Light emitting device with multi-layered barrier layer

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 as well as an active region arranged between the first and the second layer. The active region comprises a central region as well as a side region laterally surrounding the central region. In addition, the active region comprises at least one quantum well arranged between a first and a second barrier layer, wherein the first and the second barrier layer each comprise at least a first and a second sublayer, with the second sublayers each being adjacent to one of the at least one quantum well. The first sublayers at least in the central region comprise a smaller average bandgap than the second sublayers, in particular at least 5 % smaller, the at least one quantum well at least in the central region comprises a smaller average bandgap than the second sublayers, in particular at least 5 % smaller, and the at least one quantum well at least in the central region comprises a smaller average bandgap than the first sublayers, in particular at least 5 % smaller.

Description

[0001] LIGHT EMITTING DEVICE WITH MULTI-LAYERED BARRIER LAYER

[0002] The present invention concerns a light emitting device (LED ) , in particular pLED, with multi layered barrier layer ( s ) as well as a method for manufacturing the same .

[0003] 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 .

[0004] 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 of charge carriers within the pLED .

[0005] For example , plasma etching is a common and standard process for pixel etching ( etching through the active region and physical separation of individual pixels ) , but introduces plasma damage to the surface and underlying layers dependent on the specific process and parameters used . Plasma damage in this case means the creation of defect centres in the crystal lattice caused by Ion bombardment . Especially for small pixels such as for the case of pLEDs with a high surf ace-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 . Defects created on the surface and below of the active region - which is exposed during and after pixel etching by means of plasma etching - act as non-radiative recombination (NRR) 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 . To reduce non-radiative recombination at the edges of a pLED, a possible approach is to remove plasma damage in a subsequent so-called defect etching step, where defects are reduced or even removed while not creating new defects. Therefore, usually wet chemistry is used, mostly aqueous KOH. A further approach to reduce non-radiative recombination at the edges of a pLED is to keep the charge carriers away from the edges which comprise the non-radiative recombination centres. This can for example be done by quantum well intermixing the active regions in areas along the edges 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. Therefore, barrier layer (s) are used being introduced adjacent to the quantum well(s) of the active region of a pLED, which for a high intermixing potential, comprise an Aluminium (Al) to Gallium (Ga) ratio that is different from that in the quantum well(s) , with a higher value of Al content in the barrier layer (s) . The intermixing now equilibrates the Al to Ga ratio of the barrier layer (s) and the quantum well(s) in the areas along the edges of the pLED thereby increasing the bandgap in these areas due to a shift of the Al content. By this charge carriers can be kept away from the edges which comprise the non-radiative recombination centres.

[0006] However, a disadvantage of high-Al-containing barrier layer (s) in the active region is a high bandgap of the barrier layer (s) leading to a decreased overall carrier mobility. This makes higher operating voltages necessary for the pLEDs or results in less brightness of the pLEDs. Therefore, to date a certain compromise has to be made between the intermixing potential of the barrier layer (s) and the quantum well(s) vs. a high bandgap of the barrier layer (s) which limits the overall brightness of the pLED.

[0007] It is thus an object 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.

[0008] SUMMARY OF THE INVENTION This and other objects are addressed by the subject matter of the independent claims . Features and further aspects of the proposed principles are outlined in the dependent claims .

[0009] The idea of the inventors is to separate the barrier layer (s) into several sublayers with different tasks, which allows to overcome aforementioned conflict and allows high intermixing potential as well as a carrier high mobility at the same time. Each barrier layer as known to date is therefore divided into a set of sublayers with different compositions in a way, that the sublayers of the barrier layer (s) which are close to the quantum well(s) contain a higher aluminium content and the sublayers forming the edge or centre region of each barrier layer contain less aluminium than the barrier layer (s) as an average. By doing this the majority of the Al contained in the barrier layer (s) is already located close to the quantum well(s) and the intermixing, which only affects a few monolayers adjacent to the quantum well(s) , dominated by the sublayers of the barrier layer (s) which are close to the quantum well(s) , is enhanced. At the same time, the overall carrier mobility of the pLED remains high as the mean bandgap of the barrier layer (s) is affected by the mean Al content of the barrier layer (s) . In particular the sublayers of the barrier layer (s) , which are close to the quantum well(s) with a high Al content, can comprise such a small thickness such that even if having a larger bandgap, the carrier mobility is not significantly influenced by it. By means of the proposed structure, a higher intermixing of quantum well(s) is achievable at a lower mean Al content in the barrier layer (s) and thus a smaller mean band gap of the barrier layer (s) .

[0010] According to a first aspect, a light emitting device 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 arranged between the first and the second layer.

[0011] The active region of the semiconductor layer stack comprises a central region as well as a side region laterally surrounding the central region. In addition, the active region of the semiconductor layer stack comprises at least one quantum well arranged between a first and a second barrier layer . The active region can however also comprise a multi quantum well structure comprising several quantum wells as well as several barrier layers , wherein each a quantum well is arranged between the two barrier layers .

[0012] The first and the second barrier layer each comprise at least a first and a second sublayer , with the second sublayers each being adj acent to one of the at least one quantum well . The first sublayers at least in the central region comprise a smaller average bandgap than the second sublayers , in particular at least 5 % smaller , the at least one quantum well at least in the central region comprises a smaller average bandgap than the second sublayers , in particular at least 10 % smaller, and the at least one quantum well at least in the central region comprises a smaller average bandgap than the first sublayers , in particular at least 5 % smaller .

[0013] By means of the term "average" bandgap, the bandgap of the respective layer or sublayer with respect to its thickness is to be understood . The bandgap of a layer or sublayer can for example ramp up from a first side of a layer or sublayer to a second side of a layer or sublayer and can for example not be constant throughout the thickness of the layer or sublayer . The average bandgap is in such a case to be understood as the mean bandgap of the respective layer or sublayer with respect to its thickness .

[0014] By means of dividing the barrier layers into sublayers it is to be understood that the barrier layers can be divided in actually separated sublayers with different compositions and different bandgaps / average bandgaps . However, it can also be that the sublayers of a barrier layer are of substantially the same composition with only for example the Al content of the barrier layer varying from a first side of the barrier layer to a second side the barrier layer . Hence the barrier layer can vary with regard to an element concentration from a first side of the barrier layer to a second side the barrier layer resulting in an increasing or decreasing bandgap from a first side of the barrier layer to a second side the barrier layer . Still , it is to be understood that the barrier layer can, at least in a virtual way, be divided into at least a first and a second sublayer with each having a different average bandgap . For example , the barrier layer can at least virtually be divided into sublayers with each sublayer having a substantially similar slope of the band gap increase or decrease , or the barrier layer can at least virtually be divided into sublayers resulting of sequentially performed growth steps of substantially the same material with only a different composition of elements which however in the final product can be difficult to later be differentiated .

[0015] According to some aspects , the active region comprises at least two quantum wells arranged between the first and the second barrier layer , wherein at least one third barrier layer is arranged between the at least two quantum wells . Such a structure with more than one quantum well can in particular be called 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 average bandgap and can in particular be configured to emit light of a substantially equal wavelength .

[0016] According to some aspects , the at least one third barrier layer comprises a third sublayer arranged between two second sublayers , with the second sublayers each being adj acent to one of the at least two quantum wells .

[0017] According to some aspects , the at least two quantum wells at least in the central region comprise a smaller average bandgap than the third sublayer ( s ) , in particular at least 5 % smaller . In case of several third barrier layers and thus third sublayers , these can at least in the central region comprise a substantially equal average bandgap . For example , the third sublayers can at least in the central region be substantially equal in size and / or composition, can however also vary between each other .

[0018] The third sublayer ( s ) can for example at least in the central region comprise an average bandgap substantially equal to the average bandgap of the first sublayers , however the average bandgap of the third sublayer ( s ) and the first sublayers can also be different , as long as both the average bandgap of the third sublayer ( s ) and the first sublayers is larger than that of the quantum well ( s ) at least in the central region .

[0019] According to some aspects , the first sublayers at least in the central region comprise a substantially equal average bandgap . The first sublayers of the first , second and third barrier layers can for example be substantially equal in size and / or composition, can however also vary between each other .

[0020] According to some aspects , the second sublayers at least in the central region comprise a substantially equal average bandgap . The second sublayers of the first , second and third barrier layers can for example be substantially equal in size and / or composition, can however also vary between each other and for example comprise a different average bandgap .

[0021] According to some aspects , the first layer and / or the second layer comprise a smaller average bandgap than the first sublayers at least in the central region, in particular at least 5 % smaller . In particular the semiconductor layers adj acent to the active region can comprise a smaller average bandgap than the first sublayers at least in the central region . However, it is also possible that the first layer and / or the second layer comprise a larger average bandgap than the first sublayers at least in the central region, in particular at least 5 % larger . In particular the semiconductor layers adj acent to the active region can comprise a larger average bandgap than the first sublayers at least in the central region .

[0022] According to some aspects , the second sublayers 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 allows quantum tunnelling of charge carriers through the second sublayers however is enough to provide a sufficient thickness with for example a high Al content to allow an efficient quantum well intermixing with the adj acent quantum well ( s ) . In combination with the first sublayers having a smaller average bandgap and thus for example a lower Al content the overall charge carrier mobility can even with such barrier layers kept high while still providing a sufficient thickness of sublayers of the barrier layers with for example a high Al content to allow an efficient quantum well intermixing with the adj acent quantum well ( s ) .

[0023] According to some aspects , the first sublayers comprise a thickness of less than 15 nm, in particular less than 10 nm or 5 nm down to for example 2 nm.

[0024] According to some aspects , the third sublayer comprises a thickness of less than 15 nm, in particular less than 10 nm or 5 nm down to for example 2 nm.

[0025] According to some aspects , the at least one quantum well comprise a thickness of less than 15 nm, in particular less than 10 nm or 5 nm down to for example 2 nm.

[0026] According to some aspects , each of the central region and the side region comprises respective portions of the first , second and optionally third barrier layer as well as the quantum well ( s ) . In other words , the active region can be separated into a central region and a side region laterally surrounding the central region, with the first , second and optionally third barrier layer as well as the quantum well ( s ) being separated in a respective way . The separation into regions may however not necessarily be understood as a geometrical separation in terms of separate components but may for example be understood as regions of one and the same body . In some embodiments these regions can for example comprise different properties but may also be more or less similar to each other in terms of properties .

[0027] According to some aspects , the side region, and in particular quantum well portion ( s ) of the side region, comprises a quantum well intermixing resulting in an enlarged bandgap of the quantum well portion ( s ) of the side region compared to respective quantum well portion ( s ) of the central region . In particular by means of a local quantum well intermixing , the side region of the active region can be treated by controllable diffusion of a dopant into the active region to create a higher bandgap material at the sidewalls compared to the central region which minimizes carrier leakage and is a way to fabricate more efficient pLEDs .

[0028] According to some aspects , the side region, and in particular quantum well portion ( s ) of the side region, comprises a dotation with a dopant of the second conductivity type , in particular Zn . In particular quantum well portion ( s ) of the side region and barrier layer portions in the of the side region as well as portions of the first and / or second layer adj acent to the side region can comprise a dotation with the dopant . Such a dotation can in particular result from a quantum well intermixing process by diffusing the dopant into the side region of the active region .

[0029] According to some aspects , the semiconductor layer stack is of an InGaAlP or InAlGaAs material system and in particular Al and 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 ) .

[0030] According to some aspects , the first sublayers comprise at least in the central region a lower Al content than the second sublayers , in particular at least 5 % lower, the at least one quantum well comprises at least in the central region a lower Al content than the second sublayers , in particular at least 10 % lower , and the at least one quantum well comprises at least in the central region a lower Al content than the first sublayers , in particular at least 5 % lower . In other words , the second sublayers can at least in the central region comprise a higher Al content than the first sublayers , in particular at least 5 % higher, the second sublayers can at least in the central region comprise a higher Al content than the at least one quantum well , in particular at least 10 % higher , and the first sublayers can at least in the central region comprise a higher Al content than the at least one quantum well , in particular at least 5 % higher . The aforementioned Al contents can for example extend laterally throughout the whole layer ( s ) and quantum well ( s ) , can however in the final light emitting device also be present in the given ratios only in the central region . This can for example be as a quantum well intermixing in the side region may change the Al ratios in the side region .

[0031] Hence according to some aspects , first sublayer portions of the central region comprise a lower Al content than second sublayer portions of the central region, in particular at least 5 % lower, quantum well portion ( s ) of the central region comprise a lower Al content than second sublayer portions of the central region, in particular at least 10 % lower, and quantum well portion ( s ) of the central region comprise a lower Al content than first sublayer portions of the central region, in particular at least 5 % lower . In other words , second sublayer portions of the central region can comprise a higher Al content than first sublayer portions of the central region, in particular at least 5 % higher, second sublayer portions of the central region can comprise a higher Al content than quantum well portion ( s ) of the central region, in particular at least 10 % higher, and first sublayer portions of the central region can comprise a higher Al content than quantum well portion ( s ) of the central region, in particular at least 5 % higher .

[0032] According to some aspects , the first barrier layer and / or the second barrier layer and / or the third barrier layer ( s ) are tensile strained layers , in particular with regard to the growth substrate on which the semiconductor layer stack is grown . This can lead to the first barrier layer and / or the second barrier layer and / or the third barrier layer ( s ) being tensile strained layers compared to the quantum well ( s ) . The first barrier layer and / or the second barrier layer and / or the third barrier layer ( s ) can for example be tensile strained by reducing the In content of the layer ( s ) compared to the In content of the quantum well ( s ) , or by increasing the In content of the quantum well ( s ) compared to the In content of the barrier layer ( s ) .

[0033] According to some aspects , the quantum well ( s ) is / are -at least at some point of manufacture of the light emitting device and optionally also in the final device- compression strained, in particular with regard to the growth substrate on which the semiconductor layer stack is grown . This can lead to the quantum well ( s ) being compression strained compared to the first barrier layer and / or the second barrier layer and / or the barrier layer ( s ) . The quantum well ( s ) can for example be compression strained by reducing the Al content of the quantum well ( s ) compared to the Al content of the barrier layers , or by increasing the Al content of the barrier layers compared to the Al content of the quantum well ( s ) .

[0034] 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 .

[0035] 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 .

[0036] 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 .

[0037] 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 .

[0038] The method comprises at least the following step :

[0039] Providing a semiconductor layer stack of at least a first layer of a first conductivity type , a second layer of a second conductivity type as well as an active region arranged between the first and the second layer , wherein the active region comprises a central region and a side region laterally surrounding the central region, wherein the active region comprises at least one quantum well arranged between a first and a second barrier layer , wherein the first and the second barrier layer each comprise a first and a second sublayer, with the second sublayers each being adj acent to one of the at least one quantum well , wherein the first sublayers at least in the central region comprise a smaller average bandgap than the second sublayers , in particular at least 5 % smaller, wherein the at least one quantum well at least in the central region comprises a smaller average bandgap than the second sublayers , in particular at least 10 % smaller , and wherein the at least one quantum well at least in the central region comprises a smaller average bandgap than the first sublayers , in particular at least 5 % smaller .

[0040] According to some aspects , the method further comprises a step of diffusing a dopant of the second conductivity type into the side region of the active region . The diffusion of the dopant of the second conductivity type into the side region of the active region can then cause a quantum well intermixing in the side region .

[0041] According to some aspects , the step of providing the semiconductor layer stack comprises providing the first and / or second barrier layer and in particular the second sublayers with a higher Al content than the quantum well ( s ) , in particular at least 5 % higher . As a result , the first and / or second barrier layer and in particular the second sublayers at the same time comprises a lower Ga content than the quantum well ( s ) . The step of diffusing the dopant of the second conductivity type into the semiconductor layer stack may then cause an equilibration of the Al-Ga concentrations within the barrier layers , in particular second sublayers , and the quantum well ( s ) . In particular by means of the quantum well intermixing the Al content in the quantum well ( s ) is increased ( decreased in the barrier layer ( s ) ) due to Al atoms of the barrier layer ( s ) (with a higher Al concentration and thus a lower Ga concentration ) intermix with Ga atoms of the quantum well (with a higher Ga concentration and thus a lower Al concentration ) . This equilibration of the Al-Ga concentrations within the barrier layers , in particular second sublayers and the quantum well ( s ) in turn enlarges the bandgap within the quantum well ( s ) in the side region and keeps charge carriers away from the side region .

[0042] SHORT DESCRIPTION OF THE DRAWINGS

[0043] 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

[0044] Fig . 1 shows a cross section of a light emitting device in accordance with some aspects of the proposed principle ;

[0045] Fig . 2 shows a cross section of further embodiment of a light emitting device in accordance with some aspects of the proposed principle ;

[0046] Fig . 3 shows a diagram of the bandgap of the layers of an embodiment of a light emitting device with regard to its cross section in accordance with some aspects of the proposed principle ; and

[0047] Fig . 4 shows a diagram of the bandgap of the layers of another embodiment of a light emitting device with regard to its cross section in accordance with some aspects of the proposed principle . DETAILED DESCRIPTION

[0048] 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 .

[0049] 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 .

[0050] Figure 1 shows a cross section of a light emitting device 1 in accordance with some aspects of the proposed principle . The light emitting device 1 comprises a semiconductor layer stack 2 of a first layer 3 of a first conductivity type , a second layer 4 of a second conductivity type as well as an active region 5 arranged between the first and the second layer 3 , 4 .

[0051] In addition, the light emitting device 1 further comprises a first contact layer 9 arranged on the first layer 3 and a second contact layer 10 arranged on the second layer 4 . The first layer 3 is in particular an n-Type layer whereas the second layer 4 is a p-type layer . Hence the first contact layer 9 is an electrically conductive n-type contact layer, whereas the second contact layer 10 is an electrically conductive p-type contact layer . The first and second contact layer can be of the same material system as the semiconductor layer stack 2 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 9 , 10 a first and a second potential can be applied to the light emitting device 1 to operate the light emitting device 1 in a desired manner .

[0052] The active region 5 comprises a central region I la and a side region 11b laterally surrounding the central region Ila . Hence the active region 5 can in a lateral direction be divided in a central region Ila and a side region 11b . In addition, the active region 5 comprises a quantum well 6a arranged between a first and a second barrier layer 7a, 7b . Hence the active region 5 can in a vertical direction perpendicular to the lateral direction be divided into a quantum well 6a arranged between a first and a second barrier layer 7a, 7b . The barrier layers 7a, 7b are each separated into a first and a second sublayer 8a, 8b, wherein the second sublayers 8b are each arranged adj acent , in particular directly adj acent in the shown case , to the quantum well 6a .

[0053] The layers of the semiconductor layer stack 2 are made of the same material system but comprise different compound concentrations . This is the first and a second barrier layer 7a, 7b comprise a higher Al content than the quantum well 6a which is therefore compression strained . Within the first and second barrier layer 7a , 7b, the second sublayers 8b comprise a higher Al content than the first sublayers 8a . In addition, at least the second sublayers 8b comprise a thickness dl of less than 10 nm and in particular of less than 5 nm. By means of this , the first sublayers 8a can comprise a much less Al content than the second sublayers 8b while still keeping the Al content within the whole barrier layer in the vicinity of the quantum well 6a high enough to enable an efficient quantum well intermixing in side regions of the active region 5 . The reduced thickness of the second sublayers 8b with an increased Al content at the same time allows quantum tunnelling effects through the second sublayers 8b, such that the overall charge carrier mobility within the active region 5 is not or not significantly influenced and the light emitting device 1 can be operated at lower voltages .

[0054] To in addition increase the IQE of the light emitting device 1 , the side region 11b of the active region 5 can comprise a quantum well intermixing to increase the bandgap of the quantum well portion in the side region such that charge carriers are hindered to move into the direction of the side region . This can in particular be suitable as the side region may not only due to singulation processes for singulation of the light emitting device 1 comprise non-radiative recombination centres . By this radiative recombination within the central region can be improved .

[0055] Due to such quantum well intermixing, the ratios of the Al contents mentioned for the barrier layers or the sublayers can be substantially limited only to the central region Ila, since the quantum well intermixing can change the ratios of the Al contents in the side region 11b .

[0056] Figure 2 shows a cross section of a further embodiment of a light emitting device 1 in accordance with some aspects of the proposed principle . The light emitting device 1 and in particular the active region 5 of the light emitting device 1 in contrast to the embodiment of figure 1 comprises a multi quantum well structure .

[0057] In particular , the active region 5 comprises a central region I la and a side region 11b laterally surrounding the central region Ila . Hence the active region 5 can in a lateral direction be divided in a central region I la and a side region 11b . In addition, the active region 5 comprises a first and a second quantum well 6a, 6b, as well as a third barrier layer 7 c arranged between the first and second quantum well 6a, 6b . Hence the active region 5 can in a vertical direction perpendicular to the lateral direction be divided into a first and a second quantum well 6a, 6b arranged between a first and a second barrier layer 7a , 7b with a third barrier layer 7c arranged between the quantum wells 6a, 6b . The third barrier layer 7 c is separated into two second sublayers 8b between which a third sublayer 8c is arranged . The second sublayer 8b are configured and formed as the second sublayers 8b as already described with regard to figure 1 . The third sublayer in the embodiment shown is configured and formed as the first sublayers 8a s already described with regard to figure 1 .

[0058] Hence the quantum wells 6a , 6b are covered from both sides from each a thin second sublayer 8b comprising a high Al content with a third sublayer 8 c being arranged between the quantum wells 6a , 6b with a comparable low Al content . Again by this the Al content within the whole barrier layers can be kept low while in the vicinity of the quantum well 6a keeping it high enough to enable an efficient quantum well intermixing in side regions of the active region 5 . The reduced thickness of the second sublayers 8b at the same time allows quantum tunnelling effects through the second sublayers 8b , such that the overall charge carrier mobility within the active region 5 is not or not significantly influenced and the light emitting device 1 can be operated at lower voltages .

[0059] In the embodiment shown only two quantum wells 6a, 6b are drawn . It is however indicated by means of the dots and to be understood that the light emitting device can also comprise more than two quantum wells that can be added in the respective shown order . Hence the second quantum well 6b would be followed again by a third barrier layer 7 c and a third quantum well 6c and so on . In addition, in the embodiments shown, the sublayers and quantum wells are drawn symmetrically to each other as well as equal in size . This is however only for illustrative purposes and the size and so on can vary in any possible way .

[0060] Figure 3 shows a diagram of the average bandgap of the 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 3 shows a light emitting device 1 as shown in figure 2 with two quantum wells 6a , 6b but without the first and second contact layer .

[0061] In the diagram in the upper part of the figure the respective bandgap for the layer / sublayers of the semiconductor layer stack 2 , as shown in the lower part , is drawn . The two quantum wells 6a , 6b comprise the smallest bandgap and are tuned to emit light of a respective wavelength when operating the light emitting device . The quantum wells 6a, 6b comprise a thickness d2 of at least 15 nm and are arranged between the second sublayers 8b with the highest bandgap , in particular due to a very high Al content , and thickness dl of less than 10 nm and in particular less than 5 nm. The first sublayers comprise a thickness d3 of less than 7 nm, whereas the third sublayer 8c comprise a thickness d4 of less than 7 nm.

[0062] In addition, in the embodiments shown, the sublayers and quantum wells are drawn symmetrically to each other as well as equal in size and bandgap . This is however only for illustrative purposes and the size and bandgap can vary . For example , the third sublayer 8c can comprise a different bandgap that is larger or smaller than the one drawn and in particular larger or smaller than the bandgap of the first sublayers 8a, as long as it larger than that of the quantum wells 6a , 6b and smaller than that of the second sublayers 8b .

[0063] Figure 4 shows a diagram of the average bandgap of the layers of another 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 4 shows a light emitting device 1 as shown in figure 2 with two quantum wells 6a , 6b but without the first and second contact layer .

[0064] In the diagram in the upper part of the figure the respective bandgap for the layer / sublayers of the semiconductor layer stack 2 and in particular of the active region within the central region, as shown in the lower part , is drawn . The two quantum wells 6a, 6b comprise the smallest average bandgap and are tuned to emit light of a respective wavelength when operating the light emitting device . The quantum wells 6a, 6b comprise a thickness d2 of less than 15 nm and are arranged between the second sublayers 8b with the highest average bandgap, in particular due to a very high Al content , and thickness dl of less than 10 nm and in particular less than 5 nm . The first sublayers comprise a thickness d3 of less than 7 nm, whereas the third sublayer 8c comprise a thickness d4 of less than 7 nm. The division of the barrier layers 7a, 7b, 7c into sublayers can in particular be a virtual division, as the sublayers may substantially only differ in its Al content throughout its thickness but may by besides this form a continuous layer throughout the thickness of a respective barrier layer .

[0065] It is thus to be understood that the barrier layers 7a , 7b , 7c can compared to the embodiment shown be separated into further (virtual ) sublayers , wherein the further sublayers may differ in that they comprise different average bandgaps . As shown, the band gaps are graded towards the quantum wells , e . g . exponentially or quadratically increasing towards the quantum wells , and parabolic between the quantum wells . However, a continuous increase towards the quantum wells and a funnel-shaped configuration between the quantum wells is also possible .

[0066] In addition, in the embodiments shown, the sublayers and quantum wells are drawn symmetrically to each other as well as equal in size and bandgap . This is however only for illustrative purposes and the size and bandgap can vary . For example , the third sublayer 8c can comprise a different bandgap that is larger or smaller than the one drawn and in particular larger or smaller than the bandgap of the first sublayers 8a, as long as it larger than that of the quantum wells 6a , 6b and smaller than that of the second sublayers 8b .

[0067] LIST OF REFERENCES

[0068] 1 light emitting device

[0069] 2 semiconductor layer stack 3 first layer

[0070] 4 second layer

[0071] 5 active region

[0072] 6a, 6b quantum well

[0073] 7a, 7b, 7 c barrier layer 8a, 8b, 8 c sublayer

[0074] 9 first contact layer

[0075] 10 second contact layer

[0076] Ila central region

[0077] 11b side region dl , d2 , de , d4 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 as well as an active region (5) arranged between the first and the second layer (3, 4) ; wherein the active region (5) comprises a central region (Ila) and a side region (11b) laterally surrounding the central region (Ila) ; wherein the active region (5) comprises at least one quantum well (6a) arranged between a first and a second barrier layer (7a, 7b) ; wherein the first and the second barrier layer (7a, 7b) each comprise at least a first and a second sublayer (8a, 8b) , with the second sublayers (8b) each being adjacent to one of the at least one quantum well (6a) ; wherein the first sublayers (8a) at least in the central region (Ila) comprise a smaller average bandgap than the second sublayers (8b) , in particular at least 5 % smaller; wherein the at least one quantum well (6a) at least in the central region (Ila) comprises a smaller average bandgap than the second sublayers (8b) , in particular at least 10 % smaller; and wherein the at least one quantum well (6a) at least in the central region (Ila) comprises a smaller average bandgap than the first sublayers (8a) , in particular at least 5 % smaller.

2. Light emitting device according to claim 1, wherein the active region (5) comprises at least two quantum wells (6a, 6b) arranged between the first and the second barrier layer (7a, 7b) and at least one third barrier layer (7c) arranged between the at least two quantum wells (6a, 6b) .

3. Light emitting device according to claim 2, wherein the at least one third barrier layer (7c) comprise a third sublayer (8c) arranged between two second sublayers (8b) , with the second sublayers (8b) each being adjacent to one of the at least two quantum wells (6a, 6b) .

4. Light emitting device according to claim 2 or 3, wherein the at least two quantum wells (6a, 6b) at least in the central region (Ila) comprise a substantially equal average bandgap .

5. Light emitting device according to any one of claims 2 to 4 , wherein the at least two quantum wells (6a, 6b) at least in the central region (Ila) comprise a smaller average bandgap than the third sublayer (8c) , in particular at least 5 % smaller.

6. Light emitting device according to any one of the preceding claims, wherein the second sublayers (8b) at least in the central region (Ila) comprise a substantially equal average bandgap.

7. Light emitting device according to any one of the preceding claims, wherein the second sublayers (8b) comprise a thickness of less than 5 nm, in particular less than 3 nm or 2 nm.

8. Light emitting device according to any one of the preceding claims, wherein the first sublayers (8a) comprise a thickness of less than 7 nm, in particular less than 5 nm or 3 nm.

9. Light emitting device according to any one of the preceding claims, wherein the third sublayer (8c) comprises a thickness of less than 7 nm, in particular less than 5 nm or 3 nm.

10. Light emitting device according to any one of the preceding claims, wherein the at least one quantum well (6a) comprise a thickness of less than 15 nm, in particular less than 8 nm or 3 nm.

11. Light emitting device according to any one of the preceding claims, wherein the semiconductor layer stack (2) is of an InGaAlP or InAlGaAs material system.

12. Light emitting device according to any one of the preceding claims,wherein the first sublayers (8a) at least in the central region (Ila) comprise a lower Al content than the second sublayers (8b) , in particular at least 5 % lower; wherein the at least one quantum well (6a) at least in the central region (Ila) comprises a lower Al content than the second sublayers (8b) , in particular at least 10 % lower; and wherein the at least one quantum well (6a) at least in the central region (Ila) comprises a lower Al content than the first sublayers (8a) , in particular at least 5 % lower.

13. Light emitting device according to any one of the preceding claims, wherein the side region (11b) , and in particular a quantum well portion of the side region (11b) , comprises a dotation with a dopant of the second conductivity type, in particular Zn.

14. Light emitting device according to claim 13, wherein the side region (11b) , and in particular a quantum well portion of the side region (11b) , comprises a quantum well intermixing .

15. Light emitting device according to any one of the preceding claims, further comprising a first contact layer (9) arranged on the first layer (3) and / or a second contact layer (10) arranged on the second layer ( 4 ) .

16. Method for manufacturing a light emitting device (1) , in particular pLED, comprising the step:Providing 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 as well as an active region (5) arranged between the first and the second layer (3, 4) ; wherein the active region (5) comprises a central region (Ila) and a side region (11b) laterally surrounding the central region (Ila) ; wherein the active region (5) comprises at least one quantum well (6a) arranged between a first and a second barrier layer (7a, 7b) ; wherein the first and the second barrier layer (7a, 7b) each comprise at least a first and a second sublayer (8a, 8b) , with thesecond sublayers (8b) each being adjacent to one of the at least one quantum well (6a) ; wherein the first sublayers (8a) at least in the central region (Ila) comprise a smaller average bandgap than the second sublayers (8b) , in particular at least 5 % smaller; wherein the at least one quantum well (6a) at least in the central region (Ila) comprises a smaller average bandgap than the second sublayers (8b) , in particular at least 10 % smaller; and wherein the at least one quantum well (6a) at least in the central region (Ila) comprises a smaller average bandgap than the first sublayers (8a) , in particular at least 5 % smaller.

17. The method according to claim 16, further comprising a step of diffusing a dopant of the second conductivity type into the side region (11b) of the active region (5) , wherein the dopant is in particular Zn.

18. The method according to claim 16 or 17, further comprising a step of quantum well intermixing the side region (11b) of the active region (5) .

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