JP2023138306A - Surface-emitting laser, projection device, head-up display, mobile, head-mounted display and optometric device - Google Patents

Abstract

To provide a surface-emitting laser capable of improving uniformity of a density of a current injected to a resonator, a projection device, a head-up display, a mobile, a head-mounted display and an optometric device.SOLUTION: A surface-emitting laser comprises: a first reflector; a second reflector; a resonator which is provided between the first reflector and the second reflector and includes an active layer; and a conductive layer which injects a current to the resonator. The surface-emitting laser comprises a semiconductor multilayer structure including the resonator. The semiconductor multilayer structure includes: a first layer including a first p-type semiconductor layer and a second layer which is provided between the first layer and the active layer and includes a second p-type semiconductor layer. The second p-type semiconductor layer is in contact with the first layer and comprises a band gap which is larger than a band gap of the first p-type semiconductor layer. A partial or entire top face of the first layer and an interface of the first layer and the second layer are in contact with the conductive layer.SELECTED DRAWING: Figure 2

Description

The present invention relates to a surface emitting laser, a projection device, a head-up display, a moving object, a head-mounted display, and an optometry device.

A vertical cavity surface emitting laser (VCSEL) is a laser in which a thin active layer is sandwiched between a pair of reflecting mirrors, and a cavity is formed in a direction perpendicular to a substrate. Therefore, a reflecting mirror is sometimes required to have a reflectance of 99% or more.

With GaN-based materials, it is difficult to form semiconductor reflective mirrors with low resistance compared with GaAs-based materials. For this reason, when a surface emitting laser is manufactured using a GaN-based material, an intracavity contact structure is often used to inject current into the active layer, in which the reflector is not energized and the contact is made in the resonator. At this time, the p-side contact is made using a high-resistance layer such as a dielectric material on the highly doped p-GaN to form a limited opening (aperture) as a current confinement structure, and a conductive material such as indium tin oxide (ITO). Current is often injected using a transparent film.

In a VCSEL having a current injection structure using ITO, light absorption of ITO becomes a problem. Normally, ITO has a light absorption of several thousand cm ^-1 in the visible light range from the 400 nm band developed for GaN-based VCSELs. Therefore, by providing a thin layer of ITO at the nodes of electric field strength in the resonator, the influence of absorption is reduced. The thickness of ITO is almost always 50 nm or less, and often 20 nm or less.

The resistivity of ITO is usually on the order of 1×10 ⁻⁴ Ωcm, and ITO in the lateral direction inevitably has a high resistance. Furthermore, since the resistivity of p-GaN on the injected side is in the single digit Ωcm range, the current injected from ITO does not spread in the horizontal direction, but flows vertically in the resonator towards the active layer side. become. At this time, due to the influence of the thin ITO, it becomes difficult to make the current density uniform between the outer periphery and the center of the aperture, and as a result, the current injection density into the active layer becomes dense at the outer periphery and coarse at the center. It becomes easier. In particular, the larger the diameter of the aperture, the greater the effect. This makes it difficult for the active layer inside the aperture to obtain a uniform gain, and in particular, it becomes difficult to stably obtain a single mode.

Furthermore, Non-Patent Document 1 describes an attempt to make the current injection into the inside of the aperture uniform by making the n-side distributed Bragg reflector (DBR) conductive. However, even in the configuration described in Non-Patent Document 1, the non-uniformity of current injection density caused by the high electrical resistance of ITO is not solved.

An object of the present invention is to provide a surface emitting laser, a projection device, a head-up display, a moving body, a head-mounted display, and an optometry device that can improve the uniformity of the density of current injected into a resonator. .

According to one aspect of the disclosed technology, the surface emitting laser is provided with a first reflecting mirror, a second reflecting mirror, and between the first reflecting mirror and the second reflecting mirror. A semiconductor stacked structure including a resonator including an active layer and a conductive layer for injecting current into the resonator, the semiconductor stacked structure including a first p-type semiconductor layer. and a second layer provided between the first layer and the active layer and including a second p-type semiconductor layer, the second layer including the second p-type semiconductor layer. is in contact with the first layer and has a bandgap larger than the bandgap of the first p-type semiconductor layer, and is in contact with a part or all of the upper surface of the first layer and with the first layer. an interface with the second layer is in contact with the conductive layer.

According to the disclosed technology, it is possible to improve the uniformity of the density of current injected into the resonator.

FIG. 1 is a cross-sectional view showing a surface emitting laser according to a first embodiment. FIG. 2 is a cross-sectional view showing the vicinity of the ridge of the surface emitting laser according to the first embodiment. FIG. 7 is a cross-sectional view showing the vicinity of a ridge of a surface emitting laser according to a second embodiment. FIG. 7 is a cross-sectional view showing the vicinity of a ridge of a surface emitting laser according to a third embodiment. FIG. 7 is a cross-sectional view showing the vicinity of a ridge of a surface emitting laser according to a fourth embodiment. FIG. 7 is a cross-sectional view showing the vicinity of a ridge of a surface emitting laser according to a fifth embodiment. It is a schematic diagram which shows the head-up display which is an example of the projection device based on 6th Embodiment. FIG. 7 is a schematic diagram showing a car equipped with a head-up display according to a sixth embodiment. FIG. 7 is a perspective view illustrating the appearance of a head mounted display according to a seventh embodiment. It is a figure which partially illustrates the structure of the head mounted display based on 7th Embodiment. FIG. 3 is a block diagram showing an optometry apparatus according to an eighth embodiment.

Embodiments of the present disclosure will be described below with reference to the accompanying drawings. Note that, in this specification and the drawings, components having substantially the same functional configurations may be given the same reference numerals to omit redundant explanation.

(First embodiment)
First, a first embodiment will be described. The first embodiment relates to a surface emitting laser. FIG. 1 is a cross-sectional view showing a surface emitting laser according to a first embodiment. FIG. 2 is a cross-sectional view showing the vicinity of the ridge structure of the surface emitting laser according to the first embodiment. 2(a) is an enlarged cross-sectional view of a part of FIG. 1, and FIG. 2(b) is a cross-sectional view showing the current in the vicinity of the area indicated by the broken line circle in FIG. 2(a) with arrows. be.

As shown in FIG. 1, the surface emitting laser 1 according to the first embodiment includes a substrate 50, a lower reflecting mirror 10, a resonator 20, a conductive layer 40, and an upper reflecting mirror 30. The lower reflector 10 is above the substrate 50 , the resonator 20 is above the lower reflector 10 , the conductive layer 40 is above the resonator 20 , and the upper reflector 30 is above the conductive layer 40 . It is above. The surface emitting laser 1 is configured to output light with a wavelength of 450 nm.

The substrate 50 is, for example, a GaN substrate whose upper surface is c-plane. The lower reflecting mirror 10 is, for example, a DBR made of a semiconductor.

The resonator 20 has a lower spacer layer 100, an active layer 200, and an upper spacer layer 300. A lower spacer layer 100 overlies the lower reflector 10, an active layer 200 overlies the lower spacer layer 100, and an upper spacer layer 300 overlies the active layer 200. Although not essential, there may be an electron blocking layer 250 with a thickness of about 20 nm between the active layer 200 and the upper spacer layer 300. The resonator 20 is an example of a semiconductor stacked structure.

For example, the lower spacer layer 100 is an n-type GaN layer doped with Si at a concentration of 3×10 ¹⁸ /cm ^{3 ,} for example. The active layer 200 has a multiple quantum well layer including a plurality of InGaN layers and GaN layers, and emits light at 450 nm. The electron block layer 250 is, for example, an Al _0.2 Ga _0.8 N layer doped with Mg at a concentration of 2×10 ¹⁹ /cm ³ .

The upper spacer layer 300 has a first layer 310, a second layer 320, and a third layer 330, as shown in FIG. 2(a). A second layer 320 is above the third layer 330 and a first layer 310 is above the second layer 320. The third layer 330 is the layer closest to the active layer 200 among the upper spacer layers 300. The third layer 330 is, for example, a p-type GaN layer doped with Mg at a concentration of 2×10 ¹⁹ /cm ³ . The second layer 320 is, for example, a p-type Al _0.05 Ga _0.95 N layer doped with Mg at a concentration of 2×10 ¹⁹ /cm ³ . The thickness of the second layer 320 is, for example, 10 nm. The first layer 310 is, for example, a p-type In _0.07 Ga _0.93 N layer doped with Mg at a concentration of 2×10 ¹⁹ /cm ³ . The thickness of the first layer 310 is, for example, 15 nm. However, the outermost layer from the top surface of the first layer 310 to a depth of 10 nm is doped with Mg at a higher concentration, for example, at a concentration of 3×10 ²⁰ /cm ³ . The bandgap of the second layer 320 is larger than the bandgap of the first layer 310. In this embodiment, the second layer 320 is an example of a second p-type semiconductor layer, and the first layer 310 is an example of a first p-type semiconductor layer.

A mesa structure 340 is formed in the upper spacer layer 300, the active layer 200, and the lower spacer layer 100. The mesa structure 340 is formed at a height such that the lower spacer layer 100 is exposed around the mesa structure 340. The mesa structure 340 is formed into a columnar shape with a diameter of 25 μm.

A ridge structure 350 is formed in the upper spacer layer 300. The ridge structure 350 is formed at a height such that the second layer 320 is exposed around the ridge structure 350. For example, the height of the ridge structure 350 is 20 nm. The ridge structure 350 is formed into a columnar shape with a diameter of 10 μm. A dielectric layer 60 is formed on the second layer 320 exposed from the ridge structure 350. The dielectric layer 60 is in contact with the side surface of the portion of the second layer 320 that constitutes the ridge structure 350 . The upper surface of the dielectric layer 60 is closer to the active layer 200 than the interface between the first layer 310 and the second layer 320. The dielectric layer 60 is, for example, a SiO ₂ layer.

Conductive layer 40 is provided over dielectric layer 60 and ridge structure 350. The conductive layer 40 contacts the entire upper surface of the first layer 310 and the interface between the first layer 310 and the second layer 320. The conductive layer 40 is, for example, a transparent conductive layer such as an ITO layer.

The upper reflecting mirror 30 is arranged so as to overlap the ridge structure 350 in plan view. The upper reflecting mirror 30 is, for example, a dielectric DBR.

An n-side electrode 71 is formed on the n-type lower spacer layer 100 exposed from the mesa structure 340 and is in ohmic contact with the lower spacer layer 100 . The n-side electrode 71 has, for example, a laminated film in which a Ti film, an Al film, a Pt film, and an Au film are laminated in order from the bottom. A dielectric layer 80 is formed on a portion of the n-type lower spacer layer 100 excluding the portion where the n-side electrode 71 is formed, and on the side surface of the mesa structure 340. The dielectric layer 80 is, for example, a SiN layer.

A p-side electrode 72 is formed on the conductive layer 40 around the upper reflecting mirror 30 . The p-side electrode 72 has, for example, a laminated film in which a Ti film and an Au film are laminated in order from the bottom.

Note that it is preferable that the node of electric field strength be located near a highly doped portion of the first layer 310 or near the conductive layer 40.

Next, a method for manufacturing the surface emitting laser according to the first embodiment will be described.

First, the lower reflective mirror 10, the lower spacer layer 100, the active layer 200, and the upper spacer layer 300 are formed on the substrate 50 by metal organic chemical vapor deposition (MOCVD).

Next, a mesa structure 340 is formed in the stack of the upper spacer layer 300, the active layer, and the lower spacer layer 100. In forming the mesa structure 340, an etching mask is formed using photoresist or metal on the upper spacer layer 300 using photolithography, and the stacked structure of the upper spacer layer 300, the active layer, and the lower spacer layer 100 is dry etched. conduct. At this time, the dry etching is stopped halfway in the thickness direction of the lower spacer layer 100.

Next, in the vicinity of the mesa structure 340, the n-side electrode 71 is formed on the lower spacer layer 100 exposed from the mesa structure 340. The n-side electrode 71 can be formed using lift-off. After forming the metal film constituting the n-side electrode 71, the n-side electrode 71 can be brought into ohmic contact with the lower spacer layer 100 by annealing in an _N2 atmosphere at 550°C.

Next, a dielectric layer 80 covering the mesa structure 340 and the n-side electrode 71 is formed on the lower spacer layer 100. Next, a resist mask is formed using, for example, photolithography to expose only the upper surface of the mesa structure 340, and the dielectric layer 80 is removed by wet etching. Next, a ridge structure 350 is formed on the upper spacer layer 300. In forming the ridge structure 350, a resist mask is formed on the upper spacer layer 300 using photolithography, and the upper spacer layer 300 is dry etched.

Next, a dielectric layer 60 is formed on top of the upper spacer layer 300 exposed from the ridge structure 350. The thickness of the dielectric layer 60 is such that the upper surface of the dielectric layer 60 is located closer to the active layer 200 than the interface between the first layer 310 and the second layer 320 (see FIG. )reference). Next, a conductive layer 40 is formed over the dielectric layer 60 and the ridge structure 350. In forming the dielectric layer 60 and the conductive layer 40, first, a SiO ₂ layer and an ITO layer are formed by sputtering or the like while leaving the resist mask used for forming the ridge structure 350, and then the resist mask is removed. . In other words, perform liftoff. At this time, the thickness of the ITO layer is such that the upper surface of the ITO layer is substantially flush with the upper surface of the ridge structure 350. Then, after the lift-off, another ITO layer is further formed so as to be in contact with the upper surface of the ridge structure 350. Thereafter, the excess ITO layer formed on the dielectric layer 80 is removed, for example, by wet etching.

Next, the upper reflecting mirror 30 is formed on the conductive layer 40. The upper reflecting mirror 30 can be formed, for example, by lift-off. Next, a p-side electrode 72 is formed on the conductive layer 40 around the upper reflecting mirror 30. The p-side electrode 72 can be formed, for example, by lift-off. Next, a portion of the dielectric layer 80 above the n-side electrode 71 is removed by dry etching or the like.

In this way, the surface emitting laser 1 according to the first embodiment can be manufactured.

In the surface emitting laser 1 according to the first embodiment, a second layer 320 (for example, an Al _0.05 Ga _0.95 N layer) is provided under a first layer 310 (for example, an In _0.07 Ga _0.93 N layer). ), and the bandgap of the second layer 320 is larger than the bandgap of the first layer 310. Therefore, two-dimensional hole gas (2DHG) is formed near the interface between the first layer 310 and the second layer 320. 2DHG includes highly concentrated carriers formed two-dimensionally in a narrow region with a thickness of about 1 nm. Further, the conductive layer 40 is in contact with the entire upper surface of the first layer 310 and the interface between the first layer 310 and the second layer 320.

Therefore, as shown in FIG. 2B, current is not only injected from the conductive layer 40 into the resonator 20 from the upper surface of the first layer 310, but also between the first layer 310 and the second layer. Current is also injected from the interface with 320. That is, current is injected from the conductive layer 40 into the resonator 20 via the top surface and sidewall surfaces of the ridge structure 350. Further, since the electrical resistance of 2DHG is lower than that of the first layer 310 and the second layer 320, carriers tend to spread laterally. Therefore, the current injected from the top surface of the ridge structure 350 spreads laterally by 2DHG, and the current injection density tends to be uniform inside the aperture. In other words, variations in current injection density inside the ridge structure 350 are suppressed.

In this way, according to the surface emitting laser 1, the density of the current flowing inside the aperture can be improved in uniformity, and the electrical resistance can be reduced. In the surface emitting laser 1, since the phase with respect to the resonant wavelength is shifted between the inside and outside of the ridge structure 350, an effective refractive index difference occurs, and light can be confined in the lateral direction. By improving the confinement of light in the lateral direction, the single mode property in the lateral direction can be improved. Furthermore, by utilizing the refractive index difference for confining light in the lateral direction, loss due to diffraction can be reduced, making it easier to obtain a single mode with a low threshold.

Note that as long as the conductive layer 40 is in contact with the interface between the first layer 310 and the second layer 320, the second layer 320 does not need to be etched when forming the ridge structure 350. That is, if the second layer 320 is exposed by etching the first layer 310, the second layer 320 does not need to be etched. However, if the second layer 320 is also etched, the interface between the first layer 310 and the second layer 320 will clearly appear on the side wall surface of the ridge structure 350, making it easier to bring the conductive layer 40 into contact with this interface. Become. Therefore, it is more preferable to etch not only the first layer 310 but also the second layer 320.

Further, the material of the first layer 310 is not limited to InGaN, and the first layer 310 may be a p-type GaN layer. Generalizing, for example, the first layer 310 is an In _a Ga _1-a N layer (0≦a<1), and the second layer 320 is an Al _b Ga _1-b N layer (0<b<1). ). When the material of the first layer 310 is GaN, it is easy to suppress crystal defects at the interface between the first layer 310 and the second layer 320, and it is easy to obtain effectively high mobility for 2DHG. Further, when the material of the first layer 310 is InGaN, it is easy to obtain a high concentration of 2DHG. The material of the dielectric layer 60 is not limited to SiO ₂ , and the dielectric layer 60 may be a SiNx layer, a TaOx layer, or the like.

Further, in the first embodiment, the first layer 310 and the second layer 320 are provided in the resonator 20, but part or all of the upper reflecting mirror is a semiconductor DBR, and a part of the semiconductor DBR is The first layer and the second p-layer may be included in the reflector by adjusting the thicknesses of the first layer and the second layer so that the p-layer functions as a p-layer.

(Second embodiment)
A second embodiment will be described. The second embodiment differs from the first embodiment mainly in the configuration of the ridge structure. FIG. 3 is a cross-sectional view showing the vicinity of the ridge structure of the surface emitting laser according to the second embodiment. FIG. 3(b) is a cross-sectional view in which the current in the vicinity of the region indicated by the broken line circle in FIG. 3(a) is indicated by arrows.

As shown in FIG. 3, in the surface emitting laser according to the second embodiment, the first layer 310 includes a first p-type semiconductor layer 311 and an undoped semiconductor layer 312. An undoped semiconductor layer 312 is on the second layer 320, and a first p-type semiconductor layer 311 is on the undoped semiconductor layer 312. The undoped semiconductor layer 312 is, for example, an In _0.07 Ga _0.93 N layer. The thickness of the undoped semiconductor layer 312 is, for example, 2.5 nm. The first p-type semiconductor layer 311 is, for example, a p-type In _0.07 Ga _0.93 N layer doped with Mg at a concentration of 2×10 ¹⁹ /cm ³ . The thickness of the first p-type semiconductor layer 311 is, for example, 12.5 nm. However, the outermost layer from the top surface of the first p-type semiconductor layer 311 to a depth of 10 nm is doped with Mg at a higher concentration, for example, at a concentration of 3×10 ²⁰ /cm ³ . The bandgap of the second layer 320 is larger than the bandgap of the first layer 310.

The other configurations are the same as in the first embodiment.

In the surface emitting laser according to the second embodiment, an undoped semiconductor layer 312 (for example, In _0.07 Ga _0.93 N layer) is provided under the first p-type semiconductor layer 311 (for example, In _0.07 Ga _0.93 N layer). Underneath the undoped semiconductor layer 312 is a second layer 320 (eg, an Al _0.05 Ga _0.95 N layer). Further, the bandgap of the second layer 320 is larger than the bandgap of the first layer 310. Therefore, 2DHG is formed near the interface of the undoped semiconductor layer 312 with the second layer 320. 2DHG includes highly concentrated carriers formed two-dimensionally in a narrow region with a thickness of about 1 nm in the undoped semiconductor layer 312. Further, the conductive layer 40 is in contact with the entire upper surface of the first layer 310 and the interface between the first layer 310 and the second layer 320.

Therefore, as shown in FIG. 3B, current is not only injected from the conductive layer 40 into the resonator 20 from the upper surface of the first layer 310, but also between the first layer 310 and the second layer. Current is also injected from the interface with 320. That is, current is injected from the conductive layer 40 into the resonator 20 via the top surface and sidewall surfaces of the ridge structure 350. Further, the electrical resistance of 2DHG is lower than that of the first layer 310 and the second layer 320, and for example, the carrier mobility (unit: m ² /(V・s)) in the undoped semiconductor layer 312 is lower than that of the first layer 310 and the second layer 320. It is expected to be in the double digits. Therefore, if the concentration of 2DHG is 1×10 ¹⁹ /cm ³ or more, a region with a resistance more than three orders of magnitude lower than that of the p-GaN layer (usually carrier concentration in the 1×10 ¹⁷ range and mobility in the single digit) is formed. It turns out. Therefore, the current injected from the top surface of the ridge structure 350 spreads laterally by 2DHG, and the current injection density tends to be uniform inside the aperture. In other words, variations in current injection density inside the ridge structure 350 are suppressed.

In this way, the second embodiment can also provide the same effects as the first embodiment.

Note that as long as the conductive layer 40 is in contact with the interface between the undoped semiconductor layer 312 and the second layer 320, the second layer 320 does not need to be etched when forming the ridge structure 350. That is, if the second layer 320 is exposed by etching the undoped semiconductor layer 312, the second layer 320 does not need to be etched. However, if the second layer 320 is also etched, the interface between the undoped semiconductor layer 312 and the second layer 320 clearly appears on the side wall surface of the ridge structure 350, making it easier to bring the conductive layer 40 into contact with this interface. . Therefore, it is more preferable to etch not only the first layer 310 but also the second layer 320.

Further, the material of the first p-type semiconductor layer 311 is not limited to InGaN, and the first p-type semiconductor layer 311 may be a p-type GaN layer. In this case, the undoped semiconductor layer 312 is preferably an In _0.08 Ga _0.92 N layer. By making the band gap of the undoped semiconductor layer 312 smaller than that of the first p-type semiconductor layer 311, 2DHG is easily formed. In this way, the bandgap of the second layer 320 is larger than the bandgap of the first layer 310, and the bandgap of the first p-type semiconductor layer 311 is larger than or equal to the bandgap of the undoped semiconductor layer 312. is preferred. Generalizing, for example, the first p-type semiconductor layer 311 and the undoped semiconductor layer 312 are In _a Ga _1-a N layers (0≦a<1), and the second layer 320 is Al _b Ga _1-b It is an N layer (0<b<1).

(Third embodiment)
A third embodiment will be described. The third embodiment differs from the second embodiment mainly in the configuration of the insulating region. FIG. 4 is a cross-sectional view showing the vicinity of the ridge structure of the surface emitting laser according to the third embodiment.

As shown in FIG. 4, the surface emitting laser according to the third embodiment has an inactive semiconductor layer 321 instead of the dielectric layer 60. The inactive semiconductor layer 321 contains an impurity element that inactivates the acceptor, and is an electrically insulating layer.

For example, after forming the ridge structure 350, the inactive semiconductor layer 321 is formed by implanting an impurity element that inactivates the acceptor into the surface layer of the second layer 320 while leaving the resist mask used for forming the ridge structure 350. It is formed by As the impurity element that inactivates the acceptor, an element that has the effect of inactivating the acceptor by bonding with the p-type dopant to inactivate it or by forming a deep level is used. Examples of such elements include B, H and Fe.

Other configurations are similar to the second embodiment.

The third embodiment can also provide the same effects as the second embodiment. Furthermore, formation of the dielectric layer 60 can be omitted.

(Fourth embodiment)
A fourth embodiment will be described. The fourth embodiment differs from the second embodiment mainly in the structure of the conductive layer. FIG. 5 is a cross-sectional view showing the vicinity of the ridge structure of the surface emitting laser according to the fourth embodiment.

As shown in FIG. 5, in the surface emitting laser according to the fourth embodiment, the conductive layer 40 includes a transparent conductive layer 41 and a metal layer 42. Above the dielectric layer 60 is a metal layer 42, and above the metal layer 42 is a transparent conductive layer 41. Metal layer 42 directly contacts the interface between first layer 310 and second layer 320. The metal layer 42 is, for example, an Au layer. The transparent conductive layer 41 is, for example, an ITO layer. For example, the top surface of the metal layer 42 and the top surface of the first layer 310 are substantially flush with each other. The transparent conductive layer 41 is an example of a first conductive layer, and the metal layer 42 is an example of a second conductive layer.

When manufacturing the surface emitting laser according to the fourth embodiment, for example, after forming the dielectric layer 60, the metal layer 42 is formed following the dielectric layer 60 while leaving the resist mask used for forming the ridge structure 350. Then, the resist mask is removed. At this time, the thickness of the metal layer 42 is such that the upper surface of the metal layer 42 is substantially flush with the upper surface of the ridge structure 350. After lift-off, a transparent conductive layer 41 is formed so as to be in contact with the upper surface of the ridge structure 350.

Other configurations are similar to the second embodiment.

The fourth embodiment can also provide the same effects as the second embodiment. Further, since the electrical resistance of the metal layer 42 is lower than that of the transparent conductive layer, the electrical resistance of the entire surface emitting laser can be further reduced. Furthermore, since light is blocked outside the ridge structure 350 covered with the metal layer 42, it is easy to trap the light in the lateral direction.

(Fifth embodiment)
A fifth embodiment will be described. The fifth embodiment differs from the fourth embodiment mainly in the structure of the conductive layer. FIG. 6 is a cross-sectional view showing the vicinity of the ridge structure of the surface emitting laser according to the fifth embodiment. FIG. 6(b) is a cross-sectional view in which the current in the vicinity of the region indicated by the broken line circle in FIG. 6(a) is indicated by arrows.

As shown in FIG. 6A, in the surface emitting laser according to the fifth embodiment, the conductive layer 40 includes a first transparent conductive layer 43 and a second transparent conductive layer 44. A second transparent conductive layer 44 is on the dielectric layer 60 and a first transparent conductive layer 43 is on the second transparent conductive layer 44 . The second transparent conductive layer 44 is in direct contact with the interface between the first layer 310 and the second layer 320. The first transparent conductive layer 43 and the second transparent conductive layer 44 are, for example, ITO layers. The electrical resistance of the second transparent conductive layer 44 is lower than that of the first transparent conductive layer 43. For example, the upper surface of the second transparent conductive layer 44 and the upper surface of the first layer 310 are substantially flush with each other. The first transparent conductive layer 43 is an example of a first conductive layer, and the second transparent conductive layer 44 is an example of a second conductive layer.

When manufacturing the surface emitting laser according to the fifth embodiment, for example, after forming the dielectric layer 60, the resist mask used for forming the ridge structure 350 is left and the second transparent conductive layer is formed next to the dielectric layer 60. 44 is formed, and then the resist mask is removed. At this time, the thickness of the second transparent conductive layer 44 is such that the upper surface of the second transparent conductive layer 44 is substantially flush with the upper surface of the ridge structure 350. After lift-off, the first transparent conductive layer 43 is formed so as to be in contact with the upper surface of the ridge structure 350.

Other configurations are similar to the fourth embodiment.

The fifth embodiment can also provide the same effects as the fourth embodiment. In addition, while the first transparent conductive layer 43 is made of a material such as ITO, which is difficult to absorb light and is easy to obtain good flatness, the second transparent conductive layer 44 is made of a material that is less likely to absorb light and is easier to obtain good flatness. A material such as ITO that easily absorbs light or has low electrical resistance even if the flatness is low can be used. Therefore, the electrical resistance of the second transparent conductive layer 44 is lower than that of the first transparent conductive layer 43, and as shown in FIG. Current is likely to be injected from the interface between the layer 310 and the second layer 320. Therefore, the electrical resistance of the entire surface emitting laser can be further reduced.

Furthermore, compared to the fourth embodiment, loss due to diffraction can be reduced, and a single mode can be easily obtained with a low threshold.

(Sixth embodiment)
A sixth embodiment will be described. The sixth embodiment relates to a head-up display (HUD), which is an example of a projection device. FIG. 7 is a schematic diagram showing a HUD that is an example of a projection device according to a sixth embodiment. FIG. 8 is a schematic diagram showing a car equipped with a HUD according to the sixth embodiment.

The projection device is a device that projects an image by optical scanning, and is, for example, a HUD.

As shown in FIG. 8, the HUD 500 according to the sixth embodiment is installed near the windshield (windshield 401, etc.) of the automobile 400, for example. Projection light L emitted from the HUD 500 is reflected by the windshield 401 and is directed toward the observer (driver 402) who is the user. Thereby, the driver 402 can visually recognize the image projected by the HUD 500 as a virtual image. Note that a combiner may be installed on the inner wall surface of the windshield, and a configuration may be adopted in which a virtual image is made visible to the user by projected light reflected by the combiner. Car 400 is an example of a moving object.

As shown in FIG. 7, the HUD 500 emits laser light from red, green, and blue laser light sources 501R, 501G, and 501B. After the emitted laser light passes through an input optical system consisting of collimating lenses 502, 503, 504 provided for each laser light source, two dichroic mirrors 505, 506, and a light amount adjustment section 507, It is deflected by a movable device 513 having a reflective surface 514. The deflected laser beam passes through a projection optical system including a free-form mirror 509, an intermediate screen 510, and a projection mirror 511, and is projected onto a screen. In addition, in the above HUD 500, the laser light sources 501R, 501G, 501B, collimating lenses 502, 503, 504, and dichroic mirrors 505, 506 are unitized by an optical housing as a light source unit 530. The laser light sources 501R, 501G, and 501B include surface emitting lasers according to any of the first to fifth embodiments. The laser light sources 501R, 501G, and 501B may include a surface emitting laser array including a plurality of surface emitting lasers according to any of the first to fifth embodiments.

HUD 500 projects an intermediate image displayed on intermediate screen 510 onto windshield 401 of automobile 400, thereby allowing driver 402 to view the intermediate image as a virtual image.

The laser beams of each color emitted from the laser light sources 501R, 501G, and 501B are made into substantially parallel beams by collimating lenses 502, 503, and 504, respectively, and are combined by two dichroic mirrors 505 and 506, which serve as a combining section. The combined laser beams are subjected to two-dimensional scanning by a movable device 513 having a reflective surface 514 after the light intensity is adjusted by a light intensity adjustment unit 507 . The projection light L that has been two-dimensionally scanned by the movable device 513 is reflected by the free-form mirror 509 to correct distortion, and then is focused on the intermediate screen 510 to display an intermediate image. The intermediate screen 510 is composed of a microlens array in which microlenses are two-dimensionally arranged, and magnifies the projected light L incident on the intermediate screen 510 in units of microlenses.

The movable device 513 reciprocates the reflective surface 514 in two axial directions, and scans the projection light L incident on the reflective surface 514 two-dimensionally. The drive control of this movable device 513 is performed in synchronization with the emission timing of the laser light sources 501R, 501G, and 501B.

The light source unit 530 and the movable device 513 are controlled by a control device 515.

The HUD 500 has been described above as an example of a projection device, but the projection device may be any device as long as it projects an image by performing optical scanning with the movable device 513 having a reflective surface 514. For example, a projector that is placed on a desk or the like and projects an image onto a display screen, a projector that is mounted on a mounting member that is attached to the observer's head, etc., that projects the image onto a reflective/transmissive screen that the mounting member has, or a projector that projects an image on the eyeball as a screen. The present invention can be similarly applied to a head-mounted display or the like that projects an image.

In addition, projection devices can be used not only for vehicles and mounting members, but also for mobile objects such as aircraft, ships, and mobile robots, or non-mobile objects such as work robots that operate drive objects such as manipulators without moving from the location. It may be mounted on a moving body.

(Seventh embodiment)
Next, a seventh embodiment will be described. The seventh embodiment relates to a head mount display (HMD). FIG. 9 is a perspective view illustrating the appearance of the HMD according to the seventh embodiment.

An HMD is a head-mounted display that can be mounted on a human head, and can have a shape similar to glasses, for example.

As shown in FIG. 9, the HMD 600 according to the seventh embodiment includes a front 600a and a temple 600b, which are provided substantially symmetrically, one on each side. The front 600a can be configured by, for example, a light guide plate 610, and an optical system, a control device, etc. can be built into the temple 600b.

FIG. 10 is a diagram partially illustrating the configuration of HMD 600. Although FIG. 10 illustrates a configuration for the left eye, the HMD 600 has a similar configuration for the right eye.

The HMD 600 includes a control device 515, a light source unit 530, a light amount adjustment section 507, a movable device 513 having a reflective surface 514, a light guide plate 610, and a half mirror 620.

As described above, the light source unit 530 is a unit made up of the laser light sources 501R, 501G, and 501B, the collimating lenses 502, 503, and 504, and the dichroic mirrors 505 and 506 using an optical housing. In the light source unit 530, the three-color laser beams from the laser light sources 501R, 501G, and 501B are combined by dichroic mirrors 505 and 506, which serve as a combining section. The light source unit 530 emits combined parallel light.

The light from the light source unit 530 enters the movable device 513 after the light amount is adjusted by the light amount adjusting section 507. The movable device 513 moves the reflective surface 514 in the X and Y directions based on a signal from the control device 515, and performs two-dimensional scanning with the light from the light source unit 530. The drive control of this movable device 513 is performed in synchronization with the emission timing of the laser light sources 501R, 501G, and 501B, and a color image is formed by scanning light.

The scanning light from the movable device 513 is incident on the light guide plate 610. The light guide plate 610 guides the scanning light to the half mirror 620 while reflecting the scanning light on the inner wall surface. The light guide plate 610 is made of resin or the like that is transparent to the wavelength of the scanning light.

The half mirror 620 reflects the light from the light guide plate 610 toward the back side of the HMD 600 and emits it toward the eyes of the wearer 630 of the HMD 600. The half mirror 620 has, for example, a free-form surface shape. The image created by the scanning light is reflected by the half mirror 620 and forms an image on the retina of the wearer 630. Alternatively, an image is formed on the retina of the wearer 630 due to the reflection by the half mirror 620 and the lens effect of the crystalline lens in the eyeball. Further, due to the reflection by the half mirror 620, the spatial distortion of the image is corrected. The wearer 630 can observe an image formed by light scanned in the XY directions.

Since the half mirror 620 is provided at the front 600a, the wearer 630 observes an image created by light from the outside world and an image created by the scanning light in a superimposed manner. By providing a mirror in place of the half mirror 620, a configuration may be adopted in which light from the outside world is eliminated and only images generated by scanning light can be observed.

(Eighth embodiment)
Next, an eighth embodiment will be described. The eighth embodiment relates to an optometric apparatus. FIG. 11 is a block diagram showing an optometry apparatus according to the eighth embodiment.

The optometric apparatus 800 according to the eighth embodiment is an apparatus that can perform various tests such as a visual acuity test, an eye refractive power test, an intraocular pressure test, and an axial length test. The optometry device 800 is a device that can examine an eyeball 830 without contacting it, and includes a light source unit 810, a control section 821, an input section 822, a storage section 823, and a display section 824. The light source unit 810 includes a light source 811 and a projection optical system 812. During eye examination, the control unit 821 controls the light source 811, and the projection optical system 812 projects the light emitted by the light source 811 onto the eyeball 830 of the subject. In other words, light is emitted from the light source unit 810 to the eyeball 830 of the subject as test information. The input unit 822 is a device through which the subject or operator inputs information used for optometry. Information input to the input section 822 is transmitted to the control section 821. The storage unit 823 stores information output by the control unit 821. The display unit 824 displays information output by the control unit 821. The subject fixes his or her face on a support that supports the subject's face, and gazes at the test information projected by the projection optical system 812 through the optometry window. The surface emitting laser according to any of the first to fifth embodiments can be used as the light source 811 of the light source unit 810 for projecting inspection information. A surface emitting laser array including a plurality of surface emitting lasers according to any of the first to fifth embodiments may be used as the light source 811 for projecting inspection information. Furthermore, the optometry device may be in the form of a glass. The glass-shaped optometry device eliminates the need for space and large-sized optometry equipment required for testing, and enables testing regardless of location with a simple configuration.

Although the preferred embodiments have been described in detail above, they are not limited to the embodiments described above, and various modifications may be made to the embodiments described above without departing from the scope of the claims. Variations and substitutions can be made.

Aspects of the present disclosure are, for example, as follows.
<1>
a first reflecting mirror;
a second reflecting mirror;
a resonator including an active layer provided between the first reflecting mirror and the second reflecting mirror;
a conductive layer for injecting current into the resonator;
has
comprising a semiconductor stacked structure including the resonator,
The semiconductor stacked structure is
a first layer including a first p-type semiconductor layer;
a second layer provided between the first layer and the active layer and including a second p-type semiconductor layer;
has
The second p-type semiconductor layer is in contact with the first layer and has a bandgap larger than the bandgap of the first p-type semiconductor layer,
A surface emitting laser characterized in that a part or all of the upper surface of the first layer and an interface between the first layer and the second layer are in contact with the conductive layer.
<2>
The first layer further includes an undoped semiconductor layer having a bandgap less than or equal to the bandgap of the first p-type semiconductor layer,
The surface emitting laser according to <1> above, wherein the undoped semiconductor layer is in contact with the second layer.
<3>
The laminate of the first layer and the second layer has a ridge structure,
As described in <1> or <2> above, the outer periphery of the first layer is located inside the outer periphery of the active layer when viewed in plan from a direction perpendicular to the upper surface of the first layer. surface emitting laser.
<4>
The surface emitting laser according to <3>, further comprising an insulating region that electrically insulates a portion of the laminate located outside the ridge structure in plan view from the conductive layer.
<5>
The ridge structure has, in the thickness direction,
All of the first layer;
Part or all of the second p-type semiconductor layer,
including;
The surface emitting laser according to <4>, wherein the insulating region has a dielectric layer whose upper surface is closer to the active layer than the interface between the first layer and the second layer.
<6>
The ridge structure includes the entire first layer in the thickness direction,
The insulating region is characterized in that its upper surface is closer to the active layer than the interface between the first layer and the second layer, and includes an inactive semiconductor layer containing an impurity element that inactivates acceptors. The surface emitting laser according to <4> above.
<7>
The conductive layer is
a first conductive layer that is in contact with the upper surface of the first layer and transmits at least a portion of the emitted light;
a second conductive layer in contact with an interface between the first layer and the second layer;
including;
The surface emitting laser according to any one of <1> to <6>, wherein the electrical resistance of the second conductive layer is lower than the electrical resistance of the first conductive layer.
<8>
The surface emitting laser according to <7>, wherein the second conductive layer is a metal layer.
<9>
The first p-type semiconductor layer is an In _a Ga _1-a N layer (0≦a<1),
The surface emitting laser according to any one of <1> to <8>, wherein the second p-type semiconductor layer is an Al _b Ga _1-b N layer (0<b<1).
<10>
The surface emitting laser according to any one of <1> to <9> above,
an optical deflection device that deflects the light emitted by the surface emitting laser;
Equipped with
A projection device that deflects and projects the light.
<11>
A head-up display comprising the surface emitting laser according to any one of <1> to <9>.
<12>
A mobile object comprising the head-up display according to <11>.
<13>
A head-mounted display comprising the surface emitting laser according to any one of <1> to <9>.
<14>
An optometry device comprising the surface emitting laser according to any one of <1> to <9>.

1 Surface-emitting laser 20 Resonator 40 Conductive layer 41 Transparent conductive layer 42 Metal layer 43 First transparent conductive layer 44 Second transparent conductive layer 310 First layer 311 First p-type semiconductor layer 312 Undoped semiconductor layer 320 Second layer 321 inactive semiconductor layer 330 third layer

Japanese Journal of Applied Physics 59, SGGE08 (2020)

Claims (14)

a first reflecting mirror;
a second reflecting mirror;
a resonator including an active layer provided between the first reflecting mirror and the second reflecting mirror;
a conductive layer for injecting current into the resonator;
has
comprising a semiconductor stacked structure including the resonator,
The semiconductor stacked structure is
a first layer including a first p-type semiconductor layer;
a second layer provided between the first layer and the active layer and including a second p-type semiconductor layer;
has
The second p-type semiconductor layer is in contact with the first layer and has a bandgap larger than the bandgap of the first p-type semiconductor layer,
A surface emitting laser characterized in that a part or all of the upper surface of the first layer and an interface between the first layer and the second layer are in contact with the conductive layer. The first layer further includes an undoped semiconductor layer having a bandgap less than or equal to the bandgap of the first p-type semiconductor layer,
The surface emitting laser according to claim 1, wherein the undoped semiconductor layer is in contact with the second layer. The laminate of the first layer and the second layer has a ridge structure,
The surface emitting device according to claim 1 or 2, wherein the outer periphery of the first layer is located inside the outer periphery of the active layer when viewed in plan from a direction perpendicular to the upper surface of the first layer. laser. 4. The surface emitting laser according to claim 3, further comprising an insulating region that electrically insulates a portion of the laminate located outside the ridge structure in plan view from the conductive layer. The ridge structure has, in the thickness direction,
All of the first layer;
Part or all of the second p-type semiconductor layer,
including;
5. The surface emitting laser according to claim 4, wherein the insulating region includes a dielectric layer whose upper surface is closer to the active layer than the interface between the first layer and the second layer. The ridge structure includes the entire first layer in the thickness direction,
The insulating region is characterized in that its upper surface is closer to the active layer than the interface between the first layer and the second layer, and includes an inactive semiconductor layer containing an impurity element that inactivates acceptors. The surface emitting laser according to claim 4. The conductive layer is
a first conductive layer that is in contact with the upper surface of the first layer and transmits at least a portion of the emitted light;
a second conductive layer in contact with an interface between the first layer and the second layer;
including;
3. The surface emitting laser according to claim 1, wherein the electrical resistance of the second conductive layer is lower than the electrical resistance of the first conductive layer. 8. The surface emitting laser according to claim 7, wherein the second conductive layer is a metal layer. The first p-type semiconductor layer is an In _a Ga _1-a N layer (0≦a<1),
3. The surface emitting laser according to claim 1, wherein the second p-type semiconductor layer is an Al _b Ga _1-b N layer (0<b<1). The surface emitting laser according to claim 1 or 2,
an optical deflection device that deflects the light emitted by the surface emitting laser;
Equipped with
A projection device that deflects and projects the light. A head-up display comprising the surface emitting laser according to claim 1 or 2. A mobile object comprising the head-up display according to claim 11. A head mounted display comprising the surface emitting laser according to claim 1 or 2. An optometric apparatus comprising the surface emitting laser according to claim 1 or 2.

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