Optoelectronic device having multiple epitaxial layers and method of manufacture
By designing optoelectronic devices with the boundary surface located outside the pn junction in the epitaxial stack, the efficiency loss problem caused by miniaturization is solved, and efficient red light emission is achieved, which is suitable for augmented reality and mixed reality applications.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- OSRAM OPTO SEMICON GMBH & CO OHG
- Filing Date
- 2020-12-09
- Publication Date
- 2026-07-10
AI Technical Summary
Miniaturization of LEDs leads to efficiency loss, especially in the red spectrum.
By embedding first and second semiconductor layers in the epitaxial layer stack, a boundary surface is formed to avoid non-radiative recombination of charge carriers in the space charge region of the pn junction. A specific epitaxial layer growth method is used to ensure that the boundary surface is located outside the pn junction, including setting the boundary surface portion staggered outside the active layer or in the doped layer.
It improves the efficiency of optoelectronic devices in small sizes, especially in red-emitting μLEDs, by enhancing the radiative recombination efficiency of charge carriers and improving luminous efficiency.
Smart Images
Figure CN114830359B_ABST
Abstract
Description
[0001] Cross-reference of related applications
[0002] This application claims priority to German application DE 10 2019 134 216.3, the disclosure of which is incorporated herein by reference. Technical Field
[0003] The present invention relates to an optoelectronic device having multiple epitaxial layers and a method for manufacturing such an optoelectronic device. Background Technology
[0004] The widespread application of LEDs (light emitting diodes) necessitates their miniaturization. However, miniaturization typically results in efficiency losses, particularly in the red spectrum. Summary of the Invention
[0005] Therefore, the present invention further aims to realize an optoelectronic device that exhibits high efficiency even in embodiments with a small size. Furthermore, a method for manufacturing the optoelectronic device should be provided.
[0006] One object of the present invention is achieved by an optoelectronic device having the features of the present invention. Another object of the present invention is achieved by a method for manufacturing an optoelectronic device having the features of the present invention. Preferred embodiments and improvements of the present invention are given in the following description.
[0007] The optoelectronic device according to a first aspect of this application includes an epitaxial layer stack, said epitaxial layer stack being composed of at least one first epitaxial layer and a second epitaxial layer disposed on the first epitaxial layer. The epitaxial layer stack may particularly include additional epitaxial layers. The epitaxial layers of the epitaxial layer stack are epitaxially grown layers, particularly semiconductor layers. Boundary surfaces or interfaces exist between the stacked epitaxial layers. In particular, the second epitaxial layer is grown directly on the first epitaxial layer, i.e., there is no intermediate layer between the first and second epitaxial layers.
[0008] A first semiconductor layer, a second semiconductor layer, and an active layer are embedded in the epitaxial layer stack, particularly in the first and second epitaxial layers.
[0009] Here, the first semiconductor layer is of the first conduction type, and the second semiconductor layer is of the second conduction type. The second conduction type is the opposite of the first conduction type.
[0010] Different conduction types can be generated through doping, i.e., by introducing impurity atoms into the semiconductor material. One of the two conduction types can be n-type and the other can be p-type. Therefore, the first semiconductor layer is n-type doped and the second semiconductor layer is p-type doped, or the first semiconductor layer is p-type doped and the second semiconductor layer is n-type doped.
[0011] An active layer is disposed above the first semiconductor layer and is configured to generate light. A second semiconductor layer is disposed above the active layer. Therefore, the active layer is disposed between the first semiconductor layer and the second semiconductor layer.
[0012] The boundary surface between the first and second epitaxial layers, or between other epitaxial layers in a stack of epitaxial layers, extends at least partially through the first and / or second semiconductor layers. Accordingly, the boundary surface or interface between the first and second epitaxial layers is at least partially located outside the pn junction space charge region. Defects formed at the boundary surface are not occupied by charge carriers, i.e., electrons and holes, during the operation of the optoelectronic device, thereby preventing non-radiative recombination of charge carriers and improving the efficiency of the optoelectronic device even with a small lateral dimension.
[0013] Optoelectronic devices can be semiconductor chips manufactured in semiconductor wafers and divided, for example, by sawing from a wafer composite. Optoelectronic devices can, in particular, form pixels or subpixels for optoelectronic applications.
[0014] Furthermore, optoelectronic devices can be configured as light-emitting diodes (LEDs), superluminescent light-emitting diodes (SLEDs or SLDs), laser diodes (also known as semiconductor lasers), surface emitters (VCSELs), resonant tunneling diodes (RTDs), heterojunction bipolar transistors (HBTs), or high-electron-mobility transistors (HEMTs).
[0015] According to one design, the optoelectronic device is configured as a μLED, i.e., a microLED. μLEDs have small lateral extensions, particularly in the μm range. Epitaxial materials used for the first and second epitaxial layers can be, for example, InGaAlP, InAlGaN, or AlGaAs.
[0016] In a specific manner, the present invention can be used in optoelectronic devices that require an additional artificial interface between two epitaxial layers due to technical requirements.
[0017] The light emitted by optoelectronic devices can be, for example, light in the visible range, ultraviolet (UV) light, and / or infrared (IR) light.
[0018] In particular, the device can emit red light and is configured, for example, as a μLED that emits red light.
[0019] Optoelectronic devices can be used, for example, in augmented reality or mixed reality applications. Furthermore, optoelectronic devices can be used in pixelated arrays or pixelated light sources.
[0020] It can be proposed that all portions of the boundary surface between the first and second epitaxial layers, extending parallel to the main surface of the active layer, do not extend through the active layer and, in particular, do not extend through the undoped barrier layer described below, in which the active layer is embedded. This can also be applied, in particular, to other boundary surfaces between upper and lower stacked epitaxial layers in an epitaxial layer stack. In other words, it can be proposed that all portions of the boundary surface between two upper and lower stacked epitaxial layers in an epitaxial layer stack, extending parallel to the main surface of the active layer, do not extend through the active layer and, in particular, do not extend through the barrier layer.
[0021] A first portion of the boundary surface between the first and second epitaxial layers can extend through the first semiconductor layer, and a second portion of the boundary surface can extend through the second semiconductor layer. The first and second portions can be arranged laterally offset from each other and, in particular, spaced apart from each other. Laterally offset means that the portions are offset from each other in a direction parallel to the main surface of the active layer.
[0022] Furthermore, the first portion of the boundary surface may be located outside the outline of the active layer, while the second portion of the boundary surface may be located within the outline of the active layer. Here, the outline of the active layer represents the lateral extension of the active layer. That is, the first portion of the boundary surface is laterally spaced from the active layer, while the second portion is located directly above or below the active layer.
[0023] The first and / or second portion of the boundary surface may extend parallel to the main surface of the active layer. The boundary surface may also have one or more additional portions. For example, another portion of the boundary surface may connect the first and second portions to each other.
[0024] Generally, at least a portion of the boundary surface between the first epitaxial layer and the second epitaxial layer may be parallel to the main surface of the active layer and further extend above or below the main surface of the active layer.
[0025] The active layer may have one or more side surfaces that connect the two main surfaces of the active layer to each other. At least a portion of the boundary surface between the first and second epitaxial layers may extend along at least one of the side surfaces of the active layer.
[0026] The active layer may have a mesa structure, meaning that one or more sides do not form a 90° angle with the main surface. For example, the active layer may taper upwards, i.e., the cross-section of the active layer decreases upwards. Therefore, at least one side of the active layer forms an angle of less than 90° with the underlying main surface. A portion of the boundary surface between the first and second epitaxial layers may extend along said side.
[0027] An active layer can be embedded within an undoped barrier layer. The barrier layer can cover the main surface of the active layer and one or more side surfaces. The barrier layer is disposed on top of a first semiconductor layer. A second semiconductor layer is disposed on top of the barrier layer.
[0028] Furthermore, the first semiconductor layer may be disposed on a substrate, particularly a semiconductor substrate. The semiconductor substrate may be a component of the first epitaxial layer.
[0029] The method according to a second aspect of this application is used to manufacture optoelectronic devices. The method proposes that an epitaxial layer stack is generated from at least one first epitaxial layer and a second epitaxial layer disposed on the first epitaxial layer. Furthermore, the epitaxial layer stack may include additional epitaxial layers. Embedded in the epitaxial layer stack, and particularly in the first and second epitaxial layers, are: a first semiconductor layer of a first conductivity type; an active layer disposed on the first semiconductor layer, configured to generate light; and a second semiconductor layer of a second conductivity type disposed on the active layer. The boundary surface between the first and second epitaxial layers extends at least partially through the first semiconductor layer and / or the second semiconductor layer.
[0030] After the first epitaxial layer is grown, it can be structured to obtain a three-dimensional surface. A second epitaxial layer is then grown on this surface.
[0031] By structuring the first epitaxial layer, especially the active layer.
[0032] The second epitaxial layer can be generated directly on the first epitaxial layer.
[0033] The method of the second aspect can have the above-described design scheme of the optoelectronic device according to the first aspect. Attached Figure Description
[0034] Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. These drawings schematically illustrate:
[0035] Figure 1A A diagram showing an optoelectronic device not according to an embodiment of the invention;
[0036] Figure 1B and 1C Shown at different locations Figure 1A A diagram illustrating the structure of an optoelectronic device in a photograph;
[0037] Figure 2A A diagram illustrating an optoelectronic device according to an embodiment of the present invention;
[0038] Figure 2B Shown at one location Figure 2A A diagram illustrating the structure of an optoelectronic device in a photograph;
[0039] Figure 3A A diagram illustrating another embodiment of an optoelectronic device according to the present invention; and
[0040] Figure 3B Shown at one location Figure 3A A diagram illustrating the structure of an optoelectronic device. Detailed Implementation
[0041] Referring to the accompanying drawings, which form part of the description and illustrate specific embodiments in which the invention can be practiced, the invention is explained in detail below. Because components of the embodiments can be positioned in multiple different orientations, directional terms are used for illustration and are by no means limiting. It is self-evident that other embodiments can be utilized and structural or logical changes can be made without departing from the scope of protection. It is self-evident that features of the different embodiments described herein can be combined with each other unless otherwise specifically stated. Therefore, the following detailed description is not to be construed as limiting. In the drawings, the same or similar elements are given the same reference numerals, as is appropriate.
[0042] Figure 1A A schematic structure of an optoelectronic device configured as μLED 10, which is not an embodiment according to the present invention, is shown in cross-section in the xz plane.
[0043] The μLED 10 is fabricated, for example, from an InGaAlP compound and emits red light. The μLED 10 includes a substrate 11, on which an n-type doped first semiconductor layer 12 is applied. An undoped barrier layer 13 is applied on the first semiconductor layer 12, and an active layer 14 is integrated into the barrier layer. The active layer 14 has a direct bandgap lower than the surrounding potential barrier of the barrier layer 13. A p-type doped second semiconductor layer 15 is applied on the barrier layer 13.
[0044] The μLED 10 also has a stack composed of multiple epitaxial layers. In this embodiment, the stack consists of a first epitaxial layer 16 and a second epitaxial layer 17 disposed on the first epitaxial layer 16. In these two epitaxial layers 16 and 17, as in... Figure 1A As shown, an embedded substrate 11, an n-type doped first semiconductor layer 12, an undoped barrier layer 13, an active layer 14, and a p-type doped second epitaxial layer 15 are present. A boundary surface 18 extends between the first epitaxial layer 16 and the second epitaxial layer 17. Figure 1A The boundary surface 18 is shown by arrows and dotted lines. It extends substantially through the undoped barrier layer 13 and over the active layer 14.
[0045] In addition, Figure 1A In the diagram, the width of the upper main surface of the active layer 14 is represented by Sa in the xz plane shown. W represents the vertical extension of the active layer 14 and Sm represents the lateral width of the boundary surface 18 adjacent to the active layer 14.
[0046] exist Figure 1B and 1C The image shows μLED 10 in Figure 1A The band structure at location x1 or x2 shown in the diagram. That is, Figure 1B The band structure of μLED 10 in the region outside the active layer 14 is shown, while Figure 1C The strip structure is shown in the region extending through the active layer 14. Figure 1B and 1C The energy is plotted at the z-coordinate at location x1 or x2 respectively. The extension of boundary surface 18 is shown in... Figure 1B and 1C In the middle Figure 1A The arrows and dotted lines are used to illustrate this. Furthermore, the arrows illustrate the flow of electrons (“e”) and holes (“h”) during the weak current operation of the μLED 10.
[0047] exist Figure 1B In this configuration, boundary surface 18 is situated within the space charge region of the pn junction. At location x1, electrons and holes recombine nonradiatively via states at boundary surface 18. This recombination competes with the radiative recombination occurring in the active layer 14.
[0048] Figure 1C As shown, at location x2, boundary surface 18 is also within the pn junction. The band gap decreases in the region of the active layer 14. Radial recombination of charge carriers occurs in this region, as indicated by arrow 20. However, there are also paths along the boundary surface indicated by arrow 21, which result in non-radiative recombination of charge carriers.
[0049] The efficiency of the red-emitting μLED is significantly reduced due to the non-radiative recombination of charge carriers as described above.
[0050] Figure 2A A schematic structure of an optoelectronic device configured as a μLED 30 according to an embodiment of the present invention is shown in cross-section in the xz plane.
[0051] The μLED 30 has a first epitaxial layer 31 and a second epitaxial layer 32 disposed on the first epitaxial layer 31. To fabricate the μLED 30, the first epitaxial layer 31 is first grown. The first epitaxial layer is then structured, particularly by etching, to give it a three-dimensional structure on its upper side. The second epitaxial layer 32 is then grown directly on the structured first epitaxial layer 31. The boundary surface 33 between the first epitaxial layer 31 and the second epitaxial layer 32 is... Figure 2A The middle part is represented by a dotted line and additionally by an arrow.
[0052] In the first epitaxial layer 31 and the second epitaxial layer 32, and in Figure 1A The μLED 10 in the image has a substrate 11, an n-type doped first semiconductor layer 12, an undoped barrier layer 13, an active layer 14 with a direct bandgap, and a p-type doped second semiconductor layer 15 embedded or integrated in the image.
[0053] The n-type doped first semiconductor layer 12 and the p-type doped second semiconductor layer 15 each contain a contact and a redistribution layer.
[0054] The active layer 14 has a lower main surface 34, an upper main surface 35 opposite to the lower main surface 34, and side surfaces 36. The side surfaces 36 form an angle α with the lower main surface 34, the angle being less than 90°.
[0055] The boundary surface 33 between the first epitaxial layer 31 and the second epitaxial layer 32 has a first portion 40 and a second portion 41. The first portion 40 of the boundary surface 33 is within the n-type doped first semiconductor layer 12 and extends parallel to the main surfaces 34 and 35 of the active layer 14.
[0056] Furthermore, the first portion 40 of the boundary surface 33 extends beyond the contour 42 of the active layer 14, the contour being... Figure 2A The outline is represented by a dashed line. Outline 42 shows the lateral extension of the active layer 14, i.e., the extension along the x-direction.
[0057] The second portion 41 of the boundary surface 33 extends within the p-type doped second semiconductor layer 15 and parallel to the main surfaces 34, 35 of the active layer 14. Furthermore, the second portion 41 extends directly over the active layer 14 within the contour 42 of the active layer 14.
[0058] In other words, this means that the second portion 41 of the boundary surface 33 at the height of the active layer 14 is located in the p-type doped second semiconductor layer 15, while the first portion 40 of the boundary surface 33 outside the active layer 14 is located in the n-type doped first semiconductor layer 12. Therefore, the two portions 41 and 42 of the boundary surface 33 are located outside the pn junction.
[0059] Furthermore, the boundary surface 33 has one or more lateral portions 43 that connect the first portion 40 to the second portion 41. The lateral portions 43 extend along the side surface 36 of the active layer 36 and, in particular, have the same slope as the side surface 36.
[0060] exist Figure 2B The image shows μLED 30 in Figure 2A The strip structure at location x2 shown is situated at the height of the active layer 14. Figure 2B The energy is plotted at the z-coordinate of location x2. The orientation of boundary surface 33 is indicated by arrows and dotted lines. Furthermore, the arrows illustrate the flow of electrons (“e”) and holes (“h”) during the weak current operation of the μLED 30.
[0061] Because boundary surface 33 is located outside the pn junction, therefore... Figure 2B Only radiative recombination of charge carriers occurs in the process, thus the efficiency of μLED 30 is relatively low compared to... Figure 1A The μLED 10 in the sample was significantly improved.
[0062] Charge carriers recombine nonradiatively in an intermediate state outside the active layer 33, as they do in... Figure 1B As shown, this also occurs in μLED 30. However, in weak current operation, the total number of charge carriers in the active layer 14 is an exponential function of the applied voltage. Therefore, radiative recombination of charge carriers occurs significantly more frequently in the region of the active layer 14, thereby improving the efficiency by more than an order of magnitude relative to μLED 10.
[0063] By structuring the first epitaxial layer 31, the active layer 14 is also structured, thereby enabling carriers to recombine without radiation in the region of the side surface 36 of the active layer 14 via a state at the boundary surface 33 during the operation of the μLED 30. However, in cases where the typical vertical extension W of the active layer 14 is 5 nm to 100 nm and the lateral extension of the μLED 30 is 1 μm to 100 μm, the ratio of the width of the upper main surface 35 of the active layer 14 to the portion of the boundary surface 33 at the side surface 36 of the active layer 14 is at least 10. μLEDs suitable for augmented reality or mixed reality applications, for example, have a lateral extension of 1 μm to 5 μm and a vertical extension W of the active layer 14 of 5 nm to 50 nm. Therefore, in these LEDs, the ratio of the width of the upper main surface 35 of the active layer 14 to the portion of the boundary surface 33 at the side surface 36 of the active layer 14 is at least 20.
[0064] Figure 3A A schematic structure of an optoelectronic device configured as a μLED 50 according to another embodiment of the invention is shown in cross-section in the xz plane.
[0065] exist Figure 3A The μLED 50 shown in the image is... Figure 2A The μLEDs 30 in the μLED 50 are as identical as possible. The difference is that in the μLED 50, the first semiconductor layer 12 below the active layer 14 is p-type doped, while the second semiconductor layer 15 above the active layer 14 is n-type doped.
[0066] Therefore, the second portion 41 of the boundary surface 33 at the height of the active layer 14 is located in the n-type doped second semiconductor layer 15, while the first portion 40 of the boundary surface 33 outside the active layer 14 is located in the p-type doped first semiconductor layer 12.
[0067] Consequently, the strip structure of μLED 50 also changes, and the strip structure in Figure 3B In China Figure 3A The portion x2 at the height of the active layer 14 is shown in the diagram. Figure 3B The energy is plotted at the z-coordinate of location x2. The orientation of boundary surface 33 is indicated by arrows and dotted lines. Because boundary surface 33 extends outside the pn junction, therefore... Figure 3B Basically, only the recombination of charge carriers occurs radiatively.
[0068] List of reference numerals 10μLED
[0069] 11 substrate
[0070] 12 First semiconductor layer 13 Barrier layer
[0071] 14 Active Layer
[0072] 15 Second semiconductor layer 16 First epitaxial layer 17 Second epitaxial layer 18 Boundary surface
[0073] 20 arrows 21 arrows 30μLED
[0074] 31 First epitaxial layer 32 Second epitaxial layer 33 Boundary surface
[0075] 34 Lower main surface 35 Upper main surface 36 Side surface
[0076] 40 Part 1
[0077] 41 Part Two
[0078] 42 Outline 43 Lateral Section 50μLED
Claims
1. An optoelectronic device (30, 50), comprising: An epitaxial layer stack, wherein the epitaxial layer stack comprises at least one first epitaxial layer (31) and a second epitaxial layer (32) disposed on the first epitaxial layer (31). The following layers are embedded in the epitaxial stack: First semiconductor layer (12) of first conductivity type; An undoped barrier layer disposed on the first semiconductor layer (12), an active layer (14) embedded in the barrier layer, the active layer being configured to generate light, wherein the active layer (14) has a first main surface and a second main surface, wherein the main surface is connected by one or more side surfaces, wherein the barrier layer covers the main surface of the active layer and one or more side surfaces, and wherein the active layer is separated from the first semiconductor layer and the second semiconductor layer by the barrier layer; and A second semiconductor layer (15) of the second conductivity type is disposed on the barrier layer (13). The boundary surface (33) between the first epitaxial layer (31) and the second epitaxial layer (32) extends at least partially through the first semiconductor layer (12) and the second semiconductor layer (15).
2. The optoelectronic device (30, 50) according to claim 1. The first portion (40) of the boundary surface (33) between the first epitaxial layer (31) and the second epitaxial layer (32) extends through the first semiconductor layer (12), and the second portion (41) of the boundary surface (33) between the first epitaxial layer (31) and the second epitaxial layer (32) extends through the second semiconductor layer (15).
3. The optoelectronic device (30, 50) according to claim 2. The first portion (40) of the boundary surface (33) is located outside the outline (42) of the active layer (14), and the second portion (41) of the boundary surface (33) is located inside the outline (42) of the active layer (14).
4. The optoelectronic device (30, 50) according to claim 2 or 3. The first portion (40) and / or the second portion (41) of the boundary surface (33) extends parallel to the main surface (34, 35) of the active layer (14).
5. The optoelectronic device (30, 50) according to claim 1. At least a portion (40) of the boundary surface (33) between the first epitaxial layer (31) and the second epitaxial layer (32) is parallel to the main surface (34, 35) of the active layer (14) and extends above or below the main surface (34, 35) of the active layer (14).
6. The optoelectronic device (30, 50) according to any one of the preceding claims. The active layer (14) has one or more sides (36), and at least a portion (43) of the boundary surface (33) between the first epitaxial layer (31) and the second epitaxial layer (32) extends along at least one side of the side (36) of the active layer (14).
7. The optoelectronic device (30, 50) according to any one of the preceding claims. The active layer (14) therein has a mesa structure.
8. The optoelectronic device (30, 50) according to any one of the preceding claims. The width of the upper main surface (35) of the active layer (14) is at least 10 times the ratio of the portion (43) of the boundary surface (33) extending along at least one side (36) of the active layer (14).
9. The optoelectronic device (30, 50) according to claim 8. The ratio mentioned therein is at least 20.
10. The optoelectronic device (30, 50) according to any one of the preceding claims. In this case, one of the first and second conduction types is a p-type conduction type and the other is an n-type conduction type.
11. The optoelectronic device (30, 50) according to any one of the preceding claims. The optoelectronic device mentioned therein is a μLED (30, 50).
12. The optoelectronic device (30, 50) according to any one of the preceding claims. The first semiconductor layer (12) is disposed on the substrate (11).
13. A method for manufacturing optoelectronic devices (30, 50), comprising: An epitaxial layer stack is generated, the epitaxial layer stack being composed of at least one first epitaxial layer (31) and a second epitaxial layer (32) disposed on the first epitaxial layer (31). The following layers are embedded in the epitaxial stack: First semiconductor layer (12) of first conductivity type; An undoped barrier layer disposed on the first semiconductor layer (12), an active layer (14) embedded in the barrier layer, the active layer being configured to generate light, wherein the active layer (14) has a first main surface and a second main surface, wherein the main surface is connected by one or more side surfaces, wherein the barrier layer covers the main surface of the active layer and one or more side surfaces, and wherein the active layer is separated from the first semiconductor layer and the second semiconductor layer by the barrier layer; and A second semiconductor layer (15) of the second conductivity type is disposed on the barrier layer (13). The boundary surface (33) between the first epitaxial layer (31) and the second epitaxial layer (32) extends at least partially through the first semiconductor layer (12) and the second semiconductor layer (15).
14. The method according to claim 13, After the first epitaxial layer (31) is generated, the first epitaxial layer (31) is structured, and the second epitaxial layer (32) is generated on the structured first epitaxial layer (31).
15. The method according to claim 14, The active layer (14) is structured by structuring the first epitaxial layer (31).
16. The method according to any one of claims 13 to 15, The second epitaxial layer (32) is generated directly on the first epitaxial layer (31).