JPH11312847A - Vertical resonator type semiconductor laser and manufacture of the same element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify a transverse mode, and to obtain dynamically stable operation, by making the effective refractive indices of each layer constituting a resonator region higher than those of other each layer and that of a layer configuring a semiconductor buried layer. SOLUTION: First growth is stated from p-DBR on a P-GaAs substrate, and growth is conducted up to an MQW active layer and n-DBR. The Al composition of a low refractive-index layer having several periods close to the active layers of n-DBR and p-DBR is set at a value lower than those of other DBR sections, a current constriction layer is grown, and the current constriction layer is made lower than an optical resonator section in index distribution. A mask at the time of mesa formation is used as the selection mask of crystal growth as it is, and second growth (the current constriction layer) is formed. The mask on a mesa upper section is removed at a final stage, third growth is performed, and n-DBR is grown in a period section only by the obtaining of reflectivity satisfying laser oscillation conditions.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a vertical cavity type semiconductor laser device, which is a light source for performing optical interconnection between chips or boards and for performing two-dimensional parallel signal processing. The present invention relates to a cavity type semiconductor laser.

[0002]

2. Description of the Related Art A vertical cavity type semiconductor laser can be easily formed into a two-dimensional array, and a circular light emitting pattern enables highly efficient coupling with a fiber without a coupling lens. It is important as a light source for optical interconnection and two-dimensional parallel signal processing, and it is considered that it is also important for the purpose of low power consumption because an extremely low threshold can be achieved by a microcavity structure.

FIG. 1 is a cross-sectional view of a conventional vertical cavity semiconductor laser in a direction perpendicular to the crystal plane (reference: (1) B.
-S. Yoo. HY Chu, H.-H, Park, HG Lee and J. Le
e, IEEE Journal of Quantum Electronics. vol.33, N
o.10, 1997, pp.1794. (2) CJ Chang-Hasnain, YA
Wu. GS Li. G. Hasnain. KD Choquete. C. Caneau
and LT Florez, Applied Physics Letters.
No. 10, 1993, pp. 1307). This element is p-GaAs
Sequentially on the substrate _{101 p-Al y Ga 1-} y As / Al z G
a _1-z As (0 <y <z) distributed reflection type (distributed Br
agg reflector, DBR) Multi-layered film reflector 102 (shaded area is Al _z Ga _{1 -z} As, white area is Al _y Ga _{1 -y} A)
s), non-doped-Al _w Ga _{1 -w} As lower spacer layer 103, GaAs / Al _x Ga _{1 -x} As (x ≦
w) Multiple quantum well active layer 104, non-doped-
Al _w Ga _1-w As upper spacer layer 105, n-Al _y
Ga _1-y As / Al _z Ga _1-z As (0 <y <z) DB
R reflector 106, semiconductor buried layer 107, lower electrode 1
08, an insulating film 109, an upper electrode 110, and an element isolation structure 111. Each layer of the DBR is set to have a film thickness of a quarter of a value obtained by dividing the oscillation wavelength by the refractive index of each layer.

[0004] In the device of FIG.
As a report, an AlGaAs / AlGaAsn-ipi structure or an amorphous GaAs layer has been reported, and an oscillation operation in a single transverse mode has been obtained.

[0005]

However, the above-described structure is not an optical confinement by a refractive index waveguide type, but an anti-guide type waveguide structure. Therefore, in principle, there are not a single transverse mode but a plurality of transverse modes.However, by cutting a higher-order transverse mode by using a structure having a high loss outside the waveguide, Single transverse mode operation has been obtained. However, in the dynamic characteristic in which the carrier density fluctuates greatly in the active layer, there is a problem that an unstable operation occurs due to a higher mode depending on the distribution of the carrier density in the active layer.

Accordingly, a first object of the present invention is to provide a vertical cavity semiconductor laser which has a single transverse mode and can achieve dynamically stable operation as compared with the prior art.

A second object of the present invention is to provide a small element capacitance and high-speed modulation characteristics as compared with the prior art, and a single transverse mode which is dynamically stable as compared with the conventional technique. An object of the present invention is to provide a vertical cavity semiconductor laser capable of obtaining an operation.

A third object of the present invention is to provide a method of manufacturing a vertical cavity type semiconductor laser device having a single transverse mode and a dynamically stable operation as compared with the prior art. .

A fourth object of the present invention is to provide a device having a small element capacity and a high-speed modulation characteristic as compared with the prior art, and a single transverse mode which is dynamically stable as compared with the conventional technology. An object of the present invention is to provide a vertical cavity type semiconductor laser manufacturing method capable of obtaining an operation.

[0010]

A vertical cavity semiconductor laser according to the present invention comprises a substrate, a lower DBR structure comprising a plurality of layers provided on the substrate, and a lower DBR structure provided on the lower DBR structure. And a semiconductor buried structure portion including at least one layer in which the active layer is buried, and an upper DBR structure portion including a plurality of layers provided on the active layer. A resonator region is formed by layers located above and below the active layer, and the effective refractive index of each layer forming the resonator region is determined by the effective refractive index of each of the other layers forming the upper and lower DBR structures. It is characterized in that the refractive index is higher than the effective refractive index of the layer constituting the semiconductor buried layer.

Preferably, the semiconductor buried structure has an np repeating laminated structure or a pn structure in the semi-insulating layer.
It has a structure in which a repeated laminated structure is laminated.

Preferably, the semiconductor buried structure portion is a semi-insulating n-p repeating laminated structure or a semi-insulating p-type structure.
-N It has a repeating laminated structure.

Preferably, the semiconductor buried portion is formed only of a semi-insulating layer.

Preferably, the semiconductor buried portion is formed of one layer, and the layer is ion-implanted.

Preferably, the semiconductor buried portion is formed of AlGaAs having an effective refractive index lower than that of the resonator region.

Preferably, the semiconductor buried portion is formed of InGaP having an effective refractive index lower than that of the resonator region.

Preferably, the lower DBR structure has at least one layer made of InGaP having an effective refractive index lower than that of the resonator region.

A vertical cavity type semiconductor laser according to the present invention comprises a substrate, a lower DBR structure comprising a plurality of layers provided on the substrate, and a lower DBR structure provided on the lower DBR structure.
And a semiconductor buried structure portion comprising at least one layer in which the active layer is buried, and an upper DBR structure portion comprising a plurality of layers provided on the semiconductor buried structure portion in which the active layer is buried. A resonator region is formed by the active layer and layers located above and below the active layer,
Further, the effective refractive index of each layer constituting the resonator region is larger than the effective refractive index of each of the other layers constituting the upper and lower DBR structures and the effective refractive index of the layer constituting the semiconductor buried layer. It is characterized by being expensive.

Preferably, the resistance of the upper DBR structure on the semiconductor buried portion is higher than the resistance of the upper DBR structure on the active layer.

[0020] Preferably, the semiconductor buried structure portion has an np repeating laminated structure or a pn repeating laminated structure.

Preferably, the semiconductor buried structure has an np repeating laminated structure or a pn structure in the semi-insulating layer.
It has a structure in which a repeated laminated structure is laminated.

Preferably, the semiconductor buried portion is formed only of a semi-insulating layer.

Preferably, the semiconductor buried portion is formed of one layer, and the layer is implanted with ions.

Preferably, the semiconductor buried portion is formed of AlGaAs having an effective refractive index lower than that of the optical resonator region.

Preferably, the semiconductor buried portion is formed of InGaP having an effective refractive index lower than that of the optical resonator region.

Preferably, the lower DBR structure part is
It has one or more layers formed of nGaP.

A method of manufacturing a vertical cavity type semiconductor laser device according to the present invention includes a substrate, a lower DBR structure comprising a plurality of layers provided on the substrate, and a lower DBR structure provided on the lower DBR structure. And a vertical cavity type having a semiconductor buried structure portion including at least one layer in which the active layer is buried, and an upper DBR structure including a plurality of layers provided on the semiconductor buried structure portion in which the active layer is buried. A method of manufacturing a semiconductor laser device, comprising: a first growth step of growing a lower DBR structure part on an active layer or a part of an upper DBR structure part on a substrate; and forming a mesa structure part by etching to a lower part of the active layer. A second growth step of forming a semiconductor buried structure to bury the active layer, and forming an upper DB on the semiconductor buried structure.
A third growth step of re-growing the R structure, further comprising providing a resonator region by the active layer and layers located above and below the active layer, wherein each layer constituting the resonator region is provided. Is higher than the effective refractive index of each of the other layers constituting the upper and lower DBR structures and the effective refractive index of the layer constituting the semiconductor buried structure. It is characterized by controlling.

Preferably, a thickness of the semiconductor buried structure is lower than a height of the mesa structure.

Preferably, the semiconductor buried structure portion has an np repeating laminated structure or a pn repeating laminated structure.

Preferably, the semiconductor buried structure has an np repeating laminated structure or a pn structure in the semi-insulating layer.
It has a structure in which a repeated laminated structure is laminated.

Preferably, the semiconductor buried portion is formed only of a semi-insulating layer.

[0032] Preferably, the semiconductor buried portion is formed of one layer, and the layer is implanted with ions.

Preferably, the semiconductor buried portion is formed of AlGaAs having an effective refractive index lower than that of the optical resonator region.

Preferably, the semiconductor buried portion is formed of InGaP having an effective refractive index lower than that of the optical resonator region.

Preferably, the lower DBR structure part is
It has one or more layers formed of nGaP.

Preferably, in the first growth step, the lower layer of the lower DBR structure is made of InGaP.

Further, a vertical cavity semiconductor laser according to the present invention is manufactured by the above manufacturing method.

[0038]

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

<First Embodiment> FIG. 2 is a cross-sectional view in a direction perpendicular to the crystal growth surface of the present embodiment. This structure is p
Sequentially on the -GaAs substrate _{1 p-Al y Ga 1-} y As / A
l _z Ga _1-z As (0 <y <z) distributed reflection type (distribute
ted Bragg reflector, DBR) multilayer mirror 2 (the hatched portion is Al _z Ga _1-z As, the white portions Al _y Ga _1-y A
s), p-InGaP etching stop layer 3, pA
_{l y Ga 1-y As /} Al u Ga 1-u As (0 <y <u <
z) Distributed Bragg reflector, DB
R) multilayer mirror 4 (the hatched portion is Al _u Ga _1-u As, the white portion is _{Al y Ga 1-y As)} , non-doped-
Al _w Ga _{1 -w} As lower spacer layer 5, GaAs / Al
_x Ga _{1 -x} As multiple quantum well active layer 6, non-dop
ed-Al _w Ga _{1 -w} As upper spacer layer 7, n-Al
_y Ga _1-y As / Al _u Ga _1-u As (0 <y <u <
z) Distributed Bragg reflector, DB
R) multilayer mirror 8 (the hatched portion is Al _u Ga _1-u As, the white portion is _{Al y Ga 1-y As)} , n-InGaP first round growth final layer 9, AlGaAs or InGaP semiconductor buried layer (second second growth layer) 10, n-Al _y Ga
_1-y As / Al _z Ga _1-z As (0 <y <z) DBR reflector (third growth layer) 11, lower electrode 12, insulating film 1
3, an upper electrode 14, and an element isolation structure 15. Each layer of the DBR is set to have a film thickness of a quarter of a value obtained by dividing the oscillation wavelength by the refractive index of each layer.

FIGS. 3A to 3F show the growth process. Since the first growth is on the p-GaAs substrate, it starts from the p-DBR, and starts with the MQW active layer and the n-DBR.
(Part of) (FIG. 3A). The Al composition of the low-refractive index layer having several periods close to the active layers of the n-DBR and p-DBR (thickness corresponding to the depth at which a mesa is formed in a later step) is set lower than the Al composition of the other DBR portions. After growing the current confinement layer, a so-called refractive index waveguide is formed in which the current confinement layer has a refractive index distribution lower than that of the light resonator. A
Similar effects can be obtained by using InGa (As) P having a refractive index such that the effective refractive index of the optical resonator portion is higher than that of the current confinement layer, in addition to AlGaAs having a low l composition. The period of the DBR structure in which the Al composition is set low near the active layer is sufficient as a light confinement effect when the period is equal to or greater than the penetration depth into the DBR. Although p-InGaP is used for a part of the low refractive index layer of the p-DBR, it is intended to be used as an etching stop layer.
The final layer is n-InGaP. The purpose of this is that when the surface at the time of regrowth is AlGaAs, the influence of the surface oxide layer is large, and the higher the Al composition, the more difficult it is to obtain a high-quality layer as the regrown layer.
This is because a layer containing no l is used. Next, a mesa structure is formed using an insulating film such as a photoresist or SiO ₂ (FIG. 3B). As a forming method, both wet etching and dry etching are effective. The etch depth is stopped short of the p-InGaP etch stop layer, taking into account optical monitoring or the etch rate. Then, using a selective etchant, p-I
The surface of the nGaP is exposed (FIG. 3C). The second growth (current constriction layer) is formed by using the mask at the time of forming the mesa as it is as a selection mask for crystal growth ((1) in FIG. 3D). As the current confinement layer which is a semiconductor buried layer, an AlGaAs or InGaP layer having a doping type of pnpn-... When AlGaAs is used for the current confinement layer, the upper and lower DBR structures near the active layer have an Al composition of, for example, Al _0.15 G
a In the case of _0.35 As / Al _0.5 Ga _0.5 As, it is set to 0.33 or more. InGaP wavelength 0.
Since the refractive index at 85 μm is 3.34, a refractive index waveguide structure is formed in the DBR structure having the Al composition or less. Alternatively, a high-resistance semi-insulating layer is used as the regrown first layer.
In that case, the effect of current constriction is further enhanced. Since polycrystal is usually laminated on the mask of the uppermost layer of the mesa, the polycrystal in the laser resonator portion is removed by etching using a photoresist as a mask (FIG. 3E). The removal method is wet
Either etching, dry etching, or a combination of both is effective. Alternatively, by utilizing the tendency that the step between the mesa portion and the portion other than the mesa becomes smaller as the thickness of the grown layer becomes larger, regrowth is performed until the step becomes about 1000 A ((2) in FIG. 3D). Thereafter, it is also effective to perform uniform etching without using a mask until the mask on the mesa is exposed by wet etching or dry etching. If a growth condition in which no polycrystal is stacked is used for the mask of the top layer of the mesa, the etching step of FIG. 3E can be omitted and the process can be simplified. As a final stage, after removing the mask on the mesa, a third growth is performed (FIG. 3F), and an n-DBR is grown for a period sufficient to obtain a reflectance satisfying the laser oscillation condition.

FIG. 4 is a cross-sectional view of another example of the present embodiment in a direction perpendicular to the crystal growth surface. Although the structure is not much different from FIG. 2, the semiconductor buried layer 16 is characterized by being formed as a single layer. The structure is AlGaAs or InGaP, which is non-doped or doped with a metal such as Cr for the purpose of improving high resistance characteristics. Further, by doping with O ⁺ ions, it becomes more effective.

FIGS. 5A and 5B explain the device characteristics of the vertical cavity semiconductor laser shown in FIGS. 2 and 4. FIG.
It is. 5A is a current-light output characteristic and a current-voltage characteristic. As shown by the solid line, in the new structure according to the present invention shown by the solid line as compared with the conventional structure shown by the broken line, the area of the electrode layer is increased, thereby reducing the series resistance. In addition, since it is not a structure that causes a loss in a higher-order mode like an anti-guide type waveguide, it is a structure in which only a single mode is essentially excited. Coupling is efficiently performed, and improvement in efficiency is realized. Further, since the non-radiative recombination at the interface of the active layer is suppressed, the threshold value is reduced and the efficiency is further increased.

The far-field pattern (Far Field Patter) shown in FIG.
n, FFP) for different current drive values. Immediately after oscillation, both the conventional structure (1) and the present invention (i) show unimodal characteristics and operate in the basic transverse mode. However, as the current value increases, the bilateral higher-order transverse mode is dominant in the conventional structure. (2) and (3), however, in the present invention, the monomodality is maintained.

Although the above description has been given of the structure on the p-GaAs substrate, the same effect can be obtained in the case of the structure on the n-GaAs substrate. Although the structure using the InGaP etch stop layer has been described, the same effect can be obtained in a structure using an AlGaAs layer having an Al composition different from other DBR portions. The case where the final layer of the first growth is InGaP is described,
The same effect is obtained in the case of an AlGaAs layer in which the Al composition is kept low. Although the description has been given of the AlGaAs / GaAs system, the same effect can be obtained in the InGaAs / GaAs system.

As described above, in the present embodiment, in the vertical cavity semiconductor laser manufacturing method and the vertical cavity semiconductor laser, the first growth is performed up to (part of) the DBR above the active layer. After the mesa structure is formed, an InGaP or AlGaAs current confinement layer whose composition is controlled, that is, a semiconductor buried layer, is formed in a second growth so as to form a refractive index waveguide type resonator, and is formed in a third growth. By forming the rest of the required DBR structure,
There is an effect that a vertical cavity semiconductor laser can be formed in which the lateral mode operates stably in the basic mode not only statically but also dynamically, and which can obtain a low threshold current, a low series resistance, and a high luminous efficiency.

<Second Embodiment> FIG. 6 is a sectional view of the present embodiment in a direction perpendicular to the crystal growth surface. This structure is pG
sequentially on the aAs substrate _{1 p-Al y Ga 1-} y As / Al z
Ga _1-z As (0 <y <z) distributed reflection type (distributed
Bragg reflector, DBR) Multilayer reflector 2 (shaded area is A
l _z Ga _1-z As, the white portion is _{Al y Ga 1-y As)} ,
p-InGaP etch stop layer 3, p-Al _y G
a _1-y As / Al _u Ga _1-u As (0 <y <u <z) distributed Bragg reflector (DBR) multilayer film reflector 4 (the shaded portion is Al _z Ga _1-z As, white parts _{Al y Ga 1-y As)} , non-doped-Al w G
a _{1 -w} As lower spacer layer 5, GaAs / Al _X Ga
_1-X As multiple quantum well active layer 6, non-doped-
Al _w Ga _1-w As upper spacer layer 7, n-Al _y Ga
_1-y As / Al _u Ga _1-u As (0 <y <u <z) distributed Bragg reflector (DBR) multilayer reflector 8 (shaded area is Al _z Ga _1-z As, white part Is A
_{l y Ga 1-y As)} , n-Al y Ga 1-y As / Al z
Ga _{1 -z} As (0 <y <z) DBR reflector 9, AlGa
As or InGaP semiconductor buried layer 10, lower electrode 12, insulating film 13, upper electrode 14, device isolation structure 15
Formed. Among the above-mentioned structures, reference numerals 4 to 8 indicate the ranges in which electric field components of light are almost confined.
Is formed. Each layer of the DBR is set to have a film thickness of a quarter of a value obtained by dividing the oscillation wavelength by the refractive index of each layer.

The growth process will be described below. Since the first growth is on the p-GaAs substrate, it starts from the p-DBR and grows to the MQW active layer and the n-DBR (FIG. 5).
(A)). Several cycles close to the active layer of n-DBR and p-DBR (thickness corresponding to the depth at which a mesa is formed in a later step)
The Al composition of the low refractive index layer is set lower than the Al composition of the other DBR portions, and after growing the current confinement buried layer, the refractive index distribution is lower in the current confinement layer than in the optical resonator portion. An index waveguide is formed. AlGaAs with low Al composition
In addition, the same effect is obtained when using InGa (As) P having a refractive index such that the effective refractive index of the light resonator portion is higher than that of the current confinement layer. The period of the DBR structure in which the Al composition is set low near the active layer is D
When the penetration depth is equal to or more than the penetration depth into the BR, the effect of confining light is sufficient. p-In is added to a part of the low refractive index layer of p-DBR.
GaP is used, which is intended to be used as an etching stop layer. In addition, the surface during regrowth has A
In the case of lGaAs, the influence of the surface oxide layer is large, and the higher the Al composition, the more difficult it is to obtain a high-quality layer as a regrown layer. Of course, when the Al composition is as low as about 0.1 to 0.2 and the oxidation of the surface does not greatly affect the regrowth of the crystal, the same applies to the case where the AlGaAs layer is used by appropriately selecting an etchant in the process step. The effect can be expected. Next, photoresist,
A mesa structure is formed using an insulating film such as SiO ₂ . As a forming method, both wet etching and dry etching are effective. The etching depth is p-In considering the optical monitor or the etching rate.
Stop just before the GaP etching stop layer. Then, the surface of p-InGaP is exposed using a selective etchant. A second growth layer (current confinement buried layer) is formed by using the mask for forming the mesa as it is as a selection mask for crystal growth. As the current confinement layer, A having a doping type of pnpn-...
An lGaAs or InGaP layer is used. AlGa
When As is used for the current confinement layer, the upper and lower DBR structures near the active layer have an Al composition of Al _0.15 Ga _0.85 As /
When configured in Al _0.5 Ga _0.5 As 0.3
Set to 3 or more. Since the refractive index of InGaP at a wavelength of 0.85 μm is 3.34, a refractive index waveguide structure is formed in a DBR structure having the above Al composition or less. Alternatively, a high-resistance semi-insulating layer is used as the regrown first layer. In that case, the effect of current constriction is further enhanced. As a final step, after removing the mask above the mesa, an insulating film is formed, a window for flowing current is formed, electrodes are formed, and the element is completed.

FIGS. 7A and 7B illustrate the device characteristics of the vertical cavity semiconductor laser shown in FIG. FIG. 7A shows the current vs. light output characteristics and the current vs. voltage characteristics. Regarding the element resistance, there is almost no difference between the conventional structure and the present structure. With respect to the threshold current, the reflectivity of the DBR can be designed to be the same as that of the conventional structure. However, this structure is not a structure that causes a loss in a higher-order mode like an anti-guide type waveguide, but is essentially a single structure. Since only one mode is excited, the threshold current is reduced, and the light emitting component from the active layer is efficiently coupled to the oscillation mode, thereby improving the efficiency. FIG. 7B shows the far field pattern FFP for different current drive values. Immediately after oscillation, both the conventional structure (1) and the present invention (i) show unimodal characteristics and operate in the basic transverse mode. However, as the current value increases, the bilateral higher-order transverse mode is dominant in the conventional structure. (2),
(3) In the present invention, unimodality is maintained.

Although the above description has been given of the structure on the p-GaAs substrate, the same effect can be obtained in the case of the structure on the n-GaAs substrate. Although the structure using the InGaP etch stop layer has been described, the same effect can be obtained in a structure using an AlGaAs layer having an Al composition different from other DBR portions. The case where the final layer of the first growth is InGaP is described,
The same effect is obtained in the case of an AlGaAs layer in which the Al composition is kept low. Although the description has been given of the AlGaAs / GaAs system, the same effect can be obtained in the InGaAs / GaAs system.

As described above, in the present embodiment, in the vertical cavity type semiconductor laser having the buried semiconductor structure, the effective refractive index of the buried layer is set to be lower than that of the cavity portion of light. The transverse mode operates stably in the basic mode not only statically but also dynamically, and has an effect of forming a vertical cavity semiconductor laser having a low threshold current and high luminous efficiency.

<Third Embodiment> FIG. 8 is a sectional view of the present embodiment in a direction perpendicular to the crystal growth surface. This structure is pG
sequentially on the aAs substrate _{1 p-Al y Ga 1-} y As / Al z
Ga _1-z As (0 <y <z) distributed reflection type (distributed
Bragg reflector, DBR) Multilayer reflector 2 (shaded area is A
l _z Ga _1-z As, the white portion is _{Al y Ga 1-y As)} ,
p-InGaP etch stop layer 3, p-Al _y G
a _1-y As / Al _z Ga _1-z As (0 <y <z) distributed Bragg reflector (DBR) multilayer film reflector 2 (the shaded portion is Al _z Ga _1-z As, and the white portion is Al
_y Ga _1-y As), non-doped-Al _w Ga
_1-w As lower spacer layer 5, GaAs / Al _x Ga _1-x
As multiple quantum well active layer 6, non-doped-Al
_y Ga _1-y As upper spacer layer _{7, n-Al y Ga 1} -y
As / Al _u Ga _1-u As (0 <y <z) distributed Bragg reflector (DBR) multilayer reflector 8, n-InGaP first growth final layer 9, AlGaAs
s or InGaP semiconductor buried layer (second round growth _{layer) 10, n-Al y Ga} 1-y As / Al z Ga 1-z A
s (0 <y <z) DBR reflector (third growth layer) 1
1, a lower electrode 12, an insulating film 13, an upper electrode 14, and an element isolation structure 15. Each layer of the DBR is set to have a film thickness of 分 の of the value obtained by dividing the oscillation wavelength by the refractive index of each layer.

Here, the structure manufacturing process will be described.
When the structure of FIG. 8 is manufactured, it can be roughly divided into three stages of growth. The first growth starts from the p-DBR on the p-GaAs substrate and grows to (part of) the MQW active layer and the n-DBR (corresponding to structures 2 to 9 in FIG. 8). The Al composition of the low-refractive index layer having several periods close to the active layers of the n-DBR and p-DBR (thickness corresponding to the depth at which a mesa is formed in a later step) is set lower than the Al composition of the other DBR portions. After growing the current confinement layer, a so-called refractive index waveguide is formed in which the current confinement layer has a refractive index distribution lower than that of the light resonator. Part of the low refractive index layer of p-DBR has p
-InGaP is used, which is intended to be used as an etching stop layer. The last layer is nI
nGaP. The purpose is to make the surface during regrowth AlG
This is because in the case of aAs, the influence of the surface oxide layer is large, and the higher the Al composition, the more difficult it is to obtain a high-quality layer as a regrown layer. Of course, the Al composition is 0.1 to 0.1.
When it is as low as about 2 and the oxidation of the surface does not greatly affect the regrowth of the crystal, a similar effect can be expected even if an AlGaAs layer is used by selecting an appropriate etchant in the process step. Next, photoresist, SiO
_A mesa structure is formed using an insulating film such as ₂ . As a forming method, both wet etching and dry etching are effective. The etching depth is p-InGaP considering optical monitoring or etching rate.
Stop short of the etch stop layer. Then, the surface of p-InGaP is exposed using a selective etchant. The second growth (current confinement layer, corresponding to the structure 10) is formed by using the mask for forming the mesa as it is as a selection mask for crystal growth.

At this time, the growth thickness at the flat portion is intentionally set lower than the mesa height. Then, the mesa becomes convex with respect to the current confinement layer. When the crystal is re-grown on this shape, a transition region 16 having a high growth rate appears outside the mesa (or in the in-plane low direction). Since the dopant flow rate during growth is constant, the doping concentration is lower in the region where the growth rate is higher than in other regions, and is reduced to one half or one third by setting the thickness of the current confinement layer. . The resistance in the thickness direction of the semiconductor DBR is sensitive to the doping concentration, and a difference of one or more digits can be obtained as the resistance due to the above-mentioned change in the doping concentration. When a voltage is applied to the upper and lower electrodes in the forward direction, the electric field is effectively concentrated inside the transition region where the resistance is high. Therefore, the contribution of the portion outside the electrode to the element content is reduced. In addition, since the electrode area is larger than the mesa diameter, the element resistance does not greatly increase. Overall, the CR self-constant is reduced as compared with the conventional structure, which has the effect of improving high-speed modulation characteristics.

The current confinement layer is formed by pnpn
.. Having a doving type of AlGaAs or I
An nGaP layer is used. Alternatively, a high-resistance semi-insulating layer is used as the regrown first layer. In that case, the effect of current constriction is further enhanced. Since polycrystal is usually laminated on the mask of the uppermost layer of the mesa, the polycrystal in the laser resonator portion is removed by etching using a photoresist as a mask (FIG. 3E). As a removing method, wet etching, dry etching, or a combination of both is effective. Further, if a growth condition in which polycrystal is not stacked is used for the mask of the uppermost layer of the mesa, the etching step of FIG. 3E can be omitted and the process can be simplified. As a final step, a third growth is performed after removing the mask above the mesa (structure 1).
1), and the n-DBR is grown for a period sufficient to obtain a reflectance satisfying the laser oscillation condition.

FIGS. 9A and 9B illustrate the device characteristics of the vertical cavity semiconductor laser shown in FIG. In the figure, the solid line is the case of the present embodiment, and the broken line is the conventional structure as shown in the first embodiment or FIG. 10 (reference: KLLear,
et al. Electronics Letters, vol.32, No.5, pp.457-5
8, 1996). FIG. 9A shows the element capacitance versus voltage characteristics. This shows how the element capacitance has been reduced by the new structure.

FIG. 9B shows the modulation characteristics. FIG. 9A shows an element having improved modulation characteristics due to the effect of reducing the element capacitance shown in FIG. 9A.

In this embodiment, the refractive index waveguide structure is used. However, even when the refractive index waveguide structure is not used, the same effect can be obtained with respect to the reduction of the device capacitance.

Although the above description has been given of the structure on the p-GaAs substrate, the same effect can be obtained in the case of the structure on the n-GaAs substrate. Although the description has been given of the AlGaAs / GaAs system, the same effect can be obtained in the InGaAs / GaAs system.

[0059]

As described above, in the present embodiment, in the vertical cavity type semiconductor laser, the DBR above the active layer is used.
(A part of), the mesa structure is formed, and then the thickness of the current constriction layer formed in the second growth is set lower than the mesa height to make the transition region having a high resistance outside the mesa. And the remaining DB needed for the third growth
Forming the R structure has the effect of reducing the element capacitance without significantly deteriorating the element resistance, and forming a vertical cavity semiconductor laser capable of improving high-speed modulation.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a conventional vertical cavity semiconductor laser.

FIG. 2 is a cross-sectional view in a direction perpendicular to a crystal growth surface of the vertical cavity semiconductor laser device according to the first embodiment of the present invention.

3A to 3F are cross-sectional views illustrating each step of a method for manufacturing the vertical cavity semiconductor laser device shown in FIG. 2;

FIG. 4 is a cross-sectional view in a direction perpendicular to a crystal growth surface of the vertical cavity semiconductor laser device according to the first embodiment of the present invention.

FIGS. 5A and 5B are graphs for explaining the characteristics of a vertical cavity semiconductor laser manufactured by the method for manufacturing a vertical cavity semiconductor laser device according to the first embodiment of the present invention; FIGS. FIG. 2 is a diagram showing current-to-light output characteristics and current-to-voltage characteristics of a vertical cavity semiconductor laser according to the present invention, and FIG. B is a diagram comparing a light-emitting far-field image of the present invention with a conventional light-emitting far-field image.

FIG. 6 is a cross-sectional view in a direction perpendicular to a crystal growth surface of a vertical cavity semiconductor laser device according to a second embodiment of the present invention.

FIGS. 7A and 7B are graphs for explaining characteristics of the vertical cavity semiconductor laser manufactured by the method for manufacturing a vertical cavity semiconductor laser device according to the first embodiment of the present invention; FIG. FIG. 2 is a diagram showing current-to-light output characteristics and current-to-voltage characteristics of a vertical cavity semiconductor laser according to the present invention, and FIG. B is a diagram comparing a light-emitting far-field image of the present invention with a conventional light-emitting far-field image.

FIG. 8 is a cross-sectional view in a direction perpendicular to a crystal growth surface of a vertical cavity semiconductor laser device according to a third embodiment of the present invention.

FIGS. 9A and 9B are graphs for explaining characteristics of a vertical cavity semiconductor laser manufactured by the method for manufacturing a vertical cavity semiconductor laser device according to the first embodiment of the present invention; FIGS. FIG. 3 is a diagram showing the element capacitance vs. voltage characteristic, and FIG.

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

[Explanation of symbols]

1 p-GaAs substrate _{2 p-Al y Ga 1-} y As / Al z Ga 1-z As (0
<Y <z) Distributed Bragg reflector,
DBR) multilayer mirror 3 p-InGaP etch stop layer _{4 p-Al y Ga 1-} y As / Al u Ga 1-u As (0
<Y <u <z) Distributed Bragg reflec
tor, DBR) multilayer mirror _{5 non-doped-Al w Ga} 1-w As lower spacer layer _{6 GaAs / Al X Ga 1-} X As multi-quantum well active layer _{7 non-doped-Al w Ga} 1-w As The upper spacer layer _{8 n-Al y Ga 1-} y As / Al u Ga 1-u As (0
<Y <u <z) DBR reflector 9 n-InGaP first round growth final layer 10 AlGaAs or InGaP semiconductor buried layer (second round growth _{layer) 11 n-Al y Ga 1} -y As / Al z Ga 1- _z As
(0 <y <z) DBR reflector (third time growth layer) 12 lower electrode 13 insulating film 14 upper electrode 15 for element isolation structure 16 monolayers semiconductor buried layer 101 p-GaAs substrate 102 p-Al _y Ga _{1 -y} As / Al _z Ga _1-z As
(0 <y <z) Distributed Bragg reflec
tor, DBR) Multi-layer reflector (shaded area is Al _z Ga _{1 -z} A)
s, white part is _{Al y Ga 1-y As)} 103 non-doped-Al w Ga 1-w As lower spacer layer _{104 GaAs / Al X Ga 1-} X As (x ≦ w) multiple quantum well active layer 105 non _{-doped-Al w Ga 1-w} As upper spacer layer _{106 n-Al y Ga 1-} y As / Al z Ga 1-z As
(0 <y <z) DBR reflector 107 Semiconductor buried layer 108 Lower electrode 109 Insulating film 110 Upper electrode

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Osamu Tadanaga, Inventor 3--19-2, Nishi-Shinjuku, Shinjuku-ku, Tokyo Within Nippon Telegraph and Telephone Corporation (72) Inventor Amano Main Tax 3-19, Nishi-Shinjuku, Shinjuku-ku, Tokyo No. 2 Inside Nippon Telegraph and Telephone Corporation (72) Takashi Kurokawa, inventor Nippon Telegraph and Telephone Corporation, 3-19-2 Nishi Shinjuku, Shinjuku-ku, Tokyo

Claims (28)

[Claims] 1. A semiconductor comprising a substrate, a lower DBR structure comprising a plurality of layers provided on the substrate, and at least one layer provided on the lower DBR structure and having an active layer embedded therein. A buried structure portion, and an upper DBR structure portion including a plurality of layers provided on the active layer; further, a resonator region is formed by the active layer and layers located above and below the active layer. , And the effective refractive index of each layer constituting the resonator region is the upper and lower DB.
A vertical cavity semiconductor laser, wherein the effective refractive index is higher than the effective refractive index of each of the other layers constituting the R structure and the effective refractive index of the layer constituting the semiconductor buried layer. 2. The vertical cavity semiconductor laser according to claim 1, wherein the semiconductor buried structure portion has an np repeating laminated structure or a pn repeating laminated structure. 3. The vertical resonance according to claim 1, wherein the semiconductor buried structure portion has a structure in which a semi-insulating layer is laminated with an np repeating laminated structure or a pn repeating laminated structure. Semiconductor laser. 4. The vertical cavity semiconductor laser according to claim 1, wherein said semiconductor buried portion is formed only of a semi-insulating layer. 5. The vertical cavity semiconductor laser according to claim 1, wherein said semiconductor buried portion is formed of one layer, and said layer is ion-implanted. 6. The vertical cavity semiconductor laser according to claim 1, wherein the semiconductor buried portion is formed of AlGaAs having an effective refractive index lower than that of the cavity region. 7. The vertical cavity semiconductor laser according to claim 1, wherein the semiconductor buried portion is formed of InGaP having an effective refractive index lower than that of the resonator region. 8. The vertical cavity semiconductor laser according to claim 1, wherein the lower DBR structure has at least one layer made of InGaP having an effective refractive index lower than that of the resonator region. . 9. A semiconductor comprising a substrate, a lower DBR structure comprising a plurality of layers provided on the substrate, and at least one layer provided on the lower DBR structure and having an active layer embedded therein. A buried structure, and an upper DBR structure comprising a plurality of layers provided on the semiconductor buried structure in which the active layer is buried, further comprising the active layer and layers located above and below the active layer And the effective refractive index of each layer forming the resonator region is determined by the effective refractive index of each of the other layers forming the upper and lower DBR structures and the semiconductor buried layer. A vertical cavity semiconductor laser characterized by having a higher effective refractive index than a constituent layer. 10. The resistance of the upper DBR structure on the semiconductor buried structure is higher than the resistance of the upper DBR on the active layer.
The vertical cavity semiconductor laser according to claim 9, wherein the resistance is higher than the resistance of the R structure. 11. The semiconductor buried structure portion includes an np
The vertical cavity semiconductor laser according to claim 9, wherein the semiconductor laser has a repeating laminated structure or a pn repeated laminated structure. 12. The vertical resonance according to claim 9, wherein the semiconductor buried structure portion has a structure in which an np repeating laminated structure or a pn repeating laminated structure is laminated on a semi-insulating layer. Semiconductor laser. 13. The vertical cavity semiconductor laser according to claim 9, wherein the embedded semiconductor structure is formed only of a semi-insulating layer. 14. The vertical cavity semiconductor laser according to claim 9, wherein the semiconductor buried structure is formed of one layer, and the layer is implanted with ions. 15. The vertical cavity semiconductor laser according to claim 9, wherein said embedded semiconductor structure is made of AlGaAs having an effective refractive index lower than that of said optical resonator region. 16. The vertical cavity semiconductor laser according to claim 9, wherein said embedded semiconductor structure is made of InGaP having an effective refractive index lower than that of said optical resonator region. 17. The method according to claim 17, wherein the lower DBR structure is made of InGaP.
2. The vertical cavity semiconductor laser according to claim 1, comprising at least one layer formed by: 18. A semiconductor, comprising: a substrate; a lower DBR structure comprising a plurality of layers provided on the substrate; and at least one layer provided on the lower DBR structure and having an active layer embedded therein. A method for manufacturing a vertical cavity semiconductor laser device having a buried structure portion and an upper DBR structure including a plurality of layers provided on a semiconductor buried structure portion in which the active layer is buried, comprising: A first growth step of growing from the structure part to the active layer or a part of the upper DBR structure part; a step of forming a mesa structure part by etching to a lower part of the active layer; A second growth step of embedding a layer; and a third growth step of re-growing an upper DBR structure on the semiconductor buried structure. A resonator region is provided by layers above and below the active layer, and the effective refractive index of each layer constituting the resonator region is equal to the effective refractive index of each of the other layers constituting the upper and lower DBR structures. And so as to be higher than the effective refractive index of the layer constituting the semiconductor buried structure,
A method for manufacturing a vertical cavity semiconductor laser device, comprising controlling the composition of a mixed crystal. 19. The method of manufacturing a vertical cavity semiconductor laser device according to claim 18, wherein the thickness of the embedded semiconductor structure is smaller than the height of the mesa structure. 20. The semiconductor buried structure portion, wherein np
The method for manufacturing a vertical cavity semiconductor laser device according to claim 18, wherein the vertical cavity semiconductor laser device has a repeating laminated structure or a pn repeated laminated structure. 21. The vertical resonance according to claim 18, wherein the semiconductor buried structure portion has a structure in which a semi-insulating layer is laminated with an np repeated laminated structure or a pn repeated laminated structure. For manufacturing a semiconductor laser device having a rectangular shape. 22. The method according to claim 18, wherein the semiconductor buried portion is formed only of a semi-insulating layer. 23. The method according to claim 18, wherein the semiconductor buried portion is formed of one layer, and the layer is implanted with ions. 24. The method according to claim 18, wherein the semiconductor buried portion is formed of AlGaAs having an effective refractive index lower than that of the optical resonator region. . 25. The method of manufacturing a vertical cavity semiconductor laser device according to claim 18, wherein said semiconductor buried portion is formed of InGaP having an effective refractive index lower than that of said optical resonator region. . 26. The lower DBR structure section is made of InGaP.
19. The method for manufacturing a vertical cavity semiconductor laser device according to claim 18, comprising one or more layers formed by: 27. In the first growth step, a lower portion D
19. The method according to claim 18, wherein the BR structure has a final layer of InGaP. 28. A vertical cavity semiconductor laser manufactured by the manufacturing method according to claim 18. Description: