Light emitting device with at least one sacrificial quantum well

Abstract

The invention concerns a light emitting device, in particular µLED, comprising a semiconductor layer stack of at least a first layer of a first conductivity type, a second layer of a second conductivity type, an active region comprising at least one quantum well arranged between the first and the second layer and being configured to emit light of a first wavelength, and at least one first sacrificial quantum well arranged adjacent to the active region between the active region and the second layer. The semiconductor layer stack comprises a top surface, a bottom surface opposite the top surface and at least one side surface extending from the top surface into the direction of the bottom surface and extending through at least the second layer, the at least one first sacrificial quantum well and the active region. The at least one first sacrificial quantum well thereby comprises a larger effective bandgap than the at least one quantum well of the active region. In addition, at least one regrowth layer, in particular of the second conductivity type, is arranged on the at least one side surface.

Description

[0001] LIGHT EMITTING DEVICE WITH AT LEAST ONE SACRIFICIAL QUANTUM WELL

[0002] The present application claims priority from German patent application DE 10 2024 100 920 . 9 filed on January 12 , 2024 , the disclosure of which is incorporated by way for reference in its entirety .

[0003] The present invention concerns a light emitting device (LED ) , in particular pLED, with at least one sacrificial quantum well as well as a method for manufacturing the same .

[0004] BACKGROUND pLEDs are optoelectronic devices that comprise a lateral dimension in the range from a few pm to about 40 pm. Such devices provide a variety of different applications , including but not limited to displays .

[0005] In order to increase the external quantum efficiency ( EQE ) of for example pLEDs , or more general light emitting nanostructures , one can engineer the geometry, shape and surroundings (passivation, reflective mirror, ...) of the pLEDs in a way that the light extraction efficiency (LEE ) in a specific solid angle is maximized . Apart from the LEE the internal quantum efficiency ( IQE ) is as important , where a main loss factor originates from non-radiative recombination (NRR) of charge carriers within the pLED .

[0006] In particular pLEDs based on an InGaAlP material system suffer from decreasing performance with smaller size . A reason for this efficiency drop can be NRR of inj ected charge carriers at etched surfaces . For example , etching is a common and standard process for pixel etching ( etching through the active region and physical separation of individual pixels ) , that introduces damage to the surface and underlying layers dependent on the specific process and parameters used . Damage in this case means the creation of defect centres in the crystal lattice of the etched structure . Defects created on the surface and below of the active region - which is exposed during and after pixel etching - act as non-radiative recombination channels which in combination with NRR occurring anyhow for some material systems at the outer surfaces of the pLED dramatically reduce the IQE of the pLED leading to a bad overall performance . This effect is particularly pronounced for the InGaAlP material system due to its high charge carrier diffusion length and surface recombination velocities , as well as Fermi level pinning at the semiconductor surface . Especially for small pixels such as for the case of pLEDs with a high surface-to- volume ratio , in particular a high ratio of the exposed active region surface on the pixel ' s sidewall vs . the total active region volume , this is a maj or challenge .

[0007] To reduce non-radiative recombination at the edges of a pLED, a possible approach is a passivation of the pLED surface by, e . g . , dielectrics . However , by this the performance cannot be improved significantly and in a desired way . A further approach to reduce non-radiative recombination at the side surfaces of a pLED is to keep the charge carriers away from the side surfaces which comprise the non-radiative recombination centres . This can for example be done by quantum well intermixing the active regions in areas along the side surfaces of the pLED by means of which a respective dopant is diffused into the vicinity of the active region causing the bandgap of the active region along the side surfaces to enlarge due to intermixing processes . By this , charge carriers can be kept away from the side surfaces which comprise the non-radiative recombination centres . However, such an approach is limited for pLED sizes larger than several micrometres , as the intermixing resolution is insufficient for pLEDs in the micrometre size .

[0008] Another approach is a so-called epitaxial regrowth . After a first epitaxially growth step, including the active region, the epitaxially grown layers including the active region are structured and locally etched away where the later pLED side surfaces will be formed . This etching is realized ex-situ by dry or wet etching , or in-situ by Cl- containing vapor within the epi reactor . Using this approach, structured active regions in the micrometre range are possible . Then, a second epitaxially growth step with higher bandgap material is conducted over the whole structure , leading to an overgrowth of the non-etched islands as well as the etched regions . By this , some of the defects at the etched surface are passivated due to the similarity of the materials comprised in the active region and the regrown layers . Furthermore , like in the intermixing approach, charge carriers are blocked by high energy barriers to prevent diffusion to the pixel side surfaces . However , especially the etching process involves problems due to different layer compositions of the pLEDs showing different etching behaviour , which can lead to different etch slopes and kinks along the sensitive side surfaces of the etched pLEDs . During regrowth, this typically leads to crystal defects originating at the regrowth interface or close to it , thus potentially contributing to performance drops . Particularly, due to the different etching slopes , planar defect ( s ) such as 2D defect ( s ) can be generated in the active region creating NRR and reducing the internal quantum efficiency ( IQE ) of the pLEDs . In particular , defects located at the etched side surfaces of the quantum wells create NRRs that reduce the internal quantum efficiency of the pLEDs since the carrier densities are particularly high there .

[0009] Despite all the efforts , a change in the etching behavior has however not been achieved yet .

[0010] It is thus an obj ect of the present application to provide an LED which overcomes at least some of aforementioned aspects , as well as to provide a method for manufacturing such an LED .

[0011] SUMMARY OF THE INVENTION

[0012] 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 .

[0013] This invention targets a new approach . Instead of changing the etching behavior, the idea is to change the position of the 2D defect ( s ) in the semiconductor layer stack of a light emitting device , in particular pLED . In particular the invention is based on the incorporation of a sacrificial quantum well (QW) into the semiconductor layer stack of a pLED to move the 2D defect ( s ) away from the active region . The 2D defect ( s ) will then be generated in the sacrificial QW but not the active region thereby increasing the IQE of the pLED . The sacrificial quantum well thereby differs from the active region and in particular from a quantum well of the active region in that that it comprises a larger effective bandgap . As a result of the higher bandgap, under current inj ection, the carrier densities in the sacrificial QW are kept very low and no significant recombination takes place in them. Not least because of this , the sacrificial quantum layer is compared to the active region configured to not cause any carrier recombination such that NRR centres in the sacrificial quantum layer do not cause significant efficiency loss of the pLED .

[0014] Advantages that may result from the proposed concept can be a reduction of defects close to the active region, less NRR in the active region, and thus a better brightness of the light emitting device due to a better IQE .

[0015] According to a first aspect , a light emitting device , in particular pLED, comprising a semiconductor layer stack is provided . The semiconductor layer stack comprises at least a first layer of a first conductivity type , a second layer of a second conductivity type as well as an active region comprising at least one quantum well arranged between the first and the second layer . The active region is thereby configured to emit light of a first wavelength . In particular the active region of the semiconductor layer stack comprises at least one quantum well , however the active region can also comprise a multi quantum well structure comprising several quantum wells .

[0016] The semiconductor layer stack comprises a top surface , a bottom surface opposite the top surface and at least one side surface extending from the top surface into the direction of the bottom surface . The at least one side surface thereby in particular comprises at least the second layer , the active region and the at least one first sacrificial quantum well . For example the at least one side surface can result from a step of structuring the semiconductor layer stack thereby removing a portion of the semiconductor layer stack and remaining another portion of the semiconductor layer stack . The at least one side surface can be a therefrom resulting side surface of the remained portion . In particular the at least one side surface can result of an etching step for structuring the semiconductor layer stack resulting in an etched side surface extending at least through the second layer, the at least one first sacrificial quantum well and the active region .

[0017] The light emitting device further comprises at least one regrowth layer , in particular of the second conductivity type , arranged on the at least one side surface . By means of the regrowth layer defects created at the side surface can be passivated due to the similarity of the materials comprised in the active region and the regrown layers . In addition, by means of the regrowth layer charge carriers can be blocked by high energy barriers to prevent diffusion to the side surfaces .

[0018] Further , the semiconductor layer stack comprises at least one first sacrificial quantum well arranged adj acent to the active region between the active region and the second layer . The at least one first sacrificial quantum well thereby comprises a larger effective bandgap than the at least one quantum well of the active region .

[0019] By means of the term "quantum well" a potential well with discrete energy values is to be understood . One of the simplest quantum well systems can be constructed by inserting a thin layer of one type of semiconductor material between two layers of another with a different bandgap . An example can be two layers of for example InGaAlP with a large bandgap surrounding a thin layer of InGaP with a smaller bandgap . Since the bandgap of the contained material is lower than the surrounding InGaAlP, a quantum well (potential well ) is created in the InGaP region . This change in band energy across the structure can be seen as a change in the potential that a carrier would feel , therefore low energy carriers can be trapped in these wells . Within the quantum well , there are discrete energy eigenstates that carriers can have . For example , an electron in the conduction band can have lower energy within the well than it could have in the InGaAlP region of this structure . Consequently, an electron in the conduction band with low energy can be trapped within the quantum well . Similarly, holes in the valence band can also be trapped in the top of potential wells created in the valence band .

[0020] By means of the term "effective" bandgap, the bandgap of the respective quantum well , layer, or sublayer in terms of the energy difference between the lowest electron and hole bound states ( sometimes called ground states ) is to be understood . The effective bandgap can for example be determined by the bulk bandgap of the material of the quantum well and the potential profile of the quantum well ( depth, thickness , composition gradings , ...) . For example , in a thinner quantum well , the ground states shift to higher energies above the bottom of the well potential and thus the "effective bandgap" increases .

[0021] By means of the term "sacrificial" quantum well a quantum well is to be understood that is conf igured / designed to not cause any carrier recombination when using the light emitting device as intended . This means that the sacrificial quantum well is conf igured / designed to not cause radiative nor non radiative recombination . In particular the sacrificial quantum wells can comprise a different material composition than QWs of the active region so that their effective bandgap is larger . In addition or as an alternative , the the sacrificial quantum wells can comprise a different thickness than QWs of the active region and in particular a thickness that is such small that its effective bandgap increases to such an extent that carriers will preferentially stay away from it . At the same time the presence of the sacrificial QWs does however not hinder carriers from reaching the QWs of the active region .

[0022] According to some aspects , the semiconductor layer stack is of an InGaAlP or InGaAlAs material system . For example the semiconductor layer stack can be of an Al and / or In containing semiconductor material system. For example , the semiconductor layer stack can be of a material system comprising Indium ( In) and Aluminium (Al ) and Gallium ( Ga ) and Arsenide (As ) and / or Phosphide ( P ) . The semiconductor layer stack can however also be also of any other semiconductor material system .

[0023] According to some aspects , the active region comprises a multi quantum well structure . The quantum wells can thereby be substantially equal in size and / or composition, can however also vary between each other . The at least two quantum wells can for example comprise a substantially equal effective bandgap and can in particular be configured to emit light of a substantially equal wavelength .

[0024] According to some aspects , the semiconductor layer stack comprises more than one first sacrificial quantum well arranged between the active region and the second layer . In particular one or a number of the first sacrificial quantum wells are arranged directly adj acent to the active region and optionally one or some other sacrificial quantum wells are arranged between other layers of the semiconductor layer stack between the active region and the second layer . In all cases it can be desired that the first sacrificial quantum wells are conf igured / designed to not cause any or at least only little carrier recombination when using the light emitting device as intended .

[0025] According to some aspects , the at least one first sacrificial quantum well comprises a doping of the second conductivity type . In particular the at least one first sacrificial quantum well or QWs can be doped in the way the second layer is . This can further supress any unwanted residual recombination within the sacrificial quantum well or QWs . For example , the first sacrificial quantum well or QWs can be doped using Mg .

[0026] According to some aspects , the light emitting device further comprises at least one second sacrificial quantum well arranged adj acent to the active region between the active region and the first layer . The at least one second sacrificial quantum well thereby comprises a larger effective bandgap than the at least one quantum well of the active region . In particular the at least one second sacrificial quantum well can compared to the at least one first sacrificial quantum well be arranged on the other side of the active region and can as the at least one first quantum well be conf igured / designed to not cause any or at least only little carrier recombination when using the light emitting device as intended . According to some aspects , the at least one second sacrificial quantum well comprises a doping of the first conductivity type . In particular the at least one second sacrificial quantum well or QWs can be doped in the way the first layer is . This can further supress any unwanted residual recombination in the second sacrificial quantum well or QWs .

[0027] According to some aspects , the thickness of the at least one first and / or second sacrificial quantum well is smaller than the thickness of the at least one quantum well of the active region, in particular by a factor of 2 . According to some aspects , the at least one first and / or second sacrificial quantum well ( s ) comprise a thickness of less than 10 nm, in particular less than 5 nm, or less than 3 nm, or less than 2 nm . Such a thickness increases the effective bandgap of the sacrificial quantum well ( s ) to such an extent that carriers will preferentially stay away from it . At the same time the presence of the sacrificial QWs does however not hinder carriers from reaching the QWs of the active region .

[0028] In particular the first and / or second sacrificial QW can have different thickness and / or material composition than the QW ( s ) of the active region so that their effective bandgap is larger . In particular , the thickness of the sacrificial QW ( s ) is smaller than that of the QW ( s ) of the active region . As a result of the higher bandgap, under current inj ection, the carrier densities in the sacrificial QW ( s ) are kept low and no significant recombination takes place in them.

[0029] According to some aspects , the at least one side surface comprises at least a first and a second side surface portion with a different slope , wherein the slope changes in the area of the at least one first sacrificial quantum well .

[0030] Especially an etching process , for example wet etching process , for structuring the semiconductor layer stack can involve problems due to different layer compositions of the semiconductor layer stack showing different etching behaviour , which can lead to different etch slopes and kinks along the side surfaces of the etched semiconductor layer stack . In particular a change from the material of the second layer to the active region can lead to different etch slopes and kinks along the side surfaces of the etched semiconductor layer stack . These different etch slopes and kinks can result in planar defect ( s ) such as 2D defect ( s ) generated in the active region creating NRR and reducing the internal quantum efficiency of the later light emitting device . By now introducing a first sacrificial quantum well between the active region and the second layer , the change of material can be shifted away from the active region and a slope change and thus kink of / in the side surface can be moved to the first sacrificial quantum well . Although planar defect ( s ) such as 2D defect ( s ) can still be generated at the side surfaces , these will now at least mostly occur in the area of slope change and thus in the area of the first sacrificial quantum well . As the first sacrificial quantum well is at the same time anyhow conf igured / designed to not cause any or at least only little carrier recombination the defects cause no further harm in reducing the IQE of the later light emitting device .

[0031] According to some aspects , the at least one side surface comprises a third side surface portion with the second side surface portion being arranged between the first and second side surface portion . The third side surface portion comprises a different slope than the second side surface portion and the slope between the second and third side surface portion changes in the area of the at least one second sacrificial quantum well .

[0032] In particular a change from the material of the first layer to the active region can also lead to different etch slopes and kinks along the side surfaces of the etched semiconductor layer stack . These different etch slopes and kinks can again result in planar defect ( s ) such as 2D defect ( s ) generated in the active region creating NRR and reducing the internal quantum efficiency of the later light emitting device . By now introducing a second sacrificial quantum well between the active region and the first layer , the change of material on the other side of the active region can be shifted away from the active region and a slope change and thus kink of / in the side surface can be moved to the second sacrificial quantum well . Although planar defect ( s ) such as 2D defect ( s ) can still be generated at the side surfaces , these will now at least mostly occur in the area of slope changes and thus in the area of the first and second sacrificial quantum well . As the first and second sacrificial quantum well are at the same time anyhow conf igured / designed to not cause any or at least only little carrier recombination, the defects cause no further harm in reducing the IQE of the later light emitting device .

[0033] According to some aspects , a defect density of the semiconductor layer stack at the at least one side surface is higher in the area of the at least one first sacrificial quantum well than in the area of the active region . In addition or as an alternative , a defect density of the semiconductor layer stack at the at least one side surface is higher in the area of the at least one second sacrificial quantum well than in the area of the active region . In particular the first and / or second sacrificial quantum well are respectively placed where defects are observed during for example a subsequent regrowth process covering the at least one side surface of the semiconductor layer stack . In many cases these defects are originated due to a change of slope within the at least one side surface caused by a structuring of the semiconductor layer stack using for example wet etching . However, the defects can also result from different material compositions at the interface between adj acent layers of the semiconductor layer stack due to mass transport during a subsequent regrowth process covering the at least one side surface of the semiconductor layer stack . These defects can then be directly at the regrowth interface to the at least one side surface or close to it .

[0034] According to some aspects , the at least one first sacrificial quantum well comprises a first sublayer with a first bandgap arranged between two second sublayers with a second bandgap larger than the first bandgap . Further the at least one quantum well of the active region comprises a third sublayer with a third bandgap arranged between two fourth sublayers with a fourth bandgap larger than the third bandgap . One of the second layers is thereby arranged directly adj acent to one of the fourth layers . By this in particular the structure of the quantum wells is defined each having a larger bandgap material enclosing a smaller bandgap material forming aforementioned potential well . According to some aspects , the adj acent second and fourth sublayer of the first sacrificial quantum well and the at least one quantum well of the active region comprise a substantially equal bandgap and in particular a substantially equal material composition . In particular the adj acent second and fourth sublayer of the first sacrificial quantum well and the at least one quantum well of the active region can be the same layer of the same material only being virtually divided into the second and fourth sublayer .

[0035] According to some aspects , the adj acent second and fourth sublayer of the first sacrificial quantum well and the at least one quantum well of the active region comprise a total thickness of less than 10 nm, in particular less than 5 nm, or less than 3 nm, or less than 2 nm . Such a thickness allows good transport of charge carriers through the second and fourth sublayer . By this , we the capture of carriers within the sacrificial quantum well ( s ) as well as a subsequent recombination can be minimized .

[0036] According to some aspects , the active region, the at least one first sacrificial quantum well , and the optional at least one second sacrificial quantum well are arranged between a first and a second barrier layer . According to some aspects , the active region, the at least one first sacrificial quantum well , and the optional at least one second sacrificial quantum well are arranged between a first and a second cladding layer . These cladding layers can further also be arranged between aforementioned first and a second barrier layer .

[0037] The barrier layer ( s ) and the cladding layers ( s ) can for example be undoped layers an can comprise a thickness between 200 nm and a few tens of nm . The main reasons of the cladding and the barrier layer is to reduce a doping of the active region with the first and / or second conductivity type . In particular a dif f usion / segregation of the doping of the first and / or second conductivity type from the first and / or second layer or from contact layers arranged on the first and second layer can be prevented by means of the barrier layer ( s ) and / or cladding layer ( s ) . The barrier layer ( s ) can for example be provided with the highest band gap material in the system . The cladding layer ( s ) can for example be provided with the same material as the barrier ( s ) of the QWs . A purpose of the high bandgap material in the barrier layer ( s ) can for example be to avoid minority carrier leakage out of the active region .

[0038] According to some aspects , the regrowth layer is of the second conductivity type . By means of the regrowth layer some of the defects created at the etched surface are passivated due to the similarity of the materials comprised in the active region and the regrown layers . In addition, by means of the regrowth layer charge carriers can be blocked by high energy barriers to prevent diffusion to the side surfaces . Therefore , the regrowth layer is in particular of the second conductivity type electrically coupled to a potential applied to the second layer . By this NRR can further be reduced within the active region .

[0039] Defects , in particular planar defects such as 2D defects , within the regrowth layer can in particular exist mostly close to or in the vicinity of the sacrificial quantum well ( s ) . This can in particular be desired as less defects existing close to or in the vicinity of the active region result in less NRR within the active region .

[0040] According to some aspects , the at least one regrowth layer comprises a sublayer of the material of the second layer and / or a sublayer of the material of a second barrier layer arranged between the active region and the second layer . In particular the sublayers can each be connected to the second layer and / or the second barrier layer respectively thereby connecting the regrowth layer to the same potential as applied to the second layer .

[0041] According to some aspects , the first conductivity type is a n-type and the second conductivity type is a p-type . The first layer can thus be a n-type semiconductor layer and the second layer can be a p-type semiconductor layer .

[0042] According to some aspects , the light emitting device further comprises a first contact layer arranged on the first layer and / or a second contact layer arranged on the second layer . In particular the first contact layer can be electrically conductive n-type contact layer, whereas the second contact layer can be electrically conductive p-type contact layer . The first and second contact layer can thereby of the same material system as the semiconductor layer stack but can also be contact layers comprising a metal and / or a transparent conductive oxide (TCO ) such as for example indium tin oxide ( ITO ) . By means of the first and second contact layer a first and a second potential can be applied to the light emitting device to operate the light emitting device in a desired manner .

[0043] The light emitting device can in particular be a small light emitting component / element such as a small LED or pLED . A pLED can in particular be a very small LED with edge lengths down to 40 pm, down to 10 pm, down to 5 pm or even less . Such small LEDs can be free of a growth substrate and require a special handling and processing to improve their IQE and light outcoupling efficiency .

[0044] According to a further aspect , a method for manufacturing a light emitting device is provided . The method can in particular be a method for manufacturing a light emitting device according to at least some of aforementioned aspects . Hence all aspects already described for the light emitting device can in the same way be applied to the method for manufacturing the same .

[0045] The method comprises at least the following step :

[0046] Providing on a growth substrate a semiconductor layer stack of at least :

[0047] - a first layer of a first conductivity type

[0048] - a second layer of a second conductivity type

[0049] - an active region comprising at least one quantum well arranged between the first and the second layer and being configured to emit light of a first wavelength

[0050] - at least one first sacrificial quantum well arranged adj acent to the active region between the active region and the second layer wherein the at least one first sacrificial quantum well comprises a larger effective bandgap than the at least one quantum well of the active region;

[0051] Structuring the semiconductor layer stack thereby remaining at least one first portion of the semiconductor layer stack and removing a second portion of the semiconductor layer stack adj acent to the at least one first portion, resulting in at least one exposed side surface of the at least one first portion comprising at least the second layer , the at least one first sacrificial quantum well layer and the active region; and

[0052] Regrowing at least one regrowth layer in particular of the second conductivity type , on the at least one side surface .

[0053] According to some aspects , the step of structuring comprises a step of mesa etching the semiconductor layer stack, in particular using a wet chemical etchant , resulting in the at least one side surface comprising at least a first and a second side surface portion with a different slope . The slope in particular changes in an area of the at least one first sacrificial quantum well .

[0054] SHORT DESCRIPTION OF THE DRAWINGS

[0055] 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

[0056] Figures 1A to ID show steps of a method for manufacturing a light emitting device in accordance with some aspects of the proposed principle ;

[0057] Figure 2 shows another embodiment of a step of a method for manufacturing a light emitting device in accordance with some aspects of the proposed principle ; Figure 3 shows an embodiment of a light emitting device some in accordance with some aspects of the proposed principle ;

[0058] Figure 4 shows a further embodiment of a light emitting device some in accordance with some aspects of the proposed principle ; and

[0059] Figure 5 shows a diagram of the bandgap of layers of an embodiment of a light emitting device with regard to its cross section in accordance with some aspects of the proposed principle .

[0060] DETAILED DESCRIPTION

[0061] 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 .

[0062] 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 . The term "semiconductor layer stack" used in the following description may include any semiconductor-based structure that has a semiconductor surface . The layer stack is to be understood to include doped and undoped semiconductors , epitaxial semiconductor layers , possibly supported by a base , and further semiconductor structures . For example , several layers made of a semiconductor material may be grown on a growth substrate made of another semiconductor material or of an insulating material , for example , on a sapphire substrate . Depending on the intended use , the semiconductor may be based on a direct or an indirect semiconductor material . Examples of semiconductor materials particularly suited for generating electromagnetic radiation include , in particular , nitride semiconductor compounds through which, for example , ultraviolet , blue or longer-wave light may be generated, such as GaN, InGaN, AIN, AlGaN, AlGalnN, AlGalnBN, phosphide semiconductor compounds , through which, for example , green or longer-wave light may be generated, such as GaAsP, AlGalnP , GaP, AlGaP, as well as other semiconductor materials such as AlGaAs , SiC , ZnSe , GaAs , ZnO, Ga2O3, diamond, hexagonal BN, and combinations of the materials mentioned . The stoichiometric ratio of the compound semiconductor materials may vary . Further examples of semiconductor materials may include silicon, silicon germanium and germanium. In the context of the present description, the term "semiconductor" also includes organic semiconductor materials .

[0063] The terms "lateral" and "horizontal" , as used in this description, are intended to describe an orientation or alignment which runs essentially parallel to a top surface of the semiconductor layer stack . The horizontal direction may, for example , lie in a plane perpendicular to a direction of growth when layers are grown on .

[0064] The term "vertical" , as used in this description, is intended to describe an orientation which is essentially perpendicular to the top surface of the semiconductor layer stack . The vertical direction may, for example , correspond to a direction of growth when layers are grown on . To the extent that the terms "have" , "contain" , "comprise" , "include" and the like are used herein, they are open-ended terms that indicate the presence of said elements or features , but do not rule out the presence of other elements or features . The indefinite articles and the definite articles include both the plural and the singular , unless the context clearly indicates otherwise .

[0065] Figures 1A to ID show steps of a method for manufacturing a light emitting device 1 in accordance with some aspects of the proposed principle . In a first step , shown in Figure 1A, a semiconductor layer stack 2 is provided on a growth substrate 15 . Between the semiconductor layer stack 2 and the growth substrate 15 an additional buffer layer 14 is arranged to counteract stresses / strains that may be present during the growth of the semiconductor layer stack 2 on the growth substrate 15 .

[0066] The semiconductor layer stack 2 comprises , arranged on the buffer layer 14 in the following order, a first layer 3 of a first conductivity type , a first cladding layer 13a, a first barrier layer 7a , an active region 5 comprising one or more quantum wells , a first sacrificial quantum well 10a , a second cladding layer 13b, a second barrier layer 7b of a second conductivity type and a second layer 4 of the second conductivity type .

[0067] The first conductivity type is thereby in particular an n-type and the second conductivity type is a p-type . The first layer 3 can thus be a n-type semiconductor layer and the second layer 4 can be a p-type semiconductor layer .

[0068] The active region 5 and in particular the quantum well ( s ) included therein can in particular be configured to emit light of a first wavelength when provided with a respective current supply whereas the first sacrificial quantum well 10a can in particular be conf igured / designed to not or substantially not cause any carrier recombination . This can in particular be achieved by that the first sacrificial quantum well 10a comprises a larger effective bandgap than the quantum well ( s ) of the active region 5 and by choosing the material and / or the thickness of the first sacrificial quantum well 10a such that no or substantially no carrier recombination takes place when powering the semiconductor layer stack .

[0069] In a further step, shown in Figure IB, the semiconductor layer stack 2 is structured thereby remaining a first portion 17a of the semiconductor layer stack 2 and removing a second portion 17b of the semiconductor layer stack 2 adj acent to the first portion 17a . This structuring results in exposed side surfaces 11c of the first portion 17a each comprising the second layer 4 , the second barrier layer 7b , the second cladding layer 13b , the first sacrificial quantum well layer 10a , the active region 5 and a portion of the first cladding layer 13a .

[0070] The structuring in particular comprises a step of mesa etching the semiconductor layer stack 2 using a wet chemical etchant , resulting in the side surfaces 11c comprising a first and a second side surface portion 12a , 12 with a different slope . This can in particular result from different layer compositions of the semiconductor layer stack 2 showing different etching behaviour , which can lead to different etch slopes and kinks along the side surfaces 11c . The sacrificial quantum well layer 10a is therefore configured and placed such that the slope of the first and a second side surface portions 12a, 12 changes in an area of the first sacrificial quantum well 10a . These different etch slopes can in particular result in planar defect ( s ) such as 2D defect ( s ) . However as these defect ( s ) will now at least mostly occur in the area of slope change and thus in the area of the first sacrificial quantum well the defects cause no further harm in reducing the IQE of the later light emitting device .

[0071] In a further step , shown in Figure 1C, a regrowth layer 16 is grown on the side surfaces 11c . By means of the regrowth layer 16 some of the defects left in the non etched island can be passivated and charge carriers can be blocked by high energy barriers to prevent diffusion to the side surfaces 11c . Therefore , the regrowth layer 16 is in particular of the second conductivity type electrically connected to a potential applied to the second layer 4 . By this NRR can further be reduced within the active region . In the embodiment shown, the regrowth layer comprises a sublayer of the material of the second barrier layer 7b covering the side surfaces 11c as well as a sublayer of the second layer 4 covering the underlying structure .

[0072] In a further step, shown in Figure ID, a contact layer 9 is provided on the underlying structure , in particular a contact layer 9 of a semiconductor material of the second conductivity type . The contact layer 9 can in particular act as a current spreading layer for a potential applied to a later on the contact layer 9 provided contact element .

[0073] Figure 2 shows another embodiment of a step of a method for manufacturing a light emitting device 1 in accordance with some aspects of the proposed principle . According to Figure 2 the side surfaces 11c do not comprise side surface portions with a changing slope but due to other reasons an increased defect density in the area where the first sacrificial quantum well 10a is placed . In particular these defects can occur on the side surfaces 11c even without the first sacrificial quantum well 10a and the first sacrificial quantum well 10a is used as a sacrificial layer to include these defects at its side surfaces . As these defect ( s ) will now at least mostly occur in the area of the first sacrificial quantum well 10a the defects cause no further harm in reducing the IQE of the later light emitting device , as the first sacrificial quantum well 10a is anyhow configured not to cause any carrier recombination in first place .

[0074] For all embodiments shown in aforementioned Figures it should be understood that these are not limited to the structure shown nor are they limited to only one first portion 17a of the semiconductor layer stack 2 remained after structuring . The structure shown is rather to be understood as exemplary and can vary in any other possible way as well as can be extended to several remained first portions 17a forming several light emitting devices 1 at a later point of the manufacture . Figures 3 and 4 now show embodiments of a light emitting device 1 in accordance with some aspects of the proposed principle that can result from aforementioned steps .

[0075] Therefore , the growth substrate as well as the buffer layer has been removed exposing a bottom surface 11b of the semiconductor layer stack . Then individual pixels / light emitting devices have been separated by cutting through the remained continuous portions of the first layer 3 , the first barrier layer 7a and the first cladding layer 13a . Then a passivation layer 20 covering the regrowth layer 16 , the contact layer 9 as well as the exposed side surfaces of the first layer 3 , the first barrier layer 7a and the first cladding layer 13a has been provided as well as a current spreading layer 19 has been provided on the bottom surface 11b . Lastly a first and a second contact element 18a , 18b has been provided on the current spreading layer 19 and in an opening of the passivation layer contacting the contact layer 9 respectively for being able to provide a first and a second potential to power the resulting light emitting device .

[0076] Due to the arrangement of the first sacrificial quantum well 10a adj acent to the active region 5 between the second layer 4 and the active region 5 and in case of figure 4 also the arrangement of a second sacrificial quantum well 10b adj acent to the active region 5 between the first layer 3 and the active region 5 , defects at the side surfaces 11c of the semiconductor layer stack 2 at least mostly occur in the area ( s ) of the first and optionally second sacrificial quantum well 10a , 10b . As the first and optional second sacrificial quantum well 10a , 10b are however anyhow configured not to cause any carrier recombination in first place the defects cause no further harm in reducing the IQE of the light emitting device 1 .

[0077] Figure 5 shows a diagram of the bandgap of layers of an embodiment of a light emitting device 1 with regard to its cross section in accordance with some aspects of the proposed principle . In particular Figure 5 shows a diagram of the bandgap of a first sacrificial quantum well 10a arranged between an active region 5 comprising exemplary three quantum wells 6a , 6b, 6c . As can be seen from the diagram the effective bandgap of the first sacrificial quantum well 10a is larger than the effective bandgap of the quantum wells 6a , 6b, 6c of the active region 5 . Not only by this a carrier recombination within the first sacrificial quantum well 10a is suppressed . In addition, the thickness dl of the first sacrificial quantum well 10a is chosen such that it is small than the thickness d2 of the quantum wells 6a, 6b, 6c of the active region 5 . In particular the thickness dl of the first sacrificial quantum well 10a is less than 10 nm, in particular less than 5 nm, or less than 3 nm. Such a thickness allows good carrier transport and minimizes carrier capture and recombination in the first sacrificial quantum well 10a .

[0078] The first sacrificial quantum well 10a as well as the quantum wells 6a, 6b , 6c of the active region 5 each comprise sublayers with a larger bandgap enclosing a layer with a smaller bandgap forming a potential well . In case of the first sacrificial quantum well 10a two second sublayers 8b with a larger bandgap enclose a first sublayer 8a with a smaller bandgap, whereas in case of the quantum wells 6a , 6b, 6c of the active region 5 these each comprise two fourth sublayers 8d with a larger bandgap enclose a third sublayer 8 c with a smaller bandgap .

[0079] The second and fourth sublayers 8b, 8d can thereby be of the same configuration and material and a differentiation between the sublayers of the wells can in particular be only virtually . To allow aforementioned good carrier transport , it can also be conceived that a thickness d3 of adj acent second and fourth sublayers 8b, 8d is less than 10 nm, in particular less than 5 nm, or less than 3 nm, as such a thickness allows a good carrier transport of charge carriers through the adj acent second and fourth sublayer 8b , 8d to further supress carrier recombination within the first sacrificial quantum well 10a . LIST OF REFERENCES light emitting device

[0080] 2 semiconductor layer stack

[0081] 3 first layer

[0082] 4 second layer

[0083] 5 active region

[0084] 6a, 6b, 6c quantum well

[0085] 7a, 7b barrier layer

[0086] 8a, 8b, 8 c, 8d sublayer

[0087] 9 contact layer

[0088] 10a , 10b sacrificial quantum well

[0089] Ila top surface

[0090] 11b bottom surface

[0091] 11c side surface

[0092] 12a , 12b side surface portion

[0093] 13a , 13b cladding layer

[0094] 14 buffer layer

[0095] 15 growth substrate

[0096] 16 regrowth layer

[0097] 17a , 17b portion

[0098] 18a , 18b contact element

[0099] 19 current spreading layer

[0100] 20 passivation layer dl , d2 , d3 thickness

Claims

CLAIMS1. Light emitting device (1) , in particular pLED, comprising a semiconductor layer stack (2) of at least: a first layer (3) of a first conductivity type; a second layer (4) of a second conductivity type; an active region (5) comprising at least one quantum well (6a) arranged between the first and the second layer (3, 4) and being configured to emit light of a first wavelength; and at least one first sacrificial quantum well (10a) arranged adjacent to the active region (5) between the active region (5) and the second layer (4) ; wherein the semiconductor layer stack (2) comprises a top surface (Ila) , a bottom surface (11b) opposite the top surface (Ila) and at least one side surface (11c) extending from the top surface (Ila) into the direction of the bottom surface (11b) and extending through at least the second layer (4) , the at least one first sacrificial quantum well (10a) and the active region (5) ; wherein the at least one first sacrificial quantum well (10a) comprises a larger effective bandgap than the at least one quantum well (6a) of the active region (5) ; wherein at least one regrowth layer (16) , in particular of the second conductivity type, is arranged on the at least one side surface (11c) ; and wherein the at least one side surface (11c) comprises at least a first and a second side surface portion (12a, 12b) with a different slope .

2. Light emitting device (1) according to claim 1, wherein the active region (5) comprises a multi quantum well (6a, 6b, 6c) structure.

3. Light emitting device (1) according to claim 1 or 2 , wherein the at least one first sacrificial quantum well (10a) comprises a doping of the second conductivity type.

4. Light emitting device (1) according to any one of claims 1 to 3,further comprising at least one second sacrificial quantum well (10b) arranged adjacent to the active region (5) between the active region (5) and the first layer (3) .

5. Light emitting device (1) according to claim 4, wherein the at least one second sacrificial quantum well layer (10b) comprises a doping of the first conductivity type.

6. Light emitting device (1) according to any one of claims 1 to 5 , wherein the thickness (dl) of the at least one first and / or second sacrificial quantum well (10a, 10b) is smaller than the thickness (d2) of the at least one quantum well (6a) of the active region(5) , in particular by a factor of 2.

7. Light emitting device (1) according to any one of claims 1 to 6, wherein the slope changes in the area of the at least one first sacrificial quantum well (10a) .

8. Light emitting device (1) according to claim 7, wherein the at least one side surface comprises a third side surface portion with the second side surface portion being arranged between the first and third side surface portion; wherein the third side surface portion comprises a different slope than the second side surface portion; and wherein the slope changes in the area of the at least one second sacrificial quantum well.

9. Light emitting device (1) according to any one of claims 1 to 8 , wherein a defect density of the semiconductor layer stack (2) at the at least one side surface (11c) is higher in the area of the at least one first sacrificial quantum well (10a) than in the area of the active region (5) ; and / or wherein a defect density of the semiconductor layer stack (2) at the at least one side surface (11c) is higher in the area of the at least one second sacrificial quantum well (10b) than in the area of the active region (5) .

10. Light emitting device (1) according to any one of claims 1 to 9, wherein the at least one first sacrificial quantum well (10a) comprises a first sublayer (8a) with a first bandgap arranged between two second sublayers (8b) with a second bandgap larger than the first bandgap; wherein the at least one quantum well (6a) of the active region (5) comprises a third sublayer (8c) with a third bandgap arranged between two fourth sublayers (8d) with a fourth bandgap larger than the third bandgap; and wherein one of the second layers (8b) is arranged directly adjacent to one of the fourth layers (8d) .

11. Light emitting device (1) according to claim 10, wherein the adjacent second and fourth sublayer (8b, 8d) comprise a substantially equal bandgap and in particular an substantially equal material composition.

12. Light emitting device (1) according to claim 10 or 11, wherein the adjacent second and fourth sublayer (8b, 8d) comprise a total thickness (d3) of less than 10 nm.

13. Light emitting device (1) according to any one of claims 1 to 12, wherein the active region (5) , the at least one first sacrificial quantum well (10a) , and the optional at least one second sacrificial quantum well (10b) are arranged between a first and a second barrier layer (7a, 7b) .

14. Light emitting device (1) according to any one of claims 1 to 13, wherein the active region (5) , the at least one first sacrificial quantum well (10a) , and the optional at least one second sacrificial quantum well (10b) are arranged between a first and a second cladding layer (13a, 13b) .

15. Light emitting device (1) according to any one of claims 1 to 14, wherein the at least one regrowth layer (16) comprises a sublayer of the material of the second layer (4) and / or a sublayer of thematerial of a second barrier layer (7b) arranged between the active region (5) and the second layer (4) .

16. Method for manufacturing a light emitting device (1) comprising the steps :Providing on a growth substrate (15) a semiconductor layer stack (2) of at least: a first layer (3) of a first conductivity type, a second layer (4) of a second conductivity type, an active region (5) comprising at least one quantum well (6a) arranged between the first and the second layer (3, 4) and being configured to emit light of a first wavelength, and at least one first sacrificial quantum well (10a) arranged adjacent to the active region (5) between the active region (5) and the second layer (4) , wherein the at least one first sacrificial quantum well (10a) comprises a larger effective bandgap than the at least one quantum well (6a) of the active region (5) ;Structuring the semiconductor layer stack (2) thereby remaining at least one first portion (17a) of the semiconductor layer stack (2) and removing a second portion (17b) of the semiconductor layer stack (2) adjacent to the at least one first portion (17a) , resulting in an at least one exposed side surface (11c) of the at least one first portion (17a) comprising at least the second layer (4) , the at least one first sacrificial quantum well layer (10a) and the active region (5) ; andRegrowing at least one regrowth layer (16) in particular of the second conductivity type, on the at least one side surface (He) .

17. Method according to claim 16, wherein the step of structuring comprises a step of mesa etching the semiconductor layer stack (2) , in particular using a wet chemical etchant, resulting in the at least one side surface (11c) comprising at least a first and a second side surface portion (12a,12b) with a different slope, wherein the slope changes in an area of the at least one first sacrificial quantum well (10a) .

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