JP6660052B2 - Optical switching element - Google Patents

Description

  The present invention relates to an optical switching element having a high withstand voltage used for power equipment, particularly to a photoconductive element and an optical coupling element using the same.

  2. Description of the Related Art In power equipment, a technology of controlling a drive system from a control system of the power equipment using an optical coupling element (photocoupler) is used. The optical coupling element guides the light emitted from the light emitting element of the control system to the drive system of the power equipment by an optical fiber, and switches the electric circuit of the drive system by the photoconductive element, and electrically connects the control system and the drive system. The control circuit can be protected from a high voltage of, for example, several hundred V or more and switching noise.

  A photoconductive element that receives light becomes conductive when irradiated with light, and therefore requires high light receiving sensitivity. Patent Document 1 discloses a photoconductive element including a light-receiving layer made of a non-doped GaAs-based semiconductor quantum well in order to enhance light-receiving sensitivity.

JP-A-4-346478

  2. Description of the Related Art In recent years, there has been an increasing demand for electric circuits used for power equipment to have higher withstand voltage and smaller size for energy saving and the like. Therefore, it is necessary to achieve both the miniaturization of the photocoupler, the high breakdown voltage of the photoconductive element, and the low resistance during conduction. In the photoconductive element of Patent Document 1, although the light receiving sensitivity is high, GaAs is The band gap is about 1.4 [eV], and it is difficult to increase the breakdown voltage. When a similar structure is made of gallium nitride, high withstand voltage can be easily achieved, but even if impurities are not doped due to spontaneous polarization of the material and piezo polarization generated by internal strain due to stress during crystal growth. Carriers are generated. As a result, the switching element is turned on before light irradiation, so that a switching element cannot be realized.

  In view of the above problems, an object of the present invention is to provide a photoconductive element having high light-receiving sensitivity, achieving both high withstand voltage and low resistance during conduction, and a compact optical coupling element using the same.

The photoconductive element according to the present invention,
A stacked body in which a plurality of GaN layers and a plurality of InGaN layers having a first In composition are alternately stacked on a substrate;
A first electrode and a second electrode are provided at both ends of the laminate,
At least one or both of the InGaN layer and the GaN layer having the first In composition of the stacked body contain at least one impurity selected from C (carbon), F (fluorine), or a transition metal at 1 × 10 ¹⁶ to contains a concentration of ^{2 × 10 19 [/ cm 3} ],
The wavelength of light absorbed by the first In composition-containing InGaN layer or the impurity-containing GaN layer is the wavelength of light having the same energy as the band gap energy of the GaN layer and the first In composition InGaN layer. It is characterized by being longer.

Further, the photoconductive element according to the present invention,
Longer than the wavelength of light having the same energy as the band gap energy of the GaN layer and the first In composition InGaN layer;
Irradiation of light having a wavelength that is absorbed by the first In composition-containing InGaN layer or the GaN layer containing impurities of the stacked body increases the electrical conductivity between the first electrode and the second electrode. I do.

In the configuration of such a photoconductive element,
The stacked structure of the GaN layer and the InGaN layer of the first In composition improves the light receiving sensitivity by spatial separation of electrons and holes, and the plurality of stacked structures reduces the number of channels through which carriers responsible for electrical conduction flow. The electric conductivity of the photoconductive element which has been secured and has become conductive by irradiation of light is increased (electrical resistance is reduced), and light is doped by doping impurities into the GaN layer and / or the InGaN layer of the first In composition. In addition to realizing a high breakdown voltage of the photoconductive element at the time of non-irradiation, irradiation with light having a relatively low energy with respect to the band gap energy (forbidden band width) of the InGaN layer of the first In composition causes a deep impurity level to be reduced. Excitation of carriers makes it possible to make the conductive state, and as a result, it is possible to provide a variety of photoconductive elements which are highly sensitive and which can achieve both high withstand voltage and low resistance.

That is, when the GaN layer and the InGaN layer are stacked as described above, high electrical conductivity is realized because carriers are generated by spontaneous polarization and piezo polarization. Further, one of the InGaN layer and the GaN layer, or both the InGaN layer and the GaN layer, contains C, F, and a transition metal as impurities at a concentration of 1 × 10 ¹⁶ to 2 × 10 ¹⁹ [/ cm ³ ]. By (doping), a deep level formed in the forbidden band by an impurity captures carriers, the resistance of the stacked body is increased, and a higher breakdown voltage of the photoconductive element can be realized. When no impurities are contained, the carriers are excited by light having a shorter wavelength (energy is larger) than the forbidden band width of the InGaN layer. However, by containing C, F, and transition metal in the above concentration range as impurities, Light having a longer wavelength (smaller energy) than the forbidden band width of the InGaN layer excites the carriers trapped by the deep level, so that the light can be detected.
As the transition metal, Fe (iron) can be used, but Sc (scandium), Ti (titanium), V (vanadium), Cr (chromium), Mn (manganese), Co (cobalt), Ni ( Nickel), Cu (copper), and Zn (zinc) can also be used.

Further, the photoconductive element according to the present invention,
A stacked body in which a plurality of GaN layers and a plurality of InGaN layers having a first In composition are alternately stacked on a substrate;
A first electrode and a second electrode are provided at both ends of the laminate,
The GaN layer contains at least one impurity selected from C (carbon), F (fluorine) or a transition metal at a concentration of 1 × 10 ¹⁶ to 2 × 10 ¹⁹ [/ cm ³ ], and the first In The InGaN layer having the composition does not contain the above impurities,
The wavelength of light absorbed by the impurity-containing GaN layer is longer than the wavelength of light having the same energy as the band gap energy of the GaN layer and the first In composition InGaN layer.

  In the configuration of such a photoconductive element, electrons and holes formed by light irradiation in the GaN layer are supplied from the GaN layer to the InGaN layer having the first In composition, function as carriers, and serve as carriers. Since has no impurities, carrier scattering is reduced, mobility is increased, and the on-resistance can be further reduced.

The optical coupling element according to the present invention,
A sapphire substrate is provided, at least one light-emitting element facing the laminate of the photoconductive elements,
The light emitting layer of the light emitting element has a second In composition InGaN layer,
The In composition of the second In composition InGaN layer is not less than the In composition of the first In composition InGaN layer of the laminate.

By adopting such a configuration of the optical coupling element,
The light emitting diode and the photoconductive element can be integrated, the optical coupling element can be miniaturized,
The band gap energy of the second In composition InGaN layer of the light emitting element is equal to or less than the band gap energy of the first In composition InGaN layer of the photoconductive element stack,
Light emitted from the second In composition InGaN layer makes the photoconductive element conductive,
Furthermore, by directly irradiating the light emitted from the light emitting element to the photoconductive element, light loss can be suppressed, and the irradiated light can be efficiently used for photoexcitation in the photoconductive element.

Note that the InGaN layer whose resistance has been increased by including a transition metal may be directly excited.
In particular, since the band of the InGaN layer is tilted due to polarization, when used as a light receiving element, the absorption wavelength becomes longer due to the Stark effect. On the other hand, when used as a light emitting element, the electric field is blocked by the injected carriers, so that the band becomes flat and the emission wavelength becomes shorter. By utilizing such characteristics, there is also an advantage that even if the InGaN layers having the same composition are used, a combination of a short emission wavelength and a long absorption wavelength is obtained, and even if the composition ratio is slightly shifted, direct excitation is possible.

In the present invention, InGaN is a ternary compound of In, Ga, and N represented by the chemical formula In _x Ga _1-x N (0 <x <1), and the In composition is represented by x in the above chemical formula. Equivalent to.

FIG. 2 is a cross-sectional view of the photoconductive element according to the first embodiment of the present invention. FIG. 9 is a sectional view of an optical coupling element according to a second embodiment of the present invention.

(First embodiment)
FIG. 1 is a sectional view of a photoconductive element according to the first embodiment of the present invention.
On a substrate, for example, a sapphire substrate 1, an InGaN layer 2a is formed, a GaN layer 3a is further formed, and a stacked body 4 in which InGaN layers 2a, 2b, 2c and GaN layers 3a, 3b, 3c are sequentially stacked alternately. Are formed. Note that a gallium oxide substrate, a GaN substrate, an AlN substrate, or the like may be used instead of the sapphire substrate.

  These GaN layers and InGaN layers can be formed by MOCVD. For example, TMG (trimethylgallium) and TEG (triethylgallium) as Ga (gallium) sources, ammonia and hydrazine as N (nitrogen) sources, and TMI (trimethylindium) and TEI (triethyl) as In (indium) sources. A gas such as indium) is used. The GaN layer and the InGaN layer can be alternately formed by controlling the flow rate ratio (partial pressure ratio) of these gases.

  Further, the In composition of the InGaN layer can be adjusted by setting the partial pressure ratio of the gas in the MOCVD method.

  The laminate 4 has, for example, a strip shape, and an anode electrode 5 and a cathode electrode 6 are formed at both ends. The sapphire substrate 1, the laminate 4, the anode electrode 5, and the cathode electrode 6 constitute a photoconductive element 7. The shape of the stacked body 4 is not limited to a strip shape, but may be a connected (connected) shape having both ends, and may be another shape such as a stepped shape, a rectangular wave shape, or an arc shape.

  Both ends of the laminate 4 are tapered to ensure ohmic contact between the laminate 4 and the anode electrode 5 and the cathode electrode 6. That is, as shown in FIG. 1, both end portions of the stacked body 4 have a shape having inclined side surfaces and a bottom surface in the lowermost InGaN layer 2a.

  When the shape of both ends of the laminate 4 is vertical, a conductive film for the electrodes of the anode electrode 5 and the cathode electrode 6, for example, a combination of Ti (titanium) and Al (aluminum) or Ni (nickel) and Au (gold) The coverage (step coverage) when forming a damaged alloy by vacuum evaporation or the like decreases, causing an increase in contact resistance or a disconnection failure when a high voltage is applied, which may result in a decrease in product yield. . Therefore, by forming both end portions of the stacked body 4 in a tapered shape, coverage at the time of forming the conductive film for an electrode can be improved. The tapered shape also has the effect of increasing the contact area between the InGaN layer and the anode electrode 5 and the cathode electrode 6 and reducing the contact resistance.

  For forming the tapered shape, a known etching method, for example, an etching method such as Japanese Patent Application Laid-Open No. H11-214747 can be used.

  When both ends of the laminate are vertical or overhanging, a p-type or n-type GAN or InGaN material is applied to the ends by MOCVD or the like, for example, by the method described in JP-A-2008-124262. It is effective to regrow in advance. An ohmic electrode may be formed on the regrown end by, for example, vacuum-depositing the above alloy and performing high-temperature treatment. When the material is regrown so that one of the ends becomes p-type and the other becomes n-type, diode-like characteristics can be imparted.

  Hereinafter, the operation of the photoconductive element 7 of FIG. 1 will be described.

  The photoconductive element 7 to which a voltage is applied between the anode electrode 5 and the cathode electrode 6 is irradiated with light emitted from a light emitting element of a control system (not shown) and guided by an optical fiber or the like. Compared to the GaN layer, the InGaN layer has a relatively small bandgap energy, and the impurity level formed by doping an impurity is smaller than the bandgap energy of the material itself of these layers. The wavelength of light to be applied is selected from wavelengths of light having energy smaller than the band gap of the GaN layer and the InGaN layer and larger than the impurity level.

  The irradiated light is absorbed in the InGaN layer and / or the GaN layer doped with impurities, and excites carriers. The excited carriers are electrically conducted by moving by the applied voltage, so that the photoconductive element 7 is in a conducting state (on state). In addition, when light is irradiated from the sapphire substrate 1 side, the irradiated light is transmitted without being absorbed by the sapphire substrate 1.

  In addition, as described above, since the stacked body 4 has a plurality of stacked structures of the GaN layer and the InGaN layer, the stacked body 4 has a plurality of channels through which carriers (electrons and holes) for performing electric conduction flow. Therefore, the plurality of stacked structures increase the electrical conductivity during light irradiation (the electrical conductivity between the conductive anode electrode 5 and the cathode electrode 6) and reduce the on-resistance (electrical resistance during conduction).

In the present photoconductive element, even if the number of layers of the GaN layer and the InGaN layer is increased, the wavelength of the irradiated light is longer than the wavelength of the absorption edge of InGaN. Is characterized by the absence of absorption. Accordingly, although the on-resistance decreases as the number of layers increases, the internal stress increases due to a difference in lattice constant between GaN and InGaN when the number of layers increases, and further, as described later, doped C, Since there is absorption of irradiation light by transition metals such as F and Fe, there is also a problem that the light does not reach the underlying InGaN layer even if it is too much. Further, as the number of stacked layers increases, the processing capacity (throughput) of the MOCVD apparatus for forming the stacked body 4 decreases, and the manufacturing cost increases. Therefore, the number of stacked GaN layers and InGaN layers does not exceed at most 100 and is in the range of ³ to 100. For example, the doping amount of Fe is 1 × 10 ¹⁸ [/ cm ³ ], and the film thickness of each is 10 to 10. Assuming light absorption of about several percent to about 10% for 50 [nm], the number of layers can be preferably 3 to 10 in consideration of manufacturing costs.

  It has been confirmed that there is no decrease in breakdown voltage (dielectric breakdown field) with an increase in the number of layers.

  Since the stacked GaN layer and InGaN layer have different lattice constants, piezoelectric polarization occurs in the InGaN layer due to stress caused by the difference in lattice constant, and a piezoelectric field is formed in the stacking direction of the GaN layer and the InGaN layer. Is done. As is clear from FIG. 2, the direction of the piezo electric field is perpendicular to the electric field generated by the applied voltage.

  The electrons and holes generated in the impurity-containing GaN layer or InGaN layer by light irradiation are transferred to the InGaN layer having a small band gap, and the two-dimensional electron gas and the two-dimensional hole gas are caused by the Stark effect caused by the piezoelectric field. And spatially separated into For this reason, recombination of electrons and holes is suppressed, and the electrical conductivity (light receiving sensitivity) of the photoconductive element at the time of light irradiation can be increased.

  Further, the thicknesses of the GaN layer and the InGaN layer of the stacked body 4 can be set by controlling the film formation time in the MOCVD method.

  Since the electrons and holes generated by light irradiation are spatially separated in the InGaN layer as described above, the recombination time of electrons and holes is adjusted by changing the thickness of the InGaN layer within the above range. It is possible. For example, when the thickness of the InGaN layer is reduced, the recombination time can be shortened. By adjusting the recombination time, it is possible to adjust the response speed to light irradiation and non-light irradiation. Further, as described above, the resistance (on-resistance) during conduction can be controlled by the number of stacked GaN layers and InGaN layers. Therefore, the response speed and the on-resistance can be controlled independently, and it is possible to easily provide photoconductive elements having various characteristics in accordance with customer requirements (specifications).

  Further, when the In composition is small, the effect of improving the electric conductivity due to the Stark effect also decreases. On the other hand, if the In composition is too large, crystal defects increase, the breakdown voltage without irradiation with light decreases, and the amount of expensive In source gas used increases, and the manufacturing cost increases. The In composition of the InGaN layer used in the present embodiment is preferably 5 to 20%.

Further, one or both of the InGaN layer and the GaN layer contained a transition metal such as C (carbon), F (fluorine) or Fe (iron) as an impurity in an amount of 1 × 10 ¹⁶ to 2 × 10 ¹⁹ [/ cm ³ ]. The stacked body 4 also has the effect of trapping carriers at a deep level formed in the forbidden band by these impurities and increasing the resistance (for example, JP-A-2015-57474).

Alternatively, a structure may be employed in which only the GaN layer contains the above concentration of impurities to increase the resistance and the InGaN layer does not contain impurities. In this case, the electrons and holes generated in the GaN layer by the light irradiation are supplied into the InGaN layer and function as carriers. , The mobility of carriers is increased and the conductivity of the InGaN layer is improved. As compared with the case where both layers contain impurities, although the breakdown voltage during non-irradiation is inferior, there is an advantage that the on-resistance is reduced. Note that, in this case, containing no impurity means that the InGaN layer does not substantially contain an impurity, and even if an impurity having a concentration of less than 1 × 10 ¹⁶ [/ cm ³ ] is contained, The effect is obtained.

  The impurity concentration of C can be determined by adjusting the film forming conditions of the InGaN layer by the MOCVD method, specifically, by adjusting the partial pressure of each source gas of MOCVD and the film forming temperature. In the case of a metal, for example, Fe, Cp2Fe is added as a source gas, and it can be determined by the conditions for forming the InGaN layer by the MOCVD method. Further, F can be introduced by ion implantation after the formation of the laminate 4. Note that C and Fe may be doped by ion implantation. Further, not only one element selected from transition metals such as C, F, and Fe, but also two or three elements may be doped so as to have an impurity concentration in the above range.

  Due to the doping of the impurity, a level of the doped impurity is generated in the band gap of the GaN layer and / or the InGaN layer. Therefore, light having an energy smaller than the band gap energy determined by the In composition of the GaN layer and / or the InGaN layer is absorbed. As described above, the light absorbed by the GaN layer and / or the InGaN layer by containing impurities is contained. Is shifted to the longer wavelength side.

  Further, by doping the GaN layer and / or the InGaN layer with the above impurities, the resistance of the photoconductive element 7 when light is not irradiated (non-conductive state) is increased, and the withstand voltage of the photoconductive element 7 is further increased. Can be. Therefore, the photoconductive element is operated (conducted) by light having energy smaller than the band gap energy, that is, light having a wavelength longer than the wavelength of light having energy corresponding to the band gap energy, as well as increasing the withstand voltage by the impurity doping. be able to.

  In addition, a laminate having an InGaN layer having a predetermined In composition is prepared in advance, and the type and the doping amount (impurity concentration) of the impurity to be doped by ion implantation according to the wavelength of light generated from the control system. The wavelength of the light at which the photoconductive element operates can be adjusted. Therefore, a photoconductive element customized for a specific wavelength of light according to customer requirements can be manufactured in a short delivery time.

  The critical electric field strength of GaN is predicted to be 3 [MV / cm], but it is experimentally confirmed that the critical electric field strength in the case of lamination is about 1 [MV / cm]. It is. Therefore, in the photoconductive element according to the present invention, for example, by setting the distance between the ends to 100 [μm], it is possible to obtain 10,000 [V] as the withstand voltage (dielectric breakdown field strength) when light is not irradiated. it can.

  As described above, according to the photoconductive element 7 of the present invention, the multilayer structure of the GaN layer and the InGaN layer reduces the resistance during light irradiation (conduction state) and reduces the space of the carrier due to the Stark effect. By the separation, the light sensitivity (light receiving sensitivity) can be improved. Furthermore, by doping an impurity that forms a deep level, the wavelength of light to be absorbed can be adjusted and a high breakdown voltage can be realized by the impurity species and the impurity concentration, which are parameters independent of the In composition. . Further, the response speed of the photoconductive element can be adjusted by the thickness of the InGaN layer. As a result, various photoconductive elements can be easily provided according to various customer's required specifications.

(Second embodiment)
FIG. 2 is a sectional view of an optical coupling element in which the photoconductive element according to the first embodiment and a light emitting element, for example, a light emitting diode, are fused.

  Hereinafter, an optical coupling element according to the second embodiment will be described with reference to FIG.

  As shown in FIG. 2, a light emitting layer having a quantum well structure in which a buffer layer 9 made of a GaN layer, an n-type contact layer 10 made of Si-doped n-type GaN, and a GaN layer and an InGaN layer are alternately stacked on a sapphire substrate 8. 11 (active layer), a Mg-doped p-type AlGaN layer 12, and a stacked structure of a p-type contact layer 13 made of Mg-doped p-type GaN. The n-type contact layer 10 has an n-type contact layer made of Ti and Al. On the mold electrode 14 and the p-type contact layer 13, a p-type electrode 15 made of Ni and Au is formed. A light emitting diode 16 is constituted by the stacked structure of the GaN-based semiconductor on the sapphire substrate 8 and the n-type electrode 14 and the p-type electrode 15. The light emitting layer 11 may be a single InGaN layer.

  The sapphire substrate 8 of the light emitting diode 16 is joined to the sapphire substrate 1 of the photoconductive element 7, and the photoconductive element 7 and the light emitting diode 16 are joined to face each other via the sapphire substrate. Therefore, the photoconductive element 7 and the light emitting diode 16 are located close to each other.

  The fusion of the light emitting diode 16 and the photoconductive element 7 constitutes one optical coupling element 17, and the light emitted from the light emitting diode 16 is directly irradiated on the photoconductive element 7 without being absorbed by the sapphire substrate. You.

  Note that the sapphire substrate 1 and the sapphire substrate 8 can be bonded to each other by, for example, irradiating argon ions in a vacuum to activate the sapphire substrate and bonding them together in a vacuum using a surface activation method. In the configuration of the embodiment, the light emitting diode and the photoconductive element can be easily combined. Further, the sapphire substrate 1 and the sapphire substrate 8 may be bonded using water glass. Further, by using the c-plane sapphire substrate, the sapphire substrate 1 and the sapphire substrate 8 are made to be the same sapphire substrate, and the light emitting diode and the photoconductive element are formed on the front surface and the back surface (opposing surface), respectively, and integrated. Is also good.

  FIG. 2 shows an example in which three light emitting diodes having the same structure are joined on the photoconductive element 7, but the number is not limited to three, and one or more arbitrary numbers are joined as necessary. be able to. Although the three light emitting diodes in FIG. 2 are formed on separate sapphire substrates, a plurality of light emitting diodes formed on the same sapphire substrate may be joined to a sapphire substrate of a photoconductive element. .

  As described above, since the light emitting diode 16 is electrically insulated from the photoconductive element 7 by the sapphire substrate 8 and the sapphire substrate 1, the light emitting diode 16 is not affected by the voltage applied to the photoconductive element 7. The withstand voltage between the light emitting diode 16 and the photoconductive element 7 can be adjusted by the total film thickness of the sapphire substrate 8 and the sapphire substrate 1, and the thicker the film thickness, the higher the withstand voltage. Therefore, the required film thickness may be set according to the voltage applied to the photoconductive element 7, for example.

  Further, the present optical coupling element 17 is entirely surrounded by a light-shielding member, for example, a mold resin or ceramic, by a known mounting technique, to prevent the influence of unnecessary extraneous light, and to provide an n-type electrode 14 and a p-type electrode 15. The anode electrode 5 and the cathode electrode 6 can be connected to external terminals by using a wire bonding technique.

  Hereinafter, the operation principle of the optical coupling element 17 will be described.

  When a necessary power is supplied between the n-type electrode 14 and the p-type electrode 15 in the optical coupling element 17, light is generated in the light emitting layer 11 of the light emitting diode 16 by recombination of electrons and holes. The light generated in the light emitting layer 11 passes through the n-type contact layer 10 composed of a GaN layer, the buffer layer 9 and the sapphire substrate 8, and irradiates the photoconductive element 7. The light applied to the photoconductive element 7 passes through the sapphire substrate 1 and is absorbed by the InGaN layer of the stacked body 4. As a result, as described in the first embodiment, the photoconductive element 7 becomes conductive.

  By setting the bandgap energy of the InGaN layer of the light emitting layer 11 of the light emitting diode 16 to be equal to or less than the bandgap energy of the InGaN layer of the stacked body 4 of the photoconductive element 7, light emitted from the light emitting diode 16 can be reduced. 7, and the photoconductive element 7 becomes conductive. That is, by setting the In composition of the InGaN layer of the light emitting layer 11 of the light emitting diode 16 to be equal to or greater than the In composition of the InGaN layer of the stacked body 4 of the photoconductive element 7, light emitted from the light emitting diode 16 is transmitted to the photoconductive element 7. Absorbed.

  In the present optical coupling element 17, the distance between the light emitting diode 16 and the photoconductive element 7 can be accurately determined by the total film thickness of the hard sapphire substrate 8 and the sapphire substrate 1, and the distance can be precisely determined in accordance with the required withstand voltage. Can be set. Therefore, it is not necessary to set the distance unnecessarily long in consideration of the variation. As a result, light emitted from the light emitting diode 16 can be efficiently used for photoexcitation (photoelectric conversion) in the photoconductive element 7, and variation in product performance due to variation in the distance between the light emitting diode and the photoconductive element is reduced. can do.

  As the light emitting diode, for example, a light emitting diode on a sapphire substrate using a GaN-based semiconductor by a known manufacturing method such as Japanese Patent Laid-Open No. 11-261108 and Japanese Patent Laid-Open No. 11-14749 may be used. The wavelength of the emitted light determined by the band gap energy of the light emitting layer (active layer) of the light emitting diode may be a wavelength that is absorbed by the InGaN layer of the stacked body 4 of the photoconductive element 7 and not absorbed by the GaN layer.

  As described above, by combining the light emitting diode and the photoconductive element via the sapphire substrate and integrating them, it is possible to provide an optical coupling element having various characteristics such as small size, high withstand voltage, high noise resistance, and high sensitivity. be able to.

REFERENCE SIGNS LIST 1 sapphire substrate 2 a, 2 b, 2 c InGaN layer 3 a, 3 b, 3 c GaN layer 4 laminate 5 anode electrode 6 cathode electrode 7 photoconductive element 8 sapphire substrate 9 buffer layer 10 n-type contact layer 11 light-emitting layer 12 p-type AlGaN layer 13 p-type contact layer 14 n-type electrode 15 p-type electrode 16 light-emitting diode 17 optical coupling device

Claims (4)

A stacked body in which a GaN layer and an InGaN layer having a first In composition are alternately stacked on a substrate;
A first electrode and a second electrode are provided at both ends of the laminate,
At least one of the first In composition InGaN layer and / or the GaN layer of the laminate has at least one impurity selected from C, F or transition metal in a concentration of 1 × 10 ¹⁶ to 2 × 10 Contained at a concentration of ¹⁹ [/ cm ³ ],
The wavelength of light absorbed by the first In composition-containing InGaN layer containing the impurity or the GaN layer containing the impurity depends on the band gap energy of the GaN layer and the first In composition InGaN layer. A photoconductive element having a wavelength longer than that of light having the same energy. The photoconductive element according to claim 1 is
Longer than the wavelength of light having the same energy as the bandgap energy of the GaN layer and the first In composition InGaN layer of the laminate,
The electric conductivity between the first electrode and the second electrode is increased by irradiation with light having a wavelength absorbed by the first In composition-containing InGaN layer containing the impurity or the GaN layer containing the impurity. It is characterized by doing. A stacked body in which a plurality of GaN layers and a plurality of InGaN layers having a first In composition are alternately stacked on a substrate;
A first electrode and a second electrode are provided at both ends of the laminate,
The GaN layer of the laminate contains at least one impurity selected from C (carbon), F (fluorine), and transition metal at a concentration of 1 × 10 ¹⁶ to 2 × 10 ¹⁹ [/ cm ³ ]. The InGaN layer of the first In composition does not contain the impurity,
The wavelength of light absorbed by the impurity-containing GaN layer of the stacked body is longer than the wavelength of light having the same energy as the band gap energy of the GaN layer and the first In composition InGaN layer. The photoconductive element according to claim 1 or 2, wherein The substrate of the photoconductive element according to claim 1, wherein the substrate is a sapphire substrate, and the photoconductive element includes at least one light emitting element facing the stacked body of the photoconductive element via the sapphire substrate. ,
The light emitting layer of the light emitting element has an InGaN layer having a second In composition,
The optical coupling element, wherein the In composition of the second In composition InGaN layer is not less than the In composition of the first In composition InGaN layer of the laminate.

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