second partially reflective layer on the surface of the carrier substrate comprises the steps :Arranging the actuator on an upper surface of the carrier substrate corresponding to the light emitting surface , such that the actuator is laterally adj acent to the light emitting surface ;Depositing a sacrificial layer on the upper surface of the carrier substrate ;Etching through the sacrificial layer and depositing a support , such that the support is in contact with a surface of the carrier substrate , wherein the sidewalls of the support are laterally adj acent to the light-emitting surface and the actuator, andoptionally laterally enclose and / or surround the light-emitting surface and the actuator;Planarizing the sacrificial layer such that upper surfaces of the support and the actuator are exposed;Depositing the second partially reflective layer on the upper surfaces of the sacrificial layer, the actuator and the support ;Patterning and etching the partially reflective layer to form a first region vertically above the light-emitting surface and a connector coupling the first region to the support ;Removing the sacrificial layer .21 . Method according to claim 19 , wherein the step of arranging the second partially reflective layer arrangement on the surface of the carrier substrate comprises the steps :Arranging the actuator on an upper surface of the carrier substrate corresponding to the light emitting surface , such that the actuator is laterally adj acent to the light emitting surface ;Depositing a support on the upper surface of the carrier substrate laterally adj acent to the light-emitting surface and the actuator, wherein the sidewalls of the support structure optionally laterally enclose and / or surround the light-emitting surface and the actuator;Depositing a sacrificial layer on the surface of the carrier substrate such that the support and the actuator are enclosed within the sacrificial layer ;Planarizing the sacrificial layer such that upper surfaces of the support and the actuator are exposed;Depositing the second partially reflective layer on the upper surfaces of the sacrificial layer and the support ;Patterning and etching the partially reflective layer to form a first region vertically above the light-emitting surface and a connector coupling the first region to the support ;Removing the sacrificial layer .22 . Method according to claim 19 , wherein the step of arranging the second partially reflective layer arrangement on the surface of the carrier substrate comprises the steps :Arranging the actuator on an upper surface of the carrier substrate corresponding to the light emitting surface , such that the actuator is laterally adj acent to the light emitting surface ;Depositing a support on the surface of the carrier substrate laterally adj acent to the light-emitting surface , wherein the sidewalls of the support optionally laterally enclose and / or surround the light-emitting surface and the actuator ;Providing a growth substrate ;Depositing the second partially reflective layer on a surface of the growth substrate ;Patterning and etching the partially reflective layer to form a first region vertically above the light-emitting surface and a connector coupling the first region to the support ;Bonding the second partially reflective layer arrangement to the surface of the support and the actuator through a wafer bonding process ;Removing the growth substrate .23 . Method according to claim 19 , wherein the step of arranging the second partially reflective layer arrangement on the surface of the carrier substrate comprises the steps :Providing a growth substrate ;Depositing the second partially reflective layer on a surface of the growth substrate ;Patterning and etching the partially reflective layer to form a first region corresponding to the light-emitting surface and a connector coupling the first region to a second region corresponding to a support ;Arranging the actuator on an upper surface of the second partially reflective layer;Depositing the support on the surface of the second partially reflective layer laterally adj acent to the actuator;Bonding the second partially reflective layer arrangement to the surface of the carrier substrate through a wafer bonding process ;Removing the growth substrate .24 . Method according to claim 22 , wherein a sacrificial layer is arranged on an upper surface of the carrier substrate prior to the wafer bonding process such that the upper surface of the sacrificial layer is substantially coplanar with an upper surface of the support and the actuator , and wherein the sacrificial layer is removed after the wafer bonding process .25 . Method according to claim 23 , wherein a sacrificial layer is arranged on an upper surface of the second partially reflective layer prior to the wafer bonding process such that the upper surface of the sacrificial layer is substantially coplanar with an upper surface of the support and the actuator , and wherein the sacrificial layer is removed after the wafer bonding process .26 . Method according to any of claims 22 or 23 , wherein an adhesive layer is deposited on the exposed surface of the actuator and / or the support prior to the wafer bonding process .27 . Method according to any of the preceding claims 19 to 26 , further comprising a step of depositing a third partially reflective layer on an upper surface of the carrier substrate corresponding to the light emitting surface of the at least one light-emitting device .

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