WO2024156595A1

WO2024156595A1 - Optoelectronic device with oxidized isolation layer

Info

Publication number: WO2024156595A1
Application number: PCT/EP2024/051192
Authority: WO
Inventors: Martin Hetzl; Norwin Von Malm
Original assignee: Ams-Osram International Gmbh
Priority date: 2023-01-23
Filing date: 2024-01-18
Publication date: 2024-08-02

Abstract

The invention concerns an optoelectronic device comprising a layer stack having a first charge transportation layer of a first doping type, a second charge transportation layer of a second doping type, and an active region arranged between the first and the second charge transportation layer, wherein the layer stack comprises a top surface as well as side surfaces adjacent to the top surface, and wherein the side surfaces are inclined with respect to a normal of the top surface. The optoelectronic device further comprises a first regrowth layer covering the side surfaces and leaving at least portions of the top surface exposed, wherein the first regrowth layer is undoped or comprises a plurality of sublayers of a different doping type arranged in an alternating order, and a second regrowth layer arranged on the first regrowth layer and the exposed portions of the top surface. The first regrowth layer further comprises an at least partially oxidized sublayer arranged between the side surfaces of the layer stack and the second regrowth layer.

Description

OPTOELECTRONIC DEVICE WITH OXIDIZED ISOLATION LAYER

The present application claims priority from German patent application DE 10 2023 101 566 . 4 filed on January 23 , 2023 , the disclosure of which is incorporated by way for reference in its entirety .

The present invention concerns an optoelectronic device with an oxidized isolation layer to increase the quantum efficiency of the optoelectronic device , as well as a method for manufacturing the optoelectronic device .

BACKGROUND

Mesa etching of optoelectronic device , in particular p-LEDs , is done to optically and electrically isolate the individual devices on a wafer . This mesa etching however causes non-radiative recombination (NRR) of charge carriers at the mesa edges , due to resulting defects ( dangling bonds/ non-radiative recombination centers ) in the structure of the optoelectronic device along the mesa edges . Current spreading in the layers above and below the active region and also through the active region allows charge carriers to propagate in the direction of the pixel edges , which can then recombine nonradiatively at the defect , lowering the quantum efficiency of the optoelectronic device . This effect is particularly pronounced for Indium Gallium Aluminium Phosphide ( InGaAlP ) -based p-LEDs , which are usually applied for red colour emission .

So far different methods to passivate the mesa edges can be employed, depending on the material system used for the optoelectronic device to counteract aforementioned problem.

For the InGaAlP material system, which is usually used for yellow/red emission, two main methods in order to reduce NRR at the mesa facet have been employed : quantum well intermixing ( QWI ) & regrowth .

In QWI , intentional diffusion of impurities or vacancies ( impurity- free QWI ) leads to an intermixing of the QWs in the active region with the adj acent high-bandgap barriers , leading to an overall increase of the local bandgap . When applied at the pixel edges , this leads to a lateral barrier for charge carriers to avoid leakage from the inner are to the outer are of the active region . However , QWI has technological limitations , in particular when reducing the pixel sizes in particular down to the size of p-LEDs .

For very small optoelectronic devices , multi-step epitaxy ( regrowth approach ) can be done . Thereby an epi structure including active region is grown on a wafer in a first step . Then the wafer surface is prestructured ( first mesa etching ) to isolate individual islands of the active region which each form a later optoelectronic device . Afterwards a high-bandgap material is regrown on the same wafer in order to encapsulate the "active region islands" , and in particular the mesa etches of the active region . In another etching step ( second mesa etching ) , the optoelectronic device , are then optically and electrically isolated outside the passivated "active region islands" the optoelectronic devices and to not again etch through the active region again causing defects at the mesa edges .

In this way, a potential barrier in between the pixel core and the mesa facet appears , blocking charge carriers from diffusing to the side surfaces . However , parallel/parasitic ( nonradiative ) diodes along the mesa edges besides the "active region islands" , which again can lead to an intrinsic reduction of quantum efficiency of the optoelectronic devices .

It is an obj ect of the present application to provide an optoelectronic device , in particular small optoelectronic device such as a p-LED, with an increased quantum efficiency . It is a further obj ect to provide a method for manufacturing an optoelectronic device , in particular small optoelectronic device such as a p-LED, with an increased quantum efficiency . SUMMARY OF THE INVENTION

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 .

According to a first aspect of the present invention, an optoelectronic device comprises a layer stack, in particular semiconductor layer stack, having a first charge transportation layer of a first doping type , a second charge transportation layer of a second doping type , and an active region arranged between the first and the second charge transportation layer . The layer stack thereby comprises a top surface as well as side surfaces adj acent to the top surface , wherein the side surfaces are inclined with respect to a normal of the top surface . This inclination can in particular result of a first etching step of an epi structure on a wafer, to separate individual islands of the active region, which later then are each part of one optoelectronic device .

The optoelectronic device further comprises a first regrowth layer covering the side surfaces and leaving at least portions of the top surface exposed . The first regrowth layer is undoped or comprises a plurality of sublayers of a different doping type arranged in an alternating order . For example , the first regrowth layer can comprise a plurality of sublayers of n- and p-doping in an alternating order forming a npnp-barrier . In addition, the optoelectronic device further comprises a second regrowth layer arranged on the first regrowth layer and the exposed portions of the top surface forming a top contact of the optoelectronic device .

The first and second regrowth layer can in particular result from a multi-step regrowth, combined with a selective area growth ( SAG) mas k placed on top of separate individual islands of the active region resulting from the first etching step of the epi structure on the wafer . In a first step of regrowth an undoped or npnp current blocking layer of high bandgap ( e . g . Indium Aluminium Phosphite ( InAlP ) ) is grown at the island sidewalls and also areas in between the islands . Then, the SAG mas k is removed and a second regrowth step is done to deposit the topside of the structure of the optoelectronic device , including a highly conductive contact layer (Gallium Phosphite (GaP ) or Gallium Arsenide (GaAs ) ) . After pixelation, into the optoelectronic devices this leads to a preferential current flow through the center of the islands of the active region .

However, due to the high charge carrier mobility in InGaAlP structures , undoped InAlP layers will not completely block the current flowing along/through the side surfaces of the semiconductor layer stack, whereas npnp structures lead to additional challenges in terms of dopant diffusion into the active region . For Gallium Nitride (GaN) / Indium Gallium Nitride ( InGaN ) -based structures , passivating dielectrics such as atomic layer deposited (ALD) Aluminium oxide (A1₂O₃ ) and Silicon dioxide ( SiO₂ ) can be used for reducing NRR at the side surface of the optoelectronic device . However, depending on the chip size and epi configuration, some of these precautions may still not show the desired effect for certain applications . This is in particular the case for optoelectronic devices with edge length of less than 10pm such as p-LEDs .

The inventors therefore propose an optoelectronic device according to a second aspect of the invention, the optoelectronic device comprising a layer stack having a first charge transportation layer of a first doping type , a second charge transportation layer of a second doping type , and an active region arranged between the first and the second charge transportation layer . The layer stack comprises a top surface as well as side surfaces adj acent to the top surface , wherein the side surfaces are inclined with respect to a normal of the top surface . This inclination can in particular result of a first etching step of an epi structure on a wafer , to separate individual islands of the active region, which later then each form an optoelectronic device .

In comparison to the first aspect of the invention, the first regrowth layer further comprises an at least partially oxidized sublayer arranged between the side surfaces of the layer stack and the second regrowth layer , to prevent a direct current leakage from the second regrowth layer through the first regrowth layer at the side surfaces of the layer stack .

The optoelectronic device according to the second aspect proposes an alternative to the 2-step regrowth approach according to the first aspect of the invention, in order to tackle both, NRR reduction at the active region and elimination of a possible parasitic diode .

Therefore , a semiconductor layer that can easily be oxidized, namely the first regrowth layer or a sublayer of the first regrowth layer , is regrown on the side surfaces of the layer stack . After etching the individual islands of the active region and structuring the SAG mask, the semiconductor layer that can easily be oxidized is epitaxially grown on the islands ' sidewalls . In a subsequent process step , this layer is oxidized at least partly from the top surface in order to electrically isolate the second regrowth layer grown after SAG mas k removal against the layer stack and in particular the active region and a bottom contact optoelectronic device (preventing parasitic diodes ) . The oxidation step can thereby be done prior or after the removal of the SAG mask . In a second regrowth step, the second regrowth layer, in particular a contact layer is then implemented on top of the islands of the layer stack as well as on the oxidized regions along the side surfaces of the islands .

According to at least one aspect , the at least partially oxidized sublayer is arranged adj acent to the second regrowth layer . The at least partially oxidized sublayer of the first regrowth layer can in particular be the outermost area of the first regrowth layer opposite the side surfaces and adj acent to the second regrowth layer . The at least partially oxidized sublayer can in particular result from an surface oxidation of the first regrowth layer covering the side surfaces of the layer stack .

The thickness of the at least partially oxidized sublayer can thereby in particular relate to degree of surface oxidation of the first regrowth layer and can in particular be less than 20nm . The thickness of the at least partially oxidized sublayer can be influenced by the choice of process parameters under which oxidation takes place . Process parameters that particularly influence oxidation and thus the thickness of the sublayer can, for example , be the temperature during an oxidation step and the duration of the oxidation step , as well as the choice of material of the first regrowth layer .

According to at least one aspect , the at least partially oxidized sublayer is an intermediate layer in-between further sublayers of the first regrowth layer . The at least partially oxidized sublayer can, for example , be formed by an intermediate layer that oxidizes particularly easily . In particular , this intermediate layer can be oxidized starting from the upper side of the layer stack along the main propagation direction, so that at least the portion of the intermediate layer adj acent to the side surfaces is oxidized . A portion of the intermediate layer opposite the top surface , on the other hand, may not be oxidized . The intermediate layer can thus comprise an oxidized portion and a not oxidized portion, wherein the oxidized portion extends from the top surface along the side surfaces and the not oxidized portion makes up the rest of the intermediate layer up to the side opposite the top surface . The further sublayers on both sides of the intermediate layer can on the other hand comprise a material which has poorer oxidation behaviour , i . e . oxidizes less quickly, hardly at all or not at all .

In order to provide a current leakage barrier , the first regrowth layer comprises according to at least one aspect a material with a larger bandgap than the active region of the layer stack and in particular a larger bandgap than the all of the layers of the layer stack . This can on the one hand side be achieved by choosing an undoped material for the first regrowth layer with a larger bandgap than the active region of the layer stack or can on the other hand be achieved by choosing differently doped sublayers forming a npnp current blocking layer of a high bandgap .

According to at least one aspect , the first regrowth layer is a II I-V semiconductor layer, in particular containing : Indium ( In) and/or aluminium (Al ) and/or gallium ( Ga ) and/or arsenide (As ) and/or phosphorus ( P ) . For better oxidation, the first regrowth layer and in particular the at least partially oxidized sublayer comprises aluminium, wherein the content of aluminium in the first regrowth layer and in particular the at least partially oxidized sublayer can be greater than 25% . In particular , for the first regrowth layer material systems with high Al content might be used, e . g . InAlP, or a sandwich structure based on InAlP + AlGaAs + InAlP , whereas the AlGaAs relates to the intermediate layer and consists of a high molar fraction of Al of approx . 98% (Al₉₈GaAs ) .

According to at least one aspect , the optoelectronic device is a p- LED . p-LEDs can in particular be very small LEDs with edge lengths of less than, 20pm, less than 10pm or even less than 5pm. for such small LEDs it can in particular be very difficult top provide a good quantum efficiency with structures and methods known from the state of the art .

According to a further aspect of the invention, a method for manufacturing an optoelectronic device is provided, the method comprises the following steps :

Providing a layer stack having a first a first charge transportation layer of a first doping type , a second charge transportation layer of a second doping type , and an active region arranged between the first and the second charge transportation layer;

Providing a structured mas k on a top surface of the layer stack;

Structuring the layer stack such that the layer stack comprises side surfaces adj acent to the top surface , wherein the side surfaces are inclined with respect to a normal of the top surface ;

Regrowing a first regrowth layer on the side surfaces and leaving at least portions of the top surface exposed, wherein the first regrowth layer is undoped or comprises a plurality of sublayers of a different doping type arranged in an alternating order;

Oxidizing at least partially a sublayer of the first regrowth layer; and

Regrowing a second regrowth layer on the first regrowth layer and the exposed portions of the top surface ; wherein the at least partially oxidized sublayer of the first regrowth layer is arranged between the side surfaces of the layer stack and the second regrowth layer .

According to at least one aspect , the step of oxidizing comprises oxidizing the outermost area of the first regrowth layer opposite the side surfaces . The step of oxidizing can in particular be a step of surface oxidizing the first regrowth layer covering the side surfaces of the layer stack resulting in an at least partially oxidized sublayer in the outermost area of the first regrowth layer opposite the side surfaces . The thickness of the at least partially oxidized sublayer can thereby in particular relate to degree of surface oxidation of the first regrowth layer . The thickness of the at least partially oxidized sublayer can be influenced by the choice of process parameters under which oxidation takes place . Process parameters that particularly influence oxidation and thus the thickness of the sublayer can, for example , be the temperature during an oxidation step and the duration of the oxidation step, as well as the choice of material of the first regrowth layer .

According to at least one aspect , the step of regrowing the first regrowth layer comprises regrowing a first sublayer , in particular undoped sublayer such as for example InAlP , on the the side surfaces and leaving at least portions of the top surface exposed, regrowing an intermediate layer, in particular layer comprising aluminium such as for example Al₉₈GaAs , on the the first sublayer and leaving at least portions of the top surface exposed, and regrowing a second sublayer , in particular undoped sublayer such as for example InAlP, on the the intermediate layer and leaving at least portions of the top surface exposed . The step of oxidizing can then comprise oxidizing the intermediate layer from an exposed side surface of the intermediate layer adj acent to the top surface along the main propagation direction of the intermediate layer . Due to such a step , the intermediate layer can be oxidized starting from an exposed side surface of the intermediate layer adj acent to the top surface along the main propagation direction, so that at least the portion of the intermediate layer adj acent to the side surfaces is oxidized . A portion of the intermediate layer opposite the top surface , on the other hand, may not be oxidized . The intermediate layer can thus comprise an oxidized portion and a not oxidized portion, wherein the oxidized portion extends from the top surface along the side surfaces and the not oxidized portion makes up the rest of the intermediate layer up to the side opposite the top surface .

According to at least one aspect , the step of oxidizing comprises an oven process . The oxidation can be realized, e . g . in an oxidation oven based on hot water steam. Process parameters that particularly influence oxidation and thus the thickness of the sublayer can, for example , be the temperature in the oxidation oven during the step of oxidizing, the duration of the the step of oxidizing, the water content of the water steam as well as the choice of material of the first regrowth layer .

According to at least one aspect , the step of structuring the layer stack comprises a step of etching the layer stack such that the structured mask protrudes over the side surfaces of the layer stack . The step of etching the layer stack can in particular result in a light "underetching" of the layer stack in the area of the structured mas k arranged on the top surface . This "underetched" area can afterwards again at least partially be filled with the step of regrowing the first regrowth layer . SHORT DESCRIPTION OF THE DRAWINGS

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

Fig . 1 shows an optoelectronic device with resulting parasitic diodes ;

Fig . 2 shows an optoelectronic device in accordance with a first aspect of the present invention;

Fig . 3A to 3 F show steps of a method for manufacturing an optoelectronic device in accordance with some aspects of the present invention; and

Fig . 4A to 4 F show steps of a method for manufacturing an optoelectronic device in accordance with some other aspects of the present invention .

DETAILED DESCRIPTION

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 .

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 .

Figure 1 shows a cross section of an optoelectronic device with a reduced quantum efficiency due to parasitic diodes that form inside the optoelectronic device . The optoelectronic device comprises an epi structure including a first charge transportation layer 3 , an active region 5 , as well as a first portion of a second charge transportation layer 4 , grown on a carrier substrate 11 . The epi structure is structured due to a first mesa etching process resulting in the epi structure having side surfaces 2b . On the epi structure and in particular the side surfaces 2b, a high-bandgap material , and in particular a second portion of the second charge transportation layer 4 is regrown, in order to encapsulate the side surfaces 2b , and in particular the portions of the active region at the side surfaces 2b . The optoelectronic device as a whole is also structured due to a second mesa etching process to optically and electrically isolate several optoelectronic components , whereas in comparison to the first mesa etching process the resulting side surf aces /mesa edges do not comprise portions of the active region . In this way, a potential barrier in between the core of the optoelectronic device and the mesa edges appears , blocking charge carriers from diffusing to the side surfaces . In addition, an immediately subsequent encapsulation of the etched side surfaces of the active region 5 and subsequent etching steps , which no longer affect at least the active region, the risk of nonradiative recombination centres along the side surfaces 2b can be reduced . However, parasitic ( nonradiative ) diodes along the mesa edges besides the active region can lead to an intrinsic reduction of quantum efficiency of the optoelectronic devices . This parasitic diodes are exemplarily shown by use of the two vertical arrows next to the active region 5 .

To counteract aforementioned problem, the invention proposes an improved optoelectronic device with an increased quantum efficiency . Fig . 2 shows an optoelectronic device 1 in accordance with a first aspect of the present invention . The optoelectronic device 1 comprises a layer stack 2 , in particular semiconductor layer stack, having a first charge transportation layer 3 of a first doping type , a second charge transportation layer 4 of a second doping type , an active region 5 arranged between the first and the second charge transportation layer, as well as ca carrier substrate 11 on which the first charge transportation layer 3 is arranged . The layer stack 2 comprises a top surface 2a as well as side surfaces 2b adj acent to the top surface , wherein the side surfaces are inclined with respect to a normal N of the top surface 2a . The side surfaces 2b can for example be inclined with respect to the surface normal with an angle a of 0 ° to 80 ° , and in particular with an angle of 40 ° to 75 ° .

The first and the second charge transportation layer can, as shown, each comprise several sublayers to provide together with the active region a layer stack configured to emit light of a desired wavelength when supplied with a sufficient current . The first charge transportation layer can for example comprise one or several n-doped layers , as well as one or several diffusion barrier layers adj acent to the active region . The second charge transportation layer can on the other hand for example comprise one or several p-doped layers , as well as one or several diffusion barrier layers adj acent to the active region . The diffusion barrier layers can in particular be configured to prevent a diffusion of the n- or p-dopant of the n- or p-doped layers into the active region 5 .

The optoelectronic device 1 further comprises a first regrowth layer 6 covering the side surfaces 2b and leaving at least portions of the top surface 2a exposed . The first regrowth layer , in the embodiment shown, comprises two undoped sublayer , but can also comprise a plurality of sublayers of a different doping type arranged in an alternating order , forming a npnp-barrier . In addition, the optoelectronic device further comprises a second regrowth layer 7 arranged on the first regrowth layer 6 and the exposed portions of the top surface 2a forming a top contact of the optoelectronic device 1 . The first and second regrowth layer can result from a multi-step regrowth, combined with a selective area growth ( SAG) mask placed on top of separate individual islands of the active region 5 . The islands of the active region 5 in turn can result from a first etching step of an epi structure on a wafer . In a first step of regrowth an undoped or npnp-current blocking layer of high bandgap ( e . g . Indium Aluminium Phosphide ( InAlP ) ) is grown on the side surfaces 2b and areas between adj acent islands of the active region 5 . Then, the SAG mask is removed and a second regrowth step is done to deposit the second regrowth layer, including a highly conductive contact layer (Gallium Phosphide (GaP ) or Gallium Arsenide (GaAs ) ) . Optoelectronic devices 1 as shown in Fig . 2 can then be separated by use of a further etching step . By means of aforementioned steps and respectively the therefrom resulting structure of the optoelectronic device , the risk of parasitic diodes , as shown for the optoelectronic device in Fig . 1 can be greatly reduced .

Fig . 3A to 3F show steps of a method for manufacturing a further improved optoelectronic device with a further increased quantum efficiency as well as the optoelectronic device 1 in accordance with a second aspect of the present invention .

The optoelectronic device 1 , as shown in Fig . 3 F, comprises a layer stack 2 , in particular semiconductor layer stack, having a first charge transportation layer 3 of a first doping type , a second charge transportation layer 4 of a second doping type , an active region 5 arranged between the first and the second charge transportation layer , as well as ca carrier substrate 11 on which the first charge transportation layer 3 is arranged . The layer stack 2 comprises a top surface 2a as well as side surfaces 2b adj acent to the top surface , wherein the side surfaces 2b are inclined with respect to a normal N of the top surface 2a . The side surfaces 2b can for example be inclined with respect to the surface normal N with an angle a of 0 ° to 45 ° , and in particular with an angle of 5 ° to 15 ° . This inclination can in particular result of a first etching step (prior to the step shown in Fig . 3A) of an epi structure on a wafer, to separate individual islands of the active region 5 , which later are then each part of one optoelectronic device 1 . The optoelectronic device 1 further comprises a first regrowth layer 6 covering the side surfaces 2b and leaving at least portions of the top surface 2a exposed, wherein the first regrowth layer 6 is in particular an undoped layer . In addition, the optoelectronic device 1 further comprises a second regrowth layer 7 arranged on the first regrowth layer 6 and the exposed portions of the top surface 2a forming a top contact of the optoelectronic device 1 .

In comparison to the embodiment shown in Fig . 2 , the first regrowth layer 6 comprises an at least partially oxidized sublayer 8 arranged between the side surfaces 2b of the layer stack and the second regrowth layer 7 , to prevent a direct current leakage from the second regrowth layer 7 through the first regrowth layer 6 at the side surfaces 2b of the layer stack 2 . The partially oxidized sublayer 8 thus functions as a current blocking layer encapsulating the active region 5 in lateral direction . By this the ris k of a possible parasitic diode in an area adj acent to the active region can further be reduced .

The steps necessary to manufacture such an optoelectronic device shown in Fig . 3 F are illustrated in Figs . 3A to 3E . In a step prior to the step shown in Fig . 3A, a structured mask 9 , in particular a structured SAG mas k, is arranged on the top surface 2a of an epi structure on a wafer to separate individual islands of the active region 5 of the epi structure by for example etching . Exemplarily in Figs . 3A to 3E only one resulting individual island of the active region 5 is shown, but by means of the it is to be understood that a plurality of such individual islands can be arranged next to each other on the carrier substrate 11 . Due to the etching , each of the individual islands of the active region 5 is bordered by the inclined side surfaces 2b . In addition, as shown in Fig . 3A, the structured mask 9 protrudes the side surfaces 2b, which can in particular result from an underetching of the epi structure in areas below the structured mask 9 .

Then, as shown in Fig . 3B , a semiconductor layer that can easily be oxidized, namely the first regrowth layer 6 , is grown, in particular epitaxially grown, on the side surfaces 2b of the layer stack 2 , while remaining the structured mas k 9 on the top surface 2a . By this it can be ensured that the top surface 2a remains free of the first regrowth layer 6 and a later top contact on top of the top surface 2a can directly contact the layer stack 2 .

In a subsequent step , as shown in Fig 3C, the first regrowth layer 6 is surface oxidized to provide an oxidized sublayer 8 making up a sublayer of the first regrowth layer 6 along substantially the entire surface of the first regrowth layer 6 opposite the side surfaces 2b .

The structured mask 9 is then removed exposing the top surface 2a, as shown in Fig . 3D, and the second regrowth layer 7 is grown, in particular epitaxially grown, on the top surface 2a as well as on the first regrowth layer 6 as shown in Fig . 3E . The second regrowth layer 7 can thereby in particular be in particular a contact layer arranged on the top surface 2a of the layer stack configured to an electric contact for the optoelectronic device . The oxidized sublayer 8 arranged between the side surfaces 2b and the second regrowth layer 7 thereby acts as an electric isolator/current blocking layer to prevent parasitic diodes between the second regrowth layer 7 and the charge transportation layer 3 adj acent to the active region 5 . Optoelectronic devices 1 as shown in Fig . 3F can then be separated by use of a further etching step .

Figs . 4A to 4 F show steps of a method for manufacturing an optoelectronic device in accordance with some further aspects of the present invention . As shown for Fig . 3A, separate individual islands of the active region 5 of an epi structure are provided by for example etching using a structured mas k 9 . The resulting structure is shown in Fig . 4A and is formed in the same way as the structure shown in Fig . 3A . Again, exemplarily in Figs . 4A to 4E only one resulting individual island of the active region 5 is shown, but by means of the it is to be understood that a plurality of such individual islands can be arranged next to each other on the carrier substrate 11 .

Then, as shown in Fig . 4B , the first regrowth layer 6 , is grown, in particular epitaxially grown, on the side surfaces 2b of the layer stack 2 , while remaining the structured mas k 9 on the top surface 2a . The step of growing the first regrowth layer 6 comprises growing a first sublayer 10 , in particular undoped sublayer such as for example InAlP, on the the side surfaces 2b, growing an intermediate layer 8 ' , in particular a layer that can easily be oxidized such as for example Al ggGaAs , on the the first sublayer 10 and growing a second sublayer 10 , in particular undoped sublayer such as for example InAlP , on the the intermediate layer 8 ' .

The structured mask 9 is then removed exposing the top surface 2a, as shown in Fig . 4C , whereas also side surface of the intermediate layer 8 ' adj acent to the top surface 2a are also exposed upon removal of the structured mas k 9 . In a subsequent step the structure is then undertaken an oxidation step, comprising oxidizing the intermediate layer from the side surface of the intermediate layer 8 ' adj acent to the top surface 2a along the main propagation direction of the intermediate layer 8 ' ( indicated by the two arrows ) . Due to this step , the intermediate layer 8 ' is oxidized starting from the exposed side surface of the intermediate layer 8 ' adj acent to the top surface 2a along its main propagation direction, so that at least the portion 8a of the intermediate layer 8 ' adj acent to the side surfaces is oxidized . A portion 8b of the intermediate layer 8 ' opposite the top surface 2a , on the other hand, is not oxidized resulting in the at least partially oxidized sublayer 8 . The oxidized portion 8a extends from the top surface 2a along the side surfaces 2b and the not oxidized portion 8b makes up the rest of the intermediate layer 8 ' up to the side of the intermediate layer 8 ' opposite the top surface 2a .

The resulting at least partially oxidized sublayer 8 again acts as an electric isolator/current blocking layer to prevent parasitic diodes between the second regrowth layer 7 , grown, in particular epitaxially grown, on the top surface 2a as well as on the first regrowth layer 6 as shown in Fig . 4E , and the charge transportation layer 3 adj acent to the active region 5 . Optoelectronic devices 1 as shown in Fig . 4 F can then be separated by use of a further etching step . LIST OF REFERENCES

1 optoelectronic device

2 layer stack

2a top surface

2b side surface

3 charge transportation layer

4 charge transportation layer

5 active region

6 regrowth layer

7 regrowth layer

8 at least partially oxidized sublayer

8a oxidized portion

8 non-oxidized portion

8 ' intermediate layer

9 structured mask

10 sublayer

11 carrier substrate

N surface normal angle

Claims

1. An optoelectronic device (1) comprising: a layer stack (2) having a first charge transportation layer

(3) of a first doping type, a second charge transportation layer

(4) of a second doping type, and an active region (5) arranged between the first and the second charge transportation layer (3, 4) , wherein the layer stack (2) comprises a top surface (2a) as well as side surfaces (2b) adjacent to the top surface (2a) , and wherein the side surfaces (2b) are inclined with respect to a normal (N) of the top surface (2a) ; a first regrowth layer (6) covering the side surfaces (2b) and leaving at least portions of the top surface (2a) exposed, wherein the first regrowth layer (6) is undoped or comprises a plurality of sublayers of a different doping type arranged in an alternating order; and a second regrowth layer (7) arranged on the first regrowth layer (6) and the exposed portions of the top surface (2a) ; wherein the first regrowth layer (6) further comprises an at least partially oxidized sublayer (8) arranged between the side surfaces (2b) of the layer stack

(2) and the second regrowth layer(7) .

The optoelectronic device according to claim 1, wherein the at least partially oxidized sublayer (8) is arranged adjacent to the second regrowth layer (7) .

3. The optoelectronic device according to claim 1, wherein the at least partially oxidized sublayer (8) is an intermediate layer (8' ) inbetween further sublayers (10) of the first regrowth layer (6) .

4. The optoelectronic device according to any one of claims 1 to 3, wherein the first regrowth layer (6) comprises a material with a larger bandgap than the active region (5) of the layer stack (2) .

5. The optoelectronic device according to any one of claims 1 to 4, wherein the at least partially oxidized sublayer (8) comprises a thickness of less than 20nm.

6. The optoelectronic device according to any one of claims 1 to 5, wherein the first regrowth layer (6) is a III-V semiconductor layer, in particular containing: Indium and/or aluminium and/or gallium and/or arsenide and/or phosphorus.

7. The optoelectronic device according to any one of claims 1 to 6, wherein the first regrowth layer (6) and in particular the at least partially oxidized sublayer (8) comprises aluminium.

8. The optoelectronic device according to of claim 7, wherein the content of aluminium in the first regrowth layer (6) and in particular the at least partially oxidized sublayer (8) is greater than 25%.

9. The optoelectronic device according to any one of claims 1 to 8, wherein the optoelectronic device (1) is a p-LED.

10. A method for manufacturing an optoelectronic device (1) , comprising the steps :

Providing a layer stack (2) having a first a first charge transportation layer (3) of a first doping type, a second charge transportation layer (4) of a second doping type, and an active region (5) arranged between the first and the second charge transportation layer (3, 4) ;

Providing a structured mask (9) on a top surface (2a) of the layer stack (2) ;

Structuring the layer stack (2) such that the layer stack (2) comprises side surfaces (2b) adjacent to the top surface (2a) , wherein the side surfaces (2b) are inclined with respect to a normal (N) of the top surface (2a) ;

Regrowing a first regrowth layer (6) on the side surfaces (2b) and leaving at least portions of the top surface (2a) exposed, wherein the first regrowth layer (6) is undoped or comprises a plurality of sublayers of a different doping type arranged in an alternating order;

Oxidizing at least partially a sublayer (8) of the first regrowth layer; and Regrowing a second regrowth layer (7) on the first regrowth layer (6) and the exposed portions of the top surface (2a) ; wherein the at least partially oxidized sublayer (8) of the first regrowth layer (6) is arranged between the side surfaces (2b) of the layer stack (2) and the second regrowth layer (7) .

11. The method according to claim 10, wherein the step of oxidizing comprises oxidizing the outermost area of the first regrowth layer (6) opposite the side surfaces (2b) .

12. The method according to claim 10, wherein the step of regrowing the first regrowth layer (6) comprises regrowing a first sublayer 10) , in particular undoped sublayer, on the the side surfaces (2b) and leaving at least portions of the top surface (2a) exposed, regrowing an intermediate layer (8' ) , in particular layer comprising aluminium, on the the first sublayer (10) and leaving at least portions of the top surface (2a) exposed, and regrowing a second sublayer (10) , in particular undoped sublayer, on the the intermediate layer (8' ) and leaving at least portions of the top surface (2a) exposed.

13. The method according to claim 12, wherein the step of oxidizing comprises oxidizing the intermediate layer (8' ) from an exposed side surface of the intermediate layer (8' ) adjacent to the top surface (2a) along the main propagation direction of the intermediate layer (8' ) .

14. The method according to any one of claims 10 to 13, wherein the step of oxidizing comprises an oven process.

15. The method according to any one of claims 10 to 14, wherein the step of structuring the layer stack (2) comprises a step of etching the layer stack such that the structured mask (9) protrudes over the side surfaces (2b) of the layer stack (2) .