Two-dimensional photonic crystal laser

Abstract

This two-dimensional photonic crystal laser 10 is provided with: a substrate 11 that is formed of an n-type semiconductor; a p-type cladding layer (p-type semiconductor layer ) 131 that is provided above the substrate 11, while being formed of a p-type semiconductor; an active layer 14 that is provided above the p-type cladding layer 131; a two-dimensional photonic crystal layer 16 that is provided above the active layer 14, while being formed by periodically arranging different-refractive-index regions 162 on a plate-like base material 161 that is formed of an n-type semiconductor, said different-refractive-index regions 162 being formed of a material which has a refractive index different from that of the base material 161; a first tunnel layer 121 that is provided between the substrate 11 and the p-type cladding layer 131, while being formed of an n-type semiconductor that has a higher carrier density than the substrate 11; a second tunnel layer 122 that is provided between the first tunnel layer 121 and the p-type cladding layer 131 so as to be in contact with the first tunnel layer 121, while being formed of a p-type semiconductor that has a higher carrier density than the p-type semiconductor layer; a first electrode 181 that is provided below the substrate 11 or within the substrate 11; and a second electrode 182 that is provided above the two-dimensional photonic crystal layer 16.

Description

[Technical field]

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

[0002] The two-dimensional photonic crystal laser comprises an active layer and a two-dimensional photonic crystal layer. The active layer emits light in a specific emission wavelength band by injecting carriers (holes, electrons). The two-dimensional photonic crystal layer has a structure in which modified refractive index areas with a different refractive index from that of a plate-shaped base material are periodically arranged in a two-dimensional pattern. The modified refractive index areas are made of holes (air) formed in the base material, or a material different from the material of the base material. In the two-dimensional photonic crystal laser, only light of a specific wavelength corresponding to the periodic length of the arrangement of the modified refractive index areas among the light generated in the active layer is amplified and lased, and is emitted as a laser beam in a direction perpendicular to the photonic crystal layer.

[0003] A two-dimensional photonic crystal laser generally includes layers having various functions other than the above-mentioned active layer and two-dimensional photonic crystal layer. 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 block layer, a two-dimensional photonic crystal layer, a second cladding layer, and a contact layer are laminated in this order on a substrate. Electrodes are provided on the lower side of the substrate and on the upper side of the contact layer. Each layer other than the electrodes is fabricated by epitaxial growth on the substrate. An n-type semiconductor, which is less expensive than a p-type semiconductor, is used as the material for the substrate. An n-type semiconductor having the same polarity as the substrate is used for the first cladding layer, and a p-type semiconductor is used for the carrier block layer, the base 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 base 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 cladding layer and the second cladding layer are provided to enhance the efficiency of light emission in the active layer and the efficiency of light amplification in the photonic crystal layer by facilitating the confinement of light between them. The carrier block layer is provided to prevent electrons from entering the photonic crystal layer. The contact layer is provided to facilitate the injection of holes from the upper electrode. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2007-258262 A [Patent Document 2] JP 2012-033705 A [Patent Document 3] JP 2018-144664 A Summary of the Invention [Problem to be solved by the invention]

[0006] As described above, in the two-dimensional photonic crystal laser described in Patent Document 1, a p-type semiconductor is used as the base material of the two-dimensional photonic crystal layer. Since holes generally have a lower mobility than electrons, a p-type semiconductor is used as the base material of the two-dimensional photonic crystal layer, in which the band gap and impurity concentration are set 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 made of an n-type semiconductor and the first and second cladding layers made of an n-type semiconductor. However, when light generated in the active layer is amplified in the two-dimensional photonic crystal layer, a part of the light is absorbed by the holes, which are free carriers, and therefore, a problem occurs in that the efficiency of laser oscillation decreases when the density of holes in the two-dimensional photonic crystal layer becomes high.

[0007] On the other hand, Patent Document 2 describes that in a two-dimensional photonic crystal laser having the same structure as Patent Document 1, the substrate and the first cladding layer may be made of p-type semiconductors, and the second cladding layer and the contact layer may be made of n-type semiconductors. In this configuration, since an n-type semiconductor is used as the base material of the two-dimensional photonic crystal layer, the carrier (electron) density can be made lower than when a p-type semiconductor is used. This makes it possible to suppress light absorption. However, since the substrate needs to be thicker than the other layers, using a p-type semiconductor, which is more expensive than an n-type semiconductor, for the substrate increases the material cost of the two-dimensional photonic crystal laser.

[0008] Patent Document 3 describes a photonic crystal laser having a structure in which a cladding layer made of an n-type semiconductor, a two-dimensional photonic crystal layer having a base material made of an n-type semiconductor, an active layer, a carrier block layer made of a p-type semiconductor, a cladding layer made of a p-type semiconductor, and a contact layer made of a p-type semiconductor are laminated in this order on a substrate made of an n-type semiconductor. Even in this structure, since the base material of the two-dimensional photonic crystal layer is an n-type semiconductor, the absorption of light by free carriers can be suppressed more than when a p-type semiconductor is used. However, when the modified refractive index region of the two-dimensional photonic crystal layer is made of holes, unevenness is formed on the surface opposite to the substrate. Even when the modified refractive index region is made of a material different from the base material, it is difficult to fabricate the modified refractive index region without unevenness being formed on the surface of the two-dimensional photonic crystal layer. Even if another layer is formed on the surface with such unevenness, unevenness remains on the upper surface of that layer. In the semiconductor light-emitting device of Patent Document 3, an active layer must be fabricated on such an uneven surface; however, since an active layer is generally fabricated by stacking multiple semiconductor layers that are thinner than the other layers in a two-dimensional photonic crystal laser, it is difficult to form an active layer with the desired characteristics on such an uneven surface.

[0009] The problem that the present invention aims to solve is to provide a two-dimensional photonic crystal laser that can suppress a decrease in the efficiency of laser oscillation in the two-dimensional photonic crystal layer and can be easily fabricated without increasing material costs. [Means for solving the problem]

[0010] The two-dimensional photonic crystal laser according to the present invention, which has been made to solve the above problems, comprises: a) a substrate made of an n-type semiconductor; b) a p-type semiconductor layer formed on the upper side of the substrate; Clad Layers, c) The p-type Clad an active layer disposed on the upper side of the layer; d) a two-dimensional photonic crystal layer provided above the active layer, the two-dimensional photonic crystal layer being formed by periodically arranging modified refractive index areas in a plate-shaped base material made of an n-type semiconductor and having a refractive index different from that of the base material; e) an n-type cladding layer made of an n-type semiconductor provided on the upper side of the two-dimensional photonic crystal layer; f) The substrate and the p-type Clad a first tunnel layer made of an n-type semiconductor having a higher carrier density than the substrate, the first tunnel layer being provided between the layers; g) The first tunnel layer and the p-type Clad the p-type Clad a second tunnel layer made of a p-type semiconductor having a higher carrier density than the p-type semiconductor; h) a first electrode disposed beneath or within the substrate; i) The above n-type cladding layer A second electrode provided on the upper side of the The present invention is characterized by comprising:

[0011] For the sake of convenience, the terms "upper" and "lower" are used to explain the positional relationship of each component, but these terms do not limit the orientation of the two-dimensional photonic crystal laser according to the present invention.

[0012] Before describing the operation of the two-dimensional photonic crystal laser according to the present invention, the roles of the first tunnel layer and the second tunnel layer will be described. In general, when an n-type semiconductor layer made of an n-type semiconductor and a p-type semiconductor layer made of a p-type semiconductor are in contact with each other, holes can pass when a voltage is applied that makes the p-type semiconductor layer side positive, whereas holes cannot pass when a voltage is applied that makes the n-type semiconductor layer side positive. However, by providing a first tunnel layer having a higher carrier (electron) density than the n-type semiconductor layer closer to the n-type semiconductor layer between the n-type semiconductor layer and the p-type semiconductor layer, and a second tunnel layer having a higher carrier (hole) density than the p-type semiconductor layer closer to the p-type semiconductor layer, holes can pass from the n-type semiconductor layer to the p-type semiconductor layer by the tunnel effect even when a voltage is applied that makes the n-type semiconductor layer side positive. 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, or the like.

[0013] The operation of the two-dimensional photonic crystal laser according to the present invention will now be described. In this two-dimensional photonic crystal laser, by applying a voltage between the two electrodes such that the first electrode is positive and the second electrode is negative, holes are injected from the first electrode and electrons are injected from the second electrode. Then, the first tunnel layer has a higher carrier density than the substrate (corresponding to the n-type semiconductor layer) and the second tunnel layer p-type cladding layer (see above p-type semiconductor layer equivalent to Since the carrier density is higher than that of the p-type semiconductor, the holes injected from the first electrode pass through the first tunnel layer and the second tunnel layer by the tunnel effect from the substrate as described above, and become a p-type Clad The holes and electrons reach the layer and are injected into the active layer. Meanwhile, the electrons injected from the second electrode pass through the two-dimensional photonic crystal and are injected into the active layer. Injection of holes and electrons into the active layer in this way causes light to be emitted in the active layer, and the light is amplified in the two-dimensional photonic crystal layer, resulting in laser oscillation.

[0014] 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, so that the carrier density when the same amount of current is passed can be lower than when a p-type semiconductor is used as the base material. Therefore, it is possible to suppress a decrease in the efficiency of laser oscillation caused by a part of the light being absorbed by free carriers in the two-dimensional photonic crystal layer.

[0015] Furthermore, in the two-dimensional photonic crystal laser according to the present invention, an n-type semiconductor, which is less expensive than a p-type semiconductor, is used for the substrate, so that an increase in material costs can be prevented.

[0016] Furthermore, in the two-dimensional photonic crystal laser of the present invention, the two-dimensional photonic crystal layer is provided on the opposite side of the substrate from the active layer, so that the active layer can be formed without being affected by unevenness on the surface of the two-dimensional photonic crystal layer, making it easy to fabricate an active layer with desired characteristics.

[0017] Other layers made of n-type semiconductors may be provided between the substrate and the first tunnel 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 block layer made of n-type semiconductor may be provided between the active layer and the two-dimensional photonic crystal layer. A cladding layer made of n-type semiconductor or a contact layer made of n-type semiconductor may be provided between the two-dimensional photonic crystal layer and the second electrode.

[0018] In addition, the second tunnel layer and the p-type Clad Between layers and / or p-type Clad Between the layer and the active layer, another layer made of a p-type semiconductor (for example, the second tunnel layer and the p-type Clad In this case, the laser light is emitted from the second electrode side to the outside of the two-dimensional photonic crystal laser.

[0019] The first tunnel layer and the second tunnel layer have a carrier density similar to that of the substrate or p-type CladThe two-dimensional photonic crystal laser according to the present invention further comprises a first tunnel layer and a second tunnel layer, and the second tunnel layer and the p-type Clad It is desirable to provide a reflective layer between the layers that reflects the laser light generated in the two-dimensional photonic crystal layer. This makes it possible to prevent a part of the laser light from being absorbed in the first tunnel layer and the second tunnel layer, in which the carrier density is higher than in the other layers. As such a reflective layer, for example, a Distribution Bragg Reflector (DBR) can be used, which is made up of multiple layers of two types of p-type semiconductors with different refractive indices stacked alternately.

[0020] Alternatively, a reflective layer may be provided between the two-dimensional photonic crystal layer and the second electrode. In this case, another layer (the cladding layer or contact layer described above) made of an n-type semiconductor may be present between the two-dimensional photonic crystal layer and the reflective layer and / or between the reflective layer and the second electrode. In this case, the laser light is emitted to the outside of the two-dimensional photonic crystal laser from the first electrode side.

[0021] In the two-dimensional photonic crystal laser according to the present invention, a groove provided on an upper surface of the two-dimensional photonic crystal laser, the groove having a bottom surface located between the upper surface and the lower surface of the substrate, and the groove having a frame-like shape in a cross section parallel to the two-dimensional photonic crystal layer; The first electrode is provided on a bottom surface of the groove. The following configuration can be adopted.

[0022] By providing the first electrode on the bottom surface of the groove (hence, within the substrate) having a bottom surface located between the upper and lower surfaces of the substrate in this manner, the electrical resistance between the first electrode and the active layer is smaller than when the first electrode is provided on the lower surface of the substrate, and charge can be supplied to the active layer more efficiently. Furthermore, by providing the first electrode on the bottom surface of the groove having a frame-like planar shape, the shape of the first electrode is also frame-like, and the laser light oscillated in the two-dimensional photonic crystal layer passes within the frame of this first electrode and is emitted to the outside from the surface of the substrate. Therefore, it is possible to prevent the first electrode from interfering with the emission of the laser light or causing unnecessary diffraction. Furthermore, when the first electrode is provided on the lower surface of the substrate, the second tunnel layer, the first tunnel layer, the p-type Clad In contrast, when providing the first electrode on the bottom surface of such a groove, the first electrode is formed on the same side as the second tunnel layer, etc., so there is no need to turn the substrate upside down during fabrication, making manufacturing easier.

[0023] The base material of the substrate and the two-dimensional photonic crystal layer is, for example, GaAs or n-type GaAs or n-type AlGaAs in which part of Ga in GaAs is replaced with Al, and p-type Clad For the first tunnel layer or the second tunnel layer, p-type GaAs or p-type AlGaAs can be used. In this example, it is preferable to use InGaAs for the first tunnel layer and the second tunnel layer. Of GaAs and AlGaAs, InGaAs has a smaller band gap and can increase the carrier density. However, since InGaAs is prone to absorbing light, when InGaAs is used as the material for the first tunnel layer or the second tunnel layer, it is necessary to use p-type Clad It may be desirable to provide a reflective layer between the layers.

[0024] In the two-dimensional photonic crystal laser according to the present invention, a semiconductor that is not carrier-doped may be used instead of an n-type semiconductor for the whole or part of the base material. When a semiconductor that is not carrier-doped is used for a part of the base material (an n-type semiconductor for the remaining part), the absorption loss of light due to free carriers is suppressed more than when the whole base material is made of an n-type semiconductor, and a current flows more easily from the second electrode side to the active layer side than when the whole base material is made of a semiconductor that is not carrier-doped. Furthermore, by using a semiconductor that is not carrier-doped for the whole base material, the absorption loss of light can be further suppressed. Effect of the Invention

[0025] The two-dimensional photonic crystal laser according to the present invention can suppress a decrease in efficiency of laser oscillation in the two-dimensional photonic crystal layer, and can be easily fabricated without increasing material costs. [Brief description of the drawings]

[0026] [Figure 1] 1 is a schematic configuration diagram showing a first embodiment of a two-dimensional photonic crystal laser according to the present invention. [Diagram 2] 1 is a perspective view showing a photonic crystal layer, a first electrode, and a second electrode of a two-dimensional photonic crystal laser according to a first embodiment. [Diagram 3] FIG. 2 is a diagram illustrating a carrier injection region in the active layer of the two-dimensional photonic crystal laser according to the first embodiment. [Figure 4] FIG. 2 is a schematic configuration diagram showing a second embodiment of a two-dimensional photonic crystal laser according to the present invention. [Diagram 5] 13 is a graph showing the results of a simulation of the optical output characteristics performed on two-dimensional photonic crystal lasers according to the second embodiment and a comparative example. [Figure 6] 1A and 1B are a schematic longitudinal sectional view and a top view showing a third embodiment of a two-dimensional photonic crystal laser according to the present invention. [Figure 7]5A and 5B are schematic configuration diagrams showing a modified example and another modified example of the two-dimensional photonic crystal laser of the first embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] An embodiment of a two-dimensional photonic crystal laser according to the present invention will be described with reference to FIGS.

[0028] (1) Configuration of the two-dimensional photonic crystal laser according to the first embodiment The two-dimensional photonic crystal laser 10 of the first embodiment includes, in order from the bottom of FIG. 1, a substrate 11, a first tunnel layer 121, a second tunnel layer 122, and a p-type cladding layer. layer 1 31, active layer 14, carrier block layer 15, two-dimensional photonic crystal layer 16, n-type cladding layer 132, and contact layer 17. A first electrode 181 is provided on the lower side of substrate 11 (the side opposite to first tunnel layer 121), and a second electrode 182 is provided on the upper side of contact layer 17 (the side opposite to n-type cladding layer 132).

[0029] The substrate 11 is made of an n-type semiconductor, and the first tunnel layer 121 is made of an n-type semiconductor having a higher carrier (electron) density than the substrate 11. The p-type cladding layer 131 is made of a p-type semiconductor, and the second tunnel layer 122 is made of a p-type semiconductor having a higher carrier (hole) density than the p-type cladding layer 131.

[0030] The active layer 14 emits light in a specific emission wavelength band when holes and electrons are injected into it. The active layer 14 is made of, for example, a multiple-quantum well (MQW) in which a large number of thin films made of indium gallium arsenide (InGaAs) and gallium arsenide (GaAs) are alternately stacked.

[0031] As shown in FIG. 2, the two-dimensional photonic crystal layer 16 has a configuration in which a plurality of modified refractive index areas 162 are periodically arranged two-dimensionally in a plate-shaped base material 161 made of an n-type semiconductor. The modified refractive index areas 162 are typically made of holes (air), but may be made of a material other than the base material 161. The modified refractive index areas 162 are arranged in a square lattice shape in the example shown in FIG. 2, but may be arranged in other shapes such as a triangular lattice shape. The planar shape of the modified refractive index areas 162 is an equilateral triangle in the example shown in FIG. 2, but may be arranged in other shapes such as a triangle other than an equilateral triangle, such as a right-angled triangle, a circle, an ellipse, etc. One modified refractive index area 162 may be formed by combining a plurality of holes or a material other than the base material 161.

[0032] The carrier block layer 15, the n-type cladding layer 132, and the contact layer 17 are all made of an n-type semiconductor.

[0033] First electrode 181 has a shape in which the center of a plate-shaped conductor is hollowed out, and has frame portion 1811 which is the part where the conductor remains, and window portion 1812 which is the part where the conductor is hollowed out (see FIG. 2). Second electrode 182 is made of a conductor plate provided at a position facing window portion 1812 of first electrode 181, and has an area smaller than that of window portion 1812 (see FIG. 2).

[0034] Specific examples of materials for each component of the two-dimensional photonic crystal laser 10 are shown below. The substrate 11 can be made of n-type GaAs, the first tunnel layer 121 can be made of n-type GaAs having an impurity concentration (for example, 10 to 100 times) higher than that of the substrate 11, the p-type cladding layer 131 can be made of p-type AlGaAs, and the second tunnel layer 122 can be made of GaAs having an impurity concentration (for example, 10 to 100 times) higher than that of the p-type cladding layer 131. The carrier block layer 15, the base material 161 of the two-dimensional photonic crystal layer 16, and the n-type cladding layer 132 can all be made of n-type AlGaAs, and the impurity concentrations of these three layers may be the same or different. The contact layer 17 can be made of n-type GaAs. The impurity concentration of each layer other than the first tunnel layer 121 and the second tunnel layer 122 is set so that each layer made of a p-type semiconductor is higher (for example, 10 to 100 times) than each layer made of an n-type semiconductor. The materials for each layer described here are merely examples, and other p-type semiconductors can be used for each layer exemplified as p-type GaAs or AlGaAs, and other n-type semiconductors can be used for each layer exemplified as n-type GaAs or AlGaAs. GaAs and AlGaAs can transmit light in the wavelength range of 0.7 to 1.0 μm.

[0035] The material of each of these layers may be semiconductors other than GaAs and AlGaAs, such as InP, GaN, and AlInGaAsP.

[0036] The first tunnel layer 121 can be produced by epitaxial growth on the substrate 11. Similarly, each layer from the second tunnel layer 122 to the contact layer 17 can be produced by epitaxial growth on the layer closest to the layer on the substrate 11 side.

[0037] The first electrode 181 and the second electrode 182 can be fabricated using a method such as vapor deposition using a metal such as gold.

[0038] The thickness of the substrate 11 is made sufficiently thicker than the thicknesses of the layers from the first tunnel layer 121 to the contact layer 17. This makes the distance between the second electrode 182 and the active layer 14 sufficiently smaller than the distance between the first electrode 181 and the active layer 14. In addition, the thicknesses of the first tunnel layer 121 and the second tunnel layer 122 are made sufficiently thinner than the thicknesses of the substrate 11 and the layers from the p-type cladding layer 131 to the contact layer 17. This makes it easier for holes injected from the first electrode 181 to reach the p-type cladding layer 131 (and further the active layer 14 via the p-type cladding layer 131), as described below. The thickness of each layer is, for example, 60 μm or more for substrate 11, 10 to 2000 nm for first tunnel layer 121, 10 to 2000 nm for second tunnel layer 122, 1 to 10 μm for p-type cladding layer 131, 1 to 10 μm for active layer 14, 1 to 100 nm for carrier block layer 15, 10 to 100 nm for two-dimensional photonic crystal layer 16, 10 to 1000 nm for n-type cladding layer 132, and 10 to 500 nm for contact layer 17.

[0039] (2) Operation of the two-dimensional photonic crystal laser of the first embodiment The operation of the two-dimensional photonic crystal laser 10 of the first embodiment will be described. When using this two-dimensional photonic crystal laser 10, a voltage is applied between these two electrodes, with the first electrode 181 being positive and the second electrode 182 being negative. This causes holes to be injected from the first electrode 181 and electrons to be injected from the second electrode 182 into the two-dimensional photonic crystal laser 10.

[0040] Holes injected from the first electrode 181 pass through the substrate 11, the first tunnel layer 121, the second tunnel layer 122, and the p-type cladding layer 131 and are introduced into the active layer 14. Here, since the substrate 11 and the first tunnel layer 121 are made of an n-type semiconductor, and the second tunnel layer 122 and the p-type cladding layer 131 are made of a p-type semiconductor, a reverse bias voltage is applied at the boundary between the first tunnel layer 121 and the second tunnel 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 such a reverse bias voltage is applied, usually almost no current flows across the boundary between the n-type semiconductor and the p-type semiconductor. However, in the present invention, the impurity concentration of the first tunnel layer 121 is higher than that of the substrate 11, and the impurity concentration of the second tunnel layer 122 is higher than that of the p-type cladding layer 131, so that it is possible to realize a state in which the carrier (electron) density in the first tunnel layer 121 and the carrier (hole) density in the second tunnel layer 122 are high. As a result, the holes injected from the first electrode 181 and introduced into the first tunnel layer 121 from the substrate 11 side can move to the second tunnel layer 122 by the tunnel effect, and are introduced from the second tunnel layer 122 through the p-type cladding layer 131 into the active layer 14.

[0041] On the other hand, electrons injected from second electrode 182 are introduced into active layer 14 through contact layer 17, two-dimensional photonic crystal layer 16, and carrier block layer 15. Note that carrier block layer 15 prevents holes from moving from active layer 14 to two-dimensional photonic crystal layer 16, and allows electrons supplied from two-dimensional photonic crystal layer 16 to move to active layer 14.

[0042] By introducing holes and electrons into the active layer 14 in this way, light of a specific emission wavelength band is generated in the active layer 14. At this time, 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, so that the area of ​​the charge injection region 19 (see FIG. 3) in the active layer 14 into which holes and electrons are injected is close to the area of ​​the second electrode 182 and sufficiently smaller than the area of ​​the first electrode 181. By injecting charges intensively into the charge injection region 19 having such a small area, it is possible to increase the output per unit area of ​​light generated in the active layer 14. Note that, for convenience of explanation, both FIG. 1 and FIG. 3 do not accurately show the thickness ratio of each layer, but FIG. 3, in which the substrate 11 is shown sufficiently thicker than the other layers, is closer to the actual thickness ratio between the substrate 11 and the other layers.

[0043] Of the light generated in active layer 14, only light of a predetermined wavelength corresponding to the periodic length of the arrangement of modified refractive index areas 162 is amplified in two-dimensional photonic crystal layer 16 to produce laser oscillation. Here, in the two-dimensional photonic crystal laser 10 of the first embodiment, base material 161 of two-dimensional photonic crystal layer 16 is made of an n-type semiconductor, and electrons have higher mobility than holes, so that the carrier density when the same amount of current is passed can be made smaller than when base material 161 is made of a p-type semiconductor. This makes it possible to prevent a portion of the light from being absorbed by free carriers (electrons) in base material 161, and thus to prevent a decrease in the efficiency of laser oscillation.

[0044] For example, when the material of the base material 161 is made of n-type GaAs, the mobility of electrons is higher than the mobility of holes, so that the carrier density required to pass the same amount of current can be reduced to about half compared to p-type GaAs. In addition, in GaAs, the light absorption coefficient for the same carrier density is about 40% lower in n-type GaAs than in p-type GaAs (when the carrier density is 2×10 17 cm -3Considering all of these factors together, by using n-type GaAs as the material for base material 161, light absorption can be reduced to about 1 / 3 to 1 / 5 compared to using p-type GaAs. Note that although the material for base material 161 has been described here as n-type GaAs, the carrier density and light absorption coefficient can also be reduced (although the numerical values ​​are different) when other n-type semiconductors such as AlGaAs are used as the material for base material 161, and similar effects can be obtained.

[0045] Additionally, by increasing the output per unit area of ​​the light generated in active layer 14 as described above, laser oscillation in two-dimensional photonic crystal layer 16 can be made easier to occur.

[0046] The laser light thus generated is emitted to the outside through the window 1812 of the first electrode 181 .

[0047] In 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 prevent a portion of the light from being absorbed by free carriers (electrons), and thus to prevent a decrease in the efficiency of laser oscillation.

[0048] Furthermore, since base material 161 made of an n-type semiconductor is used, there is no need to use a substrate made of a p-type semiconductor, and material costs can be reduced by using substrate 11 made of a cheaper n-type semiconductor.

[0049] Furthermore, by providing the first tunnel layer 121 and the second tunnel layer 122 between the substrate 11 and the p-type cladding layer 131, it is possible to use n-type semiconductors for both the base material 161 and the substrate 11, while providing the base material 161 on the opposite side of the substrate 11 as viewed from the active layer 14. This eliminates the need to fabricate the active layer 14 on the two-dimensional photonic crystal layer 16, and therefore allows the active layer 14 to be easily fabricated with desired characteristics without being affected by unevenness that occurs on the surface of the two-dimensional photonic crystal layer 16.

[0050] (3) Configuration of the two-dimensional photonic crystal laser according to the second embodiment The two-dimensional photonic crystal laser 20 of the second embodiment includes, in order from the bottom of FIG. 4, a substrate 11, a first tunnel layer 121, a second tunnel layer 122, a reflective layer 21, and a p-type cladding layer. layer 1 31, active layer 14, carrier block layer 15, two-dimensional photonic crystal layer 16, n-type cladding layer 132, and contact layer 17 are laminated. A first electrode 281 is provided on the lower side of substrate 11 (the side opposite to first tunnel layer 121), and a second electrode 282 is provided on the upper side of contact layer 17 (the side opposite to n-type cladding layer 132). Of these components, substrate 11, p-type cladding layer 131, active layer 14, carrier block layer 15, two-dimensional photonic crystal layer 16, n-type cladding layer 132, and contact layer 17 are similar to the respective components of two-dimensional photonic crystal laser 10 of the first embodiment, and therefore description thereof will be omitted.

[0051] The reflective layer 21 is made of a DBR. The DBR used in this embodiment is formed by alternately stacking a plurality of layers made of two types of p-type semiconductors with different refractive indices. For example, the reflective layer 21 can be made of two types of p-type AlGaAs layers with different Al contents stacked alternately.

[0052] The first tunnel layer 121 is made of an n-type semiconductor having a higher carrier density than the substrate 11, and the second tunnel layer 122 is made of a p-type semiconductor having a higher carrier density than the p-type cladding layer 131, which is the same as the two-dimensional photonic crystal laser 10 of the first embodiment. In this embodiment, both the first tunnel layer 121 and the second tunnel layer 122 use an n-type semiconductor (first tunnel layer 121) and a p-type semiconductor (second tunnel layer 122) having a higher carrier density than the first embodiment. When GaAs or AlGaAs (for example, n-type GaAs for the substrate 11 and p-type AlGaAs for the p-type cladding layer 131) are used for both the substrate 11 and the p-type cladding layer 131, n-type InGaAs can be suitably used for the first tunnel layer 121 and p-type InGaAs can be suitably used for the second tunnel layer 122. InGaAs is a semiconductor that has a smaller band gap than GaAs and AlGaAs, and can thereby increase the carrier density.

[0053] 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 that of the second electrode 282. For example, the first electrode 281 may be provided on the entire lower surface of the substrate 11, and the second electrode 282 may be provided only near the center of the upper surface of the contact layer 17. The material of the second electrode 282 is transparent to the laser light oscillated 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 light. For example, the material of the first electrode 281 may be a metal material such as gold, and the material of the second electrode 282 may be indium tin oxide (ITO).

[0054] (4) Operation of the two-dimensional photonic crystal laser according to the second embodiment The operation of the two-dimensional photonic crystal laser 20 of the second embodiment will be described. As in the first embodiment, when a voltage is applied such that the first electrode 281 side is positive and the second electrode 282 side is negative, holes are injected from the first electrode 281 and electrons are injected from the second electrode 282, and light of a specific emission wavelength band occurs in the active layer 14. At this time, since the area of ​​the first electrode 281 is larger than the area 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, electric charges are injected intensively into an area smaller than the first electrode 281 in the active layer 14, and the output per unit area of ​​light generated in the active layer 14 can be increased. Of the light generated in the active layer 14, only light of a predetermined wavelength corresponding to the periodic length of the arrangement of the modified refractive index areas 162 is amplified in the two-dimensional photonic crystal layer 16 and laser oscillation occurs.

[0055] The laser light thus generated is emitted from both the upper and lower surfaces of the two-dimensional photonic crystal layer 16, but the laser light emitted toward the first electrode 281 side is reflected by the reflective layer 21 and proceeds toward the second electrode 282 side without penetrating into the second tunnel layer 122 and the first tunnel layer 121. Therefore, regardless of whether the laser light is emitted from both the upper and lower surfaces of the two-dimensional photonic crystal layer 16, it is emitted to the outside directly from the upper surface of the contact layer 17 or by passing through the second electrode 182.

[0056] According to the two-dimensional photonic crystal laser 20 of the second embodiment, as in the two-dimensional photonic crystal laser 10 of the first 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 a part of light by free carriers (electrons), and to suppress a decrease in the efficiency of laser oscillation. In addition, it is not necessary to use a substrate made of a p-type semiconductor, and it is possible to reduce material costs by using the substrate 11 made of a cheaper n-type semiconductor. Furthermore, by providing the first tunnel layer 121 and the second tunnel layer 122 between the substrate 11 and the p-type cladding layer 131, it is possible to use an n-type semiconductor for both the base material 161 and the substrate 11, while providing the base material 161 on the opposite side of the substrate 11 as viewed from the active layer 14, and therefore it is possible to easily fabricate the active layer 14 having the desired characteristics without being affected by the unevenness occurring on the surface of the two-dimensional photonic crystal layer 16.

[0057] In addition to the same effects as those of the first embodiment, according to the two-dimensional photonic crystal laser 20 of the second embodiment, by providing the reflective layer 21 between the second tunnel layer 122 and the p-type cladding layer 131, the laser light does not penetrate into the first tunnel layer 121 and the second tunnel layer 122, which have a higher carrier density than the other layers, and it is possible to prevent a part of the laser light from being absorbed in the first tunnel layer 121 and the second tunnel layer 122. Furthermore, since the absorption of the laser light is prevented in this way, a material having a higher carrier density than the material used in the first embodiment, such as InGaAs, can be used for the first tunnel layer 121 and the second tunnel layer 122, thereby making it possible to increase the carrier density injected into the active layer 14 and further increase the intensity of the laser light.

[0058] FIG. 5 shows the results of simulating the optical output characteristics of a device having the structure of Patent Document 1 (when a base material made of a p-type semiconductor is used; hereafter referred to as the "Comparative Example") and a device having the structure of the second embodiment of the present invention (when a base material made of an n-type semiconductor is used; hereafter referred to as the "Example"). As described above, by using an n-type semiconductor (n-type GaAs), it is possible to suppress optical absorption to 1 / 3 to 1 / 5 compared to when a p-type semiconductor (p-type GaAs) is used, so the absorption loss was 5 cm in the Comparative Example. -1 In the example, the thickness is 1 cm, which is 1 / 5 of that in the comparative example. -1 The simulation was performed with the in-plane loss (loss radiated to the outside of the device in a direction parallel to the surface) at 3 cm for both the comparative example and the embodiment. -1 The radiation coefficient is 12 cm for the comparative example. -1 , 8 cm in the embodiment -1 The reduction in losses leads to a threshold current density of 0.6 kA cm -2 (Comparative example) to 0.2 kA cm -2 (Example), and the oscillation threshold current value is lowered. Furthermore, the slope efficiency is 0.79 W / A in the comparative example, whereas it is 0.88 W / A in the example. As described above, the reduction in loss in the example enables oscillation at a low threshold and operation with a high slope efficiency.

[0059] (5) Two-dimensional photonic crystal laser according to the third embodiment 6 shows a schematic configuration of a two-dimensional photonic crystal laser 30 of the third embodiment. This two-dimensional photonic crystal laser 30 differs from the two-dimensional photonic crystal lasers 10 and 20 of the first and second embodiments in that it has a groove 32 with a first electrode 381 provided on the bottom surface of the groove 32, and in that a reflective layer 31 is provided between the n-type cladding layer 132 and the contact layer 17. Hereinafter, a description of the same configuration as the two-dimensional photonic crystal lasers 10 and 20 of the first and second embodiments will be omitted, and only the above differences will be described.

[0060] The groove 32 is dug down from the surface of the contact layer 17 through the reflective layer 31, the n-type cladding layer 132, the two-dimensional photonic crystal layer 16, the carrier block layer 15, the active layer 14, the p-type cladding layer 131, the second tunnel layer 122, and the first tunnel layer 121 to a position between the upper and lower surfaces of the substrate 11. The shape (planar shape) of the groove 32 in a cross section parallel to the two-dimensional photonic crystal layer 16 (as well as other layers such as the contact layer 17) is frame-like. The shape of the first electrode 381 provided on the bottom surface of this groove 32 is frame-like similar to the planar shape of the groove 32, and is similar to the shape of the frame portion 1811 of the first electrode 181 in the first embodiment. Since the first electrode 381 is provided on the bottom surface of the groove 32 in this manner, the position of the first electrode 381 in the vertical direction is between the upper and lower surfaces of the substrate 11.

[0061] As described above, the reflective layer 31 is provided between the n-type cladding layer 132 and the contact layer 17. The reflective layer 31 may be made of a DBR, similar to the reflective layer 21 in the second embodiment.

[0062] According to the two-dimensional photonic crystal laser 30 of the third embodiment, by providing a first electrode 381 on the bottom surface of the groove 32 having a bottom surface located between the upper and lower surfaces of the substrate 11, the electrical resistance between the first electrode 381 and the active layer 14 is smaller than in the first embodiment in which the first electrode 181 is provided on the lower surface of the substrate 11. This allows charges to be supplied to the active layer 14 more efficiently.

[0063] Furthermore, according to the two-dimensional photonic crystal laser 30 of the third embodiment, the planar shape of the first electrode 381 is frame-shaped, so that 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. Therefore, it is possible to prevent the first electrode 381 from interfering with the emission of the laser light or causing unnecessary diffraction.

[0064] Furthermore, the two-dimensional photonic crystal laser 30 of the third embodiment is also easier to fabricate in the following respects. In the two-dimensional photonic crystal lasers 10 and 20 of the first and second embodiments, the layers such as the second tunnel layer 122 are fabricated on the upper surface of the substrate 11, and the first electrodes 181, 281 are fabricated on the lower surface, so that it is necessary to turn the substrate 11 upside down between fabricating the above layers and fabricating the first electrodes 181, 281. In contrast, in the two-dimensional photonic crystal laser 30 of the third embodiment, both the layers such as the second tunnel layer 122 and the first electrode 381 are fabricated on the upper surface of the substrate 11, so that it is not necessary to turn the substrate 11 upside down, and fabrication is easier.

[0065] Although two embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications are possible within the scope of the gist of the present invention.

[0066] For example, in the two-dimensional photonic crystal laser 10 of each of the above embodiments, an n-type semiconductor is used as the material of the base material 161, but in order to further suppress the absorption loss of light due to free carriers, a semiconductor that is not carrier-doped (indicated as "i" in the figure) may be used as the material of the base material 161A of the two-dimensional photonic crystal layer 16A, as shown in Fig. 7(a). Alternatively, in order to facilitate the flow of current from the second electrode 182 side to the active layer 14 side, an n-type semiconductor may be used for a part 1611 (30% in terms of area in one example) of the base material 161B of the two-dimensional photonic crystal layer 16B, and a semiconductor that is not carrier-doped may be used for the remaining part 1612 (70% in terms of area in the above example), as shown in Fig. 7(b).

[0067] In the two-dimensional photonic crystal laser 20 of the second embodiment, the second electrode 282 having an area smaller than that of the first electrode 281 is provided near the center of the upper surface of the contact layer 17. Alternatively, a window-shaped electrode having a frame and a window similar to the first electrode 181 in the first embodiment may be provided as the second electrode on the upper surface of the contact layer 17. In general, when an electrode covering the entire substrate is provided as one electrode as the first electrode 281 of the second embodiment, providing a window-shaped electrode as the other electrode makes it difficult to supply electric charges near the center of the two-dimensional photonic crystal layer. However, by using an n-type semiconductor for the cladding layer (n-type cladding layer 132) and the contact layer 17 provided between the second electrode 282 and the two-dimensional photonic crystal layer 16 as in the second embodiment, the mobility of electric charges (electrons) can be increased, so that electric charges can be supplied near the center of the two-dimensional photonic crystal layer 16 even if a window-shaped electrode is used for the second electrode 282.

[0068] 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, but it is also possible to provide the first electrode 381 on the bottom surface of the groove 32 and then provide a reflective layer 21 between the second tunnel layer 122 and the p-type cladding layer 131 instead of the reflective layer 31. Alternatively, it is also possible to provide the reflective layer 31 between the n-type cladding layer 132 and the contact layer 17 and then provide a first electrode 181 on the lower surface of the substrate 11 without providing the groove 32 and the first electrode 381 on the bottom surface of the groove 32.

[0069] In addition, the components of the two-dimensional photonic crystal lasers of the above embodiments and modifications may be combined as appropriate. [Explanation of symbols]

[0070] 10, 20, 30…2D Photonic Crystal Lasers 11...Substrate 121…First tunnel layer 122…Second tunnel layer 131...p-type cladding layer 132...n-type cladding layer 14…Active layer 15…Carrier block layer 16, 16A, 16B...2D photonic crystal layer 161, 161A, 161B...Base material 1611...Part of the base material 1612: Part of the base material (part other than 1611) 162...Modified refractive index area 17…Contact layer 181, 281, 381...1st electrode 1811…Frame 1812…Window section 182, 282...Second electrode 19...Charge injection region 21, 31...Reflection layer 32…Groove

Claims

1. a) A substrate made of an n-type semiconductor; b) A p-type cladding layer made of a p-type semiconductor provided on the upper side of the substrate; c) An active layer provided on the upper side of the p-type cladding layer; d) A two-dimensional photonic crystal layer provided on the upper side of the active layer, in which a region of different refractive index made of a material having a different refractive index from that of the base material is periodically arranged in a plate-shaped base material made of an n-type semiconductor; e) An n-type cladding layer made of an n-type semiconductor provided on the upper side of the two-dimensional photonic crystal layer; f) A first tunnel layer made of an n-type semiconductor having a higher carrier density than the substrate, provided between the substrate and the p-type cladding layer; g) A second tunnel layer made of a p-type semiconductor having a higher carrier density than the p-type cladding layer, provided in contact with the first tunnel layer between the first tunnel layer and the p-type cladding layer; h) A first electrode provided on the lower side or inside the substrate; i) A second electrode provided on the upper side of the n-type cladding layer A two-dimensional photonic crystal laser characterized by comprising the above.

2. The two-dimensional photonic crystal laser according to claim 1, further comprising a reflective layer for reflecting the laser light generated in the two-dimensional photonic crystal layer, provided between the second tunnel layer and the p-type cladding layer.

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

4. Further, a groove is provided from the upper surface on the upper side of the two-dimensional photonic crystal laser, having a bottom surface at a position between the upper surface and the lower surface of the substrate, and the shape in a cross section parallel to the two-dimensional photonic crystal layer is frame-shaped, The first electrode is provided on the bottom surface of the groove The two-dimensional photonic crystal laser according to any one of claims 1 to 3, characterized by the above.

5. The materials of the substrate and the base material of the two-dimensional photonic crystal layer are n-type GaAs or n-type AlGaAs, The material of the p-type cladding layer is p-type GaAs or p-type AlGaAs, The material of the first tunnel layer is n-type InGaAs, The material of the second tunnel layer is p-type InGaAs The two-dimensional photonic crystal laser according to claim 1 or 2, characterized by the above.

6. The two-dimensional photonic crystal laser according to any one of claims 1 to 4, characterized in that all or part of the base material is made of a semiconductor that is not carrier-doped instead of an n-type semiconductor.

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