JP2001068786A - Nitride compound semiconductor light-emitting device and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease a threshold current and forward voltage and improved reliability in the nitride compound semiconductor light-emitting device where a current blocking layer is provided so as to stabilize the lateral mode. SOLUTION: This nitride compound semiconductor light-emitting device is equipped with an active layer 5 which is pinched between an upper and a lower clad layer, 4 and 6, and a current blocking layer 8a having an opening that serves as a current path is formed on the active layer 5. The current blocking layer 8a is equipped with a conductor layer and an insulating layer 7 at least on the opening under a nitride compound semiconductor layer 8, and the insulating layer 7 functions as an etching stop layer of the nitride compound semiconductor layer 8 when the opening is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nitride compound semiconductor light emitting device such as a semiconductor laser or a light emitting diode capable of emitting light in a blue region to an ultraviolet region and a method of manufacturing the same, and more particularly, to reducing a threshold current. The present invention relates to a nitride-based compound semiconductor light-emitting device having a current blocking layer provided thereon and a method of manufacturing the same.

[0002]

2. Description of the Related Art As a semiconductor light emitting device capable of emitting light in a blue region to an ultraviolet region, for example, Japanese Patent Application Laid-Open No. Hei 8-97507 discloses a gallium nitride compound semiconductor laser as shown in FIG.

This semiconductor laser has a sapphire substrate 1,
n-type GaN buffer layer 2, n-type GaN contact layer 3,
n-type AlGaN cladding layer 4, InGaN active layer 5, p
It has a structure in which an AlGaN clad layer 6, an internal current blocking layer 80 and a p-type GaN contact layer 9 are sequentially laminated. A p-type electrode 10 is formed on the p-type contact layer 9, and an n-type electrode 11 is formed on an exposed portion of the n-type contact layer 3.
Are formed.

The current blocking layer 80 has a stripe-shaped opening (stripe groove) formed by etching, and a current flowing from the p-type electrode 10 to the n-type electrode 11 passes through the opening of the current blocking layer 80. It is constricted to flow vertically. The current blocking layer 80 includes AlGaN, SiO ₂ ,
Si ₃ N ₄ and Al ₂ O ₃ are used.

[0005]

As described above, in order to reduce the threshold current of a gallium nitride-based compound semiconductor laser, a structure in which an opening is provided in the current blocking layer 80 by etching has been proposed.

However, when an opening is formed in the current blocking layer 80 by etching, there is a problem that the width of the opening and the shape (slope of the groove) 110 of the opening must be formed with good reproducibility. This is because the width of the opening and the shape of the opening affect the threshold current and the oscillation mode.

In the case where a gallium nitride-based compound semiconductor such as AlGaN is used as the current blocking layer, an optimum etching method for forming an opening in the current blocking layer is not known at present, and the selectivity is low. There is a problem that excellent etching cannot be performed. Therefore, when etching for forming a stripe-shaped opening in the current blocking layer 80 is performed, there is a possibility that the surface of the cladding layer 6 located under the current blocking layer 80 may also be etched. Shape control with good reproducibility could not be achieved unless it was strictly adjusted.

Further, after a stripe-shaped opening is formed in the current blocking layer 80 by an etching device, the semiconductor layer (contact layer 9) is re-grown so as to fill the opening. Damage and residual impurities are introduced into the exposed surface. Even if a regrowth layer is formed on such an exposed surface, a regrowth interface 100 having good crystal quality cannot be obtained, causing an interface state.

For example, a p-type gallium nitride compound semiconductor is etched by a dry etching method, and p-type
I (current) -V (voltage) between p-type electrodes by forming a p-type electrode
The result of examining the characteristics is shown in FIG. From this figure I
It can be seen that the -V characteristics are not in ohmic contact, and that damage due to dry etching, residual impurities, and the like have been introduced.

After the stripe-shaped opening is formed in the current blocking layer 80, the stripe-shaped groove of the current blocking layer 80 is formed before the semiconductor layer (contact layer 9) is regrown so as to fill the opening. The bottom corner evaporates due to lack of nitrogen. For this reason, when the contact layer 9 is regrown thereon, there is a problem that a cavity 111 as shown in FIG. 8 is generated.

Further, when the current blocking layer 80 is formed of an insulator layer, a defect 112 as shown in FIG. 9 is generated in a region regrown on the opening of the current blocking layer 80. Only a layer with poor crystallinity can be obtained. For this reason, there has been a problem that the threshold current and the series resistance increase, the forward voltage increases, and a semiconductor light emitting device with excellent reliability cannot be obtained.

SUMMARY OF THE INVENTION The present invention has been made to solve such problems of the prior art, and a nitride compound having a stable oscillation transverse mode, a reduced threshold current and a forward voltage, and a high reliability. It is an object to provide a semiconductor light emitting device and a method for manufacturing the same.

[0013]

According to the present invention, there is provided a nitride-based compound semiconductor light emitting device comprising at least a pair of cladding layers, an active layer sandwiched between both cladding layers, and a cladding layer remote from the substrate. A nitride-based compound semiconductor light-emitting device having a current blocking layer provided with an opening serving as a current path on the layer, wherein the current blocking layer comprises an insulator layer and a nitride-based compound semiconductor layer; The insulator layer is provided in at least the opening below the nitride-based compound semiconductor layer, thereby achieving the above object.

[0014] The nitride compound semiconductor layer is an In _s Al _t
It is preferably made of Ga _1-st N (0 ≦ s, 0 ≦ t, 0 ≦ s + t ≦ 1).

The cladding layer is made of Al_yGa_1-yN (0 ≦ y
≦ 1), wherein the active layer is In _zGa_1-zN (0 ≦ z
≤ 1).

The insulator layer can function as an etching stop layer for the nitride-based compound semiconductor layer when forming the opening.

It is preferable that the width of the opening of the nitride-based compound semiconductor layer is larger than the width of the opening of the insulator layer.

Preferably, the substrate is made of GaN.

It is preferable that the opening of the insulator layer is formed in a region having less crystal defects than other regions, and the active layer region located below the opening serves as a light emitting portion.

The opening of the insulator layer is formed by a nitride under the opening.
Dislocation density of the base compound semiconductor layer is 10 ⁸/ Cm^TwoThe following areas
It is preferable to form it.

The insulator layer is made of SiO ₂ , Si ₃ N ₄ , Al ₂
It preferably comprises at least one of O ₃ and TiO ₂ .

It is preferable that the insulator layer is formed on a clad layer.

It is preferable that the current blocking layer further has a conductor layer below the insulator layer.

The conductor layer is made of W, Mo, Ta, Mg,
Preferably, it consists of at least one of C, Be and their alloys.

It is preferable that the conductive layer has a thickness of 1 nm or more and 10 nm or less.

According to the method of manufacturing a nitride-based compound semiconductor light emitting device of the present invention, a lower clad layer, an active layer and an upper clad layer are formed on a substrate, and an insulator layer serving as a current blocking layer is formed on the upper clad layer. And a step of laminating and forming a nitride-based compound semiconductor layer, a step of forming an opening in the nitride-based compound semiconductor layer by dry etching and exposing the insulator layer, and a step of exposing the insulator layer by wet etching. Forming a portion and exposing the upper cladding layer, whereby the object is achieved.

According to the method of manufacturing a nitride-based compound semiconductor light-emitting device of the present invention, the lower clad layer, the active layer, and the upper clad layer are formed on a substrate, and a current blocking layer is formed on the upper clad layer. Stacking a layer, an insulator layer and a nitride-based compound semiconductor layer, forming an opening in the nitride-based compound semiconductor layer by dry etching to expose the insulator layer, Forming an opening in the conductor layer by wet etching to expose the upper cladding layer, whereby the object is achieved.

Hereinafter, the operation of the present invention will be described.

In the present invention, the current blocking layer has an insulator layer at least in the opening below the nitride-based compound semiconductor layer, and as shown in Embodiments 1 to 4 described below, Since the insulator layer can function as an etching stop layer when an opening is formed in the nitride-based compound semiconductor layer, shape control with good reproducibility is possible. Further, since the nitride-based compound semiconductor layer is provided on the insulator layer, the current blocking layer (insulator layer) as shown in FIG.
No defects 112 in the growth layer on 80 also occur.

As the substrate, for example, a sapphire substrate or a GaN substrate is used. Particularly, a fourth embodiment described later.
As shown in the figure, when the GaN substrate is used, the dislocation of the nitride-based compound semiconductor layer formed thereon is reduced as compared with the case where the sapphire substrate is used. This is preferable because warpage does not occur and damages the SiO ₂ film. Furthermore, SiO
_Although heat is difficult to escape when _two films are provided, heat can also be escaped with a GaN substrate.

As shown in Embodiment 4 described later, before forming the insulator layer, dislocations (crystal defects) which cross the active layer may be observed by a method of observing dislocations (crystal defects) from the surface of the semiconductor layer. Dislocations penetrating to the cladding layer)
It is preferable that an opening of the insulator layer is formed above a region having a smaller number than other regions. By using this region as a current path and the active layer region located thereunder as a light emitting portion, non-radiative recombination is reduced and a nitride-based compound semiconductor light emitting device with high luminous efficiency is obtained. Further, it is possible to suppress the diffusion of Mg into the active layer during regrowth from the p-type contact layer doped with Mg, for example, through the dislocation in the opening, so that the crystallinity of the active layer does not deteriorate, The luminous efficiency of the light emitting unit does not decrease.

On the other hand, an opening of the insulator layer is formed in a region where the number of dislocations crossing the active layer is larger than in other regions,
If this region is used as a current path and the active layer region located thereunder is used as a light emitting portion, non-radiative recombination increases, and only a nitride-based compound semiconductor light emitting device with low luminous efficiency can be obtained. Further, through the dislocation in the opening, for example, Mg
Is diffused into the active layer during regrowth from the heavy-doped p-type contact layer, thereby deteriorating the crystallinity of the active layer and reducing the luminous efficiency of the light emitting portion.

Therefore, the opening of the insulator layer has a dislocation density of, for example, 10 ⁸ / cm ^{2 of the} underlying nitride-based compound semiconductor layer.
It is preferably formed in the following regions.

The insulator layer can grow a nitride-based compound semiconductor layer thereon, and has a function as a growth mask layer. Then, crystal growth proceeds in the lateral direction from both sides of the insulator layer, and the lateral growth is united, so that the dislocation () defect can be grown near the center on the insulator layer so as to have few defects.

As an insulator layer, light absorption in the ultraviolet region is
Low SiO_Two, Si_ThreeN_Four, Al_TwoO _ThreeOr TiO_TwoEtc.
It is preferable to use them in combination of two or more kinds.
Is also good. The insulator layer is preferably formed on the cladding layer.
New Further, as shown in a third embodiment described later, an n-type
In the cladding layer, impurities such as Si are mixed in from the insulator layer.
However, there is no particular problem.
It is preferable to form an insulator layer on the lad layer. Insulator
The thickness of the layer is not less than 0.05 μm and not more than 0.2 μm.
Is preferred. If the thickness of the insulator layer is less than 0.05 μm
It may not function as an insulator.
If it is too thick, it is difficult to control the oscillation transverse mode with the current blocking layer.
It becomes difficult.

Further, by providing a conductor layer such as a metal layer below the insulator layer, it is possible to prevent impurities from being introduced from the insulator layer into the upper clad layer as shown in Embodiment 2 described later. Can be. Further, the conductor layer also functions as a protective layer for preventing the constituent elements of the insulator from being mixed into the base layer when the insulator layer is formed.

As the conductor layer, W, which is a high melting point metal,
Mo, Ta, etc., or Mg, C, which can be a p-type impurity,
It is preferable to use Be or the like, and these alloys or a combination of two or more thereof may be used. Further, the thickness of the conductor layer is preferably from 1 nm to 10 nm. This is because if the thickness of the conductor layer is less than 1 nm, it is impossible to prevent elements constituting the insulator layer from being mixed into the cladding layer when the insulator layer is formed, and if the thickness exceeds 10 nm, light from the active layer becomes conductive. This is because the influence absorbed by the body layer is large. More preferably, it is 5 nm or more and 10 nm or less.

In the present invention, an insulator layer, a nitride-based compound semiconductor layer, and an insulator layer are formed on the upper clad layer, and the insulator layer is exposed by dry etching. By exposing the cladding layer, damage and residual impurities due to dry etching are not introduced into the cladding layer surface or the contact layer which is a regrown layer thereon. For example, an insulator layer and a p-type nitride-based compound semiconductor are formed in a stack, and the insulator layer is etched by a dry etching method, and then the upper cladding layer is exposed by wet etching to form a p-type layer on the surface.
When the p-type electrode is formed, the IV characteristics between the p-type electrodes are shown in FIG.
As shown in FIG. Therefore, no damage due to dry etching, residual impurities, etc. were introduced, and I
It can be seen that the -V characteristic is close to ohmic contact. On the other hand, when a p-type nitride-based compound semiconductor is etched by a dry etching method as in the prior art, a p-type electrode is formed on the surface thereof, and the IV characteristics between the p-type electrodes are examined. (C). Therefore, it is found that damage due to dry etching, residual impurities, and the like are introduced, and the IV characteristics are not in ohmic contact.

Further, according to another aspect of the present invention, a conductor layer, an insulator layer, and a nitride-based compound semiconductor layer are formed on the upper clad layer, and the insulator layer is exposed by dry etching. By exposing the upper cladding layer by wet etching, damage and residual impurities due to dry etching are not introduced into the cladding layer surface or the contact layer surface which is a regrown layer thereon. For example, a conductor layer, an insulator layer, and a p-type nitride-based compound semiconductor are formed in layers, and the insulator layer is etched by a dry etching method. Thereafter, the upper cladding layer is exposed by wet etching, and p When the type electrode is formed, the IV characteristics between the p-type electrodes are as shown in FIG. Therefore, it is found that no damage due to dry etching, residual impurities, and the like are introduced, and the IV characteristics are in ohmic contact, and more preferable characteristics are obtained.

Furthermore, since the width of the opening of the nitride-based compound semiconductor layer can be made larger than the width of the opening of the insulator layer, the width of the opening of the nitride-based compound semiconductor layer is made larger than before. can do. Therefore, In _s Al _t G
Even if a nitride-based compound semiconductor layer such as a _1-st N (0 ≦ s, 0 ≦ t, 0 ≦ s + t ≦ 1) is used, as shown in FIG. The corners do not evaporate due to lack of nitrogen, and no cavities 111 are generated.

The nitride-based compound semiconductor layer is made of Al _x G
a _1-x N (0 ≦ x ≦ 1), and the cladding layer is Al _y G
a _1-y N (0 ≦ y ≦ 1), and the active layer is made of In _z Ga
_It is preferably a quantum well active layer made of _1-zN (0 ≦ z ≦ 1).

[0042]

Embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited to these embodiments. In the following embodiments, a semiconductor laser device will be described, but it goes without saying that the present invention is also applicable to a light emitting diode. In the present invention, the nitride-based compound semiconductor, an In _s Al _t Ga
_1-st N (0 ≦ s, 0 ≦ t, s + t ≦ 1). Further, As or P can be included as a group V element.

(Embodiment 1) FIG. 1 is a sectional view showing the structure of a gallium nitride-based compound semiconductor laser according to an embodiment of the present invention.

This semiconductor laser has a GaN buffer layer 2 having a thickness of about 50 nm and a thickness of 3 μm on a sapphire substrate 1.
n-type GaN contact layer 3 having a thickness of about m, n-type Al _0.08 Ga _0.92 N cladding layer 4 having a thickness of about 0.5 μm, and a thickness of 3 nm
An undoped In _0.32 Ga _{0. 68} N active layer 5 and the thickness of 0.3μm order of the p-type (Mg-doped) Al _0.08 Ga _0.92
N clad layer 6, 0.1 μm thick insulator (SiO _{2 in} this embodiment) layer 7 and 0.3 μm thick n-type GaN layer 8
And a p-type (Mg-doped) GaN contact layer 9 having a thickness of 0.3 μm. N-type cladding layer 4, active layer 5, p-type cladding layer 6, current blocking layer 8a and p-type contact layer 9
Is partially removed so as to expose the n-type contact layer 3. On the p-type contact layer 9, the p-type electrode 1
0 is formed, and an n-type electrode 11 is formed on the exposed portion of the n-type contact layer 3.

The current blocking layer 8a has a stripe-shaped opening serving as a current path in a selected area of the active layer 5 (in this embodiment, a stripe-shaped area extending in the resonator length direction). The width of the opening is determined so as to adjust the transverse mode of laser oscillation. An insulator (SiO ₂ ) layer 7 is provided under the GaN layer 8 in the opening,
The width of the opening of the GaN layer 8 is set to be larger than the width of the opening of the insulator layer 7. The insulator layer 7 has a function as an etching stop layer for the GaN layer 8.

This semiconductor laser can be manufactured, for example, as follows.

The nitride-based compound semiconductor layer is formed by a metalorganic compound vapor phase epitaxy (MOCVD) method. Ammonia (NH ₃ ) is used as a group V material, and trimethylgallium (TMG) and trimethylaluminum (T) are used as a group III material.
MA) and trimethylindium (TMIn), biscyclopentadienyl magnesium (Cp ₂ Mg) as a p-type impurity, and monosilane (Si) as an n-type impurity.
H ₄ ) and H ₂ and N ₂ as carrier gases.

In order to perform the first crystal growth by the MOCVD method, the sapphire substrate 1 is
Place on the susceptor of the device, in H2 atmosphere, substrate temperature 1
By increasing the temperature to about 200 ° C., the surface of the substrate 1 is subjected to a cleaning process.

Next, the substrate temperature is lowered to about 1000 ° C.
Then, as shown in FIG.
GaN buffer layer 2, about 3 μm thick n-type Ga
N contact layer 3, n-type Al having a thickness of about 0.5 μm_0.08
Ga_0.92The N cladding layer 4 is grown. Then, the substrate temperature
Temperature to about 700 ° C to 750 ° C, and a 3 nm thick
Undoped In_0.32Ga_0.68The N active layer 5 is grown. So
After that, the substrate temperature was raised to about 1000 ° C.
P-type (Mg-doped) Al of about 3 μm_0.08Ga _0.92N
The lad layer 6 is grown. The growth of these semiconductor layers
Without removing the substrate from the growth chamber of the MOCVD equipment,
Do it sequentially.

After that, the substrate on which the above-mentioned semiconductor layer is laminated is once taken out of the growth chamber, and the substrate is subjected to Si-beam evaporation, sputtering, chemical vapor deposition (CVD), or the like.
An insulator layer of O2 is grown. Then, an insulator layer 7 is formed on the clad layer 6 by a normal photolithography technique and an etching technique, as shown in FIG. In this embodiment, the insulator layer 7 made of SiO ₂ is used.
Was formed to a width of 20 μm, a thickness of 0.1 μm, and a period of 500 μm.

Next, in order to perform the second crystal growth, the substrate is placed on the susceptor of the MOCVD apparatus again, and the substrate temperature is raised to about 1000 ° C. Then, as shown in FIG. 2C, an n-type GaN layer 8 having a thickness of 0.3 μm is grown over the insulator layer 7 and the clad layer 6. At this time, the GaN layer 8 grows laterally from both sides of the SiO ₂ insulator layer 7, and the laterally grown layers are united. Therefore, it can be seen from the surface that crystal defects 16 occur near the center of the insulator layer 7 in a direction parallel to the insulator layer 7.

After that, the substrate on which the semiconductor layer is laminated is once taken out of the growth chamber, and a resist mask 12 a is formed on the n-type GaN layer 8. At this time, since the crystal defect 16 of the n-type GaN layer 8 can be used as a marker for mask alignment, mask alignment becomes easy. And
As shown in FIG. 2D, the resist mask in this region is removed, and the n-type G not covered with the resist mask 12a is removed.
The aN layer 8 is selectively etched. During this etching, the insulator layer 7 functions as an etching stop layer, and the etching can be stopped easily and reproducibly when the surface 13 of the insulator layer 7 is exposed. This etching is performed, for example, by RIE (reactive ion etching).
Until the insulator layer 7 is exposed using a gas such as BCl ₃ / Cl ₂ / SiCl ₄ . In the present embodiment, the width of the exposed insulator layer 7 is 7 μm. After that, the mask 12a is removed with an organic solvent.

Next, as shown in FIG.
A resist mask 12b is formed on the N layer 8 and a part of the insulator layer 7.
To form Then, the insulator layer 7 is etched by wet etching until the surface 14 of the clad layer 6 is exposed. In the present embodiment, the width of the exposed clad layer 6 is 3 μm. Then, the mask 12b is formed with an organic solvent.
Is removed.

Subsequently, in order to perform the third crystal growth, the substrate is placed on the susceptor of the MOCVD apparatus again, and the substrate temperature is raised to about 1000 ° C. Then, FIG.
As shown in FIG. 1, a 0.3 μm thick Mg-doped GaN contact layer 9 is grown. At this time, the exposed surface 14 of the clad layer 6 is not affected by surface levels due to damage during dry etching or contamination by impurities, and the MOCV
A good clean surface is maintained in the D apparatus. Since regrowth is performed on such a clean surface in a good state, a good regrowth layer having excellent crystallinity is formed.

Thereafter, the substrate on which the semiconductor layer is laminated is taken out of the MOCVD apparatus, and the surface 15 of the n-type contact layer 3 is exposed by a dry etching technique using a resist mask (not shown). Next, in an N ₂ atmosphere, 75
The Mg-doped layer is changed to p-type by performing thermal annealing at 0 ° C.

Finally, a p-type electrode 10 is formed on the p-type contact layer 9, and an n-type electrode 11 is formed on the exposed surface 15 of the n-type contact layer 3. A semiconductor laser of the form is obtained.

In this semiconductor laser, a voltage is applied to the p-type electrode 10 and the n-type electrode 11 from a current supply circuit (not shown), and a current flows from the p-type electrode 10 to the n-type electrode 11 in the semiconductor laminated structure. At this time, since the current is blocked by the current blocking layer 8a including the n-type GaN layer 8 and the insulator layer 7, the current flows from top to bottom through the opening of the current blocking layer 8a while being narrowed. As a result, laser oscillation in which the transverse mode is controlled is generated, and laser light having a wavelength in a range from the blue region to the ultraviolet region is obtained.

Further, according to this embodiment, the current confinement portion (current path) can be formed without exposing the p-type nitride-based compound semiconductor layer (p-type cladding layer and p-type contact layer) to dry etching. As a result, no interface state is generated due to damage during dry etching or mixing of residual impurities. Therefore, a good regrowth interface similar to that of the IV characteristic close to ohmic contact as shown in FIG. 3A is obtained.

The width of the opening of the n-type GaN layer 8 is
Can be set larger than the width of the internal current blocking layer 80 as in the conventional semiconductor light emitting device shown in FIG.
No cavity 111 at the corner of the bottom of the opening is formed.

Further, the width and shape of the current confined portion (opening) can be formed with good controllability by wet etching.

The insulator layer 7 of the current blocking layer 8a is a GaN layer 8
Functioning as an etching stop layer, the stop of etching can be easily controlled with good reproducibility, and interface states due to damage, residual impurities, and the like are reduced.

As described above, in this embodiment, a gallium nitride-based compound semiconductor laser in which the transverse mode is controlled, the threshold current and the forward voltage are reduced, and the reliability is excellent.

(Embodiment 2) In this embodiment, an example in which a conductor layer is provided below an insulator layer will be described.

FIG. 4 is a sectional view showing the structure of the gallium nitride-based compound semiconductor laser according to the second embodiment.

This semiconductor laser is mounted on a sapphire substrate 1.
A GaN buffer layer 2 having a thickness of about 50 nm and a thickness of 4 μm.
n-type GaN contact layer 3 having a thickness of about m and a thickness of about 0.5 μm
Degree n-type Al_0.08Ga_0.92N cladding layer 4, thickness 3 nm
In_0.15Ga_0.85Three N quantum well layers and a thickness of 4 nm
In_0.05Ga_0.95Multiple quantum with two N barrier layers
The well active layer 51 and a p-type (Mg
Dope) Al_0.08Ga _0.92N clad layer 6, thickness 5 nm
(Mg in this embodiment) layer 71 and a thickness of 0.1 μm
m insulator (in this embodiment, SiO 2_Two) Layer 7 and thickness 0.
3 μm n-type Al_0.05Ga_0.95Current blocking consisting of N layer 8
Stop layer 8b and p-type (Mg-doped) G having a thickness of 0.3 μm
It has a structure in which aN contact layers 9 are sequentially laminated.
n-type cladding layer 4, active layer 5, p-type cladding layer 6, current
The blocking layer 8b and the p-type contact layer 9 are n-type contacts.
Part of the layer 3 has been removed to expose it. p
A p-type electrode 10 is formed on the
An n-type electrode 11 is formed on the exposed portion of the mold contact layer 3.
Have been.

The current blocking layer 8b has a stripe-shaped opening serving as a current path in a selected region of the active layer 5 (in this embodiment, a stripe-shaped region extending in the resonator length direction). The width of the opening is determined so as to adjust the transverse mode of laser oscillation. In the opening, a conductor layer 71 made of Mg and an insulator layer 7 made of SiO ₂ are provided below the n-type AlGaN layer 8.
The width of the opening of the N layer 8 is set to be larger than the width of the opening of the insulator layer 7. The insulator layer 7 has a function as an etching stop layer for the AlGaN layer 8.

This semiconductor laser can be manufactured, for example, as follows.

The nitride-based compound semiconductor layer is formed by MOCV
Performed by the D method, the group V raw material, the group III raw material, the p-type impurity,
The same n-type impurities and carrier gas as in Embodiment 1 are used.

In order to perform the first crystal growth by the MOCVD method, the sapphire substrate 1 is
Placed on the susceptor of the device, in H ₂ atmosphere, substrate temperature 1
By increasing the temperature to about 200 ° C., the surface of the substrate 1 is subjected to a cleaning process.

Next, the temperature of the substrate is lowered to about 1000 ° C., and a thickness of 50 nm is formed on the substrate 1 as shown in FIG.
GaN buffer layer 2, about 4 μm thick n-type Ga
N contact layer 3, n-type Al _{0.08 having} a thickness of about 0.5 μm
A Ga _0.92 N cladding layer 4 is grown. Subsequently, the temperature of the substrate is lowered to about 700 ° C. to 750 ° C., and a 3 nm-thick I
three n _0.15 Ga _0.85 N quantum well layers and a 4 nm thick I
A multiple quantum well active layer 51 having two n _0.05 Ga _0.95 N barrier layers is grown. Thereafter, the substrate temperature is set to 1000
The temperature is raised to about ° C. to grow a p-type (Mg-doped) Al _0.08 Ga _0.92 N clad layer 6 having a thickness of about 0.3 μm.
The growth of these semiconductor layers is performed continuously without removing the substrate from the growth chamber of the MOCVD apparatus.

Thereafter, the substrate on which the semiconductor layer is laminated is once taken out of the growth chamber, and a conductive layer made of Mg is grown by electron beam evaporation, vapor deposition, or the like, and is then subjected to electron beam evaporation, sputtering evaporation, chemical vapor deposition, or the like. An insulator layer made of SiO ₂ is grown by a growth (CVD) method or the like. Then, as shown in FIG. 5B, the conductor layer 71 and the insulator layer 7 are formed by ordinary photolithography and etching.
Is formed on the cladding layer 6. In the present embodiment, the conductor layer 71 made of Mg has a width of 6 μm, a thickness of 5 nm, and a period of 50 μm.
0 μm, and the insulator layer 7 made of SiO ₂ has a width of 20 μm.
μm, a thickness of 0.1 μm, and a cycle of 500 μm.

Next, in order to perform the second crystal growth, the substrate is placed on the susceptor of the MOCVD apparatus again, and the substrate temperature is raised to about 1000 ° C. Then, as shown in FIG. 5C, an n-type Al _0.05 Ga _0.95 N layer 8 having a thickness of 0.3 μm is grown over the insulator layer 7 and the clad layer 6. At this time, the AlGaN layer 8 grows laterally from both sides of the SiO ₂ insulator layer 7, and the laterally grown layers are united.
Therefore, it can be seen from the surface that crystal defects 16 occur near the center of the insulator layer 7 in a direction parallel to the insulator layer 7.

Thereafter, the substrate on which the semiconductor layer is laminated is once taken out of the growth chamber, and a resist mask 12 a is formed on the n-type AlGaN layer 8. At this time, the n-type AlGa
Since the crystal defects 16 of the N layer 8 can be used as markers for mask alignment, mask alignment is facilitated.
Then, as shown in FIG. 5D, the resist mask in this region is removed, and portions of the n-type AlGaN layer 8 that are not covered with the resist mask 12a are selectively etched.
During this etching, the insulator layer 7 functions as an etching stop layer, and the etching can be stopped easily and reproducibly when the surface 13 of the insulator layer 7 is exposed. This etching is performed by, for example, RIE (reactive ion etching) using a gas such as BCl ₃ / Cl ₂ / SiCl ₄ until the insulator layer 7 is exposed. In the present embodiment, the width of the exposed insulator layer 7 is 7 μm. afterwards,
The mask 12a is removed with an organic solvent.

Next, as shown in FIG.
A resist mask 1 is formed on the GaN layer 8 and a part of the insulator layer 7.
2b is formed. Then, the insulator layer 7 and the conductor layer 71 are formed on the surface 1 of the clad layer 6 by wet etching.
Etch until 4 is exposed. In the present embodiment, the width of the exposed clad layer 6 is 3 μm. After that, the mask 12b is removed with an organic solvent.

Subsequently, in order to perform the third crystal growth, the substrate is placed on the susceptor of the MOCVD apparatus again, and the substrate temperature is raised to about 1000 ° C. Then, FIG.
As shown in FIG. 1, a 0.3 μm thick Mg-doped GaN contact layer 9 is grown. At this time, the exposed surface 14 of the clad layer 6 is not affected by surface levels due to damage during dry etching or contamination by impurities, and the MOCV
A good clean surface is maintained in the D apparatus. Since regrowth is performed on such a clean surface in a good state, a good regrowth layer having excellent crystallinity is formed.

Thereafter, the substrate on which the semiconductor layer is laminated is taken out of the MOCVD apparatus, and the surface 15 of the n-type contact layer 3 is exposed by a dry etching technique using a resist mask (not shown). Next, in an N ₂ atmosphere, 75
The Mg-doped layer is changed to p-type by performing thermal annealing at 0 ° C.

Finally, a p-type electrode 10 is formed on the p-type contact layer 9, and an n-type electrode 11 is formed on the exposed surface 15 of the n-type contact layer 3. A semiconductor laser of the form is obtained.

In this semiconductor laser, a voltage is applied to the p-type electrode 10 and the n-type electrode 11 from a current supply circuit (not shown), and a current flows from the p-type electrode 10 to the n-type electrode 11 in the semiconductor laminated structure. At this time, the current is n-type AlGa
Since the current is blocked by the current blocking layer 8b including the N layer 8, the insulator layer 7, and the conductor layer 71, the current flows from the top to the bottom of the opening of the current blocking layer 8b while being narrowed. As a result, laser oscillation in which the transverse mode is controlled is generated, and laser light having a wavelength in a range from the blue region to the ultraviolet region is obtained.

Further, according to the present embodiment, the current confinement portion (current path) can be formed without exposing the p-type nitride-based compound semiconductor layer (p-type cladding layer and p-type contact layer) to dry etching. As a result, no interface state is generated due to damage during dry etching or mixing of residual impurities. Accordingly, a good regrowth interface similar to that of the IV characteristic of the ohmic contact as shown in FIG. 3B is obtained.

Since the width of the opening of the n-type AlGaN layer 8 can be set to be larger than the width of the insulator layer 7, the opening of the internal current blocking layer 80 as occurs in the conventional semiconductor light emitting device shown in FIG. The cavity 111 at the corner of the bottom is not generated.

Further, the width and shape of the current confined portion (opening) can be formed with good controllability by wet etching.

The insulator layer 7 of the current blocking layer 8b is made of AlGaN
Since the layer 8 functions as an etching stop layer, the stop of etching can be easily controlled with good reproducibility, and interface states due to damage, residual impurities, and the like are reduced.

Further, in this embodiment, since the insulator layer 7 is not formed directly on the p-type cladding layer 6 but the conductor layer 71 is formed, impurities such as Si And functions as a protective layer for preventing impurities such as oxygen and Si during the formation of the insulator from being mixed into the p-type cladding layer 6. Therefore, the forward voltage can be further reduced as compared with the semiconductor laser of the first embodiment.

As described above, in this embodiment, a gallium nitride-based compound semiconductor laser in which the transverse mode is controlled, the threshold current and the forward voltage are reduced, and the reliability is excellent.

In the present embodiment, the conductor layer 71 is formed so as to remain. However, the conductor layer 71 is formed so as to have the same width as the width of the opening to expose the surface 14 of the p-type cladding layer 6. In the etching step, the entire conductor layer 71 may be removed. Further, the conductor layer 71 is narrower than the insulator layer 7, but may be provided on the entire lower surface of the insulator layer 7.

(Embodiment 3) In this embodiment, an example in which an insulator layer is provided on an n-type clad layer will be described.

FIG. 6 is a sectional view showing the structure of a gallium nitride compound semiconductor laser according to the third embodiment.

This semiconductor laser has a GaN buffer layer 2 having a thickness of about 50 nm and a thickness of 3 μm on a sapphire substrate 1.
m-type p-type (Mg-doped) GaN contact layer 31,
P-type (Mg-doped) Al _0.08 Ga about 0.5 μm thick
_0.92 N cladding layer 41, 3 nm thick non-doped In
_0.32 Ga _0.68 N active layer 5 and n having a thickness of about 0.3 μm
Type Al _0.08 Ga _0.92 N clad layer 61, thickness 0.1 μm
(SiO _{2 in} this embodiment) layer 7 and a thickness of 0.3
A current blocking layer 8c composed of a p-type (Mg-doped) GaN layer 81 of μm and an n-type GaN contact layer 91 having a thickness of 0.3 μm are sequentially laminated. The p-type cladding layer 41, the active layer 5, the n-type cladding layer 61, the current blocking layer 8c and the p-type contact layer 31
1 has been removed to expose 1. On the n-type contact layer 91, an n-type electrode 11 is formed.
On the exposed portion of the mold contact layer 31, the p-type electrode 10 is formed.

The current blocking layer 8c has a stripe-shaped opening serving as a current path in a selected region of the active layer 5 (in this embodiment, a stripe-shaped region extending in the resonator length direction). The width of the opening is determined so as to adjust the transverse mode of laser oscillation. The insulator (SiO ₂ ) layer 7 is provided under the GaN layer 81 in the opening, and the width of the opening of the GaN layer 81 is set to be larger than the width of the opening of the insulator layer 7. The insulator layer 7 is a GaN layer 8
1 has a function as an etching stop layer.

In the manufacture of this semiconductor laser, the same growth method as in the first embodiment can be used for the growth method of each layer, the group V source, the group III source, the p-type impurity, the n-type impurity, and the carrier gas.

In this semiconductor laser, a voltage is applied to the p-type electrode 10 and the n-type electrode 11 from a current supply circuit (not shown), and a current flows from the p-type electrode 10 to the n-type electrode 11 in the semiconductor laminated structure. At this time, the current is blocked by the current blocking layer 8c including the p-type GaN layer 81 and the insulator layer 7, so that the current is blocked while the current is blocked.
Flows from top to bottom through the opening. As a result, laser oscillation in which the transverse mode is controlled is generated, and laser light having a wavelength in a range from the blue region to the ultraviolet region is obtained.

Further, according to the present embodiment, the current confinement portion (current path) can be formed without exposing the n-type nitride-based compound semiconductor layer (the n-type cladding layer and the n-type contact layer) to dry etching. As a result, no interface state is generated due to damage during dry etching or mixing of residual impurities.

Since the width of the opening of the p-type GaN layer 81 can be set to be larger than the width of the insulator layer 7, the internal current blocking layer 8 which occurs in the conventional semiconductor light emitting device shown in FIG.
No cavity 111 is formed at the corner of the bottom surface of the opening 0.

Further, the width and the shape of the current confined portion (opening) can be formed with good controllability by the wet etching method.

The insulator layer 7 of the current blocking layer 8c is a GaN layer 8
In order to function as an etching stop layer for 1,
The stop of etching can be easily controlled with good reproducibility, and interface states due to damage, residual impurities, and the like can be reduced.

Furthermore, in the present embodiment, the SiO ₂ insulator layer 7 is formed on the n-type
_{2 Even if} Si or the like is mixed into the n-type cladding layer 61 during the formation of the insulator layer 7, there is no particular problem because Si acts as an n-type impurity with respect to the nitride-based compound semiconductor. When the device was actually manufactured, the voltage was slightly higher than the forward voltage obtained in the second embodiment, but it was no problem.

As described above, in the present embodiment, a gallium nitride-based compound semiconductor laser in which the transverse mode is controlled, the threshold current and the forward voltage are reduced, and the reliability is excellent.

(Embodiment 4) In this embodiment, the conductive G
An example using an aN substrate will be described.

FIG. 7 is a sectional view showing the structure of a gallium nitride compound semiconductor laser according to the fourth embodiment.

This semiconductor laser has an n-type GaN substrate 21
An n-type GaN contact layer 3 having a thickness of about 3 μm, an n-type Al _0.08 Ga _0.92 N cladding layer 4 having a thickness of about 0.5 μm, a non-doped In _0.32 Ga _0.68 N active layer 5 having a thickness of 3 nm and a thickness 0 .About.3 μm p-type (Mg-doped) Al
_0.08 Ga _0.92 N clad layer 6, 0.1 μm thick insulator (SiO _{2 in} this embodiment) layer 7 and 0.3 μm thick n
Current-blocking layer 8a composed of a GaN layer 8 and a thickness of 0.
It has a structure in which a 3 μm p-type (Mg-doped) GaN contact layer 9 is sequentially laminated. A p-type electrode 10 is formed on the p-type contact layer 9, and an n-type electrode 11 is formed on the back surface of the n-type GaN substrate 21.

The current blocking layer 8a has a stripe-shaped opening serving as a current path in a selected region of the active layer 5 (in this embodiment, a stripe-shaped region extending in the resonator length direction). The width of the opening is determined so as to adjust the transverse mode of laser oscillation. An insulator (SiO ₂ ) layer 7 is provided under the GaN layer 8 in the opening,
The width of the opening of the GaN layer 8 is set to be larger than the width of the opening of the insulator layer 7. The insulator layer 7 has a function as an etching stop layer for the GaN layer 8.

In the manufacture of this semiconductor laser, the same growth method as in the first embodiment can be used for the growth method of each layer, group V material, group III material, p-type impurity, n-type impurity and carrier gas.

In this semiconductor laser, a voltage is applied to the p-type electrode 10 and the n-type electrode 11 from a current supply circuit (not shown), and a current flows from the p-type electrode 10 to the n-type electrode 11 in the semiconductor laminated structure. At this time, since the current is blocked by the current blocking layer 8a including the n-type GaN layer 8 and the insulator layer 7, the current flows from top to bottom through the opening of the current blocking layer 8a while being narrowed. As a result, laser oscillation in which the transverse mode is controlled is generated, and laser light having a wavelength in a range from the blue region to the ultraviolet region is obtained.

Further, according to the present embodiment, the current confinement portion (current path) can be formed without exposing the p-type nitride-based compound semiconductor layer (p-type cladding layer and p-type contact layer) to dry etching. As a result, no interface state is generated due to damage during dry etching or mixing of residual impurities.

The width of the opening of the n-type GaN layer 8 is
Can be set larger than the width of the internal current blocking layer 80 as in the conventional semiconductor light emitting device shown in FIG.
No cavity 111 at the corner of the bottom of the opening is formed.

Further, the width and shape of the current confined portion (opening) can be formed with good controllability by the wet etching method.

The insulator layer 7 of the current blocking layer 8a is a GaN layer 8
Functioning as an etching stop layer, the stop of etching can be easily controlled with good reproducibility, and interface states due to damage, residual impurities, and the like are reduced.

Further, in this embodiment, the GaN substrate 21
Is used, the number of dislocations existing in the cladding layer 6 thereover is smaller than in the case where a sapphire substrate is used. Accordingly, dislocations are observed from the surface of the cladding layer 6 and the insulator layer 7 is formed on a region having few dislocations.
It can be formed in a region of ⁸ / cm ² or less. A current blocking layer 8a is formed by laminating the GaN layer 8 thereon, and an opening is formed in the current blocking layer 8a, so that a current path can be formed in a region having a small number of dislocations.

Therefore, in the present embodiment, the lateral mode is controlled, the threshold current and the forward voltage are further reduced as compared with the semiconductor lasers of the first to third embodiments, and the gallium nitride-based compound excellent in reliability is obtained. A semiconductor laser was realized.

The plane orientation of the GaN substrate is as follows.
{0001} plane, {1-100} plane, {11-20}
Plane, {1-101} plane, {11-22} plane {01-1}
It is confirmed that the same effect as in the present embodiment can be obtained even if the plane orientation is shifted by about ± 2 degrees from these plane directions.

The insulator layer 7 can grow a gallium nitride based compound semiconductor layer thereon, and has a function as a growth mask layer. In particular, SiO ₂ , Si ₃ N
_{4. It} is preferable to use a material that has low light absorption in the ultraviolet region, such as Al ₂ O ₃ or TiO ₂ .

[0112]

As described in detail above, according to the present invention,
Since the insulator layer of the current blocking layer can function as an etching stop layer of the nitride-based compound semiconductor layer,
The shape of the opening can be controlled with good controllability by stopping the etching with good reproducibility.

Since the current confinement portion (current path) can be formed without exposing the nitride-based compound semiconductor layer under the current blocking layer to dry etching, damage and residual impurities due to dry etching can be reduced on the surface of the cladding layer or the like. It is not introduced into the contact layer which is a regrown layer thereon,
-V characteristics are obtained.

Further, by providing a conductor layer below the insulator layer, it is possible to prevent impurities from being deposited on the clad layer when the insulator layer is formed, as in the case where the insulator layer is formed directly on the upper clad layer. be able to.

The width of the opening of the nitride-based compound semiconductor layer of the current blocking layer can be made larger than the width of the opening of the insulator layer. No cavities are created.

Since the width and shape of the current confinement portion (opening) can be formed by the wet etching method, the opening and the bottom of the opening can be formed with less damage than the dry etching method, and the current confinement portion can be formed with good controllability. Thus, the threshold current and the oscillation mode can be stabilized.

Therefore, according to the present invention, it is possible to realize a nitride-based compound semiconductor light-emitting device in which the lateral mode is controlled, the threshold current and the forward voltage are reduced, and the reliability is excellent.

In particular, when a GaN substrate is used, the number of dislocations in the nitride-based compound semiconductor layer formed thereon can be reduced. For example, the dislocation density can be reduced over a region having a dislocation density of 10 ⁸ / cm ² or less. An opening in the insulator layer can be formed. As a result, non-radiative recombination can be reduced,
In addition, since the crystallinity of the active layer is not deteriorated, a nitride-based compound semiconductor light emitting device having higher luminous efficiency can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a structure of a gallium nitride-based compound semiconductor laser according to a first embodiment.

FIG. 2 is a schematic cross-sectional view for explaining a manufacturing process of the gallium nitride-based compound semiconductor laser according to the first embodiment.

FIG. 3 is a diagram showing IV characteristics of the gallium nitride-based compound semiconductor lasers of the first and second embodiments and a conventional gallium nitride-based compound semiconductor laser.

FIG. 4 is a schematic sectional view showing a structure of a gallium nitride-based compound semiconductor laser according to a second embodiment.

FIG. 5 is a schematic cross-sectional view for explaining a manufacturing process of the gallium nitride-based compound semiconductor laser according to the second embodiment.

FIG. 6 is a schematic sectional view showing a structure of a gallium nitride-based compound semiconductor laser according to a third embodiment.

FIG. 7 is a schematic sectional view showing the structure of a gallium nitride-based compound semiconductor laser according to a fourth embodiment.

FIG. 8 is a schematic sectional view showing the structure of a conventional gallium nitride-based compound semiconductor laser.

FIG. 9 is a schematic sectional view showing the structure of a conventional gallium nitride-based compound semiconductor laser.

[Explanation of symbols]

 Reference Signs List 1 sapphire substrate 2 buffer layer 3, 91 n-type contact layer 4, 61 n-type cladding layer 5 active layer 6, 41 p-type cladding layer 7 current blocking layer (insulator layer) 8 current blocking layer (GaN layer) 8a, 8b 8c current blocking layer 9, 31 p-type contact layer 10 p-type electrode 11 n-type electrode 12a, 12b resist mask 13 exposed surface of insulator layer 14 exposed surface of p-type cladding layer 15 exposed surface of n-type contact layer 16 crystal Defect 21 GaN substrate 51 Multiple quantum well active layer 71 Current blocking layer (conductor layer) 81 Current blocking layer (AlGaN layer)

Claims (15)

[Claims] 1. A substrate having at least a pair of cladding layers, an active layer sandwiched between the two cladding layers, and an opening serving as a current path on the cladding layer remote from the substrate. A nitride-based compound semiconductor light-emitting device having a current-blocking layer, wherein the current-blocking layer comprises an insulator layer and a nitride-based compound semiconductor layer, and is provided at least in the opening below the nitride-based compound semiconductor layer. A nitride compound semiconductor light emitting device having an insulator layer. Wherein said nitride compound semiconductor layer is an In _s A
2. The nitride-based compound semiconductor light emitting device according to claim 1, wherein the nitride-based compound semiconductor light emitting device is composed of 1 _t Ga _1-st N (0 ≦ s, 0 ≦ t, 0 ≦ s + t ≦ 1). 3. The method according to claim 1, wherein the cladding layer is made of Al _y Ga _{1 -y} N (0 ≦
y ≦ 1), and the active layer is made of In _z Ga _{1 -zN} (0 ≦ 1).
3. The nitride-based compound semiconductor light-emitting device according to claim 2, wherein z ≦ 1). 4. The nitride according to claim 1, wherein the insulator layer functions as an etching stop layer for the nitride-based compound semiconductor layer when forming the opening. Based compound semiconductor light emitting device. 5. The width of the opening of the nitride-based compound semiconductor layer is larger than the width of the opening of the insulator layer.
The nitride-based compound semiconductor light-emitting device according to claim 4. 6. The nitride-based compound semiconductor light emitting device according to claim 1, wherein said substrate is made of GaN. 7. An opening in the insulator layer is formed in a region having less crystal defects than other regions, and an active layer region located below the opening serves as a light emitting portion. 7. The nitride-based compound semiconductor light-emitting device according to any one of 6. 8. The nitride compound according to claim 7, wherein the opening of the insulator layer is formed in a region where the dislocation density of the underlying nitride compound semiconductor layer is 10 ⁸ / cm ² or less. Semiconductor light emitting device. 9. The method according to claim 1, wherein the insulator layer is made of SiO ₂ , Si ₃ N ₄ , A
l ₂ O ₃ and the nitride based compound semiconductor light-emitting device according to any one of claims 1 to 8 comprises at least one of TiO _2. 10. The nitride-based compound semiconductor light emitting device according to claim 1, wherein said insulator layer is formed on a clad layer. 11. The nitride-based compound semiconductor light emitting device according to claim 1, wherein said current blocking layer further includes a conductor layer below said insulator layer. 12. The conductor layer is made of W, Mo, Ta, M
g, C, Be and at least one of their alloys
The nitride-based compound semiconductor light-emitting device according to any one of claims 1 to 11, comprising: 13. The conductive layer has a thickness of 1 nm or more and 10 n or more.
The nitride-based compound semiconductor light-emitting device according to claim 1, wherein m is equal to or less than m. 14. A step of laminating a lower cladding layer, an active layer and an upper cladding layer on a substrate, and laminating an insulator layer and a nitride-based compound semiconductor layer serving as a current blocking layer on the upper cladding layer. Forming an opening in the nitride-based compound semiconductor layer by dry etching to expose the insulator layer; and forming an opening in the insulator layer by wet etching to expose the upper cladding layer. A method for manufacturing a nitride-based compound semiconductor light emitting device, comprising: 15. A lower clad layer, an active layer, and an upper clad layer are formed on a substrate by lamination, and a conductor layer, an insulator layer, and a nitride-based compound semiconductor layer serving as a current blocking layer are formed on the upper clad layer. Forming an opening in the nitride-based compound semiconductor layer by dry etching to expose the insulator layer; and forming an opening in the insulator layer and the conductor layer by wet etching. And exposing the upper cladding layer.