Optoelectronic semiconductor device and method of manufacturing an optoelectronic semiconductor device

Abstract

An optoelectronic semiconductor device (10) comprises an epitaxial semiconductor layer stack (112) comprising a first semiconductor layer (110) of a first conductivity type, a second semiconductor layer (120) of a second conductivity type and an active zone (115) arranged between the first semiconductor layer (110) and the second semiconductor layer (120), the active zone (115) being configured to generate electromagnetic radiation (15). The optoelectronic semiconductor device (10) further comprises a conductive layer (122) over a first main surface (117) of the epitaxial semiconductor layer stack (112) and a dielectric or semiconducting first material layer (124) over a surface of the conductive layer (122) remote from the epitaxial semiconductor layer stack (112). A first main surface (125) of the first material layer (124) remote from the conductive layer (122) is patterned. The optoelectronic semiconductor device (10) further comprises a metal layer (126) over the first main surface (125) of the first material layer (124).

Description

[0001] OPTOELECTRONIC SEMICONDUCTOR DEVICE AND METHOD OF

[0002] MANUFACTURING AN OPTOELECTRONIC SEMICONDUCTOR DEVICE

[0003] Light-emitting diodes ( LEDs ) that are based on the AlGaN material system are configured to emit electromagnetic radiation in a UV range , e . g . the UVC range . For example , AlGaN-based LEDs are usually employed in a variety of applications , comprising e . g . disinfection .

[0004] Generally, attempts are made to improve a wall plug ef ficiency (WPE ) which corresponds to a ratio of the optical power and the electrical power .

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

[0006] SUMMARY

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

[0008] An optoelectronic semiconductor device comprises an epitaxial semiconductor layer stack comprising a first semiconductor layer of a first conductivity type , a second semiconductor layer of a second conductivity type and an active zone arranged between the first semiconductor layer and the second semiconductor layer, the active zone being configured to generate electromagnetic radiation . The optoelectronic semiconductor device further comprises a conductive layer arranged over a first main surface of the epitaxial semiconductor layer stack, and a dielectric or semiconducting first material layer arranged over a surface of the conductive layer remote from the epitaxial semiconductor layer stack . A first main surface of the first material layer remote from the conductive layer is patterned . The optoelectronic semiconductor device further comprises a metal layer over the first main surface of the first material layer .

[0009] For example , the first main surface of the first material layer is patterned to form a plurality of protruding portions .

[0010] By way of example , at least one sidewall of at least one protruding portion extends in a direction that is di f ferent from a vertical direction .

[0011] For example , the first material layer has a refractive index which is close to the refractive index of a material of the second semiconductor layer directly adj acent to the conductive layer .

[0012] According to embodiments , the refractive index of the first material layer is in a range of 2 . 2 inclusive to 2 . 8 inclusive .

[0013] For example , the active zone may comprise an AlxGai-xN layer .

[0014] According to embodiments , a surface of the metal layer remote from the first material layer may be planar .

[0015] The optoelectronic semiconductor device may further comprise a first dielectric layer between the first material layer and the conductive layer . The optoelectronic semiconductor device may further comprise a conformal second dielectric layer between the first material layer and the metal layer .

[0016] Moreover, the optoelectronic semiconductor device may comprise a transparent substrate over a second main surface of the semiconductor layer stack .

[0017] For example , an opening may be formed in the first material layer, wherein the metal layer contacts the conductive layer via the opening .

[0018] According to further embodiments , a method of manufacturing an optoelectronic semiconductor device comprises forming an epitaxial semiconductor layer stack comprising a first semiconductor layer of a first conductivity type , a second semiconductor layer of a second conductivity type and an active zone between the first semiconductor layer and the second semiconductor layer, the active zone being configured to generate electromagnetic radiation . The method further comprises forming a conductive layer over a first main surface of the epitaxial semiconductor layer stack, and forming a dielectric or semiconducting first material layer over a surface of the conductive layer remote from the epitaxial semiconductor layer stack . The method further comprises patterning a first main surface of the first material layer remote from the conductive layer, and forming a metal layer over the first main surface of the first material layer .

[0019] For example , patterning the first main surface of the first material layer may comprise forming a plurality of protruding portions . For example , at least one of the plurality of protruding portions may be formed so as to comprise a sidewal l having an extension direction that is di f ferent from a vertical extension direction .

[0020] According to embodiments , an optical device comprises the optoelectronic semiconductor device as described above . For example , the optical device may be a disinfection device .

[0021] BRIEF DESCRIPTION OF THE DRAWINGS

[0022] 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 .

[0023] Fig . 1 is a schematic cross-sectional view of an optoelectronic semiconductor device according to embodiments .

[0024] Fig . 2 is a schematic cross-sectional view of an optoelectronic semiconductor device according to further embodiments .

[0025] Fig . 3 is a schematic cross-sectional view of an optoelectronic semiconductor device according to further embodiments .

[0026] Figs . 4A to 4D show cross-sectional views of a workpiece when performing a method according to embodiments . Fig. 4E summarizes a method according to embodiments.

[0027] Fig. 5 is a schematic drawing showing an optic device according to embodiments.

[0028] DETAILED DESCRIPTION

[0029] 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.

[0030] The description of the embodiments is not limiting. In particular, elements of the embodiments described hereinafter may be combined with elements of different embodiments.

[0031] 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 semicon- ductor 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 , that may be used according to embodiments , 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 . According to further embodiments , the semiconductor material may comprise phosphide-compound semiconductors , by which e . g . green or longer wavelength light may be generated such as GaAsP, AlGalnP, GaP, AlGaP, as well as further semiconductor materials including AlGaAs , SiC, ZnSe , GaAs , ZnO, Ga203, diamond, hexagonal BN und combinations of these materials . The stoichiometric ratio of the compound semiconductor materials may vary . In the context of the present speci fication, the term " semiconductor" further encompasses organic semiconductor materials .

[0032] The term " substrate" generally refers to semiconductor substrates , conductive or insulating substrates .

[0033] 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 .

[0034] 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 .

[0035] Fig . 1 is a schematic cross-sectional view of an optoelectronic semiconductor device 10 according to embodiments . The optoelectronic semiconductor device 10 comprises an epitaxial sem- iconductor layer stack 112 which comprises a first semiconductor layer 110 of a first conductivity type , e . g . n-type , a second semiconductor layer 120 of a second conductivity type , e . g . p-type , and an active zone 115 arranged between the first semiconductor layer and the second semiconductor layer . The active zone may, for example , comprise a pn j unction, a double heterostructure , a single quantum well structure ( SQW, single quantum well ) or a multiple quantum well structure (MQW, multi quantum well ) for generating radiation . The term "quantum well structure" does not imply any particular meaning here with regard to the dimensionality of the quanti zation . Therefore it includes , among other things , quantum wells , quantum wires and quantum dots as well as any combination of these layers . The active zone 115 is configured to generate electromagnetic radiation 15 . The optoelectronic semiconductor device 10 further comprises a conductive layer 122 which is arranged over a first main surface 117 of the epitaxial semiconductor layer stack 112 . A main surface of the conductive layer 122 remote from the epitaxial semiconductor layer stack 112 may be planar . The optoelectronic semiconductor device 10 further comprises a dielectric or semiconducting first material layer 124 which is arranged over a surface of the conductive layer 122 that is remote from the epitaxial semiconductor layer stack 112 . A first main surface 125 of the first material layer 124 which is remote from the conductive layer 122 is patterned . Moreover, the optoelectronic semiconductor device 10 comprises a metal layer 126 over the first main surface 125 of the first material layer 124 . A surface 127 of the metal layer 126 may be planar .

[0036] For example , the first and the second semiconductor layers 110 , 120 may be or comprise semiconductor layers having a composition of AlxGai-xN . Further, the active zone 115 may comprise an AlyGai-yN layer . The conductive layer 122 may, for example , comprise a transparent conductive oxide such as ITO ("indium tin oxide") or ZnO. According to further embodiments, the conductive layer 122 may comprise a metal which is transparent to the emitted electromagnetic radiation 15. For example, metals of the conductive layer 122 may comprise Ni, Rh, Pt, Ti, Al and further suitable metals. Moreover, the conductive layer 122 may comprise a combination of the materials described above. The conductive layer 122 may have a thickness dl which is small to reduce absorption. For example, a thickness dl of the conductive layer 122 may be larger than 5 nm. For example, the thickness dl may be less than 100 nm, for example, less than 50 nm, less than 20 nm, or less than 10 nm.

[0037] The first material layer 124 may comprise a material having a band gap larger than a band gap corresponding to the emitted electromagnetic radiation. For example, the band gap may be larger than 5 eV. As a result, emitted electromagnetic radiation 15 is not or only absorbed to a small extent. Moreover, a refractive index of the first material layer 124 may be close to the refractive index of a material of the second semiconductor layer 120 directly adjacent to the conductive layer 122. For example, the refractive index of the first material layer 124 may be close to the refractive index of AIN. For example, the term "the refractive index nl of a first material is close to the refractive index n2 of a second material" is intended to mean that a difference of the refractive indices (nl-n2) is less than 0.1 * Min(nl, n2 ) , i. e. is less than 0.1 * the minimum of nl and n2. As a result, emitted electromagnetic radiation 15 is scarcely refracted at the interface between the second semiconductor layer 120 and the first material layer 124. Specific examples of materials of the first material layer 124 comprise SC2O3, ZrCy, SiCy, AI2O3, AIN, Ga2Os and others . The first main surface 125 of the first material layer 124 is patterned. For example, the surface 125 may be patterned to form a plurality of protruding portions 123. For example, a height d2 of the protruding portions 123 may be more than 50 nm. For example, a height d2 of the protruding portions may be less than 5 pm, for example less than 2 pm. According to further implementations, the height d2 of the protruding portions 123 may be less than 1000 nm or less than 500 nm.

[0038] A distance si between adjacent protruding portions 123 may be larger than 1 pm. For example, a typical distance may be more than 2 pm or more than 3 pm. Moreover, the distance si may be less than 20 pm, e.g. less than 15 pm. Sidewalls 121 of the protruding portions 123 may extend in a direction that is different from a vertical direction, e.g. a z-direction. As is e.g. shown in Fig. 4D, an angle a of a sidewall 121 of the protruding portion 123 with respect to a vertical direction, e.g. the z-direction, may be more than 20°, for example, more than 30°. For example, the angle may be less than 80°, for example, less than 60°. The protruding portions 123 may also be referred to as micro reflectors, since they enhance the reflectivity of the layers arranged over the semiconductor layer stack 112.

[0039] For example, the total thickness d3 of the first material layer 124 is larger than the height d2 of the protruding portions 123. According to further implementations, the thickness d3 of the first material layer 124 may correspond to the height d2 of the protruding portions.

[0040] For example, openings 132 may be formed in the first material layer 124. For example, the metal layer 126 may be in contact with the second semiconductor layer 120 via the opening 132 and the conductive layer 122. For example, the metal layer 126 may comprise any of Ni, Rh, Pt, Ti, Al, other suitable metals, and any combination thereof.

[0041] A first terminal 105 may be electrically connected to the first semiconductor layer 110. Moreover, a second terminal 107 may be electrically connected to the metal layer 126. By applying a suitable voltage between the first terminal 105 and the second terminal 107, electromagnetic radiation 15 may be emitted. The electromagnetic radiation 15 is emitted via a surface of the first semiconductor layer 110 remote from the second semiconductor layer 120.

[0042] For example, the optoelectronic semiconductor device 10 may further comprise a substrate 100 which is transparent to the emitted electromagnetic radiation. For example, the substrate 100 may comprise sapphire (AI2O3) . For example, the substrate 100 may be the growth substrate for the semiconductor layer stack 112.

[0043] By way of example, the pattern of the protruding portions 123 may be periodic or may be arbitrary. By setting any of the following parameters, the light scattering and the light extraction efficiency may be influenced: the angle a of the protruding portion 123, the height d2 of the protruding portion, the density of the protruding portions or a composition of the first material layer 124. For example, the density of the protruding portions, i.e. the ratio of the lateral extension of the protruding portions 123 to the lateral extension of the optoelectronic semiconductor device 10, may be, for example, more than 10 %, for example, more than 50 %. For example, the density may be less than 80 %.

[0044] Due to the special arrangement and as is illustrated in Fig. 1, electromagnetic radiation 15 emitted by the epitaxial semi- conductor layer stack 112 is reflected by the sidewalls 121 of the protruding portions 123 to eventually leave the optoelectronic semiconductor device 10 via the transparent substrate 100 . Due to the presence of the patterned first main surface 125 , a plurality of protruding portions 123 acting as micro reflectors are formed . As a consequence , the total internal reflections at the interface between the first semiconductor layer 110 and the substrate 100 may be reduced and the light extraction ef ficiency ( LEE ) may be increased .

[0045] Fig . 2 shows a cross-sectional view of an optoelectronic semiconductor device 10 according to further embodiments . In addition to elements illustrated in Fig . 1 , the optoelectronic semiconductor device further comprises a first dielectric layer 129 . For example , the first dielectric layer 129 may comprise SiCh or AI2O3 or other suitable materials , for example , MgF2or AIN . A thickness d5 of the first dielectric layer 129 may be less than 600 nm, for example , less than 100 nm . The first dielectric layer 129 serves as a protection layer during the patterning of the first material layer 124 to safeguard the thin conductive layer 122 . For example , when plasma etching is employed to shape the first material layer 124 , there is a risk of potential damage to the epitaxial semiconductor layer stack 112 when the process becomes uncontrollable or is not optimi zed . In such cases , the first dielectric layer 129 may act as an etch stop and protection layer which further prevents damage to the underlying semiconductor layer stack 112 during the etching process .

[0046] Fig . 3 shows a cross-sectional view of an optoelectronic semiconductor device 10 according to further embodiments . In addition to elements that are i llustrated in Fig . 1 or Fig . 2 , the optoelectronic semiconductor device further comprises a second dielectric layer 130 . For example , the second dielectric layer 130 may comprise SiCy or AI2O3. According to further embodiments, the second dielectric layer 130 may be implemented as a distributed Bragg reflector (DBR) that may comprise a laminated layer stack of alternatingly arranged layers having a comparatively high and comparatively low refractive index. For example, the second dielectric layer 130 may comprise layers of AI2O3 and MgF2that are alternatingly arranged. The second dielectric layer 130 may act as a protective layer when e.g. the material layer 124 is sensitive to humidity. Moreover, the second dielectric layer 130 may act as an adhesion promoter between the material layer 124 and the metal layer 126. Moreover, when the second dielectric layer 130 is implemented as a Bragg reflector stack, the second dielectric layer 130 may serve as a mirror to boost the reflectivity of the metal layer 126. For example, a thickness of the second dielectric layer 130 may be less than 5 pm or less than 1 pm. The second dielectric layer 130 may be a conformal layer over the patterned first main surface 125 of the first material layer 124.

[0047] Figs. 4A to 4D illustrate cross-sectional views of a workpiece when performing a method according to embodiments. Starting point of the method may be a suitable substrate 100 that may be transparent for the emitted electromagnetic radiation. For example, sapphire (AI2O3) may be used as a material of the transparent substrate 100.

[0048] As is illustrated in Fig. 4B, a semiconductor layer stack 112 may be epitaxially grown over the first main surface 101 of the transparent substrate 100. For example, first, a first semiconductor layer of a first conductivity type, e.g. n-type, may be grown, followed by the e.g. layers forming the active zone 115. Thereafter, a second semiconductor layer 120 of a second conductivity type, e.g. p-type, may be epitaxially grown . Referring to Fig . 4C, subsequently, the conductive layer 122 is formed, followed by the first material layer 124 .

[0049] Thereafter, as is illustrated in Fig . 4D, the first main surface 125 of the first material layer 124 may be patterned, e . g . using a photolithographical method using a photoresist material and, optionally, a suitable hardmask layer ( stack) . After patterning the photoresist and, optionally, the hardmask layer, an etching process may be performed to define the protruding portions 123 and the openings 132 .

[0050] For example , the openings 132 may extend to the conductive layer 122 . The protruding portions 123 have sidewalls 121 that extend in a direction that is di f ferent from a vertical direction . For example , the angle a to the vertical direction may be larger than 0 ° . Thereafter, a metal layer 126 may be formed over the resulting surface . As a result , the optoelectronic semiconductor device as is e . g . illustrated in Fig . 1 may be obtained .

[0051] Fig . 4E summari zes a method according to embodiments . As is shown, a method of manufacturing an optoelectronic semiconductor device comprises forming, S 100 , an epitaxial semiconductor layer stack comprising a first semiconductor layer of a first conductivity type , a second semiconductor layer of a second conductivity type and an active zone between the first semiconductor layer and the second semiconductor layer, the active zone being configured to generate electromagnetic radiation . The method further comprises forming, S 110 , a conductive layer over a first main surface of the epitaxial semiconductor layer stack and forming, S 120 , a dielectric or semiconducting first material layer over a surface of the conductive layer remote from the epitaxial semiconductor layer stack . The method fur- ther comprises patterning, S 130 , a first main surface of the first material layer remote from the conductive layer and forming, S 140 , a metal layer over the first main surface of the first material layer .

[0052] Fig . 5 shows an example of an optical device 20 that comprises the optoelectronic semiconductor device 10 which has been explained above . For example , the optical device 20 may be used as a disinfection device .

[0053] As has been described above , due to the special arrangement comprising the first material layer 124 having a patterned main surface to form protruding portions 123 that may act as micro reflectors , the light extraction ef ficiency of the optoelectronic semiconductor device may be largely increased . As a consequence , the wall plug ef ficiency (WPE ) of the optoelectronic semiconductor device 10 may be increased .

[0054] 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 emitted electromagnetic radiation optical device substrate first main surface first terminal second terminal first semiconductor layer semiconductor layer stack active zone first main surface second semiconductor layer sidewall conductive layer protruding portion first material layer first main surface metal layer surface first dielectric layer second dielectric layer opening

Claims

CLAIMS1. An optoelectronic semiconductor device (10) comprising: an epitaxial semiconductor layer stack (112) comprising a first semiconductor layer (110) of a first conductivity type, a second semiconductor layer (120) of a second conductivity type and an active zone (115) arranged between the first semiconductor layer (110) and the second semiconductor layer (120) , the active zone (115) being configured to generate electromagnetic radiation (15) ; a conductive layer (122) arranged over a first main surface (117) of the epitaxial semiconductor layer stack (112) ; a dielectric or semiconducting first material layer (124) arranged over a surface of the conductive layer (122) remote from the epitaxial semiconductor layer stack (112) , a first main surface (125) of the first material layer (124) remote from the conductive layer (122) being patterned; and a metal layer (126) over the first main surface (125) of the first material layer (124) .

2. The optoelectronic semiconductor device (10) according to claim 1, wherein the first main surface (125) of the first material layer (124) is patterned to form a plurality of protruding portions (123) .

3. The optoelectronic semiconductor device (10) according to claim 2, wherein at least one sidewall (121) of at least one protruding portion (123) extends in a direction that is different from a vertical direction.

4. The optoelectronic semiconductor device (10) according to any of the preceding claims, wherein the first material layer (124) has a refractive index which is close to the re-tractive index of a material of the second semiconductor layer(120) directly adjacent to the conductive layer (122) .

5. The optoelectronic semiconductor device (10) according to claim 4, wherein the refractive index of the first material layer (124) is in a range of 2.2 inclusive to 2.8 inclusive.

6. The optoelectronic semiconductor device (10) according to any of the preceding claims, wherein the active zone (115) comprises an AlxGai-xN layer.

7. The optoelectronic semiconductor device (10) according to any of the preceding claims, wherein the conductive layer (122) comprises a transparent metal or a transparent conductive oxide.

8. The optoelectronic semiconductor device (10) according to any of the preceding claims, wherein a surface of the metal layer (127) remote from the first material layer (124) is planar .

9. The optoelectronic semiconductor device (10) according to any of the preceding claims, further comprising a first dielectric layer (129) between the first material layer (124) and the conductive layer (122) .

10. The optoelectronic semiconductor device (10) according to any of the preceding claims, further comprising a conformal second dielectric layer (130) between the first material layer (124) and the metal layer (126) .

11. The optoelectronic semiconductor device (10) according to any of the preceding claims, further comprising a transpar-ent substrate (100) over a second main surface of the semiconductor layer stack (112) .

12. The optoelectronic semiconductor device (10) according to any of the preceding claims, further comprising an opening (132) in the first material layer (124) , the metal layer (126) contacting the conductive layer (122) via the opening (132) .

13. A method of manufacturing an optoelectronic semiconductor device (10) comprising: forming (S100) an epitaxial semiconductor layer stack (112) comprising a first semiconductor layer (110) of a first conductivity type, a second semiconductor layer (120) of a second conductivity type and an active zone (115) between the first semiconductor layer (110) and the second semiconductor layer (120) , the active zone (115) being configured to generate electromagnetic radiation (15) ; forming (S110) a conductive layer (122) over a first main surface (117) of the epitaxial semiconductor layer stack (112) ; forming (S120) a dielectric or semiconducting first material (124) layer over a surface of the conductive layer (122) remote from the epitaxial semiconductor layer stack (112) , patterning (S130) a first main surface (125) of the first material layer (124) remote from the conductive layer(122) ; and forming (S140) a metal layer (126) over the first main surface (125) of the first material layer (124) .

14. The method according to claim 13, wherein patterning (S130) the first main surface (125) of the first material layer (124) comprises forming a plurality of protruding portions(123) .

15. The method according to claim 14, wherein at least one of the plurality of protruding portions (123) is formed so as to comprise a sidewall (121) having an extension direction that is different from a vertical extension direction.

16. An optical device (20) comprising the optoelectronic semiconductor device (10) according to any of claims 1 to 12.

17. The optical device (20) according to claim 11, which is a disinfection device.

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