JP2005285401A - Light emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light emitting device equipped with a plurality of light emitting units in tandem, which can be driven by low voltage with high electric power efficiency. <P>SOLUTION: The light emitting device is equipped with a plurality of light emitting units 5 and a plurality of light emitting units 11 which are arranged in tandem between an anode 2 and a cathode 18. A charge inversion layer 8 which has an inorganic semiconductor pn junction consisting of an n-type semiconductor layer 6 arranged on an anode 2 side and a p-type semiconductor layer 7 arranged on a cathode 18 side, is disposed between the light emitting units 5 and the light emitting units 11. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a light emitting device in which a plurality of light emitting units are arranged in tandem between an anode and a cathode.

  In recent years, with the diversification of information equipment, there has been an increasing need for flat display devices that consume less power than CRTs (cathode ray tubes) that are generally used. As one of such flat display devices, an electroluminescence (EL) element having features such as high efficiency, thinness, light weight, and low viewing angle dependency has attracted attention, and development of a display using the EL element is active. Has been done. Such EL elements include an inorganic EL element having a light emitting layer made of an inorganic material and an organic EL element having a light emitting layer made of an organic material.

  In these light emitting elements, a light emitting element in which a plurality of light emitting units are arranged in tandem may be required. For example, a blue light emitting unit and an orange light emitting unit may be arranged in tandem to form a white light emitting element and used for a white light source. Further, by arranging the light emitting units in tandem, the light emission intensity may be increased and used as a light source for illumination.

In Patent Document 1, in an organic electroluminescence element (organic EL element) in which a plurality of light emitting units are arranged between opposing anodes and cathodes, a charge generation layer made of an electrically insulating layer is arranged between the light emitting units. Has been proposed. However, in the light emitting element having such a structure, a voltage drop occurs in the charge generation layer composed of an electrically insulating layer provided between the light emitting units, so that a high driving voltage is required, and the viewpoint of effective use of energy resources, etc. Therefore, it was not preferable.
JP 2003-272860 A

  An object of the present invention is to provide a light-emitting element having a novel structure that can be driven at a low voltage and has high power efficiency in a light-emitting element in which a plurality of light-emitting units are arranged in tandem.

  The present invention is a light-emitting element in which a plurality of light-emitting units are arranged in tandem between an anode and a cathode, and is an inorganic material comprising a p-type semiconductor layer disposed on the cathode side and an n-type semiconductor layer disposed on the anode side. A charge inversion layer having a semiconductor pn junction is provided between the light emitting units.

  In the present invention, a charge inversion layer is provided between the light emitting units, and when a forward voltage is applied between the anode and the cathode, a reverse bias is applied to the charge inversion layer, and Zener breakdown (Zener breakdown). ), Electrons are injected from the p-type semiconductor layer through the n-type semiconductor layer into the light emitting unit, recombined with the holes injected from the anode, and emit light. The holes remaining in the p-type semiconductor layer are attracted by an electric field and injected into the other light emitting unit, and recombine with electrons from the cathode to emit light. Therefore, according to the present invention, by providing the charge inversion layer between the light emitting units, each light emitting unit can emit light by applying a forward voltage between the anode and the cathode.

  FIG. 1 is a schematic diagram for explaining the light emission principle in the light emitting device of the present invention. When a positive potential is applied to the anode 2 side and a negative potential is applied to the cathode 18 side so as to be a forward voltage, a reverse bias is applied to the charge inversion layer 8 sandwiched between the two light emitting units 5 and 11. become. If the semiconductor forming the pn junction has a sufficiently high carrier concentration, Zener decay occurs, and electrons in the valence band of the p-type semiconductor layer 7 tunnel the depletion layer forming the pn junction, and the n-type It flows out into the conduction band of the semiconductor layer 6. The electrons that tunnel through the depletion layer and flow into the conduction band of the n-type semiconductor layer 6 are injected into the light-emitting layer 4 of the light-emitting unit 5 and recombined with the holes injected from the anode 2 into the hole-transport layer 3. Emits light.

  On the other hand, holes are left in the valence band of the p-type semiconductor layer 7 after the valence electrons are tunneled to the n-type semiconductor layer 6. The holes are attracted by an electric field and injected into the hole transport layer 9 of the light emitting unit 11, recombined with electrons injected from the cathode 18 into the light emitting layer 10, and emit light.

  In the above description, the light-emitting unit is described as a light-emitting unit of an organic EL element. However, when the light-emitting unit is a light-emitting unit of an inorganic semiconductor light-emitting diode element, the organic EL hole transport layer is an inorganic semiconductor light-emitting diode. The light-emitting layer corresponds to the p-type cladding layer, and the light-emitting layer corresponds to the n-type cladding layer and the light-emitting layer.

  The electric field Emax applied to the pn junction in the charge inversion layer is expressed by the following formula (1).

_{Emax = (2eN A N D /} ε S ε 0 (N A + N D)) 1/2 × (V D + V b) 1/2 ... (1)
Where N _A : acceptor concentration of p-type layer, N _D : donor concentration of n-type layer, e: charge of electrons, ε _S : relative permittivity of semiconductor layer, ε ₀ : permittivity of vacuum, V _D : pn Junction diffusion potential, _Vb : potential applied to the pn junction.

When Emax> 10 ⁸ V / m, high-density Zener decay power flows in the pn junction.

Taking GaN as an example of the material of the pn semiconductor layer, ε _S is about 8 and V _D is about 3V.
N _A , N _D > 1.5 × 10 ¹⁸ cm ⁻³ (2)
If so, a Zener decay current flows when V _b ≧ 0V. This is because if the acceptor and donor concentrations are equal to or higher than a certain value (1.5 × 10 ¹⁸ cm ^{−3 in} the case of GaN), there is almost no voltage drop in the charge inversion layer composed of a pn junction, and the drive voltage does not increase. Is shown.

As for other semiconductor materials, in the case of ZnS, since ε _S is about 8 and V _D is about 3 V, if N _A , N _D > 1.5 × 10 ¹⁸ cm ⁻³ as in GaN. When V _b ≧ 0 V, a Zener decay current flows.

In the case of ZnSe, since ε _S is about 9, and V _D is about 2.6 V, N _A , N _D > 1.5 × 10 ¹⁸ cm ⁻³
In the case of 6H, 4H-SiC and AlP, since ε _S is about 10 and V _D is about 3 V, N _A , N _D > 1.9 × 10 ¹⁸ cm ⁻³
In the case of AlAs, ZnTe and CdS, ε _S is about 10 and V _D is about 2.2 V, so that N _A , N _D > 2.6 × 10 ¹⁸ cm ⁻³
In the case of GaP, since ε _S is about 11 and V _D is about 2.2 V, N _A , N _D > 2.8 × 10 ¹⁸ cm ⁻³
If so, a Zener decay current flows when V _b ≧ 0 V, and the voltage rise due to the charge inversion layer of the pn junction hardly occurs.

The specific resistance of the charge reversal layer in the present invention is preferably less than 1.0 × 10 ² Ω · cm, more preferably 0.1 Ω · cm or less.

  Since the specific resistance of the charge inversion layer in the present invention is low as described above, at least one of the charge inversion layers is directly connected to another charge inversion layer, an anode, or a cathode, or via a resistor. Can be electrically connected. With such electrical connection, the light emission intensity of each light emitting unit can be controlled.

  The light emitting unit in the present invention may be a light emitting unit of an organic electroluminescence element or a light emitting unit of an inorganic semiconductor light emitting diode element. One element may include both a light emitting unit of an organic electroluminescence element and a light emitting unit of an inorganic semiconductor light emitting diode element.

  ADVANTAGE OF THE INVENTION According to this invention, in the light emitting element which has arrange | positioned the several light emission unit in tandem, it can drive with a low voltage and can improve power efficiency.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited to a following example.

  FIG. 2 is a cross-sectional view showing an embodiment of a light emitting device according to the present invention. As shown in FIG. 2, an anode 2 made of ITO (indium tin oxide) is formed on a glass substrate 1. Between the anode 2 and the cathode 18, the first light emitting unit 5, the second light emitting unit 11, and the third light emitting unit 17 are arranged. The first light emitting unit 5 is composed of the hole transport layer 3 and the light emitting layer 4, and the second light emitting unit 11 is composed of the hole transport layer 9 and the light emitting layer 10, and the third light emission. The unit 17 includes a hole transport layer 15 and a light emitting layer 16. The hole transport layers 3, 9 and 15 are formed of NPB (N, N′-di (naphthacene-1-yl) -N, N′-diphenylbenzidine). The light emitting layers 4, 10 and 16 are made of Alq (tris- (8-quinolinato) aluminum (III)). Alq is an organic material having an electron transporting property, and thus the light emitting layers 3, 9 and 15 are also electron transporting layers.

  A first charge inversion layer 8 is provided between the first light emitting unit 5 and the second light emitting unit 11. A second charge inversion layer 14 is provided between the second light emitting unit 11 and the third light emitting unit 17. The first charge inversion layer 8 includes an n-type semiconductor layer 6 disposed on the anode 2 side and a p-type semiconductor layer 7 disposed on the cathode 18 side. The second charge inversion layer 14 includes an n-type semiconductor layer 12 disposed on the anode 2 side and a p-type semiconductor layer 13 disposed on the cathode 18 side.

  The n-type semiconductor layers 6 and 12 are made of n-type zinc sulfide. The p-type semiconductor layers 7 and 13 are made of p-type zinc telluride. The cathode 18 is made of Al. In this embodiment, the specific resistance of the first charge inversion layer 8 and the second charge inversion layer 14 is 0.1 Ω · cm.

  The light emitting element shown in FIG. 2 can be formed by sequentially depositing and laminating thin films on the substrate 1. The anode 2 made of ITO can be formed on the substrate 1 by sputtering, for example. Each layer from the hole transport layer 3 to the cathode 18 can be formed by, for example, a vacuum evaporation method. As raw materials for NPB and Alq, for example, powders having a purity of 99% can be used. As a raw material for zinc sulfide and zinc telluride, a single crystal ingot having a purity of 99.999% can be used. 1 ppm of Al is added to zinc sulfide. Al can be used as a raw material having a wire shape with a purity of 99.99%. 1 ppm of nitrogen is added to zinc telluride.

  The thickness of the anode 2 is 1000 mm, and the thickness of the hole transport layer and the light emitting layer is 500 mm, respectively. The n-type semiconductor layer, the p-type semiconductor layer, and the cathode each have a thickness of 2000 mm.

  In the present invention, the material and thickness for forming each layer are not limited to those of the above embodiments. For example, the light emitting material used for the light emitting unit may be a polymer light emitting material, a phosphorescent material, or the like. Also, the structure of the light emitting unit is not limited to the above two-layer structure of hole transport layer / light emitting layer / electron transport layer. For example, the structure of hole transport layer / light emitting layer / electron transport layer 3 A layer structure may be sufficient and the structure in which layers, such as an electron injection layer, a hole injection layer, an electron blocking layer, and a hole blocking layer, were further provided may be sufficient.

The charge inversion layer is not limited to the above. For example, GaN (p-type is Mg-doped, n-type is Si-doped, etc.), ZnO (p-type is N-doped, n-type is Cl-doped, Al-doped, etc.), SiC (p-type is Al-doped, B-doped, Ga-doped) N-type is P-doped, As-doped, etc.), ZnSe (p-type is N-doped, n-type is Cl-doped, etc.), CuInO ₂ , CuGaO ₂ , CuAlO ₂ (p-type is Ca-doped, n-type is Sn-doped, etc. ), AlN, AlP (p-type is Mg-doped, Zn-doped, C-doped, n-type is Si-doped, S-doped, Se-doped, etc.) and mixed crystals composed of these semiconductor materials such as AlGaN, MgZnSSe, etc. A homo pn junction or a hetero pn junction may be used.

  Further, the structure of the light emitting element is not limited to the above structure. In the present invention, the number of stacked light emitting units and charge reversal layers is not limited. For example, 10 light emitting units and 9 charge reversal layers are stacked, or 100 light emitting units and 99 charge reversal layers are stacked. Also possible is an integrated device.

  FIG. 3 is a diagram schematically showing the energy state of the light emitting device shown in FIG. FIG. 3A shows a state in which no voltage is applied to the electrode, and FIG. 3B shows a state in which a forward voltage is applied to the electrode and light is emitted.

  In the forward voltage application state shown in FIG. 3B, steady light emission occurs in each light emitting unit in the following process. In the first light emitting unit 5, holes 19 are injected from the anode 2 and electrons 20 are injected from the n-type semiconductor layer 6 to emit light. At this time, holes are constantly supplied from the anode 2, and at the same time, electrons in the valence band of the p-type semiconductor layer 7 in the first charge inversion layer 8 are conducted in the n-type semiconductor layer 6 due to Zener decay. The supply continues via the electron 25. For this reason, the 1st light emission unit 5 can light-emit regularly in the voltage application state of a forward direction.

  Similarly, in the third light emitting unit 17, electrons 24 are injected from the cathode 18 and holes 23 are injected from the p-type semiconductor layer 13 to emit light. At this time, electrons are constantly supplied from the cathode 18 and at the same time, the holes 28 left in the p-type semiconductor layer 13 in the second charge inversion layer 14 are continuously supplied. The third light emitting unit 17 can emit light constantly. The holes 28 left in the p-type semiconductor layer 13 are those left after electrons in the valence band of the p-type semiconductor layer 13 are injected into the n-type semiconductor layer 12 by Zener decay. .

  In the second light emitting unit 11, electrons 22 are injected from the n-type semiconductor layer 12 in contact with the light emitting unit, and holes 21 are injected from the p-type semiconductor layer 7 to emit light. At this time, electrons in the valence band of the p-type semiconductor layer 13 in the second charge inversion layer 14 are supplied to the second light emitting unit 11 via the conduction electrons 26 of the n-type semiconductor layer 12 due to Zener decay. At the same time, since the holes 27 left in the n-type semiconductor layer 7 in the first charge inversion layer 8 are also continuously supplied to the second light emitting unit 11, the second light emitting unit 11 can be operated in the forward voltage application state. It emits light constantly.

  In this embodiment, three sets of light emitting units are stacked. However, even in a light emitting element in which more light emitting units are stacked, each light emitting unit is constantly in the same process as described above in a forward voltage application state. Luminescence occurs.

In the light-emitting element disclosed in Patent Document 1, a plurality of organic EL light-emitting units are connected in series via a charge generation layer made of an electrically insulating layer. In order to cause a current to flow and operate the light emitting element, a voltage drop occurs in the charge generation layer made of an electrically insulating layer that connects the light emitting units. Therefore, in addition to the voltage required for light emission in each organic EL light emitting unit, The voltage drop generated in the generation layer must be compensated. For this reason, a high operating voltage is required. On the other hand, in the present invention, the charge inversion layer connecting each light emitting unit is made of a low-resistance inorganic semiconductor, and current flows from zero bias to Zener decay at the pn junction. For this reason, a voltage drop substantially does not occur in the charge inversion layer. According to the present invention, since it can be driven at a low voltage, it can contribute to energy saving, and can contribute to effective use of energy resources and CO ₂ emission reduction that causes global warming. In addition, since heat generation during driving of the element can be suppressed, the life of the element can be extended.

  In the present invention, the thickness of the charge inversion layer can be freely selected without affecting the characteristics of the light emitting unit and the electrical characteristics of the entire device. By appropriately selecting the thickness of the charge inversion layer, it is possible to avoid light interference that is likely to occur in the thin film laminated structure. It is also possible to form a resonator for a specific wavelength region.

  FIG. 4 is a perspective view showing an embodiment in which the light emitting device of the present invention is applied to a liquid crystal projector. The light emitting element 29 is a light emitting element that emits blue light, and has a resonator structure for blue light emission. The light emitting element 30 is a light emitting element that emits green light, and has a resonator structure for green light emission. The light emitting element 31 is a light emitting element that emits red light, and has a resonator structure for red light emission. A liquid crystal light valve 32 for forming a blue image is provided between the prism 35 for combining the blue image, the green image, and the red image, and the light emitting element 29. A liquid crystal light valve 33 for forming a green image is provided between the light emitting element 30 and the prism 35. A liquid crystal light valve 34 for forming a red image is provided between the light emitting element 31 and the prism 35. The image synthesized by the prism 35 is emitted through the lens unit 36 in order to project an image on the screen.

  Since the light emitting elements 29 to 31 function as resonators for the respective emission colors, the light emitted from each unit has directivity and is perpendicular to the liquid crystal light valve in a form close to parallel rays. Can be incident. Since the planar light source disclosed in Patent Document 1 diverges without directivity in light emission, a large amount of light is incident obliquely when installed close to a liquid crystal light valve where vertical incident light is desirable. That is not preferable. By using the light emitting element of the present invention, the light emitting element and the liquid crystal light valve can be brought close to each other, and the liquid crystal projector can be miniaturized.

  As described above, the light emitting device of the present invention can emit high-luminance planar light having directivity if the light emitting surface is formed in a plane, but the light emitting device of the present invention is planar. It is not limited to a typical light emitting surface, and a curved light emitting surface may be formed. For example, the light emitting element of the present invention may be formed on a cylindrical substrate or a conical substrate.

  FIG. 5 shows a guide lamp in which the light emitting device of the present invention is formed on a cylindrical substrate. FIG. 6 shows a light emitting triangular cone in which the light emitting element of the present invention is formed on a conical substrate. Further, when the light emitting element of the present invention is formed on the surface of a small sphere, as shown in FIG. 7, a pseudo point light source having a high luminous intensity per unit area can be obtained although it is a surface light source. In addition, the light-emitting element of the present invention can be used for various display devices that require visibility from a wide range of distant directions, such as automobile stop lamps.

  In addition, as shown in FIG. 8, the light emitting element of the present invention may be formed on the inner surface 150 a of the concave substrate 150. Further, the light emitting element of the present invention may be formed on the inner surface 151a of the concave substrate 151 as shown in FIG. By forming the light emitting element of the present invention on the concave substrate in this way, a wide range can be illuminated, and at the same time, the light emission principle itself has little directivity, and a concave surface is formed. It is possible to irradiate stronger light near the center of the curved line or near the focal point of the curved surface. The light-emitting element manufactured in such a shape is suitable for surgical and medical surgical lamps by taking advantage of the characteristics of organic EL that has a broad emission spectrum and can produce white light with good color rendering.

  As described above, the light-emitting element of the present invention can be used for various purposes including illumination.

  Since the charge inversion layer in the light emitting device of the present invention has a low resistance, it is necessary to prevent the end face of the charge inversion layer from being short-circuited with the electrode.

  When the light emitting unit is a light emitting unit of an organic EL element, the short circuit between the end face of the charge inversion layer and the electrode can be prevented by adopting the element structure shown in FIG.

  FIG. 10 is a sectional view showing another example of the light emitting device according to the present invention. In the embodiment shown in FIG. 10, two light emitting elements are formed on the substrate 37. In each light emitting element, three light emitting units including hole transport layers 40 and 41 and light emitting layers 42 and 43 are formed on anodes 38 and 39, and an n-type semiconductor is formed between these three light emitting units. A charge inversion layer comprising layers 44 and 45 and p-type semiconductor layers 46 and 47 is provided. The side surface of the charge inversion layer is covered with hole transport layers 40 and 41 formed thereon. For this reason, the side surface of the charge inversion layer does not contact the electrode and short-circuit. A cathode 48 is provided outside each light emitting element.

  FIG. 11 is a cross-sectional view showing still another embodiment of the light emitting device according to the present invention. In the embodiment shown in FIG. 11, an anode 50 is formed on a substrate 49, and three light emitting units including a hole transport layer 51 and a light emitting layer 52 are formed on the anode 50. A charge inversion layer composed of an n-type semiconductor layer 53 and a p-type semiconductor layer 54 is provided between them. Each layer of the light emitting unit and the charge reversal layer is formed so that the area thereof is sequentially increased as the layers are stacked on the anode 50. A cathode 55 is formed on the outermost side of the light emitting element.

  In this embodiment, the area of each layer is formed so as to gradually increase. Therefore, the side surface of the charge inversion layer is covered with the hole transport layer and the light emitting layer formed thereon, It is made not to touch.

FIG. 12 is a sectional view showing still another embodiment of the light emitting device according to the present invention. In the embodiment shown in FIG. 12, an anode 57 is provided on a substrate 56, and three light emitting units each including a hole transport layer 58 and a light emitting layer 59 are provided on the anode 57. Between the units, charge inversion layers each including an n-type semiconductor layer 60 and a p-type semiconductor layer 61 are provided. An inorganic insulating layer 63 made of SiO ₂ or the like is formed on the side portions of each light emitting unit and charge inversion layer. A cathode 62 is formed above the uppermost light emitting layer 59, above the inorganic insulating layer 63, and on the side surface.

  In the present embodiment, the side surface of the charge inversion layer is covered with the inorganic insulating layer 63, and the side surface of the charge inversion layer and the cathode 62 are prevented from being short-circuited by the inorganic insulating layer 63.

  FIG. 13 is a cross-sectional view showing still another embodiment of the light emitting device according to the present invention. In the embodiment shown in FIG. 13, the anode 65 is formed on the substrate 64. Three light emitting units each including a hole transport layer 66 and a light emitting layer 67 are provided on the anode 65. A charge inversion layer composed of an n-type semiconductor layer 68 and a p-type semiconductor layer 69 is provided between each light emitting unit. The side surfaces of each light emitting unit and charge inversion layer are covered with inorganic insulating layers 71 and 72. A cathode 70 is provided on the uppermost light-emitting layer 67.

  In the embodiment shown in FIG. 13, the side surface of the lower charge inversion layer is covered by the upper light emitting unit, thereby preventing a short circuit with the cathode 70. Further, the side surface of the upper charge inversion layer is covered with inorganic insulating layers 71 and 72, thereby preventing a short circuit with the cathode 70.

  FIG. 14 is a cross-sectional view showing still another embodiment of the light emitting device according to the present invention. In the light emitting element of this embodiment, each light emitting unit can be selectively made to function. As shown in FIG. 14, an anode 74 is provided on the substrate 73. On the anode 74, a hole transport layer 75 and a light emitting layer 76 are provided, and these constitute a first light emitting unit. On the first light emitting unit, an n-type semiconductor layer 77 and a p-type semiconductor layer 78 are formed, and a first charge inversion layer is formed by these. The n-type semiconductor layer 77 and the p-type semiconductor layer 78 are formed extending to the left side of the drawing.

  A hole transport layer 79 and a light emitting layer 80 are formed on the first charge inversion layer, and a second light emitting unit is configured by these. The hole transport layer 79 and the light emitting layer 80 are formed so as to cover the right side surface of the first charge inversion layer. On the second light emitting unit, an n-type semiconductor layer 81 and a p-type semiconductor layer 82 are formed, and a second charge inversion layer is constituted by these. The n-type semiconductor layer 81 and the p-type semiconductor layer 82 are formed to extend to the right side of the drawing.

  A hole transport layer 83 and a light emitting layer 84 are formed on the second charge inversion layer, and a third light emitting unit is configured by these. The hole transport layer 83 and the light emitting layer 84 are formed so as to cover the left side surfaces of the second light emitting unit and the second charge inversion layer. A cathode 87 is formed on the third light emitting unit.

  An inorganic insulating layer 85 is formed on the left side surface of the element structure formed as described above, a contact hole is formed in a part of the inorganic insulating layer 85, and a first electrode 86 is formed in this portion. Has been. The first electrode 86 is electrically connected to the first charge inversion layer. An inorganic insulating layer 89 is formed on the right side surface of the element structure, a contact hole is formed in a part thereof, and a second electrode 88 is formed in this part. The second electrode 88 is electrically connected to the second charge inversion layer.

  The contact holes formed in the inorganic insulating layers 85 and 89 can be formed by photolithography and dry etching, and the electrodes 86 and 88 can be formed by vacuum deposition and photolithography.

  In the embodiment shown in FIG. 14, when no current is connected to the electrodes 86 and 88 and current is passed from the anode 74 to the cathode 87 in the open state, the electrodes are connected in series as in the embodiment shown in FIG. The same current flows through the first to third light emitting units, and each light emitting unit emits light. If the electrode 86 and the electrode 88 are connected by a conducting wire and short-circuited while the anode 74 is energized from the cathode 87, no current flows through the second light emitting unit, and a current flows through the conducting wire. As a result, only the first and third light emitting units emit light, and the second light emitting unit does not emit light. In addition, when a resistor is inserted into the conducting wire connecting the electrode 86 and the electrode 88, the current flows while being distributed to both the conducting wire via the resistor and the second light emitting unit. As a result, the light emission intensity of the second light emitting unit can be controlled by the resistance value of the resistor inserted into the conducting wire. Similarly, by connecting a conductive wire or a resistor between the anode 74 and the electrode 86 and bypassing a part of the current between the anode 74 and the electrode 86, the emission intensity of the first light emitting unit can be variably controlled. . Further, by connecting a lead wire or a resistor between the cathode 87 and the electrode 88 and bypassing a part of the current between them, the emission intensity of the third light emitting unit can be variably controlled.

  When the emission spectra of the light emitting units are different, the emission color emitted from the light emitting element can be freely changed by controlling the amount of current that bypasses the electrodes.

  When the light emission intensities of a plurality of light emitting units of three or more are changed independently, a general element requires the number of light emitting units minus one input voltage source or input current source. However, in the light emitting device according to the present invention, even when the number of light emitting portions is increased to three or more and these are changed independently, the light emission intensity of all the light emitting portions can be independently increased with only a single power source as described above. Can be controlled.

  In the light emitting element structure of Patent Document 1, since the charge generation layer between the light emitting units is an electrically insulating layer, an electrode connected to the charge generation layer cannot be formed as in this embodiment. For this reason, each light emission unit cannot be made to function selectively like a present Example.

  15 and 16 are cross-sectional views showing still other embodiments of the light-emitting device according to the present invention. In these embodiments, a GaN-based inorganic compound semiconductor light-emitting device is used in the light-emitting unit.

In the embodiment shown in FIG. 15, a first light-emitting unit 94, a second light-emitting unit 103, and a third light-emitting unit 112 are provided on a substrate 114 made of GaN or SiC. A first charge inversion layer 98 is provided between the light emitting unit 94 and the second light emitting unit 103, and a second charge inversion is provided between the second light emitting unit 103 and the third light emitting unit 112. A layer 107 is provided. The first to third light emitting units 94, 103, and 112 include undoped In _0.2 Ga between the Mg-doped p-type GaN cladding layers 91, 100, and 109 and the Si-doped n-type GaN cladding layers 93, 102, and 111. It is configured by providing _0.8 light emitting layers 92, 101, and 110. The first and second charge inversion layers 98 and 107 are made of high-concentration (1 × 10 ¹⁹ cm ⁻³ ) Si-doped n-type GaN layers 96 and 105 and high-concentration (3 × 10 ¹⁸ cm ⁻³ ) Mg-doped p. The GaN layers 97 and 106 are formed by pn junction.

  On the lower surface of the substrate 114, a cathode 117 made of Ti / Al is provided. An anode 90 made of Pd is provided on the first light emitting unit 94. The substrate 114 is an n-type GaN substrate or an n-type 6H—SiC substrate.

The light emitting device of the example shown in FIG. 15 can be manufactured by the following method. First, after the surface of the substrate is cleaned by Ar sputtering using MBE, nitrogen activated by RF discharge and Ga, In, Si, and Mg vapor are supplied to the substrate surface to grow crystals. The crystal growth conditions were a substrate temperature during growth of 800 ° C., a nitrogen pressure of 5 × 10 ⁻² Pa, and activation was performed by generating plasma with an RF input of 13.56 MHz and 500 W. The cell temperature of Ga and In was 500 to 700 ° C, the cell temperature of Si was 900 to 950 ° C, and the cell temperature of Mg was 200 to 250 ° C. Each layer was formed by opening and closing the shutter of each cell, and each layer was grown continuously. After crystal growth, each element was separated by photolithography and dry etching with chlorine gas, and then a Pd anode and a Ti / Al cathode were formed by vacuum deposition. Note that the formation method of the element is not limited to the above method, and the element can be similarly formed by other crystal growth methods such as MOCVD.

  FIG. 16 is a cross-sectional view showing another embodiment in which a GaN-based inorganic compound semiconductor light emitting element is used for the light emitting unit. In the embodiment shown in FIG. 16, a sapphire substrate 116 on which a GaN template 115 is formed is used. A first light emitting unit 95, a second light emitting unit 104, and a third light emitting unit 113 are provided on the GaN template 115, and between the first light emitting unit 95 and the second light emitting unit 104. The first charge inversion layer 99 is provided, and the second charge inversion layer 108 is provided between the second light emitting unit 104 and the third light emitting unit 113. The first to third light emitting units 95, 104, and 113 are configured in the same manner as in the embodiment shown in FIG. Further, the first and second charge inversion layers 99 and 108 are configured in the same manner as in the embodiment shown in FIG.

  In the embodiment shown in FIG. 16, a cathode 118 made of Ti / Al is provided on the portion of the third light emitting unit 113 that protrudes to the side of the GaN cladding layer 111. The anode 90 made of Pd is provided on the first light emitting unit 95. The light-emitting element shown in FIG. 16 can be manufactured by the same manufacturing method as that of the embodiment shown in FIG. 15 using the sapphire substrate 116 on which the GaN template 115 is formed as a substrate.

  FIG. 17 is a diagram schematically showing the energy band structure of the light emitting device of the example shown in FIG. 15 and the example shown in FIG. FIG. 17A shows a state in which no voltage is applied to the element, and FIG. 17B shows a state in which a forward voltage is applied to the element.

In FIG. 17, 119 is the energy band of the anode, 120, 125 and 130 are band gaps of the p-type GaN cladding layer, 121, 126 and 131 are band gaps of the undoped In _0.2 Ga _0.8 N light emitting layer, 112, 127 and 137 are the band gap of the n-type GaN cladding layer, 123 and 128 are the band gap of the n-type GaN charge inversion layer, 124 and 129 are the band gap of the p-type GaN charge inversion layer, and 133 is the energy band of the cathode. Respectively.

In the forward voltage application state shown in FIG. 17B, the conduction electrons 134, 135 and 136 in the n-type GaN cladding layers 122, 127 and 132 are injected into the In _0.2 Ga _0.8 N light emitting layers 121, 126 and 131. At the same time, holes 137, 138 and 139 in the p-type GaN cladding layers 120, 125 and 130 are also injected into the In _0.2 Ga _0.8 N light emitting layers 121, 126 and 131 to emit light in the light emitting layers 121, 126 and 131. Produce. At the same time, conduction electrons 140 are injected from the cathode 133 into the n-type GaN cladding layer 132, and valence electrons of the p-type GaN charge inversion layers 124 and 129 are injected into the n-type GaN charge inversion layers 123 and 128 due to Zener decay. The conduction electrons 141 and 142 are further injected into the n-type GaN cladding layers 122 and 127. Similarly, when holes are injected from the anode 119 into the p-type GaN cladding layer 120 and the valence electrons of the p-type GaN charge inversion layers 124 and 129 undergo Zener decay, the holes 143 and 144 that remain are the p-type GaN cladding. Implanted into layers 125 and 130. When such a process occurs continuously, a current constantly flows from the anode to the cathode, and steady light emission is obtained from each light emitting layer.

  The light emitting device of this example has an operating voltage that is higher by connecting a plurality of light emitting layers in series compared to a conventional GaN-based LED, but according to the number of stacked light emitting layers in the same chip area. The emission intensity can be increased. For this reason, the light emitting element of the present embodiment is optimal for applications that require a large amount of light, such as illumination applications.

  In addition, the material and thickness which form each layer in this invention are not limited to the thing of the said Example. For example, the material system used for the light emitting unit may be an AlInGaP material, an AlGaAs material, or the like.

  The laminated structure may also be a resonator structure by multilayer reflection, or the upper and lower surfaces may form a Fabry-Perot resonator.

FIG. 3 is a schematic diagram for explaining the light emission principle of the light emitting element of the present invention. Sectional drawing which shows one Example of the light emitting element according to this invention. The figure which shows typically the energy state of the light emitting element shown in FIG. 1 is a perspective view showing a liquid crystal projector using a light emitting element of the present invention. The perspective view which shows the guide lamp using the light emitting element of this invention. The perspective view which shows the light emission triangular cone using the light emitting element of this invention. The perspective view which shows the pseudo | simulation point light source using the light emitting element of this invention. The perspective view which shows the illuminating lamp using the light emitting element of this invention. The perspective view which shows the illuminating lamp using the light emitting element of this invention. Sectional drawing which shows the other example of the light emitting element according to this invention. Sectional drawing which shows the further another example of the light emitting element according to this invention. Sectional drawing which shows the further another example of the light emitting element according to this invention. Sectional drawing which shows the further another example of the light emitting element according to this invention. Sectional drawing which shows the further another example of the light emitting element according to this invention. Sectional drawing which shows the further another example of the light emitting element according to this invention. Sectional drawing which shows the further another example of the light emitting element according to this invention. The figure which shows the band structure of the light emitting element of the Example shown in FIG. 15, and the Example shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Board | substrate 2 ... Anode 3 ... Hole transport layer 4 ... Light emitting layer 5 ... 1st light emission unit 6 ... n-type semiconductor layer 7 ... p-type semiconductor layer 8 ... 1st charge inversion layer 9 ... Hole transport layer 10 ... Light-emitting layer 11 ... Second light-emitting unit 12 ... n-type semiconductor layer 13 ... p-type semiconductor layer 14 ... second charge reversal layer 15 ... hole transport layer 16 ... light-emitting layer 17 ... third light-emitting unit 18 ... cathode

Claims (5)

A light emitting device in which a plurality of light emitting units are arranged in tandem between an anode and a cathode,
A light emission characterized in that a charge reversal layer having an inorganic semiconductor pn junction comprising a p-type semiconductor layer disposed on the cathode side and an n-type semiconductor layer disposed on the anode side is provided between the light emitting units. element. ^2. The light emitting device according to claim 1, wherein a specific resistance of the charge inversion layer is less than 1.0 × 10 ² Ω · cm.   The light-emitting element according to claim 1, wherein the light-emitting unit is a light-emitting unit of an organic electroluminescence element.   The light-emitting element according to claim 1, wherein the light-emitting unit is a light-emitting unit of an inorganic semiconductor light-emitting diode element. That at least one of the charge inversion layers is electrically connected to another charge inversion layer, an anode, or a cathode directly or through a resistor, so that the light emission intensity of each light emitting unit is controlled. The light emitting device according to claim 1, wherein the light emitting device is a light emitting device.

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