JP3251771B2 - 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 semiconductor laser, and more particularly, to a semiconductor laser in which an active layer has a composition containing a group V element, and an optical waveguide layer and a cladding layer have a composition containing a group V element and a group III element. The present invention relates to a semiconductor laser provided.

[0002]

2. Description of the Related Art Conventionally, as a semiconductor laser having an oscillation wavelength in a 0.7 to 0.85 μm band, for example,
of Quantum Electronics, Vol. QE-20, No. 10, October 1
984 pp. 1119-1132, an n-AlGaAs cladding layer, n- or i-AlG
aAs optical waveguide layer, i-AlGaAs active layer, p or i
-An optical waveguide formed by forming an AlGaAs optical waveguide layer, a p-AlGaAs cladding layer, and a p-GaAs cap layer is widely known.

As a semiconductor laser having the above-mentioned oscillation wavelength band, reference (2) Japanese Journal of Applied Physics
(Japanese Journal of Applied Physics) As shown in Vol. 31 (1992) pp. L1686 to L1688, an n-GaAs substrate has an n-InGaP cladding layer and n or i-In _x2 Ga _1-x2 As. _1-y2 P _y2 optical waveguide _{layer, i-In x1 Ga 1-} x1 As 1-y1 P y1 active layer (x1 <x2,
y1 <y2), p or _{i-In x2 Ga 1-x2} As 1-y2 P y2 optical waveguide layer, p-InGaP cladding layer, and p-GaA
There has also been proposed one formed with an s cap layer.

[0004]

However, the above document (1)
In the structure shown in (1), since the Al contained in the active layer is chemically active and easily oxidized, the cavity end face formed by cleavage is easily deteriorated, and it is difficult to obtain high reliability. There's a problem.

[0005] The structure shown in Reference (2) addresses such a problem.
In crystal growth by metal organic chemical vapor deposition (MOCVD) or the like, a group V element hydride gas (PH ₃ , AsH) is formed at the interface between the cladding and the optical waveguide layer, between the optical waveguide layer and the active layer, or vice versa. ₃ ) Switching, that is, opening / closing of a gas valve or increasing / decreasing the gas flow rate by a mass flow controller, for example, makes the state of the crystal surface unstable at the time of this switching. However, there is a disadvantage that the crystal cannot be formed stably with high reproducibility, and the quality of the crystal grown on the layer interface deteriorates.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and provides a semiconductor laser having high quality of a layer interface and a crystal grown on the layer interface and having high reliability even under high output oscillation. It is intended for.

Further, the present invention has achieved the above object and
An object of the present invention is to provide a semiconductor laser in which deterioration of a cavity facet due to oxidation of an active layer is prevented and high reliability can be expected from this point as well.

[0008]

According to a first aspect of the present invention, an active layer has a composition containing at least two elements of a group V element, and a light guide sandwiching the active layer. The wave layer and the cladding layer have a composition containing a group V element and a group III element, and the composition ratio of the group V element in the optical waveguide layer and the cladding layer is the same as the composition ratio of the group V element in the active layer. The separation and confinement heterostructure is formed by changing the composition ratio of the group III element of the optical waveguide layer and the cladding layer.

According to a second aspect of the present invention, there is provided the second semiconductor laser according to the first aspect, wherein
In particular, the active layer is _{In x1 Ga 1-x1 As 1} -y1 P y1, optical waveguide layer _{In x1 (Ga 1-z1 Al} z1) 1-x1 As 1-y1 P y1, cladding layer is an In _x1 (Ga _{1 -z2 Al z2) 1-x1 as} 1-y1 P y1 ( although and is characterized in that it consists of 0 <z1 <z2).

In a third semiconductor laser according to the present invention, as described in claim 3, the active layer has a composition containing an elementary group V element, and the optical waveguide layer and the cladding layer sandwiching the active layer are: Two or more group V elements including group V elements in the active layer; and
While having a composition containing a group III element, the composition ratio of the group V element in the optical waveguide layer and the cladding layer is the same as each other,
A different confinement heterostructure is formed by changing the composition ratio of the group III element in the optical waveguide layer and the cladding layer.

A fourth semiconductor laser according to the present invention comprises:
As described in claim 4, in the third semiconductor laser, in particular, the active layer is In _x2 Ga _1-x2 As, and the optical waveguide layer is I _x
n _x1 (Ga _1-z1 Al _z1 ) _1-x1 As _{1-y1 Py 1} , cladding layer is In _x1 (Ga _1-z2 Al _z2 ) _1-x1 As _{1-y1 Py 1} (where 0 ≦ z1 <z2) ).

[0012]

In the first semiconductor laser, since the active layer, the optical waveguide layer, and the cladding layer all have the same composition ratio of the group V element, MOCVD or molecular beam epitaxial growth for their fabrication is performed. In such cases, it is not necessary to switch the group V element gas at the layer interface.

In the third semiconductor laser,
Since the composition ratio of the group V element in the optical waveguide layer and the cladding layer is common, the switching of the group V element gas at the layer interface between the active layer and the optical waveguide layer in MOCVD or molecular beam epitaxial growth for the production thereof is performed. The switching of the group V element gas between the optical waveguide layer and the cladding layer is unnecessary.

As described above, in the case of MOCVD or molecular beam epitaxy, it is not necessary to switch the group V element gas at the layer interface at all, or if it is minimized, the mutual exchange of the group V element material at the interface between the layers is possible. Substitution does not occur, and the state of the crystal surface does not become unstable. As a result, the semiconductor laser according to the present invention has high quality of the crystal grown on the layer interface and the layer interface, and ensures high reliability even under high output oscillation.

Furthermore, as described above, if the switching of the group V element gas at the layer interface is not required or is minimized, the growth interruption time at the layer interface can be shortened. Can be highly reliable without defects at the layer interface.

In addition, particularly in the second and fourth semiconductor lasers, since the active layer does not contain easily oxidizable Al, the deterioration of the cavity facet due to the oxidation of the active layer is prevented. Can be high.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings. FIG. 1 shows a layer structure of a semiconductor laser according to a first embodiment of the present invention. As an example, this semiconductor laser has an n-GaAs substrate 2 by a MOCVD apparatus having TMA, TMG, and TMI as organic metals serving as group III element materials and AsH ₃ and PH ₃ as hydride gases serving as group V element materials. N-In _x1 (Ga
_{1-z2 Alz2} ) _1-x1 As1 _{-y1 Py1} cladding layer 3, n or i- _Inx1 (Ga1 _{-z1 Alz1} ) _1-x1 As1 _{-y1 Py1} optical waveguide layer 4, i-In _{x1 Ga 1-x1 As 1-} y1 P y1 active layer 5, p or _{i-In x1 (Ga 1-} z1 Al z1) 1-x1 As 1-y1 P y1 optical waveguide layer _{6, p-In x1 (Ga} 1 _-z2 Al _z2 ) _1-x1 As _1-y1
It is formed by sequentially growing a _Py1 cladding layer 7 and a p-GaAs contact layer 8 (where 0 <z1 <z2).

In this case, the composition of the group V elements As and P is the same in all layers except the contact layer 8. Therefore, it is necessary to perform switching for changing the composition ratio (opening / closing valves and increasing / decreasing the flow rate by a mass flow controller or the like) with respect to the group V element hydride gases AsH ₃ and PH ₃ which are the raw materials of the layers 3 to 7 in MOCVD growth. Instead, only the opening and closing of the valves and the flow rate control of the group III element materials TMA and TMG need be performed.

Thereafter, an n-side electrode 1 and a p-side electrode 9 made of metal are formed on the substrate 2 and the contact layer 8, respectively.
Is formed to complete the semiconductor laser of the first embodiment.

As described above, if the switching of the group V element gas at the layer interface is not required at all during the crystal growth by MOCVD, the state of the crystal surface does not become unstable at the time of switching the group V element gas. As a result, the semiconductor laser has high quality of the layer interface and the crystal grown on the layer interface, and ensures high reliability even under high output oscillation.

The semiconductor laser according to the present embodiment has an active layer 5
Since Al which is easily oxidized is not contained, deterioration of the cavity end face due to oxidation of the active layer 5 is prevented, and in this respect, reliability can be improved.

It should be noted that the active layer shown in the above reference (2) is
n _x1 Ga _1-x1 As _1-y1 P _y1 , and the optical waveguide layer is In _x2 Ga _{1-x2
As 1-y2 P y2 (x1} <x2, y1 <y2) in structure to the active layer _{In x1 Ga 1-x1 As 1} -y1 P y1 and the optical waveguide layer an In _x2 Ga
Between the _{1-x2 As 1-y2 P} y2, Harrison LCAO theory (WAHarrison: Journal of Vacuum Society Technolo
gy (Journal of Vacuum Society Technology) Vol. 14, No. 4, 1977, pp. 1016-1021) and the like, the band offset ΔEc of the conduction band and the band offset ΔEv of the valence band are calculated as ΔEc < Δ
It becomes Ev, and it is not possible to effectively confine electrons having a lighter effective mass than holes.

On the other hand, the active layer In _x1 Ga according to the present invention
_1-x1 As _{1-y1 Py 1} and optical waveguide layer In _x1 (Ga _1-z1 Al _z1 )
Band offset Δ of conduction band between _1-x1 As _{1-y1 Py1}
When Ec and the band offset ΔEv of the valence band are calculated, ΔEc: ΔEv〜6: 4, and the structure is such that electrons are effectively confined.
In addition, there is an effect that the characteristic temperature is increased.

In the first embodiment, although the group V element composition is the same in the active layer, the optical waveguide layer and the cladding layer, only the active layer contains a strain and the group V element composition is FIG. 2 shows a second embodiment different from the cladding layer.
This will be described with reference to FIG.

In the semiconductor laser of the second embodiment, n-In _x1 (Ga _{1 -z 2} Al _z2 ) _{1 -x 1} As _{1 -y 1} P is formed on an n-GaAs substrate 12 by the same MOCVD apparatus as described above.
_y1 cladding layer 13, n or i-In _x1 (Ga _{1 -z1} A
l _z1 ) _1-x1 As _{1-y1 Py 1} optical waveguide layer 14, i-In _x2 Ga
_1-x2 As active layer 15, p or i-In _x1 (Ga _1-z1 Al
_z1 ) _1-x1 As1 _{-y1 Py1} optical waveguide layer 16, p- _Inx1 (Ga
_{1-z2 Alz2} ) _1-x1 As1 _{-y1 Py1} clad layer 17, p-Ga
It is formed by sequentially growing As contact layers 18 (where 0 ≦ z1 <z2).

In the case of this configuration, As and P are provided between the optical waveguide layer 14 and the active layer 15 and between the active layer 15 and the optical waveguide layer 16.
In order to change the composition ratio, it is necessary to switch the group V element gas. In this case, it is only necessary to open and close the PH ₃ gas valve. Further, between the cladding layer 13 and the optical waveguide layer 14, and between the optical waveguide layer 16 and the cladding layer 17, there is no need to switch the group V element gas.

Thereafter, an n-side electrode 11 and a p-side electrode 19 made of metal are formed on the substrate 12 and the contact layer 18, respectively.
Is formed to complete the semiconductor laser of the second embodiment.

As described above, if the switching of the group V element gas at the layer interface is small during the crystal growth by MOCVD,
When the group V element gas is switched, the state of the crystal surface does not become unstable. Accordingly, also in the semiconductor laser of the second embodiment, the quality of the crystal growing on the layer interface and the layer interface is high, and high reliability is ensured even under high output oscillation.

Also in the semiconductor laser of the second embodiment, since the active layer 15 does not contain easily oxidizable Al, deterioration of the cavity facet due to oxidation of the active layer 15 is prevented, and the reliability is also improved in this respect. Can be expensive.

In the above two embodiments, a simple broad area structure is formed. However, the structure of these embodiments is further processed by ordinary photolithography or etching to provide a refractive index guide mechanism. It is also possible to manufacture a semiconductor laser, a semiconductor laser with a diffraction grating, and an optical integrated circuit.

The structure of each of the above embodiments is a structure called an SQW-SCH having a single quantum well and a constant optical waveguide layer composition. However, instead of the SQW, an MQW structure having a plurality of quantum wells is used. The present invention is also applicable to this.

Further, as for the optical waveguide layer, a GRIN structure (GRadded-INDex), that is, a refractive index distribution structure is conceivable. In forming this structure, TMA and TMG can be formed without switching the hydride gas of the group V element. The refractive index profile of the GRIN structure can be obtained only by gradually changing the flow rate ratio at any time.

Further with respect to the oscillation wavelength band, a for which the active layer 5 of the first embodiment and the _{In x1 Ga 1-x1 As 1} -y1 P y1 is, x1~0.49y1,0 <y1 <1 relationship If appropriate x1 and y1 are determined so as to satisfy the condition, the oscillation wavelength λ is set to 680 nm <λ.
It can be controlled in the range of <870 nm. On the other hand, when the active layer 15 of the second embodiment is made of In _x2 Ga _1-x2 As, control can be performed up to the range of λ <1150 nm. When an InGaAsSb-based material is used, 2 μm
The present invention can be applied to a laser having a long wavelength band.

In each of the above embodiments, TMA, TMI, and TMG are used as the group III element raw material, but other organic metal gases such as TEA, TEG, and TEI may be used. On the other hand, AsH source gas is AsH
₃ , PH ₃ is used, but other hydride compounds or organometallic gases may be used. Further, a compound semiconductor composed of As and P is described as a semiconductor composed of a binary group V element, but a binary semiconductor composed of a group V element including Sb or the like may be used. Further, as a crystal growth method, a molecular beam epitaxial growth method using a solid or gas as a raw material can be employed.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a layer configuration of a semiconductor laser according to a first embodiment of the present invention.

FIG. 2 is a schematic view showing a layer configuration of a semiconductor laser according to a second embodiment of the present invention;

[Explanation of symbols]

1 n-side electrode 2 n-GaAs substrate 3 n-In _x1 (Ga _{1 -z 2} Al _z2 ) _1-x1 As _{1 -y1 Py 1}
Cladding layer 4n or i-In _x1 (Ga _1-z1 Al _z1 ) _1-x1 As
_1-y1 P _y1 optical waveguide layer _{5 i-In x1 Ga 1-} x1 As 1-y1 P y1 active layer 6 p or _{i-In x1 (Ga 1-} z1 Al z1) 1-x1 As
_{1-y1 Py1} optical waveguide layer 7 p- _Inx1 (Ga1 _{- z2Alz2} ) _{1-x1As1 - y1Py1}
Cladding layer 8 p-GaAs contact layer 9 p-side electrode 11 n-side electrode 12 n-GaAs substrate 13 n-In _x1 (Ga _{1 -z 2} Al _z2 ) _1-x1 As _{1 -y1 Py 1}
Cladding layer 14n or i-In _x1 (Ga _1-z1 Al _z1 ) _1-x1 As
_{1-y1 Py1} optical waveguide layer 15 i- _{Inx2Ga1 -x2As} active layer _16p or i- _Inx1 (Ga1 _{- z1Alz1} ) _{1-x1As
1-y1 Py1} optical waveguide layer 17 p- _Inx1 (Ga1 _{- z2Alz2} ) _{1-x1As1 - y1Py1}
Cladding layer 18 p-GaAs contact layer 19 p-side electrode

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H01S 5/00 H01S 5/50 JICST file (JOIS)

Claims (4)

(57) [Claims] An active layer having a composition containing two or more group V elements; an optical waveguide layer and a cladding layer sandwiching the active layer having a composition containing a group V element and a group III element; The composition ratio of the group V element in the wave layer and the cladding layer is the same as the composition ratio of the group V element in the active layer, while the composition ratio of the group III element in the optical waveguide layer and the cladding layer is changed to obtain the separated confinement heterostructure. A semiconductor laser having a structure formed. 2. The method according to claim 1, wherein the active layer is In _x1 Ga _1-x1 As _1-y1 P
_y1 , the optical waveguide layer is In _x1 (Ga _1-z1 Al _z1 ) _1-x1 As _1-y1
P _y1 , the cladding layer is In _x1 (Ga _{1 -z 2} Al _z2 ) _1-x1 As
_2. The semiconductor laser according to claim 1, wherein _{1-y1 Py1} (where 0 <z1 <z2). 3. The active layer has a composition containing one elemental V group element, and the optical waveguide layer and the cladding layer sandwiching the active layer are composed of at least two elemental V group elements containing the V group element of the active layer. The optical waveguide layer and the cladding layer have the same composition ratio of the group V element, and the optical waveguide layer and the cladding layer have the same composition ratio.
A semiconductor laser, wherein a separated confinement heterostructure is formed by changing the composition ratio of a group III element. 4. The active layer is In _x2 Ga _1-x2 As, and the optical waveguide layer is In _x1 (Ga _1-z1 Al _z1 ) _1-x1 As _1-y1.
P _y1 , the cladding layer is In _x1 (Ga _{1 -z 2} Al _z2 ) _1-x1 As
4. The semiconductor laser according to claim 3, wherein _{1-y1 Py1} (where 0.ltoreq.z1 <z2).