JPH07297476A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To obtain a GaN surface emission laser device having the optimum laser resonator structure by providing an active layer composed of a wurtzite semiconductor and Bragg reflection mirrors constituted by cyclically forming at least two kinds of semiconductor layers having different refractive indexes on a substrate. CONSTITUTION:An undoped Bragg reflection mirror 5 is formed by alternately forming undoped InAlN layers 3 having lower refractive indexes and lattice- matched to GaN and undoped GaN layers 4 having higher refractive indexes on a GaN buffer layer 2 by 10.5 cycles after the layer 2 is grown on a sapphire substrate 1, the surface of which is cut perpendicularly to the (10-10) axis of the sapphire. Then a resonator composed of an n-type GaN electron-injected layer 6, undoped InGaN strained quantum well layer (active layer) 7, and p-type GaN hole-injected layer 8 is provided. Successively, a p-type Bragg reflection mirror is formed by piling up p-type InAlN layers 9 having lower refractive indexes and lattice-matched to GaN and p-type GaN layers 10 having higher refractive indexes on the resonator by 10.5 cycles.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device, and more particularly to a blue surface emitting semiconductor laser device suitable for a light source of an optical disk system or the like.

[0002]

2. Description of the Related Art A III-V group surface emitting laser which does not contain N (nitrogen), for example, a surface emitting laser having a wavelength of 0.6 to 0.9 .mu.m formed on a GaAs substrate, or formed on an InP substrate. Surface emitting lasers having a wavelength of 1.3 to 1.5 μm are widely known.

A GaN-based blue light-emitting diode fabricated on a sapphire (0001) substrate has also been reported (Reference 1: S. Nakamura, Japanese Journal of Applied Physics, Volume 32, Part 2). (No. 1A / B), L8-L11, Reference 2: Nikkei Electronics, No. 598, pages 59-60, 1
January 3, 994 issue).

[0004]

A GaN-based blue semiconductor laser has not yet been realized. One of the causes is
This is because the method of forming the laser end face is not established.
The GaN-based light-emitting diodes that have been reported so far have a wurtzite-type crystal structure and include sapphire (000
1) Since it was formed on the substrate, it was difficult to obtain a mirror surface by cleavage.

Therefore, it is an object of the present invention to show an optimum laser cavity structure in a wurtzite crystal structure, G
It is to realize an aN-based surface emitting laser.

[0006]

The above-mentioned object is to provide a Bragg reflector having a substrate on which an active layer, which is at least a wurtzite semiconductor, and at least two kinds of semiconductor layers having different refractive indexes are periodically formed. It is achieved by providing. In particular, by setting the crystal growth direction parallel to the [0001] axis or an axis inclined by 5 ° to 10 ° or more from the axis equivalent thereto, the polarization direction can be controlled. In addition, the two types of semiconductor layers that form the Bragg reflector are lattice-matched to each other and are made of In _X Ga _{1 -X} N (0
It can be effectively achieved by setting ≦ x ≦ 1) and InAlN.

[0007]

The resonator of the semiconductor laser can be roughly classified into a Fabry-Perot type that utilizes reflection at the end face and a Bragg reflector type in which the refractive index changes periodically. As described above, in the wurtzite type semiconductor, since it is difficult to form the end face, it is more advantageous to form the resonator by the Bragg reflector.

FIG. 3 shows the wurtzite type semiconductor, that is, the index in the direction of the hexagonal lattice. In this figure, when crystal growth is performed in the [0001] axis direction, it is not possible to predict which direction the polarization direction of the laser light emitted from the plane is 0 to 360 ° due to the symmetry of the electronic structure. Out of control. Therefore, in order to apply it to a system that requires polarization control, it is necessary to use 5 from the [0001] axis.
It is necessary to set the axis distant by about 10 ° or more as the crystal growth direction. In particular, the [10-10] axis, [1
Crystal growth in the [1-20] axis and [10-11] axis directions is easy and is a strong candidate as a crystal axis.

Further, the Bragg reflector is manufactured by periodically forming at least two kinds of semiconductors having different refractive indexes. The thickness of each layer is 1/4 of the wavelength inside each layer. Therefore, the semiconductors forming the Bragg reflector must be lattice-matched to each other. If there is a lattice mismatch in a thick film such as a Bragg reflector, dislocations will occur and the reliability of the device will be impaired.

In the case of GaN, the high refractive index layer constituting the Bragg reflector is In _x Ga ₁ -x N (0≤x≤
1), especially GaN, which has a proven record in terms of crystallinity, is effective. On the other hand, it is lattice-matched to this In _X Ga _1-X N and
_{As a} material whose refractive index is 5% or more smaller than that of _X Ga _1-X N,
In the quaternary system, there are InGaAlN, GaAlNP, or GaAlNAs. In the ternary system, InAl
There are N, AlNP, or AlNAs. By constructing a Bragg reflector with these materials, a GaN-based blue surface emitting laser can be realized.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

<Embodiment 1> FIG. 1 is a sectional view showing the structure of a surface emitting laser according to a first embodiment of the present invention. FIG. 2 is a top view of this laser. FIG. 1 is a sectional view of a portion AB of FIG. The device structure and manufacturing process will be described below with reference to these drawings.

On the sapphire substrate 1 whose surface is perpendicular to the [10-10] axis, a GaN buffer layer (thickness 5 μm) 2 is grown by metalorganic vapor phase epitaxy (MOVPE), and then GaN lattice is formed. The matched InAlN undoped low-refractive index layer 3 and GaN undoped high-refractive index layer 4 were matched.
Five cycles are stacked to form an undoped Bragg reflector 5. However, the thickness of each layer is 1/4 of the wavelength λ inside the device.
And Next, n-type GaN (N _D = 1 × 10 ¹⁸ [/ c
m ³ ]) electron injection layer 6, undoped In _0.2 Ga _0.8 N strained quantum well layer (active layer) (thickness 7 nm) 7, p-type Ga
_A resonator including the hole injection layer 8 of N (NA = 1 × 10 ¹⁸ [/ cm ³ ]) is provided. However, the thickness of this resonator is λ. Subsequently, the p-type low-refractive index layer 9 of InAlN and the p-type high-refractive index layer 10 of GaN lattice-matched with GaN are laminated for 10.5 periods to form a p-type Bragg reflector 11. Also,
The p-GaN cap layer 12 (thickness λ / 4, N _A = 2 × 10 ¹⁸ [/ cm ³ ]) is provided to reduce the contact resistance with the electrode. Next, a p-type electrode 13 is provided by vapor deposition, and etching is further performed from the surface to reach the electron injection layer 6, thereby forming a circular mesa of 10 μmφ. Finally, the side surface of the mesa is covered with SiO ₂ 14 and then the n-type electrode 15 is vapor-deposited to manufacture the surface emitting laser of the embodiment shown in FIGS. 1 and 2.

In the device of the above embodiment, the threshold current 2
A blue surface emitting laser that oscillates at 0 mA can be realized. In addition, all the manufactured devices emit laser light linearly polarized in a specific direction.

By using the surface emitting laser of this embodiment as a light source of an optical disk system, a high performance system can be constructed.

<Embodiment 2> FIG. 4 is a sectional view showing the configuration of a surface emitting laser according to a second embodiment of the present invention. The device structure and manufacturing process will be described below with reference to this drawing.

On the sapphire substrate 21 whose surface is perpendicular to the [10-11] axis, metalorganic vapor phase epitaxy (MOVPE) is performed.
Method, a GaN buffer layer (thickness: 5 μm) 22 is grown, and then an AlNP undoped low-refractive index layer 23 and a GaN undoped high-refractive index layer 24 that are lattice-matched to GaN are stacked for 10.5 periods to perform Bragg reflection. The mirror 25 is formed.
However, the thickness of each layer is 1/4 of the wavelength λ inside the element. Next, an electron injection layer 26 of n-type GaN (N _D = 1 × 10 ¹⁸ [/ cm ³ ]), an undoped In _0.2 Ga _0.8 N strained quantum well layer (active layer) (thickness 7 nm) 27, a p-type GaN
_A resonator including the hole injection layer 28 of (NA = 1 × 10 ¹⁸ [/ cm ³ ]) is provided. However, the thickness of this resonator is λ. Subsequently, an AlNP undoped low refractive index layer 29 and a GaN undoped high refractive index layer 30 lattice-matched to GaN.
Are laminated for 10.5 cycles to form the Bragg reflector 31. Next, etching is performed from the surface to reach the hole injection layer 28 to form a circular mesa of 6 μmφ. A p-type electrode 32 is provided by using a vapor deposition method, and etching is further performed from the surface of the hole injection layer 28 to the electron injection layer 26. Finally, the side surface of the strained quantum well layer 27 is covered with SiO ₂ 33, and then the n-type electrode 34 is vapor-deposited to manufacture the surface emitting laser of the embodiment shown in FIG.

In the device of the above embodiment, the threshold current 8
A blue surface emitting laser that oscillates at mA can be realized. In addition, all the manufactured devices emit laser light linearly polarized in a specific direction.

By using the surface emitting laser of this embodiment as a light source of an optical disk system, a high performance system can be constructed.

The present invention is also effective for structures other than those shown in the embodiments. For example, in order to reduce the series resistance of the device, a structure in which a graded layer (a layer whose composition gradually changes) is provided between the high refractive index layer and the low refractive index layer forming the Bragg reflector is also available. Applicable. Further, the substrate is not limited to sapphire, a substrate from which wurtzite crystals can be obtained, for example,
It may be a ceramic substrate such as MgO, MnO, ZnO, or SiO ₂ or a semiconductor substrate.

[0021]

According to the present invention, Gs lattice-matched to each other are used.
Since the Bragg reflector made of aN / InAlN or the like forms the reflecting mirror, a high reflectance can be obtained and Ga
Laser oscillation with N-based material becomes possible. Further, by forming the active layer in the direction of the axis inclined by 5 ° to 10 ° or more from the [0001] axis, a blue surface emitting laser with a controlled polarization direction can be realized. Furthermore, by applying the semiconductor laser of the present invention to an optical disc system, the system performance can be improved.

[0022]

[Brief description of drawings]

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

FIG. 2 is a top view of FIG.

FIG. 3 is an explanatory diagram of a direction index in a hexagonal lattice (wurtzite crystal structure).

FIG. 4 is a sectional view of a semiconductor laser device according to another embodiment of the present invention.

[Explanation of symbols]

1, 21 ... Substrate, 2, 22 ... Buffer layer, 3, 23 ... Undoped low refractive index layer,
4, 24 ... Undoped high refractive index layer, 5, 25 ... Undoped Bragg reflecting mirror, 6, 26 ... Electron injection layer, 7, 27
... Strained quantum well layer, 8, 28 ... Hole injection layer, 9 ... P-type low refractive index layer, 10 ... P
Type high refractive index layer, 29 ... undoped low refractive index layer,
30 ... Undoped high refractive index layer, 11 ... P-type Bragg reflector, 12 ... P-type cap layer, 31 ... Undoped Bragg reflector, 13, 32 ... P-type electrode,
14, 33 ... SiO ₂ , 15, 34 ...
n-type electrode.

Front page continuation (72) Inventor Yoshihiro Ishitani 1-280, Higashi Koigokubo, Kokubunji, Tokyo Inside Hitachi Central Research Laboratory (72) Inventor Shinji Tsuji, 1-280 Higashi Koikeku, Tokyo Kokubunji City Inside Hitachi Research Laboratory

Claims (17)

[Claims] 1. A Bragg reflector, which is formed by periodically forming on a substrate an active layer which is at least a wurtzite semiconductor and at least two kinds of semiconductor layers having different refractive indexes by crystal growth, and the growth thereof. A surface emitting type semiconductor laser device which emits light in a direction parallel to the direction. 2. A Bragg reflector, which is formed by periodically forming on a substrate an active layer which is at least a wurtzite type semiconductor and at least two kinds of semiconductor layers having different refractive indexes by crystal growth. In a surface emitting semiconductor laser emitting light in a direction parallel to the direction, the growth direction is parallel to the [0001] axis or an axis inclined by 5 ° or more from an axis equivalent to the [0001] axis. . 3. A Bragg reflector, which is formed by periodically forming on a substrate an active layer which is at least a wurtzite semiconductor and at least two kinds of semiconductor layers having different refractive indexes by crystal growth, and the growth thereof. In a surface-emitting type semiconductor laser that emits light in a direction parallel to the direction, the growth direction is 10 ° from the [0001] axis or an axis equivalent thereto.
A semiconductor laser device characterized in that it is parallel to the inclined axis. 4. A Bragg reflector, which is formed by periodically forming on a substrate an active layer which is at least a wurtzite semiconductor and at least two kinds of semiconductor layers having different refractive indexes by crystal growth, and the growth thereof. In a surface-emitting type semiconductor laser emitting light in a direction parallel to the direction, the growth direction is parallel to an axis having a deviation of 5 ° or less from the [0001] axis or an axis equivalent thereto. Laser device. 5. A Bragg reflector, which is formed by periodically forming, on a substrate, an active layer which is at least a wurtzite semiconductor and at least two kinds of semiconductor layers having different refractive indexes are formed by crystal growth. In a surface-emitting type semiconductor laser that emits light in a direction parallel to the direction, the growth direction is 5 ° from the [10-10] axis or an axis equivalent thereto.
A semiconductor laser device characterized in that it is parallel to an axis having a deviation within. 6. A Bragg reflector, which is formed by periodically forming on a substrate an active layer of at least a wurtzite semiconductor and at least two kinds of semiconductor layers having different refractive indexes by crystal growth, and growing the crystal. In a surface-emitting type semiconductor laser that emits light in a direction parallel to the direction, the growth direction is 5 ° from the [11-20] axis or an axis equivalent thereto.
A semiconductor laser device characterized in that it is parallel to an axis having a deviation within. 7. A Bragg reflector, which is formed by periodically forming on a substrate an active layer which is at least a wurtzite semiconductor and at least two kinds of semiconductor layers having different refractive indexes by crystal growth, and the growth thereof. In a surface emitting semiconductor laser that emits light in a direction parallel to the direction, the growth direction is 5 ° from the [10-11] axis or an axis equivalent thereto.
A semiconductor laser device characterized in that it is parallel to an axis having a deviation within. 8. A binary, ternary or quaternary compound in which the semiconductor constituting the Bragg reflector is formed of any of B, Al, Ga, In, N, P, As and Sb. The semiconductor laser device according to claim 1, which is a semiconductor. 9. two semiconductor layers constituting the Bragg _{reflector, In X Ga 1-X N} (0 ≦ x ≦ 1), and the _{In X Ga 1-X N (} 0 ≦ x ≦ InG lattice-matched to 1)
The semiconductor laser device according to claim 1, which is aAlN. 10. Two semiconductor layer constituting the Bragg _{reflector, In X Ga 1-X N} (0 ≦ x ≦ 1), and the _{In X Ga 1-X N (} 0 ≦ x ≦ In lattice-matched to 1)
The semiconductor laser device according to claim 1, which is AlN. 11. Two semiconductor layer constituting the Bragg _{reflector, In X Ga 1-X N} (0 ≦ x ≦ 1), and the _{In X Ga 1-X N (} 0 ≦ x ≦ Ga lattice-matched to 1)
The semiconductor laser device according to claim 1, which is AlNP. 12. Two types of semiconductor layers constituting the Bragg _{reflector, In X Ga 1-X N} (0 ≦ x ≦ 1), and the _{In X Ga 1-X N (} 0 ≦ x ≦ Al lattice-matched to 1)
The semiconductor laser device according to claim 1, which is an NP. 13. Two semiconductor layer constituting the Bragg _{reflector, In X Ga 1-X N} (0 ≦ x ≦ 1), and the _{In X Ga 1-X N (} 0 ≦ x ≦ Ga lattice-matched to 1)
The semiconductor laser device according to claim 1, which is AINAs. 14. Two semiconductor layer constituting the Bragg _{reflector, In X Ga 1-X N} (0 ≦ x ≦ 1), and the _{In X Ga 1-X N (} 0 ≦ x ≦ AI lattice-matched to 1)
The semiconductor laser device according to claim 1, wherein the semiconductor laser device is NAs. 15. The thickness d of the region including the active layer sandwiched between the Bragg reflectors is 0.4 when the Bragg reflectors are provided above and below the active layer and the emission wavelength in the semiconductor is λ.
The semiconductor laser device according to claim 1, wherein λ ≦ d ≦ 0.6λ. 16. The Bragg reflector is provided above and below the active layer, and the thickness d of the region including the active layer sandwiched between the Bragg reflectors is 0.9 when the emission wavelength in the semiconductor is λ.
The semiconductor laser device according to claim 1, wherein λ ≦ d ≦ 1.1λ. 17. The active layer has a strained quantum well structure,
The well layer having a thickness smaller than 8 nm.
6. The semiconductor laser device according to any one of 6 above.