JP3651260B2 - Nitride semiconductor device - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a nitride semiconductor (InXAlYGa1-X-YN, 0≤X, 0≤Y, X + Y) used in light emitting elements such as light emitting diodes (LEDs), laser diodes (LD), solar cells, photosensors, etc. ≦ 1) In particular, the present invention relates to a structure of a nitride semiconductor device that emits light in a specific ultraviolet region of 365 nm to 390 nm or has light receiving sensitivity.
[0002]
[Prior art]
Nitride semiconductors are known as semiconductor materials having a band gap energy of 1.95 eV (InN) to 6.16 eV (AlN), and can theoretically emit and receive light from about 633 nm to 201 nm. The applicant used this material and released the world's first blue LED exceeding 1 cd at the end of November 1993. This LED had a double hetero structure in which an InGaN layer having a thickness of about 0.2 μm doped with Zn and Si was used as a light emitting layer. Further, the present applicant has released a blue-green LED for a signal lamp and a green LED for a display by increasing the In composition ratio of the active layer of the LED.
[0003]
Next, the present applicant has made progress in improving the output of the light-emitting element and improving the color purity of the light-emitting color, and the high-brightness pure green light-emitting LED and the high-brightness blue LED using the inter-band light emission of the InGaN active layer Develop and sell. This new LED has a single quantum well structure or a multiple quantum well structure in which an active layer has a well layer made of InGaN having a thickness of 50 angstroms or less. By adopting an InGaN quantum well structure, the output can be improved more than twice as compared to the InGaN active layer doped with Zn and Si, and the half width of the emission spectrum can be greatly improved to 40 nm or less. did it. This is because the film thickness of InGaN is reduced to form a quantum structure, and the InGaN is less than the elastic critical film thickness, so that the crystallinity of the well layer is improved and the output is improved.
[0004]
Furthermore, the present applicant has announced the world's first laser oscillation of 410 nm at room temperature under pulse current as well as LED (for example, Jpn.J.Appl.Phys.35 (1996) L74, Jpn.J.Appl. Phys. 35 (1996) L217, etc.) and also succeeded in continuous oscillation at room temperature (for example, Nikkei Electronics December 2, 1996, Technical Bulletin, Appl. Phys. Lett. 69 (1996) 3034-, Appl. Phys. Lett. 69 (1996) 4056- etc.). These laser elements also have a multiple quantum well structure in which the active layer has an InGaN well layer having a thickness of 50 angstroms or less. As described above, for a visible light emitting device having a wavelength of approximately 400 nm to 550 nm, an extremely high output can be obtained by using an InGaN layer having a quantum well structure.
[0005]
[Problems to be solved by the invention]
On the other hand, it can be understood that an ultraviolet light emitting device having a wavelength of 400 nm or less can be realized by employing a nitride semiconductor having a large band gap energy such as AlGaN, GaN, InAlN, or the like for the active layer. If an ultraviolet light emitting element can be realized, it becomes possible to convert a phosphor into visible light using ultraviolet light, and to replace a light source such as a fluorescent lamp or an incandescent lamp with an LED or LD. Also, an efficient element can be realized for an optical sensor, a solar cell, and the like. However, at present, only the visible region has been developed, and no practical ultraviolet nitride semiconductor device has been reported. Therefore, the present invention has been made in view of such circumstances, and an object of the present invention is to produce a high-output and high-sensitivity element in the ultraviolet region using a nitride semiconductor.
[0006]
[Means for Solving the Problems]
  The present invention relates to an active layer and Al having a superlattice structure on the n side and the p side._xGa_{1 -X}A nitride semiconductor device having a cladding layer made of N (0 <X ≦ 0.4) and having a light guide layer between the active layer and the cladding layer, wherein the cladding layer having the superlattice structure is , Al with large band gap energy_ZGa_{1 -Z}N (0 <Z ≦ 1.0) layer and a GaN layer having a small band gap energy, and the impurity concentration of the GaN layer is the Al concentration._ZGa_{1 -Z}Larger than impurity concentration of N (0 <Z ≦ 1.0) layerA p-side contact layer having a p-electrode and a film thickness of 500 angstroms or less is provided on the p-side superlattice clad layer.It is characterized by that. The active layer is made of In._aGa_1-aA layer made of N (0 <a ≦ 0.1) is preferred.
[0007]
The nitride semiconductor layer having a large band gap energy is preferably an AlZGa1-ZN (0 <Z ≦ 1) layer.
[0008]
It is preferable that a p-side contact layer having a p-electrode and a thickness of 500 angstroms or less is provided on the p-side superlattice structure.
[0009]
The p-side superlattice structure and the p-side contact layer are preferably in contact with each other.
[0010]
The p-electrode is preferably Ni, Pt, Pd, Ni / Au, Pt / Au, or Pd / Au.
The nitride semiconductor device preferably includes a p-side light guide layer between the active layer and the p-side cladding layer.
[0011]
The nitride semiconductor element preferably includes a p-side cap layer having a band gap energy larger than that of the p-side light guide layer between the active layer and the p-side light guide layer.
[0012]
As described above, we fabricated light emitting devices with a number of structures using nitride semiconductors with relatively large band gap energy, such as AlGaN, GaN, InAlN, etc., as the active layer. Thus, a high output light-emitting element can be obtained by forming a nitride semiconductor having a specific composition containing a small amount of In with a specific film thickness. It came.
[0013]
In the first aspect, an active layer including an InaGa1-aN layer having an n-type impurity concentration of less than 5 × 10 17 / cm 3 is provided between the n-type nitride semiconductor layer and the p-type nitride semiconductor layer. A nitride semiconductor device, wherein the In value of the InaGa1-aN layer is greater than 0 and less than or equal to 0.1, and the thickness of the InaGa1-aN layer is greater than or equal to 100 angstroms and less than or equal to 1000 angstroms To do. Adjusting the a value to 0.05 or less, more preferably 0.02 or less, and most preferably 0.01 or less is desirable for increasing the output.
[0014]
In the second embodiment, an active layer including an InbGa1-bN layer having an n-type impurity concentration of 5 × 10 17 / cm 3 or more is provided between the n-type nitride semiconductor layer and the p-type nitride semiconductor layer. The nitride semiconductor device is characterized in that the b value of the InbGa1-bN layer is greater than 0 and 0.1 or less, and the thickness of the InbGa1-bN layer is 100 angstroms or more. The b value is preferably adjusted to 0.05 or less, more preferably 0.02 or less, and most preferably 0.01 or less to increase the output.
[0015]
In this specification, general formulas such as InaGa1-aN and InbGa1-bN merely indicate the composition formula of the nitride semiconductor, and even if different layers are indicated by the same general formula, It does not indicate that the value, b value, etc. match. In the present invention, among the plurality of layers on both sides of the active layer, one is called the n-type nitride semiconductor layer side and the other is called the p-type nitride semiconductor layer side. Insulater) type nitride semiconductor is included in the claims as a layer on the p-type nitride semiconductor side.
[0016]
In the first aspect and the second aspect of the present invention, at least one of the n-type nitride semiconductor layer and the p-type nitride semiconductor layer is in contact with the active layer and AlXGa1-XN (0 < A first nitride semiconductor layer having X ≦ 0.4) is provided. More preferably, the AlxGa1-XN layer is formed on both. In addition, when the AlxGa1-XN layers are formed on both, the X values of the AlxGa1-XN layers do not need to match. That is, the active layer may be sandwiched between AlGaN having different Al composition ratios.
[0017]
When the first nitride semiconductor layer is formed on both the n-type nitride semiconductor layer and the p-type nitride semiconductor layer, the film thicknesses of the first nitride semiconductor layers are different from each other. To do. In this case, it is desirable to reduce the thickness of the first nitride semiconductor layer on the n-layer side.
[0018]
Furthermore, in the present invention, when the first nitride semiconductor layer is formed in at least one of the active layers, IncGa1-cN (0 ≦ c <) is located at a position farther from the active layer than the first nitride semiconductor layer. 0.1, a, b> c), or a second nitride semiconductor layer made of AlYGa1-YN (0 <Y ≦ 0.4). Note that IncGa1-cN and AlYGa1-YN need not be formed in contact with the first nitride semiconductor layer, but are preferably formed in contact.
[0019]
In the first and second embodiments of the present invention, at least one of the n-type nitride semiconductor layer and the p-type nitride semiconductor layer includes a GaN layer and an AlZGa1-ZN (0 <Z ≦ 1) layer. And a third nitride semiconductor layer having a superlattice structure in which are stacked. The third nitride semiconductor layer may be formed in contact with the active layer like the first nitride semiconductor layer, or may be formed on the first nitride semiconductor layer like the second nitride semiconductor layer. It may be formed in contact with or at a position farther from the active layer than the first nitride semiconductor layer.
[0020]
When the third nitride semiconductor layer is formed, the superlattice layer is doped with an impurity that determines the conductivity type, and the impurity is more doped in the AlZGa1-ZN layer. . The GaN layer is most preferably undoped.
When the third nitride semiconductor layer is formed, the superlattice layer is doped with an impurity that determines the conductivity type, and the impurity is more doped in the GaN layer. The AlZGa1-ZN layer is most preferably undoped.
[0021]
Further, in the present invention, those containing Al in an amount smaller than the amount of In in the layer represented by InGaN and those containing In in an amount smaller than the amount of Al in the layer represented by AlGaN are also within the scope of the present invention. include.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a diagram showing the relationship between the thickness of an InGaN layer having an n-type impurity of less than 5 × 10 17 / cm 3 and the output of a light emitting device having an active layer having the InGaN layer as a well layer. , B represents a conventional 450 nm blue light emitting element. The output of the conventional blue light emitting element at the maximum output and the output of the ultraviolet light emitting element of the present invention are substantially the same. The basic structure of the device is a double hetero structure in which an n-GaN contact layer, an n-AlGaN cladding layer, an undoped InGaN active layer, a p-AlGaN cladding layer, and a p-contact layer are sequentially stacked on a substrate. .
[0023]
In the conventional visible light emitting device, as shown in B, a high light emission output can be obtained by setting the thickness of the InGaN well layer to less than 100 angstroms, more preferably to 50 angstroms or less. This is because the quantum effect by reducing the thickness of the InGaN layer, the improvement of crystallinity by making the thickness of the InGaN layer below the elastic critical thickness, the exciton light emission due to the non-uniform composition of the InGaN layer, and bi-exitons. This is because the light emission output is improved by the three effects of light emission. For this reason, it can be seen that if the thin InGaN layer is a well layer and the active layer is a single quantum well and a multiple quantum well, a high output can be obtained in a conventional visible light emitting device. On the other hand, in the ultraviolet light emitting device of the present invention, as shown in A, there is no tendency as in the case of the conventional visible light emitting device. Rather, a higher output can be obtained if the well layer constituting the active layer is not a quantum structure. There is a tendency. In addition, it has been found that a light emitting element having an undoped InGaN layer as an active layer has a light emission output peak in a limited thickness range of the InGaN layer. Accordingly, the thickness of the InGaN layer is adjusted to a range of 100 angstroms or more and 1000 angstroms or less, more preferably 200 angstroms or more and 800 angstroms or less, and most preferably 250 to 700 angstroms. As for A, undoped InGaN not intentionally doped with impurities is shown. Similarly, as a result of examining an InGaN layer doped with n-type impurities such as Si, Ge, Se, and S, n-type It was confirmed that the same tendency was observed when the impurity concentration was less than 5 × 10 17 / cm 3. Further, the tendency of the output of the light emitting element depending on the film thickness of the active layer as shown in FIG. 1A is in a specific ultraviolet region of 365 nm to 390 nm having InaGa1-aN (0 <a <0.1) in the active layer. A tendency as shown in FIG. 1B was observed for nitride semiconductor light emitting elements that emit light, and other light emitting elements exceeding 390 nm and emitting near 550 nm.
[0024]
Next, FIG. 2 is a diagram showing the relationship between the thickness of an InGaN layer having an n-type impurity of 5 × 10 17 / cm 3 or more and the output of a light-emitting element having the InGaN layer as an active layer. The relative output of 100% is an undoped light emitting element, and the output is shown in comparison with the undoped one. The basic structure of the element is the same except that the InGaN layer of the element described above is doped with Si.
[0025]
When the InGaN active layer is doped with an n-type impurity of 5 × 10 17 / cm 3 or more, the thickness of the InGaN layer constituting the active layer is adjusted to 100 angstroms or more, more preferably 200 angstroms or more. Even when the film thickness is increased, the output does not decrease as in the case of undoped, and is almost constant. However, the relative output is reduced by about 10% compared to the undoped one. This figure shows Si as an n-type impurity, but other n-type impurities S, Ge, Se, etc. have the same tendency if their concentration is 5 × 10 17 / cm 3 or more. confirmed.
[0026]
Here, the nitride semiconductor (InaAlbGa1-a-bN (0.ltoreq.a, 0.ltoreq.b, a + b.ltoreq.1) constituting the active layer will be described. In order to obtain light emission of 400 nm or less, the active layer has a large band gap energy. It is desirable to use a nitride semiconductor, that is, a nitride semiconductor containing Al. For this purpose, it is ideal to use AlGaN, InAlN, or the like, but in the present invention, InaGa1-aN (0 < a ≦ 0.1) and InbGa1-bN (0 <b ≦ 0.1) For example, if the active layer is GaN, light emission of about 365 nm can be obtained, but the output is very low. When Al is included, the output tends to further decrease, which is presumably due to the crystallinity of AlGaN and InAlN. It is necessary to form a cladding layer having a high Al mixed crystal ratio because of the gap energy, because a cladding layer having a high Al mixed crystal ratio tends to make it difficult to obtain a product with good crystallinity. If the semiconductor layer is used as the active layer, the device life tends to be shortened, but the output of the device is drastically improved only by adding a small amount of In to the GaN active layer as in the present invention. When the GaN contained in the active layer is used as an active layer, the output is improved by a factor of 10 or more compared to GaN, so both the a and b values of InaGa1-aN and InbGa1-bN are 0.1 or less, preferably 0.05 or less, more preferably It is adjusted to 0.02 or less, and most preferably 0.01 or less, but in the present invention, InGaN not containing Al does not mean a state containing no Al but an impurity level (example) If those containing Al is with less) Al content than In are intended to be included within the scope of the present invention.
[0027]
Furthermore, in a preferred embodiment of the light emitting device of the present invention, the first nitride semiconductor layer made of AlxGa1-XN (0 <X≤0.4) is in contact with the active layer containing InaGa1-aN and InbGa1-bN. Have. The AlGaN layer only needs to be in contact with one of the two main surfaces of the active layer, and is not necessarily in contact with both. In other words, a single heterostructure may be used. However, the X value of AlXGa1-XN is adjusted in the range of 0 <X ≦ 0.4, more preferably 0 <X ≦ 0.2, and most preferably 0 <X ≦ 0.1. If it is larger than 0.4, cracks tend to easily occur in the AlGaN layer, and if cracks occur, it tends to be difficult to form an element structure by laminating another semiconductor thereon. The film thickness of the first nitride semiconductor layer is 0.5 μm or less, more preferably 0.3 μm or less, and most preferably 0.1 μm or less. This is because if the thickness exceeds 0.5 μm, cracks tend to easily occur in the film even if the Al mixed crystal ratio is small.
[0028]
When the first nitride semiconductor layer having an Al mixed crystal ratio in a specific range is formed in contact with both main surface sides of the active layer, the thicknesses of the first nitride semiconductor layers are made different from each other. It is desirable. In our experiment, the output tends to be improved more easily when the AlGaN layer on the n-layer side is made thinner. As described above, the first nitride semiconductor layer made of AlxGa1-XN on the n-layer side and the p-layer side may have different Al mixed crystal ratios.
[0029]
Furthermore, in the device of the present invention, IncGa1-cN (0≤c <0.1, 0≤c <0.1, at a position farther from the active layer than the first nitride semiconductor layer made of AlXGa1-XN (0 <X≤0.4). a> c, b> c) or a second nitride semiconductor layer made of AlYGa1-YN (0 <Y ≦ 0.4). The second nitride semiconductor layer is preferably GaN. In the case of an LED, it is desirable that the second nitride semiconductor layer acts as a contact layer for forming an electrode. Similar to the first nitride semiconductor layer, the second nitride semiconductor layer may be formed in either the n layer or the p layer, and is not necessarily formed in both. The thickness of the second nitride semiconductor layer is not particularly limited, but when it is formed on the n layer side, it is adjusted to 10 μm or less, more preferably 8 μm or less. On the other hand, when it is formed on the p-layer side, it is preferably formed thinner than the n-layer side, and is formed with a film thickness of 2 μm or less, more preferably 1 μm or less. A plurality of the second nitride semiconductor layers may be provided on the same conductive layer.
[0030]
In another aspect of the present invention, a GaN layer having a small band gap energy and an AlZGa1-ZN (0 <Z ≦ 1) layer having a large band gap energy are stacked on at least one of the n layer side and the p layer side. And a third nitride semiconductor layer having a superlattice structure. The third nitride semiconductor layer may be formed in contact with the active layer or may be formed at a position away from the active layer. Preferably, it is formed at a position away from the active layer, and is formed as a clad layer for confining carriers or a contact layer for forming an electrode. There may be a plurality of the third nitride semiconductor layers in the same conductive layer. Further, the third nitride semiconductor layer can be a layer in contact with the active layer, that is, the first nitride semiconductor layer.
[0031]
In the case of a superlattice structure, the thickness of the GaN layer and the AlZGa1-ZN layer is adjusted to 100 angstroms or less, more preferably 70 angstroms or less, and most preferably 50 angstroms or less. If it is thicker than 100 angstroms, each layer constituting the superlattice layer has a film thickness exceeding the elastic strain limit, and there is a tendency for minute cracks or crystal defects to easily enter the film, and the lower limit of the film thickness is not particularly limited. One atom or more is sufficient. When AlZGa1-ZN is used as the superlattice constituent layer, cracks are less likely to occur even when the Al mixed crystal ratio is higher than that of the thicker one. This is because the AlGaN layer is grown with a film thickness equal to or less than the elastic critical film thickness. Furthermore, since AlGaN and GaN can be grown at the same temperature, it is easy to form a superlattice. On the other hand, if it is InGaN, the growth atmosphere must also be changed, and it is more difficult to construct a superlattice with AlGaN and InGaN than when a superlattice layer is formed with AlGaN and GaN.
[0032]
When the third nitride semiconductor composed of a superlattice layer forms a clad layer as an optical confinement layer and a carrier confinement layer, it is necessary to grow a nitride semiconductor having a larger band gap energy than the well layer of the active layer. The nitride semiconductor layer having a large band gap energy is a nitride semiconductor having a high Al mixed crystal ratio. Conventionally, when a nitride semiconductor having a high Al mixed crystal ratio is grown as a thick film, cracks are easily generated, and thus crystal growth is very difficult. However, when a superlattice layer is formed as in the present invention, even if the single layer constituting the superlattice layer is a layer having a slightly higher Al mixed crystal ratio, it is grown with a film thickness less than the elastic critical film thickness, so that cracks are not easily generated. . Therefore, since a layer having a high Al mixed crystal ratio can be grown with good crystallinity, the optical confinement effect and the carrier confinement effect are enhanced, and the threshold voltage in the laser element and Vf (forward voltage) in the LED element can be lowered.
[0033]
Further, the superlattice layer is doped with an impurity that determines the conductivity type of the superlattice layer, and the n-type impurity concentrations of the AlZGa1-ZN layer and the GaN layer are different. This is called so-called modulation doping. When the n-type impurity concentration of one layer is low, preferably when the impurity is not doped (undoped) and the other is highly doped, the threshold voltage, Vf, etc. are lowered. be able to. This is because when a layer having a low impurity concentration is present in the superlattice layer, the mobility of the layer is increased, and a layer having a high impurity concentration is also present at the same time. By being able to form a layer. A layer having a high impurity concentration and a high carrier concentration and a layer having a high impurity concentration and a high carrier concentration are present at the same time, so that a layer having a high carrier concentration and a high mobility is formed. I guess that.
[0034]
When a nitride semiconductor layer having a large band gap energy is doped with a high concentration of impurities, this modulation doping generates a two-dimensional electron gas between the high impurity concentration layer and the low impurity concentration layer. It is presumed that the resistivity decreases due to the influence. For example, in a superlattice layer in which a nitride semiconductor layer having a large band gap doped with an n-type impurity and an undoped nitride semiconductor layer having a small band gap are stacked, a layer doped with an n-type impurity and an undoped layer The barrier layer side is depleted at the heterojunction interface, and electrons (two-dimensional electron gas) accumulate at the interface around the thickness of the layer side having a small band gap. Since the two-dimensional electron gas can be generated on the side having a small band gap, the electrons are not scattered by impurities when they travel, so that the mobility of electrons in the superlattice increases and the resistivity decreases. It is presumed that the modulation doping on the p side is also influenced by the two-dimensional hole gas. In the case of the p layer, AlGaN has a higher resistivity than GaN. Therefore, since the resistivity is lowered by doping a large amount of p-type impurities into AlGaN, the substantial resistivity of the superlattice layer is lowered. Therefore, when an element is manufactured, the threshold tends to be lowered. Inferred.
[0035]
Moreover, since the ohmic resistance with the electrode is easily obtained due to the lowering of the resistivity, and the series resistance in the film is also reduced, a nitride semiconductor element having a low threshold voltage and Vf can be obtained.
[0036]
On the other hand, it is presumed that when the nitride semiconductor layer having a small band gap energy is doped with an impurity at a high concentration, the following effects are obtained. For example, when the AlGaN layer and the GaN layer are doped with the same amount of Mg, the AlGaN layer has a large Mg acceptor level depth and a low activation rate. On the other hand, the acceptor level of the GaN layer is shallower than the AlGaN layer, and the activation rate of Mg is high. For example, even if Mg is doped 1 × 10 20 / cm 3, GaN has a carrier concentration of about 1 × 10 18 / cm 3, whereas AlGaN can obtain only a carrier concentration of about 1 × 10 17 / cm 3. Therefore, in the present invention, a superlattice with a high carrier concentration can be obtained by forming a superlattice with AlGaN / GaN and doping more impurities into the GaN layer that can obtain a high carrier concentration. In addition, since the superlattice is used, carriers move through the AlGaN layer having a low impurity concentration due to the tunnel effect, so that the carriers are not substantially affected by the AlGaN layer, and the AlGaN layer functions as a cladding layer having a high band gap energy. Therefore, even if the nitride semiconductor layer having the smaller band gap energy is doped with a large amount of impurities, it is very effective in reducing the threshold values of the laser element and the LED element. Although this description has been given of an example in which a superlattice is formed on the p-type layer side, the same effect can be obtained when a superlattice is formed on the n-layer side.
[0037]
When doping a nitride semiconductor layer having a large band gap energy with a large amount of n-type impurities, a preferable doping amount to the nitride semiconductor layer having a large band gap energy is preferably 1 × 10 17 / cm 3 to 1 × 10 20 / cm 3. Is adjusted in the range of 1 × 10 18 / cm 3 to 5 × 10 19 / cm 3. If it is less than 1 × 10 17 / cm 3, the difference from the nitride semiconductor layer having a small band gap energy tends to be small, and it tends to be difficult to obtain a layer having a high carrier concentration, and if it exceeds 1 × 10 20 / cm 3. The leak current of the element itself tends to increase. On the other hand, the n-type impurity concentration of the nitride semiconductor layer having a small band gap energy should be less than that of the nitride semiconductor layer having a large band gap energy, and preferably 1/10 or less. Most preferably, when undoped, a layer having the highest mobility is obtained, but since the film thickness is thin, there is an n-type impurity diffused from the nitride semiconductor side having a large band gap energy, and the amount is 1 × 10 19 / cm3 or less is desirable. As the n-type impurity, elements of Group IVB and VIB of the periodic table such as Si, Ge, Se, S, and O are selected. Preferably, Si, Ge, and S are n-type impurities. This effect is the same when a nitride semiconductor layer having a large band gap energy is doped with a small amount of n-type impurities and a nitride semiconductor layer having a small band gap energy is doped with a large amount of n-type impurities.
[0038]
Although the case where the impurity is preferably modulation-doped in the superlattice layer has been described above, the impurity concentration of the nitride semiconductor layer having a large band gap energy and that of the nitride semiconductor layer having a small band gap energy can be made equal.
[0039]
When the third nitride semiconductor layer of the superlattice layer is formed in the p-side layer, the action of the superlattice structure on the light emitting element is the same as the action of the n-side layer on the superlattice, but the n-layer In addition to the case where it is formed on the side, there are the following effects. That is, the resistivity of the p-type nitride semiconductor is usually two orders of magnitude higher than that of the n-type nitride semiconductor. Therefore, when the superlattice layer is formed on the p layer side, the decrease in Vf appears remarkably. More specifically, it is known that a nitride semiconductor is a semiconductor in which p-type crystals are very difficult to obtain. A technique for removing hydrogen by annealing a nitride semiconductor layer doped with a p-type impurity to obtain a p-type crystal is known (Japanese Patent No. 2540791). However, even if p-type is obtained, the resistivity is several Ω · cm or more. Therefore, by using this p-type layer as a superlattice layer, the crystallinity is improved and the resistivity is decreased by one digit or more, so that a decrease in Vf tends to appear.
[0040]
When the third nitride semiconductor layer of the superlattice is formed in the p-side layer, the p-type impurity concentration of the nitride semiconductor layer having a large band gap energy is different from that of the nitride semiconductor layer having a small band gap energy. The impurity concentration of one layer is increased, and the impurity concentration of the other layer is decreased. Similar to the n-side layer of the superlattice, the p-type impurity concentration in the nitride semiconductor layer having a larger band gap energy is increased, and the p-type impurity concentration in the nitride semiconductor layer having a smaller band gap energy is decreased. When preferably undoped, the threshold voltage, Vf, and the like can be reduced. The reverse is also possible. That is, the p-type impurity concentration of the nitride semiconductor layer having a large band gap energy may be reduced and the p-type impurity concentration of the nitride semiconductor layer having a low band gap energy may be increased. The reason is as described above.
[0041]
When the third nitride semiconductor layer is a superlattice layer, the preferred doping amount of the p-type impurity to the third nitride semiconductor is 1 × 10 18 / cm 3 to 1 × 10 21 / cm 3, more preferably 5 × 10 18. / Cm3 to 5 × 1020 / cm3. If it is less than 1 × 10 18 / cm 3, the difference from the fourth nitride semiconductor layer is also reduced, and it tends to be difficult to obtain a layer having a high carrier concentration, and it is also less than 1 × 10 21 / cm 3. When the amount is large, the crystallinity tends to deteriorate. On the other hand, the p-type impurity concentration of the nitride semiconductor layer having a small band gap energy should be less than that of the nitride semiconductor layer having a large band gap energy, and preferably 1/10 or less. Most preferably, when undoped, a layer having the highest mobility is obtained, but since the film thickness is small, there is a p-type impurity diffused from the nitride semiconductor side having a large band gap energy, and the amount thereof is 1 × 10 20 / cm3 or less is desirable. As the p-type impurities, Group IIA and IIB elements of the periodic table such as Mg, Zn, Ca and Be are selected, and preferably Mg, Ca and the like are used as p-type impurities. This effect is the same when the nitride semiconductor layer having a large band gap energy is doped with a small amount of p-type impurities and the nitride semiconductor layer having a small band gap energy is doped with a large amount of p-type impurities.
[0042]
Furthermore, in the nitride semiconductor layer constituting the superlattice, the layer doped with impurities at a high concentration has a large impurity concentration near the center of the semiconductor layer and a small impurity concentration near both ends in the thickness direction ( Preferably, it is undoped. More specifically, for example, when a superlattice layer is formed of AlGaN doped with Si as an n-type impurity and an undoped GaN layer, since AlGaN is doped with Si, electrons are emitted to the conduction band as donors. Electrons fall into the low-potential GaN conduction band. Since the GaN crystal is not doped with a donor impurity, it is not subject to carrier scattering by the impurity. Therefore, the electrons can easily move in the GaN crystal, and the substantial mobility of electrons increases. This is similar to the effect of the two-dimensional electron gas described above, and the substantial mobility in the lateral direction of the electron increases and the resistivity decreases. Further, the effect is further enhanced when the n-type impurity is doped at a high concentration in the central region of AlGaN having a large band gap energy. That is, depending on the electrons moving in GaN, the n-type impurity ions (Si in this case) contained in AlGaN are somewhat scattered. However, if both ends are undoped with respect to the thickness direction of the AlGaN layer, it is difficult to receive Si scattering, and the mobility of the undoped GaN layer is further improved. Although the operation is slightly different, there is a similar effect when a superlattice is composed of a nitride semiconductor layer having a large band gap energy on the p-layer side and a nitride semiconductor layer having a small band gap energy. It is desirable that the central region of the physical semiconductor layer is doped with a large amount of p-type impurities and the both end portions are decreased or undoped. On the other hand, a layer in which a large amount of n-type impurities are doped in a nitride semiconductor layer having a small band gap energy may be configured to have the impurity concentration.
[0043]
The superlattice layer is preferably at least in the p-side layer, and a superlattice layer in the p-side layer is preferable because the threshold value is further lowered.
[0044]
【Example】
[Example 1]
FIG. 3 is a schematic cross-sectional view showing the structure of an LED device according to an embodiment of the present invention. Hereinafter, a method for manufacturing the device of the present invention will be described based on this drawing.
[0045]
The surface of the substrate 1 made of sapphire (C surface) is cleaned at 1050 ° C. in a hydrogen atmosphere in a reaction vessel. In addition to sapphire C surface, sapphire whose main surface is R surface and A surface, other insulating substrates such as spinel (MgA12O4), SiC (including 6H, 4H, 3C), Si, A semiconductor substrate such as ZnO, GaAs, or GaN (a GaN substrate will be described later) can be used.
(Low temperature growth buffer layer 2)
Subsequently, a low temperature growth buffer layer 2 made of GaN is grown on the substrate 1 at a film thickness of about 200 Å using ammonia and TMG (trimethylgallium) at 510 ° C. in a hydrogen atmosphere.
(Second buffer layer 3)
After the growth of the buffer layer 2, the second buffer layer 3 made of an undoped GaN layer is grown to a thickness of 1 μm using TMG and ammonia at 1050 ° C. The second buffer layer 3 grown on and in contact with the low temperature growth buffer layer 2 is preferably an undoped nitride semiconductor, particularly preferably undoped GaN. When undoped GaN is used, a nitride semiconductor layer doped with an n-type impurity grown thereon can be grown with good crystallinity. The thickness of the second buffer layer 3 is desirably 100 angstroms or more and 10 μm or less, more preferably 0.1 μm or more and 5 μm or less. The second buffer layer may be doped with n-type impurities such as Si and Ge.
(N-side contact layer 4 = n-side second nitride semiconductor layer)
Next, an n-side contact layer 4 made of n-type GaN doped with Si at 1 × 10 18 / cm 3 or more is grown at a thickness of 2 μm at 1050 ° C. using TMG, ammonia, and silane (SiH 4). This n-side contact layer is a layer for forming an n-electrode. When GaN doped with an n-type impurity is used, a layer having a high carrier concentration and a low resistivity is easily obtained, and a preferable ohmic with the n-electrode is easily obtained. Further, as described later, this layer may be a superlattice layer in which impurities are modulation-doped.
(N-side cladding layer 5 = n-side first nitride semiconductor layer)
Next, an n-side cladding layer 5 made of n-type Al0.05Ga0.95N doped with Si at 1 × 10 18 / cm 3 is formed at a thickness of 300 Å using TMG, TMA (trimethylaluminum) ammonia, and silane at 1050 ° C. .
(Active layer 6)
Next, an active layer made of undoped In0.01Ga0.99N is grown to a thickness of 400 angstroms using TMI, TMG, and ammonia at 700 ° C. in a nitrogen atmosphere. The band gap energy (Eg) of the active layer InaGa1-aN is expressed by the equation
Eg = 1.96.a + 3.4 (1-a) -a. (1-a)
Can be calculated. The emission wavelength λ corresponds to 1240 / Eg.
(P-side cladding layer 7 = p-side first nitride semiconductor layer)
Next, a p-side cladding layer 7 made of Al0.05Ga0.95N doped with 1 × 10 20 / cm 3 of Mg using TMG, TMA, ammonia, Cp 2 Mg (cyclopentadienyl magnesium) at 1050 ° C. in a hydrogen atmosphere is 600 Å. Growing with a film thickness of In addition to Mg, Group II elements such as Ca, Be, Zn, and Cd can be cited as p-type impurities doped into nitride semiconductors, but Mg is most commonly used.
(P-side contact layer 8 = p-side second nitride semiconductor layer)
Subsequently, a p-side contact layer 8 made of GaN doped with 1 × 10 20 / cm 3 of Mg with TMG, ammonia, and Cp 2 Mg is grown to a thickness of 0.12 μm. The p-side contact layer 8 is a layer for forming a p-electrode. When GaN doped with a p-type impurity is used, a preferable ohmic contact with the p-electrode material is easily obtained. It is desirable to adjust the thickness of the p-side contact layer in the range of usually 100 angstroms to 1 μm.
[0046]
After completion of the growth, the wafer is annealed at 700 ° C. in a nitrogen atmosphere in a nitrogen atmosphere to further reduce the resistance of the p-type layer. Then, the wafer is taken out of the reaction container and the surface of the uppermost p-side contact layer 8 is removed. Then, a mask having a predetermined shape is formed, and etching is performed from the p-side contact layer side by an RIE (reactive ion etching) apparatus to expose the surface of the n-side contact layer 4 as shown in FIG.
[0047]
After the etching, a translucent p-electrode 9 containing Ni and Au having a thickness of 200 angstroms is formed almost on the entire surface of the p-side contact layer on the uppermost layer, and a p-pad electrode made of Au for bonding on the p-electrode 9 10 is formed with a film thickness of 0.2 μm. On the other hand, an n-electrode 11 containing W and Al is formed on the surface of the second nitride semiconductor layer 4 exposed by etching. Finally, an insulating film 12 made of SiO2 is formed as shown in FIG. 1 in order to protect the surface of the p-electrode 9, and then the wafer is separated by scribe to form a 350 μm square LED element.
[0048]
This LED element emits light of approximately 368 nm at a forward voltage of 20 mA, Vf is 3.4 V, and the output is 5 mW, which is almost the same output as a blue LED emitting light at 450 nm where the conventional active layer has a quantum well structure. Indicated. In this LED element, when the thickness of the active layer was changed, the same tendency as the solid line shown in FIG.
[Example 2]
In Example 1, an LED element was manufactured in the same manner except that the n-side first nitride semiconductor layer 5 was not grown. The emission wavelength at 20 mA and Vf were the same as in Example 1, but the output was Compared to that of Example 1, it was reduced by about 10%.
[Example 3]
In Example 1, the n-side cladding layer 5 is an undoped GaN layer, 50 angstroms, and an Al0.1Ga0.9N layer 50 angstroms doped with Si 1 × 10 18 / cm 3 is alternately laminated to a total film thickness of 300 angstroms. In addition, the p-side cladding layer 6 is an undoped GaN layer of 50 angstroms, and an Al0.1 Ga0.9N layer of 50 angstroms doped with 1 × 10 19 / cm 3 of Mg is alternately laminated to a total film thickness of 600 An LED element was fabricated in the same manner as in Example 1 except that an angstrom superlattice structure was used. As a result, Vf at 20 mA decreased by about 0.1 V, the emission wavelength was the same as in Example 1, and the output was the same as in Example 1. It was improved by about 20% compared to the product. Further, by using the superlattice layer as the cladding layer, the electrostatic withstand voltage is improved more than twice as compared with the conventional visible LED element. This superlattice layer is expressed as a third nitride semiconductor layer in the claims of the present application.
[Example 4]
An LED device was fabricated in the same manner as in Example 1 except that the In0.01Ga0.99N layer of the active layer 6 was doped with 1 × 10 18 / cm 3 of Si and the film thickness was 500 Å. The emission wavelength, Vf, was the same as in Example 1, but the output was reduced by approximately 10% compared to that in Example 1. In this LED element, when only the film thickness was changed without changing the Si concentration of the active layer, the same tendency as the solid line shown in FIG. 2 was observed.
[Example 5]
An LED element was obtained in the same manner as in Example 1 except that the composition of the active layer 6 was changed to the In0.05Ga0.95N layer. The LED element emitted light of approximately 378 nm at a forward voltage of 20 mA, Vf was 3.4 V, and the output Showed the same output as Example 1 at 5 mW.
[Example 6]
FIG. 4 is a perspective view showing the structure of the laser device according to the present invention, and also shows a cross section when cut in a direction perpendicular to the stripe-shaped electrode. Embodiment 4 will be described below with reference to this figure.
[0049]
As in Example 1, a low-temperature growth buffer layer 2 made of GaN is grown to a thickness of 200 angstroms on a sapphire substrate 1 having a 2 inch φ and C-plane as a main surface, and then the temperature is set to 1050 ° C. A second buffer layer 3 made of an undoped GaN layer is grown to a thickness of 5 μm. When this second buffer layer 3 is not a cladding layer but an underlayer for producing a GaN substrate, Al x Ga 1-XN (0 ≦ X ≦ 0.5) with an Al mixed crystal ratio X value of 0.5 or less. It is desirable to grow. If it exceeds 0.5, the crystal itself tends to crack rather than a crystal defect, so that the crystal growth itself tends to be difficult. The film thickness is desirably adjusted to 10 μm or less.
Next, the wafer is taken out of the reaction vessel, a striped photomask is formed on the surface of the second buffer layer 3, and a protective film 201 made of SiO2 having a stripe width of 20 μm and a stripe interval (window) of 5 μm is formed by a CVD apparatus. Is formed so that the stripe is parallel to the (11-00) direction of GaN. FIG. 4 shows a cross section when cut in a direction perpendicular to the major axis direction of the stripe. The shape of the protective film may be any shape such as a stripe shape, a dot shape, or a grid shape, but it protects from the exposed portion of the second buffer layer 3, that is, the portion where the protective film is not formed (window portion). Increasing the film area facilitates growth of the GaN substrate 20 with fewer crystal defects. Examples of the material of the protective film include oxides and nitrides such as silicon oxide (SiOx), silicon nitride (SiXNY), titanium oxide (TiOx), and zirconium oxide (ZrOx), and multilayer films other than 1200 ° C. A metal having a melting point of These protective film materials can withstand the nitride semiconductor growth temperature of 600 ° C. to 1100 ° C., and the nitride semiconductor does not grow or hardly grow on the surface thereof.
[0050]
After forming the protective film 201, the wafer is set in the reaction vessel again, and a GaN substrate 20 made of undoped GaN is grown at a thickness of 10 μm at 1050 ° C. The preferred growth thickness of the GaN substrate 20 varies depending on the thickness and size of the protective film 201 formed earlier, but the GaN substrate 20 is grown laterally on the protective film so as to cover the surface of the protective film 201. In the method of growing the GaN substrate 20 in the lateral direction on the protective film 201 having the property that the nitride semiconductor does not easily grow on the surface as described above, first, the GaN substrate 20 is grown on the protective film 201. First, the GaN substrate 20 is selectively grown on the surface of the second buffer layer 3 in the window portion. Subsequently, when the growth of the GaN substrate 20 is continued, the GaN substrate 20 grows in the lateral direction and covers the protective film 201 and is connected to the adjacent GaN substrates 20 to form the GaN on the protective film 201. The state is as if the substrate 20 has grown. That is, the GaN layer is grown in the lateral direction through the protective film 201. What is important is the number of crystal defects of the GaN substrate 20 grown on the window and the GaN substrate 20 grown on the protective film 201. Due to the lattice constant mismatch between the heterogeneous substrate and the nitride semiconductor, a large number of crystal defects are generated in the nitride semiconductor grown on the heterogeneous substrate, and these crystal defects are transmitted to the surface during the growth of the nitride semiconductor. . On the other hand, the GaN substrate 20 grown laterally on the protective film 201 is not grown from the sapphire substrate 1, but is connected to the adjacent GaN substrate 20 during growth. Very little compared to those grown from. Therefore, when a partially formed protective film is formed on a nitride semiconductor layer grown on a heterogeneous substrate and a GaN layer grown laterally on the protective film is used as a substrate, the present invention is implemented. Compared to the semiconductor grown on the sapphire substrate of Example 1, a laminated semiconductor layer with much fewer crystal defects is obtained. Actually, the second buffer layer 3 has a crystal defect of 10 10 / cm 2 or more, but the crystal defect of the GaN substrate 10 by this method is reduced to 10 6 / cm 2 or less.
[0051]
After the GaN substrate 20 is grown as described above, the n-side contact layer 4 made of n-type GaN doped with Si at least 1 × 10 18 / cm 3 on the GaN substrate 1 in the same manner as in the first embodiment ( An n-side second nitride semiconductor layer) is grown to a thickness of 2 μm. This layer may be a superlattice layer made of undoped GaN and Si-doped AlxGa1-XN (0 <X ≦ 0.4).
(Crack prevention layer 21 = n-side second nitride semiconductor layer)
After the growth of the n-side contact layer 4, the temperature is raised to 800 ° C., and a crack prevention layer 21 made of In0.1Ga0.9N doped with Si 5 × 10 18 / cm 3 with TMG, TMI, ammonia, silane gas in a nitrogen atmosphere is formed to 500 Grow with angstrom thickness. The crack prevention layer 21 can be prevented from being cracked in a nitride semiconductor layer containing Al to be grown later by growing it with an n-type nitride semiconductor containing In, preferably InGaN. The crack prevention layer is preferably grown with a film thickness of 100 Å or more and 0.5 μm or less. If it is thinner than 100 angstroms, it is difficult to act as a crack prevention as described above, and if it is thicker than 0.5 μm, the crystal itself tends to turn black.
(N-side cladding layer 22 = third nitride semiconductor layer)
Subsequently, using TMA, TMG, ammonia, and silane gas at 1050 ° C., the layer made of n-type Al 0.2 Ga 0.8 N doped with Si 1 × 10 19 / cm 3 is 40 Å and the undoped GaN layer is 40 Å. Then, an n-side cladding layer 22 made of a superlattice having a total thickness of 0.8 μm, in which 100 layers are alternately stacked, is grown.
(N-side light guide layer 23 = n-side first nitride semiconductor layer)
Subsequently, an n-side light guide layer 13 made of undoped Al0.05Ga0.95N is grown to a thickness of 0.1 μm. This layer acts as a light guide layer for guiding the light of the active layer, and may be doped with n-type impurities in addition to undoped. This layer can also be a superlattice layer made of GaN and AlGaN.
(Active layer 6)
Next, as in Example 1, an active layer made of undoped In0.01Ga0.99N is grown to a thickness of 400 angstroms.
(P-side cap layer 24 = p-side first nitride semiconductor layer)
Next, a p-side cap layer 24 made of p-type Al0.2Ga0.8N doped with 1 × 10 19 / cm 3 of Mg and having a band gap energy larger than that of the p-side light guide layer 25 is grown to a thickness of 300 Å.
(P-side light guide layer 25 = p-side second nitride semiconductor layer)
Next, a p-side light guide layer 25 made of Al0.01Ga0.99N having a band gap energy smaller than that of the p-side cap layer 15 is grown to a thickness of 0.1 μm. This layer acts as a light guide layer for the active layer. The p-side light guide layer can be a superlattice layer made of an undoped nitride semiconductor. In the case of a superlattice layer, the band gap energy of the layer (barrier layer) having the larger band gap energy is larger than that of the active layer and smaller than that of the p-side cladding layer.
(P-side cladding layer 26 = p-side third nitride semiconductor layer)
Subsequently, p-type Al0.2Ga0.8N layer doped with 1 × 10 19 / cm 3 of Mg and p-side consisting of a superlattice structure having a total thickness of 0.8 μm, which is formed by alternately laminating 40 angstroms of p-type Al0.2Ga0.8N layers The cladding layer 26 is grown. Thus, from the active layer to the p-layer side, the first nitride semiconductor layer made of AlGaN having a large band gap energy, and then made of GaN and AlGaN having a band gap energy smaller than that of the first nitride semiconductor layer. Providing the second nitride semiconductor layer and then the third nitride semiconductor layer having a superlattice structure having a barrier layer having a larger bandgap energy than the second nitride semiconductor layer can reduce the threshold of the laser element. It is very preferable in terms of reduction.
(P-side contact layer 27 = p-side second nitride semiconductor layer)
Finally, a p-side contact layer 26 made of p-type GaN doped with 1 × 10 20 / cm 3 of Mg is grown on the p-side cladding layer 26 to a thickness of 150 Å. In particular, in the case of a laser device, a nitride semiconductor having a small band gap energy is used as a p-side contact layer in contact with the p-side cladding layer 26 having a superlattice structure containing AlGaN, and the film thickness is reduced to 500 angstroms or less. In addition, the carrier concentration of the p-side contact layer 27 is substantially increased, a preferable ohmic with the p-electrode is obtained, and the threshold current and voltage of the device tend to decrease.
[0052]
After annealing the nitride semiconductor grown wafer as described above in the same manner as in Example 1 to further reduce the resistance of the p-type impurity doped layer, the wafer was taken out of the reaction vessel and shown in FIG. As shown, the uppermost p-side contact layer 27 and the p-side cladding layer 26 are etched by an RIE apparatus to form a ridge shape having a stripe width of 4 μm. Thus, by forming the layer above the active layer in a striped ridge shape, the emission of the active layer is concentrated under the stripe ridge, and the threshold value is lowered. The p-side cladding layer 26 and higher layers are preferably ridge-shaped.
[0053]
Next, a mask is formed on the ridge surface and etching is performed by RIE to expose the surface of the n-side contact layer 4 and to form an n-electrode 30 made of Ti and Al in a stripe shape. On the other hand, on the ridge outermost surface of the p-side contact layer 27, a p-electrode 31 made of Ni and Au is formed in a stripe shape. Examples of the electrode material that can provide a preferable ohmic with the p-type GaN layer include Ni, Pt, Pd, Ni / Au, Pt / Au, and Pd / Au. Examples of the electrode material that can provide a preferable ohmic with n-type GaN include metals, alloys such as Al, Ti, W, Cu, Zn, Sn, and In.
[0054]
Next, as shown in FIG. 4, an insulating film 32 made of SiO 2 is formed on the surface of the nitride semiconductor layer exposed between the p electrode 31 and the n electrode 30, and the p electrode 31 is interposed through the insulating film 32. A p-pad electrode 33 electrically connected to is formed. The p-pad electrode 33 substantially increases the surface area of the p-electrode 31 so that the p-electrode side can be wire-bonded or die-bonded.
[0055]
As described above, the wafer on which the n-electrode and the p-electrode are formed is transferred to a polishing apparatus, and the sapphire substrate on which the nitride semiconductor is not formed is wrapped using a diamond abrasive, The thickness is 70 μm. After lapping, the substrate surface is mirror-finished by polishing with 1 μm with a finer abrasive and the entire surface is metallized with Au / Sn.
[0056]
Thereafter, the Au / Sn side is scribed and cleaved in a bar shape in a direction perpendicular to the striped electrode, and a resonator is formed on the cleavage plane. A dielectric multilayer film made of SiO2 and TiO2 is formed on the resonator surface, and finally a bar is cut in a direction parallel to the p-electrode to form a laser chip. Next, the chip was placed face-up (with the substrate and the heat sink facing each other) on the heat sink, each electrode was wire-bonded, and laser oscillation was attempted at room temperature. At room temperature, the threshold current density was 2.0 kA / Continuous oscillation at an oscillation wavelength of 368 nm was confirmed at cm 2 and a threshold voltage of 4.0 V, and a lifetime of 1000 hours or more was shown.
[Example 7]
In Example 6, a laser device was fabricated in the same manner as in Example 6 except that the In0.01Ga0.99N layer of the active layer 6 was doped with Si 6 × 10 17 / cm 3 and the film thickness was 1000 angstroms. The current density and voltage at the threshold increased by about 10% compared to those in Example 6, and the lifetime was shortened by about 20%.
[Example 8]
In Example 6, the n-side contact layer 4 is an undoped GaN layer, 50 angstroms, and an Al0.05Ga0.95N layer doped with 1 × 10 18 / cm 3 of Si, 50 angstroms, and a total film thickness of 2 μm. When a laser device was fabricated in the same manner as in Example 6 except that the superlattice structure was used, the current density and voltage at the threshold were reduced by about 5% compared to those in Example 6, and the lifetime was 1000 hours or more. showed that.
[Example 9]
In Example 3, the n-side cladding layer 5 has an undoped Al0.1Ga0.9N layer of 50 angstroms and a Si film of 1 × 10 18 / cm 3 doped GaN layers of 50 angstroms, and has a total film thickness of 300 angstroms. It has a superlattice structure, and the p-side cladding layer 6 is an undoped Al0.1Ga0.9N layer of 50 angstroms, and a GaN layer of 50 angstroms doped with 1 × 10 19 / cm 3 of Mg is alternately laminated to a total film thickness of 600 angstroms. An LED element was fabricated in the same manner as in Example 3 except that the superlattice structure was used. As a result, good results were obtained in substantially the same manner as in Example 3.
[Example 10]
In Example 6, the n-side cladding layer 22 is formed by alternately laminating 100 Å layers of 40 angstroms of GaN layers doped with 1 × 10 19 / cm 3 of Si and 40 angstroms of undoped Al0.2Ga0.8N layers. A superlattice structure with a total film thickness of 0.8 μm, and the p-side cladding layer 26 is alternately formed with 40 angstroms of GaN layers doped with 1 × 10 19 / cm 3 of Mg and 40 angstroms of undoped Al 0.2 Ga 0.8 N layers. A laser device was fabricated in the same manner as in Example 6 except that a superlattice structure with a total thickness of 0.8 μm formed by stacking growth was used. As a result, good results were obtained in substantially the same manner as in Example 6.
[0057]
【The invention's effect】
As described above, according to the nitride semiconductor device of the present invention, an ultraviolet light emitting device having a high output from 360 nm to 390 nm can be realized. The short-wavelength light-emitting element serves as an excitation light source for a phosphor when a white LED is manufactured, for example. The current white LED is excited by visible light around 430 nm and emits orange light, and white is observed due to a mixture of blue and orange. The types of such phosphors are limited. However, if a short-wavelength light source is realized, the number of phosphors that emit light when excited by the light source increases, so that, for example, a white light source can be created by mixing phosphors of different emission colors, and the number of uses increases greatly. . Further, when an ultraviolet light source is used as a reading light source such as a DVD, the DVD capacity can be dramatically improved. Furthermore, the present invention can be applied to a light receiving element such as a sensor sensitive to ultraviolet light, and its industrial utility value is great.
[Brief description of the drawings]
FIG. 1 is a diagram showing the relationship between the thickness of an InGaN active layer of a nitride semiconductor light emitting device according to the first embodiment of the present invention and the output of the light emitting device, as compared with a conventional nitride semiconductor light emitting device. .
FIG. 2 is a diagram showing the relationship between the thickness of the InGaN active layer of the nitride semiconductor light emitting device according to the second embodiment of the present invention and the output of the light emitting device.
FIG. 3 is a schematic cross-sectional view showing the structure of an LED element according to an embodiment of the present invention.
FIG. 4 is a perspective view showing the structure of a laser device according to another embodiment of the present invention.
[Explanation of symbols]
1 .... Sapphire substrate
2. Low temperature growth buffer layer
3... Second buffer layer
4... N-side contact layer (n-side second nitride semiconductor layer)
5... N-side cladding layer (n-side first nitride semiconductor layer)
6. Active layer
7... P-side cladding layer (p-side first nitride semiconductor layer)
8... P-side contact layer (p-side second nitride semiconductor layer)

Claims (5)

Has an active layer, the _Al x Ga _{1 -x} N cladding layer made of (0 <X ≦ 0.4) of the superlattice structure in the n-side and p-side optical guide between the active layer and the cladding layer A nitride semiconductor device comprising a layer,
The cladding layer of super lattice structure is made small GaN layer of large _{Al Z Ga 1 -Z N (0} <Z ≦ 1.0) layer and the band gap energy, the impurity concentration of the GaN layer, Greater than the impurity concentration of the Al _Z Ga _{1 -ZN} (0 <Z ≦ 1.0) layer ,
A nitride semiconductor device comprising a p-side contact layer having a p-electrode and a thickness of 500 angstroms or less on a cladding layer having a superlattice structure on the p-side .   The nitride semiconductor device according to claim 1, wherein the p-side superlattice structure and the p-side contact layer are in contact with each other.   The nitride semiconductor device according to claim 1, wherein the p-electrode is made of Ni, Pt, Pd, Ni / Au, Pt / Au, or Pd / Au.   The nitride semiconductor device includes a p-side cap layer having a band gap energy larger than that of the p-side light guide layer between the active layer and the p-side light guide layer. Nitride semiconductor device. 2. The nitride semiconductor device according to claim 1, wherein the active layer is a layer made of In _a Ga _1-a N (0 <a ≦ 0.1).

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