Semiconductor laser and method for manufacturing a semiconductor laser

Abstract

To provide a semiconductor laser including photonic crystal and a semiconductor laser manufacturing method.SOLUTION: A semiconductor laser includes: a first semiconductor layer part containing a first conductivity type semiconductor layer; an active layer provided on the first semiconductor layer part; a second semiconductor layer part containing a second conductivity type semiconductor layer provided on the active layer; a third semiconductor layer part containing a semiconductor layer having an impurity of the first conductivity type with a first concentration, provided on the second semiconductor layer part; and a fourth semiconductor layer part containing a semiconductor layer having an impurity of the first conductivity type with a second concentration, provided on the third semiconductor layer part. The first concentration is higher than the second concentration. The third semiconductor layer part is directly bonded to the fourth semiconductor layer part, and at least one of the third semiconductor layer part and the fourth semiconductor layer part contains a photonic crystal.SELECTED DRAWING: Figure 1A

Description

[Technical Field]

[0001] This disclosure relates to semiconductor lasers and methods for manufacturing semiconductor lasers. [Background technology]

[0002] In recent years, there has been a surge in the development of semiconductor light-emitting devices utilizing photonic crystal structures. Such semiconductor light-emitting devices are used in semiconductor lasers and the like. For example, Patent Document 1 discloses a gallium nitride-based semiconductor surface light-emitting device. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2009-54864 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] However, semiconductor lasers and other technologies utilizing photonic crystal structures are still under development and there is room for improvement.

[0005] Therefore, the object of this disclosure is to provide a semiconductor laser including a photonic crystal and a method for manufacturing a semiconductor laser. [Means for solving the problem]

[0006] A semiconductor laser according to one embodiment of the present disclosure comprises: a first semiconductor layer including a semiconductor layer of a first conductivity type; an active layer provided on the first semiconductor layer; a second semiconductor layer providing on the active layer including a semiconductor layer of a second conductivity type; a third semiconductor layer providing on the second semiconductor layer including a semiconductor layer containing an impurity of the first conductivity type at a first concentration; and a fourth semiconductor layer providing on the third semiconductor layer including a semiconductor layer containing an impurity of the first conductivity type at a second concentration, wherein the first concentration is higher than the second concentration; the third semiconductor layer is directly bonded to the fourth semiconductor layer; and at least one of the third and fourth semiconductor layers contains a photonic crystal.

[0007] Furthermore, a method for manufacturing a semiconductor laser according to one embodiment of the present disclosure includes the steps of: preparing a semiconductor portion comprising: a first semiconductor layer portion including a semiconductor layer of a first conductivity type; an active layer provided on the first semiconductor layer portion; a second semiconductor layer portion including a semiconductor layer of a second conductivity type provided on the active layer; and a third semiconductor layer portion provided on the second semiconductor layer portion and including a semiconductor layer containing an impurity of the first conductivity type at a first concentration; preparing a fourth semiconductor layer portion including a semiconductor layer containing an impurity of the first conductivity type at a second concentration lower than the first concentration; forming a photonic crystal on at least one of the third semiconductor layer portion and the fourth semiconductor layer portion; and directly joining a first junction surface of the third semiconductor layer portion located on the side opposite to the surface on which the two semiconductor layers portion are arranged to the second junction surface of the fourth semiconductor layer portion. [Effects of the Invention]

[0008] One embodiment of the present disclosure provides a semiconductor laser and a method for manufacturing a semiconductor laser, which include a photonic crystal. [Brief explanation of the drawing]

[0009] [Figure 1A] This is a schematic cross-sectional view of a semiconductor laser according to Embodiment 1 of this disclosure. [Figure 1B]Figure 1A is a schematic cross-sectional view showing another form of the photonic crystal of a semiconductor laser. [Figure 2] Figure 1A is a schematic top view of the semiconductor laser shown. [Figure 3] Figure 1A shows an example of a photonic crystal contained in a semiconductor laser. [Figure 4A] Figure 1A is a schematic cross-sectional view showing another form of the photonic crystal of a semiconductor laser. [Figure 4B] This is a schematic cross-sectional view of a semiconductor laser having a distributed Bragg reflective coating. [Figure 4C] This is another schematic cross-sectional view of a semiconductor laser having a distributed Bragg reflective coating. [Figure 5A] This is a schematic cross-sectional view of a semiconductor laser with an anti-reflective coating applied to the light extraction surface. [Figure 5B] Figure 1A is a schematic cross-sectional view showing the case where the position of the light extraction surface of the semiconductor laser is changed. [Figure 6] This is a schematic cross-sectional view of a semiconductor laser according to Embodiment 2 of this disclosure. [Figure 7] This is a schematic cross-sectional view of a semiconductor laser according to Embodiment 3 of the present disclosure. [Figure 8A] Figure 1A is a schematic cross-sectional view showing one step in the manufacturing process of the semiconductor laser shown. [Figure 8B] Figure 1A is a schematic cross-sectional view showing one step in the manufacturing process of the semiconductor laser shown. [Figure 8C] Figure 1A is a schematic cross-sectional view showing one step in the manufacturing process of the semiconductor laser shown. [Figure 8D] Figure 1A is a schematic cross-sectional view showing one step in the manufacturing process of the semiconductor laser shown. [Figure 8E] Figure 1A is a schematic cross-sectional view showing one step in the manufacturing process of the semiconductor laser shown. [Figure 8F] Figure 1A is a schematic cross-sectional view showing one step in the manufacturing process of the semiconductor laser shown. [Figure 8G] Figure 1A is a schematic cross-sectional view showing one step in the manufacturing process of the semiconductor laser shown. [Figure 9A] Figure 7 is a schematic cross-sectional view showing one step in the manufacturing process of the semiconductor laser shown. [Figure 9B] Figure 7 is a schematic cross-sectional view showing one step in the manufacturing process of the semiconductor laser shown. [Figure 9C] Figure 7 is a schematic cross-sectional view showing one step in the manufacturing process of the semiconductor laser shown. [Figure 9D] Figure 7 is a schematic cross-sectional view showing one step in the manufacturing process of the semiconductor laser shown. [Modes for carrying out the invention]

[0010] The embodiments and examples for carrying out the invention described herein will be explained below with reference to the drawings. The semiconductor laser described below is intended to embody the technical concept of the invention described herein, and unless otherwise specified, the invention described herein is not limited to the following. In each drawing, components with the same function may be denoted by the same reference numeral. For convenience, such as explaining key points or facilitating understanding, components may be shown separately as embodiments or examples, but partial substitution or combination of components shown in different embodiments or examples is possible. In the embodiments and examples described later, descriptions of matters common to those described above will be omitted, and only the differences will be explained. In particular, similar effects and benefits from similar configurations will not be mentioned sequentially in each embodiment or example. The size and positional relationships of components shown in each drawing may be exaggerated to clarify the explanation.

[0011] In this specification, a photonic crystal refers to a structure having a refractive index distribution in which the refractive index changes with a period approximately equal to the wavelength of light emitted from the active layer. A photonic crystal may be composed of a single layer or may be composed of multiple layers. A photonic crystal is formed in which a plurality of second refractive index regions, each having a refractive index different from that of the first refractive index medium, are arranged within a first refractive index region, and at least a portion of the second refractive index regions are periodically arranged. Preferably, a photonic crystal is formed by periodically arranging all of the plurality of second refractive index regions, each having a refractive index different from that of the first refractive index medium, within a first refractive index region, each having a refractive index different from that of the first refractive index medium. When the periodic arrangement of these second refractive index regions is one-dimensional, the semiconductor laser is a distributed feedback laser (DFB laser). When the periodic arrangement of these second refractive index regions is two-dimensional, the semiconductor laser is a photonic crystal surface-emitting laser (PCSEL). A one-dimensional periodic arrangement means that there is a periodic change in the refractive index in one of the in-plane directions in each figure, i.e., one of the first direction (e.g., x direction) and the second direction (e.g., y direction). A two-dimensional periodic arrangement means that there is a periodic change in the refractive index in both of the in-plane directions in the figure, i.e., the first direction (e.g., x direction) and the second direction (e.g., y direction). When the periodic arrangement is two-dimensional, the period in the first direction and the period in the second direction may be the same or different. When focusing on multiple second refractive index regions in a photonic crystal, a set of one second refractive index region and an adjacent second refractive index region may be considered as one period as the smallest unit. Alternatively, a set containing three or more second refractive index regions can be considered as one period of refractive index change. The refractive index change in such a set containing three or more second refractive index regions may be formed so that a fluctuation in the refractive index occurs in the x direction and / or y direction. Furthermore, the photonic crystal may contain crystal defects that do not interfere with the laser oscillation of the DFB laser and PCSEL.Crystal defects can be caused by process damage such as crystal growth or etching.

[0012] In this specification, direct bonding refers to a state in which the third semiconductor layer 30 and the fourth semiconductor layer 40 are in direct contact without the use of resin or adhesive. When the third semiconductor layer 30 and the fourth semiconductor layer 40 are directly bonded, not merely contact but interatomic bonding occurs between the third semiconductor layer 30 and the fourth semiconductor layer 40, resulting in high bonding strength. Interatomic bonding can be observed, for example, by a high-resolution electron microscope. Direct bonding can be achieved, for example, by surface activation bonding or atomic diffusion bonding.

[0013] Embodiment 1. Embodiment 1 The semiconductor laser 100 according to Embodiment 1 is a photonic crystal surface-emitting laser (PCSEL). The semiconductor laser 100 of Embodiment 1 will be described below with reference to Figures 1A to 5B. As shown in Figure 1A, the semiconductor laser 100 includes a first semiconductor layer 10 provided on a substrate 60, an active layer 50 provided on the first semiconductor layer 10, a second semiconductor layer 20 provided on the active layer 50, a third semiconductor layer 30 provided on the second semiconductor layer 20, and a fourth semiconductor layer 40 provided on the third semiconductor layer 30. The first semiconductor layer 10 includes a first conductivity type semiconductor layer. The second semiconductor layer 20 includes a second conductivity type semiconductor layer. The third semiconductor layer 30 includes a semiconductor layer containing a first conductivity type impurity at a first concentration. The fourth semiconductor layer 40 includes a semiconductor layer containing a first conductivity type impurity at a second concentration. The second concentration is smaller than the first concentration. That is, the first concentration is higher than the second concentration. In this embodiment, the first conductivity type is n-type, and the second conductivity type is p-type. The third semiconductor layer 30 is directly bonded to the fourth semiconductor layer 40. The third semiconductor layer 30 contains a photonic crystal. Furthermore, the first electrode 1 is electrically connected to the fourth semiconductor layer 40, and the second electrode 2 is electrically connected to the first semiconductor layer 10 via the substrate 60. In the semiconductor laser 100, which is a photonic crystal surface-emitting laser, light emitted from the active layer 50 forms a standing wave within the photonic crystal and resonates. The resonant light oscillates as laser light from the photonic crystal in the vertical direction (+z direction and -z direction in the drawing). The laser light oscillated vertically from the semiconductor laser 100 may, for example, have the same wavelength and the same intensity. In this embodiment, the light emitted downwards and the light emitted upwards and reflected by the first electrode 1 are emitted from the bottom of the semiconductor laser 100. A translucent electrode 4 may also be provided on the lower surface 60a of the substrate 60. Therefore, the light extraction surface of the semiconductor laser 100 when the translucent electrode 4 is not provided is included in the lower surface 60a of the substrate 60. When the translucent electrode 4 is provided, the light extraction surface 5 of the semiconductor laser 100 is included in the lower surface 4a of the translucent electrode 4.

[0014] (substrate) The substrate 60 contains impurities of a first conductivity type and is conductive. The substrate 60 is, for example, an n-type GaN substrate. The thickness of the substrate 60 is such that the current injected into the semiconductor laser 100 spreads in the in-plane direction within a predetermined range, for example, 10 μm or more and 500 μm or less, preferably 50 μm or more and 500 μm or less, and more preferably 50 μm or more and 100 μm or less. A buffer layer may be provided between the substrate 60 and the first semiconductor layer 10. The semiconductor laser 100 does not necessarily have a substrate 60.

[0015] (First semiconductor layer) The semiconductor layer of the first conductivity type included in the first semiconductor layer 10 is, for example, a nitride semiconductor layer containing n-type impurities such as silicon (Si) and germanium (Ge). That is, the first conductivity type is n-type, and the first semiconductor layer 10 includes an n-type nitride semiconductor layer. The impurity concentration of the n-type impurities in the first semiconductor layer 10 is, for example, 1 × 10⁻⁶. 18 cm -3 The above 5 x 10 19 cm-3 The following may be applicable. In the present embodiment, the first semiconductor layer portion 10 is a nitride semiconductor layer portion. Also, as will be described later, in the present embodiment, the second semiconductor layer portion 20, the third semiconductor layer portion 30, and the fourth semiconductor layer portion 40 are also nitride semiconductor layer portions. Thus, by making each layer portion a nitride semiconductor layer portion, each layer portion can have light transmittance with respect to the oscillation wavelength. The first semiconductor layer portion 10, the second semiconductor layer portion 20, the third semiconductor layer portion 30, and the fourth semiconductor layer portion 40 can have a bandgap energy larger than the bandgap energy of the well layer described later. Thereby, each semiconductor layer portion can transmit the light emitted from the active layer and extract the light efficiently. The first semiconductor layer portion 10 includes one or more semiconductor layers of a first conductivity type. The first semiconductor layer portion 10 may partly include an undoped semiconductor layer. Here, the undoped semiconductor layer refers to a layer in which n-type impurities and / or p-side impurities are not intentionally added. The concentrations of n-type impurities and p-type impurities in the undoped semiconductor layer are, for example, concentrations below the detection limit in the analysis results by, for example, Secondary Ion Mass Spectroscopy (SIMS). When the undoped semiconductor layer contains Si as an n-type impurity, for example, it is 1×10 16 cm -3 or less, and when the undoped semiconductor layer contains Ge as an n-type impurity, it is 1×10 17 cm -3 or less. The thickness of the first semiconductor layer portion 10 is, for example, 1 μm or more and 5 μm or less. The first semiconductor layer portion 10 includes, for example, an n-type GaN layer, and the thickness of the n-type GaN layer can be 0.1 μm or more and 5 μm or less, preferably 0.1 μm or more and 0.5 μm or less. When the n-type GaN layer contains Si as an n-type impurity, the impurity concentration of the n-type GaN layer is, for example, 1×10 18 cm -3 or more and 5×10 19 cm -3 or less. Also, the first semiconductor layer portion 10 is not limited to GaN and may contain In and / or Al.

[0016] (Active layer) As shown in Figures 1A and 1B, the active layer 50 is a light-emitting layer provided on the first semiconductor layer 10. The light emitted by the active layer 50 is, for example, light with an emission peak wavelength in the range of 200 nm to 760 nm. The active layer 50 has a quantum well structure, for example, having one or more well layers 52 and a plurality of barrier layers. The quantum well structure may be, for example, a multiple quantum well structure having a plurality of well layers and a plurality of barrier layers. When the active layer 50 is a quantum well structure that emits light in the above wavelength range, the well layers and barrier layers are, for example, GaN, InGaN, AlGaN, or AlInGaN. The well layers are, for example, AlGaN, GaN, or InGaN, and are nitride semiconductors with a band gap smaller than that of the barrier layers. A superlattice layer may be formed between the first semiconductor layer 10 and the active layer 50 by alternately stacking undoped GaN layers and undoped InGaN layers. The barrier layer includes at least a first barrier layer 51 in contact with the first semiconductor layer 10 and a second barrier layer 53 in contact with the second semiconductor layer 20.

[0017] (Second semiconductor layer) The second semiconductor layer 20 contains a second conductivity type semiconductor layer, for example, a nitride semiconductor layer containing p-type impurities such as magnesium (Mg). The second semiconductor layer 20 contains one or more second conductivity type semiconductor layers. The impurity concentration of the p-type impurities is, for example, 1 × 10⁻⁶ 16 cm -3 The above 3 x 10 22 cm -3 The following may apply: The second conductivity type semiconductor layer is, for example, a p-type GaN layer. The second conductivity type semiconductor layer may contain In and / or Al. The thickness of the p-type GaN layer can be 0.04 μm or more and 1.5 μm or less, preferably 0.04 μm or more and 0.5 μm or less. Also, if the p-type GaN layer contains Mg as a p-type impurity, the impurity concentration of the p-type GaN layer is, for example, 1 × 10⁻⁶ 16 cm -3 The above 3 x 10 22 cm -3 Preferably, 5 × 10 16 cm -3 The above 1 x 10 21 cm -3The following is possible. The second semiconductor layer 20 may also include, for example, an undoped semiconductor layer. In order to form a tunnel junction with the first layer 31, which will be described later, it is preferable that at least the layer in contact with the first layer 31 is a nitride semiconductor layer containing p-type impurities, and 1 × 10 20 cm -3 The above 3 x 10 22 cm -3 The following impurity concentrations are also possible.

[0018] (Third semiconductor layer) The third semiconductor layer 30 forms a pn junction with the second semiconductor layer 20, and can form a so-called tunnel junction. Furthermore, the first junction surface 30a of the third semiconductor layer 30, on the side opposite to the side where the second semiconductor layer 20 is located, can be directly joined to the second junction surface 40a of the fourth semiconductor layer 40, which will be described later, by, for example, surface activation bonding.

[0019] A tunnel junction can be formed by increasing the concentration of at least one of the p-type impurities in the p-type semiconductor layer and the n-type impurities in the n-type semiconductor layer. In this tunnel junction, to improve the probability of electrons passing through the depletion layer, it is preferable that the width of the depletion layer formed by the pn junction between the p-type semiconductor layer and the n-type semiconductor layer be narrow. The width of the depletion layer can be narrowed as the concentration of at least one of the p-type impurities and the n-type impurities increases.

[0020] In this embodiment, the third semiconductor layer 30 is provided with, for example, a first layer 31 and a second layer 32 in order from the second semiconductor layer 20 side. Therefore, in this embodiment, by increasing the n-type impurity concentration of the first layer 31 that forms the tunnel junction, the width of the depletion layer of the pn junction is made relatively narrow, making it easier for electrons to pass through the depletion layer. The first layer 31 is a nitride semiconductor layer containing a first conductivity type (n-type) impurity at a first concentration. The first concentration is, for example, 1 × 10⁻⁶ 19 cm -3 The above 5 x 10 22 cm -3The following is possible: The second layer 32 is a nitride semiconductor layer containing a first conductivity type (n-type) impurity at a third concentration lower than the first concentration. The third concentration is lower than the first concentration. This makes the crystallinity of the second layer 32 higher than that of the first layer 31, so that a sufficiently flat surface can be formed when the second layer 32 is directly joined to the fourth semiconductor layer 40 described later. Also, since the third concentration of the second layer 32 is higher than the n-type impurity concentration of the fourth semiconductor layer 40 described later, the current injected when driving the semiconductor laser tends to spread more easily in the in-plane direction (width direction (x direction) and depth direction (y direction) in the drawing). The third concentration is, for example, 1 × 10 18 cm -3 The above 1 x 10 20 cm -3 The following is acceptable: The impurity concentration in the first layer 31 is, for example, 1 × 10⁻⁶ 19 cm -3 The above 5 x 10 22 cm -3 Preferably, 5 × 10 19 cm -3 The above 1 x 10 21 cm -3 The following applies, more preferably 1 × 10 20 cm -3 The above 1 x 10 21 cm -3 The following is possible. The thickness of the first layer 31 can be, for example, 1 nm to 500 nm, preferably 1 nm to 300 nm. The first layer 31 may contain n-type GaN. If the n-type GaN layer contains Si as an n-type impurity, the impurity concentration of the n-type GaN layer is, for example, 1 × 10⁻⁶ 19 cm -3 The above 5 x 10 22 cm -3 Preferably, 5 × 10 19 cm -3 The above 1 x 10 21 cm -3 The following applies, more preferably 1 × 10 20 cm -3 The above 1 x 10 21 cm -3The following can be achieved. This allows a tunnel junction to be formed between the second semiconductor layer 20 and the third semiconductor layer 30, thereby reducing the rise in forward voltage. In addition, the current can be spread in the in-plane direction (width direction (x direction) and depth direction (y direction) in the drawing). The second layer 32 includes, for example, an n-type GaN layer, and the thickness of the n-type GaN layer can be 10 nm to 500 nm, preferably 50 nm to 300 nm. If the n-type GaN layer included in the second layer 32 contains Si as an n-type impurity, the impurity concentration of the n-type GaN layer is smaller than the impurity concentration of the n-type GaN layer included in the first layer 31, for example, 1 × 10⁻⁶ 18 cm -3 The above 1 x 10 20 cm -3 The following is 1 × 10 19 cm -3 The above 5 x 10 19 cm -3 The following is possible:

[0021] The third semiconductor layer 30 includes a photonic crystal 7. In the semiconductor laser 100, the photonic crystal 7 resonates the light emitted from the active layer 50 in the in-plane direction (x and y directions in the figure), causing laser light to oscillate in the vertical direction (+z and -z directions in the figure). By including the photonic crystal 7, the semiconductor laser 100 can emit laser light with reduced generation of higher-order modes. For example, the semiconductor laser 100 can emit single-mode light in both the longitudinal and transverse modes.

[0022] (Photonic crystal) In this embodiment, the photonic crystal 7 is provided in at least the third semiconductor layer 30. The first refractive index region is the third semiconductor layer 30, for example, using a nitride semiconductor as the first refractive index medium. The second refractive index region is a plurality of holes 70 arranged within the first refractive index region, and the second refractive index medium is, for example, air. The photonic crystal 7 includes, for example, a plurality of cylindrical holes 70 and includes, for example, a part of the third semiconductor layer 30 and / or the second semiconductor layer 20. The diameter of each hole 70 may be, for example, 20 nm to 150 nm, or 20 nm to 80 nm. The depth of the holes 70 may be 50 nm to 2500 nm, 100 nm to 1000 nm, or 300 nm to 600 nm. The shape of each hole 70 may be columnar or conical. The cross-sectional shape of each hole 70 is not limited to circular, but may be, for example, elliptical or polygonal. Each of the holes 70 can be filled with a second refractive index medium, such as a vacuum, air, a noble gas like argon, or a dielectric with a refractive index lower than GaN. The dielectric is, for example, SiO2. This can increase the coupling efficiency between the photonic crystal and the resonator light.

[0023] The multiple holes 70 contained in the photonic crystal can be formed to form, for example, a square lattice, a rectangular lattice, or a triangular lattice when viewed from above. Also, λ is the wavelength in vacuum, n eff When the effective refractive index is given by , within the unit cell, 1 / (4 × n) exists in the x and y directions, respectively. effTwo holes can be formed separated by a distance of ×λ. Such a structure is called a double-hole lattice structure. The double-hole lattice structure allows for the emission of laser light with reduced generation of higher-order modes, even when the emission area is large. For example, the longitudinal and transverse modes can be maintained as single modes. Alternatively, multiple holes 70 may be provided so that lattice structures with two different periods overlap. For example, a square lattice with lattice constant a1 in both the x and y directions may overlap with a rectangular lattice where the lattice constant in one of the in-plane directions (x or y) is a1 and the other lattice constant is a2. This allows for the formation of a new band edge at a position shifted from the Γ point by a predetermined wave number δk = π(1 / a1 - 1 / a2) with respect to the corresponding wave vector direction in the plane, compared to the case where only one type of lattice structure is provided. By utilizing such a band edge, the angle θ = sin with respect to the direction perpendicular to the emission surface can be used. -1 The laser beam emission direction can be tilted by (δk / k0), k0 = 2π / λ. Therefore, the laser beam emission direction can be controlled. This lattice constant a2 can be continuously varied within a predetermined range.

[0024] The upper end 7b of the hole 70 constituting the photonic crystal 7 is located on the second junction surface 40a of the fourth semiconductor layer 40. In this embodiment, the lower end 7a of the hole 70 constituting the photonic crystal 7 is located within the second semiconductor layer 20, as shown in Figure 1A. Alternatively, for example, the lower end 7a of the hole 70 may be located within the third semiconductor layer 30, as shown in Figure 4A. The closer the lower end 7a of the hole 70 is to the active layer 50, the less the light emitted from the active layer 50 attenuates in light intensity before reaching the photonic crystal 7, thus increasing the light intensity within the photonic crystal 7. Therefore, it is preferable for the lower end 7a of the hole 70 to be located within the second semiconductor layer 20 rather than within the third semiconductor layer 30. Furthermore, the lower end 7a of the hole 70 may be located within the active layer 50 or within the first semiconductor layer 10. Compared to the case where the lower end 7a of the hole 70 is located in the third semiconductor layer 30 or the second semiconductor layer 20, when the lower end 7a of the hole 70 is located within the active layer 50 or within the first semiconductor layer 10, the volume of the active layer 50 decreases, thus lowering the threshold current. In this case, more light is confined in the photonic crystal 7, thus lowering the threshold current, which is the current at which the semiconductor laser 100 oscillates laser light. Furthermore, when the lower end 7a of the hole 70 is located within the active layer 50, as shown in Figure 1B, the lower end 7a of the hole 70 may also be located within the second barrier layer 53. This makes it possible to increase the proportion of two-dimensional diffraction of light in the photonic crystal while lowering the threshold current density. In this case, for example, the diameter of the hole 70 may be between 20 nm and 80 nm, and the depth of the hole 70 may be between 300 nm and 600 nm. The depth of the hole 70 refers to the distance from the upper end 7b to the lower end 7a of the hole 70. The semiconductor laser 100 can spread the current in the in-plane direction between the third semiconductor layer 30, which is tunnel-junctioned with the second semiconductor layer 20, and the second semiconductor layer 20. This allows the current to spread even directly beneath the insulating hole 70.

[0025] In this embodiment, as shown in Figure 2, the shape of the semiconductor laser 100 in a top view is a square with equal length in the width direction (x direction) and depth direction (y direction). Also, as shown by the dashed line in Figure 2, the region where the photonic crystal 7 is formed in a top view can be approximated as a square with a length L that is equal in both the width direction and depth direction. Here, length L is the length between the outermost first end 71 and the outermost second end 72 opposite to the first end 71 in the cross-section in the width direction and the cross-section in the depth direction shown in Figure 1A. Length L is, for example, 0.5 mm or more and 2 mm or less, preferably 0.8 mm or more and 1.5 mm or less. Note that the shape of the photonic crystal 7 in a top view is not limited to the rectangle described above. For example, it may be a circle with a diameter of L. The diameter is, for example, 0.5 mm or more and 2 mm or less, preferably 0.8 mm or more and 1.5 mm or less.

[0026] Figure 3 shows the lattice constant a of the photonic crystal, the wavelength λ in vacuum, and the effective refractive index n. eff This means a = λ / n eff The relationship satisfies the given equation. Here, the effective refractive index n eff This refers to the average refractive index, which is weighted based on the refractive index of the substrate, the refractive index of each semiconductor layer, and the refractive index of the active layer, according to the intensity distribution of light propagating through each layer. Effective refractive index n in Embodiment 1 eff This is the average refractive index obtained by weighting the refractive indices of the substrate 60, the first semiconductor layer 10, the active layer 50, the second semiconductor layer 20, the third semiconductor layer 30, and the fourth semiconductor layer 40 based on the intensity distribution of light propagating through each semiconductor layer and the active layer. Effective refractive index n eff The target value can be estimated through simulation. In actual manufacturing, the lattice constant a of the photonic crystal and the wavelength λ in vacuum can be measured, so the n can be obtained by rearranging the above relationship. eff According to the relationship =λ / a, the effective refractive index n eff This can be estimated. The lattice constant a and the wavelength λ in vacuum of the photonic crystal 7 can vary due to manufacturing variations, so the effective refractive index n can be estimated from the simulation.eff And the effective refractive index n, which is estimated from the above relationship in actual manufacturing. eff And, they don't necessarily match. When a semiconductor laser element emits blue light, for example, the effective refractive index n eff The effective refractive index n is between 2.4 and 2.5, and the lattice constant a of the photonic crystal 7 can be formed in the range of 180 nm to 200 nm. Also, when the semiconductor laser element emits green light, for example, the effective refractive index n eff The effective refractive index n is between 2.3 and 2.4, and the lattice constant a of the photonic crystal 7 can be formed in the range of 210 nm to 230 nm. Also, when the semiconductor laser element emits red light, for example, the effective refractive index n eff The value is between 2.2 and 2.3, and the lattice constant a of the photonic crystal 7 can be formed in the range of 250 nm to 280 nm.

[0027] (Fourth semiconductor layer) The fourth semiconductor layer 40 contains n-type impurities (first conductivity type impurities) at a second concentration. The second concentration is smaller than the first and third concentrations. The second concentration is smaller than the first and third concentrations, for example, 1 × 10⁻⁶ 18 cm -3 The above 5 x 10 19 cm -3 The following is possible. As described above, the fourth semiconductor layer 40 is directly bonded to the third semiconductor layer 30, for example, by surface activation bonding. That is, the fourth semiconductor layer 40 and the third semiconductor layer 30 are in contact with each other without the use of an adhesive. By directly bonding the fourth semiconductor layer 40 and the third semiconductor layer 30, the contact resistance between the fourth semiconductor layer 40 and the third semiconductor layer 30 can be reduced. The material constituting the fourth semiconductor layer portion 40 is preferably the same as the material constituting the third semiconductor layer portion 30. That is, it is desirable that the third semiconductor layer portion 30 and the fourth semiconductor layer portion 40 are made of the same material. By making the material constituting the fourth semiconductor layer portion 40 the same as the material constituting the third semiconductor layer portion 30, it becomes easier to control the effective refractive index. Further, by making the material constituting the fourth semiconductor layer portion 40 the same as the material constituting the third semiconductor layer portion 30, the thermal expansion coefficient of the fourth semiconductor layer portion 40 becomes the same as the thermal expansion coefficient of the third semiconductor layer portion 30, and the bonding strength between the fourth semiconductor layer portion 40 and the third semiconductor layer portion 30 can be increased. However, that the materials constituting the fourth semiconductor layer portion 40 and the third semiconductor layer portion 30 are the same means that it is sufficient that the base materials constituting both semiconductor layer portions are the same, and the impurity concentrations may be different. For example, both the fourth semiconductor layer portion 40 and the third semiconductor layer portion 30 are nitride semiconductor layers, for example, n-type GaN layers.

[0028] Also, the refractive index of the fourth semiconductor layer portion 40 is preferably larger than the average refractive index of the photonic crystal 7. The average refractive index of the photonic crystal 7 is the average refractive index between the refractive index of the hole 70 and the refractive index of the semiconductor layer portion where the hole 70 is provided. By providing such a fourth semiconductor layer portion 40 on the photonic crystal 7, the light intensity can also be distributed to the fourth semiconductor layer portion 40. Accordingly, compared with the case where the fourth semiconductor layer portion is not provided and the upper surface of the third semiconductor layer portion 30 is in contact with air, the light intensity of the photonic crystal is increased, the amount of light contributing to resonance is increased, and laser oscillation can be effectively achieved.

[0029] The thickness of the fourth semiconductor layer portion 40 may be, for example, 1 μm or more and 500 μm or less, preferably 1 μm or more and 400 μm or less, and more preferably 1 μm or more and 10 μm or less. When the n-type GaN layer contains Si as an n-type impurity, the impurity concentration of the n-type GaN layer is, for example, 1×10 18 cm -3 or more and 5×10 19 cm -3The following is possible. It is desirable to appropriately adjust the thickness of the fourth semiconductor layer 40 according to the size of the contact area with the first electrode 1, which will be described later.

[0030] As described above, by providing the fourth semiconductor layer 40, the fourth semiconductor layer 40 can be given light intensity, and the light intensity of the semiconductor layer containing the photonic crystal can be increased. Furthermore, by setting the thickness, refractive index, and other conditions of the fourth semiconductor layer 40 within a predetermined range, the light intensity of the active layer 50 can be maximized. By increasing the light intensity of the layer containing the photonic crystal and maximizing the light intensity of the active layer 50, a semiconductor laser 100 that efficiently emits surface light can be obtained.

[0031] Furthermore, as shown in Figures 4B and 4C, a distributed Bragg reflective film (DBR film) 45 may be placed within the fourth semiconductor layer 40 or on the upper surface 40b of the fourth semiconductor layer 40. The DBR film can be obtained, for example, by stacking two or more pairs of SiO2 / Nb2O5. Other pairs constituting the DBR film may be SiO2 / Ta2O5 pairs, SiO2 / Al2O3 pairs, or Si-doped GaN / Si-doped AlInN pairs. This allows light that resonates in the photonic crystal 7 and is emitted upward to be reflected downward, thereby increasing the light extraction efficiency of the semiconductor laser.

[0032] (First electrode and second electrode) The first electrode 1 is a light-reflective and conductive member. The material of the first electrode 1 is, for example, Ag or Al. In a plan view, the first electrode 1 is positioned to overlap with the photonic crystal 7. In this embodiment, the first electrode 1 is the positive electrode and is positioned on the upper surface 40b of the fourth semiconductor layer 40. Since the light resonating in the photonic crystal 7 oscillates vertically, by positioning the first electrode 1 on the fourth semiconductor layer 40 so as to overlap with the photonic crystal 7, the laser light oscillating upward can be reflected downwards from the semiconductor laser 100. This improves the light extraction efficiency.

[0033] The top view shape of the first electrode 1 may be a circle with a diameter of L1 in the top view, for example, as shown in Figure 2. This allows the current to spread isotropically in the in-plane direction, enabling efficient current injection. There is no limit to the diameter of the first electrode 1, but it is preferable that it be smaller than the major axis of the region where the photonic crystal 7 is formed in the top view. Furthermore, it is preferable that the position where the first electrode 1 is provided is inside the region where the photonic crystal 7 is formed in the top view. This allows for the formation of regions in the photonic crystal 7 where current is injected and regions where current is not easily injected. The spatial distribution of light confined in the photonic crystal 7 is determined by the structure of the photonic crystal and does not depend on the size of the electrode. Therefore, by adopting an electrode structure that limits the region where current is injected, the region where gain occurs can be limited. Furthermore, by providing the first electrode 1 in the center of the photonic crystal 7 in the top view, light leakage outside the photonic crystal can be reduced. This reduces the current required to drive the semiconductor laser 100. Furthermore, in the photonic crystal 7, the region where current is difficult to inject acts as a reflector, returning light leaking in the in-plane direction back towards the region where current is injected, thereby suppressing a decrease in the light contributing to resonance. Note that the shape of the first electrode 1 is not limited to a circle, but may be a square, rectangle, triangle, or other polygon. When the DBR film 45 is arranged on the upper surface 40b of the fourth semiconductor layer 40 such that at least a portion of it overlaps with the photonic crystal 7 in a plan view, the first electrode 1 may be arranged so that at least a portion of it does not overlap with the DBR film 45, or, as shown in Figures 4B and 4C, the first electrode 1 may be arranged so that at least a portion of it overlaps with the DBR film 45. When the DBR film 45 is provided, the first electrode 1 does not have to be a light-reflective material. When the DBR film 45 is provided, the first electrode 1 does not have to be positioned in a position that overlaps with the photonic crystal 7 in a plan view. Note that, as shown in Figure 4C, when at least a portion of the first electrode 1 is arranged to overlap with the DBR film 45, the fourth semiconductor layer 40 may have a thickness of, for example, 1 μm or more and 450 μm or less. This allows the current to spread even directly beneath the DBR film 45. As shown in Figure 4C, it is preferable to provide an insulating region 35 in at least one of the third semiconductor layer 30 and the fourth semiconductor layer 40 in order to suppress the flow of current from directly beneath the first electrode 1, which is located on the side surface of the DBR film 45, to the second electrode 2. For example, the insulating region 35 can be provided by ion implantation or groove formation in the second layer 32 of the third semiconductor layer 30 located directly beneath the first electrode 1, which is located on the side surface of the DBR film 45. Alternatively, the insulating region 35 may be provided in the fourth semiconductor layer 40 in a similar manner. This insulating region 35 is provided, for example, from the junction interface to a thickness of 5 nm to 200 nm, preferably 10 nm to 100 nm. This allows the current to be effectively spread directly beneath the DBR film 45. Therefore, the active layer included in the region directly beneath the DBR film 45 emits light due to current injection, and a portion of the resonant light is reflected by the DBR film 45 and can be extracted from the light extraction surface 5.

[0034] The second electrode 2 is a conductive material. The material of the second electrode 2 can be formed from a single layer or multilayer film of, for example, Al, Ti, Pt, or Au. An example of a multilayer film is a multilayer film of Ti, Pt, and Au. In this embodiment, the second electrode 2 is a negative electrode. The second electrode 2 is, for example, a ring-shaped electrode arranged to surround the photonic crystal 7 in a plan view. Alternatively, the second electrode 2 may be a ring shape arranged to overlap the photonic crystal 7 in a plan view. Furthermore, as shown in Figure 5A, an anti-reflective coating 3 may be applied to the lower surface 60a of the substrate 60 located inside the ring. By applying the anti-reflective coating 3 in this way, reflected light due to reflection between the substrate 60 and the air can be suppressed, and light loss can be reduced. In this case, the lower surface of the anti-reflective coating 3 becomes the light extraction surface 5. A translucent electrode 4 can be further arranged between the substrate 60 and the second electrode 2. An example of the translucent electrode 4 is ITO.

[0035] Here, as shown in Figure 5B, a first electrode 1 having light reflectivity and conductivity may be placed on the lower surface 60a of the substrate 60, in a position that overlaps with the photonic crystal 7 in a plan view. Alternatively, a second electrode 2 having conductivity may be placed on the upper surface 40b side of the fourth semiconductor layer 40. A light-transmitting electrode 4 may be further provided between the second electrode 2 and the fourth semiconductor layer 40. The first electrode 1 placed on the lower surface 60a of the substrate 60 functions as a negative electrode, and the second electrode 2 placed on the upper surface 40b of the fourth semiconductor layer 40 functions as a positive electrode. By arranging the first electrode 1 and the second electrode 2 in this way, light can be extracted from the upper surface 40b of the fourth semiconductor layer 40. In other words, the light extraction surface when the light-transmitting electrode 4 is not provided is included in the upper surface 40b of the fourth semiconductor layer 40, and the light extraction surface 5 when the light-transmitting electrode 4 is provided is included in the upper surface 4b of the light-transmitting electrode 4. In this configuration, the DBR film 45 may be placed on the lower surface 60a side of the substrate 60. In this case, the first electrode 1 can be placed around the DBR film 45 or around the DBR film 45 and below the DBR film 45.

[0036] The above describes a PCSEL in which the photonic crystal 7 consists of a first refractive index region including at least a third semiconductor layer 30 and a second refractive index region consisting of a plurality of holes 70, but this embodiment is not limited thereto. The photonic crystal 7 may also have, for example, a first refractive index region consisting of a first refractive index medium made of a vacuum, air, a rare gas, or a dielectric such as SiO2, and a second refractive index region consisting of a second refractive index medium made of a plurality of periodically arranged columnar semiconductor layers. This makes it possible to lower the threshold current of the PCSEL.

[0037] 2. Embodiment 2 The semiconductor laser 200 according to this embodiment, shown in Figure 6, differs from the semiconductor laser 100 of Embodiment 1 in that it is a distributed feedback type laser. The photonic crystal 7 has a periodic change in refractive index due to a first refractive index region including at least a part of the third semiconductor layer 30 and a second refractive index region consisting of grooves 75 arranged in the semiconductor layer. The first refractive index medium forming the first refractive index region is, for example, a GaN-based semiconductor, and the second refractive index medium forming the second refractive index region is, for example, a vacuum or air. The lattice constant a of the photonic crystal, the oscillation wavelength λ in a vacuum, and the effective refractive index n eff This means a = λ / (2 × n eff The relationship ) is satisfied. This allows laser light with reduced generation of higher-order modes to be emitted from the cleavage end face. For example, semiconductor laser 200 can emit laser light with a single longitudinal mode. In this embodiment, the semiconductor laser 200 has light-reflective films 203a and 203b applied to both end faces 200a and 200b of the semiconductor laminate. The light-reflective films 203a and 203b are, for example, single-layer or multi-layer films of Al2O3, ZrO2, or SiO2. The reflectivity of the light-reflective film 203b is lower than that of the light-reflective film 203a. In the semiconductor laser 200, light emitted from the active layer 50 resonates at both end faces and is emitted from the other end face 200b, which is the light extraction surface 205.

[0038] 3. Embodiment 3 The semiconductor laser 300 according to this embodiment is identical to the semiconductor laser 100 according to Embodiment 1 in that it is a PCSEL, but differs from the semiconductor laser 100 according to Embodiment 1 in that, as shown in Figure 7, the photonic crystal is formed in the fourth semiconductor layer 340. In the semiconductor laser 300, the lower end 7a of the hole 70 constituting the photonic crystal 7 is located on the second junction surface 340a of the fourth semiconductor layer 340. The upper end 7b of the hole 70 constituting the photonic crystal 7 is located inside the fourth semiconductor layer 340.

[0039] Manufacturing method 1. An example of a method for manufacturing a semiconductor laser according to Embodiment 1 (Manufacturing Method 1) Manufacturing method 1 is, (1) A step of preparing a semiconductor portion 90 comprising: a first semiconductor layer portion 10 including a first conductivity type semiconductor layer; an active layer 50 provided on the first semiconductor layer portion 10; a second semiconductor layer portion 20 including a second conductivity type semiconductor layer provided on the active layer 50; and a third semiconductor layer portion 30 provided on the second semiconductor layer portion 20 and including a semiconductor layer containing a first conductivity type impurity at a first concentration; (2) A step of preparing a fourth semiconductor layer 40 which includes a semiconductor layer containing a first conductivity type impurity at a second concentration lower than the first concentration, (3) A step of forming a photonic crystal in the third semiconductor layer 30, (4) A step of directly bonding the first bonding surface 30a of the third semiconductor layer 30, which is located on the opposite side from the surface on which the second semiconductor layer 20 is arranged, and the second bonding surface 40a of the fourth semiconductor layer 40, Includes.

[0040] The semiconductor laser 100 is manufactured by the MOCVD (metal organic chemical vapor deposition) method in a furnace where pressure and temperature can be controlled. Each semiconductor layer and semiconductor section can be formed by introducing a carrier gas and a source gas into the furnace. Hydrogen (H2) gas or nitrogen (N2) gas can be used as the carrier gas. Ammonia (NH3) gas can be used as the source gas for the N source. Trimethylgallium (TMG) gas or triethylgallium (TEG) gas can be used as the source gas for the Ga source. Trimethylindium (TMI) gas can be used as the source gas for the In source. Trimethylaluminum (TMA) gas can be used as the source gas for the Al source. Monosilane (SiH4) gas can be used as the source gas for the Si source. Bis(cyclopentadienyl)magnesium (Cp2Mg) gas can be used as the source gas for the Mg source. An example of the manufacturing method described below is a method in which each layer and section is epitaxially grown by the MOCVD method. The MOCVD method is a manufacturing method with excellent mass productivity. In addition to MOCVD, remote plasma CVD can also be used. By using remote plasma CVD, the carrier density in the semiconductor layer can be increased. Alternatively, it can be formed by physical vapor deposition (PVD). By using PVD, a large number of carriers can be introduced. Examples of PVD methods include sputtering and molecular beam epitaxy (MBE).

[0041] (Process for preparing the semiconductor part) The process for preparing the semiconductor unit 90 will be explained with reference to Figure 8A. First, prepare a substrate 60 made of, for example, n-type GaN. Next, on the substrate 60, in order from the substrate 60 side, a first semiconductor layer portion 10 including a semiconductor layer of the first conductivity type (n-type), an active layer 50, a second semiconductor layer portion 20 including a semiconductor layer of the second conductivity type (p-type), and a third semiconductor layer portion 30 including a semiconductor layer containing an impurity of the first conductivity type at a first concentration are formed to prepare a semiconductor portion 90. The formation of the third semiconductor layer portion 30 forms a first layer 31 and a second layer 32 in order from the substrate 60 side.

[0042] The first semiconductor layer portion 10 is formed, for example, by growing an n-type cladding layer on the substrate 60 side. Incidentally, the first semiconductor layer portion 10 may be formed after providing a buffer layer on the substrate 60. Further, an undoped semiconductor layer may be provided between the buffer layer and the n-type cladding layer.

[0043] Next, an active layer 50 is formed on the first semiconductor layer portion 10. For example, when the active layer 50 has a multiple quantum well structure, a barrier layer and a well layer are alternately formed in a desired number of layers in order from the substrate 60 side to form the active layer 50. In this case, the process of forming the active layer 50 ends with the process of forming the barrier layer.

[0044] Next, on the active layer 50, for example, a second semiconductor layer portion 20 is formed by growing a p-type cladding layer.

[0045] Next, a third semiconductor layer portion 30 including a first layer 31 and a second layer 32 is formed on the second semiconductor layer portion 20. First, on the second semiconductor layer portion 20, a first layer 31, which is a semiconductor layer containing an n-type impurity (an impurity of the first conductivity type) at a first concentration, is formed. The first layer 31 is, for example, n-type GaN and may contain In and / or Al. The first concentration is, for example, 19 5×10 19 cm -3 or more and 22 5×10 22 cm -3 or less, preferably 20 1×10 20 cm -3 or more and 21 1×10 21 cm -3 or less. -3 A first layer 31 containing a first concentration of n-type impurities can be formed by introducing a carrier gas, a raw material gas for forming the first layer 31, and a raw material gas containing the element that will become the n-type impurity. For example, if the n-type impurity is Si, a first layer 31 containing a first concentration of n-type impurities can be formed by supplying a raw material gas containing Si to the raw material gas for forming the first layer 31 at a predetermined flow rate.

[0046] Next, a second layer 32 containing a third concentration of n-type impurities (first conductivity type impurities) is formed on the first layer 31. The third concentration is smaller than the first concentration. The third concentration is larger than the second concentration of n-type impurities contained in the fourth semiconductor layer 40, which will be described later. It is desirable that the material constituting the second layer 32 is the same as the material constituting the first layer 31. The second layer 32 is, for example, n-type GaN and may also contain In and / or Al. The third concentration is, for example, 1 × 10 18 cm -3 The above 1 x 10 20 cm -3 The following is 1 × 10 19 cm -3 The above 5 x 10 19 cm -3 The following applies: The second layer 32 containing a third concentration of n-type impurities can be formed by introducing an element that will become an n-type impurity into the raw material gas that forms the second layer 32. For example, if the n-type impurity is Si, the second layer 32 containing a third concentration of n-type impurities can be formed by supplying a raw material gas containing Si to the raw material gas that forms the second layer 32 at a predetermined flow rate.

[0047] (Process for preparing the fourth semiconductor layer) Next, a fourth semiconductor layer 40 containing n-type impurities at a second concentration is prepared. The material constituting the fourth semiconductor layer 40 is preferably the same as the material constituting the third semiconductor layer 30. The fourth semiconductor layer 40 is, for example, GaN. The thickness of the fourth semiconductor layer 40 may be, for example, 1 μm to 500 μm, preferably 1 μm to 400 μm, and more preferably 1 μm to 10 μm. First, as shown in Figure 8B, the fourth semiconductor layer 40, made of a nitride semiconductor containing n-type impurities, is grown on a growth substrate 85 made of, for example, sapphire, by the MOCVD method. Next, as shown in Figure 8C, a resin layer 86 and a support substrate 87 are provided on the fourth semiconductor layer 40 in that order, and then the growth substrate 85 is removed.

[0048] (Process for forming photonic crystals) Next, a photonic crystal is formed by creating multiple holes in at least the third semiconductor layer. The photonic crystal can be formed, for example, by the following method. As shown in Figure 8D, the first junction surface 30a of the third semiconductor layer 30 is covered with a first mask 81 made of SiO2 or the like. This increases the selectivity ratio of the third semiconductor layer 30 to the first mask 81 in the etching process described later. Furthermore, a second mask 82 made of resin or the like is placed on the upper surface of the first mask 81. This increases the selectivity ratio of the second mask 82 to the first mask 81 in the lithography process described later. The second mask 82 is provided with a hole collection section 8 containing multiple holes arranged at a predetermined period. The hole collection section 8 is formed, for example, by electron beam lithography or nanoimprint. For example, if each hole 80 is provided to form a square lattice as shown in Figure 3, the distance between the center of each hole 80 in the hole collection section 8 and the center of the adjacent hole 80 is the lattice constant a of the photonic crystal 7. Note that the lattice constant a, the wavelength λ in a vacuum, and the effective refractive index n are all considered. eff This means a = λ / n eff The relationship satisfies the given equation.

[0049] Next, as shown in Figure 8E, the first mask 81, the third semiconductor layer 30, and the second semiconductor layer 20 exposed from the second mask 82 are removed, and a hole 70 of a desired depth is formed with the lower end 7a positioned within the second semiconductor layer 20, thereby forming a photonic crystal 7. The method for removing the first mask 81, the third semiconductor layer 30, and the second semiconductor layer 20 is etching, such as reactive ion etching using a chlorine-based gas. By forming the hole 70 using the first mask 81 and the second mask 82, the aspect ratio of the hole 70 can be increased. At this time, the lower end 7a of the hole 70 can be positioned within the third semiconductor layer 30 by changing the etching depth. After that, the first mask 81 is removed. The second mask 82 is usually removed during this reactive ion etching. However, by adjusting the depth of the hole 70, a part of the second mask 82 may remain. In this case, both the first mask 81 and the second mask 82 are removed.

[0050] (Direct joining process) Next, as shown in Figure 8F, the first bonding surface 30a of the third semiconductor layer 30, which is located on the opposite side from the surface where the second semiconductor layer 20 is placed, and the second bonding surface 40a of the fourth semiconductor layer 40 are directly bonded. The first bonding surface 30a and the second bonding surface 40a can be directly bonded, for example, by surface activation bonding. Surface activation bonding is a method of bonding after planarizing and cleaning both the first bonding surface 30a and the second bonding surface 40a.

[0051] The planarization process is carried out, for example, by chemical mechanical polishing (CMP) or immersion in an acid or alkali solution. These treatments can form a flat surface with an arithmetic mean roughness Ra of, for example, 1 nm or less, preferably 0.5 nm or less. When the target to be planarized is the +c surface of GaN, immersion in an acid or alkali solution is preferable. This removes unwanted crystals from the first main surface. Examples of acid or alkali solutions that can be used include H2SO4 (sulfuric acid), HF (hydrofluoric acid), HCl (hydrochloric acid), TMAH (tetramethylammonium hydroxide), and KOH (potassium hydroxide). TMAH is preferably used as the acid or alkali solution. When the target to be planarized is the -c surface of GaN, planarization is preferable by CMP. This can form a second bond surface with an arithmetic mean roughness of 1 nm or less, preferably 0.5 nm or less.

[0052] In the bonding process, the first bonding surface 30a and the second bonding surface 40a, which have been activated by sputter etching with an ion beam such as argon or plasma, are directly bonded under predetermined conditions. The bonding temperature is, for example, 0°C to 100°C, preferably 0°C to 70°C, and more preferably 0°C to 50°C. Surface activation bonding does not require high temperatures like fusion bonding, for example, and can bond strongly at relatively low temperatures. Furthermore, compared to the case where the fourth semiconductor layer 40 is grown by MOCVD or PVD after the photonic crystal 7 has been formed to close the upper end of the photonic crystal 7, the thermal damage to the active layer can be reduced. Also, when closing the upper end by crystal growth, the shape and size of the hole are constrained by the conditions for closing the upper end, but when closing the upper end by direct bonding, the hole can be freely designed. The pressure during surface activation bonding is, for example, 10 MPa to 200 MPa, preferably 50 MPa to 100 MPa.

[0053] Furthermore, in the direct joining process, the crystal axis direction within the plane of the first crystal plane and the crystal axis direction within the plane of the second crystal plane may or may not coincide. For example, if the first crystal plane is a +c plane and the second crystal plane is a -c plane, the a-axis direction within the plane of the first crystal plane (+c plane) and the a-axis direction within the plane of the second crystal plane (-c plane) may be offset during joining. This eliminates the need for a step to align the orientations within each joining plane during the direct joining process, thereby simplifying the manufacturing process. According to the manufacturing method of this embodiment 1, even if the crystal axis direction within the plane of the first crystal plane and the crystal axis direction within the plane of the second crystal plane are offset during direct joining, the crystal planes (first crystal plane and second crystal plane) can be joined together. The offset of the crystal axes can be confirmed by performing a φ scan of the asymmetric plane to check for rotational symmetry. The offset between the first and second crystal planes is repeatedly observed according to the rotational symmetry. An example of an asymmetrical plane is the (102) plane of gallium nitride.

[0054] Furthermore, in the direct bonding process, the first bonding surface 30a and the second bonding surface 40a can be directly bonded and then annealed. This can reduce the electrical resistance of the resulting semiconductor laser. This is thought to be because the adhesion is improved while maintaining the crystallinity near the bonding interface. This annealing is performed, for example, without applying pressure. The annealing temperature range is, for example, 300°C to 500°C, preferably 350°C to 450°C. This annealing temperature is appropriately set within the above temperature range depending on the materials constituting the third semiconductor layer 30 and the fourth semiconductor layer 40. For example, if both the third semiconductor layer 30 and the fourth semiconductor layer 40 are made of GaN, it is thought that annealing within the above temperature range can improve the adhesion between the third semiconductor layer 30 and the fourth semiconductor layer 40 while maintaining crystallinity. Furthermore, this annealing process allows for the simultaneous heating of the resin layer 86 and the support substrate 87 provided on the fourth semiconductor layer 40. In other words, this annealing process allows for the removal of the support substrate 87 by melting or burning the resin layer 86. This prevents the fourth semiconductor layer 40 from peeling off from the third semiconductor layer 30 when the support substrate 87 is removed from the resin layer 86. After removing the resin layer 86 and the support substrate 87, the surface of the fourth semiconductor layer 40 can be cleaned, and the first electrode 1 can be formed on the cleaned surface. Alternatively, the resin layer 86 and the support substrate 87 can be removed by other methods, and then the first electrode 1 can be formed. It is also possible to directly bond the substrate including the fourth semiconductor layer 40 to the third semiconductor layer 30 without using the resin layer 86 and the support substrate 87. Through the steps of forming the photonic crystal and direct bonding described above, the photonic crystal 7 is formed in the third semiconductor layer 30, and the upper ends 7b of the multiple holes 70 constituting the photonic crystal 7 are positioned on the second bonding surface 40a of the fourth semiconductor layer 40.

[0055] (Electrode formation process) Next, as shown in Figure 8G, a first electrode 1 with a predetermined pattern is formed on the upper surface 40b of the fourth semiconductor layer 40, and a second electrode 2 with a predetermined pattern is formed on the lower surface 60a of the substrate 60. Furthermore, a translucent electrode 4 may be formed between the second electrode 2 and the substrate 60. The first electrode 1 is provided such that at least a portion of it overlaps with the photonic crystal 7 in a plan view. The first electrode 1 and the second electrode 2 can be formed using known methods as appropriate. For example, the first electrode 1 and the second electrode 2 can be formed by a lift-off process or etching process using a resist.

[0056] (Singulation process) Next, the wafer is fragmented into 100 individual pieces using semiconductor lasers. This fragmentation is performed along predetermined fragmentation positions CL shown in Figure 8G, using methods such as laser scribing or dicing. Laser scribing is a method of dividing a wafer by focusing laser light into the substrate to form a modified region, and then using the cracks that develop from this region as starting points.

[0057] 2. An example of a method for manufacturing a semiconductor laser according to Embodiment 2 (Manufacturing Method 2) Manufacturing method 2 differs from manufacturing method 1 of the semiconductor laser 100 according to Embodiment 1 in that, in addition to manufacturing method 1 of the semiconductor laser according to Embodiment 1, it includes the step of applying an optical reflective film 203a to the end face 200a and an optical reflective film 203b to the end face 200b. The process of applying the light-reflective films 203a and 203b is carried out after or during the piece formation process. The light-reflective films 203a and 203b are applied, for example, by vacuum deposition or sputtering. In the process of forming the photonic crystal 7 in this manufacturing method, the lattice constant a, the wavelength λ in vacuum, and the effective refractive index n are used. eff This means a = λ / (2 × n eff The groove 75 is provided such that it satisfies the relationship ). The periodic change in refractive index due to the groove 75 is one-dimensional. That is, the semiconductor laser manufactured by this manufacturing method 2 is a DFB laser.

[0058] 3. An example of a method for manufacturing a semiconductor laser according to Embodiment 3 (Manufacturing Method 3) Manufacturing method 3 differs from semiconductor laser manufacturing method 1 according to embodiment 1 in the step of forming the photonic crystal 7. In the step of forming the photonic crystal 7 in manufacturing method 3, the photonic crystal 7 is formed in the fourth semiconductor layer 340. Specifically, as shown in Figure 9A, the first mask 81 and the second mask 82 having a hole cluster 8 are placed on the second junction surface 340a of the fourth semiconductor layer 340. Then, as shown in Figure 9B, the first mask 81 and the fourth semiconductor layer 340 exposed from the second mask 82 are removed, and holes 70 are formed such that the upper end 7b of the holes 70 constituting the photonic crystal 7 is located inside the fourth semiconductor layer 340. The steps for preparing the semiconductor portion 90, preparing the fourth semiconductor layer portion 40, the direct bonding step shown in Figure 9C, and the electrode formation step and individualization step shown in Figure 9D are the same as those steps in manufacturing method 1.

[0059] In the manufacturing method described above, a photonic crystal 7 is formed on the fourth semiconductor layer 340, which does not have an active layer 50, and then the semiconductor layer 90 having an active layer 50 is bonded to the fourth semiconductor layer 340. This method can suppress damage to the active layer 50 due to etching and the like.

[0060] Furthermore, for example, this disclosure can take the following form. Section (1) A first semiconductor layer portion including a first conductive semiconductor layer, An active layer provided on the first semiconductor layer, A second semiconductor layer portion including a second conductivity type semiconductor layer provided on the active layer, A third semiconductor layer comprising a semiconductor layer containing a first conductivity type impurity at a first concentration, provided on the second semiconductor layer, A fourth semiconductor layer comprising a semiconductor layer provided on the third semiconductor layer containing a first conductivity type impurity at a second concentration, Equipped with, The first concentration is higher than the second concentration. The third semiconductor layer is directly bonded to the fourth semiconductor layer. A semiconductor laser comprising a photonic crystal in at least one of the third semiconductor layer and the fourth semiconductor layer. Section (2) The third semiconductor layer is, A first layer is a semiconductor layer containing the first conductivity type impurity at the first concentration, A second semiconductor layer containing a first conductivity type impurity at a third concentration greater than the second concentration and less than the first concentration, Includes, The semiconductor laser according to item 1, wherein the first layer and the second layer are provided in order from the second semiconductor layer side. Section (3) The third semiconductor layer includes the photonic crystal, The semiconductor laser according to item 1 or 2, wherein the upper end of the hole constituting the photonic crystal is located at the junction surface of the fourth semiconductor layer. Section (4) The semiconductor laser according to any one of items 1 to 3, wherein the lower end of the hole constituting the photonic crystal is located within the second semiconductor layer. Section (5) The active layer includes one or more well layers and multiple barrier layers. The barrier layer includes at least a first barrier layer in contact with the first semiconductor layer and a second barrier layer in contact with the second semiconductor layer 20. The semiconductor laser according to any one of items 1 to 3, wherein the lower end of the hole constituting the photonic crystal is located within the second barrier layer. Section (6) A semiconductor laser according to any one of items 1 to 5, wherein the third semiconductor layer and the fourth semiconductor layer are made of the same material. Section (7) The semiconductor laser according to any one of claims 1 to 6, wherein the first semiconductor layer, the second semiconductor layer, the third semiconductor layer, and the fourth semiconductor layer are all nitride semiconductor layers. Section (8) The first conductivity type is n-type, The semiconductor laser according to any one of items 1 to 7, wherein the second conductivity type is p-type. Section (9) A step of preparing a semiconductor part comprising: a first semiconductor layer part including a first conductivity type semiconductor layer; an active layer provided on the first semiconductor layer part; a second semiconductor layer part including a second conductivity type semiconductor layer provided on the active layer; and a third semiconductor layer part provided on the second semiconductor layer part including a semiconductor layer containing a first conductivity type impurity at a first concentration; A step of preparing a fourth semiconductor layer portion which includes a semiconductor layer containing a first conductivity type impurity at a second concentration lower than the first concentration, A step of forming a photonic crystal in at least one of the third semiconductor layer and the fourth semiconductor layer, A step of directly joining the first bonding surface of the third semiconductor layer located on the opposite side of the surface on which the second semiconductor layer is arranged to the second bonding surface of the fourth semiconductor layer, A method for manufacturing semiconductor lasers, including Section (10) The method for manufacturing a semiconductor laser according to item 9, wherein the direct bonding step is performed by surface activation bonding. Section (11) In the process of preparing the semiconductor part, The third semiconductor layer is, A first layer is a semiconductor layer containing the aforementioned first conductivity type impurity at a first concentration, A second layer containing the first conductivity type impurity at a third concentration greater than the second concentration and less than the first concentration, A method for manufacturing a semiconductor laser as described in item 9 or 10, including the method described in item 9 or 10. Section (12) In the process of forming the photonic crystal, the photonic crystal is formed by forming a plurality of holes in the third semiconductor layer. The method for manufacturing a semiconductor laser according to any one of items 9 to 11, wherein the upper ends of the plurality of holes are located on the bonding surface of the fourth semiconductor layer. Section (13) In the process of preparing the semiconductor part, A method for manufacturing a semiconductor laser according to any one of claims 9 to 12, wherein the third semiconductor layer is made of the same material as the fourth semiconductor layer.

[0061] While embodiments and modifications of this disclosure have been described above, the disclosure may be modified in detail, and changes in the combination and order of elements in the embodiments and modifications can be realized without departing from the claimed scope and spirit of this disclosure. [Explanation of Symbols]

[0062] 1 1st electrode 2 2nd electrode 3. Anti-reflective coating 4 Translucent electrode 5, 205 Light extraction surface 7 Photonic Crystals 7a Bottom end 7b Top 8 Hole gathering part 10 First semiconductor layer 20 Second Semiconductor Layer 30 Third Semiconductor Layer 30a 1st joint surface 31 1st layer 32 2nd layer 40, 340 Fourth semiconductor layer 40a, 340a 2nd joint surface 40b Top side 45. Distributed Bragg Reflective Coating (DBR Coating) 50 active layer 51. First barrier layer 52 Well layer 53 Second barrier layer 60 circuit boards 60a, 4a bottom side 70 holes 71 1st end 72 2nd end 75 Groove 80 holes 81 First Mask 82. Second Mask 85 Growth substrate 86 Resin layer 87 Support substrate 90 Semiconductor Division 100, 200, 300 semiconductor lasers 203a, 203b Light reflective film

Claims

1. A first semiconductor layer portion including an n-type semiconductor layer, An active layer provided on the first semiconductor layer, A second semiconductor layer portion including a p-type semiconductor layer provided on the active layer, A third semiconductor layer comprising a semiconductor layer containing an n-type impurity at a first concentration, provided on the second semiconductor layer, A fourth semiconductor layer comprising a semiconductor layer containing an n-type impurity at a second concentration, provided on the third semiconductor layer, Equipped with, The first concentration is higher than the second concentration. The third semiconductor layer is directly bonded to the fourth semiconductor layer. The third semiconductor layer includes holes that constitute a photonic crystal. The holes constituting the photonic crystal are provided so as to penetrate the second semiconductor layer or so as to have the lower end of the hole located within the second semiconductor layer. The second semiconductor layer and the third semiconductor layer are connected by a tunnel junction. Semiconductor laser.

2. The third semiconductor layer is A first layer is a semiconductor layer containing the n-type impurity at the first concentration, A second layer is a semiconductor layer containing an n-type impurity at a third concentration greater than the second concentration and less than the first concentration, Includes, The semiconductor laser according to claim 1, wherein the first layer and the second layer are provided in order from the second semiconductor layer side.

3. The third semiconductor layer includes the photonic crystal, The semiconductor laser according to claim 1 or 2, wherein the upper end of the hole constituting the photonic crystal is located at the junction surface of the fourth semiconductor layer.

4. The semiconductor laser according to claim 1 or 2, wherein the lower end of the hole constituting the photonic crystal is located within the second semiconductor layer.

5. The active layer includes one or more well layers and multiple barrier layers. The barrier layer includes at least a first barrier layer in contact with the first semiconductor layer and a second barrier layer in contact with the second semiconductor layer. The semiconductor laser according to claim 1 or 2, wherein the lower end of the hole constituting the photonic crystal is located within the second barrier layer.

6. The semiconductor laser according to claim 1 or 2, wherein the third semiconductor layer and the fourth semiconductor layer are made of the same material.

7. The semiconductor laser according to claim 1 or 2, wherein the first semiconductor layer, the second semiconductor layer, the third semiconductor layer, and the fourth semiconductor layer are all nitride semiconductor layers.

8. A distributed Bragg reflective film provided on the upper surface of the fourth semiconductor layer, A first electrode is positioned on the side surface of the distributed Bragg reflective film, The insulating region provided in the second layer of the third semiconductor layer, It further possesses, The semiconductor laser according to claim 2, wherein the insulating region is located directly below the first electrode, which is positioned on the side surface of the distributed Bragg reflective film.

9. A step of preparing a semiconductor portion comprising: a first semiconductor layer portion including an n-type semiconductor layer; an active layer provided on the first semiconductor layer portion; a second semiconductor layer portion including a p-type semiconductor layer provided on the active layer; and a third semiconductor layer portion provided on the second semiconductor layer portion including a semiconductor layer containing an n-type impurity at a first concentration, wherein the second semiconductor layer portion and the third semiconductor layer portion are tunnel-junctioned, A step of preparing a fourth semiconductor layer portion which includes a semiconductor layer containing an n-type impurity at a second concentration lower than the first concentration, A step of forming a photonic crystal by forming holes in the second semiconductor layer and the third semiconductor layer such that the holes penetrate the second semiconductor layer or the lower end of the holes is located within the second semiconductor layer, A step of directly joining the first bonding surface of the third semiconductor layer located on the opposite side of the surface on which the second semiconductor layer is arranged to the second bonding surface of the fourth semiconductor layer, A method for manufacturing semiconductor lasers, including

10. The method for manufacturing a semiconductor laser according to claim 9, wherein the direct bonding step is performed by surface activation bonding.

11. In the process of preparing the semiconductor part, The third semiconductor layer is A first layer is a semiconductor layer containing the aforementioned n-type impurity at a first concentration, A second layer containing the aforementioned n-type impurity at a third concentration greater than the second concentration and less than the first concentration, A method for manufacturing a semiconductor laser according to claim 9 or 10, including the method described in claim 9 or 10.

12. In the process of forming the photonic crystal, the photonic crystal is formed by forming a plurality of holes in the third semiconductor layer. The method for manufacturing a semiconductor laser according to claim 9 or 10, wherein the upper ends of the plurality of holes are arranged on the bonding surface of the fourth semiconductor layer.

13. In the process of preparing the semiconductor part, The method for manufacturing a semiconductor laser according to claim 9 or 10, wherein the third semiconductor layer is made of the same material as the fourth semiconductor layer.

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