JP2007067454A - Nitride semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nitride semiconductor device which is superior in electric power efficiency. <P>SOLUTION: The nitride semiconductor device is provided with an active layer between an n-type nitride semiconductor layer having single layer or multiple layers and a p-type nitride semiconductor layer having single layer or multiple layers. At least one of the p-type nitride semiconductor layer and n-type nitride semiconductor layer is a super lattice layer while the super lattice layer is formed by laminating a first layer made of nitride semiconductor having a thickness of 100 Å or less and a second layer different in composition from the first layer having a thickness of 100 Å or less. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a nitride semiconductor (In _X Al _Y Ga _1-1 ) used in a light emitting element such as an LED (light emitting diode) or LD (laser diode), a light receiving element such as a solar cell or an optical sensor, or an electronic device such as a transistor. _X−Y N, 0 ≦ X, 0 ≦ Y, X +
The present invention relates to an element comprising Y ≦ 1). Note that the general formula In _X used in this specification is used.
Ga _1-X N, Al _Y Ga _1-Y N, and the like simply indicate the composition formula of the nitride semiconductor layer, and even if different layers are represented by the same general formula, for example, It does not indicate that the value and the Y value match.

Nitride semiconductors are used as materials for high-brightness blue LEDs and pure green LEDs.
It has just been put into practical use for ED displays and traffic signals. The LED used for these various devices has an active layer made of InGaN having a single quantum well structure (SQW) between an n-type nitride semiconductor layer and a p-type nitride semiconductor layer. It has a double heterostructure sandwiched between them. The wavelength of blue, green, etc. is In
It is determined by increasing or decreasing the In composition ratio of the GaN active layer.

Also, the applicant has recently used this material with 410 nm at room temperature under pulsed current.
For the first time in the world (for example, Jpn.J.Appl.Phys. Vol35 (1996
) pp.L74-76). This laser element exhibits oscillation of a threshold current of 610 mA, a threshold current density of 8.7 kA / cm 2, and 410 nm under conditions of a pulse width of 2 μs and a pulse period of 2 ms. Furthermore, an improved laser device having a low threshold current is disclosed in Appl. Phys. Lett., Vol.
.69, No. 10, 2 Sep. 1996, p.1477-1479. This laser element
a ridge stripe is formed on a part of the p-type nitride semiconductor layer;
Pulse width 1 μs, pulse period 1 ms, duty ratio 0.1%, threshold current 18
The oscillation is 7 mA, the threshold current density is 3 kA / cm 2, and 410 nm.

Blue and green LEDs made of a nitride semiconductor have a forward current (If) of 20 mA and a forward voltage (Vf) of 3.4 V to 3.6 V, which is 2 V higher than a red LED made of a GaAlAs semiconductor. Further reduction of Vf is desired. Also, in LD, the current and voltage at the threshold are still high, and in order to oscillate continuously at room temperature,
It is necessary to realize an element with higher power efficiency that lowers the threshold current and voltage.

Therefore, the object of the present invention is to realize continuous oscillation by lowering the current and voltage at the threshold value of the LD element mainly made of a nitride semiconductor, and to reduce Vf in the LED element and to have high reliability. The object is to realize a nitride semiconductor device having excellent power efficiency.

As a result of intensive studies to improve the p-type layer and / or the n-type layer sandwiching the active layer in the nitride semiconductor element, the present inventors have found that the p-type layer and / or the n-type layer excluding the active layer By using a superlattice layer, the crystallinity of the layer using the superlattice layer can be improved,
The present inventors have newly found that the above problems can be solved, and have made the present invention.
That is, the first nitride semiconductor device according to the present invention includes one or multiple p-type nitride semiconductor layers including a p-side contact layer, and carriers are injected through the p-type nitride semiconductor layer to obtain a predetermined In a nitride semiconductor device comprising an active layer made of a nitride semiconductor that operates,
The p-side contact layer is a superlattice layer.
The second nitride semiconductor device according to the present invention has an active layer between one or multiple n-type nitride semiconductor layers including the n-side contact layer and one or multiple p-type nitride semiconductor layers. In nitride semiconductor devices,
The n-side contact layer is a superlattice layer.
Furthermore, the third nitride semiconductor device according to the present invention includes a single or multilayer p-type nitride semiconductor layer and a nitride semiconductor in which carriers are injected through the p-type nitride semiconductor layer and perform a predetermined operation. In a nitride semiconductor device comprising an active layer made of
At least one of the p-type nitride semiconductor layers is a superlattice layer.
As a result, the resistance value of the p-type nitride semiconductor layer made of the superlattice layer can be made extremely low, so that the power efficiency of the nitride semiconductor device can be increased.

The fourth nitride semiconductor device according to the present invention is a nitride semiconductor device having an active layer between one or multiple n-type nitride semiconductor layers and one or multiple p-type nitride semiconductor layers.
At least one of the p-type nitride semiconductor layer and the n-type nitride semiconductor layer is a superlattice layer.

In the first to fourth nitride semiconductor elements of the present invention, in order to further improve the crystallinity of the superlattice layer, the superlattice layer is made of a nitride semiconductor having a thickness of 100 angstroms or less. It is preferable that a first layer and a second layer made of a nitride semiconductor having a composition different from that of the first layer and having a film thickness of 100 angstroms or less be stacked.

Furthermore, in the first to fourth nitride semiconductor elements of the present invention, in order to confine carriers in the active layer, at least one of the first layer and the second layer is
It is preferably made of a nitride semiconductor containing at least Al having a relatively large energy band gap, and more preferably Al _Y Ga _1-Y N (0 <Y ≦ 1).
) Is used.

In the first to fourth nitride semiconductor elements of the present invention, the superlattice layer is In _X G
a _first layer made of a _1-X N (0 ≦ X ≦ 1), and Al _Y Ga _1-Y N (0 ≦ Y ≦
1 and X = Y.noteq.0) is preferably laminated. However, it goes without saying that the same applies to the case where the first layer is Al _Y Ga _1-Y N and the second layer is In _X Ga _1-X N. The general formula _Al Y _{Ga 1-Y} N, and _{an In} X _{Ga 1-
The} nitride semiconductor represented by XN provides a semiconductor layer with good crystallinity and can form a layer with few crystal defects, so that the crystallinity of the entire nitride semiconductor is improved and the output of the device is improved (power efficiency In the case where the element is an LED element or an LD element, V
f, threshold current, voltage and the like can be lowered.
Incidentally, in the first to fourth nitride semiconductor device of the present invention further in order to form a small layer of crystal defects, the in superlattice layer, said first layer formula In _{X Ga} 1-X
N (0 ≦ X <1) is formed of a nitride semiconductor, and the second layer has the formula Al
_{Y Ga 1-Y N (0} <Y <1) is more preferably formed of a nitride semiconductor represented by.

In the first to fourth nitride semiconductor elements of the present invention, the film thicknesses of the first layer and the second layer are preferably 70 angstroms or less, more preferably 40 angstroms or less. To do. The first layer and the second layer
The film thickness of this layer is preferably 5 angstroms or more, more preferably 10 angstroms or more. By setting within this range, a nitride semiconductor layer such as Al _Y Ga _1-Y N (0 <Y ≦ 1), which has been difficult to grow in the past, can be formed with good crystallinity.
In particular, at least one of the p-type nitride semiconductor layers between the p electrode and the active layer and / or between the n-side contact layer and the active layer as a current injection layer in which the n electrode is formed. When at least one of the n-type nitride semiconductor layers is a superlattice layer, the effect of setting the first and second layers constituting the superlattice layer to the above-described film thickness is great.

In the first to fourth nitride semiconductor elements of the present invention, the p-type nitride semiconductor layer includes a p-side contact layer for forming a p-electrode, and the p-side contact layer has a thickness of 500. It is preferable to set it below angstrom. Thus, by forming the thin film, the resistance value in the thickness direction of the p-side contact layer can be lowered. Therefore, in the present invention, it is preferable to set it to 300 angstroms or less. The lower limit of the thickness of the p-side contact layer is preferably set to 10 angstroms or more so as not to expose the semiconductor layer under the p-type contact layer.

The second to third nitride semiconductor elements of the present invention are the p-type nitride semiconductor layers,
When a single-layer p-side contact layer for forming a p-electrode is provided,
The superlattice layer is preferably formed between the active layer and the p-side contact layer.

In addition, the first to fourth nitride semiconductor elements of the present invention further include a second buffer layer made of a nitride semiconductor having a thickness of 0.1 μm or more formed on the substrate via the first buffer layer. And an n-side contact layer made of a nitride semiconductor doped with an n-type impurity, formed on the second buffer layer, and an n-electrode is preferably formed on the n-side contact layer. As a result, an n-side contact layer having a high carrier concentration and good crystallinity can be formed.
In order to form the second buffer layer having better crystallinity, it is preferable that the impurity concentration of the second buffer layer is lower than that of the n-side contact layer.

In the nitride semiconductor device, the first buffer layer and the second buffer layer
At least one of the buffer layers is preferably made of a superlattice layer in which nitride semiconductor layers having different compositions and having a thickness of 100 angstroms or less are stacked.

When the first, third, and fourth nitride semiconductor elements of the present invention include a single n-side contact layer for forming an n electrode as the n-type nitride semiconductor layer,
The superlattice layer is preferably formed between the active layer and the n-side contact layer.
The layer formed between the active layer and the p-side contact layer or between the active layer and the n-side contact layer is, for example, a carrier confinement layer in an LD element,
It is a clad layer that acts as a light guide layer, and by applying to these layers, the threshold current and voltage can be significantly reduced.
In particular, the effect of lowering the threshold current and voltage by applying, for example, a p-type cladding layer between the active layer and the p-type contact layer is great.

In the first to fourth nitride semiconductor elements of the present invention, it is preferable that at least one of the first layer and the second layer is doped with an impurity that determines a conductivity type. Furthermore, it is preferable that the first layer and the second layer have different impurity concentrations in the superlattice layer. The impurities that determine the conductivity type are the n-type impurities belonging to Groups 4A, 4B, 6A, 6B and 1A, 1B, 2A, A p-type impurity belonging to Group 2B (hereinafter, referred to as an n-type impurity or a p-type impurity as appropriate in this specification).
Furthermore, when the band gap energy differs between the first layer and the second layer, it is desirable to increase the impurity concentration of the layer having the larger band gap energy. As a result, high output by modulation doping can be expected when a superlattice layer is formed on the p-type nitride semiconductor layer side.

In the second nitride semiconductor device of the present invention, the superlattice layer is formed as an n-side contact layer in contact with an n-electrode. In this case, in particular, the first layer and the second layer constituting the superlattice layer By increasing the impurity concentration of the layer having the larger band gap energy, the power efficiency can be improved by an effect similar to that of the HEMT described later. For example, in a laser element, the threshold voltage and the threshold current tend to further decrease.

The present invention relates to a nitride semiconductor device having an active layer between an n-type nitride semiconductor layer including an n-side cladding layer and a p-type nitride semiconductor layer including a p-side cladding layer, and lasing in the active layer. Thus, the nitride semiconductor device can reduce the threshold current and threshold voltage during laser oscillation.
Further, in the nitride semiconductor device for laser oscillation according to the present invention, a ridge portion having a peak shape in the resonance direction may be formed in the p-side cladding layer and the layer formed above the p-side cladding layer. preferable.

As described above, the nitride semiconductor device according to the present invention is configured using the superlattice layer in the p-type nitride semiconductor region or the n-type nitride semiconductor region other than the active layer. Can be very good.
That is, in the conventional nitride semiconductor device, it has been proposed that the active layer has a multiple quantum well structure, but the active layer is sandwiched, for example, the cladding layer is composed of a single nitride semiconductor layer. Was normal. However, in the nitride semiconductor device of the present invention, since the superlattice layer having a layer in which a quantum effect appears is provided as a cladding layer or a contact layer for injecting current, the resistivity on the cladding layer side is reduced. Can do. Thereby, for example, the threshold current and threshold voltage of the LD element can be lowered, and the element can have a long lifetime. Furthermore, although the conventional LED was weak against static electricity, in the present invention, an element having a high electrostatic withstand voltage can be realized. Since Vf and the threshold voltage can be lowered in this manner, the amount of heat generation is reduced, and the reliability of the element can be improved. According to the nitride semiconductor device of the present invention, not only a light emitting device such as an LED and an LD, but also a solar cell, a photosensor, a transistor, etc. using a nitride semiconductor can realize a highly efficient device. And its industrial utility value is very large.

A nitride semiconductor device according to an embodiment of the present invention will be described below with reference to the drawings.
Embodiment 1. FIG.
FIG. 1 is a schematic cross-sectional view showing the structure of a nitride semiconductor device according to a first embodiment of the present invention. The nitride semiconductor device has a basic structure on a substrate 1 made of sapphire. Buffer layer 2 made of GaN, n made of Si-doped n-type GaN
Side contact layer 3, active layer 4 made of InGaN having a single quantum well structure, p-side cladding layer 5 made of a superlattice layer in which a first layer and a second layer having different compositions are laminated, Mg-doped GaN LE in which the p-side contact layer 6 is sequentially laminated.
D element. In the nitride semiconductor device of the first embodiment, a light-transmitting full-surface electrode 7 is formed on almost the entire surface of the p-side contact layer 6, and a bonding p-electrode 8 is provided on the surface of the full-surface electrode 7. Furthermore, an n-electrode 9 is provided on the surface of the n-side contact layer 2 exposed by etching away a part of the nitride semiconductor layer from the p-side contact layer 6.

Here, the nitride semiconductor device of Embodiment 1 is the same as the first layer having a thickness of 30 Å, for example, made of In _X Ga _1-X N (0 ≦ X ≦ 1) doped with Mg as a p-type impurity. A superlattice in which a second layer having a thickness of 30 Å made of p-type Al _Y Ga ₁ -YN (0 ≦ Y ≦ 1) doped with Mg as a p-type impurity in the same amount as the first layer is stacked. Since the p-side cladding layer 5 having a low resistance value composed of layers is provided, Vf can be lowered. When the superlattice layer is formed on the p-layer side in this way, the p-type conductivity type is obtained by doping the first layer and / or the second layer with p-type impurities such as Mg, Zn, Cd, and Be. A superlattice layer having The order of stacking may be the order of first + second + first... Or second + first + second..., And a total of at least two layers are stacked.

The first layer and the second layer made of a nitride semiconductor constituting the superlattice layer are made of In
_{A layer made of X} Ga _1-X N (0 ≦ X ≦ 1) and Al _Y Ga _1-Y N (0 ≦ Y ≦ 1)
It is not necessarily limited to the layer formed of (), and may be composed of nitride semiconductors having different compositions. Further, the band gap energy of the first layer and the second layer may be different or the same. For example, the first layer may be In _X Ga _1-X.
N (0 ≦ X ≦ 1) and when the second layer is composed of Al _Y Ga _1-Y N (0 <Y ≦ 1), the band gap energy of the second layer is always higher than that of the first layer. However, the first layer is composed of In _X Ga _1-X N (0 ≦ X ≦ 1), and the second layer is In
By configuring in _{Z Al 1-Z N (0} <Z ≦ 1), the first layer and the second layer but different compositions may be the case that the band gap energy of the same. Also, the first layer is made of Al
_Y Ga _1-Y N (0 ≦ Y ≦ 1), and the second layer is In _Z Al _1-Z N (0 <
If Z ≦ 1), similarly, the first layer and the second layer may have the same band gap energy although the compositions are different. That is, in the present invention, the band gap energy of the first layer and the second layer may be the same as or different from each other as long as the superlattice layer has an action described later. As described above, the superlattice layer referred to here is a laminate of extremely thin layers having different compositions, and each layer is sufficiently thin so that no defects due to lattice irregularities occur. This is a broad concept including a quantum well structure. This superlattice layer does not have a defect inside, but usually has a strain associated with lattice irregularity, and is also called a strained superlattice. In the present invention, even if N (nitrogen) in the first layer and the second layer is partially substituted with a group V element such as As or P, it is included in the nitride semiconductor as long as N is present.

In the present invention, if the thickness of the first layer and the second layer constituting the superlattice layer is thicker than 100 angstroms, the first layer and the second layer have a thickness equal to or greater than the elastic strain limit. Since minute cracks or crystal defects are likely to enter the film,
It is preferable to set the film thickness to 00 angstroms or less. The first layer,
The lower limit of the film thickness of the second layer is not particularly limited as long as it is one atomic layer or more. However, in the present invention, if the film thickness of the first layer and the second layer is 100 angstroms, the critical (elastic strain) limit film thickness of the nitride semiconductor is not sufficiently reached, and the elastic strain limit film thickness is not reached. In order to reduce the number of crystal defects in the nitride semiconductor, it is preferably set to 70 angstroms or less, more preferably set to be thinner.
Most preferably, it is set to angstrom to 10 angstrom. In the present invention, the thickness may be set to 10 angstroms or less (one atomic layer or two atomic layers). However, when the thickness is set to 10 angstroms or less, for example, a cladding layer having a thickness of 500 angstroms or more is formed as a superlattice layer. In this case, the number of stacked layers increases, and the manufacturing process takes time and labor, so the film thicknesses of the first layer and the second layer are
It is preferable to set it thicker than 10 angstroms.

In the case of the nitride semiconductor device of Embodiment 1 shown in FIG. 1, a p-type cladding layer 5 made of a superlattice layer is formed between an active layer 4 and a p-side contact layer 6 that is a current injection layer. Acts as a carrier confinement layer. Thus, particularly when the superlattice layer is a carrier confinement layer, it is necessary to make the average band gap energy of the superlattice layer larger than that of the active layer. In nitride semiconductors, AlN, AlGaN,
Since a nitride semiconductor containing Al such as InAlN has a relatively large band gap energy, these layers are used as a carrier confinement layer. However, when a thick film is grown with a single AlGaN film as in the prior art, it has the property of being prone to cracks during crystal growth.

Therefore, in the present invention, at least one of the first layer and the second layer of the superlattice layer is a nitride semiconductor containing at least Al, preferably Al _Y Ga _1-Y N (0 <
By forming a superlattice layer by forming Y ≦ 1) with a film thickness below the elastic strain limit,
A superlattice layer having very good crystallinity with few cracks is grown and a layer with a large band gap energy is formed. In this case, more preferably, the first
When a nitride semiconductor layer not containing Al is grown to a thickness of 100 angstroms or less in this layer, it also acts as a buffer layer when growing the second layer made of a nitride semiconductor containing Al. Makes layers difficult to crack. Therefore, even if the first layer and the second layer are stacked, a superlattice layer having good crystallinity without cracks can be formed.
Therefore, in the first embodiment, the superlattice layer is composed of a first layer (second layer) made of In _X Ga _1-X N (0 ≦ X ≦ 1) and Al _Y Ga _1-Y N (0 ≦ Y). It is preferable to use the second layer (first layer) composed of ≦ 1, X ≠ Y = 0.

In the nitride semiconductor device of Embodiment 1, the carrier concentration is adjusted in at least one of the first layer and the second layer constituting the p-side cladding layer 5 that is a superlattice layer. Therefore, it is preferable that a p-type impurity that sets the conductivity type of the layer to be p-type is doped. In addition, when the p-type impurity is doped in the first layer and the second layer, the first layer and the second layer may be doped with different concentrations, and further, the first layer and the second layer may be doped. When the band gap energy is different from that of the layer, it is desirable that the layer having a larger band gap energy has a higher concentration. This is because if the first layer and the second layer are doped with impurities at different concentrations, the carrier concentration of one layer is substantially increased due to the quantum effect of modulation doping, and the resistance value of the entire superlattice layer is lowered. Because it can. Thus, in the present invention, the first
Both the first layer and the second layer may be doped with impurities at different concentrations,
Either one of the first layer and the second layer may be doped with impurities.

The impurity concentration doped in the first layer and the second layer is not particularly limited to the present invention, but it is a p-type impurity and is usually 1 × 10 ¹⁶ / cm ³ to 1 × 10 ²² /.
It is desirable to adjust to cm ³ , more preferably 1 × 10 ¹⁷ / cm ³ to 1 × 10 ²¹ / cm ³ , and most preferably 1 × 10 ¹⁸ / cm ³ to 2 × 10 ²⁰ / cm ³ . If it is less than 1 × 10 ¹⁶ / cm ³ , the effect of lowering Vf and the threshold voltage is difficult to obtain, and if it exceeds 1 × 10 ²² / cm ³ , the crystallinity of the superlattice layer tends to deteriorate. . It is desirable to adjust the n-type impurity within the same range. The reason is the same.

However, in the present invention, the superlattice layer may not be doped with impurities that determine the conductivity type in the first layer and the second layer. The superlattice layer not doped with impurities may be any layer between the active layer and the substrate as long as it is an n-type nitride semiconductor layer region, while it is a p-type nitride semiconductor layer region. Any layer between the carrier confinement layer (light confinement layer) and the active layer may be used.

Since the superlattice layer configured as described above is formed by laminating the first layer and the second layer with a film thickness equal to or less than the elastic strain limit, it can reduce crystal lattice defects. And fine cracks can be reduced, and crystallinity can be remarkably improved. As a result, the doping amount of impurities can be increased without significantly degrading the crystallinity, whereby the carrier concentration of the n-type nitride semiconductor layer and the p-type nitride semiconductor layer can be increased, and the carriers are crystallized. Since it can move without being scattered by defects, the resistivity can be reduced by one digit or more as compared with a p-type or n-type nitride semiconductor having no superlattice structure.

Therefore, in the nitride semiconductor element (LED element) of the first embodiment, the p-layer side (p-type semiconductor layer region (p-type cladding layer 5 and By forming the p-type cladding layer 5 in the region comprising the p-type contact layer 6) using a superlattice layer and reducing the resistance value of the p-type cladding layer 5, V
f can be lowered. That is, a p-type nitride semiconductor is a semiconductor in which p-type crystals are very difficult to obtain, and even if obtained, the resistivity is usually two orders of magnitude higher than that of an n-type nitride semiconductor. Therefore, by forming the p-type superlattice layer on the p-layer side, the p-type layer composed of the superlattice layer can be made extremely low in resistance, and the decrease in Vf appears remarkably. Conventionally, as a technique for obtaining a p-type crystal, a technique for producing a p-type nitride semiconductor by annealing a nitride semiconductor layer doped with a p-type impurity and removing hydrogen (Patent No. 1) is known. 2540791). However, even if a p-type nitride semiconductor is obtained, the resistivity is several Ω · cm or more. Therefore, by making this p-type layer a p-type superlattice layer, the crystallinity is improved. According to our study, the resistivity of the p-type layer can be lowered by an order of magnitude or more compared to the conventional one. , The effect of reducing Vf appears significantly.

In the first embodiment, the first layer (second layer) is preferably I as described above.
n _X Ga _1-X N (0 ≦ X ≦ 1) and the second layer (first layer) is Al _Y Ga ₁₋
By constituting in _{Y N (0 ≦ Y ≦ 1} , X ≠ Y = 0), it is possible to form a no good crack crystallinity superlattice layer, thereby improving the device lifetime.

Next, the present invention will be described in comparison with conventional examples disclosed in publicly known documents including patent gazettes previously filed by us.
First, as a technique similar to the present invention, we previously proposed JP-A-8-228048. In this technique, a laser light reflection film is formed on the outside of the n-type cladding layer sandwiching the active layer and / or the outside of the p-type cladding layer (that is, the side farther from the active layer).
This is a technique for forming a multilayer film made of lGaN, GaN, InGaN or the like. Since this technique forms a multilayer film as a light reflecting film, the thickness of each layer is designed to be λ / 4n (n: refractive index of nitride semiconductor, λ: wavelength), which is very thick. Therefore, each film thickness of the multilayer film is not less than the elastic strain limit. USP 5,146,465
Laser device sandwiched by the mirror the active layer made of _{Al X Ga 1-X N /} Al Y Ga 1-Y N are described in EP. This technology is also AlGaN /
In order to make AlGaN act as a mirror, the thickness of each layer must be increased. Furthermore, it is very difficult to stack multiple layers of hard semiconductors such as AlGaN without cracks.

On the other hand, in the present embodiment, the thicknesses of the first and second layers are set so as to constitute the superlattice layer.
It is set (preferably, both are set to 100 angstroms or less and a critical film thickness or less), which is different from the above technique. In the present invention, the effect of the strained superlattice of the nitride semiconductor constituting the superlattice layer is utilized to improve crystallinity and lower Vf.

Further, JP-A-5-110138 and JP-A-5-110139 describe a method of obtaining Al _Y Ga _1-Y N crystals by laminating thin films of AlN and GaN. This technique is a technique of stacking AlN and GaN having a film thickness of several tens of angstroms in order to obtain a mixed crystal of Al _Y Ga _1-Y N having a predetermined mixed crystal ratio, and is different from the technique of the present invention. In addition, since there is no active layer made of InGaN, the superlattice layer tends to crack. Japanese Patent Application Laid-Open Nos. 6-21511 and 6-268257 describe a light emitting element having a double hetero structure having an active layer having a multiple quantum well structure in which GaN and InGaN or InGaN and InGaN are stacked. The present invention is a technique in which layers other than the active layer have a multiple quantum well structure, which is different from this technique.

Furthermore, in the device of the present invention, when the active layer is provided with a nitride semiconductor containing at least indium such as InGaN, the effect of the superlattice appears remarkably. InGaN
The active layer has a small band gap energy and is most suitable as an active layer of a nitride semiconductor device. Therefore, if a superlattice layer made of In _X Ga _1-X N and Al _Y Ga _1-Y N is formed as a layer sandwiching the active layer, the band gap energy difference and the refractive index difference can be increased from the active layer. The superlattice layer operates as a very excellent optical confinement layer when realizing a laser device (applied to the nitride semiconductor device of Embodiment 2). Furthermore, since InGaN is softer than other nitride semiconductors containing Al, such as AlGaN, when InGaN is used as an active layer, cracks are less likely to form in the entire laminated nitride semiconductor layers. On the other hand, when a nitride semiconductor such as AlGaN is used as the active layer, the crystal tends to be easily cracked due to its hard crystal properties.

Further, it is desirable to adjust the thickness of the p-side contact layer to 500 angstroms or less, more preferably 300 angstroms or less, and most preferably 200 angstroms or less. Because, as described above, the resistivity can be further reduced by adjusting the film thickness of the p-type nitride semiconductor layer having a resistivity of several Ω · cm or more to 500 angstroms or less. Current and voltage decrease. Further, the amount of hydrogen removed from the p-type layer can be increased, and the resistivity can be further reduced.

As described above in detail, in the nitride semiconductor device of the first embodiment, the p-type cladding layer 5 is composed of a superlattice layer in which a first layer and a second layer are stacked. The p
The mold cladding layer 5 can have a very low resistance, and the Vf of the element can be lowered.

Although the superlattice layer is used for the p-side cladding layer 5 in the first embodiment, the present invention is not limited to this, and a p-type superlattice layer may be used for the p-side contact layer 6. That is,
The p-side contact layer 6 into which current (holes) is injected is, for example, a p in which a _first layer made of In _X Ga _1-X N and a second layer made of Al _Y Ga _1-Y N are stacked. It can also be a superlattice layer of the type. When the p-type contact layer 6 is a superlattice layer and the band gap energy of the first layer is smaller than that of the second layer, the first layer made of In _X Ga _1-X N having a small band gap energy is used as the outermost surface. Thus, a layer in contact with the p-electrode is preferably used, whereby the contact resistance with the p-electrode is reduced and a preferable ohmic is obtained. This is the first with a small band gap energy
This is because this layer tends to provide a nitride semiconductor layer having a higher carrier concentration than the second layer. In the present invention, when a p-type nitride semiconductor layer other than the p-side cladding layer and the p-side contact layer is further formed in the p-type nitride semiconductor layer region, the p-type nitride semiconductor layer is super You may comprise by a lattice layer.

In Embodiment 1 described above, a superlattice layer is used for the p-side cladding layer 5.
An n-type superlattice layer may be used for the n-side contact layer 3 in the n-type nitride semiconductor region, not limited to the type nitride semiconductor layer region. Thus, when the n-side contact layer 3 is a superlattice layer, for example, an n-type conductivity type is doped by doping an n-type impurity such as Si or Ge into the first layer and / or the second layer. Can be formed as an n-type contact layer 3 between the substrate 1 and the active layer 4. In this case, it was confirmed that when the n-type contact layer 3 is a superlattice layer having a different impurity concentration, the resistance value in the lateral direction decreases, and the threshold voltage and current tend to decrease in the LD.

This is because the following HEMT (High-Electron-Mobility-Transistor) is formed in the case where a superlattice layer doped with a large number of n-type impurities is formed as a contact layer on the n-layer side in the layer having a larger band gap energy. It is inferred that an effect similar to that appears. a first layer (second layer) having a large band gap doped with an n-type impurity and an undoped {(undope) having a small band gap; hereinafter, an undoped state is referred to as undoped} In a superlattice layer in which a layer (first layer) is stacked, a layer side having a large band gap energy is depleted at a heterojunction interface between an n-type impurity-added layer and an undoped layer, and the band gap energy is small. Electrons (two-dimensional electron gas) accumulate at the interface around the layer side thickness (100 angstroms). Since this two-dimensional electron gas can be formed on the layer side with a small band gap energy, it is assumed that the electron mobility of the superlattice layer increases and the resistivity decreases because electrons are not scattered by impurities when traveling. The

In the present invention, when an n-side cladding layer is provided in the n-type nitride semiconductor layer region, the n-side cladding layer may be a superlattice layer. When an n-type nitride semiconductor layer other than the n-side contact layer and the n-side cladding layer is formed in the n-type nitride semiconductor layer region, the n-type nitride semiconductor layer may be a superlattice layer. However, when a nitride semiconductor layer composed of a superlattice layer is provided in the n-type nitride semiconductor layer region, the n-side cladding layer as a carrier confinement layer or the n-side contact layer 3 into which current (electrons) is injected is superlattice. Needless to say, a structure is desirable.

As described above, when the superlattice layer is provided in the n-type nitride semiconductor layer region between the active layer 4 and the substrate 1, the first layer and the second layer constituting the superlattice layer are doped with impurities. You don't have to. This is because nitride semiconductors have the property of becoming n-type even when undoped. However, even when forming on the n layer side, as described above, the first layer, the second layer
It is desirable to provide a difference in impurity concentration by doping n-type impurities such as Si and Ge into this layer.

As described above, the effect when the superlattice layer is formed in the n-type nitride semiconductor layer region is as follows.
As in the case where the superlattice layer is provided in the p-type nitride semiconductor layer region, the crystallinity is improved. More specifically, in the case of a nitride semiconductor device having a heterojunction, the n-type and p-type carrier confinement layers are usually made of AlGaN having a larger band gap energy than the active layer. AlGaN is very difficult to grow a crystal. For example, when it is intended to grow with a single composition and a film thickness of 0.5 μm or more, there is a property that cracks are likely to occur in the crystal. However, if the superlattice layer is formed by laminating the first layer and the second layer with a film thickness equal to or less than the elastic strain limit as in the present invention, a single first layer,
Since only the second layer has good crystallinity, the clad layer can be grown while maintaining good crystallinity even if the whole is a thick superlattice layer. For this reason, the crystallinity of the entire nitride semiconductor is improved and the mobility of the n-type region is increased, so that Vf is lowered in an element having the superlattice layer as a cladding layer. Further, when the superlattice layer is doped with impurities of Si and Ge, and the superlattice layer is used as a contact layer, it seems that an effect similar to the above-mentioned HEMT appears remarkably, and the threshold voltage, Vf Can be further reduced.

Thus, in the present invention, the superlattice layer is an n-type region or p that sandwiches the active layer.
The average band gap of the nitride semiconductor constituting the superlattice layer because it is used as a clad layer as a carrier confinement layer formed in the mold region, a light guide layer of the active layer, or a current injection layer formed in contact with the electrode It is desirable to adjust so that the energy is larger than that of the active layer.

Embodiment 2. FIG.
Next, Embodiment 2 according to the present invention will be described.
FIG. 2 is a schematic cross-sectional view (cross-section perpendicular to the resonance direction of laser light) showing the structure of the nitride semiconductor device according to the second embodiment of the present invention. N-type nitride semiconductor layer region (on the substrate 10 such as sapphire whose principal surface is sapphire)
It consists of an n-side contact layer 12, a crack prevention layer 13, an n-side cladding layer 14 and an n-side light guide layer 15. ) And a p-type nitride semiconductor region (consisting of a cap layer 17, a p-side light guide layer 18, a p-side cladding layer 19 and a p-side contact layer 20). A nitride semiconductor laser diode element provided.

Here, in the nitride semiconductor device of Embodiment 2, the n-side cladding layer 14 in the n-type nitride semiconductor layer region is formed of a superlattice layer, and the p-side cladding layer 19 in the p-type nitride semiconductor region is superposed. By forming the lattice layer, the threshold voltage of the nitride semiconductor element which is an LD element is set low. Hereinafter, the nitride semiconductor device according to the second embodiment of the present invention will be described in detail with reference to FIG.

In the nitride semiconductor device according to the second embodiment, first, the n-side contact layer 12 is formed on the substrate 10 via the buffer layer 11 and the second buffer layer 112, and the n-side contact layer 12 is further cracked. The prevention layer 13, the n-side cladding layer 14, and the n-side light guide layer 15 are laminated to form an n-type nitride semiconductor layer region. still,
An n-side electrode 23 in ohmic contact with the n-side contact layer 12 is formed on the surface of the n-side contact layer 12 exposed on both sides of the crack prevention layer 13.
On the side electrode 23, for example, an n-side pad electrode for wire bonding is formed. An active layer 16 made of a nitride semiconductor is formed on the n-side light guide layer 15, and a cap layer 17, a p-side light guide layer 18, a p-side cladding layer 19, and a p-side contact are further formed on the active layer 16. Layer 20 is laminated to form a p-type nitride semiconductor layer region. Further, a p-side electrode 21 that is in ohmic contact with the p-side contact layer 20 is formed on the p-side contact layer 20, and a p-side pad electrode for wire bonding, for example, is formed on the p-side electrode 21. . The p-side contact layer 2
0 and the upper part of the p-side cladding layer 19 form a ridge-like ridge portion extending in the resonance direction. By forming the ridge portion, light is transmitted in the width direction (perpendicular to the resonance direction) in the active layer 16. A resonator that resonates in the longitudinal direction of the ridge portion is produced using a cleavage plane that is confined in a direction perpendicular to the ridge portion (stripe-shaped electrode) and laser oscillation is performed.

Next, each component of the nitride semiconductor device of Embodiment 2 will be described.
(Substrate 10)
In addition to sapphire whose principal surface is C-plane, sapphire whose principal surface is R-plane and A-plane, and other insulating substrates such as spinel (MgA1 ₂ O ₄ ), Si 10
A semiconductor substrate such as C (including 6H, 4H, and 3C), ZnS, ZnO, GaAs, and GaN can be used.

(Buffer layer 11)
The buffer layer 11 is made of, for example, AlN, GaN, AlGaN, InGaN, etc.
The film is grown at a temperature of 0 ° C. or less to form a film thickness of several tens of angstroms to several hundreds of angstroms. The buffer layer 11 is formed in order to mitigate the irregularity of the lattice constant between the substrate and the nitride semiconductor, but may be omitted depending on the growth method of the nitride semiconductor, the type of the substrate, and the like.

(Second buffer layer 112)
The second buffer layer 112 is a layer made of a single crystal nitride semiconductor grown on the buffer layer 11 at a higher temperature than the buffer layer 11, and has a thicker film than the buffer layer 11. When the second buffer layer 112 is a layer having a lower n-type impurity concentration than the n-side contact layer 12 to be grown next, or a nitride semiconductor layer not doped with an n-type impurity, preferably a GaN layer, Two buffer layers 11
The crystallinity of 2 is improved. Most preferably, when the n-type impurity is undoped GaN, a nitride semiconductor having the best crystallinity can be obtained. N to form a negative electrode as in the prior art
If the side contact layer is formed of a single nitride semiconductor layer having a thickness of several μm or more and a high carrier concentration, it is necessary to grow a layer having a high n-type impurity concentration. A thick film layer having a high impurity concentration tends to have poor crystallinity. For this reason, even if another nitride semiconductor such as an active layer is grown on the layer having poor crystallinity, the crystal defect cannot be improved because the other layer takes over the crystal defects. Therefore, the n-side contact layer 12
Before growing the layer, the second buffer layer 11 having a low impurity concentration and good crystallinity
By growing 2, the n-side contact layer 12 having a high carrier concentration and good crystallinity can be grown. The thickness of the second buffer layer 112 is 0.
1 μm or more, more preferably 0.5 μm or more, most preferably 1 μm or more, 2
It is desirable to adjust to 0 μm or less. If the second buffer layer 112 is thinner than 0.1 μm, the n-type contact layer 12 having a high impurity concentration must be grown thick, and the crystallinity of the n-side contact layer 12 tends not to be improved much. . On the other hand, if the thickness is greater than 20 μm, the second buffer layer 112 itself tends to have many crystal defects. Further, as an advantage of growing the second buffer layer 112 thickly, an improvement in heat dissipation can be mentioned. That is, when a laser element is manufactured, heat is likely to spread in the second buffer layer 112, and the lifetime of the laser element is improved. Further, the leakage light of the laser beam spreads in the second buffer layer 112, and it becomes easy to obtain a laser beam having an elliptical shape. Note that the second buffer layer 112 may be omitted when a conductive substrate such as GaN, SiC, or ZnO is used for the substrate.

(N-side contact layer 12)
The n-side contact layer 12 is a layer that acts as a contact layer for forming a negative electrode, and is preferably adjusted to 0.2 μm or more and 4 μm or less. If it is thinner than 0.2, it is difficult to control the etching rate so that this layer is exposed when a negative electrode is formed later. It is in. The range of the n-type impurity doped into the nitride semiconductor of the n-side contact layer 12 is in the range of 1 × 10 ¹⁷ / cm ³ to 1 × 10 ²¹ / cm ³ , more preferably 1 × 10 ¹⁸ / cm ³ to 1. It is desirable to adjust to × 10 ¹⁹ / cm ³ . If it is less than 1 × 10 ¹⁷ / cm ^3, it is difficult to obtain a preferable ohmic with the material of the n electrode, so that a reduction in threshold current and voltage cannot be expected in the laser element.
^If it is greater than ²¹ / cm ³ , the leakage current of the element itself increases and the crystallinity also deteriorates, so that the lifetime of the element tends to be shortened. N-side contact layer 1
2, in order to reduce the ohmic contact resistance with the n-electrode 23, it is desirable that the impurity concentration for increasing the carrier concentration of the n-side contact layer 12 is higher than that of the n-cladding layer 14. The n-side contact layer 12 is formed on the substrate with GaN,
When a conductive substrate such as SiC or ZnO is used and a negative electrode is provided on the back side of the substrate, it functions as a buffer layer, not as a contact layer.

Further, at least one of the second buffer layer 11 and the n-side contact layer 12 may be a superlattice layer. When a superlattice layer is used, the crystallinity of this layer is dramatically improved, and the threshold current is reduced. The n-side contact layer 12 that is preferably thinner than the second buffer layer 11 is a superlattice layer. n-side contact layer 1
2 is a superlattice structure in which a first layer and a second layer having different band gap energies are laminated, preferably, an n-electrode 23 is formed by exposing a layer having a small band gap energy. As a result, the contact resistance with the n-electrode 23 can be lowered and the threshold value can be lowered. As the material of the n-electrode 23 that can obtain a preferable ohmic with the n-type nitride semiconductor, Al, Ti, W, Si, Zn
, Sn, In or other metals or alloys.

Further, by making the n-type contact layer 12 a superlattice layer having a different impurity concentration, the lateral resistance value can be lowered by the effect similar to the HEMT described in the first embodiment, and the threshold voltage and current of the LD element can be lowered. can do.

(Crack prevention layer 13)
For example, the crack prevention layer 13 is made of In doped with Si of 5 × 10 ¹⁸ / cm ^3.
_{It is made of 0.1} Ga _0.9 N and has a film thickness of, for example, 500 Å. This crack prevention layer 13 is an n-type nitride semiconductor containing In, preferably InG.
By growing aN, it is possible to prevent cracks from entering into the nitride semiconductor layer containing Al formed thereon. The crack prevention layer 13 is preferably grown to a 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 crack prevention as described above, and if it is thicker than 0.5 μm, the crystal itself tends to turn black.
The crack prevention layer 13 is formed of the n-side contact layer 12 as in the first embodiment.
May be omitted if the n-side cladding layer 14 to be grown next is a superlattice layer.

(N-side cladding layer 14 made of n-type superlattice)
The n-side cladding layer is, for example, n-type A10 doped with Si of 5 × 10 ¹⁸ / cm ^3.
. A superlattice layer composed of 2Ga0.8N, a first layer having a thickness of 20 Å, and a second layer made of undoped GaN and having a thickness of 20 Å are alternately stacked. For example, it has a film thickness of 0.5 μm. This n-type cladding layer 14 functions as a carrier confinement layer and an optical confinement layer. When a superlattice layer is formed, it is desirable to grow a nitride semiconductor containing Al, preferably AlGaN, in any one of the layers. A favorable carrier confinement layer can be grown by growing at a thickness of 100 Å or more and 2 μm or less, more preferably 500 Å or more and 1 μm or less. The n-type cladding layer 14 can be grown from a single nitride semiconductor. However, if a superlattice layer is formed, a carrier confinement layer having good crystallinity without cracks can be formed.

(N-side light guide layer 15)
The n-side light guide layer 15 is made of, for example, n-type GaN doped with Si at 5 × 10 ¹⁸ / cm ³ and has a thickness of 0.1 μm. The n-side light guide layer 6 functions as a light guide layer of the active layer, and is preferably formed by growing GaN and InGaN, and is usually grown to a thickness of 100 angstroms to 5 μm, more preferably 200 angstroms to 1 μm. It is desirable to make it. The light guide layer 15 can also be a superlattice layer. n-side light guide layer 15, n-side cladding layer 14
Is made a superlattice layer, the average band gap energy of the nitride semiconductor layer constituting the superlattice layer is made larger than that of the active layer. In the case of a superlattice layer, at least one of the first layer and the second layer may be doped with an n-type impurity or may be undoped. The light guide layer 15 may be an undoped nitride semiconductor alone or a superlattice in which undoped nitride semiconductors are stacked.

(Active layer 16)
The active layer 16 is, for example, In _0.2 doped with Si at 8 × 10 ¹⁸ / cm ^3.
A well layer made of Ga _0.8 N and having a film thickness of 25 Å, In _0.05 1Ga _0.95 N doped with Si 8 × 10 ¹⁸ / cm ³ , 50
A barrier layer having an angstrom thickness is alternately stacked to form a multiple quantum well structure (MQW) having a predetermined thickness. In the active layer 16,
Both the well layer and the barrier layer may be doped with impurities, or one of them may be doped. When the n-type impurity is doped, the threshold tends to decrease. In addition, when the active layer 16 has a multiple quantum well structure in this way, a well layer having a small band gap energy and a barrier layer having a band gap energy smaller than that of the well layer are necessarily stacked. Differentiated. The thickness of the well layer is 100 angstroms or less, preferably 70 angstroms or less, and most preferably 50 angstroms or less. The thickness of the barrier layer is 150 angstroms or less, preferably 100 angstroms or less, and most preferably 70 angstroms or less.

(P-side cap layer 17)
The p-side cap layer 17 has a larger band gap energy than the active layer 16, for example, p-type Al _0.3 Ga _0.7 N doped with 1 × 10 ²⁰ / cm ^{3 of} Mg.
For example, it has a film thickness of 200 Å. In Embodiment 2, it is preferable to use the cap layer 17 as described above.
Since it is formed in a thin film thickness, in the present invention, it may be an i-type in which carriers are compensated by doping an n-type impurity. The film thickness of the p-side cap layer 17 is adjusted to 0.1 μm or less, more preferably 500 angstroms or less, and most preferably 300 angstroms or less. This is because if the film is grown to a thickness greater than 0.1 μm, cracks are likely to occur in the p-side cap layer 17 and a nitride semiconductor layer with good crystallinity is difficult to grow. Moreover, when the film thickness of the p-side cap layer 17 is 0.1 μm or more,
This is because carriers cannot pass through the p-type cap layer 17 serving as the energy barrier due to the tunnel effect, and considering the passage of carriers due to the tunnel effect, as described above, it is set to 500 angstroms or less, and further to 300 angstroms or less. It is preferable.

The p-side cap layer 17 is preferably formed using AlGaN having a large Al composition ratio in order to make the LD element easy to oscillate. The thinner the AlGaN, the easier the LD element oscillates. Become. For example, Al with a Y value of 0.2 or more
_{If Y} Ga _1-Y N, it is desirable to adjust to 500 angstroms or less. The lower limit of the thickness of the p-side cap layer 17 is not particularly limited, but it is desirable to form the p-side cap layer 17 with a thickness of 10 angstroms or more.

(P-side light guide layer 18)
The p-side light guide layer 18 has a band gap energy smaller than that of the p-side cap layer 17, for example, p-type GaN doped with 1 × 10 ²⁰ / cm ^{3 of} Mg, and has a thickness of 0.1 μm. The p-side light guide layer 18 functions as a light guide layer of the active layer 16 and is preferably formed by growing with GaN and InGaN as with the n-side light guide layer 15. This layer also functions as a buffer layer when the p-side cladding layer 19 is grown, and functions as a preferable light guide layer by growing it at a film thickness of 100 angstroms to 5 μm, more preferably 200 angstroms to 1 μm. . This p-side light guide layer is usually doped with a p-type impurity such as Mg to have a p-type conductivity, but it is not particularly necessary to dope the impurity. In addition,
The p-side light guide layer can be a superlattice layer. In the case of a superlattice layer, at least one of the first layer and the second layer may be doped with a p-type impurity, or may be undoped.

(P-side cladding layer 19 = superlattice layer)
The p-side cladding layer 19 is made of, for example, p-type Al _0.2 Ga _0.8 N doped with 1 × 10 ²⁰ / cm ^{3 of} Mg. It is made of p-type GaN doped with 1 × 10 ²⁰ / cm ^{3 of} Mg, and consists of a superlattice layer in which second layers having a thickness of 20 Å are alternately stacked. The p-side clad layer 19 acts as a carrier confinement layer like the n-side clad layer 14, and particularly acts as a layer for reducing the resistivity of the p-type layer. The thickness of the p-side cladding layer 19 is not particularly limited, but is 100 angstroms or more and 2 μm or less, more preferably 500 angstroms or more and 1 μm.
It is desirable to form the following.

(P-side contact layer 20)
The p-side contact layer 20 is made of, for example, 2 × 1 Mg on the p-side cladding layer 19.
It is made of p-type GaN doped with 0 ²⁰ / cm ³ and has a film thickness of 150 Å, for example. The p-side contact layer 20 is made of p-type In _X Al _Y Ga _1-X.
−YN (0 ≦ X, 0 ≦ Y, X + Y ≦ 1), and preferably Mg-doped GaN as described above provides the most preferable ohmic contact with the p-electrode 21. . Further, it is desirable to adjust the thickness of the p-side contact layer to 500 angstroms or less, more preferably 300 angstroms or less, and most preferably 200 angstroms or less. Because, as described above, the resistivity can be further reduced by adjusting the thickness of the p-type nitride semiconductor layer having a resistivity of several Ω · cm or more to 500 angstroms or less. Current and voltage decrease. Further, the amount of hydrogen removed from the p-type layer can be increased, and the resistivity can be further reduced.

In the present invention, the p-side contact layer 20 can also be a superlattice layer. When the superlattice layer is used, the first layer and the second layer having different band gap energies are used.
Are stacked in the order of 1 + 2 + 2 + 1 + 2 + ...
Finally, when the layer having the smaller band gap energy is exposed, a preferable ohmic contact with the p-electrode 21 can be obtained. Examples of the material for the p-electrode 21 include Ni, Pd, Ni / Au, and the like.

In the second embodiment, an insulating film 25 made of SiO ₂ is formed on the surface of the nitride semiconductor layer exposed between the p-electrode 21 and the n-electrode 23 as shown in FIG. A p-pad electrode 22 electrically connected to the p-electrode 21 and an n-pad electrode 24 connected to the n-electrode 23 are formed through the opening formed in the first and second electrodes. The p-pad electrode 22 substantially increases the surface area of the p-electrode 21 so that the p-electrode side can be wire bonded or die-bonded, while the n-pad electrode 24 is n
The peeling of the electrode 23 is prevented.

The nitride semiconductor device according to the second embodiment described above is a p-type cladding layer 19 with good crystallinity, which is a superlattice layer in which the first layer and the second layer are stacked with a film thickness equal to or less than the elastic strain limit. It has. As a result, the nitride semiconductor device according to the second embodiment can reduce the resistance value of the p-side cladding layer 19 by one digit or more as compared with the p-side cladding layer having no superlattice structure. , Current can be lowered.

Further, in the nitride semiconductor device of the second embodiment, p containing p _- type Al _Y Ga _1-Y N is used.
By forming a nitride semiconductor having a small band gap energy in contact with the side cladding layer 19 as a p-side contact layer 20 and having a film thickness as thin as 500 angstroms or less, the carrier concentration of the p-side contact layer 20 is substantially reduced. P higher
A preferable ohmic with the electrode can be obtained, and the threshold current and voltage of the element can be lowered. Further, the second buffer layer 112 is grown before the n-side contact layer is grown.
Therefore, the crystallinity of the nitride semiconductor layer grown on the second buffer layer 112 is improved, and a long-life device can be realized. Preferably, when the n-side contact layer grown on the second buffer layer 112 is a superlattice, a lateral resistance value is low, and an element having a low threshold voltage and threshold current can be realized.

In the LD element of the second embodiment, when the active layer 16 is provided with a nitride semiconductor containing at least indium such as InGaN, In _X Ga _1-X N,
A superlattice layer in which Al _Y Ga _1-Y N is alternately stacked is preferably used as a layer (n-side cladding layer 14 and p-side cladding layer 19) that sandwiches the active layer 16.
As a result, the band gap energy difference and the refractive index difference between the active layer 16 and the superlattice layer can be increased, so that the superlattice layer can be operated as a very excellent optical confinement layer when realizing a laser device. it can. Furthermore, since InGaN is softer than other nitride semiconductors containing Al like AlGaN, InG
When aN is used as the active layer, cracks are less likely to occur in the entire laminated nitride semiconductor layers. Thereby, the lifetime of the LD element can be extended.

In the case of a semiconductor device having a double hetero structure having an active layer 16 having a quantum well structure as in the second embodiment, a film thickness of 0.1 μm or less having a band gap energy larger than that of the active layer 16 in contact with the active layer 16 A p-side cap layer 17 made of a nitride semiconductor, preferably a p-side cap layer 17 made of a nitride semiconductor containing Al, is provided, and the p-side cap layer is located farther from the active layer than the p-side cap layer 17. A p-side light guide layer 18 having a band gap energy smaller than 17 and a nitride semiconductor having a band gap larger than that of the p-side light guide layer 18 at a position farther from the active layer than the p-side light guide layer 18; It is very preferable to provide the p-side cladding layer 19 having a superlattice structure preferably containing a nitride semiconductor containing Al. In addition, since the band gap energy of the p-side cap layer 17 is increased, the electrons injected from the n-layer are blocked and confined by the p-side cap layer 17 and the electrons do not overflow the active layer. Less leakage current.

The nitride semiconductor device of the second embodiment has a preferable structure as a laser device. In the present invention, the n-type superlattice layer is an n-type nitride semiconductor layer region (n-type) below the active layer 16. At least one layer on the layer side) and a p-type superlattice layer in the p-type nitride semiconductor layer region (p-type layer side) above the active layer 16 as well. Well, the element configuration is not particularly specified. However, when the superlattice layer is formed on the p-layer side, it is formed on the p-side cladding layer 19 as a carrier confinement layer, and when it is formed on the n-layer side, it is an n-contact as a current injection layer in contact with the n-electrode 23. The formation of the layer 12 or the n-cladding layer 14 for carrier confinement tends to be most preferable in reducing the Vf and threshold value of the device. Further, it goes without saying that the same configuration as that of the element of Embodiment 2 can be applied to the LED element (
However, the LED element does not require a ridge portion).

In the nitride semiconductor device according to the second embodiment configured as described above, after each layer is formed, in an atmosphere not containing H, for example, a nitrogen atmosphere, 400 ° C. or higher, for example, 7
Annealing is preferably performed at 00 ° C., whereby the resistance of each layer in the p-type nitride semiconductor layer region can be further reduced, thereby further reducing the threshold voltage.

In the nitride semiconductor device of the second embodiment, N is formed on the surface of the p-side contact layer 12.
A p-electrode 21 made of i and Au is formed in a stripe shape, the n-side contact layer is exposed symmetrically with respect to the p-electrode 21, and an n-electrode 23 is provided on almost the entire surface of the n-side contact layer. Yes. Thus, when an insulating substrate is used, the p-electrode 2
The structure in which the n-electrodes 23 are provided symmetrically on both sides of 1 is very advantageous in reducing the threshold voltage.

In the second embodiment, a dielectric multilayer film made of SiO ₂ and TiO ₂ may be formed on a cleaved surface (resonator surface) cleaved in a direction perpendicular to the ridge portion (stripe-shaped electrode).

Thus, in the present invention, the superlattice layer is an n-type region or p that sandwiches the active layer.
The average band gap of the nitride semiconductor constituting the superlattice layer because it is used as a clad layer as a carrier confinement layer formed in the mold region, a light guide layer of the active layer, or a current injection layer formed in contact with the electrode It is desirable to adjust so that the energy is larger than that of the active layer.

Hereinafter, the present invention will be described in detail in Examples.
[Example 1]
Example 1 according to the present invention is an example of producing the nitride semiconductor device (LD device) shown in FIG. 2, and is produced by the following procedure.
First, the substrate 10 made of sapphire (C-plane) is set in a reaction vessel, and the inside of the vessel is sufficiently replaced with hydrogen, and then the temperature of the substrate is raised to 1050 ° C. while flowing hydrogen to clean the substrate.
Subsequently, the temperature is lowered to 510 ° C., hydrogen is used as the carrier gas, ammonia (NH ₃ ) and TMG (trimethyl gallium) are used as the source gas, and the first buffer layer 11 made of GaN is formed on the substrate 10 at about 200 Å. Growing with a film thickness of

After growth of the buffer layer 11, only TMG is stopped and the temperature is raised to 1050 ° C. When the temperature reaches 1050 ° C., the second buffer layer 1 made of undoped GaN having a carrier concentration of 1 × 10 ¹⁸ / cm ³ , similarly using TMG and ammonia gas as the source gas.
12 is grown to a film thickness of 5 μm. The second buffer layer is In _X Al _Y Ga _{1-X
-Y N (0 ≦ X, 0} ≦ Y, X + Y ≦ 1) can be configured with, but not its composition asks particularly preferably Al (Y value) in undoped 0.1 following _Al Y _{Ga 1- Y} N
Most preferably, it is undoped GaN.
Subsequently, at 1050 ° C., TMG, ammonia, impurity gas and silane gas (SiH
₄ ), an n-side contact layer 12 made of n-type GaN doped with Si at 1 × 10 ¹⁹ / cm ³ is grown to a thickness of 1 μm. The n-side contact layer 12 is more preferably formed of a superlattice.

Next, the temperature is set to 800 ° C., TMG, TMI (trimethylindium), ammonia, silane gas is used as an impurity gas, and Si is 5 × 10 ¹⁸ / cm.
^A crack prevention layer 13 made of ^3- doped In _0.1 Ga _0.9 N is grown to a thickness of 500 Å.
Then, the temperature is set to 1050 ° C., and the first layer made of n-type Al _0.2 Ga _0.8 N doped with Si at 5 × 10 ¹⁸ / cm ³ using TMA, TMG, ammonia, and silane gas is formed to a thickness of 20 Å. Then, TMA and silane are stopped, and a second layer made of undoped GaN is grown to a thickness of 20 Å. This operation is repeated 100 times to grow an n-side cladding layer 14 made of a superlattice layer having a total film thickness of 0.4 μm.

Subsequently, an n-side light guide layer 15 made of n-type GaN doped with Si at 5 × 10 ¹⁸ / cm ³ is grown at 1050 ° C. to a thickness of 0.1 μm.
Next, the active layer 16 is grown using TMG, TMI, ammonia, and silane. The active layer 16 is maintained at a temperature of 800 ° C., and a well layer made of In _0.2 Ga _0.8 N doped with Si at 8 × 10 ¹⁸ / cm ³ is first grown to a thickness of 25 Å. Next, Si is changed to 8 × at the same temperature only by changing the molar ratio of TMI.
A barrier layer made of 10 ¹⁸ / cm ³ doped In _0.01 Ga _0.99 N is grown to a thickness of 50 Å. This operation is repeated twice, and an active layer 16 having a total quantum film structure (MQW) having a total film thickness of 175 angstroms and finally a well layer is grown.

Next, the temperature is raised to 1050 ° C., TMG, TMA, ammonia are used as the source gas, Cp ₂ Mg (cyclopentadienylmagnesium) is used as the impurity gas, the band gap energy is larger than that of the active layer, and Mg is 1 × 10 ^A p-side cap layer 17 made of p-type Al _0.3 Ga _0.7 N doped with ²⁰ / cm ³ is grown to a thickness of 300 Å.
Subsequently, the p-side light guide layer 18 made of p-type GaN doped with 1 × 10 ²⁰ / cm ^{3 of} Mg and having a band gap energy smaller than that of the p-side cap layer 17 at 1050 ° C. has a thickness of 0.1 μm. Grow.

Subsequently, using TMA, TMG, ammonia, Cp ₂ Mg, Mg at 1050 ° C.
A first layer made of p-type Al _0.2 Ga _0.8 N doped with 1 × 10 ²⁰ / cm ³ is grown to a thickness of 20 angstroms. Subsequently, only TMA is stopped and Mg is reduced to 1
A second layer of p-type GaN doped with × 10 ²⁰ / cm ³ is grown to a thickness of 20 Å. Then, this operation is repeated 100 times, and the total film thickness is 0.
. A p-side cladding layer 19 made of a 4 μm superlattice layer is formed.
Finally, Mg is 2 × 10 ²⁰ / cm on the p-side cladding layer 19 at 1050 ° C.
^A p-side contact layer 20 made of ^3- doped p-type GaN is grown to a thickness of 150 Å.

After the completion of the reaction, the temperature is lowered to room temperature, and the wafer is annealed in a reaction vessel at 700 ° C. in a nitrogen atmosphere to further reduce the resistance of the p-type layer.
After annealing, the wafer is removed from the reaction vessel and RI as shown in FIG.
The uppermost p-side contact layer 20 and the p-side cladding layer 19 are etched by an E device to form a ridge shape having a stripe width of 4 μm.

Next, a mask is formed on the ridge surface, and as shown in FIG. 2, the surface of the n-side contact layer 12 is exposed so as to be symmetrical with respect to the striped ridge.
Next, Ni and Au are formed on almost the entire surface of the stripe ridge of the p-side contact layer 20.
A p-electrode 21 is formed. On the other hand, an n electrode 23 made of Ti and Al is formed on almost the entire surface of the striped n-side contact layer 3.

Next, as shown in FIG. 2, an insulating film 25 made of SiO ₂ is formed on the surface of the nitride semiconductor layer exposed between the p-electrode 21 and the n-electrode 23, and the p-electrode is interposed through this insulating film 25. A p-pad electrode 22 and an n-pad electrode 24 electrically connected to 21 are formed.
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 1 on the side where the nitride semiconductor is not formed is lapped with a diamond abrasive, The thickness is 50 μm. After lapping, the substrate surface is mirror-finished by polishing with 1 μm with a finer abrasive.

After polishing the substrate, the polished surface side is scribed and cleaved in a bar shape in a direction perpendicular to the striped electrode to produce a resonator on the cleaved surface. A dielectric multilayer film made of SiO ₂ and TiO ₂ was formed on the resonator surface, and finally a bar was 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. The threshold current density was 2.9 kA at room temperature.
/ Cm ² and a threshold voltage of 4.4 V, continuous oscillation with an oscillation wavelength of 405 nm was confirmed, and 50
It showed a lifetime of more than hours.

(Comparative Example 1)
On the other hand, the second buffer layer 112 is not grown, and the n-side contact layer 12 is further grown to a thickness of 5 μm by a single n-type GaN doped with 1 × 10 ¹⁹ / cm ³ of Si. × 10 ¹⁹ / cm ³ doped n-type Al _0.2 Ga _0.8
N is grown by 0.4 μm, and the p-side cladding layer 19 is made of 1 × 10 ²⁰ / m ³ of Mg.
A single doped p-type Al _0.2 Ga _0.8 N is grown to 0.4 μm, and the p-side contact layer 20 is made of single p-type GaN doped with 2 × 10 ²⁰ / cm ³ of Mg.
. A laser device was obtained in the same manner as in Example 1 except that the growth was 2 μm. That is, the basic configuration is as shown in Table 1.

In the laser element of the comparative example configured as described above, continuous oscillation was confirmed at a threshold current density of 7 kA / cm ² , but the threshold voltage was 8.0 V or more and was cut off in several minutes.

[Example 2]
In Example 1, the n-side contact layer 12 is grown to a thickness of 30 Å by forming a first layer made of n-type Al _0.05 Ga _0.95 N doped with Si 2 × 10 ¹⁹ / cm ³ . Subsequently, a second layer made of undoped GaN is grown to a thickness of 30 Å, and this is repeated to obtain a superlattice structure with a total thickness of 1.2 μm. The other structure was a laser device having the same structure as that of Example 1. The threshold current density was 2.7 kA / cm ² , the threshold voltage was 4.2 V, and the lifetime was 60 hours or longer.

[Example 3]
In Example 2, in the superlattice constituting the n-side contact layer 12, a laser element having the same structure as that of Example 2 except that the second layer is GaN doped with Si of 1 × 10 ¹⁸ / cm ³ As a result, a laser device having substantially the same characteristics as in Example 2 was obtained.

[Example 4]
In Example 1, a laser element having the same structure as that of Example 1 was fabricated except that the second buffer layer 112 was grown to 4 μm using GaN doped with Si of 1 × 10 ¹⁷ / cm ^3. Current density 2.9 kA / cm ² , threshold voltage 4.5
Although it rose to V, the lifetime showed more than 50 hours.

[Example 5]
In Example 1, the n-side contact layer 12 is grown to a thickness of 60 Å by forming a first layer made of n-type Al _0.2 Ga _0.8 N doped with Si 2 × 10 ¹⁹ / cm ³ . Subsequently, a second layer made of GaN doped with Si at 1 × 10 ¹⁹ / cm ³ is grown to a thickness of 40 Å, and this is sequentially repeated to obtain a superlattice structure with a total thickness of 2 μm. The n-side cladding layer 14 is made of 1 × 10 Si.
^{A 19} / cm ³ doped n-type Al _0.2 Ga _0.8 N single layer is grown to 0.4 μm. The other structure was a laser device having the same structure as in Example 1. As a result, the threshold current density was 3.2 kA / cm ² , the threshold voltage was 4.8 V, and the lifetime was 30 hours or longer.

[Example 6]
The sixth embodiment is configured in the same manner as the first embodiment except that the following (1) and (2) are different from the first embodiment.
(1) After growing the buffer layer 11, only TMG is stopped and the temperature is raised to 1050 ° C. When the temperature reaches 1050 ° C., the first layer made of n-type Al _0.2 Ga _0.8 N doped with 1 × 10 ¹⁹ / cm ^{3 of} Si using TMA, TMG, ammonia, and silane as the source gas is 60 angstroms. Followed by silane, T
The MA is stopped and a second layer of undoped GaN is grown to a thickness of 40 Å. Then, the superlattice layer is configured as first layer + second layer + first layer + second layer +..., 500 layers for the first layer and 500 layers for the second layer, respectively. Then, the n-side contact layer 12 made of a superlattice having a total film thickness of 5 μm is formed.
(2) Next, in the same manner as in Example 1, I was doped with Si at 5 × 10 ¹⁸ / cm ^3.
A crack prevention layer 13 made of n _0.1 Ga _0.9 N is grown to a thickness of 500 Å.
Then, the n-side cladding layer 14 made of n-type Al _0.2 Ga _0.8 N doped with Si at 5 × 10 ¹⁸ / cm ³ at 0 ° C. using TMA, TMG, ammonia, and silane is set to 0 Growing with a film thickness of 5 μm.
A laser element having a structure similar to that of the laser element of Example 1 is formed above the n-side cladding layer 14 later. That is, in the basic structure of Table 1, the n-side contact layer 12
Then, a laser device is manufactured in which the p-side cladding layer 19 is a superlattice and the thickness of the p-side contact layer 20 is 150 Å as in the first embodiment. This laser device had a threshold current density of 3.2 kA / cm ² , a threshold voltage of 4.8 V, a continuous oscillation of 405 nm, and a lifetime of 30 hours or more.

Furthermore, when the thickness of the p-side contact layer of the LD element having the structure of Example 6 is sequentially changed, the relationship between the thickness of the p-side contact layer and the threshold voltage of the LD element is shown in FIG. This is because the p-side contact layer has A (10 angstroms or less), B in order from the left.
(10 angstroms), C (30 angstroms), D (150 angstroms, this example), E (500 angstroms), F (0.2 μm), G
The threshold voltages in the case of (0.5 μm) and H (0.8 μm) are shown. As shown in this figure, when the thickness of the p-side contact layer exceeds 500 angstroms, the threshold voltage tends to gradually increase. The thickness of the p-side contact layer 20 is desirably 500 angstroms or less, more preferably 300 angstroms or less. When the thickness is 10 angstroms or less (approximately 1 atomic layer or 2 atomic layers), the surface of the lower p-side cladding layer 19 is exposed, so that the contact resistance of the p-electrode deteriorates and the threshold voltage tends to increase. is there. However, the LD of the present invention
Since the element has a superlattice layer, the threshold voltage is significantly lower than that of the comparative example.

(Comparative Example 2)
In the laser device having the configuration shown in Table 1, the n-side cladding layer 14 is made of 1 × 10 ¹⁹ Si.
A first layer of n-type Al _0.2 Ga _0.8 N doped with / cm ³ is grown to a thickness of 180 Å, and then a second layer of undoped GaN is grown to 1
A multilayer film having a total film thickness of 0.6 μm is grown by a film thickness of 20 Å. In other words, when a laser element was fabricated with a structure in which the thicknesses of the first layer and the second layer were increased, continuous oscillation was confirmed at a threshold current density of 6.5 kA / cm ² and a threshold voltage of 7.
It was 5V. This laser element was cut off in a few minutes.

[Example 7]
In Example 6, the p-side cladding layer 19 is formed of a first layer made of Al _0.2 Ga _0.8 N, 60 angstroms doped with 1 × 10 ²⁰ / cm ^{3 of} Mg, and 1 × 10 ²⁰ / cm of Mg. 2nd made of ³ doped p-type GaN, 40 Å
A laser element similar to that of Example 6 is manufactured except that a superlattice structure with a total thickness of 0.5 μm is formed by laminating these layers. That is, when the laser device was fabricated in the same manner except that the film thickness of the superlattice layer constituting the p-side cladding layer 19 of Example 6 was changed, the threshold voltage slightly increased compared to the laser device of Example 6. Although there was a tendency, the lifetime of 20 hours or more was shown.

[Example 8]
In Example 7, the n-side clad layer 14 is further formed of a first layer made of n-type Al _0.2 Ga _0.8 N, 60 angstroms doped with Si 1 × 10 ¹⁹ / cm ³ , and Si 1 × 10 Example 7 except that a superlattice structure having a total film thickness of 0.5 μm is formed by laminating a ¹⁹ / cm ³ -doped n-type GaN and a second layer made of 40 Å.
A laser element similar to the above is manufactured. That is, the n-side contact layer 12, p of Example 6
The laser device using the n-side cladding layer as a superlattice in addition to the side cladding layer 19 had substantially the same characteristics as in Example 6.

[Example 9]
In Example 1, without growing the second buffer layer 112, as shown in Table 1, 1 × Si was directly formed on the first buffer layer 11 as the n-side contact layer 12.
An n-type GaN layer doped with 10 ¹⁹ / cm ³ is grown to 5 μm. The other elements are laser elements having the same structure as in the first embodiment. In other words, in the basic structure of Table 1,
The n-side cladding layer 14 includes a first layer made of Si (1 × 10 ¹⁹ / cm ³ ) doped n-type Al _0.2 Ga _0.8 N and a second layer made of 20 Å undoped GaN. And a superlattice structure having a total film thickness of 0.4 μm. Further, the p-side cladding layer 19 is made of 20 angstrom Mg (1 × 10
²⁰ / cm ³ ) doped p-type Al _0.2 Ga _0.8 N first layer and 20 angstrom Mg (1 × 10 ²⁰ / cm ³ ) doped p-type GaN A superlattice structure having a total thickness of 0.4 μm is formed. Further, the p-side contact layer 20 is formed with 150 Å Mg (2 × 10 ²⁰ /
cm ³ ) When doped p-type GaN, the threshold current density is 3.3 kA / cm ² and 40
A continuous oscillation of 5 nm was confirmed, the threshold voltage was 5.0 V, and the lifetime was 30 hours or more.

[Example 10]
In Example 9, the second layer constituting the superlattice of the n-side cladding layer 14 is made of Si.
A laser element similar to that in Example 9 is manufactured except that GaN doped with 1 × 10 ¹⁷ / cm ³ is used. That is, the laser device manufactured in the same manner as in Example 9 except that the layer having the larger band gap energy was doped with a large amount of Si exhibited substantially the same characteristics as in Example 9.

[Example 11]
In Example 9, the second layer constituting the n-side cladding layer 14 is made of 1 × 1 Si.
A laser device is fabricated in the same manner _except that n-type In _0.01 Ga _0.99 N doped with 0 ¹⁹ / cm ³ is used. In other words, the second layer composing the superlattice of the n-side cladding layer 14 is made of InGaN, and the first layer and the second layer have the same impurity concentration, and are manufactured in the same manner as in Example 9. The laser element exhibited substantially the same characteristics as in Example 9.

[Example 12]
In Example 9, the first layer constituting the n-side cladding layer 14 (Si: 1 × 10
¹⁹ / cm ³ -doped Al _0.2 Ga _0.8 N) with a thickness of 60 Å, and the second layer with 40 Å of Ga doped with 1 × 10 ¹⁹ / cm ³ of Si
N and a superlattice structure with a total film thickness of 0.5 μm. Further, the thickness of the first layer (Mg: 1 × 10 ²⁰ / cm ³ doped Al _0.2 Ga _0.8 N) constituting the p-side cladding layer 19 is set to 60 Å, and the second layer (Mg: 1 The film thickness of × 10 ²⁰ / cm ³ doped: GaN) is 40 Å, and a superlattice structure with a total film thickness of 0.5 μm is formed. That is, the first layer and the second layer constituting the n-side cladding layer 14 have the same doping amount, the film thickness is changed, and the first layer and the second layer constituting the p-side cladding layer 19 are changed. A laser element was fabricated in the same manner as in Example 9 except that the film thickness was changed. As a result, continuous oscillation at 405 nm was confirmed at a threshold current density of 3.4 kA / cm ² , the threshold voltage was 5.2 V, and the lifetime was Also showed over 20 hours.

[Example 13]
In Example 11, S of the second layer (GaN) constituting the n-side cladding layer 14
A laser element having a structure similar to that of Example 11 was produced except that the i concentration was 1 × 10 ¹⁷ / cm ³ .

[Example 14]
In Example 11, a laser device having the same structure as that of Example 11 was produced except that the second layer (GaN) constituting the n-side cladding layer 14 was undoped. A laser device having

[Example 15]
In Example 9, a laser element was fabricated in the same manner except that the n-side cladding layer 14 was grown by a single n-type Al _0.2 Ga _0.8 N doped with 1 × 10 ¹⁹ / cm ³ of Si by 0.4 μm. To do. That is, in the basic structure of Table 1, only the p-side cladding layer 19 is doped with 1 × 10 ²⁰ / cm ³ Mg as in Example 1 and is p-type Al _0.2 Ga _0.
. First layer of ₈ N, 20 angstroms, Mg 1 × 10 ¹⁹ / cm ³
A superlattice structure with a total film thickness of 0.4 μm composed of a second layer 20 Å of doped p-type GaN is formed, and the p-side contact layer 20 is made of 150 Å of Mg (2 × 10 5 as in the first embodiment). ^{When 20} / cm ³ ) doped p-type GaN was used, continuous oscillation at 405 nm was confirmed at a threshold current density of 3.4 kA / cm ² , the threshold voltage was 5.1 V, and the lifetime was 20 hours or longer.

[Example 16]
In Example 15, the thickness of the superlattice layer constituting the p-side cladding layer 19 is 60 Å for the first layer (Al _0.2 Ga _0.8 N), and the second layer (GaN
1) except that the total film thickness is 0.5 μm.
As a result, the threshold voltage tended to increase slightly.
The lifetime was 20 hours or more.

[Example 17]
In Example 9, a laser device was fabricated in the same manner except that the p-side cladding layer 19 was grown by a single p-type Al _0.2 Ga _0.8 N doped with 1 × 10 ²⁰ / cm ³ of Mg and having a thickness of 0.4 μm. To do. That is, in the basic structure of Table 1, only the n-side cladding layer 14 is doped with Si at 1 × 10 ¹⁹ / cm ³ as in Example 1 and is n-type Al _0.2 Ga _0.
. A superlattice structure having a total film thickness of 0.4 μm composed of a first layer made of ₈ N, 20 angstroms, and a second layer 20 angstroms made of undoped GaN, and the p-side contact layer 20 in Example 1 When Mg (2 × 10 ²⁰ / cm ³ ) -doped p-type GaN with 150 Å is used, continuous oscillation at 405 nm is confirmed at a threshold current density of 3.5 kA / cm ² , and the threshold voltage is 5.4 V.
The lifetime was 10 hours or more.

[Example 18]
In Example 17, the thickness of the superlattice layer constituting the n-side cladding layer 14 is 70 angstroms for the first layer (Al _0.2 Ga _0.8 N), and Si is 1 × 10 6 for the second layer. A laser element similar to that in Example 17 was obtained except that ¹⁹ / cm ³ -doped In _0.01 Ga _0.99 N and 70 angstroms were stacked and the total film thickness was 0.49 μm. The threshold voltage tended to increase slightly,
Similarly, a laser element having a lifetime of 10 hours or longer was obtained.

[Example 19]
In Example 17, the thickness of the superlattice layer constituting the n-side cladding layer 14 is 60 Å for the first layer (Al _0.2 Ga _0.8 N) and 40 Å for the second layer (undoped GaN). A laser element similar to that of Example 16 was obtained except that the film was stacked in angstroms and the total film thickness was 0.5 μm. The threshold voltage tended to slightly increase compared to Example 17, but it was also 10 hours or more. As a result, a laser device having a lifetime of 5 nm was obtained.

[Example 20]
In Example 9, the n-side light guide layer 15 is further laminated with a first layer made of undoped GaN, 20 Å, and a second layer made of undoped In _0.1 Ga _0.9 N, 20. The resulting superlattice layer has a total film thickness of 800 angstroms. In addition, the p-side light guide layer 18 is also made of a first non-doped GaN layer.
And a superlattice structure with a total thickness of 800 Å, which is a stack of 20 Å, a second layer made of undoped In _0.1 Ga _0.9 N, and 20 Å. That is, in the basic structure of Table 1, the n-side cladding layer 14
, The n-side light guide layer 15, the p-side light guide layer 18, and the p-side cladding layer 19 have a superlattice structure. ²⁰ / cm ³ ) doped p-type GaN, continuous oscillation at 405 nm was confirmed at a threshold current density of 2.9 kA / cm ² , and the threshold voltage was 4
. 4V and the lifetime also showed 60 hours or more.

[Example 21]
This embodiment will be described based on the LED element of FIG. In the same manner as in Example 1, a buffer layer 2 made of GaN is grown on a substrate 1 made of sapphire to a thickness of 200 Å, and then a contact layer made of n-type GaN doped with Si at 1 × 10 ¹⁹ / cm ^3. Then, an active layer 4 having a single quantum well structure having a thickness of 30 Å made of In _0.4 Ga _0.6 N is grown.

(P-side superlattice layer)
Next, in the same manner as Example 1, p-type Al doped with 1 × 10 ²⁰ / cm ^{3 of} Mg
_A first layer made of _0.2 Ga _0.8 N is grown to a thickness of 20 angstroms, and then a second layer made of p-type GaN doped with 1 × 10 ¹⁹ / cm ^{3 of} Mg is added.
A p-side cladding layer 5 made of a superlattice with a total film thickness of 0.4 μm is grown by growing it to a thickness of 0 angstrom. The thickness of the p-side cladding layer 4 is not particularly limited,
It is desirable to grow at a thickness of 100 Å or more and 2 μm or less, more preferably 500 Å or more and 1 μm or less.

Next, p-type G doped with 1 × 10 ²⁰ / cm ³ of Mg on the p-side cladding layer 5.
The aN layer is grown to a thickness of 0.5 μm. After the growth, the wafer is taken out of the reaction vessel, annealed in the same manner as in Example 1, and then etched from the p-side contact layer 6 side to expose the surface of the n-side contact layer 3 where the n-electrode 9 is to be formed. . N of 200 angstroms thick on almost the entire surface of the uppermost p-side contact layer 6
A translucent p-electrode 7 made of i-Au is formed, and a p-pad electrode 8 made of Au is formed on the entire surface electrode 7. Ti-Al is also applied to the surface of the exposed n-side contact layer.
An n electrode 9 is formed.

When the wafer on which the electrodes were formed as described above was separated into 350 μm square chips to form LED elements, green light emission of 520 nm was exhibited at If20 mA,
Vf was 3.2V. In contrast, the p-side cladding layer 5 is made of a single Mg-doped A
The Vf of the LED element composed of l _0.2 Ga _0.8 N was 3.4V. Furthermore, the electrostatic withstand voltage of the present example was twice or more.

[Example 22]
In Example 21, the superlattice layer constituting the p-side cladding layer 5 has a first layer thickness of 50 angstroms, and a second layer of GaN doped with 1 × 10 ²⁰ / cm ³ of Mg, 50 angstroms. Each of the 25 layers was laminated to a total film thickness of 0.2.
An LED element was prepared in the same manner except that the superlattice was 5 μm. Example 21
As a result, an LED element having substantially the same characteristics was obtained.

[Example 23]
In Example 21, the superlattice layer constituting the p-side cladding layer 5 has a thickness of a first layer of 100 Å and a second layer of 70 Å, and a superlattice with a total thickness of 0.25 μm. Other than that, when LED elements were created in the same way,
Vf was 3.4 V, but the electrostatic withstand voltage was 20% or more better than the conventional one.

[Example 24]
In Example 21, when the n-side contact layer 3 is grown, Si is 2 × 10 ^1.
A first layer made of ⁹ / cm ³ doped n-type Al _0.2 Ga _0.8 N is grown to a thickness of 60 Å, and a second layer made of undoped GaN is grown to a thickness of 40 Å. The superlattice having a total thickness of 5 μm is formed by alternately stacking 500 layers and 500 second layers. Other than that, an LED element was fabricated in the same manner as in Example 12. At the same If of 20 mA, Vf was reduced to 3.1 V, and the electrostatic withstand voltage was improved by 2.5 times or more compared to the conventional case.

[Example 25]
In Example 23, the first layer of the superlattice (Al ₀ constituting the p-side cladding layer 5)
_{. 2} Ga _0.8 N) is set to 60 Å, and the second layer is set to 40 Å.
As an angstrom, an LED element having a similar structure except that 25 layers were alternately laminated to have a total film thickness of 0.3 μm was obtained. Vf was 3.2 V,
The electrostatic withstand voltage was more than twice that of the prior art.

[Example 26]
This embodiment will be described based on the laser element shown in FIG. FIG. 4 is also a cross-sectional view when the element is cut in a direction perpendicular to the resonance direction of the laser beam as in FIG. 2, except that a substrate 101 made of GaN is used as the substrate 10. But second
The third buffer layer 113 doped with n-type impurities is grown without growing the first buffer layer 112. The laser element shown in FIG. 4 is obtained by the following method.

First, a GaN layer doped with Si of 5 × 10 ¹⁸ / cm ³ is grown to a thickness of 300 μm on the sapphire substrate by using MOVPE method or HVPE method, and then the sapphire substrate is removed to make Si doping with a thickness of 300 μm. A GaN substrate 101 is produced. The GaN substrate 101 is thus formed on a substrate different from the nitride semiconductor, for example, 1
After growing with a film thickness of 00 μm or more, the heterogeneous substrate is removed. The GaN substrate 101 may be undoped or may be produced by doping an n-type impurity. In the case of doping with n-type impurities, usually 1 × 10 ¹⁷ / cm ³ to 1
When impurities are doped in the range of × 10 ¹⁹ / cm ^3, a GaN substrate with good crystallinity can be obtained.

After producing the GaN substrate 101, the temperature is set to 1050 ° C., and Si is 3 × 10 ¹⁸ / cm.
^{A third} buffer layer 113 made of ^3- doped n-type GaN is grown to a thickness of 3 μm. The third buffer layer 113 is the n-side contact layer 1 in FIGS.
Although it is a layer corresponding to 4, it is not a layer for forming an electrode, and is not referred to as a contact layer here, but is referred to as a third buffer layer 113. Note that the first buffer layer grown at a low temperature may be grown between the GaN substrate 101 and the third buffer layer 113 in the same manner as in the first embodiment. However, when the first buffer layer is grown. Is 300
It is desirable to make it angstrom or less.

Next, Si is formed on the third buffer layer 113 in the same manner as in Example 1 at 5 × 10 ¹⁸ /.
A crack preventing layer 13 made of cm ³ -doped In _0.1 Ga _0.9 N is grown to a thickness of 500 Å.
Next, a first layer made of n-type Al _0.2 Ga _0.8 N doped with Si 5 × 10 ¹⁸ / cm ³ , 20 Å, and GaN doped with Si 5 × 10 ¹⁸ / cm ³ An n-side cladding layer 14 made of a superlattice layer having a total film thickness of 0.4 μm is grown by alternately laminating the second layer 20 angstroms 100 times.
Next, as in Example 1, an n-side light guide layer 15 made of n-type GaN doped with Si at 5 × 10 ¹⁸ / cm ³ is grown to a thickness of 0.1 μm.

Next, a well layer made of undoped In _0.2 Ga _0.8 N, 25 angstroms, and a barrier layer made of undoped GaN 50 angstroms were grown,
The active layer 16 having a multiple quantum well structure (MQW) having a total film thickness of 175 angstroms, in which the well layers are stacked, is finally grown twice.

Next, as in Example 1, p-type Al doped with Mg at 1 × 10 ²⁰ / cm ³ _.
A p-side cap layer 17 made of ₃ Ga _0.7 N is grown to a thickness of 300 angstroms, and a p-side light guide layer 18 made of p-type GaN doped with 1 × 10 ²⁰ / cm ^{3 of} Mg is formed to a thickness of 0.1 μm. Grow with film thickness.

Next, in the same manner as Example 1, p-type Al ₀ doped with 1 × 10 ²⁰ / cm ^{3 of} Mg
_{. A} first layer of ₂ Ga _0.8 N, 20 Å, and 1 × 10 Mg
^A second layer made of p-type GaN doped with ²⁰ / cm ³ , a p-side cladding layer 19 made of a superlattice layer with a total thickness of 0.4 μm made of 20 Å, and finally a p-side cladding layer 19 P-type Ga doped with 2 × 10 ²⁰ / cm ^{3 of} Mg
A p-side contact layer 20 made of N is grown to a thickness of 150 Å.

After completion of the reaction, annealing was performed at 700 ° C., and then the uppermost p-side contact layer 20 and the p-side cladding layer 19 were etched by an RIE apparatus in the same manner as in Example 1 to form a ridge shape having a stripe width of 4 μm. And

Next, as in Example 1, a p-electrode 21 made of Ni and Au is formed on almost the entire surface of the stripe ridge of the p-side contact layer 20, and n made of Ti and Al is formed on almost the entire back surface of the GaN substrate 101. The electrode 23 is formed.

Next, the Si of the p-side cladding layer 19 excluding the area of the p-electrode 21 as shown in FIG.
An insulating film 25 made of O ₂ is formed, and a p-pad electrode 22 electrically connected to the p-electrode 21 is formed through the insulating film 25.

After the electrode formation, the GaN substrate 101 is cleaved into a bar shape in a direction perpendicular to the p-electrode 21,
A resonator is fabricated on the cleavage plane. The cleavage plane of the GaN substrate is the M plane. S on cleavage plane
A dielectric multilayer film made of iO ₂ and TiO ₂ was formed, and finally the bar was cut in the direction parallel to the p-electrode to obtain the laser chip shown in FIG. Next, the chip was placed face up (the substrate and the heat sink face each other) on the heat sink, the p pad electrode 22 was wire-bonded, and laser oscillation was attempted at room temperature. At room temperature, the threshold current density was 2.5 kA. / Cm ² , threshold voltage 4.0 V, oscillation wavelength 405
Continuous oscillation of nm was confirmed, and the lifetime was 500 hours or more. This is Ga
This is because the use of N reduces the spread of crystal defects.

It is a schematic cross section which shows the structure of the nitride semiconductor element (LED element) of Embodiment 1 which concerns on this invention. It is a schematic cross section which shows the structure of the nitride semiconductor element (LD element) of Embodiment 2 which concerns on this invention. It is a graph which shows the relationship between the film thickness of the p side contact layer in the LD element of Example 1 which concerns on this invention, and a threshold voltage. It is a schematic cross section of the LD element of Example 26 according to the present invention.

Explanation of symbols

1, 10 ... the substrate,
2, 11... Buffer layer,
3, 12... N-side contact layer,
13... Crack prevention layer,
14... N-side cladding layer (superlattice layer),
15... N-side light guide layer,
4, 16 .... active layer,
17... Cap layer,
18... P-side light guide layer,
5, 19... P-side cladding layer (superlattice layer),
6, 20... P-side contact layer,
7, 21... P electrode,
8, 22... P pad electrode,
9, 23... N electrode,
24... N pad electrode,
25 .. Insulating film,
101... GaN substrate,
112... Second buffer layer,
113... Third buffer layer.

Claims (22)

Nitriding comprising one or multiple layers of a p-type nitride semiconductor layer including a p-side contact layer, and an active layer made of a nitride semiconductor in which carriers are injected through the p-type nitride semiconductor layer to perform a predetermined operation In semiconductor devices,
The nitride semiconductor device, wherein the p-side contact layer is a superlattice layer. In a nitride semiconductor device having an active layer between one or multiple n-type nitride semiconductor layers including an n-side contact layer and one or multiple p-type nitride semiconductor layers,
The nitride semiconductor device, wherein the n-side contact layer is a superlattice layer. In a nitride semiconductor device comprising one or multiple layers of a p-type nitride semiconductor layer and an active layer made of a nitride semiconductor in which carriers are injected through the p-type nitride semiconductor layer and perform a predetermined operation,
A nitride semiconductor device, wherein at least one of the p-type nitride semiconductor layers is a superlattice layer. In a nitride semiconductor device having an active layer between one or multiple n-type nitride semiconductor layers and one or multiple p-type nitride semiconductor layers,
A nitride semiconductor device, wherein at least one of the p-type nitride semiconductor layer and the n-type nitride semiconductor layer is a superlattice layer. The superlattice layer includes a first layer made of a nitride semiconductor having a thickness of 100 angstroms or less, and a second layer made of a nitride semiconductor having a composition different from that of the first layer and having a thickness of 100 angstroms or less. The nitride semiconductor device according to claim 1, wherein the layers are stacked. At least one of the first layer and the second layer is made of Al.
The nitride semiconductor device according to claim 5, comprising a nitride semiconductor containing The nitride semiconductor device according to claim 6, wherein the nitride semiconductor containing Al is a nitride semiconductor represented by a formula Al _Y Ga _1-Y N (where 0 <Y ≦ 1). In the superlattice layer, the first layer has the formula In _X Ga _1-X
N (0 ≦ X ≦ 1) is formed of a nitride semiconductor, and the second layer has the formula Al
_The nitride semiconductor device according to claim 7, comprising a nitride semiconductor represented by _Y Ga _1-Y N (0 ≦ Y ≦ 1, X = Y ≠ 0). In the superlattice layer, the first layer has the formula In _X Ga _1-X
N (0 ≦ X <1) is formed of a nitride semiconductor, and the second layer has the formula Al
_The nitride semiconductor device according to claim 8, comprising a nitride semiconductor represented by _Y Ga _1-Y N (0 <Y <1). 10. The nitride semiconductor device according to claim 5, wherein each of the first layer and the second layer is made of a nitride semiconductor having a thickness of 70 angstroms or less. 10. The nitride semiconductor device according to claim 5, wherein film thicknesses of the first layer and the second layer are in a range of 10 angstroms to 70 angstroms, respectively. 12. The nitride semiconductor device further includes a p-side contact layer for forming a p-electrode as the p-type nitride semiconductor layer, and the thickness of the p-side contact layer is 500 angstroms or less. The nitride semiconductor device according to any one of the above. 13. The nitride semiconductor device according to claim 12, wherein the thickness of the p-side contact layer is 300 angstroms or less, 10 angstroms or more. The nitride semiconductor device further includes a p-side contact layer for forming a p-electrode as the p-type nitride semiconductor layer,
The nitride semiconductor device according to any one of claims 3 to 13, wherein the superlattice layer is formed between the active layer and the p-side contact layer. The nitride semiconductor element is further formed on the substrate via the first buffer layer, the second buffer layer made of a nitride semiconductor having a thickness of 0.1 μm or more, and the second buffer layer on the second buffer layer The n-side contact layer made of a nitride semiconductor doped with an n-type impurity is formed, and an n-electrode is formed on the n-side contact layer. The nitride semiconductor device described. The nitride semiconductor device according to claim 15, wherein an impurity concentration of the second buffer layer is lower than that of the n-side contact layer. At least one of the first buffer layer and the second buffer layer is formed of a superlattice layer in which nitride semiconductor layers having different compositions and having a thickness of 100 angstroms or less are stacked. Item 15 or 1
6. The nitride semiconductor device according to 6. The nitride semiconductor device further includes an n-side contact layer for forming an n-electrode as the n-type nitride semiconductor layer,
The nitride semiconductor device according to any one of claims 3 to 14, wherein the superlattice layer is formed between the active layer and the n-side contact layer. At least one of the first layer and the second layer,
19. An impurity that sets the conductivity type of the layer to n-type or p-type is doped.
The nitride semiconductor device according to any one of the above. The concentration of impurities doped in the first layer and the second layer to set the conductivity type of the layer to n-type or p-type is different from each other. Nitride semiconductor device. In the nitride semiconductor device, the first layer and the second layer
21. The nitride semiconductor device according to claim 20, wherein the impurity concentration of the layer having a band gap energy different from that of the other layer and having a large band gap energy is increased. The nitride semiconductor device according to any one of claims 5 to 21, wherein the superlattice layer is formed as an n-side contact layer on which an n-electrode is formed.

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