JP2912482B2 - Semiconductor laser - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a III-V compound semiconductor laser.

[0002]

2. Description of the Related Art Among conventional semiconductor lasers of this type, A
A typical example of an lGaAs / GaAs laser is shown in FIG. 8 as a cross-sectional view (JJ Coleman, Applie).
d Physics Letter, Vol. 3
Pages 262 to 263, FIG. 1).
In this figure, A1 is an n-GaAs substrate, A2 is an n-GaAs substrate.
_{Al x Ga 1 - x As (} x = 0.35) lower cladding layer,
A3 is GaAs active layer, A4 is _{p-Al x Ga 1 - x} A
s (x = 0.35) upper cladding layer, A5 is n-GaAs
Current confinement and optical horizontal transverse mode confinement layer (hereinafter, the current-optical confinement layer), A6 is _{n-Al x Ga 1 - x} As (x =
0.35) Second upper cladding layer, A7 is a p-GaAs contact layer. Hereinafter, a manufacturing method will be briefly described. n-
N-AlGaAs lower cladding layer A on a GaAs substrate A1
2. A GaAs active layer A3 and a p-AlGaAs upper cladding layer A4 are continuously grown. Next, a channel having a width of 4 μm is imprinted on the n-GaAs current / light confinement layer. Then, n
-AlGaAs second upper cladding layer A6 and p-GaAs contact layer A7 are sequentially grown. All of the above crystal growth is performed by metal organic chemical vapor deposition (MOCVD).

Next, the operation will be described. p-GaAs
When a voltage is applied between the s-contact layer A7 and the n-GaAs substrate, a forward current flows through the pn junction including the active layer A3 in the stripe portion where the n-GaAs current / light confinement layer A5 is removed. On the other hand, in a region including the current / light confinement layer A5, a pnpn junction is formed, and a current does not flow because a reverse bias is applied between the current / light confinement layer A5 and the upper cladding layer A4. Thus, the current is confined within the stripe. In the region including the current / light confinement layer A5, the laser beam is confined in the stripe because the equivalent refractive index becomes smaller than that in the channel inner layer due to light absorption in the layer.

[0004] Next, another conventional example is shown in FIG.
Amoto et al., Applied Physics Le
ters Vol. 40, No. 3, 372 pages 1982
Year). In the figure, B1 is a p-GaAs substrate, B2 is n-Ga
As the current-optical confinement layer, B3 is _{p-Al x Ga 1 - x} A
s (x = 0.4) bottom cladding layer, B4 is Al _x Ga _{1 - x}
As (x = 0.13) active layer, B5 is p-Al _x Ga <sub>1
- x</sub> As _(x = 0.4) upper cladding layer, B6 is p-G
This is an aAs contact layer.

Next, a brief description will be given of a manufacturing method.
p-Ga having grown n-GaAs current / light confinement layer B2
A 4 μm channel is formed on the As substrate B1 by p-GaAsB.
Mark until 1 is reached. Next, a lower cladding layer B3, an active layer B4, an upper cladding layer B5, and a contact layer B6 are sequentially laminated. The crystal growth method of this conventional example is a liquid phase growth method (LPE
Law). The current confinement and light confinement mechanisms of the laser are the same as those of the laser of FIG.

In the above two conventional examples, the current / light confinement layer is a single layer of n-GaAs. Next, the current
Conventional example in which a plurality of light confinement layers are provided (Japanese Patent Laid-Open No. 1-3047)
No. 93) is shown in FIG. C1 is an n-GaAs substrate, C
2 is an n-AlGaAs lower cladding layer, C3 is an active layer, C
4 is a p-AlGaAs upper cladding layer, C5 is n-GaAs
s meltback layer, C6 is _{n-Al x Ga 1 - x} As
(X = 0.4) Etch stop layer, C7 is n-GaAs
Current blocking layer, C8 is _{n-Al x Ga 1 - x} As (x
= 0.4) Anti-melt back layer, C9 is n-GaAs
A melt back layer, C10 is a p-AlGaAs cap layer, and C11 is a p-GaAs contact layer. The fabrication method is almost the same as that of FIG. 8, but selective etching is performed to improve the controllability of the stripe depth. Because of this, C6
Layers are attached. Further, in order to prevent deterioration of the regrowth interface at the time of the second growth, a C5 n-GaAs layer is provided, and at the time of the second growth, C5 is removed by melt-back. Therefore, the second growth is LPE
Perform by the method. The C8 layer is a layer for preventing the C7 current block layer from being melted back during the meltback, and the C9 layer is for facilitating regrowth on the C8 layer.

Next, another conventional example having a plurality of current / light confinement layers (H. Ishikawa et al., Applied
Physics Letters Vol. 36 No. 7 5
20 (1980) is shown in FIG. In the figure, D1 is n
-GaAs substrate, D2 is _{p-Al x Ga 1 - x} As (x
= 0.32, d _{D 2} = 0.7 μm) current / optical confinement layer,
D3 is _{n-GaAs (d D 3 =} 0.1~0.2μm) optical confinement layer, D4 is _{n-Al x Ga 1 - x} As (x =
0.32) cladding layer, D5 is _{p-Al x Ga 1 - x} A
s (x = 0.05) active layer, D6 is p-Al _x Ga _{1 −
An} xAs (x = 0.32) cladding layer and a p-GaAs contact layer. The manufacturing method is almost the same as the example of FIG. 10 except that the current and light confinement layers are two layers.

[0008]

A conventional semiconductor laser has a structure as shown in FIGS. 8 to 11 and is currently in practical use. However, the present inventors have studied the above-described semiconductor laser in detail, and as a result, have found that there are the following four serious problems.

(Problem 1) In the conventional example shown in FIGS.
The current confinement mechanism is n-GaAs outside the stripe channel.
It depends on the pn reverse bias between the s-current / light confinement layer and the cladding layer. FIG. 4 shows a band diagram of the pnpn junction in this region at the time of thermal equilibrium. 8 and 9, the materials of the respective layers and the mixed crystal ratios are different, but the relative magnitude relation of the forbidden band width is the same. As will be described later, E _{g 2} of the current / light confinement layer is sufficiently smaller than E _{g 1 of the} active layer due to a request for light confinement. The current is n-GaAs for the p-side cladding layer.
The hole in the p-side cladding layer does not flow due to the valence band barrier of the current / light confinement layer, so that the layer is narrowed. In the conventional example, the current / light confinement layer is n-GaAs and E _{g 2} = 1.42 eV.
And the barrier height is not large. Also, E _{g 1} ≧ E _{g 2}
Therefore, laser light is absorbed in the current / light confinement layer. The holes generated as a result of absorption, which are minority carriers in the hole-hole pairs, diffuse and disappear from the current / light confinement layer, leaving only electrons. Therefore, the layer is turned on by the phototransistor operation and the current is confined. No function is lost. In the prior art, the thickness of the current / light confinement layer had to be greater than the minority carrier diffusion length so that the above-mentioned operation did not occur. For this reason, the diffusion length is short (〜1 μm).
m) Even if n-GaAs is used so that holes serve as minority carriers, the thickness of the current / light confinement layer needs to be as thick as about 1 μm. In order to obtain p-GaAs, the diffusion length of electrons is long (長 く 2 μm), and it is necessary to further increase the thickness. For this reason, it turned out that a layer structure has a remarkable restriction | limiting. For this reason, the current / light confinement layer is as thick as 1 μm,
It has been found that, when a stripe is imprinted through this, the etching time is long, so that the side etch amount on the stripe side wall becomes large, and there is a problem that the stripe width becomes wider than a desired stripe width.

(Problem 2) The above-mentioned four conventional semiconductor lasers are confined in the horizontal and transverse modes by absorption of the laser light by an n-GaAs current / light confinement layer. That is, the following relationship exists between the real component ε _r of the complex permittivity ε of each layer, the refractive index n, and the extinction coefficient κ.

[0011] ^{_{ε r / ε 0 = n 2}} -κ eventually equivalent refractive index so than epsilon _r decreases above formula refractive index i.e. the equivalent refractive index sensed by the ^second mode is dependent on the complex dielectric constant but absorbing layer of each layer Become smaller. For this reason, the equivalent refractive index outside the stripe is smaller than the equivalent refractive index inside the stripe, and the horizontal transverse mode is confined within the stripe. However, in the conventional examples shown in FIGS. 8 and 9, the current / light confinement layer must be thickened to about 1 μm for the reason described in the above problem 1, so that the trapped transverse mode receives unnecessary excess absorption. I will. Also, Figure 10 the _{C6 n-Al x Ga 1 -} x As (x = 0.4) is primarily because the etch stop layer is capable thin n-GaAs layer. However, since this problem is not considered at all until pointed out in the present invention, the thickness d of the n-GaAs layer is set to 0.3 ≦ d ≦ 2 μm. As described later, the thickness of the absorption layer is １ ／ of the reciprocal of the absorption coefficient (α) at the laser oscillation wavelength of the layer (0.25 at λ = 780 nm).
μm) or less, excessive absorption occurs.
In the embodiment of the present invention, the horizontal and transverse modes still receive excessive absorption.

For the reasons described above, it has been found that the absorption loss in the horizontal and transverse modes is excessive in the conventional example. If the mode loss is large, the external differential quantum efficiency becomes small, so that the driving current becomes large at the time of high output operation, which is disadvantageous in reliability. Therefore, it was found that if the mode loss can be reduced to an appropriate value, it is effective for improving the reliability of the high output operation.

(Problem 3) In the conventional example shown in FIG. 11, the D3 layer has the same conductivity type as the D4 layer, and has no current confinement effect. Therefore, the current spread to the active layer is large. Further even as different conductivity type D3, layer thickness d _{D 3} = 0.1 to
Since it is as thin as 0.2 μm, it is turned on as described in Task 1 and has no current confinement effect. Further, the equivalent refractive index difference inside and outside the stripe and the mode loss that determine the behavior of the horizontal and transverse modes are uniquely determined by the layer thickness of the D3 layer and the layer thickness of the D4 layer, as described in detail in the reference paper. As a result, the desired equivalent refractive index difference inside and outside the stripe could not be controlled independently of the mode loss.

(Problem 4) As described in the above-mentioned problem 2, since the mode absorption loss outside the stripe is large, the wavefront outside the stripe is significantly delayed from the electric field wavefront inside the stripe. The wavefront delay causes astigmatic difference and has an adverse effect on the imaging characteristics.

[0015]

Means for Solving the Problems The first invention of the present application has been made to solve the above-mentioned problems, and has a first conductive type clad layer and a forbidden band width Eg ₁ on a first conductive type substrate. In the non-embedded internal stripe semiconductor laser including the active layer, the second conductivity type cladding layer, and the second conductivity type contact layer, a layer group (hereinafter referred to as a current / light confinement layer) for confining current confinement and optical horizontal / lateral mode is provided. the forbidden band width Eg ₂ in order to close the active layer, the forbidden band width Eg _3, made of successive two or more layers of the _{Eg 2 ≧ Eg 1 ≧ Eg 3} , wherein the current-optical closed
The carrier generated by Eg ₃ in the confined layer is
In front of the confinement layer, a valence band barrier with a forbidden band width of Eg ₂
The layer thickness of the current / light confinement layer group is set such that diffusion into the second conductivity type clad is suppressed and the equivalent refractive index of the vertical transverse mode outside the stripe is smaller than the equivalent refractive index inside the stripe. Is set in the current / light confinement layer.
The thickness of the band gap Eg ₃ is determined by the laser oscillation wavelength of the layer.
The semiconductor laser is characterized in that the reciprocal of the absorption coefficient is 1/2 or less .

Further, the second invention of the present application is directed to a _first conductive type clad layer, an active layer having a forbidden band width Eg _1, a second conductive type clad layer, and a second conductive type contact layer on a first conductive type substrate. in a more becomes non-embedded type internal stripe semiconductor laser, current confinement and the optical horizontal transverse mode confinement layer group (hereinafter the current-optical confinement layer) is forbidden band width Eg ₂ in order of proximity to the active layer, the forbidden band width Eg _3, made of three or more layers of successive forbidden band width Eg _4, Eg ₂ and ≧ Eg ₁ ≧ Eg ₃ and _{Eg 4 ≧ Eg 1 ≧ Eg 3} , occurs in Eg ₃ of the current-optical confinement layer Career
Of the current / optical confinement layer having a forbidden band width of Eg ₂ .
A diffusion barrier suppresses diffusion to the second conductivity type clad,
And setting the layer thickness of the current / light confinement layer group such that the equivalent refractive index of the vertical transverse mode outside the stripe is smaller than the equivalent refractive index inside the stripe. To provide.

Further, the present invention provides a semiconductor laser in which the thickness of the forbidden band width E _{g 3 in} the current / optical confinement layer is not more than の of the reciprocal of the absorption coefficient at the laser oscillation wavelength of the layer. is there.

The forbidden band width Eg ₅ ≧ forbidden band width Eg ₂
And a semiconductor laser having the following relationship.

[0019]

According to the first aspect of the present invention, in the case of a laser structure having a cladding layer on the opposite side of the active layer from the current / light confinement layer, the bandgap is larger than that of the active layer and is transparent to laser light. For the current / light confinement layer consisting of two layers, a laser layer and a laser light absorption layer, the transparent layer having a large forbidden band width prevents the diffusion of minority carriers generated by the light absorption, thereby preventing the turn-on phenomenon. it can, further, (because there is no need to over diffusion length of minority carriers) the thickness of the absorbing layer by the child small, the mode loss can be set to appropriate value. Furthermore, by appropriately combining the thicknesses of the two layers, the transmission refractive index inside and outside the stripe can be arbitrarily set independently of the mode loss amount.

Further, in the second invention, the electric current
In the case of a laser structure having an absorption layer such as a substrate on the opposite side of the active layer with the light confinement layer interposed therebetween, the first current / light confinement layer is formed as three layers, and the light absorption layer is sandwiched between transparent layers. A semiconductor laser having the same function and effect as the invention of the third aspect can be realized.

Further, the thickness of the inner absorption layer of the current / light confinement layer is set to の of the reciprocal of the absorption coefficient at the laser wavelength of the layer.
By doing the following, a semiconductor laser with reduced loss in the horizontal and transverse modes can be realized.

[0022]

FIG. 1 is a sectional view of a semiconductor laser according to a first embodiment of the present invention. This embodiment is invented as an improvement of the conventional example shown in FIG.

[0023] In FIG. 1, the n-GaAs substrate 101, 102 _{n-Al x Ga 1 - x} As (x = 0.5,
d _{1 0 1} = 1μm) cladding layer, 103 is Al _x Ga <sub>1
- x As (x = 0.13,</sub> d 1 0 3 = 0.1μm) active layer, 104 _{p-Al x Ga 1 - x} As (x = 0.5,
Stripe outer layer thickness d _{1 0 4} = 0.1μm) cladding layer,
105 _{p-Al x Ga 1 - x} As (x = 0.05, d
_{1 0 5} = 3nm) epi promoting layer, 106 p-Al _x Ga
_{1 - x As (x = 0.6} , d 1 0 6 = 30nm) etch stop layer, each of 107, 108, 109 n-Al _{x
Ga 1 - x As (x =} 0.2, d 1 0 7 = 0.1μ
m), n-GaAs (d 1 0 8 = 0.1μm), n-A
_{l x Ga 1 - x As (} x = 0.2, d 1 0 9 = 0.2μ
m), a current / light confinement layer consisting of n-GaAs 110
(D _{1 1 0} = 0.05nm) epi promoting layer, is 111 n-
_{Al x Ga 1 - x As (} x = 0.5, d 1 1 1 = 1μ
m) clad layer, 112 _{p-GaAs (d 1 1 2} = 1
μm) is a contact layer. The semiconductor laser of this embodiment oscillates at a wavelength of 780 nm.

Next, a manufacturing method will be described. n-GaAs10
On top of this, 102 to 110 layers are sequentially laminated. Next, 106
, A stripe having a width of 4 μm and a depth of about 0.4 μm is imprinted. At this time, if an ammonia-based etchant (NH ₄ OH: H ₂ O ₂ = 1: 10) is used, A
_{l x Ga 1 - x As (} x = 0.5) etch stop layer 1
Since 06 is not etched, the depth can be set with good controllability. Next, 106 in the stripe is removed with hydrofluoric acid (HF). In this _{case, p-Al x Ga 1 -} x As (x =
0.05) Since the epi-promoting layer 105 is not etched by HF, only 106 can be removed. Next, 111,
112 are sequentially laminated. The MOCVD method is used as the growth method. The oscillation wavelength is 780 nm.

Next, the function of this embodiment will be described. FIG. 2 shows only layers that are essential in this embodiment for the purpose of explaining the function.

First, the current confinement function will be described. Compared with the conventional example shown in FIG. 8 in this embodiment, n-Al _x Ga ₁ in the current-optical confinement layer _{- x As (x = 0.2)} 107 is attached. FIG. 3 shows a band diagram outside the stripe shown in FIG. Here, the magnitude relation of the forbidden band width of each layer is as follows.

[0027] E _g the _{2 ≧ E g 1 ≧ E g} 3, E g 5 ≧ E g 2 3 As is apparent from the comparison with FIG. 4, this embodiment is transparent to laser light _{(E g 2} ≧ E _{g 1} ) n-Al _x Ga
_{1 - x As (x = 0.2} ) for the current-optical confinement layer 107 is attached, the cladding on the barrier of the valence band of 107 layers of carriers generated light absorption (holes) in n-GaAs108 Diffusion to the layer side is suppressed, and even if the n-GaAs 108 is thin, it does not turn on and the restriction on the thickness of the layer is relaxed (solution of the problem 1).

Next, the confinement function in the transverse optical mode will be described. FIG. 5 shows the mode distribution and the refractive index distribution inside and outside the stripe of the laser structure of FIG. Outside the stripe, the cladding layers 102 and 104 having a low refractive index sandwich the active layer 103 having a high refractive index and the waveguides 104 and 111 sandwiching the n-GaAs 108.
The mode distribution has two peaks. Strictly speaking, "low refractive index" means that the refractive index of the layer is smaller than the mode equivalent refractive index.

Here, the refractive index of the 107 layer does not have to be low, and the aluminum mixed crystal ratio is made small (x) so that the refractive index of the layer is relatively large for extracting light from the active layer to the 108 layer. = 0.2) is set.

The equivalent refractive index according to the approximate horizontal transverse mode in the stripe (equivalent refractive index n _{e m,} α _m) is the equivalent refractive index n _{e i} of the vertical transverse mode in the stripe, the equivalent of the vertical transverse mode outside the stripe It depends on the refractive index _{ne o} , the mode loss α _o , and the width W of the stripe. In order to reduce the alpha _m general, alpha _o the equivalent refractive index difference between the stripes and out 2 × 10 with a smaller ^- may be increased to ² or more, because this is necessary to reduce the effective refractive index outside the stripe is there. However, as described in the above problem 2, α ₀ could not be reduced in the conventional example. This is because the thickness of the absorption layer (A5 layer in FIG. 8) is larger than the reciprocal of the absorption coefficient at the laser wavelength of the layer (that is, the penetration depth).
This is because α ₀ automatically increases.

Then, as a result of calculating the mode loss by changing the thickness of the absorbing layer in the structure of the present invention, the thickness of the absorbing layer is determined to be の of the reciprocal of the absorption coefficient (0.55 μm in this embodiment).
It has been found that the mode loss can be significantly reduced by setting it to the following level (in this embodiment, n-GaAs 108
The thickness of the layer was d _{1 0 8} = 0.1μm).

This embodiment (FIG. 2), the prior art A (in FIG. 8, d _{A 5} = 1.0 μm), and the prior art B (FIG. 9)
Where d _{C 6} = 0.1 μm, d _{C 7} = 0.3 μm, d
The equivalent refractive index and the like at _{C 8} = 0.4 μm) are described below.

[0033] This example prior art A conventional example _{B n e i 3.38635 3.38635 3.38635 n} e o 3.36414 3.36638 3.3842318 n e i -n e o 2.2 × 10 - 2 ^{2.2 × 10 - 2 2.1 × 10} - 3 α o (cm - 1) -1615.2 -4390.73 -1379.55 n e m 3.38529 3.38524 3.38524 α m (cm - ¹⁾ -10.6 -20.1 -41.7 wavefront lag 4.9 ° 9.3 ° 12.3 ° of the light intensity 1 / e ² Note that the prior art a, the cladding layer in the calculation of B, active The layers had the same mixed crystal ratio and layer thickness as in the present example. As described above, in the structure of this embodiment, the equivalent refractive index difference can be increased by appropriately setting the thicknesses of the two layers 107 and 108 and the aluminum mixed crystal ratio, and α _m is reduced by half compared to the conventional example. It can be set as small as １ ／ (solution of problem 2).

Further, it is possible to reduce the thickness of the current-optical confinement layer (1μm → 0.4μm) (solving the problem _1), d _D 1 ₀
The equivalent refractive index difference of the stripe out with a small mode loss independently of other structural parameters can be set to a desired value by setting the ₇ and d _{D 1 0 8} appropriately (solving problems 3).

Further, the wavefront delay that causes the astigmatic difference can be reduced to 1/2 to 1/3 of the conventional wavefront (solution of problem 4).

Next, 105, 106, 107, and 1 in FIG.
The functions of the additional layers 08 and 110 will be described. As described above, in order to set the stripe depth with good control, 10
5,106 layers are required. When laminating 111 and 112 layers, it is necessary to secure the quality of the regrown layer by using GaAs not containing aluminum for the growth interfaces inside and outside the stripe.
It is. The p-GaAs 105 has a layer thickness of 3 nm and has a larger forbidden band width than the active layer due to the quantum well effect, and does not become an absorption layer. Equivalent refractive index of the stripe and out (n _{e i,} n _e
o ), 109 increases the degree of freedom in setting the mode loss α _m .

FIGS. 6 and 7 are sectional views of a semiconductor laser showing a second embodiment of the present invention. In the figure, 401 is p-GaAs
s substrates, 402, 403, and 404 are each n-Al _x G
_{a 1 - x As (x =} 0.5, the layer thickness d _{4 0} = 0.2μ
m), n-GaAs (d 4 0 3 = 0.1μm), n-A
_{l x Ga 1 - x As (} x = 0.2, d 4 0 4 = 0.1μ
m), a current / light confinement layer composed of three layers, and 405 is nG
aAs epi promoting layer _{(d 4 0 5 = 0.05μm)} , 406
The _{p-Al x Ga 1 - x} As (x = 0.5, the stripe layer thickness d _{4 0 6} = 0.1μm) cladding layer, 407 A
_{l x Ga 1 - x As (} x = 0.13, d 4 0 7 = 0.1
[mu] m) active layer, 408 is _{n-Al x Ga 1 - x} As (x
_{= 0.5, d 4 0 8 =} 1μm) cladding layer, 409 an n
-GaAs is (d _{4 0 9} = 1μm) contact layer.
The growth was performed by the LPE method. The semiconductor laser of this embodiment also oscillates at a wavelength of 780 nm.

FIG. 7 shows only the layers essential for clarifying the function of each layer in the embodiment of FIG. FIG.
Although in the embodiment to sandwich the n-GaAs current-light confining layer with a low refractive index layer _{n-Al x Ga 1 - x} As (x =
0.5) 402 is required.

The functions of the other layers of the second embodiment are the same as those of the first embodiment.
The description is omitted because it is almost the same as the embodiment. Incidentally, 4
The layer 05 is added in order to secure the quality of the regrown layer by using GaAs not containing aluminum as the growth interface outside the stripe when the layers 406 to 409 are stacked.

Next, a third embodiment of the present invention will be described.
FIG. 1 is a cross-sectional view of a semiconductor laser according to the first embodiment.
, Except that the 106 layer in the figure is unnecessary, the description will be made with reference to FIG. In this embodiment, 101 is an n-GaAs substrate, and 102 is n- (A
_{l x Ga 1 - x) 0} · 5 In 0 · 5 P (x = 1.0, d
_{1 0 1} = _1μm) cladding layer, 103 (Al _x Ga <sub>1
- x) 0 · 5 In 0</sub> · 5 P (x = 0.0, d 1 0 3 =
0.1 μm) active layer, 104 is p- (Al _x Ga _{1 −)
x) 0 · 5 In 0 ·} 5 P (x = 1.0, the stripe layer thickness d _{1 0 4} = 0.1μm) cladding layer, the 105 (Al
_{x Ga 1 - x) 0 ·} 5 In 0 · 5 P (x = 0.0, d 1
_{0 5} = 3 nm) epitaxial promoting layer, 107, 108, and 109 are each _{n- (Al x Ga 1 - x} ) 0 · 5 In 0 · 5 P (x
_{= 0.1, d 1 0 7 =} 0.1μm), n-GaAs (d
_{1 0 8 = 0.1μm), n-} (Al x Ga 1 - x) 0 ·
_{5 In 0 · 5 P (x} = 0.2, d 1 0 9 = 0.1μm)
A current / light confinement layer made of n-GaAs (d
_{1 1 0} = 0.05nm) epi promoting layer 111 is n-(A
_{l x Ga 1 - x) 0} · 5 In 0 · 5 P (x = 1.0, d
_{1 1 1} = 1 μm) cladding layer, 112 is p-GaAs
It is a (d _{1 1 2} = 1μm) contact layer. The semiconductor laser of this embodiment oscillates at a wavelength of 670 nm. The growth method is the MOCVD method.

The manufacturing method is as follows. n-GaAs
On the s substrate 101, 102 to 110 layers are sequentially laminated.
Next, a stripe (width 4 μm, depth 1 μm) is imprinted. This inscription, 105 of _{p- (Al x Ga 1 - x} )
_{0 · 5 In 0 · 5 P} (X = 0.0) is sulfuric acid (H ₂ SO
₄ : H ₂ O ₂ = 1: 4) Since the stripes can be formed on the 105 layers with good control by utilizing the fact that they are not etched by the etchant, it is possible to form the stripes as described in the second embodiment.
6 of _{n-Al x Ga 1 - x} As (x = 0.6) etch stop layer is not required.

The materials of the structures of the first to third embodiments are respectively AlGaAs / GaAs, AlGaInP /
Although described as GaAs, these materials are applicable to all the structures.

[0043]

As described above, according to the present invention, the current confinement function of the semiconductor laser can be improved, the equivalent refractive index difference between the inside and outside of the stripe in the optical confinement structure can be changed in a wide range with good control, and the mode loss can be reduced. Since the astigmatic difference can also be reduced, a semiconductor laser having excellent low-drive current, high-output operation, and excellent optical characteristics can be provided.

[Brief description of the drawings]

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

FIG. 2 is a sectional view of a main part for explaining a function of the first embodiment of the present invention.

FIG. 3 is a band energy diagram of FIG. 2;

FIG. 4 is a band energy diagram of a conventional example.

FIG. 5 is a diagram showing an optical mode distribution inside and outside a stripe of the semiconductor laser according to the first embodiment of the present invention.

FIG. 6 is a sectional view of a semiconductor laser according to a second embodiment of the present invention.

FIG. 7 is a sectional view of an essential part for describing a function of a second embodiment of the present invention.

FIG. 8 is a sectional view of a conventional semiconductor laser.

FIG. 9 is a cross-sectional view of a conventional semiconductor laser.

FIG. 10 is a sectional view of a conventional semiconductor laser.

FIG. 11 is a sectional view of a conventional semiconductor laser.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Satoshi Sugawara 22-22 Nagaikecho, Abeno-ku, Osaka City Inside Sharpe Co., Ltd. (72) Inventor Mototaka 22-22 Nagaikecho, Abeno-ku, Osaka City Sharpe Co., Ltd. (56) reference Patent Sho 56-135994 (JP, a) JP Akira 63-222490 (JP, a) JP flat 2-181486 (JP, a) (58 ) investigated the field (Int.Cl. ⁶ , DB name) H01S 3/18

Claims (4)

(57) [Claims] 1. A first conductivity type cladding layer of the first conductivity type on a substrate, the active layer of the forbidden band width Eg _1, the inside of the second conductivity type cladding layer, a non-implantable made of the second conductive type contact layer In the striped semiconductor laser, a group of layers for confining current confinement and an optical horizontal transverse mode (hereinafter referred to as a current / optical confinement layer) in the order of approaching the active layer has two consecutive forbidden band widths Eg ₂ and Eg ₃ . Eg ₂ ≧ Eg ₁ ≧
Eg ₃ and the carrier generated by Eg ₃ in the current / light confinement layer
Of the current / optical confinement layer having a forbidden band width of Eg ₂ .
A diffusion barrier suppresses diffusion to the second conductivity type clad,
And stripe external equivalent refractive index of the vertical transverse mode sets the thickness of the current-optical confinement layer group to be smaller than the effective refractive index of the inner stripe of the current-optical confinement layer The layer thickness of the forbidden band width Eg ₃ is
The reciprocal of the absorption coefficient at the laser oscillation wavelength of the layer is 1 /
2. A semiconductor laser characterized by being 2 or less . 2. A cladding layer of the first conductivity type to the first conductivity type on a substrate, the active layer of the forbidden band width Eg _1, a second conductivity type cladding layer, of the non-embedded type made of the second conductive type contact layer
In Part stripe semiconductor laser, current confinement and the optical horizontal transverse mode confinement layer group (hereinafter the current-optical confinement layer) bandgap Eg ₂ in the order of proximity to the active layer, the forbidden band width Eg _3, the forbidden band And three or more continuous layers having a width of Eg ₄ , wherein Eg ₂ ≧ Eg ₁ ≧ Eg ₃ and Eg ₄ ≧ Eg ₁ ≧ Eg _3, and carriers generated in Eg ₃ of the current / light confinement layer
Of the current / optical confinement layer having a forbidden band width of Eg ₂ .
A diffusion barrier suppresses diffusion to the second conductivity type clad,
And a layer thickness of the current / light confinement layer group is set such that an equivalent refractive index in a vertical transverse mode outside the stripe is smaller than an equivalent refractive index inside the stripe. 3. The forbidden band width E of the current / light confinement layer.
The thickness of the g ₃ is claim 2, characterized in that less than half of the reciprocal of the absorption coefficient at the lasing wavelength of the layer
4. The semiconductor laser according to claim 1. 4. The function of the forbidden band width Eg ₅ ≧ forbidden band width Eg ₂ .
To any one of claims 1 to 3, feature that it is engaged
A semiconductor laser as described in the above.