JPH05343813A - Quantum-well-structure semiconductor laser and manufacture thereof - Google Patents

Abstract

PURPOSE:To prevent that an edge is destroyed due to instantaneous optical damage and to achieve the high output of a laser device by a method wherein a quantum well-type active layer is formed in such a way that its stripe width is made gradually narrow toward the inside and the thickness of an active layer is made thick with reference to the stripe width and the thickness on the edge side of a resonator. CONSTITUTION:When carriers are injected into an active region in an active layer 8, light is emitted, by the recombination of electrons and holes, at a light-emitting wavelength which is decided by a quantum well width and a material composition, it is reflected anal amplified between two edges of a resonator and a laser is oscillated. A pattern width is made wide on the edge side in such a way that a stripe width 2b in the active layer 8 on the edge side becomes larger than a stripe width 2a at the inside of the resonator; a crystal is grown in such a way that it is thin on the edge side (an energy band gap becomes large) and the it is thick at the inside of the resonator (the energy band gap becomes large). Thereby, the threshold value by instantaneous optical damage at the edge of the resonator can be increased, an edge structure which is easy to destroy is prevented and the high output of a laser beam can be achieved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly reliable and high power semiconductor laser device and a manufacturing method thereof.

[0002]

2. Description of the Related Art In a normal semiconductor laser in which the end face of a resonator is not specially processed, a high output cannot be obtained due to deterioration of the end face. A so-called window structure has been proposed as one method of increasing the output. In this, as shown in FIG. 5, the end face of the resonator is provided with a region having a band gap energy higher than that of the inside of the resonator and being transparent to the resonance light.

A conventional technique will be described with reference to FIG. On the n-type GaAs substrate 22, the n-type AlGaAs first clad layer 23, the n-type AlGaAs active layer 24, and the n-type AlGaA.
The s-type second cladding layer 25 is crystal-grown. Then 2
A p-type impurity such as zinc is selectively diffused only inside the resonator away from the two end faces 14 and 15 to form a p-type diffusion region 28 shown by a shaded portion in FIG. 5, and n-type AlGa is formed from the surface.
A double hetero structure is formed by forming the p-type up to the As active layer 24. The n-type electrode 21 is provided on the lower surface of the laminated structure thus formed, and the p-type electrode 27 is provided on the upper surface of the insulating film 26.
Provided through.

Generally, in the case of the same material, the n-type has a larger effective energy band gap than the p-type, so that a window structure transparent to resonance light is formed in the vicinity of the end faces 14 and 15. It will be.

[0005]

However, in the conventional example shown in FIG. 5, the n-type AlGaAs active layer 24 is heavily doped with p-type impurities. In other words, since the active layer itself, which is the central part of the light emitting action in the semiconductor laser, is heavily doped, (a) deterioration of crystallinity,
(B) There are problems such as an increase in oscillation threshold current due to an increase in free carrier absorption, a decrease in oscillation efficiency accompanying this, and (c) a decrease in reliability. Further, in order to obtain a pn junction at the boundary between the n-type clad layer and the active layer, (d)
It has a drawback that it is very difficult to control the impurity diffusion in the manufacturing process.

Therefore, the present invention has been made to solve the above problems, and an object thereof is to provide a highly reliable and high power semiconductor laser device.

[0007]

According to the present invention, there is provided a semiconductor laser device having an active layer having a single or multiple quantum well structure and having a first end face and a second end face. There is provided a semiconductor laser device characterized in that an energy band gap value of an active layer on an end face side corresponding to at least one of the two end faces is larger than an energy band gap value of an active layer at a central portion.

A buffer layer, a first layer and a first layer are formed on the semiconductor substrate.
A clad layer, an active layer having a single or multiple quantum well structure or a layer in which the active layer is sandwiched by first and second graded index layers, a second clad layer, and a cap layer are stripe-shaped in this order. In the method for manufacturing a semiconductor laser device in which a p-type electrode and an n-type electrode are provided on both sides so as to sandwich the laminated structure thus formed, the active layer is formed. An insulating mask having a non-rectangular mask hole in which the width of at least one end of the mask hole of the used insulating mask is thicker than the width of the central portion of the mask hole is used, and the active layer is formed by the selective crystal growth method. A method of manufacturing a semiconductor laser device is provided.

[0009]

In the semiconductor laser device according to the present invention, the bandgap energy of the active region at the end face of the resonator having the laminated structure is made relatively larger than that at the central part to form a window structure and instantaneous optical damage at the end face. (COMD: Catascopic Optical
The threshold of the Mirror Image can be increased. Furthermore, it is possible to form an active layer or the like without using a diffusion process.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing a top view of an embodiment of the present invention and a graph showing a corresponding emission energy state. In this top view, the stripe portion is schematically shown in which the portion located on the end face side is thick and the central portion side is relatively thin. FIG. 2 is a sectional view taken along the line AA ′ of FIG. FIG. 3 is a sectional view taken along the line BB ′ of FIG. 2 and 3 also schematically show a cross section of the laminated structure. Note that the thickness of the stripe portion is emphasized for the sake of understanding.

Description will be made with reference to FIG. An inverted trapezoidal groove is formed on the GaAs n-type substrate 2 by dry etching or wet etching using an insulating mask of SiO2, Si3 N4 or the like. At this time, the width of the insulating mask is wide at the end face portion of the resonator, and narrowed inside the end face of the resonator.

After that, MO-CVD (Metal-Or
ganic CVD), MBE (Molecular)
The following laminated structure is formed using a selective crystal growth technique such as beam epitaxy (molecular beam epitaxy) or MO-MBE.

First, the buffer layer 5 made of n-type GaAs,
a first cladding layer 6 made of n-type Al0.5 Ga0.5 As,
Undoped AlX Ga1-X As (X = 0.2 to 0.5)
The first graded index layer 7 (Gra
A ded-Index layer, a refractive index changing layer, which is hereinafter abbreviated as GRIN layer), and a non-doping MQW (Mul).
active layer 8 having a Ti Quantum Well: multiple quantum wells, non-doped AlY Ga1-Y As (Y =
0.2-0.5) second GRIN layer 9, p-type Al
Second cladding layer 10 made of 0.5 Ga0.5 As, p-type G
The cap layer 11 made of aAs is grown.

Further, a p-type electrode 4 and an n-type electrode 1 are formed. Since the ends of the p-type electrode 4 on the upper surface are formed only inside the resonators apart from the two end faces of the resonator, non-radiative recombination, which is a negative factor in the laser emission operation, can be suppressed. it can. It is also possible to further insert a buffer layer such as a superlattice between the first buffer layer 5 and the first cladding layer 6 to improve the crystallinity. 1G
The laser emission operation is possible without providing the RIN layer 7 and the second GRIN layer 9. In terms of the light emission threshold value, it is preferable to provide the threshold value.

After providing such a laminated structure, the laminated structure is cleaved to a desired resonator length, and the end face (which becomes the emitting end face) in the laser light extraction direction has a reflectance of about 10%. The low reflection film 12 (hereinafter abbreviated as AR film)
The end face, which is located on the opposite side and is a non-emission end face, is coated with a reflection film 13 (hereinafter, abbreviated as HR film) having a reflectance of about 90% to increase the output of laser light and oxidize the end face itself. We are taking precautions.

In FIG. 3, the thickness of the stripe portion on the central portion side is relatively thicker than that on the end surface side, and therefore the drawing is emphasized as if it is raised on the central portion side from the end surface side. Correspondingly, in FIG. 2, the cap layer 1
It is assumed that the slope portion 1 (between the cross section and the p-type electrode) is visible immediately above the cross section. In reality, it is a laminated structure that is macroscopically almost flat. Further, a protective film may be further provided on the surface of the cap layer 11 that does not directly contact the p-type electrode 4.

Next, the basic operation of this semiconductor laser device will be described. A positive voltage is applied to the p-type electrode 4, and n
A negative voltage is applied to the mold electrode 1. In this embodiment, the p-type electrode 4 acts as a current injection electrode. The current is limited to the groove on the inverted trapezoid and the active layer 8 having the non-doped MQW is formed.
In the active region corresponding to the p-type electrode 4. When carriers are injected into the active region of the active layer 8, electrons and holes are recombined to emit light at an emission wavelength determined by the quantum well width and the material composition, and the emitted light is emitted between the two end faces of the resonator. It is reflected and amplified, and laser oscillation occurs when it exceeds a certain current value, a so-called oscillation threshold value.

The relation between the well width of a quantum well such as GaAs or AlGaAs and its emission energy is that the emission wavelength becomes longer (the emission energy becomes smaller) as the quantum well width becomes larger. Then, depending on other conditions, when the quantum well width exceeds 20 nm, the change in emission wavelength tends to saturate and approaches a certain value. For example Ga
Taking As as an example, the characteristics as shown in FIG. 4 are shown.

In the semiconductor laser shown in FIG. 1, for example, the quantum well width of GaAs is 6n on the end face side of the resonator.
m, and 8.6 nm inside the resonator (center part with respect to the end face side). With this structure, the difference in emission energy between the end face side and the central portion is ΔE = about 40 meV (millielectron volt), which can be increased on the end face side of the resonator.

As described above, a crystal having a different quantum well width depending on the part of the active layer can be realized by using a selective crystal growth technique such as MO-CVD or MO-MBE. That is, as shown in FIG. 1, the stripe width of the active layer 8 on the end face side is 2b, the stripe width is 2a inside the resonator, and the pattern width on the end face side is widened so that 2b> 2a. , Wide in the portion (end face side), thin (that is, energy band gap = large Eg). Crystals can be grown thick (that is, energy bandgap = small Eg) in a narrow portion (inside the resonator).

Since crystal growth does not occur on the insulating mask, the raw material species present in the vapor phase on the insulating mask diffuse laterally in the vapor phase and reach the growth region to contribute to the growth. Is. That is, the larger the mask width and the smaller the mask hole (that is, the larger the proportion of the mask), the thicker the growth.

The shape is shown in FIG. The width at the end face of the stripe-shaped structure to be stacked in the groove provided in the n-type substrate 2 is set to about 2b, and the width at the center is set to about 2.
a. The BB ′ cutting line also serves as the center line, and W represents almost ½ of the width of the semiconductor laser device having the laminated structure. Therefore, by changing the dimensional ratio of W, a, and b shown in FIG. 1, the end face side (a <b <W) can be made thin and the inside of the resonator (the center part with respect to the end face side) can be made thicker, and the window The structure is formed.

At the same time, since the waveguide region is gradually widened on the end face side of the resonator, the light density can be reduced. This shape is almost determined by the shape of the mask hole. Instantaneous optical damage (COMD) due to the above effects
Can be improved by about one digit compared to the conventional one. Further, since the pattern width is gently changed inside the resonator and on the end face side, it is possible to simultaneously reduce the waveguide loss.

In this embodiment, the stripe width is gradually changed into a curved shape as shown in FIG. 1, but the stripe width may be changed into a linear shape. Further, it may be of a type that opens more as it approaches the end face.

In the above embodiment, the multiple quantum well type (MQ
However, the active layer may be a single quantum well (SQW). Not only the FP type semiconductor laser as shown in the embodiment but also a DBR provided with a diffraction grating or a DFB type laser can be applied. Further, the stripe structure can be applied to structures other than those shown in the embodiments, for example, stripes such as buried type and planar type.

[0026]

As described above, according to the present invention, the threshold value of the instantaneous optical damage (COMD) on the end face of the resonator can be increased, the end face structure which is easily destroyed can be protected, and the output power of laser light can be increased. Can be achieved, and the reliability of the semiconductor laser device can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram corresponding to a top view of a first embodiment and a graph showing a light emission energy state.

FIG. 2 is a sectional view of the first embodiment as viewed from the front (BB ′ cutting line).

FIG. 3 is a cross-sectional view of the first embodiment as seen from the side surface (cut line AA ′).

FIG. 4 is a graph showing the relationship between the quantum well width of GaAs and the emission energy.

FIG. 5 is a side view showing a window structure in a conventional example.

[Explanation of symbols]

 1: n-type electrode 2: n-type substrate 3: insulating film 4: p-type electrode 5: buffer layer 6: first cladding layer 7: first graded index layer 8: active layer 9: second graded index Layer 10: Second clad layer 11: Cap layer 12: Low reflection film 13: Reflection film

Claims (5)

[Claims] 1. A semiconductor laser device comprising a single or multiple quantum well structure active layer and having a first end face and a second end face, which corresponds to at least one of the first end face and the second end face. A semiconductor laser device characterized in that the energy band gap value of the active layer on the end face side is larger than the energy band gap value of the active layer in the central portion. 2. The semiconductor laser device according to claim 1, wherein at least one end of a current injection electrode for injecting a current into the active layer is provided so as not to contact the first end face or the second end face. A semiconductor laser device, wherein carriers are injected in an active region of an active layer corresponding to an electrode. 3. The thickness of the active layer is made thinner on at least one end face side than on the central portion.
Or the semiconductor laser device of 2. 4. The semiconductor laser device according to claim 1, wherein a low reflection film is provided on one end face and a reflection film is provided on the other end face. 5. A buffer layer, a first cladding layer, an active layer having a single or multiple quantum well structure, or a layer in which the active layer is sandwiched between first and second graded index layers on a semiconductor substrate. , A second clad layer, and a cap layer are formed in this order in a stripe shape by a vapor deposition method, and p is formed so as to sandwich the laminated structure thus provided.
In a method for manufacturing a semiconductor laser device having a mold electrode and an n-type electrode on both sides, at least one end of a mask hole of an insulating mask used for forming the active layer has a width larger than a width of a central portion of the mask hole. A method for manufacturing a semiconductor laser device, which comprises using an insulating mask having a thick non-rectangular mask hole and forming an active layer by a selective crystal growth method.