Optoelectronic semiconductor device and method of manufacturing an optoelectronic semiconductor device

Abstract

An optoelectronic semiconductor device (10) comprises an epitaxial semiconductor layer stack (124). The epitaxial semiconductor layer stack (124) comprises a superlattice layer stack (109) comprising a sequence of alternating InxGa1-xN- and GaN-layers (135, 136), a p-type semiconductor layer (120), and an active zone (115) arranged between the p-type semiconductor layer (120) and the superlattice layer stack (109) and configured to generate and / or absorb electromagnetic radiation (15). The optoelectronic semiconductor device (10) further comprises an n-type semiconductor layer (110) arranged on a side of the superlattice layer stack (109) remote from the active zone (115) and a plurality of V-pits (125) formed in the active zone (115) and in the superlattice layer stack (109). The superlattice layer stack (109) further comprises AlyGa1-yN layers (137).

Description

[0001] OPTOELECTRONIC SEMICONDUCTOR DEVICE AND METHOD OF

[0002] MANUFACTURING AN OPTOELECTRONIC SEMICONDUCTOR DEVICE

[0003] Gallium nitride ( GaN) -based optoelectronic and electronic semiconductor devices such as light-emitting diodes ( LEDs ) are widely used and their reliability is of great importance for many applications . Generally, optoelectronic semiconductor devices may comprise an underlying epitaxial (EPI ) structure including an active layer which comprises a quantum wel l structure and which is employed as a light-emitting layer . For example , when a voltage is applied electrons and holes may recombine in a quantum well layer of the active zone to generate electromagnetic radiation .

[0004] Generally, attempts are being made to improve GaN-based semiconductor devices .

[0005] It is an obj ect of the present invention to provide an improved optoelectronic semiconductor device and an improved method of manufacturing an optoelectronic semiconductor device .

[0006] SUMMARY

[0007] According to embodiments , the above obj ects are achieved by the claimed matter according to the independent claims . Further developments are defined in the dependent claims .

[0008] According to embodiments , an optoelectronic semiconductor device comprises an epitaxial semiconductor layer stack . The epitaxial semiconductor layer stack comprises a superlattice layer stack comprising a sequence of alternating InxGai-xN- and GaN-layers , a p-type semiconductor layer, and an active zone arranged between the p-type semiconductor layer and the superlattice layer stack and configured to generate and / or absorb electromagnetic radiation . The epitaxial layer stack further comprises an n-type semiconductor layer arranged on a side of the superlattice layer stack remote from the active zone , and a plurality of V-pits formed in the active zone and in the superlattice layer stack . The superlattice layer stack further comprising AlyGai-yN layers .

[0009] For example , each of the AlyGai-yN layers is arranged directly adj acent to a corresponding one of the GaN-layers .

[0010] According to embodiments , an In-content x of the InxGai-xN-layer is less than 20 % .

[0011] For example , an Al-content y of the AlyGai-yN layers is less than 50 % .

[0012] According to embodiments , a thickness of the AlyGai-yN layers is less than 30 nm .

[0013] The optoelectronic semiconductor device may further comprise an electron blocking layer between the active zone and the p- type semiconductor layer .

[0014] According to embodiments , the p-type semiconductor layer is selected from GaN, InGaN, AlGaN, Al InGaN and hexagonal BN .

[0015] Moreover, the n-type semiconductor layer may be selected from GaN, InGaN, AlGaN, Al InGaN and hexagonal BN .

[0016] The optoelectronic semiconductor device may further comprise a substrate and a buf fer layer including dislocations . The buf fer layer may be arranged between the substrate and the n- doped semiconductor layer .

[0017] According to embodiments , a material of the buf fer layer may be selected from GaN, AlGaN, AlGalnN or InGaN .

[0018] The optoelectronic semiconductor device may further comprise a V-pit generation layer between the n-doped semiconductor layer and the superlattice layer stack .

[0019] A method of manufacturing an optoelectronic semiconductor device comprises forming an epitaxial semiconductor layer stack . For example , forming the epitaxial semiconductor layer stack may comprise forming an n-type semiconductor layer, forming a superlattice layer stack over the n-type semiconductor layer, the superlattice layer stack comprising a sequence of alternating InxGai-xN- and GaN-layers and AlyGai-yN layers and forming an active zone over the superlattice layer stack, the active zone being configured to generate and / or absorb electromagnetic radiation . The method may further comprise forming a p-type semiconductor layer . During the formation of the superlattice layer stack and the active zone a plurality of V-pits are formed in the superlattice layer stack and in the active zone .

[0020] For example , during the formation of the superlattice layer stack Al is introduced in a reaction chamber .

[0021] According to embodiments , during the formation of the superlattice layer stack hydrogen is mixed to a reactor chamber .

[0022] For example , at least part of the p-type semiconductor layer is formed in the V-pits . The method may further comprise forming a buf fer layer over a substrate before forming the n-type semiconductor layer, wherein the n-type semiconductor layer is formed over the buf fer layer .

[0023] BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings are included to provide a further understanding of embodiments of the invention and are incorporated in and constitute a part of this speci fication . The drawings illustrate the embodiments of the present invention and together with the description serve to explain the principles . Other embodiments of the invention and many of the intended advantages will be readily appreciated, as they become better understood by reference to the following detailed description . The elements of the drawings are not necessarily to scale relative to each other . Like reference numbers designate corresponding similar parts .

[0025] Fig . 1A shows a schematic cross-sectional view of an optoelectronic semiconductor device according to embodiments .

[0026] Fig . IB shows an example of an energy band diagram of portions of the optoelectronic semiconductor device .

[0027] Fig . 2A shows a distribution of measurement results of relative power .

[0028] Fig . 2B shows an example of measurement results of relative forward voltage .

[0029] Fig . 2C shows measurement results of relative forward voltage at low current . Fig. 3 summarizes a method according to embodiments.

[0030] DETAILED DESCRIPTION

[0031] In the following detailed description reference is made to the accompanying drawings, which form a part hereof and in which are illustrated by way of illustration specific embodiments in which the invention may be practiced. In this regard, directional terminology such as "top", "bottom", "front", "back", "over", "on", "above", "leading", "trailing" etc. is used with reference to the orientation of the Figures being described. Since components of embodiments of the invention can be positioned in a number of different orientations, the directional terminology is used for purposes of illustration and is in no way limiting. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope defined by the claims .

[0032] The description of the embodiments is not limiting. In particular, elements of the embodiments described hereinafter may be combined with elements of different embodiments.

[0033] The terms "wafer" or "semiconductor substrate" used in the following description may include any semiconductor-based structure that has a semiconductor surface. Wafer and structure are to be understood to include doped and undoped semiconductors, epitaxial semiconductor layers, e.g. supported by a base semiconductor foundation, and other semiconductor structures. For example, a layer of a first semiconductor material may be grown on a growth substrate of a second semiconductor material. According to further embodiments, the growth substrate may be an insulating substrate such as a sapphire substrate . Depending on the purpose of use , the semiconductor may be based on a direct or an indirect semiconductor material . Examples of semiconductor materials described herein and particularly suitable for generation of electromagnetic radiation comprise nitride-compound semiconductors , by which e . g . ultraviolet or blue light or longer wavelength light may be generated, such as GaN, InGaN, AIN, AlGaN, AlGalnN, hexagonal BN und combinations of these materials . The stoichiometric ratio of the compound semiconductor materials may vary .

[0034] The term " substrate" generally refers to semiconductor substrates , conductive or insulating substrates .

[0035] The terms " lateral" and "hori zontal" as used in this speci fication intends to describe an orientation parallel to a first surface of a substrate or semiconductor body . This can be for instance the surface of a wafer or a die .

[0036] The term "vertical" as used in this speci fication intends to describe an orientation which is arranged perpendicular to the first surface of a substrate or semiconductor body .

[0037] Fig . 1A shows a vertical cross-sectional view of a portion of an optoelectronic semiconductor device according to embodiments . As is illustrated in Fig . 1A, the optoelectronic semiconductor device 10 comprises an epitaxial semiconductor layer stack 124 . The epitaxial semiconductor layer stack 124 comprises a superlattice layer stack 109 which comprises a sequence of alternating InxGai-xN- and GaN-layers 135 , 136 , a p- type semiconductor layer 120 and an active zone 115 arranged between the p-type semiconductor layer 120 and the superlattice layer stack 109 and configured to generate and / or absorb electromagnetic radiation 15 . The optoelectronic semiconductor device 10 further comprises an n-type semiconductor layer 110 which is arranged on a side of the superlattice layer stack 109 remote from the active zone 115 and a plurality of V-pits 125 which are formed in the active zone 115 and in the superlattice layer stack 109 . A superlattice layer stack 109 further comprises AlyGai-yN-layers 137 .

[0038] For example , the p-type semiconductor layer and the n-type semiconductor layer may be nitride semiconductor layers . In more detail , any of the p-type semiconductor layer 120 and the n-type semiconductor layer 110 may comprise GaN or a compound semiconductor material including GaN, e . g . InGaN . According to further embodiments , any of the p-type semiconductor layer 120 and the n-type semiconductor layer 110 may comprise hexagonal boron nitride (hBN) . Moreover, the active zone may be implemented as a multi-quantum well layer including quantum well layers 138 and quantum barrier layers 139 . Materials of the quantum well layer 138 and / or the quantum barrier layer 139 also may comprise GaN or a compound semiconductor material including GaN .

[0039] For example , the epitaxial semiconductor layer stack 124 may be arranged over a substrate 100 , e . g . a transparent substrate , for example sapphire . A buf fer layer 105 may be arranged over the substrate 100 . The buf fer layer 105 may comprise layers . A material of the buf fer layer 105 or of layers constituting the buf fer layer 105 may comprise AlGalnN, GaN or AlGaN . For example , spiral or helical dislocations 134 ("threading dislocations" ) may be embedded in the buf fer layer 105 which may give rise to V-pits 125 . An intermediate layer 107 may be arranged over the buf fer layer 105 . The intermediate layer 107 may comprise GaN or AlGaN (with a ratio of Al of less than 0 . 2 ) and may be of n-type due to nitrogen vacancy or impurities . The n-type semiconductor layer 110 may be arranged over the intermediate layer 107 . The n-type semiconductor layer 110 may comprise for example GaN, a compound semiconductor material such as AlGaN and may have a content of Al of less than 0 . 2 , for example . An n-contact element 133 may be electrically connected to the n-type semiconductor layer 110 .

[0040] A V-pit generation layer 108 may be arranged over the n-type semiconductor layer 110 . For example , the V-pit generation layer 108 may be an n-type GaN layer having a doping concentration which is lower than the doping concentration of the n-type semiconductor layer 110 . According to further embodiments , the V-pit generation layer 108 may include a composition which is di f ferent from the composition of the n- type semiconductor layer 110 . For example , the V-pit generation layer 108 may have a composition of a compound semiconductor material including GaN such as AlGalnN or InGaN .

[0041] A superlattice layer stack 109 is arranged over the V-pit generation layer 108 . The superlattice layer stack comprises a sequence of alternating InxGai-xN-layers 135 and GaN-layers 136 and further AlyGai-yN-layers 137 as is schematically illustrated in the right-hand portion of Fig . 1A. For example , the AlyGai-yN-layers 137 are arranged so that a GaN-layer 136 is disposed on either surfaces of the AlyGai-yN-layer 137 . Accordingly, the AlyGai-yN-layer is arranged directly adj acent to a corresponding one of the GaN-layers 136 . For example , a sequence of an InxGai-xN-layer 135 , a GaN-layer 136 , an AlyGai-yN-layer 137 , a GaN-layer 136 , and an InxGai-xN-layer 135 may be repeated several times . For example , an Al-content y of the AlyGai-yN- layers 137 may be less than 50 % and more than 0 % . Further, a thickness of the AlyGai-yN-layers 137 may be less than 30 nm. For example , the InxGai-xN-layers 135 do not include aluminum .

[0042] The active zone 115 may comprise a multi-quantum well structure including quantum well layers 138 and quantum barrier layers 139 wherein quantum barrier layers 139 are arranged on either side of each of the quantum well layers 138 . The quantum well layers 138 have a relatively low bandgap, whereas the quantum barrier layers 139 have a relatively large bandgap . For example , the quantum barrier layers 139 may comprise GaN . Further, the quantum well layers 138 may comprise AlGalnN or InGaN which does not include Al . Further, an electron blocking layer 122 may be arranged over the active zone 115 . For example , the electron blocking layer 122 may be a p-type AlGaN layer .

[0043] The p-type semiconductor layer 120 is filled in the V-pits 125 . A portion of the p-type semiconductor layer 120 may also be arranged over hori zontal portions of the electron blocking layer 122 . Moreover, a p-contact layer 121 , e . g . a heavily p- doped GaN, InGaN or hBN layer may be arranged over the p-type semiconductor layer 120 . Moreover, a current spreading layer 127 may be arranged over the p-contact layer 121 . For example , a material of the current spreading layer 127 may comprise a transparent conductive oxide , e . g . ITO ( indium tin oxide ) , ZnO or other transparent conductive materials . A p-contact element may be arranged in electrical contact with the current spreading layer 127 . When a corresponding voltage is applied between the p-contact element 128 and the n-contact element 133 , electrons 131 are inj ected from the n-type semiconductor layer 110 towards the active zone 115 . Moreover, holes 132 are inj ected via the sidewalls 126 of the V-pits 125 into the active zone 115 . Moreover, holes 132 may also be inj ected via a hori zontal surface of the electron blocking layer 122 into the active zone 115 .

[0044] Electrons 131 usually have a much higher mobility than holes and tend to overflow through the active zone 115 . For this reason, the electron blocking layer 122 is used to decrease an electron overflow through the active region . According to embodiments , due to additional AlyGai-yN-layer 137 being a component of the superlattice layer stack 109 , an AlGaN barrier is formed in the superlattice layer stack 109 . Accordingly, a higher barrier height is created than it would be the case i f only GaN layers were present in the superlattice layer stack 109 . In other words , the higher bandgap energy of AlyGai-yN may result in a higher barrier height in the superlattice layer stack 109 . Further, the AlyGai-yN-layer 137 may decrease the electron mobility in a vertical direction ( e . g . perpendicularly to the c-plane direction) by spreading electrons in a direction parallel to the c-plane . Accordingly, electrons may be ef ficiently blocked by the AlyGai-yN barrier layer and may be spread parallel to the c-plane .

[0045] Usually, hydrogen is mixed to the reactor chamber during the growth of the active zone 115 and the growth of the superlattice layer stack 109 . For example , during a comparatively high temperature growth e . g . the GaN barrier, hydrogen is mixed . As a consequence , a density of point defects from the V-pit generation layer 108 may be decreased resulting in an increase of the radiative ef ficiency .

[0046] Fig . IB shows a schematic diagram illustrating the bandgap energy at di f ferent locations of the superlattice layer stack 109 and the active zone 115 . As is shown in Fig . IB, due to the presence of the AlyGai-yN-layer 137 the barrier height is locally increased so as to reduce electron overflow through the active zone 115 by enhancing electron spreading parallel to the c-plane in the superlattice layer stack 109 .

[0047] Fig . 2A shows a comparison of a measured relative optical power of a conventional device 140 in comparison with a device 141 in accordance with embodiments . As can be taken from Fig . 2A showing a distribution of measurement results , the optical power is increased for devices 141 in accordance with embodiments .

[0048] Moreover, Fig . 2B shows a distribution of measurement results of the relative forward or operating voltage of a conventional device 140 in comparison to a device 141 in accordance with embodiments . As can be seen, the relative forward voltage of the device may be decreased as a result of the presence of the AlyGai-yN-layers in the superlattice layer stack 109 .

[0049] Moreover, Fig . 2C shows a comparison of a distribution of measurement results for a conventional device 140 and a device 141 in accordance with embodiments of the voltage at a low current ( 10 pA) . As is seen, at a low current , the voltage is increased for devices 141 in accordance with embodiments . This may be due to the fact that the quality of the material is improved when aluminum is supplied during growth of the superlattice layer stack 109 .

[0050] Fig . 3 summari zes a method according to embodiments . A method of manufacturing an optoelectronic semiconductor device comprising forming an epitaxial semiconductor layer stack . Forming the epitaxial semiconductor layer stack comprises forming ( S 100 ) an n-type semiconductor layer, forming ( S 110 ) a superlattice layer stack over the n-type semiconductor layer, the superlattice layer stack comprising a sequence of alternating InxGai-xN- and GaN-layers and AlyGai-yN layers , forming ( S 120 ) an active zone over the superlattice layer stack, the active zone being configured to generate and / or absorb electromagnetic radiation, and forming ( S 130 ) a p-type semiconductor layer . During the formation of the superlattice layer stack and the active zone a plurality of V-pits are formed in the superlattice layer stack and the active zone .

[0051] As is illustrated, the respective layers illustrated in Fig . 1A may be formed over a substrate 100 . During growth of the intermediate layer 107 and the n-type semiconductor layer 110 , dislocations 134 may be generated and may result in V-pits generated within the V-pit generation layer 108 . The V-pits 125 extend through the active zone 115 and the superlattice layer stack 109 . The p-type semiconductor layer 120 is formed so that at least a part of this layer is arranged within the V-pits 125 . Finally, a p-contact layer 121 and a current spreading layer 127 may be formed over the p-type semiconductor layer 120 .

[0052] For example , while forming the GaN-layer 136 or a quantum barrier layer 139 of the multi-quantum well structure forming the active zone 115 , a hydrogen content and a temperature may be increased .

[0053] While embodiments of the invention have been described above , it is obvious that further embodiments may be implemented . For example , further embodiments may comprise any subcombination of features recited in the claims or any subcombination of elements described in the examples given above . Accordingly, this spirit and scope of the appended claims should not be limited to the description of the embodiments contained herein . LIST OF REFERENCES optoelectronic semiconductor device electromagnetic radiation substrate buf fer layer intermediate layer V-pit generation layer superlattice layer stack n-type semiconductor layer active zone p-type semiconductor layer p-contact layer electron blocking layer epitaxial semiconductor layer stack V-pit sidewall of V-pit current spreading layer p-contact element electron hole n-contact element dislocation InxGai-xN-layer GaN-layer AlyGai-yN layer quantum well layer quantum barrier layer conventional device device in accordance with embodiments

Claims

CLAIMS1. An optoelectronic semiconductor device (10) comprising an epitaxial semiconductor layer stack (124) , the epitaxial semiconductor layer stack (124) comprising: a superlattice layer stack (109) comprising a sequence of alternating InxGai-xN- and GaN-layers (135, 136) ; a p-type semiconductor layer (120) ; an active zone (115) arranged between the p-type semiconductor layer (120) and the superlattice layer stack (109) and configured to generate and / or absorb electromagnetic radiation (15) ; an n-type semiconductor layer (110) arranged on a side of the superlattice layer stack (109) remote from the active zone (115) ; and a plurality of V-pits (125) formed in the active zone (115) and in the superlattice layer stack (109) , the superlattice layer stack (109) further comprising AlyGai-yN layers (137) , wherein each of the AlyGai-yN layers (137) is arranged directly adjacent to two of the GaN-layers (136) , the GaN-layers (136) being disposed on either surface of an adjacent one of the AlyGai-yN-layers (137) .

2. The optoelectronic semiconductor device (10) according to claim 1, wherein the superlattice layer stack (109) comprises a sequence of an InxGai-xN-layer (135) , a GaN-layer (136) , an AlyGai-yN-layer (137) , a GaN-layer (136) , and an InxGai-xN-layer (135) .

3. The optoelectronic semiconductor device (10) according to claim 1 or 2, wherein an In-content x of the InxGai-xN-layer (135) is less than 20 %.

4. The optoelectronic semiconductor device (10) according to any of the preceding claims, wherein an Al-content y of the AlyGai-yN layers (137) is less than 50 %.

5. The optoelectronic semiconductor device (10) according to any of the preceding claims, wherein a thickness of the AlyGai-yN layers (137) is less than 30 nm.

6. The optoelectronic semiconductor device (10) according to any of the preceding claims, further comprising an electron blocking layer (122) between the active zone (115) and the p- type semiconductor layer (120) .

7. The optoelectronic semiconductor device (10) according to any of the preceding claims, wherein the p-type semiconductor layer (120) is selected from GaN, InGaN, AlGaN, AlInGaN and hexagonal BN.

8. The optoelectronic semiconductor device (10) according to any of the preceding claims, wherein the n-type semiconductor layer (110) is selected from GaN, InGaN, AlGaN, AlInGaN and hexagonal BN.

9. The optoelectronic semiconductor device (10) according to any of the preceding claims, further comprising a substrate (100) and a buffer layer (105) including dislocations (134) , the buffer layer (105) being arranged between the substrate (100) and the n-doped semiconductor layer (110) .

10. The optoelectronic semiconductor device (10) according to claim 9, wherein a material of the buffer layer (105) is selected from GaN, AlGaN, AlGalnN or InGaN.

11. The optoelectronic semiconductor device (10) according to claim 9 or 10, further comprising a V-pit generation layer (108) between the n-doped semiconductor layer (110) and the superlattice layer stack (109) .

12. A method of manufacturing an optoelectronic semiconductor device (10) comprising forming an epitaxial semiconductor layer stack (124) , wherein forming the epitaxial semiconductor layer stack (124) comprises: forming (S100) an n-type semiconductor layer (110) ; forming (S110) a superlattice layer (109) stack over the n-type semiconductor layer (110) , the superlattice layer stack (109) comprising a sequence of alternating InxGai-xN- and GaN-layers (135, 136) and AlyGai-yN layers (137) , wherein each of the AlyGai-yN layers (137) is arranged directly adjacent to two of the GaN-layers (136) , the GaN-layers (136) being disposed on either surface of an adjacent one of the AlyGai-yN- layers ( 137 ) ; forming (S120) an active zone (115) over the superlattice layer stack (109) , the active zone (115) being configured to generate and / or absorb electromagnetic radiation (15) ; forming (S130) a p-type semiconductor layer (120) ; wherein during the formation of the superlattice layer stack (109) and the active zone (115) a plurality of V-pits (125) are formed in the superlattice layer stack (109) and in the active zone (115) .

13. The method of claim 12, wherein during the formation (S110) of the superlattice layer stack (109) Al is introduced in a reaction chamber.

14. The method of claim 13, wherein during the formation of the superlattice layer stack (109) hydrogen is mixed to a reaction chamber.

15. The method according to any of claims 12 to 14, wherein at least part of the p-type semiconductor layer (120) is formed in the V-pits (125) .

16. The method according to any of claims 13 or 15, further comprising forming a buffer layer (105) over a substrate (100) before forming the n-type semiconductor layer (110) , wherein the n-type semiconductor layer (110) is formed over the buffer layer (105) .

17. The method according to any of claims 12 to 16, wherein forming the superlattice layer stack (109) comprises sequentially forming an InxGai-xN-layer (135) , a GaN-layer (136) , an AlyGai-yN-layer (137) , a GaN-layer (136, ) and an InxGai-xN-layer (135) .

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