Vertical cavity light emitting element and light emitting device
By forming an annular insulating film on the p-type semiconductor layer of the light-emitting diode on the vertical cavity surface, the current leakage problem caused by pinholes is solved, and the stability and efficiency of the equipment are improved.
Patent Information
- Application Number
- JP2023151872
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2023-09-20
- Publication Date
- 2025-04-02
AI Technical Summary
In the vertical cavity surface light emitting diode, improper thickness of the .insulating layer may lead to the occurrence of pinholes, which in turn causes current leakage and reduce the efficiency and reliability of the equipment.
By forming a ring-shaped insulating film above the p-type semiconductor layer, it is ensured that current can only flow through a specific area, thereby avoiding current leakage.
It effectively suppresses current leakage, reduces the risk of equipment failure, and improves the stability and efficiency of the light-emitting diodes on the vertical cavity surface.
Smart Images
Figure 2025044353000001_ABST
Abstract
Description
[Technical field]
[0001] The present invention relates to a vertical cavity light emitting device and a light emitting device. [Background technology]
[0002] A vertical cavity light emitting device is known as one type of semiconductor laser. For example, Patent Document 1 discloses a vertical cavity surface emitting laser (VCSEL) including a semiconductor structure layer including an n-type semiconductor layer, a light emitting layer, and a p-type semiconductor layer, with a protrusion formed on the upper surface of the p-type semiconductor layer, an insulating layer formed on the upper surface of the p-type semiconductor layer excluding the upper surface of the protrusion, and a light-transmitting electrode layer formed so as to cover the p-type semiconductor layer. [Prior art documents] [Patent documents]
[0003] [Patent Document 1] Patent Publication No. 2021-197437 Summary of the Invention [Problem to be solved by the invention]
[0004] In the vertical cavity surface emitting laser disclosed in Patent Document 1, pinholes may occur in the insulating layer depending on the thickness of the insulating layer during manufacturing. For example, if an electrode is provided directly above the insulating layer in which a pinhole occurs via a transparent electrode layer, the pinhole portion may become a conductive portion, causing current leakage from a portion other than the portion through which current is intended to flow. If such current leakage occurs, it may lead to a decrease in gain or a failure of the vertical cavity surface emitting laser.
[0005] The present invention has been made in consideration of the above-mentioned points, and aims to provide a vertical cavity light emitting element and a light emitting device that can suppress current leakage and reduce the risk of device failure. [Means for solving the problem]
[0006] A vertical cavity light emitting device according to the present invention includes a substrate, a first multilayer film reflector formed on the substrate, a first semiconductor layer having a first conductivity type formed on the first multilayer film reflector, a light emitting layer formed on the first semiconductor layer, and a semiconductor structure layer including a second semiconductor layer having a second conductivity type opposite to the first conductivity type and having a protruding portion protruding upward from the center of an upper surface of the light emitting layer, a first insulating film having insulating properties formed in a ring shape in a region along an outer edge of the protruding portion in an outer region outside the protruding portion on the upper surface of the second semiconductor layer, and a second insulating film having insulating properties formed in a ring shape in the outer region spaced outward from the first insulating film in a top view. a translucent conductive film covering an upper surface of the protrusion and formed from the upper surface of the protrusion to the surface of the second insulating film, the translucent conductive film having a contact portion in direct contact with an upper surface of the second semiconductor layer exposed between the first insulating film and the second insulating film; a first electrode electrically connected to the first semiconductor layer; a second electrode provided in a region on the outer region of the conductive film and electrically connected to the second semiconductor layer via the conductive film; and a second multilayer film reflector formed on the semiconductor structure layer covering the protrusion and constituting a resonator between itself and the first multilayer film reflector, wherein the second semiconductor layer has an inactive region that is inactivated at least in the contact portion. [Brief description of the drawings]
[0007] [Figure 1] 1 is a perspective view of a vertical cavity surface emitting laser in accordance with a first embodiment. [Diagram 2] 1 is a top view of a vertical cavity surface emitting laser in accordance with a first embodiment. [Diagram 3] 1 is a cross-sectional view of a vertical cavity surface emitting laser in accordance with a first embodiment. [Figure 4] 1 is an enlarged view of a portion of a cross section of a vertical cavity surface emitting laser in accordance with a first embodiment. [Diagram 5] FIG. 1 is an enlarged view of a portion of a cross section of a vertical-cavity surface-emitting laser according to a conventional example. [Figure 6]1 is a top view of a light emitting device according to an application example of the vertical cavity surface emitting laser of Example 1. FIG. [Figure 7] 1 is a cross-sectional view of a light-emitting device according to an application example of the vertical-cavity surface-emitting laser of Example 1. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0008] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In the drawings, the same components are designated by the same reference numerals, and the description of the same components will be omitted. EXAMPLES
[0009] The configuration of a vertical cavity surface emitting laser 100 (hereinafter referred to as surface emitting laser 100) according to Example 1 will be described with reference to Figs. 1 to 4. Fig. 1 is a perspective view of the surface emitting laser 100. Fig. 2 is a top view of the surface emitting laser 100. Fig. 3 is a cross-sectional view taken along line 3-3 of the surface emitting laser 100 shown in Fig. 2. Fig. 4 is an enlarged view of a portion A of the surface emitting laser 100 in Fig. 3. Note that the up-down direction in Figs. 3 and 4 corresponds to the height direction of the surface emitting laser 100.
[0010] The substrate 11 is a flat, transparent substrate with a rectangular upper surface. The substrate 11 is a growth substrate on which a semiconductor crystal can be grown. The substrate 11 is made of a material that is translucent to light having a blue wavelength, such as undoped gallium nitride (GaN). In the following description, an axis that passes through the center of the upper surface of the substrate 11 and is perpendicular to the upper surface is referred to as a central axis CA. The direction radially away from the central axis CA is referred to as an outward direction.
[0011] The first multilayer film reflector 12 is a semiconductor multilayer film reflector made of semiconductor layers grown on the upper surface of the substrate 11. The first multilayer film reflector 12 is a so-called distributed Bragg reflector (DBR) in which high-refractive index semiconductor films having a relatively high refractive index and low-refractive index semiconductor films having a refractive index lower than that of the high-refractive index semiconductor films are alternately laminated on the upper surface of the substrate 11.
[0012] The first multilayer film reflector 12 is formed by, for example, stacking 42 pairs of a high refractive index semiconductor film made of GaN and a low refractive index semiconductor film made of aluminum indium nitride (AlInN) on the upper surface of the substrate 11. The first multilayer film reflector 12 has such a configuration and is reflective to light in the blue wavelength range. A buffer layer (not shown) made of GaN is provided between the substrate 11 and the first multilayer film reflector 12.
[0013] The semiconductor structure layer EM is a laminated structure made up of a plurality of semiconductor layers formed on the first multilayer reflector 12. The semiconductor structure layer EM has an n-type semiconductor layer 13 formed on the first multilayer reflector 12, a light emitting layer 14 formed on the n-type semiconductor layer 13, and a p-type semiconductor layer 15 formed on the light emitting layer 14.
[0014] Hereinafter, the structures of the n-type semiconductor layer 13, the light emitting layer 14, and the p-type semiconductor layer 15 that constitute the semiconductor structure layer EM will be described.
[0015] N-type semiconductor layer 13 as a first semiconductor layer having a first conductivity type is a semiconductor layer formed over the upper surface of first multilayer film reflector 12. N-type semiconductor layer 13 is made of GaN and is doped with silicon (Si) as an n-type impurity.
[0016] The n-type semiconductor layer 13 has a so-called mesa-shaped structure composed of a flat lower portion 13A and a cylindrical upper portion 13B protruding upward from the center of the lower portion 13A along a central axis CA (see FIG. 3).
[0017] The light emitting layer 14 is formed over the upper portion 13B of the n-type semiconductor layer 13, and is a semiconductor layer having a quantum well structure in which a well layer made of InGaN and a barrier layer made of GaN are stacked on each other. The light emitting layer 14 is formed so that its light emission center is brought onto the central axis CA. The light emitting layer 14 emits blue light having a peak wavelength of, for example, 450 nm.
[0018] P-type semiconductor layer 15 as a second semiconductor layer having a second conductivity type is a semiconductor layer formed over the upper surface of light emitting layer 14. P-type semiconductor layer 15 includes a p-type GaN layer doped with p-type impurities and a p-type AlGaN layer doped with p-type impurities.
[0019] In the p-type semiconductor layer 15, the p-type AlGaN layer is formed between the light emitting layer 14 and the p-type GaN layer, and functions as an electron blocking layer. Note that an undoped GaN layer that prevents diffusion of p-type impurities from the p-type AlGaN layer to the light emitting layer 14 may be formed between the light emitting layer 14 and the p-type AlGaN layer.
[0020] 3, the p-type semiconductor layer 15 has a central protrusion 15P1 having a circular shape on the top surface and protruding upward in a region including the central axis CA at the center of the top surface. The p-type semiconductor layer 15 also has a peripheral protrusion 15P2 as a step portion on the top surface that is spaced apart from the central protrusion 15P1 in the radial direction of the central axis CA and protrudes upward in a region along the outer edge of the top surface of the p-type semiconductor layer 15.
[0021] In other words, the p-type semiconductor layer 15 has a first region 15R1 that is a region passing through the central axis CA, a ring-shaped second region 15R2 that is a region outside the outer periphery of the first region 15R1 and recessed downward from the first region 15R1, and a third region 15R3 that is a region outside the outer periphery of the second region 15R2 and protrudes upward from the second region 15R2. That is, the p-type semiconductor layer 15 has a ring-shaped recess on the upper surface that surrounds the central protrusion 15P1 and has the second region 15R2 as a bottom surface.
[0022] In the p-type semiconductor layer 15, the surfaces of the central protrusion 15P1 and the outer peripheral protrusion 15P2 are at the same height. The side surface of the central protrusion 15P1 is inclined inward with respect to the upper surface of the p-type semiconductor layer 15, and the inner side surface of the outer peripheral protrusion 15P2 is inclined outward with respect to the upper surface of the p-type semiconductor layer 15. In other words, the annular recess having the second region 15R2 as its bottom surface has an inverted trapezoidal cross-sectional shape.
[0023] In the p-type semiconductor layer 15, the upper surface of the p-type semiconductor layer 15 corresponding to the second region 15R2 is an inactive region in which the p-type impurity (Mg) doped in the p-type semiconductor layer 15 is electrically inactivated. The second region 15R2 is formed, for example, by masking the first region 15R1 and the third region 15R3 on the upper surface of the flat p-type semiconductor layer and dry etching only the second region R2. In other words, the central protrusion 15P1 and the peripheral protrusion 15P2 are formed by forming the second region 15R2 as a recess.
[0024] In the p-type semiconductor layer 15 before the central protrusion 15P1 is formed, i.e., in the p-type semiconductor layer 15 before dry etching is performed, the p-type impurities in the upper surface of the p-type semiconductor layer 15 are in an electrically activated state.
[0025] In the p-type semiconductor layer 15 after dry etching, the p-type impurities in the second region 15R2 are in an electrically inactive state due to etching damage. In other words, the second region 15R2 is a region where the p-type impurities are unlikely to generate carriers. Therefore, the second region 15R2 is a high-resistance region having a higher electrical resistance than the first region 15R1 and the third region 15R3 that are not damaged by etching.
[0026] In other words, the first region 15R1 and the third region 15R3, which are regions of the upper surface of the p-type semiconductor layer 15 that have not been damaged by etching in the dry etching process, become low-resistance regions having a relatively low electrical resistance lower than that of the second region 15R2.
[0027] The first insulating film 17 is an electrically insulating coating layer formed in a ring shape in a region along the outer edge of the central protrusion 15P1 in the second region 15R2. The first insulating film 17 is made of a material having a lower refractive index than the p-type semiconductor layer 15, such as silicon dioxide (SiO2). The first insulating film 17 has a thickness t1 equal to the height of the first region 15R1 from the second region 15R2 (see FIG. 4).
[0028] The thickness t1 of the first insulating film 17 is, for example, about 4 to 20 nm. The first insulating film 17 may cover a part of the periphery of the upper surface of the central protrusion 15P1. This makes it possible to suppress electric field concentration on the outer periphery of the central protrusion 15P1.
[0029] The second insulating film 18 is an electrically insulating, transparent coating layer that is formed in a ring shape on the upper surface of the p-type semiconductor layer 15 and spaced outward from the first insulating film 17 in a plan view of the surface-emitting laser 100 from above.
[0030] The second insulating film 18 continuously covers the inner side surface of the outer circumferential protrusion 15P2, the third region 15R3, and each of the side surfaces of the p-type semiconductor layer 15, the light emitting layer 14, and the upper portion 13B of the n-type semiconductor layer 13, and its outer edge reaches a part of the upper surface of the lower portion 13A. The second insulating film 18 is made of SiO2 like the first insulating film 17.
[0031] 4, the thickness t2 of the second insulating film 18 on the third region 15R3 is configured to be thicker than the thickness t1 of the first insulating film 17. The thickness t2 of the second insulating film 18 is a thickness that can insulate the conductive film 21 from the third region 15R3, and is, for example, about 100 to 200 nm. This makes it possible to prevent unintended pinholes from occurring in the second insulating film 18.
[0032] The above-mentioned first insulating film 17 and second insulating film 18 are fabricated, for example, by patterning them in order to a predetermined thickness on the upper surface of the p-type semiconductor layer 15 on which the central protruding portion 15P1 and the peripheral protruding portion 15P2 are formed.
[0033] The conductive film 21 is a light-transmitting conductive film that covers the first region 15R1 and is formed from the first region 15R1 to the surface of the second insulating film 18 on the third region 15R3. That is, the conductive film 21 is in direct contact with the upper surface of the central protrusion 15P1 and covers the first insulating film 17 and the second insulating film 18.
[0034] 4, the conductive film 21 has a contact portion 21C that is in direct contact with the upper surface of the p-type semiconductor layer 15 exposed between the first insulating film 17 and the second insulating film 18. In other words, the contact portion 21C of the conductive film 21 separates the first insulating film 17 and the second insulating film 18 on the second region 15R2 in a plan view of the surface-emitting laser 100 seen from above. The conductive film 21 is formed to have an inclined surface that follows the inclined inner side surface of the second insulating film 18.
[0035] The conductive film 21 is made of a metal oxide, such as indium tin oxide (ITO) or indium zinc oxide (IZO), that is translucent to the blue light emitted from the light emitting layer 14 of the semiconductor structure layer EM described above.
[0036] The n-electrode NE as a first electrode is formed on the upper surface of the lower portion 13A of the n-type semiconductor layer 13, and is a metal electrode with a ring-shaped upper surface that is electrically connected to the n-type semiconductor layer 13. The n-electrode NE is formed on the upper surface of the lower portion 13A so that a portion of the n-electrode NE covers the outer edge of the second insulating film 18. The n-electrode NE is formed, for example, by stacking titanium (Ti) and aluminum (Al) in this order on the upper surface of the lower portion 13A.
[0037] The p-electrode PE as a second electrode is a metal electrode made of gold (Au) that is formed on the conductive film 21 and is electrically connected to the p-type semiconductor layer 15. The p-electrode PE is made up of a first p-electrode PE1 and a second p-electrode PE2.
[0038] The first p electrode PE1 of the p electrodes PE has an annular shape on the top surface and is formed along the outer edge of the conductive film 21 so as to surround the first region 15R1. In a plan view of the surface-emitting laser 100 seen from above, the inner edge of the first p electrode PE1 and the outer edge of the first insulating film 17 are spaced apart by a distance L as shown in FIG. 4. The inner edge of the first p electrode PE1 is located on the contact portion 21C of the conductive film 21. That is, when viewed from above, there is no portion where all three films, the first p electrode PE1, the conductive film 21, and the first insulating film 17, overlap each other.
[0039] In this embodiment, the first p electrode PE1 is formed so as to cover the inclined surface of the above-mentioned conductive film 21. Since the first p electrode PE1 has such a configuration, it can be expected that the durability against cracks and the like during long-term use will be improved, compared to a case in which the first p electrode PE1 does not cover the inclined surface of the conductive film 21.
[0040] The second multilayer film reflector 23 is a cylindrical dielectric multilayer film reflector made of dielectric layers formed on the conductive film 21. The second multilayer film reflector 23 is formed so as to cover the first region 15R1 and the inner edge of the first p-electrode PE1 in a plan view of the surface-emitting laser 100 seen from above.
[0041] The second multilayer film reflector 23 is a so-called distributed Bragg reflector (DBR) in which a high refractive index dielectric film having a relatively high refractive index and a low refractive index dielectric film having a lower refractive index than the high refractive index dielectric film are alternately stacked on the upper surface of the conductive film 21.
[0042] The second multilayer film reflector 23 is formed, for example, by laminating 10.5 pairs of a high refractive index dielectric film made of niobium pentoxide (Nb2O5) and a low refractive index dielectric film made of SiO2 on the upper surface of the conductive film 21. The second multilayer film reflector 23 has reflectivity for the blue light emitted from the light emitting layer 14 by having such a configuration.
[0043] A transparent dielectric layer (not shown) having a circular upper surface shape may be formed as, for example, a phase adjustment layer between the second multilayer film reflector 23 and the conductive film 21. The dielectric layer is made of, for example, Nb2O5, tantalum pentoxide (Ta2O5), zinc oxide (ZrO2), titanium oxide (TiO2), hafnium oxide (HfO2), or the like.
[0044] The second p electrode PE2 of the p electrodes PE is a metal electrode made of Au having a circular upper surface shape formed so as to cover the first p electrode PE1 and the second multilayer film reflector 23. The second p electrode PE2 is electrically connected to the p-type semiconductor layer 15 via the first p electrode PE1 and the conductive film 21.
[0045] In the surface-emitting laser 100, the bottom surface of the second multilayer film reflector 23 faces the top surface of the first multilayer film reflector 12, sandwiching the conductive film 21 and the semiconductor structure layer EM therebetween. As a result, the first multilayer film reflector 12 and the second multilayer film reflector 23 form a resonator OC between the first multilayer film reflector 12 and the second multilayer film reflector 23, with the resonator length direction being the direction perpendicular to the semiconductor structure layer EM (the up-down direction in FIG. 3).
[0046] In the surface-emitting laser 100, the reflectance of the first multilayer film reflector 12 for blue light is slightly lower than the reflectance of the second multilayer film reflector 23 for blue light. Therefore, part of the blue light resonated in the resonator OC passes through the first multilayer film reflector 12 and the substrate 11 and is extracted to the outside. That is, the light resonated between the first multilayer film reflector 12 and the second multilayer film reflector 23 is emitted downward in FIG.
[0047] An antireflection film (not shown) made of a laminate of Nb2O5 and SiO2 is formed on the lower surface of the substrate 11. The antireflection film is a so-called AR coat that suppresses the blue light emitted from the substrate 11 from being reflected upward in FIG.
[0048] Here, we will explain the operation and optical characteristics of the surface-emitting laser 100. When a voltage is applied to the above-mentioned n-electrode NE and p-electrode PE and a current flows between the n-electrode NE and the p-electrode PE, the current flows in the light-emitting layer 14 of the semiconductor structure layer EM as shown by the thick two-dot chain arrow in Fig. 3, and when the current reaches a threshold current, which is a predetermined current value, the intensity of the blue light emitted from the light-emitting layer 14 increases rapidly.
[0049] The blue light emitted from the light-emitting layer 14 when the threshold current is reached is repeatedly reflected between the first multilayer film reflector 12 and the second multilayer film reflector 23, i.e., within the resonator OC, and reaches a resonant state (i.e., laser oscillation occurs).
[0050] As described above, the conductive film 21 is in direct contact with the first region 15R1 on the upper surface of the p-type semiconductor layer 15, and is formed to cover the second insulating film 18 formed on the third region 15R3. That is, the conductive film 21 is electrically insulated from the third region 15R3.
[0051] As described above, since the second region 15R2 is a high-resistance region that has been made highly resistive due to etching damage, the current flowing through the conductive film 21 is less likely to flow through the second region 15R2 into the p-type semiconductor layer 15. Therefore, on the upper surface of the p-type semiconductor layer 15, only the first region 15R1, which is the upper surface of the central protrusion 15P1, is electrically connected to the conductive film 21.
[0052] Therefore, in the p-type semiconductor layer 15, most of the current flowing from the p-electrode PE to the conductive film 21 is supplied to the semiconductor structure layer EM via the first region 15R1, which is a low-resistance region, and flows to the n-electrode NE. Therefore, in the surface-emitting laser 100, a current is supplied to the light-emitting layer 14 via the first region 15R1, and blue light is emitted from the first region 15R1 along the central axis CA. That is, in the surface-emitting laser 100, the central protrusion 15P1 of the p-type semiconductor layer 15 functions as a current constriction portion that limits the supply range of the current so that the current does not spread any further.
[0053] As described above, the blue light emitted from the light emitting layer 14 and resonated in the resonator OC is partially extracted to the outside through the first multilayer reflector 12 and the substrate 11 because the optical reflectance of the first multilayer reflector 12 is lower than that of the second multilayer reflector 23. In other words, the lower surface of the substrate 11 serves as the light emission surface of the surface emitting laser 100.
[0054] In the surface-emitting laser 100, the first insulating film 17 has a refractive index lower than that of the p-type semiconductor layer 15. Therefore, the effective refractive index of the resonator OC, which is a cylindrical region including the central protrusion 15P1, is higher than the effective refractive index of the cylindrical peripheral region along the first insulating film 17 around it.
[0055] In addition, in the surface-emitting laser 100, the effective refractive index in the cylindrical peripheral region along the first insulating film 17 is greater than the effective refractive index in the cylindrical peripheral region along the second region 15R2 around which the first insulating film 17 is not formed.
[0056] That is, in the surface-emitting laser 100, the effective refractive index decreases from the center of the central protrusion 15P1 toward the radial direction. Since the surface-emitting laser 100 is configured in this way, the optical loss caused by the standing wave in the resonator OC diverging (radiating) to the first peripheral region is suppressed. That is, a large amount of light remains in the resonator OC, and the laser light is extracted to the outside in this state.
[0057] Therefore, a large amount of light emitted from the light emitting layer 14 is concentrated around the central axis CA of the resonator OC, so that high-output and high-density laser light can be generated and emitted. Therefore, the intensity distribution in the transverse cross section of the laser light emitted from the surface emitting laser 100, that is, the transverse mode of the laser light, can be stabilized.
[0058] [Suppression of current leakage in surface-emitting laser 100] Hereinafter, the suppression of current leakage in the surface emitting laser 100 of this embodiment will be described with reference to FIGS.
[0059] As described above, in the surface-emitting laser 100, the conductive film 21 has a contact portion 21C in direct contact with the upper surface of the p-type semiconductor layer 15 exposed between the first insulating film 17 and the second insulating film 18. Also, in the surface-emitting laser 100, as described above, the inner edge of the first p-electrode PE1 is separated from the first insulating film 17 in a plan view of the surface-emitting laser 100 seen from above.
[0060] In this embodiment, since the surface-emitting laser 100 has the above-mentioned configuration, when a voltage is applied to the p-electrode PE and the n-electrode NE and a current flows from the first p-electrode PE1 through the conductive film 21 to the p-type semiconductor layer 15, it is possible to prevent the current from leaking into the p-type semiconductor layer 15 from regions other than the first region 15R1.
[0061] Here, a conventional surface-emitting laser will be described with reference to Fig. 5. Fig. 5 is an enlarged view showing a portion A in the conventional surface-emitting laser, similar to Fig. 4. The conventional surface-emitting laser is different from Example 1 in that it has an insulating layer 25, but is otherwise similar to Example 1.
[0062] In the conventional surface-emitting laser, the insulating layer 25 has a first portion 25A having a thickness t1 formed across the second region 15R2 and a second portion 25B having a thickness t2 formed across the third region 15R3. That is, the insulating layer 25 can be said to be the first insulating film 17 in the surface-emitting laser 100 formed across the second region 15R2.
[0063] In the surface-emitting laser, the thickness t1 of the first portion 25A of the insulating layer 25 is the same as the height of the first region 15R1 from the second region 15R2. Since the height of the first region 15R1 is preferably about 20 nm from the viewpoints of lateral mode control and suppression of damage to the light-emitting layer 14, the thickness t1 of the first portion 25A can also be the same thickness. During the manufacture of the surface-emitting laser, if the thickness t1 is, for example, about 10 nm or less, pinholes penetrating the first portion 25A in the vertical direction are likely to occur in the first portion 25A.
[0064] For example, as shown in Figure 5, if a pinhole Ph occurs in a region of the first portion 25A closer to the outer peripheral protrusion 15P2 than the center of the first portion 25A, when a conductive film 21 is formed on top of the insulating layer 25 by sputtering or the like, the nano-metal particles that make up the conductive film 21 will penetrate into the pinhole Ph, and the pinhole Ph itself will become a conductive portion.
[0065] For example, when a voltage is applied between the p-electrode PE and the n-electrode NE, a current flowing from the first p-electrode PE1 to the n-electrode NE flows from the first p-electrode PE1 to the first region 15R1, which is a low-resistance region, along the extending direction of the conductive film 21, and also flows into the pinhole Ph formed in the first insulating film 17. Note that the inner edge of the first p-electrode PE1 is a region where current concentration is likely to occur on the current path from the first p-electrode PE1 to the first region 15R1.
[0066] In the conventional surface-emitting laser, the inner edge of the first p electrode PE1 is located directly above the region of the first portion 25A in which the pinhole Ph is formed, as shown in Fig. 5. That is, in the conventional surface-emitting laser, when the pinhole Ph exists directly below the inner edge of the first p electrode PE1, the distance between the first p electrode PE1 and the pinhole Ph becomes very short.
[0067] A Schottky contact is made between the pinhole Ph, which is a conductive part, and the second region 15R2 of the p-type semiconductor layer 15. However, when the distance between the first p electrode PE1 and the pinhole Ph is very short as described above, a local high voltage is applied to the interface between the pinhole Ph and the second region 15R2 of the p-type semiconductor layer 15, and a current can flow from the pinhole Ph into the p-type semiconductor layer 15 across the Schottky barrier.
[0068] If this occurs, current leakage may occur in the surface-emitting laser from the conductive film 21 through the pinhole Ph. For example, if current leakage occurs, the amount of current flowing through the central protrusion 15P1 of the p-type semiconductor layer, through which current should flow, decreases, which may lead to a decrease in gain or a breakdown of the surface-emitting laser 100.
[0069] In the surface-emitting laser 100 of this embodiment, as described above, the first insulating film 17 and the second insulating film 18 are formed to be separated by the contact portion 21C of the conductive film 21, and the inner edge of the first p electrode PE1 is located on the contact portion 21C. In other words, the first insulating film 17 is not formed in the region directly below the first p electrode PE1. That is, the first p electrode PE1 and the first insulating film 17 are spaced apart from each other.
[0070] Therefore, when a voltage is applied to the n-electrode NE and the p-electrode PE in the surface-emitting laser 100 and a current flows from the p-electrode PE to the n-electrode NE, the current flowing in the conductive film 21 flows along the extension direction of the conductive film 21 as shown in FIG. 4, and most of the current passes through the first region 15R1, which is a low-resistance region, and proceeds into the p-type semiconductor layer 15 and toward the n-electrode NE.
[0071] At this time, even if a pinhole occurs in the first insulating film 17, since the inner edge of the first p-electrode PE1 and the outer edge of the first insulating film 17 are separated by a distance L in the surface-emitting laser 100 of this embodiment, a local high voltage is unlikely to be applied as in the conventional example. In other words, a current leak as in the conventional example is unlikely to occur. Note that the distance L is preferably 5 μm or more.
[0072] Therefore, according to the surface-emitting laser 100 of this embodiment, even when the first p-electrode PE1 is brought close to the first region 15R1, by increasing the distance between the first insulating film 17 and the first p-electrode PE1 in the top view, it is possible to prevent the current flowing through the conductive film 21 from flowing into the p-type semiconductor layer 15 from the second region 15R2.
[0073] Therefore, according to the surface-emitting laser 100 of this embodiment, it is possible to suppress the occurrence of current leakage from portions other than the portion through which current is originally desired to flow, thereby reducing the risk of failure of the surface-emitting laser 100.
[0074] In this embodiment, the upper surface of the p-type semiconductor layer 15 has been described as having the outer circumferential protrusion 15P2, but the outer circumferential protrusion 15P2 may not be provided, and the second region 15R2 may be formed up to the outer edge of the p-type semiconductor layer 15. That is, the entire region of the upper surface of the p-type semiconductor layer 15 other than the first region 15R1 may be etched (inactive region).
[0075] In this embodiment, the second region 15R2 is passivated by dry etching the upper surface of the p-type semiconductor layer 15, but the method of passivation is not limited to dry etching. For example, the p-type impurity may be passivated by ion implantation after removing a small amount of the surface of the p-type semiconductor layer, or the p-type impurity may be passivated by ashing.
[0076] [Applications of surface-emitting lasers] An application example using the surface-emitting laser of Example 1 will be described with reference to Fig. 6 and Fig. 7. Fig. 6 is a top view of a light-emitting device 200 as an application example, and Fig. 7 is a cross-sectional view of the light-emitting device 200 taken along line 7-7 in Fig. 6. In Fig. 7, the vertical direction is the height direction of the light-emitting device 200.
[0077] The light emitting device 200 is obtained by flip-chip mounting the surface emitting laser 100 according to the first embodiment on a mounting substrate 31 and packaging the same. The light emitting device 200 includes the mounting substrate 31 on which the surface emitting laser 100 is mounted, a frame 37, and a light-transmitting plate 41. The configuration of the surface emitting laser 100 is the same as that of the first embodiment.
[0078] The mounting substrate 31 serving as the bottom is a plate-like body having a rectangular upper surface shape. The mounting substrate 31 is made of an insulating material such as ceramics such as aluminum nitride (AlN), aluminum oxide (Al2O3), silicon (Si), or silicon carbide (SiC).
[0079] The n-electrode NE of the surface-emitting laser 100 is joined to a first pad electrode (not shown) provided on the upper surface of the mounting substrate 31 via an n-electrode joining member 33 made of Au extending downward in the figure and a joining member 34 made of Au-Sn eutectic bonding.
[0080] The second p-electrode PE2 of the surface-emitting laser 100 is bonded to a second pad electrode (not shown) provided on the upper surface of the mounting substrate 31 at a distance from the first pad electrode via a bonding member 35 made of Au-Sn eutectic bonding.
[0081] The first pad electrode and the second pad electrode are electrically connected to back electrodes (not shown) provided at a distance from each other on the back surface of the mounting substrate 31 through vias penetrating the mounting substrate 31. That is, the surface-emitting laser 100 can receive power through the back surface electrode of the mounting substrate 31.
[0082] The frame 37 is formed along the outer edge of the mounting substrate 31 so as to expose the region of the upper surface of the mounting substrate 31 on which the surface-emitting laser 100 is mounted. In other words, in a plan view of the light-emitting device 200 seen from above, the frame 37 surrounds the surface-emitting laser 100 on the mounting substrate 31. Like the mounting substrate 31, the frame 37 is made of an insulating material such as ceramics such as AlN, Al2O3, Si, or SiC.
[0083] The light-transmitting plate 41 is a transparent plate-like body with a rectangular upper surface. The lower surface of the light-transmitting plate 41 is joined to the frame body 37 via a metal layer 42 made of Au formed on the upper surface of the frame body 37 and a joining member 43. In other words, the light-transmitting plate 41 is held by the frame body 37 so as to cover the surface-emitting laser 100. The light-transmitting plate 41 is made of a material having translucency to the light emitted from the surface-emitting laser 100, such as borosilicate glass.
[0084] In the light emitting device 200, light emitted from the surface emitting laser 100 passes through the light-transmitting plate 41 and is emitted to the outside of the light emitting device 200. That is, in this embodiment, the upper surface of the light-transmitting plate 41 is the light emitting surface of the light emitting device 200.
[0085] Also in the light emitting device 200, by separating the outer edge of the first insulating film 17 and the inner edge of the first p-electrode PE1 by the distance L, it is possible to prevent the current flowing through the conductive film 21 from leaking from the second region 15R2 and flowing into the p-type semiconductor layer 15. Therefore, also in the light emitting device 200, it is possible to reduce the risk of failure of the surface emitting laser 100 due to the occurrence of current leakage.
[0086] In the light emitting device 200, the surface emitting laser 100 may be mounted by wire bonding in addition to flip chip mounting. In this case, the p-electrode PE of the surface emitting laser 100 may be provided with only the first p-electrode PE1. For example, when the surface emitting laser 100 is connected by wire bonding in the light emitting device 200, the first p-electrode PE1 may be directly wire bonded. [Explanation of symbols]
[0087] 100, 110 Surface-emitting laser (vertical cavity light-emitting device) 200 Light emitting device 11 Substrate 12 First multilayer mirror 13 n-type semiconductor layer 14 Emitting layer 15 p-type semiconductor layer 17 First insulating film 18 Second insulating film 21 Conductive film 23 Second multilayer mirror 31 Mounting board 33 n-electrode bonding material 34, 35, 43 Joint members 37 Frame 41 Translucent plate 42 Metal layer NE n electrode PE p electrode
Claims
1. A substrate; a first multilayer film reflector formed on the substrate; a semiconductor structure layer including a first semiconductor layer having a first conductivity type formed on the first multilayer film reflector, a light emitting layer formed on the first semiconductor layer, and a second semiconductor layer having a second conductivity type opposite to the first conductivity type formed on the light emitting layer and having a protruding portion protruding upward from the center of an upper surface; a first insulating film having insulating properties and formed in a ring shape in a region along an outer edge of the protruding portion in an outer region on the upper surface of the second semiconductor layer that is outside the protruding portion; a second insulating film having insulating properties and formed in a ring shape in the outer region and spaced outward from the first insulating film in a top view; a transparent conductive film that covers an upper surface of the protruding portion and is formed from the upper surface of the protruding portion to a surface of the second insulating film, and has a contact portion that is in direct contact with an upper surface of the second semiconductor layer exposed between the first insulating film and the second insulating film; a first electrode electrically connected to the first semiconductor layer; a second electrode provided in a region of the conductive film on the outer region and electrically connected to the second semiconductor layer via the conductive film; a second multilayer film reflector formed on the semiconductor structure layer to cover the protruding portion and forming a resonator between the second multilayer film reflector and the first multilayer film reflector; having The vertical cavity light emitting device according to claim 1, wherein the second semiconductor layer has an inactive region at least in the contact portion.
2. 2. The vertical cavity light emitting device according to claim 1, wherein the first insulating film and the second electrode are spaced apart from each other in a radial direction from a center of the protrusion.
3. 3. The vertical cavity light emitting device according to claim 2, wherein an inner edge of the second electrode is located on the contact portion of the conductive film.
4. 3. The vertical cavity light emitting device according to claim 1, wherein the first insulating film has a thickness equal to the height of the upper surface of the protrusion from the outer region.
5. the second semiconductor layer has an annular step portion formed along an outer edge of an upper surface of the second semiconductor layer, 3. The vertical cavity light emitting device according to claim 1, wherein each of the second insulating film, the conductive film and the second electrode is formed so as to cover the step portion.
6. A light emitting device comprising the vertical cavity light emitting device according to claim 1, a flat bottom portion having the vertical cavity light emitting device provided in one region of one main surface; a frame formed on the first main surface of the bottom portion and surrounding the vertical cavity light emitting device so as to expose the first region; a light-transmitting plate having light-transmitting properties and held by the frame so as to cover the first region; A light emitting device comprising:
Citation Information
Patent Citations
Vertical resonator type light emitting element
JP2021197437A