TECHNICAL FIELD OF THE INVENTION
The present invention relates to a light-emitting element capable of emitting light in a wide range from the near ultraviolet region to the visible light region, and a light-emitting device including a substrate that converts the wavelength of light from the light-emitting element. Semiconductor (InxAlyGa1-xyN, 0 ≦ X ≦ 1, 0 ≦ Y ≦ 1, X + Y ≦ 1), and an activator having a different emission light wavelength is added to the substrate, so that even at the longer wavelength side of visible light, An object of the present invention is to provide a light emitting device capable of emitting mixed color light having high color rendering properties by emitting light with high luminance.
Nitride semiconductor (InxAlyGa1-xyN, 0 ≦ X ≦ 1, 0 ≦ Y ≦ 1, X + Y ≦ 1) has been developed, and it is possible to emit red light, which is a long-wavelength side of visible light from near-ultraviolet light, so that illumination using a semiconductor is possible. Demand for liquid crystal and display devices is increasing.
Under such circumstances, the present applicant has developed a light-emitting element made of a gallium nitride semiconductor formed on a sapphire substrate that emits blue light of visible light, and absorbs blue light from this light-emitting element to emit a complementary yellow color. Y activated by possible Ce3Al5O12(Hereinafter referred to as YAG) based fluorescent powder. With such a combination, a part of the light emitted from the light emitting element hits the particles of the YAG-based fluorescent powder, and the emitted yellow light is mixed with the blue light from the light emitting element to form white light. A practical white light emitting device that can emit light with high luminance and high luminance has been realized. Such a light emitting diode has begun to be applied to various fields because it is possible to obtain practically reliable high-luminance white light with a relatively simple structure of two terminals and one chip. Since this white light emitting diode uses a phosphor, it can also emit a reddish component in visible light and have color rendering properties of Ra = 85 or more.
[Patent Document 1] JP-A-2000-208815
[Patent Document 2] JP-A-2002-27831
[Problems to be solved by the invention]
However, it can be said that it is difficult to obtain white light uniformity with the above configuration. The reason is that it is difficult to make the particle diameter of the YAG fluorescent powder mixed into the resin uniform. Further, it is considered that the powder settles. This is due to the weight of the powder, and because the particle size is non-uniform, the powder having a large particle size sediments quickly, so that there is a spatial distribution of the powder, and the white light becomes non-uniform. . Further, as the field of use expands, a light-emitting device having higher color rendering properties, for example, a light-emitting diode is required, and further improvements are required. Therefore, an object of the present invention is to provide a light emitting device which can emit a white light having a high color rendering property as uniform light with a relatively simple configuration.
[Means to solve the problem]
The present invention is a light-emitting device including a light-emitting element having a light-emitting layer made of a nitride-based compound semiconductor on a substrate, wherein the substrate absorbs light emitted from the light-emitting layer made of a nitride-based compound semiconductor, A sapphire substrate containing a first element composed of Cr or Fe as an activator that emits light of a longer wavelength and a second element having an ionic radius in the range of 70% to 130% of Al It is a light emitting device characterized by the following. The substrate used in the present invention may be a transparent substrate that transmits at least 1% or more, preferably 10% or more of light emitted from the light emitting layer, but sapphire is preferable for uniformly containing the activator. There is a combination technique of a sapphire substrate containing Cr and a light-emitting element having a light-emitting layer made of a nitride-based compound semiconductor. However, for practical use, it was necessary to further improve the color rendering. Therefore, the present invention includes a first element composed of Cr or Fe as an activator to be contained in a sapphire substrate and a second element in addition to the activator to emit light from the sapphire substrate at 530 to 680 nm, preferably 550 to 680 nm. By converting the wavelength to 650 nm light and combining with light emitted from the light emitting layer, a light emitting device capable of emitting mixed color light having high color rendering properties can be obtained. Since the light emitted from the substrate can be made not only sharp light but also broad light depending on the content ratio of two or more kinds of activator elements, the lighting device and the lighting device can have the same yellow band. It is possible to adjust not only the wavelength band but also its half-value width according to the use of a medical device or the like. Further, a highly reliable light-emitting diode can be provided with a relatively simple configuration.
The sapphire substrate is a substrate excellent in heat resistance and has durability such that a wafer can be processed after being obtained in an ingot. However, the inclusion of an activator in the crystal significantly lowers the crystallinity. Therefore, sapphire (Al2O3Elements in the position of Al in parentheses) must be limited. Therefore, in the present invention, the activator reduces the crystallinity of sapphire by adding, as an activator, a second element having an ionic radius of 70% to 130% of Al in addition to the first element. Without entering the Al site. With the above structure, a light emitting device capable of emitting mixed color light having high color rendering properties can be provided. Further, a highly reliable light-emitting device with a relatively simple structure can be provided.
In the light emitting device according to claim 2 of the present invention, the second element is at least one selected from the group consisting of Fe, Ti, V, Mn, Co, Ni, Cu, and Mg. These elements are divalent to tetravalent. Accordingly, a red component can emit light with higher luminance, and a light-emitting device with a high yield can be obtained in which cracking of a substrate or the like during formation of a light-emitting element or a light-emitting device is suppressed.
In the light emitting device according to claim 3 of the present invention, Cr contained in the sapphire substrate has an absorbance at a wavelength of 550 nm of 10 cm.― 1That is all. As a result, the red component can emit light with higher luminance, and a light-emitting device with a high yield can be obtained even by scribing the sapphire substrate when forming the light-emitting element.
In the light emitting device according to claim 4 of the present invention, the first emission light from the light emitting layer and the sapphire substrate absorb at least the first emission light and perform wavelength conversion to convert the first emission light. A light-emitting device that emits second emission light having a main emission peak on a longer wavelength side than the main emission peak, and is capable of emitting white light by mixed light of the first and second emission lights.
This makes it possible to provide a light emitting device, for example, a light emitting diode that can be used for various indicators, a backlight light source, an illumination light source, and the like without deterioration of the phosphor and the resin even when the phosphor is sealed with a resin.
In the light emitting device according to claim 5 of the present invention, the emission light from the light emitting layer has a main emission peak within a range from 360 nm to 490 nm. Thereby, the light emitted from the light emitting device can be made into an arbitrary color. If the light from the light emitting layer is in the near ultraviolet region (360 nm to 400 nm), the light transmitted through the sapphire substrate becomes colorless, and only the light whose wavelength has been converted in the sapphire substrate becomes emission light. Obtainable.
BEST MODE FOR CARRYING OUT THE INVENTION
The present inventor has found that practical reliability, high luminance, and high color rendering properties can be achieved at the same time by using a specific material having high conversion efficiency according to the embodiment described below.
That is, a light-emitting element having a light-emitting layer made of a nitride-based compound semiconductor capable of emitting light in a wide range from the near ultraviolet to a long wavelength region, and an activator capable of converting light into a longer wavelength using light from the light-emitting element In this case, a light-emitting device including a sapphire substrate containing a light-emitting diode or the like capable of emitting more practical white light is formed.
In the present invention, as shown in FIG. 1, an n-type impurity is doped on a sapphire substrate 101 containing a first element 201 and a second element 202 via a buffer layer 102 made of InAlGaN and a dislocation reduction layer 103. The first n-type nitride semiconductor layer 104 on which an electrode is formed, which has functions such as a carrier supply effect, a carrier confinement effect, and a light confinement effect in which an n-type impurity is doped on the first n-type nitride semiconductor layer. A second n-type nitride semiconductor layer 105, a light-emitting layer 106 having a barrier layer and a well layer to form a single or multiple quantum well structure, a p-type impurity-doped carrier supply effect, a carrier confinement effect, Light emission comprising a first p-type nitride semiconductor layer 107 having a function of light confinement and the like, and a second p-type nitride semiconductor layer 108 on which an electrode is formed by doping a p-type impurity. To form a child 120. The dislocation reduction layer 103 can be omitted. An n-type electrode 121 is formed on the first n-type nitride semiconductor layer 104, and a p-type electrode 122 and a pad electrode 123 are formed on the second p-type nitride semiconductor layer. After the electrodes are formed, a protective film 131 is formed on the light emitting element.
[Sapphire substrate 101]
The sapphire substrate preferably has a (0001) plane or a (11-20) plane as a main surface. This is because the nitride-based compound semiconductor grown on the substrate has good crystallinity. Hereinafter, a method for producing a sapphire substrate containing an activator will be described.
Crystals can be grown on a sapphire substrate by a method such as the EFG method, the heme method, and the Cyprus method. Among them, the CZ method is preferable for a substrate growth method because the composition is uniform and there is no uneven distribution of additives. Furthermore, since the substrate pulled up at an arbitrary angle can be cut out, the (0001) plane, which is the growth surface of the nitride semiconductor, can be easily formed. In the CZ method, a single crystal having a uniform crystal orientation is grown in a raw material melt based on a seed crystal. The rotated seed crystal is brought into contact with the raw material melt and maintained at such a temperature that the tip melts. Then, the seed crystal is raised to create a temperature gradient with the melt and cool. Thereafter, crystal growth is roughly divided into three steps. It comprises a mold making step for increasing the diameter of the crystal, a straight body growing step for obtaining a crystal of a constant diameter, and a step for separating the crystal from the melt. The raw materials may be weighed and mixed at a desired composition ratio. The raw material is filled in the crucible. The crucible is made of Ir. In a crystal growing furnace, an Ir crucible is placed in a high-temperature part made of a refractory material and filled with a raw material. Here, the activator can be added by coprecipitation. The activator is evenly distributed within the raised sapphire.
As a method for manufacturing a sapphire substrate, first, a predetermined amount of alumina, an oxide of a raw material used as an activator, and the like are charged into an Ir crucible. Here, the ratio of the first element and the second element, which are activators, is such that the amount that substitutes for Al sites is 5% or less, preferably 3% or less of the total amount of Al. Next, the temperature is raised to 1500 ° C. or higher, preferably about 2080 ° C. in an argon atmosphere in a high frequency furnace, and the alumina seed crystal is pulled up by the CZ method. The alumina seed crystal is immersed in the crystal liquid level, and the crystal is pulled up at 0.1 to 10.0 mm / h, preferably 0.3 to 5 mm / h, more preferably 0.5 to 2.0 mm / h. The crystal pulling axis is not particularly limited in the a-axis direction, the c-axis direction, and the like. The rotation speed is 0.5 to 10 rpm, preferably 1 to 3 rpm. Here, the diameter of the alumina seed crystal is 1 mm to 30 mm, more preferably 5 mm to 20 mm, and most preferably 10 mm.
Lift the sapphire substrate to H2Annealing is performed in an atmosphere at 1000 ° C. or higher, preferably about 1400 ° C. Thereby, it is possible to obtain a crystallinity having a half width of 30 arcsec or less, preferably 25 arcsec or less, and a crystal defect of 5 × 102~ 5 × 104Pieces / cm2It can be. After that, the wafer is cut into a wafer by a wire saw, and a sapphire substrate containing an activator is obtained by lapping and polishing.
In the present embodiment, the thickness of the substrate is not particularly limited as long as it can transmit light, but is preferably 3 mm or less. Processing is possible if the thickness of the substrate is 30 μm, but more preferably 50 μm or more and 2 mm or less. This is a film thickness that allows the substrate to be sliced and stepped. In the substrate according to the present invention, the surface on which slicing can be performed can be a growth surface of a nitride semiconductor.
In the embodiment of the present invention, a first element 201 and a second element 202 are used for the activator 200. Here, the first element is Cr or Fe. Cr is Cr3+Or Cr4+And Fe is Fe3+Contained as The second element is at least one selected from the group consisting of Fe, Ti, V, Mn, Co, Ni, Cu, and Mg. As the combination of the first element and the second element, the first element:4+: Fe3+, Cr4+: Mg2+, Fe3+: Ti3+Since the light emitted from the sapphire substrate can be converted into yellow light with high conversion efficiency, white light with high luminance can be obtained by using the light emitted from the light emitting element 120 as blue light.
[Light emitting element 120]
In the embodiment of the present invention, the light emitting device 120 is made of a nitride-based compound semiconductor, and is undoped or doped with an n-type impurity such as Si, Ge, Sn, or S, or a p-type semiconductor such as Mg or Zn. A nitride-based compound semiconductor doped with a p-type impurity, or a nitride-based compound semiconductor doped with an n-type impurity and a p-type impurity simultaneously can be used. The method for growing the nitride-based compound semiconductor is not particularly limited, but MOVPE (organic metal vapor phase epitaxy), HVPE (halide vapor phase epitaxy), MBE (molecular beam epitaxy), and MOCVD (organic metal organic phase epitaxy). A method such as chemical vapor deposition can be applied. The details of the layer structure of the light-emitting element are described below.
A predetermined amount of alumina, a raw material oxide used as an activator, and the like are charged into an Ir crucible. Here, the ratios of the first element and the second element, which are activators, are set to 2%, respectively, assuming that the amount of substitution at the Al site is 4% of the total amount of Al. Next, the temperature is raised to about 2080 ° C. in an argon atmosphere in a high frequency furnace, and the alumina seed crystal is pulled up by the CZ method. The alumina seed crystal is immersed in the crystal liquid surface, and the crystal is pulled up at 1.50 mm / h. The pulling axis of the crystal is in the c-axis direction. The rotation speed is 2.0 rpm. Here, the alumina seed crystal has a diameter of 10 mm.
Lift the sapphire substrate to H2Annealing is performed at about 1400 ° C. in an atmosphere. Thereby, crystallinity with a half width of 25 arcsec or less is obtained. 5 × 10 crystal defects2Pieces / cm2And After that, the wafer is cut into a wafer with a wire saw, and lapping and polishing are performed.3+And Fe3+Sapphire substrate. This sapphire substrate is 2 inches and has a thickness of 200 to 400 μm.
A buffer layer 102 (not shown) is formed on the sapphire substrate 101. For this buffer layer, the general formula is InxAlyGa1-xyN (0 ≦ x <1, 0 ≦ y <1). Preferably, the composition ratio of Al is 0.5 or less. If the composition ratio of Al is high, the crystallinity is reduced, but if Al is contained in the buffer layer in the above range, it can be easily planarized at the time of growth of the nitride-based compound semiconductor in a later step. The growth temperature of the buffer layer is adjusted to a range from 300 ° C. to 1000 ° C., preferably from 400 ° C. to 900 ° C. When the buffer layer is formed as a good polycrystal, a nitride-based compound semiconductor having good crystallinity can be formed on the buffer layer using the polycrystal as a seed crystal. The buffer layer is grown with a thickness of 10 Å to 0.5 μm. Adjustment within this range is preferable from the viewpoint of reducing crystal defects because lattice mismatch between the substrate and the nitride semiconductor can be reduced. The buffer layer has an effect of alleviating the lattice constant irregularity between the substrate and the nitride semiconductor.9Pieces / cm2It is preferable in that it is reduced to the extent.
On the buffer layer, a dislocation reduction layer 103 is formed by using an ELO method using a mask or a method of forming irregularities on a nitride semiconductor layer grown on a substrate and then growing the same in a lateral direction again (omitted). To grow the first n-type nitride semiconductor layer 104.
(First n-type nitride semiconductor layer 104)
The first n-type nitride semiconductor layer 104 is an n-type contact layer containing an n-type impurity, and has an n-type impurity of 1 × 1017/ Cm3Above, preferably 3 × 1018/ Cm3It is contained in the above concentration. By doping a large amount of n-type impurities in this manner, when a light emitting diode is formed, Vf (forward voltage) can be reduced. The limit of maintaining the function as an n-type contact layer is 5 × 1021/ Cm3It is desirable to make the following. The measurement of the impurity concentration in the present invention is based on Secondary Ion Mass Spectrometry (SIMS). The n-type contact layer is represented by InAlGaN, and has InxGa1-xN (0 ≦ x ≦ 0.2) in order to reduce crystal defects. The n-type contact layer is a layer for forming the n-type electrode 121, and the thickness of the n-type contact layer is set to 1 to 10 μm in order to lower the resistance value and lower the Vf of the light emitting element.
(Second n-type nitride semiconductor layer 105)
Next, an n-side first multilayer film layer and an n-side second multilayer film layer are grown as second n-type nitride semiconductor layers 105 on the n-type contact layer. When the n-side first multilayer film layer including the undoped lower layer, the n-type impurity-doped intermediate layer, and the undoped upper layer is formed, the light emitting output and the electrostatic breakdown voltage can be improved. As the nitride semiconductor constituting these three layers, nitride semiconductors having various compositions represented by InAlGaN can be used. The compositions may be the same or different. The thickness of the n-side first multilayer film is set to 175 to 12000 ° in order to optimize Vf and improve the electrostatic withstand voltage. Preferably it is 2000-6000 °. The thickness of the first multilayer film is adjusted so that the total thickness falls within the above range. Thereby, light emission output and electrostatic withstand voltage can be significantly improved. The thickness of the lower layer of the undoped layer is 100 to 10000 °. As for the lower layer of the undoped layer, the electrostatic breakdown voltage increases as the film thickness increases, but Vf sharply increases near 1000 °, while the Vf decreases as the film thickness decreases, but the electrostatic breakdown voltage decreases. When the temperature is less than 100 °, the yield tends to decrease with the decrease in electrostatic withstand voltage. Further, since the undoped lower layer has a function of improving the influence of the decrease in the crystallinity of the n-type contact layer containing the n-type impurity, from the viewpoint of effectively exhibiting the function of improving the crystallinity, It is preferable to grow with a film thickness of about 500 to 8000 °. The thickness of the n-type impurity-doped intermediate layer is preferably smaller than the thickness of the n-type contact layer, and is 50 to 1000 °. The intermediate layer doped with the n-type impurity is a layer having a function of sufficiently increasing the carrier concentration and relatively increasing the light emission output. The light emitting element having this layer has a higher light emission output than a light emitting element not formed. Decrease. On the other hand, when the film thickness exceeds 1000 °, the luminous output decreases. On the other hand, considering only the electrostatic withstand voltage, if the thickness of the intermediate layer is more than 50 °, the electrostatic withstand voltage can be improved, but if the thickness is smaller than this, the electrostatic withstand voltage decreases. The thickness of the upper layer of the undoped layer is preferably smaller than that of the lower layer of the undoped layer. The upper layer of the undoped layer is formed in contact with or closest to the active layer in the first multilayer film, and greatly contributes to prevention of leakage current. Increase cannot be effectively prevented. On the other hand, if the thickness of the upper layer exceeds 1000 °, Vf increases and the electrostatic breakdown voltage decreases. By forming the film thickness of each of the lower layer to the upper layer within the above range, a good balance of element characteristics can be obtained, and particularly, a light emission output and an electrostatic withstand voltage can be made good.
The composition of each layer constituting the first multilayer film layer is InxAlyGa1-xyIt is represented by N (0 ≦ x <1, 0 ≦ y <1), and the composition of each layer may be the same or different. The doping amount of the n-type impurity in the first multilayer film layer is preferably 3 × 1018/ Cm3The above concentration is set. The upper limit is 5 × 1021/ Cm3The following is desirable. As the n-type impurity, an element of Group IVB or VIB of the periodic table such as Si, Ge, Se, S, or O is selected. When an active layer is formed on the first multilayer film, the upper layer 5c of the first multilayer film that is in contact with the active layer is formed using, for example, GaN, thereby forming a barrier layer in the active layer. Can work. The first multilayer film layer may be any two of the three layers represented by the above composition formula or a single undoped layer.
Next, an n-side second multilayer film layer is formed on the first multilayer film layer. This layer is formed by stacking a first nitride semiconductor layer containing In and a second nitride semiconductor layer having a composition different from that of the first nitride semiconductor layer. In the n-side second multilayer film layer, at least one first nitride semiconductor layer and at least one second nitride semiconductor layer are formed, and preferably at least two layers are stacked, and a total of four or more layers are stacked. Is desirable. As for the film thickness of the n-side second multilayer film layer, at least one film thickness is 100 ° or less, and preferably both film thicknesses are 100 ° or less. When at least one of the film thicknesses is 100 ° or less, one of the thin film layers has an elastic critical film thickness or less, and the crystallinity can be improved, and the crystallinity of the entire multilayer film layer can be improved. If the thickness of both layers is 100 ° or less, the n-side second multilayer film layer has a superlattice structure, and the n-side second multilayer film layer has the effect of a buffer layer. Thus, the output can be further improved. In the n-side second multilayer film layer, the first nitride semiconductor layer is a nitride semiconductor containing In, preferably a ternary mixed crystal of In.xGa1-xN (0 <x <1), and preferably the x value is 0.5 or less. The second nitride semiconductor layer may be a nitride semiconductor having a composition different from that of the first nitride semiconductor layer, and may be a binary mixed crystal or ternary mixed crystal In.xGa1-xN (0 ≦ x <1). Further, the n-side second multilayer film layer may be undoped, or one of the two may be doped with an impurity. This impurity is an n-type impurity, and is preferably a modulation dope. With modulation doping, the output can be increased. The doping amount of the n-type impurity is preferably 3 × 1018/ Cm3The above concentration is set. The upper limit is 5 × 1021/ Cm3The following is desirable. As the n-type impurity, an element of Group IVB or VIB of the periodic table such as Si, Ge, Se, S, or O is selected.
(Light-emitting layer 106)
Next, a light emitting layer having a quantum well structure is formed. The light emitting layer (active layer) is either undoped, doped with one of an n-type impurity and a p-type impurity, or doped with both. When the light emitting layer is doped with an n-type impurity, the light emission intensity between bands can be increased as compared with the case of undoping. If the light emitting layer is doped with a p-type impurity, the peak wavelength can be shifted to the energy side lower by about 0.5 eV than the peak wavelength of the interband emission, but the half width becomes wider. In order to grow a light emitting layer having good crystallinity, undoping is most preferable. Although a single quantum well structure may be used, a multiquantum well structure can provide characteristics of high emission output and good electrostatic withstand voltage. The stacking order of the barrier layer and the well layer is as follows: stacking from the well layer and ending with the well layer, stacking from the well layer and ending with the barrier layer, stacking from the barrier layer and ending with the barrier layer, and stacking from the barrier layer May end with a well layer. The number of pairs may be about 1 to 15 pairs. When the film thickness is in this range, the output can be improved. The layer in contact with the light-emitting layer may function as the first layer (well layer or barrier layer) in the light-emitting layer in some cases.
The composition formula of the well layer is InAlGaN, the thickness is 100 ° or less, and the lower limit of the film thickness is 1 atomic layer or more, preferably 10 ° or more. When a plurality of well layers are provided, if the well layer closest to the n-side second multilayer film layer is formed from an n-type impurity doped layer and the other well layers are undoped, Vf can be reduced. it can. This n-type impurity is preferably Si and is 5 × 1021/ Cm3Adjust to the following. On the other hand, the composition formula of the barrier layer is InAlGaN, the film thickness is 2000 ° or less, preferably 500 ° or less, and the lower limit of the film thickness is adjusted to 1 atomic layer or more, preferably 10 ° or more.
(First p-type nitride semiconductor layer 107)
A first p-type nitride semiconductor layer 107 is grown on the light emitting layer. The p-side nitride semiconductor layer 4 is composed of a p-type cladding layer and a p-type lightly doped layer. The p-type cladding layer has a multilayer film structure (superlattice structure) or a single film structure doped with p-type impurities. As a multilayer film constituting the p-type cladding layer, a film containing a p-type impurity in at least one of the layers is mentioned. The general formula is AlxGa1-xN (0 ≦ x ≦ 1) and InxAlyGa1-xyN (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1). The composition ratios of Al and In in the p-type multilayer film indicate average values, similarly to the other multilayer films in the present invention. When the p-type cladding layer has a superlattice structure, the crystallinity is good and the resistivity can be lowered, so that Vf can be lowered. As the p-type impurity to be doped into the p-type cladding layer, a group IIA or IIB element of the periodic table, such as Mg, Zn, Ca, or Be, is selected. Next, when the p-type cladding layer is a single layer, the p-type impurity-containing AlxGa1-xN (0 ≦ x ≦ 1). By containing Al, the light emission output is improved, and the electrostatic withstand voltage is as good as GaN.
After forming the p-type cladding layer, a p-type lightly doped layer can be formed. The p-type lightly doped layer may have a lower p-type impurity concentration than the p-type cladding layer, and may be a multilayer film. As an effect, the emission voltage can be improved and the electrostatic withstand voltage can be improved. The p-type lightly doped layer can be omitted depending on the p-type impurity concentration in the p-type clad layer.
(Second p-type nitride semiconductor layer 108)
Next, a second p-type nitride semiconductor layer 108 is grown. The second p-type nitride semiconductor layer 108 has a general formula In formed on a p-type clad layer or a p-type lightly doped layer.xAlyGa1-xyA p-type contact layer represented by N (0 ≦ x <1, 0 ≦ y <1, 0 ≦ x + y <1) and doped with a p-type impurity such as Mg. By using a nitride semiconductor made of GaN that does not contain In and Al, ohmic contact with the p-type electrode 122 can be improved, and luminous efficiency can be improved. The thickness of the p-type contact layer is not particularly limited, but is about 1000 °. Thus, a nitride semiconductor device can be obtained on a wafer.
The n-type electrode 121 is formed on the n-type contact layer, and the p-type electrode 122 is formed on the p-type contact layer. For example, Ti / Al or W / Al can be used for the n-type electrode, and Ni / Au can be used for the p-type electrode. After that, a light emitting element is formed by forming a chip (FIG. 5). Further, the light emitting element can be formed into a flip chip type by forming a bump on an electrode (FIG. 2).
In another embodiment, the sapphire substrate 101 has a structure in which the light emitting element formation surface and / or the back surface has irregularities (FIGS. 3 and 4). The planar shape of the sapphire substrate on which the unevenness is formed is a rectangular shape, a stripe shape, a lattice shape, or an island shape. If a nitride semiconductor is grown on an uneven sapphire substrate without forming an air gap, the incidence efficiency on the substrate is improved. A nitride semiconductor device is formed on a substrate on which a convex portion a and a concave portion b are formed, and a take-out efficiency in a range of a dimple angle α of 0 ° (vertical) to 90 ° (flat substrate) in which unevenness is formed on the substrate. Indicates that if the dimple angle is 0 ° to 75 °, the sapphire substrate has a substrate incidence efficiency of 45% or more. By inclining the taper angle, the light incident on the sapphire substrate 101 increases, so that the wavelength conversion efficiency is greatly improved, and the emission in the yellow band is enhanced. That is, the emission color can be changed by adjusting the angle of the taper angle. Further, when the taper angle is 10 ° to 30 °, a nitride semiconductor can be easily formed without having an air gap. By promoting lateral growth during growth of the nitride-based compound semiconductor, dislocations can be reduced, crystallinity can be improved, and the total thickness of the substrate and the nitride semiconductor can be reduced. The planar shape of the substrate unevenness formed by etching includes a stripe shape, a lattice shape, an island shape, and a shape in which a convex shape is extracted into a polygonal shape and a concave shape is extracted into a polygonal shape.
Next, the buffer layer 102 is formed on the uneven surface of the substrate 101. The nitride semiconductor that grows with the buffer layer as a nucleus is grown with the upper surface of the convex portion and the lower surface of the concave portion as nuclei as compared with the case of using the side surface of the concave portion as a nucleus. The higher the growth rate. In addition, since there is a height difference between the upper surface of the convex portion and the bottom surface of the concave portion, even at the same growth rate, the growth from the upper surface of the convex portion of the substrate extends not only in the vertical direction but also in the horizontal direction, so that the adjacent upper surface of the convex portion can be obtained. The grown nitride semiconductors are joined and planarized. Since the cavity remains in the concave portion even after the planarization, the warpage of the substrate can be reduced and the light extraction efficiency can be improved. The substrate may have a slope on a main surface on which a nitride semiconductor is grown. Preferably, the inclination of the surface of the substrate with the main surface is within 10 °. As described above, the light emission efficiency can be increased by providing the substrate with the uneven steps.
As a method of forming a step on the sapphire substrate, a protective film having an opening is formed on the substrate. Thereafter, the substrate surface exposed from the opening of the protective film is removed by etching. As a result, an uneven step is formed on the sapphire substrate. Thereafter, by removing the protective film, a sapphire substrate having uneven steps is obtained. The protective film may be any as long as it has etching selectivity with the substrate. As a specific example, silicon oxide (SiOx), Silicon nitride (SixNy), Silicon nitride oxide (SiOxNy), Titanium oxide (TiO)x), Zirconium oxide (ZrO)x), A multi-layered film thereof, or a metal having a melting point of 1200 ° C. or more. As a method of forming the protective film, for example, a film is formed by using CVD, sputtering, or an evaporation method to form a patterned protective film.
Examples of the shape of the protective film include those having a stripe shape, a grid shape, an island shape, a circular shape, or a polygonal opening portion. As a specific pattern shape having a polygonal opening, there is a hexagonal blank type or a hexagonal column type of the reverse pattern. In the case of a stripe shape, the lateral growth region of the nitride semiconductor becomes a stripe-like low defect region, and thus can be used for a laser diode. Further, if a circular or polygonal opening is formed, the nitride semiconductor is bonded at one point at the center of the opening, so that the stress applied to the entire substrate can be equalized and the warpage of the nitride semiconductor substrate can be suppressed. Furthermore, circular or polygonal patterns can be easily flattened if the arrangement is made six-fold or three-fold symmetrical.
The width of the opening of the protective film is equal to the width of the recess of the sapphire substrate 101. The stripe width and the grating width of the protective film are not particularly limited. When the protective film is formed as a stripe, the stripe width of the protective film is preferably 1 to 50 μm, more preferably 5 to 20 μm. Here, the depth of the concave portion of the sapphire substrate is 0.1 μm or more, and when the nitride semiconductor has a cavity in the concave portion after growth, the depth of the concave portion is preferably 0.2 μm or more.
As an etching method for forming irregularities on the substrate, there are methods such as wet etching and dry etching, but anisotropic etching is preferable, and dry etching is used. Examples of the dry etching include apparatuses such as reactive ion etching (RIE), reactive ion beam etching (RIBE), electron cyclotron etching (ECR), and ICP plasma etching, all of which are performed by appropriately selecting an etching gas. The semiconductor is etched.
Here, in the second embodiment, the buffer layer 102 is an InGaN layer in which the composition ratio of Al is 0.2 or less. The composition ratio of Al may be zero. When the composition ratio of Al is set to zero, it is preferable that InbGa1-bN (0.2 ≦ b ≦ 0.9). Including In has a strain relaxation effect. Further, since InN is unstable, it is preferable to contain Ga.
The light emitting element having the above configuration is electrically connected to the electrode of the light emitting element using a gold bump on a glass epoxy circuit board on which a pattern serving as a pair of lead electrodes of a copper foil is formed, and is arranged in a flip chip type. Next, a shell-type light emitting diode, which is one embodiment of the light emitting device, can be formed by applying and curing an epoxy resin.
Otherwise, after mounting the light emitting element on a heat sink 301 provided with a lead frame 302, a conductive wire 303 is bonded. Next, another light emitting device can be obtained by sealing with transparent glass (FIG. 6). Further, a light emitting device as shown in FIG. 7 can be provided. A light emitting element is mounted on a heat sink 301 having a lead frame 302, and a conductive wire 303 is bonded.
When a current is applied between the lead electrodes of the light emitting diode, light emitted from the light emitting layer and light having a main emission peak at a long wavelength of 600 to 680 nm are emitted from the sapphire substrate, and white light with high color rendering properties is obtained by each color mixture. Light can be emitted. By changing the In concentration of the white light emitting diode, the first wavelength that can be emitted from the light emitting layer can be adjusted to some extent. Further, in a sapphire substrate activated with Cr, Fe, or the like, the output of the red component can be adjusted by increasing or decreasing the concentration of Cr. When a sapphire substrate having a thickness of 150 μm or less is used, the absorbance at a wavelength of 550 nm is 10 cm.― 1Preferably, the absorbance is 25 cm or more.― 1More preferably 125 cm― 1That is all. As a result, it is possible to form from mixed color light having a high red component to white light having a high color rendering property. Hereinafter, specific examples of the present invention will be described in detail, but are not limited thereto.
A light emitting diode as shown in FIG. 1 is formed using a light emitting layer having a well layer of an InGaN semiconductor having a light emission peak of about 470 nm as a light emitting element. The light-emitting element comprises a TMG (trimethylgallium) gas, a TMA (trimethylaluminum) gas, a nitrogen gas and a dopant gas on an α-sapphire substrate containing 2% of Cr and 2% of Fe as a cleaning activator. And gallium nitride-based compound semiconductor by MOCVD. SiH as dopant gas4And Cp2By switching between Mg and Mg, a gallium nitride semiconductor having n-type conductivity and a gallium nitride semiconductor having p-type conductivity were formed, and a pn junction was formed. Specifically, on the sapphire substrate, Al0.1Ga0.9An undoped GaN layer is grown to a thickness of 1.5 μm via an N buffer layer. Next, an n-type contact layer of GaN, on which Si is contained and an electrode is formed, and a multilayer film of undoped GaN / Si-doped GaN / undoped GaN are grown thereon. Thereafter, a superlattice layer made of GaN and InGaN is grown with a total film thickness of about 650 °. Next, a light emitting layer in which five layers of GaN (barrier layer) / InGaN (well layer) having a multiple quantum well structure are stacked, a cladding layer having a superlattice structure composed of Mg-doped AlGaN and Mg-doped InGaN, and non-doped AlGaN A layer, a p-type contact layer made of p-type GaN doped with Mg, is grown. Further, a p-type electrode is formed on the p-type contact layer, and an n-type electrode is formed on the n-type contact layer. (The p-type semiconductor is annealed at 400 ° C. or higher after film formation.)
After exposing each pn semiconductor surface by etching, each electrode was formed by sputtering. After the sapphire substrate containing Cr and Fe of the semiconductor wafer thus completed is polished to a thickness of about 100 μm, a scribe line is drawn and divided by an external force to form a light emitting element.
Next, the light emitting element was die-bonded with epoxy resin to a mount lead having a cup at the tip of a silver-plated copper lead frame. Each electrode of the light emitting element 120 was bonded to the mount lead and the inner lead with a conductive wire made of a gold wire to establish electrical continuity.
Furthermore, after mixing the translucent epoxy resin, it was cured at 150 ° C. for 5 hours. The light emitting diode thus formed has significantly improved color rendering properties compared to a white light emitting diode using a normal sapphire substrate.
【The invention's effect】
By using the light emitting device having the structure of the present invention, a light emitting diode capable of emitting practical white light with high luminance and high color rendering using visible light from near ultraviolet can be obtained. In particular, by obtaining, as uniform light, emission light containing a relatively long-wavelength red component emitted from a sapphire substrate containing the first element made of Cr or Fe and the above-described second element as an activator. A highly reliable light emitting device with high color mixing properties can be obtained.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of a light emitting device capable of emitting white light according to the present invention.
FIG. 2 is a schematic cross-sectional view of a light emitting device capable of emitting white light according to the present invention.
FIG. 3 is a schematic cross-sectional view of a light emitting device capable of emitting white light according to the present invention.
FIG. 4 is a schematic sectional view of a light emitting device capable of emitting white light according to the present invention.
FIG. 5 is a schematic perspective view of a light emitting device capable of emitting white light according to the present invention.
6A is a schematic cross-sectional view of a light-emitting device mounted with a light-emitting element capable of emitting white light according to the present invention, and FIG. 6B is a schematic perspective view.
7A is a schematic cross-sectional view of a light-emitting device mounted with a light-emitting element capable of emitting white light according to the present invention, and FIG. 7B is a schematic perspective view.
[Explanation of symbols]
101 ... Sapphire substrate
102 ... buffer layer
103: Dislocation reduction layer
120 ... light emitting element
121 ... n-type electrode
122 ... p-type electrode
123 ... Pad electrode
131 ... Protective film
132 ... Bump
200 ... activator
301 ... heat sink
302: Lead frame
303 ... conductive wire
304: translucent glass
305… Package resin
306 ... Plastic lens