Two-dimensional photonic crystal lasers

Abstract

The two-dimensional photonic crystal laser comprises: a substrate composed of an n-type semiconductor; a p-type cladding layer (p-type semiconductor layer) disposed on the upper side of the substrate and composed of a p-type semiconductor; an active layer disposed on the upper side of the p-type cladding layer; a two-dimensional photonic crystal layer disposed on the upper side of the active layer and formed by periodically disposing different refractive index regions composed of a material having a refractive index different from that of the base material in a plate-shaped base material composed of an n-type semiconductor; a first tunneling layer disposed between the substrate and the p-type cladding layer and composed of an n-type semiconductor having a carrier density higher than that of the substrate; a second tunneling layer disposed between the first tunneling layer and the p-type cladding layer in contact with the first tunneling layer and composed of a p-type semiconductor having a carrier density higher than that of the p-type semiconductor layer; a first electrode disposed on the lower side of or within the substrate; and a second electrode disposed on the upper side of the two-dimensional photonic crystal layer.

Description

Technical Field

[0001] The present invention relates to a two-dimensional photonic crystal laser which amplifies light using a two-dimensional photonic crystal. Background Art

[0002] A two-dimensional photonic crystal laser comprises an active layer and a two-dimensional photonic crystal layer. The active layer generates light of a specific wavelength range by being injected with carriers (holes, electrons). The two-dimensional photonic crystal layer has a structure in which different refractive index regions having a refractive index different from that of the parent material are periodically arranged in a two-dimensional manner on a plate-like parent material. The different refractive index regions include holes (air) formed in the parent material or components made of a material different from that of the parent material. In a two-dimensional photonic crystal laser, among the light generated by the active layer, only light of a specified wavelength corresponding to the period length of the arrangement of the different refractive index regions is amplified and laser oscillated, and is emitted as a laser beam in a direction perpendicular to the photonic crystal layer.

[0003] Generally speaking, in addition to the above-mentioned active layer and two-dimensional photonic crystal layer, a two-dimensional photonic crystal laser also has layers with various functions. For example, the two-dimensional photonic crystal laser described in Patent Document 1 has a structure in which a first cladding layer, an active layer, a carrier blocking layer, a two-dimensional photonic crystal layer, a second cladding layer, and a contact layer are stacked in this order on a substrate. Electrodes are provided on the lower side of the substrate and the upper side of the contact layer. Each layer other than the electrode is produced by epitaxial growth on the substrate. An n-type semiconductor, which is cheaper than a p-type semiconductor, is used as the material of the substrate. Moreover, an n-type semiconductor with the same polarity as the substrate is used in the first cladding layer, and a p-type semiconductor is used in the carrier blocking layer, the mother material of the two-dimensional photonic crystal layer, the second cladding layer, and the contact layer. In this two-dimensional photonic crystal laser, holes are injected into the active layer from the upper electrode through the contact layer, the second cladding layer, and the mother material of the two-dimensional photonic crystal layer, and electrons are injected into the active layer from the lower electrode through the substrate and the first cladding layer.

[0004] The first and second cladding layers are provided to enhance the luminescence efficiency of the active layer and the light amplification efficiency of the photonic crystal layer by facilitating light confinement between them. The carrier blocking layer is provided to prevent electrons from invading the photonic crystal layer. The contact layer is provided to facilitate hole injection from the upper electrode.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 2007-258262

[0008] Patent Document 2: Japanese Patent Application Laid-Open No. 2012-033705

[0009] Patent Document 3: Japanese Patent Application Laid-Open No. 2018-144664 Summary of the Invention

[0010] Problems to be solved by the invention

[0011] In the two-dimensional photonic crystal laser described in Patent Document 1, as described above, a material composed of a p-type semiconductor is used as the base material of the two-dimensional photonic crystal layer. Generally speaking, the mobility of holes is lower than that of electrons. Therefore, a p-type semiconductor with a set band gap, impurity concentration, etc. is used as the base material of the two-dimensional photonic crystal layer, so that the density of carriers (holes) in the two-dimensional photonic crystal layer is higher than the density of carriers (electrons) in the substrate composed of an n-type semiconductor and the first and second cladding layers composed of an n-type semiconductor. However, the following problem arises: when light generated in the active layer is amplified within the two-dimensional photonic crystal layer, part of the light is absorbed by holes, which are free carriers. Therefore, if the density of holes in the two-dimensional photonic crystal layer increases, the efficiency of laser oscillation decreases.

[0012] On the other hand, Patent Document 2 describes the following: In a two-dimensional photonic crystal laser having the same structure as Patent Document 1, a material composed of a p-type semiconductor can be used in the substrate and the first cladding layer, and a material composed of an n-type semiconductor can be used in the second cladding layer and the contact layer. In the case of this structure, since an n-type semiconductor is used in the base material of the two-dimensional photonic crystal layer, the carrier (electron) density can be reduced compared to the case of using a p-type semiconductor. Therefore, the absorption of light can be suppressed. However, the substrate needs to be thicker than the other layers, so if a p-type semiconductor, which is more expensive than an n-type semiconductor, is used in the substrate, the material cost of the two-dimensional photonic crystal laser increases.

[0013] In addition, Patent Document 3 describes a photonic crystal laser having a structure in which a cladding layer composed of an n-type semiconductor, a two-dimensional photonic crystal layer having a base material composed of an n-type semiconductor, an active layer, a carrier blocking layer composed of a p-type semiconductor, a cladding layer composed of a p-type semiconductor, and a contact layer composed of a p-type semiconductor are stacked in this order on a substrate composed of an n-type semiconductor. In this structure, the base material of the two-dimensional photonic crystal layer is also an n-type semiconductor, so the absorption of light by free carriers can be suppressed compared to the case of using a p-type semiconductor. However, when the different refractive index region of the two-dimensional photonic crystal layer includes holes, unevenness is formed on the surface of the two-dimensional photonic crystal layer on the side opposite to the substrate. When the different refractive index region includes a component made of a material different from that of the base material, it is also very difficult to produce the different refractive index region in a manner that does not form unevenness on the surface of the two-dimensional photonic crystal layer. Even if other layers are formed on such a surface with unevenness, unevenness will remain on the upper surface of the layer. The semiconductor light-emitting element of Patent Document 3 must have an active layer produced on such a surface with bumps and recesses, but the active layer is generally produced by stacking multiple semiconductor layers that are thinner than other layers in the two-dimensional photonic crystal laser. Therefore, it is difficult to form an active layer with desired characteristics on such a surface with bumps and recesses.

[0014] The problem to be solved by the present invention is to provide a two-dimensional photonic crystal laser that can suppress a decrease in laser oscillation efficiency in a two-dimensional photonic crystal layer and can be easily manufactured without increasing material costs.

[0015] Solutions for solving problems

[0016] The two-dimensional photonic crystal laser according to the present invention, which has been developed to solve the above-mentioned problems, comprises:

[0017] a) a substrate composed of an n-type semiconductor;

[0018] b) a p-type semiconductor layer, which is provided on the upper side of the substrate and is composed of a p-type semiconductor;

[0019] c) an active layer disposed on an upper side of the p-type semiconductor layer;

[0020] d) a two-dimensional photonic crystal layer disposed on the upper side of the active layer, formed by periodically disposing different refractive index regions composed of a material having a refractive index different from that of the base material within a plate-shaped base material composed of an n-type semiconductor;

[0021] e) a first tunneling layer, disposed between the substrate and the p-type semiconductor layer, and composed of an n-type semiconductor having a higher carrier density than that of the substrate;

[0022] f) a second tunneling layer, disposed between the first tunneling layer and the p-type semiconductor layer in contact with the first tunneling layer, and composed of a p-type semiconductor having a higher carrier density than that of the p-type semiconductor layer;

[0023] g) a first electrode disposed on the underside of the substrate or within the substrate; and

[0024] h) a second electrode, which is arranged on the upper side of the two-dimensional photonic crystal layer.

[0025] In addition, in order to explain the positional relationship of each component, the terms "upper" and "lower" are used for convenience, but these terms are not used to limit the direction of the two-dimensional photonic crystal laser involved in the present invention.

[0026] Before describing the operation of the two-dimensional photonic crystal laser of the present invention, the functions of the first tunneling layer and the second tunneling layer will be described. Generally speaking, when an n-type semiconductor layer composed of an n-type semiconductor contacts a p-type semiconductor layer composed of a p-type semiconductor, holes can pass through when a positive voltage is applied to the p-type semiconductor layer. In contrast, holes cannot pass through when a positive voltage is applied to the n-type semiconductor layer. However, by providing a first tunneling layer with a higher carrier (electron) density than that of the n-type semiconductor layer, located near the n-type semiconductor layer, between the n-type semiconductor layer and the p-type semiconductor layer, and providing a second tunneling layer with a higher carrier (hole) density than that of the p-type semiconductor layer, located near the p-type semiconductor layer, between the n-type semiconductor layer and the p-type semiconductor layer, holes can tunnel from the n-type semiconductor layer to the p-type semiconductor layer through the tunneling effect, even when a positive voltage is applied to the n-type semiconductor layer. These carrier (electron, hole) densities can be set by reducing the band gap of the p-type or n-type semiconductor, increasing the impurity concentration, and the like.

[0027] The operation of the two-dimensional photonic crystal laser involved in the present invention is described. In this two-dimensional photonic crystal laser, holes are injected from the first electrode and electrons are injected from the second electrode by applying a voltage between the two electrodes, with the first electrode side being positive and the second electrode side being negative. As a result, the carrier density of the first tunneling layer is higher than the carrier density of the substrate (equivalent to the n-type semiconductor layer), and the carrier density of the second tunneling layer is higher than the carrier density of the p-type semiconductor layer. Therefore, the holes injected from the first electrode pass through the first tunneling layer and the second tunneling layer from the substrate to the p-type semiconductor layer by the tunneling effect as described above, and are injected into the active layer. On the other hand, the electrons injected from the second electrode pass through the two-dimensional photonic crystal and are injected into the active layer. By injecting holes and electrons into the active layer in this way, light is emitted in the active layer, and laser oscillation is performed by amplifying the light in the two-dimensional photonic crystal layer.

[0028] According to the two-dimensional photonic crystal laser of the present invention, an n-type semiconductor is used as the base material of the two-dimensional photonic crystal layer. Therefore, compared to a case where a p-type semiconductor is used as the base material, the carrier density can be reduced when the same current flows. Consequently, it is possible to suppress the reduction in laser oscillation efficiency caused by partial absorption of light by free carriers within the two-dimensional photonic crystal layer.

[0029] Furthermore, in the two-dimensional photonic crystal laser according to the present invention, an n-type semiconductor, which is cheaper than a p-type semiconductor, is used in the substrate, and thus an increase in material cost can be prevented.

[0030] Furthermore, the two-dimensional photonic crystal layer of the two-dimensional photonic crystal laser involved in the present invention is arranged on the side opposite to the substrate when viewed from the active layer, so the active layer can be formed without being affected by the surface unevenness of the two-dimensional photonic crystal layer, thereby making it easy to produce an active layer with desired characteristics.

[0031] Other layers composed of n-type semiconductors may also be disposed between the substrate and the first tunneling layer, between the active layer and the photonic crystal layer, and / or between the photonic crystal layer and the second electrode. For example, a carrier blocking layer composed of an n-type semiconductor may be disposed between the active layer and the two-dimensional photonic crystal layer. A cladding layer composed of an n-type semiconductor or a contact layer composed of an n-type semiconductor may also be disposed between the two-dimensional photonic crystal layer and the second electrode.

[0032] Alternatively, another layer composed of a p-type semiconductor (e.g., a reflective layer between the second tunneling layer and the p-type semiconductor layer as described below) may be provided between the second tunneling layer and the p-type semiconductor layer and / or between the p-type semiconductor layer and the active layer. In this case, laser light is emitted from the second electrode side to the outside of the two-dimensional photonic crystal laser.

[0033] The carrier density of the first tunneling layer and the second tunneling layer is higher than that of the substrate and the p-type semiconductor layer, so it is easy for free carriers to absorb the laser. Therefore, it is expected that the two-dimensional photonic crystal laser involved in the present invention also has a reflection layer between the second tunneling layer and the p-type semiconductor layer to reflect the laser generated in the two-dimensional photonic crystal layer. In this way, it is possible to prevent a portion of the laser from being absorbed in the first tunneling layer and the second tunneling layer where the carrier density is higher than that of other layers. As such a reflection layer, for example, a distributed Bragg reflector (DBR) can be used. The distributed Bragg reflector is obtained by alternately stacking layers composed of two p-type semiconductors with different refractive indices in units of multiple layers.

[0034] Alternatively, a reflective layer may be provided between the two-dimensional photonic crystal layer and the second electrode. In this case, another layer (the aforementioned cladding layer, contact layer) composed of an n-type semiconductor may be provided between the two-dimensional photonic crystal layer and the reflective layer and / or between the reflective layer and the second electrode. In this case, laser light is emitted from the first electrode side toward the exterior of the two-dimensional photonic crystal laser.

[0035] In the two-dimensional photonic crystal laser involved in the present invention, the following structure can be taken:

[0036] The substrate further comprises a groove, the groove being provided from the upper surface of the two-dimensional photonic crystal laser, the groove having a bottom surface between the upper surface and the lower surface of the substrate, the cross section of the groove being parallel to the two-dimensional photonic crystal layer being in a frame shape,

[0037] The first electrode is arranged on the bottom surface of the groove.

[0038] By arranging the first electrode on the bottom surface of the groove having a bottom surface at a position between the upper surface and the lower surface of the substrate (thus, inside the substrate), the resistance between the first electrode and the active layer becomes smaller than when the first electrode is arranged on the lower surface of the substrate, and the charge can be supplied to the active layer more efficiently. In addition, by arranging the first electrode on the bottom surface of the groove having a frame-shaped plane shape, the shape of the first electrode is also frame-shaped, and the laser light oscillating in the two-dimensional photonic crystal layer passes through the frame of the first electrode and is emitted from the surface of the substrate to the outside. Therefore, it is possible to suppress the emission of the laser light from being obstructed by the first electrode or generating unnecessary diffraction. In addition, when the first electrode is arranged on the lower surface of the substrate, the second tunneling layer, the first tunneling layer, the p-type semiconductor layer, etc. are made on one of the two surfaces of the substrate, and the first electrode is made on the other surface, so it is necessary to turn the substrate upside down during production. In contrast, when the first electrode is arranged on the bottom surface of the groove, the first electrode is made on the same side as the second tunneling layer, etc., so it is not necessary to turn the substrate upside down during production, and production becomes easy.

[0039] For example, n-type GaAs or n-type AlGaAs obtained by replacing a portion of Ga in GaAs with Al can be used as the material of the substrate and the base material of the two-dimensional photonic crystal layer, and p-type GaAs or p-type AlGaAs can be used in the p-type semiconductor layer. In this example, InGaAs is preferably used in the first tunnel layer and the second tunnel layer. InGaAs has a small band gap among GaAs and AlGaAs, which can increase the carrier density. However, InGaAs easily absorbs light, so when InGaAs is used as the material of the first tunnel layer or the second tunnel layer, it is desirable to provide a reflective layer between the second tunnel layer and the p-type semiconductor layer as described above.

[0040] In the two-dimensional photonic crystal laser involved in the present invention, a semiconductor that has not been carrier doped (carrier doping) can also be used in place of an n-type semiconductor for the entire or a portion of the base material. When a semiconductor that has not been carrier doped is used in a portion of the base material (and an n-type semiconductor is used in the remaining portion), compared to the case where the base material is entirely composed of an n-type semiconductor, the absorption loss of light caused by free carriers is suppressed, and compared to the case where the base material is entirely composed of a semiconductor that has not been carrier doped, current is more likely to flow from the second electrode side to the active layer side. In addition, by using a semiconductor that has not been carrier doped for the entire base material, the absorption loss of light can be further suppressed.

[0041] Effects of the Invention

[0042] According to the two-dimensional photonic crystal laser of the present invention, it is possible to suppress a decrease in the efficiency of laser oscillation in the two-dimensional photonic crystal layer and to easily manufacture the laser without increasing the material cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is a schematic configuration diagram showing a first embodiment of a two-dimensional photonic crystal laser according to the present invention.

[0044] Figure 2 This is a perspective view showing a photonic crystal layer, a first electrode, and a second electrode included in the two-dimensional photonic crystal laser according to the first embodiment.

[0045] Figure 3 This is a diagram schematically showing a carrier injection region in the active layer of the two-dimensional photonic crystal laser according to the first embodiment.

[0046] Figure 4 This is a schematic configuration diagram showing a second embodiment of the two-dimensional photonic crystal laser according to the present invention.

[0047] Figure 5 Graphs showing the results of simulations of light output characteristics of the two-dimensional photonic crystal lasers according to the second embodiment and a comparative example.

[0048] Figure 6 (a) and (b) are a schematic longitudinal sectional view and a plan view showing a third embodiment of a two-dimensional photonic crystal laser according to the present invention.

[0049] Figure 7 Schematic diagrams showing a modification (a) and another modification (b) of the two-dimensional photonic crystal laser according to the first embodiment. DETAILED DESCRIPTION

[0050] use Figures 1 to 7An embodiment of the two-dimensional photonic crystal laser according to the present invention will be described.

[0051] (1) Structure of the Two-Dimensional Photonic Crystal Laser of the First Embodiment

[0052] The two-dimensional photonic crystal laser 10 of the first embodiment has Figure 1 The structure is obtained by stacking a substrate 11, a first tunneling layer 121, a second tunneling layer 122, a p-type cladding layer (p-type semiconductor layer in the present invention) 131, an active layer 14, a carrier blocking layer 15, a two-dimensional photonic crystal layer 16, an n-type cladding layer 132, and a contact layer 17 in this order from the bottom side. A first electrode 181 is provided on the bottom side of the substrate 11 (the side opposite to the first tunneling layer 121), and a second electrode 182 is provided on the top side of the contact layer 17 (the side opposite to the n-type cladding layer 132).

[0053] The substrate 11 is composed of an n-type semiconductor, and the first tunneling layer 121 is composed of an n-type semiconductor having a higher carrier (electron) density than the substrate 11. The p-type cladding layer 131 is composed of a p-type semiconductor, and the second tunneling layer 122 is composed of a p-type semiconductor having a higher carrier (hole) density than the p-type cladding layer 131.

[0054] The active layer 14 emits light in a specific wavelength range by injecting holes and electrons. For example, the active layer 14 is composed of a multiple-quantum well (MQW), which is formed by alternating thin films of indium gallium arsenide (InGaAs) and gallium arsenide (GaAs).

[0055] like Figure 2 As shown, the two-dimensional photonic crystal layer 16 has a structure in which a plurality of different refractive index regions 162 are periodically arranged two-dimensionally on a plate-shaped matrix 161 composed of an n-type semiconductor. The different refractive index regions 162 are typically composed of holes (air), but components composed of materials other than the matrix 161 can also be used. Regarding the arrangement of the different refractive index regions 162, Figure 2 In the example shown, the shape of the lattice is square, but other shapes such as triangular lattice can also be used. Figure 2 In the example shown, the equilateral triangle is used, but other shapes such as a right triangle, a circle, an ellipse, etc. can also be used. In addition, a plurality of cavities or components made of materials other than the base material 161 can be combined to form a different refractive index region 162.

[0056] The carrier blocking layer 15 , the n-type cladding layer 132 , and the contact layer 17 are all made of an n-type semiconductor.

[0057] The first electrode 181 has a shape in which the center of a plate-like conductor is hollowed out, and includes a frame portion 1811 and a window portion 1812 (see FIG. Figure 2 ), wherein the frame portion 1811 is the portion where the conductor remains, and the window portion 1812 is the portion where the conductor is hollowed out. The second electrode 182 is formed by a conductive plate that is provided at a position facing the window portion 1812 of the first electrode 181 and has an area smaller than that of the window portion 1812 (see Figure 2 ).

[0058] Specific examples of the materials for each component of the two-dimensional photonic crystal laser 10 are shown. n-type GaAs can be used for the substrate 11, n-type GaAs with an impurity concentration higher than that of the substrate 11 (e.g., 10 to 100 times) can be used for the first tunneling layer 121, p-type AlGaAs can be used for the p-type cladding layer 131, and GaAs with an impurity concentration higher than that of the p-type cladding layer 131 (e.g., 10 to 100 times) can be used for the second tunneling layer 122. Furthermore, n-type AlGaAs can be used for the carrier blocking layer 15, the base material 161 of the two-dimensional photonic crystal layer 16, and the n-type cladding layer 132. The impurity concentrations of these three layers can be the same or different. n-type GaAs can be used for the contact layer 17. Regarding the impurity concentration in each layer other than the first tunnel layer 121 and the second tunnel layer 122, the impurity concentration in each layer composed of a p-type semiconductor is higher (for example, 10 to 100 times) than the impurity concentration in each layer composed of an n-type semiconductor. Furthermore, the materials for each layer described here are merely examples. For the p-type GaAs or AlGaAs layers exemplified, other p-type semiconductors can also be used, and for the n-type GaAs or AlGaAs layers exemplified, other n-type semiconductors can also be used. These GaAs and AlGaAs layers can transmit light in the wavelength range of 0.7 μm to 1.0 μm.

[0059] As materials for these layers, semiconductors such as InP, GaN, and AlInGaAsP other than GaAs and AlGaAs may be used.

[0060] The first tunnel layer 121 can be formed by epitaxial growth on the substrate 11. Similarly, each layer from the second tunnel layer 122 to the contact layer 17 can also be formed by epitaxial growth on the layer closest to the substrate 11 side.

[0061] The first electrode 181 and the second electrode 182 can be produced using a metal such as gold by using a vapor deposition method or the like.

[0062] The thickness of substrate 11 is sufficiently thicker than the thickness of each layer from first tunneling layer 121 to contact layer 17. Consequently, the distance between second electrode 182 and active layer 14 is sufficiently smaller than the distance between first electrode 181 and active layer 14. Furthermore, the thickness of first tunneling layer 121 and second tunneling layer 122 is sufficiently thinner than the thickness of each layer from substrate 11 and p-type cladding layer 131 to contact layer 17. Consequently, as described later, holes injected from first electrode 181 easily reach p-type cladding layer 131 (and, in turn, easily reach active layer 14 via p-type cladding layer 131). Regarding the thickness of each layer, for example, the substrate 11 is set to be greater than 60 μm, the first tunneling layer 121 is set to be 10 nm to 2000 nm, the second tunneling layer 122 is set to be 10 nm to 2000 nm, the p-type cladding layer 131 is set to be 1 μm to 10 μm, the active layer 14 is set to be 1 nm to 100 nm, the carrier blocking layer 15 is set to be 10 nm to 100 nm, the two-dimensional photonic crystal layer 16 is set to be 10 nm to 1000 nm, the n-type cladding layer 132 is set to be 1 μm to 2 μm, and the contact layer 17 is set to be 10 nm to 500 nm.

[0063] (2) Operation of the Two-Dimensional Photonic Crystal Laser of the First Embodiment

[0064] The operation of the two-dimensional photonic crystal laser 10 according to the first embodiment will be described. When using this two-dimensional photonic crystal laser 10, a voltage is applied between the first electrode 181, with a positive voltage applied to the first electrode 181 and a negative voltage applied to the second electrode 182. This causes holes to be injected into the two-dimensional photonic crystal laser 10 from the first electrode 181, and electrons to be injected into the two-dimensional photonic crystal laser 10 from the second electrode 182.

[0065] Holes injected from the first electrode 181 pass through the substrate 11, first tunneling layer 121, second tunneling layer 122, and p-type cladding layer 131 and are introduced into the active layer 14. Here, because the substrate 11 and first tunneling layer 121 are composed of an n-type semiconductor, and the second tunneling layer 122 and p-type cladding layer 131 are composed of a p-type semiconductor, a reverse bias voltage is applied to the boundary between the first tunneling layer 121 and the second tunneling layer 122, with the n-type semiconductor side being positive and the p-type semiconductor side being negative. As is well known in diodes, when this reverse bias voltage is applied, little current typically flows beyond the boundary between the n-type and p-type semiconductors. However, in the present invention, since the impurity concentration of first tunneling layer 121 is higher than that of substrate 11, and the impurity concentration of second tunneling layer 122 is higher than that of p-type cladding layer 131, a high carrier (electron) density in first tunneling layer 121 and a high carrier (hole) density in second tunneling layer 122 can be achieved. Consequently, holes injected from first electrode 181 and introduced into first tunneling layer 121 from the substrate 11 side can move toward second tunneling layer 122 through the tunneling effect, and from there, through p-type cladding layer 131, are introduced into active layer 14.

[0066] On the other hand, electrons injected from the second electrode 182 pass through the contact layer 17, the two-dimensional photonic crystal layer 16, and the carrier blocking layer 15 and are introduced into the active layer 14. Furthermore, the carrier blocking layer 15 prevents holes from migrating from the active layer 14 to the two-dimensional photonic crystal layer 16, allowing electrons supplied from the two-dimensional photonic crystal layer 16 to migrate toward the active layer 14.

[0067] By introducing holes and electrons into the active layer 14 in this manner, light emission in a specific wavelength range is generated in the active layer 14. At this time, since the area of ​​the first electrode 181 is larger than the area of ​​the second electrode 182, and the distance between the second electrode 182 and the active layer 14 is sufficiently smaller than the distance between the first electrode 181 and the active layer 14, the charge injection region 19 (see FIG. 1 ) in the active layer 14 into which holes and electrons are injected is formed. Figure 3 ) is close to the area of ​​the second electrode 182 and is sufficiently smaller than the area of ​​the first electrode 181. By injecting charges into the small-area charge injection region 19 in this manner, the output per unit area of ​​light generated in the active layer 14 can be increased. Figure 1 and Figure 3 For the sake of convenience, the thickness ratio of each layer is not accurately shown, but the substrate 11 is shown in a manner that is sufficiently thicker than other layers. Figure 3 This is close to the actual thickness ratio of the substrate 11 to other layers.

[0068] In the two-dimensional photonic crystal layer 16, only light of a predetermined wavelength corresponding to the periodic length of the arrangement of the different-refractive-index regions 162 is amplified from the light generated in the active layer 14, resulting in laser oscillation. In the two-dimensional photonic crystal laser 10 of the first embodiment, the base material 161 of the two-dimensional photonic crystal layer 16 is composed of an n-type semiconductor. The mobility of electrons is higher than the mobility of holes. Therefore, compared to a case where the base material 161 is composed of a p-type semiconductor, the carrier density can be reduced when the same current flows. Consequently, it is possible to suppress the absorption of a portion of the light by free carriers (electrons) in the base material 161, thereby suppressing a decrease in the efficiency of laser oscillation.

[0069] For example, when the base material 161 is composed of n-type GaAs, compared to the case of p-type GaAs, since the mobility of electrons is higher than the mobility of holes, the carrier density required for the same amount of current to flow can be reduced to about 1 / 2. In addition, in the case of GaAs, compared to p-type, the n-type can suppress the light absorption coefficient under the same carrier density to about 40% (carrier density is 2×10 17 cm -3 If these factors are taken into consideration, the use of n-type GaAs as the material for the base material 161 can suppress light absorption to approximately 1 / 3 to 1 / 5 compared to the case of using p-type GaAs. In addition, the description here uses n-type GaAs as the material for the base material 161 as an example, but when other n-type semiconductors such as AlGaAs are used as the material for the base material 161 (the values ​​are different), the carrier density and light absorption coefficient can also be suppressed, thereby achieving the same effect.

[0070] At the same time, by increasing the output per unit area of ​​light generated in the active layer 14 as described above, laser oscillation can be easily generated in the two-dimensional photonic crystal layer 16 .

[0071] The laser light generated in this manner is emitted to the outside from the window portion 1812 of the first electrode 181 .

[0072] According to the two-dimensional photonic crystal layer 16 of this embodiment, by using an n-type semiconductor as the material of the base material 161 of the two-dimensional photonic crystal layer 16 , it is possible to suppress absorption of part of light by free carriers (electrons) and suppress a decrease in laser oscillation efficiency.

[0073] Furthermore, since the base material 161 composed of an n-type semiconductor is used, it is not necessary to use a substrate composed of a p-type semiconductor. Instead, the substrate 11 composed of a cheaper n-type semiconductor can be used to reduce material costs.

[0074] Furthermore, by providing first tunneling layer 121 and second tunneling layer 122 between substrate 11 and p-type cladding layer 131, n-type semiconductors can be used for both base material 161 and substrate 11, and base material 161 can be provided on the side opposite to substrate 11 as viewed from active layer 14. This eliminates the need to form active layer 14 above two-dimensional photonic crystal layer 16, and therefore eliminates the effects of surface irregularities on two-dimensional photonic crystal layer 16, making it easy to form active layer 14 having desired properties.

[0075] (3) Structure of the Two-Dimensional Photonic Crystal Laser of the Second Embodiment

[0076] The two-dimensional photonic crystal laser 20 of the second embodiment has Figure 4 The structure is formed by stacking, starting from the bottom side of the substrate 11, a substrate 11, a first tunneling layer 121, a second tunneling layer 122, a reflective layer 21, a p-type cladding layer (p-type semiconductor layer in the present invention) 131, an active layer 14, a carrier blocking layer 15, a two-dimensional photonic crystal layer 16, an n-type cladding layer 132, and a contact layer 17. A first electrode 281 is provided on the bottom side of the substrate 11 (the side opposite to the first tunneling layer 121), and a second electrode 282 is provided on the top side of the contact layer 17 (the side opposite to the n-type cladding layer 132). The substrate 11, p-type cladding layer 131, active layer 14, carrier blocking layer 15, two-dimensional photonic crystal layer 16, n-type cladding layer 132, and contact layer 17 are the same as the components of the two-dimensional photonic crystal laser 10 of the first embodiment, and therefore their description is omitted.

[0077] The reflective layer 21 is composed of a DBR. The DBR used in this embodiment is formed by alternating multiple layers composed of two p-type semiconductors with different refractive indices. For example, a layer composed of two layers composed of p-type AlGaAs with different Al contents can be used as the reflective layer 21.

[0078] Similar to the two-dimensional photonic crystal laser 10 of the first embodiment, the first tunneling layer 121 is composed of an n-type semiconductor with a higher carrier density than that of the substrate 11, while the second tunneling layer 122 is composed of a p-type semiconductor with a higher carrier density than that of the p-type cladding layer 131. In this embodiment, both the first tunneling layer 121 and the second tunneling layer 122 use an n-type semiconductor (first tunneling layer 121) and a p-type semiconductor (second tunneling layer 122) with higher carrier densities than those in the first embodiment. When GaAs or AlGaAs is used for both the substrate 11 and the p-type cladding layer 131 (for example, n-type GaAs is used in the substrate 11 and p-type AlGaAs is used in the p-type cladding layer 131), n-type InGaAs can be preferably used for the first tunneling layer 121, and p-type InGaAs can be preferably used for the second tunneling layer 122. InGaAs is a semiconductor that can increase carrier density because its band gap is smaller than that of GaAs and AlGaAs.

[0079] The first electrode 281 is provided on the lower surface of the substrate 11, and the second electrode 282 is provided on the upper surface of the contact layer 17. The area of ​​the first electrode 281 is larger than the area of ​​the second electrode 282. For example, it is preferred that the first electrode 281 is provided on the entire lower surface of the substrate 11, and the second electrode 282 is provided only near the center of the upper surface of the contact layer 17. The material of the second electrode 282 is a material that is transparent to the laser oscillating in the two-dimensional photonic crystal layer 16. On the other hand, the material of the first electrode 281 may be either transparent or opaque to the laser. For example, a metal material such as gold can be used as the material of the first electrode 281, and indium tin oxide (ITO) can be used as the material of the second electrode 282.

[0080] (4) Operation of the Two-Dimensional Photonic Crystal Laser of the Second Embodiment

[0081] The operation of the two-dimensional photonic crystal laser 20 according to the second embodiment will be described. Similar to the first embodiment, when a positive voltage is applied to the first electrode 281 and a negative voltage is applied to the second electrode 282, holes are injected from the first electrode 281 and electrons are injected from the second electrode 282, generating light emission within a specific wavelength range within the active layer 14. In this case, the area of ​​the first electrode 281 is larger than that of the second electrode 282, and the distance between the second electrode 282 and the active layer 14 is sufficiently smaller than the distance between the first electrode 281 and the active layer 14. This allows concentrated charge injection into an area of ​​the active layer 14 that is smaller than the first electrode 281, thereby increasing the output per unit area of ​​light generated in the active layer 14. In the two-dimensional photonic crystal layer 16, only light of a predetermined wavelength corresponding to the periodic length of the arrangement of the different refractive index regions 162 is amplified, resulting in laser oscillation.

[0082] The laser light thus generated is emitted from both the upper and lower surfaces of the two-dimensional photonic crystal layer 16. However, the laser light emitted toward the first electrode 281 is reflected by the reflective layer 21 and does not penetrate into the second tunneling layer 122 and the first tunneling layer 121, but rather travels toward the second electrode 282. Therefore, the laser light emitted from either the upper or lower surface of the two-dimensional photonic crystal layer 16 is emitted directly to the outside from the upper surface of the contact layer 17 or is emitted through the second electrode 182.

[0083] According to the two-dimensional photonic crystal laser 20 of the second embodiment, similarly to the two-dimensional photonic crystal laser 10 of the first embodiment, by using an n-type semiconductor in the material of the base material 161 of the two-dimensional photonic crystal layer 16, it is possible to suppress a portion of the light from being absorbed by free carriers (electrons), thereby suppressing a decrease in the efficiency of laser oscillation. In addition, there is no need to use a substrate composed of a p-type semiconductor, and a substrate 11 composed of a cheaper n-type semiconductor can be used to suppress material costs. Furthermore, by providing a first tunneling layer 121 and a second tunneling layer 122 between the substrate 11 and the p-type cladding layer 131, it is possible to use an n-type semiconductor in both the base material 161 and the substrate 11, and the base material 161 can be provided on the side opposite to the substrate 11 when viewed from the active layer 14, thereby making it possible to easily produce an active layer 14 having desired characteristics without being affected by the unevenness generated on the surface of the two-dimensional photonic crystal layer 16.

[0084] In addition to the same effects as those of the first embodiment, the two-dimensional photonic crystal laser 20 of the second embodiment, by providing the reflective layer 21 between the second tunneling layer 122 and the p-type cladding layer 131, prevents laser light from penetrating the first tunneling layer 121 and the second tunneling layer 122, which have a higher carrier density than the other layers, thereby preventing a portion of the laser light from being absorbed in these first tunneling layers 121 and the second tunneling layer 122. Furthermore, since laser light absorption is prevented in this manner, materials such as InGaAs, which have a higher carrier density than the material used in the first embodiment, can be used for the first tunneling layer 121 and the second tunneling layer 122. This further increases the carrier density injected into the active layer 14, thereby further increasing the laser light intensity.

[0085] exist Figure 5The simulation results of the light output characteristics of the device of the structure of patent document 1 (the case of using a base material composed of a p-type semiconductor. Hereinafter referred to as a "comparative example") and the device of the structure of the second embodiment of the present invention (the case of using a base material composed of an n-type semiconductor. Hereinafter referred to as an "example") are shown. As described above, by using an n-type semiconductor (n-type GaAs), the absorption of light can be suppressed to 1 / 3 to 1 / 5 compared to the case of using a p-type semiconductor (p-type GaAs), so the absorption loss is set to 5 cm in the comparative example. -1 The simulation was carried out and the absorption loss in the embodiment was set to 1 / 5 of that in the comparative example, i.e. 1 cm -1 In addition, at this time, the in-plane loss (loss radiated to the outside of the device in a direction parallel to the surface) was set to 3cm in both the comparative example and the embodiment. -1 In the comparative example, the radiation coefficient is set to 12cm -1 And calculated, in the embodiment, the radiation coefficient is set to 8cm -1 By reducing the loss, the threshold current density is increased from 0.6 kA·cm -2 (Comparative Example) reduced to 0.2 kA·cm -2 (Example), the oscillation threshold current value is lowered. Furthermore, while the slope efficiency is 0.79 W / A in the comparative example, it is 0.88 W / A in the example. As described above, the example achieves low-threshold oscillation and high-slope-efficiency operation by reducing losses.

[0086] (5) Two-dimensional Photonic Crystal Laser of the Third Embodiment

[0087] Figure 6 The schematic structure of a two-dimensional photonic crystal laser 30 according to the third embodiment is shown. This two-dimensional photonic crystal laser 30 differs from the two-dimensional photonic crystal laser 10 according to the first embodiment and the two-dimensional photonic crystal laser 20 according to the second embodiment in that it includes a groove 32 with a first electrode 381 disposed on the bottom surface of the groove 32, and a reflective layer 31 disposed between the n-type cladding layer 132 and the contact layer 17. Below, descriptions of the same structures as the two-dimensional photonic crystal laser 10 according to the first embodiment and the two-dimensional photonic crystal laser 20 according to the second embodiment are omitted, and only the differences described above are described.

[0088] Groove 32 extends from the surface of contact layer 17 through reflective layer 31, n-type cladding layer 132, two-dimensional photonic crystal layer 16, carrier blocking layer 15, active layer 14, p-type cladding layer 131, second tunneling layer 122, and first tunneling layer 121, reaching a position between the upper and lower surfaces of substrate 11. The shape (planar shape) of the cross section of groove 32 parallel to two-dimensional photonic crystal layer 16 (and similarly to other layers such as contact layer 17) is frame-shaped. The shape of first electrode 381, disposed on the bottom surface of groove 32, is the same frame-shaped shape as the planar shape of groove 32, similar to the shape of frame portion 1811 of first electrode 181 in the first embodiment. By disposing first electrode 381 on the bottom surface of groove 32 in this manner, the vertical position of first electrode 381 becomes a position between the upper and lower surfaces of substrate 11.

[0089] As described above, the reflective layer 31 is provided between the n-type cladding layer 132 and the contact layer 17. As with the reflective layer 21 in the second embodiment, a reflective layer composed of a DBR can be used for the reflective layer 31.

[0090] According to the two-dimensional photonic crystal laser 30 of the third embodiment, a first electrode 381 is provided on the bottom surface of a groove 32 having a bottom surface located between the upper and lower surfaces of the substrate 11. This reduces the resistance between the first electrode 381 and the active layer 14 compared to the case of the first embodiment where the first electrode 181 is provided on the lower surface of the substrate 11. This allows for more efficient charge supply to the active layer 14.

[0091] Furthermore, according to the two-dimensional photonic crystal laser 30 of the third embodiment, the first electrode 381 has a frame-like planar shape. Therefore, the laser light passes through the frame of the first electrode 381 and is emitted to the outside from the surface of the substrate 11. This prevents the emission of the laser light from being obstructed by the first electrode 381 or from causing unnecessary diffraction.

[0092] Furthermore, the two-dimensional photonic crystal laser 30 of the third embodiment is also easy to manufacture in the following respects. In the two-dimensional photonic crystal laser 10 of the first embodiment and the two-dimensional photonic crystal laser 20 of the second embodiment, the second tunneling layer 122 and other layers are formed on the upper surface of the substrate 11, and the first electrodes 181 and 281 are formed on the lower surface. Therefore, the substrate 11 needs to be inverted between the formation of these layers and the formation of the first electrodes 181 and 281. In contrast, in the two-dimensional photonic crystal laser 30 of the third embodiment, both the second tunneling layer 122 and other layers and the first electrode 381 are formed on the upper surface of the substrate 11. Therefore, the substrate 11 does not need to be inverted, making manufacture easier.

[0093] As mentioned above, although two embodiments according to the present invention have been described, the present invention is not limited to these embodiments, and various modifications can be made within the scope of the gist of the present invention.

[0094] For example, in the two-dimensional photonic crystal laser 10 of each of the above-mentioned embodiments, an n-type semiconductor is used as the material of the base material 161, but it is also possible to Figure 7 As shown in (a) of FIG. 1 , a semiconductor that is not doped with carriers (represented as “i” in the figure) is used as the material of the base material 161A of the two-dimensional photonic crystal layer 16A to further suppress the absorption loss of light caused by free carriers. Alternatively, Figure 7 As shown in (b), an n-type semiconductor is used in a portion 1611 (in one example, the area ratio is 30%) of the base material 161B of the two-dimensional photonic crystal layer 16B, and a semiconductor that is not carrier-doped is used in the remaining portion 1612 (in the above example, the area ratio is 70%), so that current can easily flow from the second electrode 182 side to the active layer 14 side.

[0095] In the two-dimensional photonic crystal laser 20 of the second embodiment, a second electrode 282 having an area smaller than that of the first electrode 281 is disposed near the center of the upper surface of the contact layer 17. However, a window-shaped electrode having the same frame and window as the first electrode 181 in the first embodiment may alternatively be disposed on the upper surface of the contact layer 17 as the second electrode. Generally speaking, when an electrode covering the entire substrate is provided as one electrode, as in the first electrode 281 of the second embodiment, providing a window-shaped electrode as another electrode makes it difficult to supply charge near the center of the two-dimensional photonic crystal layer. However, as in the second embodiment, by using an n-type semiconductor in the cladding layer (n-type cladding layer 132) and the contact layer 17 disposed between the second electrode 282 and the two-dimensional photonic crystal layer 16, the mobility of charge (electrons) can be improved. Therefore, even if a window-shaped electrode is used as the second electrode 282, charge can be supplied near the center of the two-dimensional photonic crystal layer 16.

[0096] In the two-dimensional photonic crystal laser 30 of the third embodiment, a first electrode 381 is provided on the bottom surface of the groove 32, and a reflective layer 31 is provided between the n-type cladding layer 132 and the contact layer 17. However, after providing the first electrode 381 on the bottom surface of the groove 32, a reflective layer 21 may be provided between the second tunneling layer 122 and the p-type cladding layer 131 instead of the reflective layer 31. Alternatively, after providing the reflective layer 31 between the n-type cladding layer 132 and the contact layer 17, the groove 32 and the first electrode 381 on the bottom surface of the groove 32 may be omitted, and the first electrode 181 may be provided on the lower surface of the substrate 11.

[0097] Furthermore, the components of the two-dimensional photonic crystal lasers of the above-described embodiments and modifications may be appropriately combined.

[0098] Description of Reference Numerals

[0099] 10, 20, 30: two-dimensional photonic crystal laser; 11: substrate; 121: first tunneling layer; 122: second tunneling layer; 131: p-type cladding layer; 132: n-type cladding layer; 14: active layer; 15: carrier blocking layer; 16, 16A, 16B: two-dimensional photonic crystal layer; 161, 161A, 161B: base material; 1611: part of the base material; 1612: part of the base material other than 1611; 162: different refractive index region; 17: contact layer; 181, 281, 381: first electrode; 1811: frame; 1812: window; 182, 282: second electrode; 19: charge injection region; 21, 31: reflection layer; 32: groove.

Claims

1. A two-dimensional photonic crystal laser, characterized in that have: a) a substrate composed of an n-type semiconductor; b) a p-type semiconductor layer, which is provided on the upper side of the substrate and is composed of a p-type semiconductor; c) an active layer disposed on an upper side of the p-type semiconductor layer; d) a two-dimensional photonic crystal layer disposed on the upper side of the active layer, formed by periodically disposing different refractive index regions composed of a material having a refractive index different from that of the base material within a plate-shaped base material composed of an n-type semiconductor; e) a first tunneling layer, disposed between the substrate and the p-type semiconductor layer, and composed of an n-type semiconductor having a higher carrier density than that of the substrate; f) a second tunneling layer, disposed between the first tunneling layer and the p-type semiconductor layer in contact with the first tunneling layer, and composed of a p-type semiconductor having a higher carrier density than that of the p-type semiconductor layer; g) a first electrode disposed within the substrate; and h) a second electrode disposed on an upper side of the two-dimensional photonic crystal layer, The two-dimensional photonic crystal laser further comprises a groove, the groove being provided from the upper surface of the two-dimensional photonic crystal laser, the groove having a bottom surface between the upper surface and the lower surface of the substrate, and the cross section of the groove parallel to the two-dimensional photonic crystal layer being frame-shaped. The first electrode is arranged on the bottom surface of the groove.

2. The two-dimensional photonic crystal laser according to claim 1, characterized in that A reflective layer for reflecting the laser light generated in the two-dimensional photonic crystal layer is further provided between the second tunneling layer and the p-type semiconductor layer.

3. The two-dimensional photonic crystal laser according to claim 1, characterized in that A reflective layer for reflecting laser light generated in the two-dimensional photonic crystal layer is further provided between the two-dimensional photonic crystal layer and the second electrode.

4. The two-dimensional photonic crystal laser according to claim 1 or 2, characterized in that: The substrate and the base material of the two-dimensional photonic crystal layer are made of n-type GaAs or n-type AlGaAs. The material of the p-type semiconductor layer is p-type GaAs or p-type AlGaAs, The material of the first tunneling layer is n-type InGaAs, The material of the second tunneling layer is p-type InGaAs.

5. The two-dimensional photonic crystal laser according to any one of claims 1 to 3, characterized in that: The whole or part of the base material is composed of a semiconductor that is not doped with carriers, instead of being composed of an n-type semiconductor.

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