JP7527093B2 - Surface emitting laser array, detection device and laser device - Google Patents

Description

The present invention relates to a surface-emitting laser array, a detection device, and a laser device.

A surface-emitting laser array in which multiple surface-emitting laser elements (VCSEL: Vertical Cavity Surface Emitting Laser) are arranged in a plane is used as the laser light source.

Conventionally, a semiconductor light-emitting device (VCSEL array) has been proposed in which a laminate including an active layer is formed on a semiconductor substrate, and a light-emitting window is formed on the back surface of the substrate (see, for example, Patent Document 1).

However, with conventional semiconductor light-emitting devices, it was difficult to control the radiation angle of the laser light emitted from the surface-emitting laser.

The present invention has been made in consideration of the above, and aims to control the radiation angle of laser light emitted from a surface-emitting laser.

In order to solve the above-mentioned problems and achieve the object, the present invention provides a surface-emitting laser array including: a plurality of surface-emitting laser elements provided on a first surface of a substrate made of a semiconductor , and emitting light in a direction intersecting the first surface; a plurality of optical elements arranged on a second surface opposite to the first surface of the substrate corresponding to each of the plurality of surface-emitting laser elements, and changing the radiation angle of the light emitted from each of the plurality of surface-emitting laser elements and transmitted through the substrate; and a light-shielding member provided on the second surface side of the substrate , and continuously shading a region between two adjacent optical elements among the plurality of optical elements and each peripheral portion of the two adjacent optical elements.

The present invention has the effect of being able to control the radiation angle of the laser light emitted from the surface-emitting laser.

FIG. 1 is a partial side cross-sectional view showing an example of the configuration of a surface-emitting laser array according to a first embodiment. FIG. 2 is a partial bottom view showing an example of the configuration of the surface emitting laser array according to the first embodiment. 3A to 3C are cross-sectional views that diagrammatically show an example of a procedure for the method of forming the light blocking member 42 according to the first embodiment. FIG. 4 is a partial cross-sectional view showing another example of the configuration of the surface-emitting laser array according to the first embodiment. FIG. 5 is a partial cross-sectional view showing an example of the configuration of a surface-emitting laser array according to a comparative example. FIG. 6 is a partial bottom view showing an example of the configuration of the surface emitting laser array according to the second embodiment. FIG. 7 is a partial side cross-sectional view showing an example of the configuration of a surface-emitting laser array according to the third embodiment. FIG. 8 is a partial bottom view showing an example of the configuration of the surface emitting laser array according to the third embodiment. FIG. 9 is a diagram showing the intensity distribution of light that has passed through a microlens when no light blocking member is provided. FIG. 10 is a diagram showing the intensity distribution of light that has passed through a microlens when a light blocking member is provided only in the residual portion. FIG. 11 is a diagram showing the intensity distribution of light that has passed through a microlens when a light blocking member is provided in the residual portion and the peripheral edge portion of the lens. FIG. 12 is a cross-sectional view showing an example of the configuration of a microlens portion of a surface-emitting laser array according to the fourth embodiment. FIG. 13 is a schematic diagram showing an example of the configuration of a LiDAR device according to the fifth embodiment. FIG. 14 is a schematic diagram showing an example of the configuration of a laser device according to the sixth embodiment.

The following describes in detail the embodiments of the surface-emitting laser array, the detection device, and the laser device with reference to the attached drawings. Note that the present invention is not limited to these embodiments.

First Embodiment
FIG. 1 is a partial side cross-sectional view showing an example of the configuration of a surface-emitting laser array according to a first embodiment, and FIG. 2 is a partial bottom view showing an example of the configuration of the surface-emitting laser array according to the first embodiment.

The surface-emitting laser array 1 includes a plurality of surface-emitting laser elements (hereinafter referred to as light-emitting elements) 20 arranged on the first surface 10a of the semiconductor substrate 10, a plurality of microlenses 41 provided on the second surface 10b, a light-shielding member 42 provided on the second surface 10b, and a surface electrode 51. In the example of FIG. 1, an n-type semiconductor substrate 10 is used. In addition, the semiconductor substrate 10 is made of a material that is transparent to the laser light emitted by the light-emitting elements 20.

The light-emitting element 20 is an element that emits laser light in a direction intersecting (generally perpendicular to) the first surface 10a. The light-emitting element 20 includes a lower reflective layer 21, a resonator-forming layer 22, an upper reflective layer 23, a current confinement layer 24, and a protective film 26.

The lower reflective layer 21 is disposed on the semiconductor substrate 10 and is composed of a semiconductor multilayer reflective film in which a high refractive index n-type semiconductor film having an optical film thickness of λ/4 (where λ is one wavelength of the laser light emitted from the light emitting element 20) and a low refractive index n-type semiconductor film having an optical film thickness of λ/4 are alternately stacked.

The resonator-forming layer 22 is disposed between the lower reflective layer 21 and the upper reflective layer 23, and is a layer that constitutes an optical resonator. The resonator-forming layer 22 has a structure in which an active layer is sandwiched between a lower spacer layer and an upper spacer layer, for example. The lower spacer layer and the upper spacer layer are made of, for example, non-doped semiconductor layers. The active layer is made of a semiconductor material selected according to the wavelength of the emitted laser light. The thickness of the resonator-forming layer 22 in a direction perpendicular to the first surface 10a of the semiconductor substrate 10 is set to, for example, one wavelength (= λ) of the laser light emitted from the light-emitting element 20. In addition, the wavelength of the laser light emitted from the resonator-forming layer 22 is selected to be a wavelength that is not absorbed by the semiconductor substrate 10.

The upper reflective layer 23 is disposed on the resonator-forming layer 22 and is composed of a semiconductor multilayer reflective film in which a high-refractive index p-type semiconductor film having an optical thickness of λ/4 and a low-refractive index p-type semiconductor film having an optical thickness of λ/4 are alternately laminated.

The current confinement layer 24 is a layer provided in the upper reflective layer 23 to reduce the area through which current passes. The current confinement layer 24 has a current confinement region 241 provided in a predetermined area including the center of the formation position of the light emitting element 20, and an oxidation region 242 provided around the current confinement region 241. By narrowing the area through which current passes with the current confinement layer 24, the oscillation threshold of the laser can be reduced. The current confinement region 241 is made of the same material as the semiconductor film that constitutes the upper reflective layer 23, and the oxidation region 242 is made of the same material as the semiconductor film that constitutes the current confinement region 241, which is obtained by oxidizing the same semiconductor film.

The upper reflective layer 23 and the current confinement layer 24 are processed into a mesa shape on the resonator-forming layer 22. That is, the upper reflective layer 23 and the current confinement layer 24 have a structure in which they are separated between adjacent light-emitting elements 20. Hereinafter, the upper reflective layer 23 and the current confinement layer 24 processed into a mesa shape are referred to as a mesa structure 25. In the first embodiment, the mesa structure 25 is provided on the first surface 10a of the semiconductor substrate 10 so as to be located at the lattice points of a square lattice (hereinafter referred to as a square lattice shape).

The protective film 26 is provided so as to cover the side surface of the mesa structure 25 and the top of the resonator layer 22. In other words, the protective film 26 is provided on the resonator layer 22 on which the mesa structure 25 is provided so that the top surface of the mesa structure 25 is exposed.

The microlens 41 is provided on the second surface 10b of the semiconductor substrate 10 in correspondence with the arrangement position of the light-emitting element 20. Since the light-emitting element 20 (mesa structure 25) is provided in a square lattice pattern, the microlenses 41 are also arranged in a square lattice pattern as shown in FIG. 2. The microlens 41 is an optical element that reduces the radiation angle of the laser light emitted from the corresponding light-emitting element 20. By reducing the radiation angle of the laser light, the spot diameter can be reduced when the laser light passing through the microlens 41 is focused on an object through a focusing lens or the like. The microlens 41 is obtained, for example, by processing the area corresponding to the arrangement position of the light-emitting element 20 on the second surface 10b side of the semiconductor substrate 10 into a convex lens. Note that the radiation angle here refers to the angle at which the laser light has an intensity of 10% of the maximum intensity.

Here, when trying to control the radiation angle of the laser light emitted from the surface-emitting laser using a lens, it is desirable to use a lens with a long focal length. For example, it is desirable to provide a certain optical length (up to several hundred μm) between the light-emitting unit and the lens. However, if the optical length between the light-emitting unit and the lens is long, the beam diameter of the laser light will expand before it reaches the lens unit. As a result, the beam diameter when it reaches the lens unit will be larger than the lens diameter, and light may enter the residual portion between the lenses, generating stray light. Therefore, in this embodiment, a light-shielding member 42 is placed in the residual portion to suppress stray light.

2, the light shielding member 42 covers the spaces between the microlenses 41 on the second surface 10b of the semiconductor substrate 10, and has the function of reflecting or absorbing the light emitted from the light emitting element 20. As a result, as shown in FIG. 1, the laser light B that reaches the outer periphery of the microlens 41 among the laser light emitted from the light emitting element 20 is not emitted from the second surface 10b of the semiconductor substrate 10. In addition, the light shielding member 42 makes it difficult for the laser light from the light emitting element 20 corresponding to the adjacent microlens 41 to reach the microlens 41, and stray light can be significantly reduced. As the light shielding member 42, a metal film that reflects laser light, a semiconductor multilayer reflective film, or a semiconductor film that has a smaller band gap than the laser light emitted from the light emitting element 20 and absorbs laser light can be used. The semiconductor multilayer reflective film and the semiconductor film are formed, for example, by epitaxial growth on the second surface 10b side of the semiconductor substrate 10. Note that the light shielding member 42 is not limited to these, and may be, for example, a material that can be applied by spin coating. Also, here, the light blocking member 42 is shown as being film-like, but it does not have to be film-like and may be bulk-like.

Here, we will explain the desirable lens diameter (lens diameter) φ of the microlenses 41. When forming the microlenses 41 by dry etching the semiconductor substrate 10 using a lens-shaped photoresist as a mask, the lens diameter φ of the microlenses 41 must be smaller than the pitch X of the light-emitting elements 20 to prevent interference between the photoresists. In other words, there is a gap of X-φ between adjacent microlenses 41. This gap is called a residual. By coating this residual with a light-shielding member 42 that prevents the transmission of laser light, stray light can be prevented and the laser light can be focused to a small beam spot diameter.

The surface electrode 51 is provided on the protective film 26 of the light-emitting element 20. Since the protective film 26 is not provided on the upper part of the mesa structure 25, the surface electrode 51 is in electrical contact with the upper reflective layer 23. In addition, a back electrode is provided on the second surface 10b side of the semiconductor substrate 10. The surface electrode 51 and the back electrode are provided to pass a current through the active layer of the light-emitting element 20. If the light-shielding member 42 is made of a conductive material, the light-shielding member 42 can also serve as the back electrode.

A GaAs substrate can be used as the semiconductor substrate 10, and InGaAs can be used as the active layer. When InGaAs is used as the active layer, the peak wavelength of the oscillation wavelength of the light-emitting element 20 is approximately 860 to 1200 nm. In addition, the wavelength band around 940 nm included in this wavelength band is one of the wavelength bands absorbed by the Earth's atmosphere, and it is possible to configure a low-noise system when applied to a distance measuring device using laser light. Similarly, the 940 nm band is a wavelength band with a large absorption coefficient of Yb:YAG (Yttrium Aluminum Garnet) solid-state laser, and high-efficiency excitation of the Yb:YAG solid-state laser is possible. InGaAs is a material that has compressive strain relative to GaAs, and when used as the active layer of a semiconductor laser, it has a high differential gain. Therefore, low-threshold oscillation is possible, and a highly efficient surface-emitting laser array 1 can be provided.

Alternatively, an InP substrate may be used as the semiconductor substrate 10, and InGaAs may be used as the active layer. In this case, the peak wavelength of the oscillation wavelength of the light-emitting element 20 is 1.3 to 1.6 μm.

The lower reflective layer 21 and the upper reflective layer 23 may be formed by stacking a plurality of pairs of AlAs and AlGaAs films. The current narrowing layer 24 may be formed by stacking an AlAs film or an AlGaAs film, which is a material for forming the upper reflective layer 23. Although the lower reflective layer 21 and the upper reflective layer 23 are formed by stacking a plurality of low-refractive index dielectric films and a plurality of high-refractive index dielectric films, a semiconductor multilayer reflective film may be used. As such a dielectric multilayer film, for example, a film formed by stacking a plurality of tantalum pentoxide and silicon dioxide (Ta ₂ O ₅ /SiO ₂ ) alternately may be used. However, in this case, since it is not possible to pass a current through the lower reflective layer 21 and the upper reflective layer 23, it is necessary to form an electrode in an intra-cavity structure.

AlGaInP, GaInP, AlGaAs, or the like can be used as the lower spacer layer and the upper spacer layer in the resonator layer 22. InGaAsP may also be used as the active layer.

For example, a multilayer film of Cr/AuZn/Au or Ti/Pt/Au can be used as the surface electrode 51 from the first surface 10a side. When these materials are used as the surface electrode 51, high reliability can be obtained because the outermost surface is Au, which is chemically stable. In addition, a metal capable of ohmic contact can be used as the material for the back electrode. For example, a multilayer film of AuGe/Ni/Au can be used as the back electrode from the second surface 10b side.

A metal material such as Au can be used as the light-shielding member 42. When a metal material such as Au is used as the light-shielding member 42, the light-shielding member 42 can also serve as the back electrode.

In the above description, an n-type semiconductor substrate 10 is used, but a p-type semiconductor substrate 10 may also be used. In this case, the current confinement layer 24 is provided on the lower reflective layer 21 side. In this case, the front electrode 51 may be a multilayer film of AuGe/Ni/Au from the first surface 10a side. In addition, the back electrode may be a multilayer film of Cr/AuZn/Au or Ti/Pt/Au from the second surface 10b side.

Next, a method for manufacturing the surface-emitting laser array 1 having such a structure will be described. Since the light-emitting element 20 can be manufactured using known techniques, an outline will be given and the process for forming the light-shielding member 42 will be described with reference to the drawings. FIG. 3 is a cross-sectional view showing a schematic example of the steps of the method for forming the light-shielding member 42 according to the first embodiment. FIG. 3 shows a case where the second surface 10b of the semiconductor substrate 10 is arranged facing upward.

First, a semiconductor layer including a lower reflective layer 21, a resonator-forming layer 22 including an active layer, and an upper reflective layer 23 is laminated and formed on the first surface 10a of the semiconductor substrate 10. The semiconductor layer can be formed by, for example, MOCVD (Metal Organic Chemical Vapor Deposition) or MBE (Molecular Beam Epitaxy).

Next, a photoresist is applied onto the upper reflective layer 23, and a resist pattern is formed in the area where the mesa structure 25 is to be formed by performing exposure and development processes using lithography. After this, the resist pattern is used as a mask to perform etching using dry etching techniques such as RIE (Reactive Ion Etching) until the resonator-forming layer 22 is exposed, thereby forming the mesa structure 25. The shape of the upper surface of the mesa structure 25 may be, for example, a circle, an ellipse, a square, a rectangle, or other shape. The mesa structure 25 is also formed so as to be arranged in a square lattice on the first surface 10a.

Then, the semiconductor film that becomes the current confinement layer 24 exposed on the side surface of the mesa structure 25 is oxidized, for example, by high-temperature treatment in a water vapor atmosphere, to form an oxidized region 242 on the periphery of the semiconductor film. The region of the semiconductor film that constitutes the current confinement layer 24 that is not oxidized becomes the current confinement region 241. In this way, the current confinement layer 24 is formed.

When InGaAs is used for the active layer, since InGaAs is a material that does not contain chemically active Al, the oxygen present in trace amounts in the reaction chamber for crystal growth is less likely to be incorporated into the active layer. This makes it possible to provide a highly reliable surface-emitting laser array 1.

Next, a protective film 26 is formed on the entire surface of the resonator-forming layer 22 having the mesa structure 25. For example, a plasma CVD method or the like can be used as a method for forming the protective film 26. After that, a photoresist is applied onto the protective film 26 by a method such as a spin coating method, and a resist pattern with an opening on the upper surface of the mesa structure 25 is formed by performing an exposure process and a development process using a lithography technique. Next, the protective film 26 formed on the upper surface of the mesa structure 25 is removed by an anisotropic etching technique such as an RIE method using the resist pattern as a mask. As a result, the protective film 26 has an opening on the upper surface of the mesa structure 25. After removing the resist pattern, a surface electrode 51 is formed on the protective film 26. As a result, the surface electrode 51 is electrically connected to the upper reflective layer 23.

After that, a photoresist is applied to the second surface 10b of the semiconductor substrate 10, and a lens-shaped resist pattern is formed at the position where the microlens 41 is to be formed by performing an exposure process using, for example, gray-tone mask lithography technology and a development process. Then, using this resist pattern as a mask, etching is performed using a dry etching technique such as an RIE method, thereby forming the microlens 41 on the second surface 10b of the semiconductor substrate 10. The microlenses 41 are formed in a square lattice shape corresponding to the light-emitting elements 20 formed on the first surface 10a.

However, the method of forming the microlens 41 is not limited to this. For example, a semiconductor film is epitaxially grown on the second surface 10b of the semiconductor substrate 10, a resist is applied to this semiconductor film, and the resist is patterned so that it remains in the position where the microlens 41 is to be formed. The resist is then reflowed to form a resist pattern that is deformed into a convex lens shape. Then, using this resist pattern as a mask, the epitaxially grown semiconductor film is etched by a dry etching technique such as the RIE method, thereby forming a semiconductor film in the shape of a microlens 41.

The microlens 41 can also be formed by dropping a solution of a precursor of a light-transmitting curable resin onto the position where the microlens 41 is to be formed on the second surface 10b of the semiconductor substrate 10 and curing the precursor. Furthermore, the microlens 41 may be formed by a method other than the above.

After that, as shown in FIG. 3(a), a resist is applied onto the second surface 10b of the semiconductor substrate 10 on which the microlens 41 is formed, and a lift-off resist pattern 71 is formed on the microlens 41 by performing an exposure process and a development process using lithography technology.

Next, as shown in FIG. 3(b), a light-shielding member 42 is formed on the second surface 10b on which the resist pattern 71 has been formed. The light-shielding member 42 is formed by a method such as vacuum deposition or sputtering depending on the type of light-shielding member 42. The light-shielding member 42 is formed on the second surface 10b and the resist pattern 71. Then, as shown in FIG. 3(c), the resist pattern 71 is lifted off to remove unnecessary portions, so that the light-shielding member 42 remains in the area other than the microlenses 41. In this manner, the surface-emitting laser array 1 shown in FIG. 2 is obtained.

In addition, by using a metal material such as Au as the light-shielding member 42, the light-shielding member 42 can have the function of a back electrode. This allows the light-shielding member 42 and the back electrode to be formed simultaneously, simplifying the manufacturing process. The back electrode in this case can be formed in the same manner as in FIG. 3 above.

The configuration of the surface-emitting laser is not limited to that shown in FIG. 1. FIG. 4 is a partial cross-sectional view showing another example of the configuration of the surface-emitting laser array according to the first embodiment. In FIG. 4, the configuration is drawn upside down compared to FIG. 1, and the surface electrode 51 is configured to be connected to a heat sink 55 via a bonding material 56. An electrode may be used instead of the bonding material 56. Note that the same components as those in FIG. 1 are denoted by the same reference numerals and their description will be omitted.

This configuration reduces the distance between the active layer, which is where heat is primarily generated during operation, and the heat sink 55, improving heat dissipation and enabling the surface-emitting laser array 1 to be made more efficient.

Next, the effects of the first embodiment compared to a comparative example in which no light-shielding member 42 is provided on the second surface 10b of the semiconductor substrate 10 will be described. FIG. 5 is a partial cross-sectional view showing an example of the configuration of a surface-emitting laser array according to the comparative example. Note that the same components as those in FIG. 1 are given the same reference numerals and their description will be omitted. That is, in the surface-emitting laser array 1C of the comparative example, no light-shielding member 42 is provided in areas other than the positions where the microlenses 41 are formed on the second surface 10b of the semiconductor substrate 10.

The laser light emitted from the light-emitting region 221 in the resonator-forming layer 22 of each light-emitting element 20 passes through the semiconductor substrate 10 and is emitted to the outside from the microlens 41. At this time, the laser light A that passes through the inside of the microlens 41 is directly incident on the focusing lens. However, the laser light B that is emitted from outside the microlens 41, i.e., from the residual between the microlenses 41 on the second surface 10b, becomes stray light. This stray light causes a problem in that the spot diameter becomes large when the light is focused through a focusing lens, etc.

In the first embodiment, of the laser light oscillated from the light-emitting region 221 in the resonator-forming layer 22 of each light-emitting element 20, the laser light A that passes through the inside of the microlens 41 enters the condenser lens as it is, as in the comparative example. On the other hand, the laser light B that reaches the residual outside the microlens 41 is reflected or absorbed by the light-shielding member 42. In addition, unintended laser light that enters the microlens 41 from other light-emitting regions 221 is also reflected or absorbed by the light-shielding member 42. As a result, the stray light emitted from the residual portion to the outside of the surface-emitting laser array 1 can be significantly reduced. By being able to significantly reduce stray light, the radiation angle of the laser light emitted from the surface-emitting laser can be controlled, and the radiation angle when the laser light emitted from the light-emitting region 221 passes through the microlens 41 can be kept small. Therefore, it is possible to reduce the size of the object such as a reflecting mirror for scanning the laser light, and the effect of being able to miniaturize the device compared to the comparative example is obtained.

In addition, the microlenses 41 are formed on the second surface 10b of the semiconductor substrate 10 by etching the semiconductor substrate 10 or by hardening a resin that is transparent to laser light. Therefore, there is no need to fabricate and mount the microlenses 41 from quartz or glass, etc., which reduces the number of parts and the manufacturing process, and also has the effect of allowing the surface-emitting laser array 1 to be manufactured at low cost.

Second Embodiment
Fig. 6 is a partial bottom view showing an example of the configuration of the surface-emitting laser array according to the second embodiment. Fig. 6 is a view of the surface-emitting laser array 1 as viewed from the second surface 10b side of the semiconductor substrate 10. In the first embodiment, the microlenses 41 are also arranged in a square lattice shape in accordance with the arrangement positions of the light-emitting elements 20, but in the second embodiment, the light-emitting elements 20 and the microlenses 41 are provided so as to be located at each corner and the center of a regular hexagon. The other configurations are the same as those in the first embodiment, so a description thereof will be omitted.

In the second embodiment, the light-emitting elements 20 and the microlenses 41 are arranged so as to be positioned at each corner and the center of a regular hexagon, so that the light-emitting elements 20 can be arranged most densely when arranged at equal intervals. As a result, when obtaining the same laser light output, the chip size can be reduced compared to the arrangement as shown in FIG. 2 of the first embodiment.

Third Embodiment
Fig. 7 is a partial side cross-sectional view showing an example of the configuration of a surface-emitting laser array according to the third embodiment, and Fig. 8 is a partial bottom view showing an example of the configuration of a surface-emitting laser array according to the third embodiment. In the surface-emitting laser array 1 according to the third embodiment, a light-shielding member 42 provided on the second surface 10b side of the semiconductor substrate 10 is configured to cover not only the residual portion but also a peripheral portion within a predetermined range from the outer edge of the microlens 41. Note that the same components as those in the first embodiment are given the same reference numerals and their description will be omitted.

As described above, in order to reduce the radiation angle (divergence angle) of the laser light emitted from the light-emitting element 20, the semiconductor substrate 10 must be thickened and the light must be focused by a microlens 41 with a large focal length. However, if the semiconductor substrate 10 is thickened, the laser light from a certain light-emitting element will diverge due to the laser light in the semiconductor substrate 10, causing the laser light from the certain light-emitting element to enter the microlens 41 corresponding to the adjacent light-emitting element, particularly its peripheral portion, resulting in stray light. Therefore, as in the third embodiment, by providing a light-shielding member 42 to cover the outer edge of the microlens 41 and its peripheral portion, it is possible to reduce the radiation angle of the emitted laser light while suppressing stray light due to the laser light B from the adjacent light-emitting element 20, and to further reduce the diameter of the focused spot.

In addition, with typical microlens formation methods, it is difficult to form the peripheral portion of the microlens 41 in the desired shape. As a result, the curvature of the peripheral portion of the microlens 41 may differ from the curvature of the central portion of the microlens 41. When using such a microlens array, light that is incident on a portion of the peripheral portion that does not have the desired curvature may become stray light, even if that light is emitted from a light-emitting portion corresponding to the lens.

In this embodiment, the light-shielding member 42 is configured to cover not only the residual portion but also the peripheral portion of the microlens 41, making it possible to suppress stray light that may be generated by the laser light emitted from the light-emitting portion corresponding to the lens.

Here, we will explain the desired range of the peripheral portion of the microlens 41 that is covered by the light-shielding member 42. As mentioned above, it is generally difficult to manufacture a microlens array with a peripheral portion having a desired curvature. The size of the portion of the peripheral portion that is outside the effective range can be up to 10% of the lens diameter φ (5% from the outer periphery of the lens), depending on the manufacturing method.

On the other hand, if the light-shielding member 42 is provided within the effective range of the lens, it will block the laser light that would otherwise be shaped into the desired beam, thereby reducing the output from the surface-emitting laser. Therefore, it is desirable to select the range in which the light-shielding member 42 is provided on the periphery of the microlens 41 appropriately according to the profile, within the range of 0 to φ/20 from the outer periphery of the lens.

As shown in FIG. 8, the coverage width h of the light blocking member 42 from the outer edge of the microlens 41 is in the range of 0≦2h≦φ/10. In this way, the light blocking member 42 is provided in the residual portion between the microlenses 41 and in the peripheral portion of the microlens 41 with a coverage width h that satisfies 0≦2h≦φ/10 from the outer edge of the microlens 41.

Next, the desirable thickness of the semiconductor substrate 10 will be described. As described above, if the thickness of the semiconductor substrate 10 is increased, the emitted laser light can be condensed into a smaller beam spot diameter. However, the beam diameter inside the semiconductor substrate 10 becomes large, and the laser light enters the adjacent microlens 41, generating stray light. The beam diameter D when the laser light emitted from the light emitting element 20 enters the microlens 41 arranged on the semiconductor substrate 10 is expressed by the following formula (1), where a is the size of the light emitting region 221 of the light emitting element 20 (the largest opening length of the current confinement region 241), θ is the radiation angle of the laser light in the semiconductor substrate 10, and t is the distance from the light emitting portion to the lens exit surface. However, since the lens height is minute compared to the substrate thickness, t is considered to be the same over the entire exit surface.

It is undesirable that the light from the light emitting element 20 passes over the light shielding member of the microlens 41 (41-2) adjacent to the microlens 41 (41-1) and enters the adjacent microlens 41 (41-2). Therefore, it is preferable that the following formula (2) is satisfied so that the beam diameter D of the beam incident on the microlens 41 is "the pitch X of the microlenses 41 + the width 2h of the light shielding member + the residual X - the lens diameter φ".

From formulas (1) and (2), the thickness t of the semiconductor substrate 10 becomes a value that satisfies the following formula (3) with respect to the inter-element pitch X and the width 2h of the light blocking member.

In particular, when 10% of the lens diameter φ is covered by the light blocking member, 2h=φ/10, and therefore, formula (3) becomes the following formula (4).

The method of forming the light shielding member 42 in such a surface-emitting laser array 1 may be achieved by reducing the size of the resist pattern 71 formed on the microlens 41 in the substrate in-plane direction compared to the first embodiment in FIG. 3(a). For example, the size of the resist pattern 71 is set to 90% of the lens diameter φ of the microlens 41. As a result, when the light shielding member 42 is formed on the second surface of the semiconductor substrate 10 in FIG. 3(b), an area of the periphery of the microlens 41 that is 10% or less of the lens diameter φ can be covered with the light shielding member 42.

Next, the results of a simulation performed on the surface-emitting laser of this embodiment will be described. The configuration of the surface-emitting laser that was the subject of the simulation is as follows: the size a of the light-emitting region 221 of the light-emitting element 20 is 10 μm, the radiation angle θ of the laser light in the semiconductor substrate 10 is 6 degrees, the semiconductor layer (mainly the lower DBR) from the light-emitting portion to the substrate is 2.8 μm, the substrate thickness is 300 μm, the pitch of the light-emitting element and the lens is 30 μm, the lens diameter is 28 μm, and the residual difference between the lenses is 2 μm.

Figure 9 shows the intensity distribution of light passing through a microlens in the above-mentioned surface-emitting laser when the light-shielding member 42 is not provided. In addition to the light (A) emitted from the lens corresponding to the light-emitting element, light (B) emitted from the residual portion between the lenses and light (C) emitted from an adjacent lens were confirmed.

Figure 10 shows the intensity distribution of light passing through a microlens in the above-mentioned surface-emitting laser in which the light-shielding member 42 is provided only in the residual portion. Compared to Figure 9, the light (B) emitted from the residual portion between the lenses is suppressed. Meanwhile, the light (C) emitted from the adjacent lens is generated in the same manner as in Figure 9.

Figure 11 shows the intensity distribution of light passing through a microlens in the above-mentioned surface-emitting laser when a light-shielding member 42 is provided in the residual portion and the lens periphery. Note that the area covered by the light-shielding member is set to 10% of the lens diameter. Comparing with Figure 10, it can be seen that the light (C) emitted from the adjacent lens can also be suppressed.

(Fourth embodiment)
12 is a cross-sectional view showing an example of the configuration of the microlens portion of the surface-emitting laser array according to the fourth embodiment. In the fourth embodiment, a transparent conductive material is used for the back electrode 43, and the back electrode 43 is formed on the entire surface of the second surface 10b of the semiconductor substrate 10. As the transparent conductive material, for example, In ₂ O ₃ :Sn, SnO ₂ :F, ZnO:Al, ZnO:Ga, graphene, etc. can be used. The other configurations are the same as those described in the first to third embodiments.

The method for manufacturing a surface-emitting laser array 1 having such a structure involves forming a light-shielding member 42 in the residual portion between the microlenses 41 as in the first embodiment, or in the residual portion and the peripheral portion of the microlenses 41 as in the third embodiment, and then forming a back electrode 43 made of a transparent conductive material on the second surface 10b of the semiconductor substrate 10.

In the fourth embodiment, a transparent conductive material is used for the back electrode 43, so that the back electrode 43 can be formed on the entire surface of the second surface 10b of the semiconductor substrate 10 on which the microlenses 41 and the light blocking member 42 are formed. This allows the back electrode 43 to be in closer contact with the surface of the microlenses 41, which has the effect of lowering the resistance.

Fifth embodiment
In the fifth embodiment, a case will be described in which the surface-emitting laser array 1 described in the first to fourth embodiments is applied to a detection device. Here, as an example of the detection device, a LiDAR (Light Detection and Ranging, or Laser Imaging Detection and Ranging) device 100 that measures the distance to an object and maps the shape by using laser light will be taken.

Figure 13 is a schematic diagram showing an example of the configuration of a LiDAR device according to the fifth embodiment. The LiDAR device 100 is an example of a distance measurement device that optically measures distance. The LiDAR device 100 has a light-projecting unit 110 that projects laser light, a light-receiving unit 120 that receives reflected light Lref from an object 141, and a control and signal processing unit 130 that controls the light-projecting unit 110 and performs distance calculations based on the received reflected light.

The light projection unit 110 has a laser light source 111, a light projection lens 113, and a movable mirror 114 as a scanning unit. The laser light source 111 uses the surface-emitting laser array 1 described in the first to fourth embodiments. The movable mirror 114 scans the laser light incident from the light projection lens 113 into the desired scanning range 140.

The light receiving unit 120 has a focusing optical system 121, an optical filter 122, and a light receiving element 123. The focusing optical system 121 focuses the reflected light Lref from the object 141 and makes it incident on the light receiving element 123 through the optical filter 122. The optical filter 122 is a filter that transmits only wavelengths in a predetermined range near the oscillation wavelength of the laser light source. By cutting wavelengths different from the oscillation wavelength, the S/N (signal-to-noise) ratio of the light incident on the light receiving element 123 is improved. The light receiving element 123 converts the light that has passed through the optical filter 122 into an electrical signal.

The control and signal processing unit 130 has a laser light source driving circuit 131 that drives the laser light source 111, a control circuit 132 that controls the movement (or deflection angle) of the movable mirror 114, and a signal processing circuit 133 that calculates the distance to the target object 141. The laser light source driving circuit 131 controls the emission timing and emission intensity of the laser light source 111.

The operation of the LiDAR device 100 will be described. Light from the laser light source 111 is guided by the light projecting lens 113 to the movable mirror 114, which then irradiates the object 141 present within the scanning range 140 as scanning light Lscan. The reflected light Lref reflected by the object 141 passes through the focusing optical system 121 and the optical filter 122 and is received by the light receiving element 123. The light receiving element 123 outputs a photocurrent according to the amount of incident light as a detection signal. The signal processing circuit 133 performs distance calculations based on the time difference between the light emission timing signal supplied from the laser light source driving circuit 131 and the detection signal, and calculates the distance from the object 141.

In the fifth embodiment, the surface-emitting laser array 1 described in the first to fourth embodiments is used as the laser light source 111, which can focus the laser light emitted from the microlens 41 to a smaller beam spot diameter. Therefore, the optical components that receive the laser light emitted from the laser light source 111 can be made smaller, which has the effect of making it possible to make the detection device itself smaller as well.

Sixth embodiment
In the sixth embodiment, a case will be described in which the surface emitting laser array 1 described in the first to fourth embodiments is applied to a laser device.

Figure 14 is a schematic diagram showing an example of the configuration of a laser device according to the sixth embodiment. The laser device 200 includes a laser light source 201, a first focusing optical system 203, an optical fiber 204, a second focusing optical system 205, a laser resonator 206, and an emission optical system 207. Note that in Figure 14, an XYZ three-dimensional orthogonal coordinate system is used, and the emission direction of light from the laser light source 201 is described as the +Z direction.

The laser light source 201 is an excitation light source and has multiple light-emitting elements. The surface-emitting laser array 1 described in the first to fourth embodiments is used for the laser light source 201. When light is emitted from the laser light source 201, the multiple light-emitting elements emit light simultaneously.

Since the wavelength shift caused by temperature is very small in surface-emitting laser arrays, they are advantageous light sources for exciting Q-switched lasers, whose characteristics change significantly due to wavelength shift. Therefore, using a surface-emitting laser array as an excitation light source has the advantage of making it easier to control the environmental temperature.

The first focusing optical system 203 is a focusing lens that focuses the light emitted from the laser light source 201. The first focusing optical system 203 may be composed of multiple optical elements.

The optical fiber 204 is arranged so that the center of the -Z end face of the core is located at the position where the light is focused by the first focusing optical system 203. By providing the optical fiber 204, the laser light source 201 can be placed at a position away from the laser resonator 206. The light that enters the optical fiber 204 propagates within the core and is emitted from the +Z end face of the core.

The second focusing optical system 205 is a focusing lens that is disposed on the optical path of the light emitted from the optical fiber 204 and focuses the light. Depending on the quality of the light, etc., multiple optical elements may be used as the second focusing optical system 205. The light focused by the second focusing optical system 205 enters the laser resonator 206.

The laser resonator 206 is a Q-switched laser that resonates and amplifies the laser light emitted from the second focusing optical system 205, and has, for example, a solid-state laser medium 206a and a saturable absorber 206b. For example, a Yb:YAG crystal can be used as the solid-state laser medium 206a. For example, a Cr:YAG crystal can be used as the saturable absorber 206b. The laser resonator 206 has the solid-state laser medium 206a and the saturable absorber 206b bonded together.

The light from the second focusing optical system 205 is incident on the solid-state laser medium 206a. That is, the solid-state laser medium 206a is excited by the light from the second focusing optical system 205. The peak wavelength of the light emitted from the laser light source 201 is preferably 910 to 970 nm, which is the wavelength with the highest absorption efficiency in Yb:YAG crystal. The saturable absorber 206b then performs the operation of a Q switch.

The incident side (-Z side) surface 2061 of the solid-state laser medium 206a and the exit side (+Z side) surface 2062 of the saturable absorber 206b are optically polished and function as mirrors. For convenience, the incident side surface 2061 of the solid-state laser medium 206a is also referred to as the "first surface" below, and the exit side surface 2062 of the saturable absorber 206b is also referred to as the "second surface."

The first surface 2061 and the second surface 2062 are coated with a dielectric multilayer film that corresponds to the wavelength of the light emitted from the laser light source 201 and the wavelength of the light emitted from the laser resonator 206.

Specifically, the first surface 2061 is coated with a coating that exhibits sufficiently high transmittance for light with a wavelength of 910 to 970 nm and sufficiently high reflectance for light with a wavelength of 1030 nm. The second surface 2062 is coated with a coating that exhibits a reflectance selected to obtain a desired threshold for light with a wavelength of 1030 nm. This causes the light to resonate and be amplified within the laser resonator 206.

The emission optical system 207 focuses the laser pulse emitted from the laser resonator 206 and emits it to the outside.

Laser devices with this configuration are used, for example, in ignition devices for internal combustion engines, laser processing machines, laser peening devices, terahertz generators, etc.

REFERENCE SIGNS LIST 1 Surface-emitting laser array 10 Semiconductor substrate 10a First surface 10b Second surface 20 Light-emitting element 21 Lower reflective layer 22 Resonator-forming layer 23 Upper reflective layer 24 Current-confining layer 25 Mesa structure 26 Protective film 41 Microlens 42 Light-shielding member 43 Back electrode 51 Surface electrode 221 Light-emitting region 241 Current-confining region 242 Oxidized region

JP 2014-007293 A

Claims (11)

a plurality of surface-emitting laser elements provided on a first surface of a substrate made of a semiconductor and emitting light in a direction intersecting the first surface;
a plurality of optical elements arranged on a second surface of the substrate opposite to the first surface, the optical elements being arranged corresponding to the plurality of surface-emitting laser elements, the optical elements changing a radiation angle of the light emitted from the plurality of surface-emitting laser elements and transmitted through the substrate ;
a light shielding member provided on the second surface side of the substrate, the light shielding member continuously shielding a region between two adjacent optical elements among the plurality of optical elements and a peripheral portion of each of the two adjacent optical elements;
A surface emitting laser array comprising: The surface-emitting laser array according to claim 1, wherein the light-shielding member has openings at positions corresponding to each of the optical elements. The surface-emitting laser array according to claim 1 or 2, wherein the plurality of optical elements include a lens having a curved surface formed on the substrate, or a lens formed on the substrate from a material different from that of the substrate. A surface-emitting laser array according to any one of claims 1 to 3, wherein the area of the optical element covered by the light-shielding member is 10% or less of the diameter of the optical element. A surface-emitting laser array according to any one of claims 1 to 4, in which the light-shielding member also serves as an electrode on the second surface side of the substrate. The surface-emitting laser array according to any one of claims 1 to 4, further comprising an electrode on the second surface side, the electrode being made of a transparent conductive material and provided on the optical element and the light-shielding member on the second surface. the substrate is a GaAs substrate,
7. The surface emitting laser array according to claim 1, wherein the surface emitting laser element includes an active layer made of InGaAs. A surface-emitting laser array according to any one of claims 1 to 7, wherein the peak wavelength of the light emitted by the surface-emitting laser element is in the range of 910 to 970 nm. The surface-emitting laser array according to any one of claims 1 to 8, wherein a thickness t of the substrate satisfies the following formula (1), where θ is the radiation angle of the light in the substrate, X is the pitch between the surface-emitting laser elements, φ is the diameter of the optical element, and a is the size of the light-emitting region of the surface-emitting laser element:
A surface emitting laser array according to any one of claims 1 to 9,
a light receiving unit that receives light emitted from the surface emitting laser element of the surface emitting laser array;
A detection device comprising: A surface emitting laser array according to any one of claims 1 to 9,
a laser resonator including a solid-state laser medium that resonates light emitted from the surface-emitting laser array;
A laser device comprising:

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