WO2005022711A1

WO2005022711A1 - Nitride semiconductor light emitting element and process for fabricating the same

Info

Publication number: WO2005022711A1
Application number: PCT/JP2004/012216
Authority: WO
Inventors: Kazuhisa Fukuda; Atsushi Yamaguchi; Chiaki Sasaoka
Original assignee: Nec Corporation
Priority date: 2003-08-29
Filing date: 2004-08-25
Publication date: 2005-03-10
Also published as: JPWO2005022711A1

Abstract

A p-type clad layer (111) is composed of IncGa1-cN. Mixed crystal ratio c of In is set lower than that of an active layer (108). A lattice relaxation layer (112) is provided between the active layer (108) and the p-type clad layer (111). The lattice relaxation layer (112) is provided in order to grow the p-type clad layer (111) with good crystallinity. The lattice relaxation layer is composed of a nitride semiconductor having a lattice constant different from that of an adjacent layer and grows about 5-10 nm at a temperature as low as 500-600˚C. Inserting position may be on the interface of p-type light guide layer/clad layer or in the middle of the p-type clad layer. The nitride semiconductor to be inserted may be made of InGaN, GaN, AlGaN, and the like, and InGaN is especially preferable.

Description

Specification

Nitride semiconductor light emitting device and method of manufacturing the same

Technical field

The present invention relates to a light emitting device having an active layer composed of a nitride semiconductor containing indium and a method for manufacturing the same.

Background art

[0002] A blue-violet (405 nm) semiconductor laser, which has been studied as a light source for high-density recording devices such as DVDs, has already become practical with the use of nitride semiconductor AlInGaN. FIG. 4 shows a cross-sectional structure diagram of the blue-violet laser reported in Non-Patent Document 1. The laser with this structure has been reported to have a continuous oscillation life of 10,000 hours or more at 2 mW output at room temperature. The structure consists of a double heterostructure formed on a GaN substrate or a heterogeneous substrate, and generally has an active layer using an InGaN quantum well,

0.1 0.9

Structure between n-type and p-type cladding layers containing AlGaN and p-type light guide layer

[0003] On the other hand, mV group compound semiconductors containing arsenic arsenide as a group V element have conventionally been used as light emitting elements in the visible-infrared long wavelength region, but AlInGaN-based semiconductors have an In composition ratio of the active layer. Since the emission wavelength can be extended to the infrared by increasing the wavelength, it is attracting attention as a light-emitting element material containing neither phosphorus nor arsenic. for that reason

Research is also being conducted on a long wavelength light emitting device using AlInGaN.

Non-Patent Document l: Jpn.J. Appl. Phys. Vol. 36 (1997), Nakamura etc., pp. L1568-1571 Patent Document 1: JP 2003-152219 A

Patent Document 2: Japanese Patent Application Laid-Open No. 9-283799

Patent Document 3: Japanese Patent Application Laid-Open No. 2000-236142

Patent Document 4: JP-A-8-316528

Disclosure of the invention

[0004] Light emitting diodes (LEDs) have already been developed for such AlInGaN-based long-wavelength light emitting devices. Patent Documents 1 and 2 disclose such long-wavelength light emitting An example of a diode (LED) is shown.

[0005] However, AlInGaN-based long-wavelength semiconductor lasers have not yet been manufactured in practical use. In the case of a semiconductor laser, there is a problem that when the In composition ratio of the active layer is increased to increase the emission wavelength, the emission efficiency is significantly reduced. This is because when the In composition ratio is increased, the lattice mismatch with GaN or AlGaN increases, and it becomes difficult to obtain an active layer with good crystallinity.

[0006] In designing a semiconductor laser, it is necessary to further improve the light confinement efficiency above the active layer, and it is desired to ensure a sufficient thickness of the upper cladding layer. However, in this case, the active layer is subjected to a high-temperature treatment for a long time in the upper clad layer forming step and the like, and the quality of the active layer is likely to be significantly deteriorated. Particularly, in a semiconductor containing indium, problems such as a change in composition due to evaporation of indium are likely to occur.

[0007] As described above, in designing a semiconductor laser having an active layer containing indium, it is an important technical problem to stably form an active layer of good quality.

[0008] An effective solution to such a problem peculiar to a semiconductor laser is described in Patent Documents 1 and 2 relating to a light emitting diode.

Also, the LED described in Patent Document 1 has a low indium composition of 0.15 in the active layer because it has a low composition.

Thus, the problem of quality deterioration of the active layer as described above does not occur.

On the other hand, the LED described in Patent Document 2 has an active layer indium composition of 0.9 and a cladding layer indium composition of 0.2. The growth temperature of InGaN with an indium composition of 0.9 is usually about 400-500 ° C, and the growth temperature of InGaN with an indium composition of 0.2 is usually about 700-800 ° C. The active layer of this LED is subjected to a heat treatment at a temperature 200 ° C. or higher in the cladding layer formation step than that during the growth of the active layer, and the physical properties change greatly in that step, and the light emission characteristics as designed are obtained. It becomes difficult.

[0010] On the other hand, as a technique relating to a long wavelength semiconductor laser, Patent Document 3 discloses an optical guide layer.

A semiconductor laser having a SCH structure in which InGaN is used, the cladding layer is GaN, and the contact layer is GaN power, that is, a device structure that does not use A1 is described. According to the literature, it is shown that the absence of A1 reduces the difference in lattice constant between the active layer and the cladding layer, so that an InGaN active layer with good crystallinity can be grown. [0011] Patent Document 4 reports a structure using AlGaN for the cladding but using InGaN for the optical guide layer. According to the document, InGaN has a softer crystal than AlGaN, so the InGaN light guide layer acts as a buffer layer and can grow an InGaN active layer with a large In composition with good crystallinity. . In this way, the structure in which the active layer is sandwiched between the InGaN optical guide layers certainly reduces the lattice strain of the active layer. The crystallinity of the active layer deteriorates. In addition, as the In composition ratio increases, the decomposition temperature of InGaN becomes GaN.

1

And a very low quality compared to AlGaN.

1

However, the crystallinity of the active layer tends to deteriorate during the high-temperature growth of the optical guide layer and the cladding layer located thereabove, and the above prior art still has room for improvement.

The present invention has been made to solve these problems, and an object of the present invention is to provide a light emitting device having an active layer made of an indium-containing semiconductor, particularly a light emitting device that emits light in a long wavelength region. In the above, the object is to stably improve the light emission characteristics and the like.

[0013] Another object of the present invention is to improve the quality of the upper clad layer formed on the active layer and stably improve the light emission characteristics and the like in the light emitting device.

[0014] In a light emitting device having an active layer made of an indium-containing nitride semiconductor, sufficient light emitting characteristics cannot be obtained because, after the active layer is formed, the quality of the active layer deteriorates during the process of forming a semiconductor layer on the active layer. This is considered to be caused by the occurrence of (described later in Example 7).

[0015] The present invention provides the following first means for solving the above problems.

[0016] The first means is to make a difference in indium composition or a difference in growth temperature between these layers less than a certain value when both the active layer and the cladding layer are made of an indium-containing semiconductor. Among the nitride semiconductors, InN has a low decomposition temperature, so low-temperature crystal growth is required to capture a large amount of In. Even InGaN used for the active layer of the blue-violet laser is grown at about 800 ° C, and is used for the light guide layer and the cladding layer.

0.1 0.9

It is about 100-200 ° C lower than the growth temperature of GaN and AlGaN. In order to increase the emission wavelength, it is necessary to increase the In content of the active layer. In this case, the growth temperature of the active layer is further limited to a lower temperature. When a light guide layer and a cladding layer made of GaN or AlGaN are grown at 900-1000 ° C, the active layer is grown during growth of these layers. Is decomposed, and the luminous efficiency is reduced. On the other hand, in the present invention, the quality deterioration of the active layer is suppressed by setting the difference between the indium composition of the active layer and the cladding layer or the difference between the growth temperatures to a certain value or less.

As described above, in order to suppress the quality deterioration of the active layer, it is effective to configure the upper cladding layer with an indium-containing semiconductor. Alternatively, it is effective to form the upper cladding layer with a semiconductor that can be grown at a low temperature. However, in such a case, there is a problem that the crystal quality of the cladding layer itself is deteriorated. For example, when the upper cladding layer is made of InGaN, many defects occur in the film due to the difference in lattice constant from the substrate material such as GaN or sapphire, and the function as the cladding layer cannot be obtained sufficiently. There is. Therefore, the present invention provides the following second means for solving the problems that occur when the upper cladding layer is made of an indium-containing semiconductor or the like. That is, the second means is to interpose a lattice relaxation layer between the active layer and the cladding layer. In general, when growing InGaN with a different lattice constant on GaN, a lattice relaxation layer is provided, and lattice strain is relaxed there. However, in designing a semiconductor laser, it is necessary to grow a thick upper cladding layer after the active layer, and here also crystallinity is deteriorated due to lattice distortion. The inventors have found through experiments that the upper cladding layer can be grown with good crystallinity by providing the lattice relaxation layer after growing the active layer. The lattice relaxation layer is a layer that relieves lattice distortion between the semiconductor layer serving as an underlayer and the semiconductor layer crystal-grown thereon. The lattice relaxation layer itself is a low-order film, and such a structure reduces strain between semiconductor layers. By providing such a layer, even when the upper clad layer is made of an indium-containing semiconductor or the like, it is possible to provide a device that maintains the crystal quality of the clad layer well and stably exhibits excellent light emitting characteristics. it can.

Hereinafter, the configuration of the present invention will be described more specifically.

According to the present invention, a substrate, a lower cladding layer formed on the substrate, an active layer formed on the lower cladding layer, and an upper cladding formed on the active layer Wherein the active layer and the upper cladding layer are both made of a nitride semiconductor containing indium, and the indium composition of the active layer is x, and the indium composition of the upper cladding layer is y. X force is 3 or more, and (X-y) is 0.4 or less. A nitride semiconductor light emitting device is provided.

In the present invention, the indium composition of the active layer is 0.3 or more. When such a long-wavelength light-emitting composition is used, quality degradation of the active layer during the growth of the semiconductor layer above the light-emitting composition becomes apparent. According to the present invention, the indium composition difference between the active layer and the upper cladding layer is set to 0.4 or less. As will be described later in the examples, with such a composition difference, a layer structure can be suitably formed under the condition that the growth temperature of both is within 100 ° C., and the active layer containing indium can be formed. The upper cladding layer can be formed without deteriorating the quality of the device, and a light emitting device that stably emits light in a long wavelength region can be realized.

Here, by adopting a configuration in which the indium composition difference between the active layer and the upper clad is 0.2 or less, or a configuration in which the growth temperature of both is within 70 ° C., the activity due to the high-temperature thermal history Deterioration of the quality of the layer can be more effectively suppressed. In particular, the life of the light emitting element can be stably improved.

[0022] In the case of a quantum well structure, the indium composition of the active layer means the indium composition of the well layer.

Further, according to the present invention, a substrate, a lower cladding layer formed on the substrate, an active layer formed on the lower clad layer, and an upper layer formed on the active layer Wherein the active layer and the upper cladding layer are both made of a nitride semiconductor containing indium, the growth temperature of the active layer is T (° C.), and the

2

Assuming that the growth temperature of the film is T (° C), the nitrogen has a T-T force of not more than sioo ° c.

1 1 2

A nitride semiconductor light emitting device is provided.

Further, according to the present invention, a step of forming a lower cladding layer on a substrate, a step of forming an active layer made of a nitride semiconductor containing indium on the lower cladding layer, Forming an upper cladding layer made of a nitride semiconductor containing indium on the upper surface of the substrate, setting the growth temperature of the active layer to T (° C.),

2

When the growth temperature of the system is T (° C), the nitriding characteristic is that the T-T force is not more than ioo ° c.

1 1 2

A method for manufacturing a semiconductor light emitting device is provided.

According to the present invention, since the difference between the growth temperatures of the active layer and the upper clad layer is 100 ° C. or less, the upper clad layer is formed while suppressing the quality deterioration of the active layer due to the high-temperature thermal history. And a light-emitting element that stably emits light in a long wavelength region can be realized.

Further, according to the present invention, a substrate, a lower cladding layer formed on the substrate, an active layer formed on the lower clad layer, and an upper layer formed on the active layer A cladding layer, wherein the active layer is made of a nitride semiconductor containing indium, and a lattice relaxation layer is provided between the active layer and the upper cladding layer or in the upper cladding layer. A nitride semiconductor light emitting device is provided.

Further, according to the present invention, a step of forming a lower cladding layer on a substrate, a step of forming an active layer made of a nitride semiconductor containing indium on the lower cladding layer, Forming a lattice relaxation layer at a temperature equal to or lower than 600 ° C., and forming an upper cladding layer above the lattice relaxation layer. A manufacturing method is provided.

[0028] In the present invention, since the lattice relaxation layer is provided on the active layer, the crystal quality of the cladding layer is improved. As a result, a good light confinement structure is realized. The lattice relaxation layer is preferably made of, for example, a semiconductor containing indium. Further, since the quality of the upper cladding layer is improved, the thickness of the cladding layer can be made relatively thin, and as a result, the quality of the active layer can be improved. Here, the upper cladding layer may be made of a nitride semiconductor containing indium. By doing so, quality degradation of the active layer can be suppressed more reliably.

In the present invention, the lattice relaxation layer can be a low-temperature growth layer formed at a temperature of 600 ° C. or lower. Further, the lattice relaxation layer can be made of InGaN. By doing so, the lattice relaxation effect can be obtained more reliably, and the quality of the semiconductor layer above the active layer can be more effectively improved. The thickness of the lattice relaxation layer is, for example, not less than lOnm and not more than 100 nm. By doing so, it is possible to surely improve the crystal quality of the semiconductor layer structure.

[0030] In the present invention, the indium composition ratio of the upper cladding layer can be smaller than the indium composition ratio of the active layer. Here, each of the semiconductor layers above the active layer may be made of a semiconductor having a smaller indium composition ratio than the active layer.

The upper cladding layer may be made of InGaN (0 <y <l) force. By doing this As a result, quality degradation of the active layer can be suppressed more reliably. The structure of the upper cladding layer is the same as the superlattice structure In Ga N / In Ga N (0 x yl x 1, 0 x y2 x 1, yl ≠ y2).

yl 1-yl y2 l-y2

In this case, the In composition y of the clad means the average composition. Note that In Ga N (0 <y

y i— y

(1) The thickness of the upper cladding layer is preferably, for example, not less than 0.1 and not more than 1. O x m. By doing so, the quality of the upper cladding layer can be stably improved, and the light emission characteristics and the like can be stably improved.

In addition, the structure of the upper cladding layer is different from the superlattice structure.

y l— y

If it is powerful, a more stable light confinement effect may be obtained.

Further, the semiconductor layer located above the active layer may be entirely made of a nitride semiconductor containing indium. In the present invention, a sufficient difference in refractive index for light confinement is also important. From such a viewpoint, for example, it is preferable that the difference between the indium compositions of the active layer and the upper cladding layer be 0.1 or more.

In the present invention, it is preferable that the structure further includes a contact layer provided on the active layer and made of a nitride semiconductor containing indium, and an electrode provided in contact with the contact layer.

The light emitting device of the present invention can be applied to a light emitting device such as a semiconductor laser and a light emitting diode, and is particularly effective when applied to a semiconductor laser. This is because the problem unique to the semiconductor laser described above can be effectively solved.

According to the present invention, in a light-emitting element having an active layer made of an indium-containing semiconductor, particularly in a light-emitting element that emits light in a long wavelength region, the light-emitting characteristics and the like can be stably improved.

Further, according to the present invention, in the above light emitting device, the quality of the upper cladding layer formed on the active layer can be improved, and the light emitting characteristics and the like can be stably improved.

Although the configuration and the preferred embodiment of the present invention have been described above, the above configuration may be appropriately combined. For example, an element can be configured by combining the above-described first means and second means.

Brief Description of Drawings

[0033] The above-mentioned objects, and other objects, features, and advantages will be described in more detail below. The embodiments will be further clarified by the following drawings accompanying the embodiments.

FIG. 1 is a sectional structural view of a nitride semiconductor laser device according to the present embodiment.

FIG. 2 is a sectional structural view of a nitride semiconductor laser device according to an example.

FIG. 3 is a sectional structural view of the nitride semiconductor laser device according to the present embodiment.

FIG. 4 is a cross-sectional view showing a structure of a conventional nitride semiconductor laser.

FIG. 5 is a graph showing PL characteristics of a nitride semiconductor light emitting device evaluated in an example.

FIG. 6 is a force saddle luminescence image of a nitride semiconductor light emitting device evaluated in an example.

FIG. 7 is a force saddle luminescence image of a nitride semiconductor light emitting device evaluated in an example.

FIG. 8 is a diagram showing a relationship between an indium composition ratio and a band gap energy Eg in an InGaN active layer.

FIG. 9 is a graph showing the relationship between the growth temperature of an InGaN active layer and the PL peak energy obtained by PL measurement.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a schematic cross-sectional view showing one embodiment of the element structure of the present invention, and shows a view when the element is cut in a direction perpendicular to the laser light resonance direction. In the nitride semiconductor laser device of the present embodiment, as shown in this figure, a GaN film 102, a Si〇2 mask 103, and an InGaN layer 105 are formed on an ELOG substrate 104 on which n-type GaN is grown on a sapphire substrate 101. , N-type

0.1 0.9

Lad layer 106, n-type optical guide layer 107, active layer 108 composed of InGaN multiple quantum wells, p-type cap layer 109, p-type optical guide layer 110, p-type cladding layer 111, lattice relaxation layer 112, p-type contact A layer 113 is formed in order, and a p-electrode 114 is formed on the p-type contact layer 113 serving as a ridge stripe, and an n-electrode 115 is formed on the n-type ELOG substrate 104 exposed by etching from the p-side layer. .

[0036] The n-type light guide layer 107 and the p-type light guide layer 110 are made of InGaN doped with impurities having respective conductivity types. The mixed crystal ratio b of In is the In mixed b 1-b

Smaller than the crystal ratio.

[0037] The p-type cladding layer 111 is made of an InGaN force doped with an impurity exhibiting its conductivity type. In

c 1-c

The mixed crystal ratio c of the active layer 108 is smaller than the In mixed crystal ratio of the active layer 108. On the other hand, since the n-type cladding layer 106 is grown before the active layer 108, the growth temperature can be set relatively high. Not only aN but also GaN can be used. However, from the viewpoint of improving the quality of the active layer 108, it is more preferable to use InGaN having the same composition as the p-type cladding.

The lattice relaxation layer 112 is provided for growing the p-type cladding layer 111 with good crystallinity. The lattice relaxation layer is made of a nitride semiconductor having a lattice constant different from that of an adjacent layer, and is grown at a low temperature of 600 ° C. or less, preferably 400 ° C. and about 10 100 nm. It is preferable that the insertion position be above the active layer. For example, it is preferable to be between the active layer and the upper cladding layer or in the upper cladding layer. By arranging at such a position, introduction of dislocations into the active layer can be suppressed. Examples of a material used for the lattice relaxation layer 112 include InGaN, GaN, and AlGaN. Among them, a material containing indium, particularly InGaN, is preferable. In this case, the In composition is preferably, for example, 0.1 or more and 0.7 or less. This is because the lattice relaxation effect can be reliably obtained. Note that this lattice relaxation layer can be omitted as appropriate.

The active layer 108 has a quantum well structure. Increasing the In mixed crystal ratio a of the In Ga N well layer a 1-a

Thus, a nitride semiconductor laser device oscillating at a long wavelength can be obtained. In this case, it is desirable to change the In mixed crystal ratio of the barrier layer as well. The In-crystal ratio of the barrier layer should be selected so as to obtain a sufficient energy gap difference for mini-band formation, but the closer the In-crystal ratio to the well layer is as small as possible, the smaller the lattice mismatch, the smaller the active layer. It is expected that the crystallinity of the crystal will be improved, and that the luminous efficiency will be increased and the oscillation threshold will be reduced.

If the In-crystal ratio in the well layer of the active layer is 0.44, the In-crystal ratio of the barrier layer with a band gap energy difference of 0.3 eV from this well layer is 0.34.

[0040] In the present embodiment, the mixed crystal ratio x of In consisting of InGaN (0≤x≤1)

1- Relational formula with the gap energy,

Eg = x * 0.77 + (l-x) * 3.42-1.43 * (l-x) * x

It is a value estimated using For example, the photon energy (Eg) at a wavelength of 650 nm is 1.91 eV, and the value of X is calculated to be 0.44 from the above relational expression, and is set as the In mixed crystal ratio of the well layer.

The p-type cap layer 109 is an InGaN force doped with an impurity exhibiting p-type conductivity.

d 1- d

The In crystal ratio d is set to be smaller than the In crystal ratio of the p-type cladding layer. This p-type cap layer Although GaN or AlGaN may be used, InGaN is preferable to suppress the thermal decomposition of the active layer. The p-side cap layer can be omitted.

[0042] The p-type contact layer 113 is made of GaN or InGaN which is doped with an impurity exhibiting p-type conductivity. The use of GaN makes it easier to obtain a preferable ohmic material with the electrode material, but the use of InGaN suppresses the thermal decomposition of the active layer and reduces the threshold current.

(Example)

Hereinafter, the present invention will be described in detail with reference to Examples. In each example, a metal organic chemical vapor deposition apparatus (hereinafter referred to as MOCVD) was used to form each semiconductor layer. Ammonia was used as a group V element source, and trimethylgallium (TMG), trimethylaluminum (TMA), and trimethylindium (TMI) were used as group III element sources.

[Example 1]

FIG. 1 is a sectional structural view of the nitride semiconductor laser device according to the present embodiment. This semiconductor laser device is manufactured as follows. First, a GaN film 102 is grown on a sapphire substrate 101 by MOCVD. Thereafter, a stripe-shaped SiO film (mask) is formed on the GaN film 102.

2

) 103 is formed in the [1, -1, 0, 0] direction, n-type GaN with Si is selectively grown on it by MOCVD, and low dislocation density GaN is grown laterally on the mask. Then, an n-type GaN-ELOG substrate 104 is manufactured.

On this substrate, at 800 ° C, Si-doped n-type InGaN layer 105, Si-doped n-type In

0.1 0.9 0.27

N-type cladding layer 106 composed of GaN (thickness 0.6 μππι), Si-doped n-type InGaN (thickness 0.1 μππι)

0.73 0.31 0.69

) After growing the η-type optical guide layer 107, the temperature is set to 700 ° C and the InGaN quantum well

0.44 0.56 The activity of a multiple quantum well structure consisting of a door layer (3.5 nm thick) and an InGaN barrier layer (10.5 nm thick)

0.34 0.66

The active layer 108 is grown. Subsequently, the temperature is set to 750 ° C and the Mg-doped p-type In GaN cap layer

0.2 0.8

(Thickness 20 nm) 109, p-type light guide layer 110 made of Mg-doped p-type InGaN (0.1 μm thickness) 110

0.31 0.69

Grow. After that, the temperature was lowered to 500 ° C, and Mg-doped p-type InGaN (10 nm thick)

0.1 0.9

A strong P-type lattice relaxation layer 112 is grown, the temperature is again raised to 750 ° C, and a p-type cladding layer 111 made of Mg-doped p-type InGaN (0.6 xm thick) and a Mg-doped p-type InGaN ( Thickness 0.05

0.27 0.73 0.1 0.9

A p-type contact layer 113 made of zm) is grown in order. Thereafter, a ridge structure as shown in FIG. 1 is formed by dry etching or the like, and finally, a p-electrode 114 composed of Ni and Au, and Ti and A1 are formed. An n-electrode 115 is deposited.

As described above, in the layer structure according to the present embodiment, when the indium composition of the active layer 108 (the indium composition of the quantum well layer) is x, and the indium composition of the p-type cladding layer 111 is y, X is 0. 44 and (X-y) force SO.

[0045] As described above, the sapphire substrate of the wafer on which the n-electrode and the p-electrode are formed is polished to 70 zm, and then cleaved into a bar from the substrate side in a direction perpendicular to the laser stripe. Next, a resonator is manufactured. A dielectric multilayer film consisting of TiO and A10 is formed on the resonator surface.

2 2 3

Then, the bar is cut in the direction parallel to the p-electrode to obtain a laser device as shown in FIG. Note that the resonator length is desirably 300 to 500 am.

The obtained laser element was set on a heat sink, and each electrode was wire-bonded, and laser oscillation was attempted at room temperature. As a result, the threshold current density at room temperature

At 5 kA m ² and a threshold voltage of 6 V, continuous oscillation with an oscillation wavelength of approximately 650 nm was confirmed, and a lifetime of 1000 hours or more was shown at room temperature.

In this example, all of the semiconductor layers located above the active layer were made of InGaN having a smaller In composition ratio than the active layer. Further, a p-type lattice relaxation layer 112, which is a low-temperature growth layer, is provided between the active layer 108 and the p-type cladding layer 111. With such a configuration, a good and stable laser element was obtained even at a long wavelength.

[Example 2]

FIG. 2 is a sectional structural view of the nitride semiconductor laser device according to the present embodiment. This semiconductor laser device differs from the device of Example 1 in that a GaN substrate is used.

This semiconductor laser device is manufactured as follows. First, an n-type low dislocation GaN substrate 201 was used as a substrate, and a Si-doped n-type InGaN layer 105 and a Si

0.1 0.9

N-type cladding layer 106 consisting of n-type InGaN layer (1.5 μm thick), Si-doped n-type InGaN

0.27 0.73 0.31 0.69

After growing the η-type optical guide layer 107 (thickness: 0.1 μm), the temperature is increased to 700 ° C and the undoped InGaN quantum well layer (thickness: 3 nm) and the undoped InGaN barrier layer (thickness: 3 nm). Thickness 5nm)

0.44 0.56 0.34 0.66

Active layer 108 with multiple quantum well structure consisting of Mg-doped p-type InGaN carrier at 750 ° C

0.2 0.8 p-layer (thickness: 20 nm) 109, Mg-doped p-type InGaN (0.16 μm thickness)

0.31 0.69

Grow layer 110. Then, a Si〇 mask (thickness 0.3 μηι) 202 is formed on the p-type light guide layer 110.

2 An opening is formed in a stripe shape with a width of 2 / m by etching. Furthermore, following this opening, a Mg-doped p-type InGaN layer was formed as a p-type lattice relaxation layer 112 with a thickness of 500 p.

0.1 0.9

After growing 10nm at a low temperature of ° C, raise the temperature to 750 ° C to increase the Mg-doped p-type InGaN layer (thickness

0.27 0.73 0.6 μπι) p-type cladding layer 111, Mg-doped p-type InGaN (0.05 μm thick)

0.1 0.9

A ridge structure is formed by selectively growing the p-type contact layer 113. SiO on top

After forming a mask and forming an opening in the stripe portion by etching, a p-electrode 114 made of Ni and Au is deposited. Thereafter, the back surface of the n-type GaN substrate 201 is polished to deposit the n-electrode 115 of Ti and A. As described above, the wafer on which the n-electrode and the p-electrode are formed is cleaved in a bar shape in the direction perpendicular to the stripe-shaped electrodes, and a resonator is formed on the cleavage plane. A dielectric multilayer film consisting of TiO and A10 is formed on the resonator surface.

2 2 3

Is cut into a laser device as shown in FIG. Note that the resonator length is desirably 500 800 μm.

As described above, in the layer structure according to the present embodiment, when the indium composition of the active layer 108 (the indium composition of the quantum well layer) is x, and the indium composition of the p-type cladding layer 111 is y, X is equal to 0. 44 and (xy) force SO.

[0050] The obtained laser element was set on a heat sink, each electrode was wire-bonded, and laser oscillation was attempted at room temperature. As a result, the threshold current density at room temperature

At 4 kA m ² and a threshold voltage of 7 V, continuous oscillation with an oscillation wavelength of approximately 650 nm was confirmed, and a lifetime of 1000 hours or more was shown at room temperature.

In this example, all the semiconductor layers located above the active layer were made of InGaN having a smaller In composition ratio than the active layer. Further, a p-type lattice relaxation layer 112, which is a low-temperature growth layer, is provided between the active layer 108 and the p-type cladding layer 111. A semiconductor laser structure is formed on a GaN substrate. With such a configuration, a good and stable laser element was obtained even at a long wavelength.

[Example 3]

FIG. 3 is a sectional structural view of the nitride semiconductor laser device according to the present embodiment. Embodiments 1 and 2 Force using a lattice relaxation layer made of InGaN In this embodiment, a lattice relaxation layer made of GaN is used. This semiconductor laser device is manufactured as follows. First, an n-type low dislocation GaN substrate 201 was used as a substrate, and a Si-doped n-type InGaN layer 105 and a Si

0.1 0.9

N-type cladding layer 106 consisting of n-type InGaN layer (1.5 / im thick), Si-doped n-type InGaN

0.27 0.73 0.31 0.69

0.44 0.56 0.34 0.66

0.31 0.69

2

An opening is formed in a stripe shape with a width of 2 m by etching. Further, after this opening, a Mg-doped p-type GaN layer is grown as a p-type lattice relaxation layer 120 at a low temperature of 500 ° C to a thickness of 10 nm. Thickness 0.6

0.27 0.73

m) p-type cladding layer 111, Mg-doped p-type InGaN (thickness 0.05 μm) p-type

0.1 0.9

A ridge structure is formed by selectively growing the contact layer 113. SiO mask on top

2 is formed, and an opening is provided in the stripe portion by etching, and then a p-electrode 114 made of Ni and Au is deposited. Thereafter, the back surface of the n-type GaN substrate 201 is polished to deposit an n-electrode 115 made of Ti and ^. As described above, the wafer on which the n-electrode and the p-electrode are formed is cleaved in a bar shape in a direction perpendicular to the stripe-shaped electrodes, and a resonator is formed on the cleavage plane. A dielectric multilayer film composed of TiO and A10 is formed on the resonator surface, and finally a bar is formed in the direction parallel to the p-electrode.

2 2 3

It is cut into a laser device as shown in FIG. The resonator length is desirably 500-800 μm.

[0054] The obtained laser element was placed on a heat sink, each electrode was wire-bonded, and laser oscillation was attempted at room temperature. As a result, the threshold current density at room temperature

[Example 4] FIG. 2 shows a cross-sectional structure of the nitride semiconductor laser device according to the present example. Although the cross-sectional structure is similar to that of the second embodiment, the n-type cladding layer is made of InGaN in the second embodiment, whereas GaN is used in the present embodiment.

This semiconductor laser device is manufactured as follows. N-type low dislocation as substrate

Using a GaN substrate 201, a Si-doped n-type InGaN layer 105 was grown on this substrate at 800 ° C.

0.1 0.9

Thereafter, the temperature was raised to 900 ° C to grow an η-type cladding layer 106 composed of a Si-doped n-type GaN layer (1.5 μm thick), and then the temperature was lowered to 750 ° C to reduce the Si-doped η-type InGa From N (thickness Ο. Ϊ́ μ πι)

0.31 0.69

The η-type light guide layer 107 is grown. Subsequently, the temperature was set to 700 ° C and undoped In Ga

0.44 0.56

Multiple quantum consisting of N quantum well layer (thickness 3nm) and undoped InGaN barrier layer (thickness 5nm)

0.34 0.66

An active layer 108 having a well structure is grown, and a Mg-doped p-type InGaN cap layer (750 ° C) is formed.

0.2 0.8

20 nm thick) 109, Mg-doped p-type InGaN (0.16 μm thick) force, p-type light guide layer 1 10

0.31 0.69

Grow.

After that, an SiO mask (thickness 0.3 μπι) 202 is formed on the p-type light guide layer 110 by sputtering.

2

Then, an opening is formed in a stripe shape having a width of 2 / m by etching. Following this opening, an Mg-doped p-type InGaN layer was formed as a p-type lattice relaxation layer 112 at a low temperature of 500 ° C to a thickness of 10 nm.

0.1 0.9

After the growth, the temperature was raised to 750 ° C and the Mg-doped p-type InGaN layer (thickness: 0.6 μm) was removed.

0.27 0.73

P-type cladding layer 1 1 1, p-type contact layer 1 made of Mg-doped p-type InGaN (0.05 μm thick)

0.1 0.9

A ridge structure is formed by selectively growing 13. Form a SiO mask on top

2

After an opening is provided in the stripe portion by tuning, a p-electrode 114 made of M and Au is deposited. Thereafter, the back surface of the n-type GaN substrate 201 is polished to deposit the n-electrode 115 made of Ti. As described above, in the layer structure according to the present embodiment, the indium composition of the active layer 108 (the indium of the quantum well layer) Assuming that x is the composition) and y is the indium composition of the p-type cladding layer 111, X is 0.44 and the (X-y) force is SO.

[0058] As described above, the wafer on which the n-electrode and the p-electrode are formed is cleaved in a bar shape in a direction perpendicular to the stripe-shaped electrodes, and a resonator is formed on the cleavage plane. More than TiO and Al 0 on the cavity surface

After forming a dielectric multilayer film, a bar is cut in a direction parallel to the P electrode to obtain a laser device as shown in FIG. The length of the resonator is desirably 500-800 zm. Obtained The laser element thus obtained was placed on a heat sink, and the respective electrodes were wire-bonded, and laser oscillation was attempted at room temperature. As a result, continuous oscillation with an oscillation wavelength of approximately 650 nm was confirmed at room temperature with a threshold current density of 6 kA m ² and a threshold voltage of 7 V, and showed a life of 1000 hours or more at room temperature.

In the present embodiment, the force in which the n-type cladding layer is made of GaN instead of InGaN. Thus, even if a semiconductor layer other than InGaN is provided on the substrate side with respect to the active layer 108, the layer above the active layer 108 If it is made of InGaN, good device performance can be obtained.

[Example 5]

FIG. 2 shows a cross-sectional structure of the nitride semiconductor laser device according to the present example. The cross-sectional structure is similar to that of the second embodiment. However, in the second embodiment, the p-type contact layer is made of InGaN, whereas in this embodiment, GaN is used.

[0061] This semiconductor laser device is manufactured as follows. N-type low dislocation as substrate

Using a GaN substrate 201, a Si-doped n-type InGaN layer 105 and a Si-doped n

0.1 0.9

N-type cladding layer 106 consisting of n-type InGaN layer (1.5 / im thick), Si-doped n-type InGaN (

After growing an η-type optical guide layer 107 of 0.27 0.73 0.31 0.69 thickness 0.1 μm), the temperature is increased to 700 ° C and the undoped In Ga N quantum well layer (thickness 3 nm) and undoped In Ga N Barrier layer (5nm thickness)

0.44 0.56 0.34 0.66

0.2 0.8 P-layer (20 nm thick) 109, Mg-doped p-type InGaN (0.16 μm thick)

0.31 0.69

Grow layer 110. Then, a Si〇 mask (thickness 0.3 / m) 2O2 is placed on the p-type light guide layer 110.

2

An opening is formed in a stripe shape with a width of 2 / m by etching. Furthermore, following this opening, an Mg-doped p-type InGaN layer is formed as a p-type lattice relaxation layer 112 for 500 μm.

0.1 0.9

A ridge structure is formed by selectively growing a p-type cladding layer 111 composed of 0.27 0.73 and 0.6 μm) and a p-type contact layer 113 composed of Mg-doped p-type GaN (thickness 0.05 μm). On top of that, a SiO mask

2 After forming and opening an opening in the stripe portion by etching, a p-electrode 114 made of Ni and Au is deposited. Thereafter, the back surface of the n-type GaN substrate 201 is polished to deposit an n-electrode 115 of Ti and A.

As described above, in the layer structure according to the present embodiment, the indium composition of the active layer 108 (quantum well Assuming that x is the indium composition of the door layer and y is the indium composition of the p-type cladding layer 111, X is 0.44 and the (xy) force is SO.

[0062] As described above, the wafer on which the n-electrode and the p-electrode are formed is cleaved in a bar shape in a direction perpendicular to the stripe-shaped electrodes, and a resonator is formed on the cleavage plane. More than TiO and A10 on the cavity surface

After forming a dielectric multilayer film, a bar is cut in a direction parallel to the P electrode to obtain a laser device as shown in FIG. The length of the resonator is desirably 500-800 zm. The obtained laser element was placed on a heat sink, and the respective electrodes were wire-bonded, and laser oscillation was attempted at room temperature. As a result, continuous oscillation with an oscillation wavelength of approximately 650 nm was confirmed at room temperature with a threshold current density of 6 kA m ² and a threshold voltage of 6 V, and showed a life of 1000 hours or more at room temperature.

In the present embodiment, the force at which the p-type contact layer is made of GaN instead of InGaN. Thus, even if the thin film at a position away from the active layer 108 is made of a semiconductor other than InGaN, If most of the upper layer is made of InGaN, good device performance can be obtained.

Example 6

In this example, the PL (photoluminescence) characteristics of the quantum well active layer made of InGaN were evaluated. In the evaluation, a structure in which a quantum well active layer was formed on a GaN substrate was used as a measurement sample. A quantum well layer was formed by the same structure and formation method as in Example 2. The growth temperature is 700 ° C. The composition and thickness of the well layer and barrier layer are as follows

[0065] Undoped InGaN quantum well layer (thickness: 3 nm)

0.44 0.56

Undoped In GaN barrier layer (5 nm thick)

0.34 0.66

After growth, the sample was obtained by cooling to room temperature without raising the temperature. On the other hand, after growth, heat treatment was performed at 900 ° C for 10 minutes and then cooled to room temperature to obtain Sample 2.

[0066] PL characteristics of Samples 1 and 2 were evaluated. FIG. 5 shows the result. In FIG. 5, a corresponds to sample 1 and b corresponds to sample 2. In sample 1, good emission was observed in the long wavelength region, whereas in sample 2, emission in both the long wavelength region and the short wavelength region was observed. Was.

FIG. 6 and FIG. 7 are diagrams showing CL (force saddle luminescence image) observation results of these samples. Here, a plurality of filters for observing red light emission and blue light emission were prepared, and the light emission state was observed by observing through these filters. Fig. 6 corresponds to sample 1, and only red light emission of 500 nm or more was observed. FIG. 7 corresponds to Sample 2, in which blue light emission of less than 50 Onm and red light emission of 500 nm or more were observed.

[0068] According to the results of this example, when the InGaN active layer formed at a growth temperature of 700 ° C is subsequently heat-treated at 900 ° C, the properties of the active layer are changed, and the desired light emitting characteristics can be obtained. It was confirmed that there was not.

[Example 7]

In the present embodiment, an example is shown in which the relationship between the indium composition ratio of the InGaN active layer and the growth temperature suitable for forming the active layer is examined.

FIG. 8 is a diagram showing the relationship between the indium composition ratio and the band gap energy Eg in the InGaN active layer.

FIG. 9 is a diagram showing the relationship between the growth temperature of the InGaN active layer and the PL peak energy obtained by PL measurement. The PL peak energy ideally matches the band gap Eg.

The following approximate expression is obtained from the graph of FIG.

E = -2.9x + 3.2

E indicates Eg, that is, band gap energy.

X indicates the In composition ratio.

On the other hand, the following approximate expression is obtained from the graph of FIG.

E = 0.012Ts-6.42

Ts is the growth temperature.

[0074] From the above,

Ts = -240x + 800… Equation (A)

The following relational expression is obtained. In the above treatment, both band gap energy and PL peak energy were treated the same as E. From the above formula (A), the relationship between the indium composition ratio of the InGaN active layer and the growth temperature suitable for forming the active layer is as follows.

[0076] Indium composition 0.2: Growth temperature about 750 ° C

Indium composition 0.4: Growth temperature about 700 ° C

Indium composition 0.6: Growth temperature about 650 ° C

In order to suitably form the InGaN active layer, it is important to lower the growth temperature of the clad layer and the like located thereon. Specifically, it is preferable to set the temperature not to exceed (active layer growth temperature + 100 ° C.). By doing so, quality degradation of the active layer due to heat history can be effectively suppressed. When this is converted into the composition by using the formula (A), the composition ratio is 0.41, that is, the difference between the indium composition ratio of the active layer and the indium composition of the cladding layer is 0.41 or less. Corresponding. Therefore, the difference between the indium compositions of the active layer and the upper cladding layer is preferably set to 0.41 or less, whereby the power for realizing stable long-wavelength light emission can be obtained.

[Example 8]

A laser device was obtained in the same manner as in Example 1, except that the materials and the growth temperatures of the active layer 108 and the p-type cladding layer 111 were changed as follows.

(i) Active layer 108

Structure: InGaN quantum well layer (3.5nm thick) and InGaN barrier layer (10.5nm thick)

0.47 0.53 0.36 0.64

Multiple quantum well structure

Growth temperature: 680 ° C

(ii) p-type cladding layer 111

Structure: Mg-doped p-type In GaN (thickness Ο.δ μ πι)

0.07 0.93

Growth temperature: 780 ° C

As described above, in the layer structure according to the present embodiment, when the indium composition of the active layer 108 (the indium composition of the quantum well layer) is x and the indium composition of the p-type cladding layer 111 is y, X is 0.47. Yes, and (X-y) is 0.4.

The obtained laser element was placed on a heat sink, each electrode was wire-bottled, and laser oscillation was attempted at room temperature. As a result, the threshold current density at room temperature At 6.5 kA / cm ² and a threshold voltage of 7 V, continuous oscillation with an oscillation wavelength of approximately 680 nm was confirmed.

[Example 9]

(i) Active layer 108

0.47 0.53 0.36 0.64

Multiple quantum well structure

Growth temperature: 680 ° C

(ii) p-type cladding layer 111

Structure: Mg-doped p-type In GaN (thickness Ο.δ μ πι)

0.04 0.96

Growth temperature: 780 ° C

As described above, in the layer structure according to the present embodiment, when the indium composition of the active layer 108 (the indium composition of the quantum well layer) is x and the indium composition of the p-type cladding layer 111 is y, X is 0.47. Yes, and (X-y) is 0.43.

The obtained laser device was placed on a heat sink, and each electrode was wire-bonded, and laser oscillation was attempted at room temperature. As a result, the threshold current density at room temperature

At 10 kA m ² and a threshold voltage of 9 V, continuous oscillation with an oscillation wavelength of approximately 680 nm was confirmed. The threshold current density was slightly higher than in Example 1. It is considered that the structure of Example 1 was more effectively suppressed from deteriorating the film quality of the active layer and the like during wire bonding.

As can be seen from the comparison between Examples 8 and 9, when (X−y) is 0.4 or less, the threshold current density is improved as compared with the case where (X−y) exceeds 0.4. This tendency was the same in some experimental results when x was in the range of 0.3 or more.

As described above, the forces described in the embodiments of the present invention with reference to the drawings are merely examples of the present invention, and various configurations other than those described above can be adopted.

For example, the structure of the laser element is not limited to the ridge type shown in the above-described embodiment. For example, an inner stripe type in which a current blocking layer is provided in the laser structure may be used. In the laser structure, a structure in which the lattice relaxation layer 112 is not provided may be employed.

Claims

The scope of the claims

[1] a substrate,

A lower cladding layer formed on the substrate,

An active layer formed on the lower cladding layer,

An upper cladding layer formed on the active layer,

With

Both the active layer and the upper cladding layer are made of a nitride semiconductor containing indium,

The indium composition of the active layer is x, and the indium composition of the upper cladding layer is y.

X is 0.3 or more, and (X−y) is 0.4 or less, a nitride semiconductor light emitting device.

[2] The nitride semiconductor light-emitting device according to claim 1,

The growth temperature of the active layer is T (° C), and the growth temperature of indium in the upper cladding layer is T

2

(° c),

A nitride semiconductor light-emitting device having a T-T force of at most sioo ° c.

1 2

[3] The nitride semiconductor light-emitting device according to claim 1,

A nitride semiconductor light emitting device comprising a lattice relaxation layer provided between the active layer and the upper cladding layer or in the upper cladding layer.

[4] The nitride semiconductor light-emitting device according to claim 3,

The nitride semiconductor light emitting device, wherein the lattice relaxation layer is a low-temperature growth layer formed at a temperature of 600 ° C. or less.

[5] The nitride semiconductor light-emitting device according to claim 3,

The nitride semiconductor light emitting device, wherein the lattice relaxation layer contains indium.

[6] The nitride semiconductor light-emitting device according to claim 3,

A nitride semiconductor light emitting device, wherein the thickness of the lattice relaxation layer is 10 nm or more and 100 nm or less.

[7] The nitride semiconductor light emitting device according to claim 1, A nitride semiconductor light emitting device, wherein an indium composition ratio of the upper cladding layer is smaller than an indium composition ratio of the active layer.

[8] The nitride semiconductor light emitting device according to claim 1,

A contact layer provided on the active layer and made of a nitride semiconductor containing indium;

An electrode provided in contact with the contact layer;

A nitride semiconductor light emitting device comprising:

[9] The nitride semiconductor light-emitting device according to claim 1,

The nitride semiconductor light emitting device, wherein each of the semiconductor layers located above the active layer is made of a nitride semiconductor containing indium.

[10] The nitride semiconductor light-emitting device according to claim 1,

The upper cladding layer is made of InGaN (0 <y <l), and the nitride semiconductor y 1—y

Body light emitting element.

[11] The nitride semiconductor light emitting device according to claim 10, wherein

Thickness of the upper cladding layer composed of In GaN (0 <y <l) 0.4 μ · ≥η or more 1 · y μ y y

m or less.

[12] a substrate,

A lower cladding layer formed on the substrate,

An active layer formed on the lower cladding layer,

An upper cladding layer formed on the active layer,

With

2

(° C),

1 2

[13] a substrate,

A lower cladding layer formed on the substrate, An active layer formed on the lower cladding layer,

An upper cladding layer formed on the active layer,

With

The active layer is made of a nitride semiconductor containing indium,

[14] The nitride semiconductor light emitting device according to claim 13, wherein

The nitride semiconductor light emitting device, wherein the upper cladding layer is made of a nitride semiconductor containing indium.

[15] The nitride semiconductor light emitting device according to claim 13, wherein

[16] The nitride semiconductor light-emitting device according to claim 13,

[17] The nitride semiconductor light-emitting device according to claim 13, wherein

[18] The nitride semiconductor light-emitting device according to claim 12 or 13,

A nitride semiconductor light emitting device, wherein an indium composition ratio of the upper cladding layer is smaller than an indium composition ratio of the active layer.

[19] The nitride semiconductor light-emitting device according to claim 12 or 13,

An electrode provided in contact with the contact layer;

A nitride semiconductor light emitting device comprising:

[20] The nitride semiconductor light-emitting device according to claim 12 or 13,

A nitride semiconductor light emitting device, wherein each of the semiconductor layers located above the active layer is made of a nitride semiconductor containing indium.

[21] The nitride semiconductor light emitting device according to claim 12, wherein the upper cladding layer is made of InGaN (0 <y <l).

y 1— y

Body light emitting element.

[22] The nitride semiconductor light emitting device according to claim 12 or 13,

In GaN (0 <y <l) force, the thickness of the upper cladding layer is 0.4 111 or more 1. Ο μ y i— y

m or less.

[23] forming a lower cladding layer on the substrate;

Forming an active layer made of a nitride semiconductor containing indium on the lower clad layer;

Forming an upper cladding layer made of a nitride semiconductor containing indium on the active layer;

Including

2

(° C),

A method for producing a nitride semiconductor light emitting device, wherein the TT force is not more than sioo ° c.

1 2

[24] forming a lower cladding layer on the substrate,

Forming a lattice relaxation layer on the active layer at a temperature of 600 ° C. or lower; forming an upper cladding layer on the lattice relaxation layer;

A method for manufacturing a nitride semiconductor light emitting device, comprising: