JPH0997950A - Semiconductor laser and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a semiconductor laser in which the value of a threshold current is reduced and which can be oscillated in a single transverse mode by a method wherein a second clad layer and a third clad layer are formed of ZnMgSSe and compositions of Mg and S for an optical confinement layer are made larger than compositions of Mg and S for the second and third clad layers. SOLUTION: An n-type GaAs buffer layer 102, an n-type ZnSe buffer layer 103, a first n-type ZnMgSSe clad layer 104, a first ZnSSe light guide layer 105, a multiple quantity well layer 106, a second ZnSSe light guide layer 107, a second p-type ZnMgSSe clad layer 108 and a ZnMgSSe optical confinement layer 109 are laminated sequentially on an n-type GaAs substrate 101. A groove 111 which reaches the second clad layer 108 is formed in the optical confinement layer 109, and a third p-type ZnMgSSe clad layer 112 is formed so as to bury the groove 111. At this time, compositions of Mg and S for the optical confinernent layer 109 are made larger than compositions of Mg and S for the second and third clad layers 108, 112.

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 a manufacturing method thereof, and more particularly to a semiconductor laser which oscillates in a single transverse mode (hereinafter also referred to as "single mode") and a manufacturing method thereof.

[0002]

2. Description of the Related Art Continuous oscillation at room temperature is possible by establishing a doping technique for p-type and n-type impurities, introducing a quaternary mixed crystal structure using Mg, and adopting a contact layer using ZnTe. -Group VI semiconductor lasers are being realized. The realization of this semiconductor laser will increase the possibility of recording high-quality video information on a compact disc recording medium in the future.

FIG. 1 is a sectional view showing the structure of a conventional semiconductor laser 20 formed using a II-VI group semiconductor.

In manufacturing the semiconductor laser 20, first, on the n-type GaAs substrate 1 by the molecular beam epitaxy method,
n-type GaAs buffer layer (thickness: about 1 μm) 2, n-type ZnSe layer (thickness: about 30 nm) 3, n-type ZnMgSSe layer (thickness: about 1.2)
μm) 4, ZnSSe layer (thickness about 0.13 μm) 5, ZnCdSe
Active layer (thickness: about 8 nm) 6, second ZnSSe layer (thickness: about 0.
13 μm) 7, p-type ZnMgSSe layer (thickness 0.7 μm)
8, p-type ZnSSe layer (thickness about 0.4 μm) 9, p-type ZnSe layer (thickness about 0.1 μm) 10, p-type ZnSeTe layer (thickness about 50)
nm) 11 and the p-type ZnTe layer 12 are sequentially stacked. After that, while forming a stripe-shaped mesa structure (hereinafter, also referred to as “mesa stripe”), the above laminated structure is etched until the p-type ZnMgSSe layer 8 is exposed. Subsequently, an insulator, for example, a ZnS layer 13 is formed on both sides of the formed mesa stripe to fill the mesa stripe (hereinafter, this layer 13 is also referred to as "buried layer 13"). Then, Au / P is formed on the upper surface of the mesa stripe (specifically, the uppermost p-type ZnTe layer 12) and the ZnS layer 13.
d electrode 15 is formed, and In is further formed on the back surface of the n-type GaAs substrate 1.
The electrode 14 is formed, and the semiconductor laser 20 is completed.

In this structure, current confinement is realized by forming a mesa stripe in the grown semiconductor laminated structure for laser oscillation, and the mesa stripe is further embedded in the buried layer 1.
Semiconductor laser 2 formed by embedding with 3
The surface of 0 is flattened. In addition, the buried layer 1
As the constituent material of No. 3, the constituent material of the clad layer included in the semiconductor laminated structure for laser oscillation (ZnMg in the above example)
Material with a lower refractive index than SSe (Zn in the above example)
S) is used to realize lateral light confinement.

On the other hand, FIG. 2 is a sectional view showing the structure of another conventional semiconductor laser 30 disclosed in Japanese Patent Laid-Open No. 7-7183. The semiconductor laser 30 is a blue light-emitting laser in which a ZnCdSSe system II-VI group semiconductor material is epitaxially grown on an n-type GaAs substrate 31 to form a semiconductor laminated structure for laser oscillation, and has a short wavelength of about 500 nm. A laser beam having a wavelength can be emitted.

Specifically, n on the n-type GaAs substrate 31
-Type ZnSe buffer layer 32, n-type ZnSSe first optical confinement layer 3
3, the ZnCdSe active layer 34, and the p-type ZnSSe second optical confinement layer 35 are sequentially stacked. Further, on the second optical confinement layer 35, a GaAs current blocking layer 36 having a strip-shaped opening region 36a provided at the center is formed. A p-type ZnSSe third optical confinement layer 37 and a p-type ZnSe contact layer 38 are formed on the current blocking layer 36. Then, electrodes 39 and 40 are provided on the upper surface of the contact layer 38 and the back surface of the substrate 31, respectively, to complete the semiconductor laser 30.

In the semiconductor laser 30, when the current L flowing from the electrode 39 to the active layer 34 passes through the current blocking layer 36, it passes only through the band-shaped opening region 36a. Therefore, the current L is generated in the active layer 34 in the band-shaped opening region 36a.
Flowing into the area 34a facing the
Only 4a contributes to laser oscillation. In addition to such a current concentration effect, the current blocking layer 36 and the active layer 34 are provided close to each other, whereby the current spreading in the second optical confinement layer 35 is suppressed. As a result, in the semiconductor laser 30, the bias voltage applied between the electrodes 39 and 40 is reduced, and as a result, the power consumption is reduced and the temperature dependence of the operation is improved.

Further, in the semiconductor laser 30, the GaAs forming the current blocking layer 36 and the second and third optical confinement layers 3 are formed.
Since there is a difference in the refractive index between the II-VI group semiconductor material (ZnSSe) constituting 5 and 37, there is a difference in light absorption between them. As a result, the strip-shaped opening region 36a of the current block layer 36 functions as a lateral optical waveguide, and the lateral spread state of light can be controlled by appropriately adjusting the width of the strip-shaped opening region 36a.

[0010]

The conventional semiconductor laser 20 having the structure shown in FIG. 1 has the following problems.

First, the buried layer 13 which realizes current confinement and lateral mode control is polycrystalline or amorphous. Impurities introduced between the crystal grain boundaries contained therein and the thin film layer included in the laminated structure for laser oscillation and the buried layer 13 may form an abnormal current path. Therefore, there may occur reliability problems such as deterioration of current characteristics.

Further, since the buried layer 13 is not a single crystal layer, it is impossible to grow a single crystal layer on the buried layer 13. Therefore, the p-type contact layer that occupies a larger area than the mesa stripe cannot be grown on the mesa stripe, and the contact resistance cannot be reduced.

Further, the buried depth for realizing lateral light confinement, that is, the height of the mesa stripe is set to a predetermined value by etching, but its control is very difficult. Further, the width of the mesa stripe needs to be extremely narrowed in order to realize single transverse mode oscillation, but it is difficult to form a sufficiently narrow stripe structure using a mask.

In addition, since the p-type electrode and the contact layer included in the semiconductor laminated structure for laser oscillation are in contact only with the width of the mesa stripe, the contact area between them is small. Therefore, a very large resistance is generated between the p-type electrode and the active layer.

On the other hand, in the conventional semiconductor laser 30 described with reference to FIG. 2, the contact layer 38 occupying a large area can be formed by crystal growth. Further, since the p-type electrode 39 is formed on the contact layer 38 thus formed, the contact layer 38 and the electrode 3 are formed.
The resistance between 9 and 9 is reduced. Therefore, the above-mentioned problem can be solved to some extent.

However, in the semiconductor laser 30, the substrate 31
As the constituent material of the semiconductor laminated structure formed on
A material that is lattice-matched to the substrate 31, except for the active layer 34, is used. Therefore, the composition of the cladding layer (optical confinement layer) is uniquely determined (specifically, ZnS _0.06 S
e _0.94 ), there is no freedom in designing the laser structure.

Further, in the structure of the semiconductor laser 30, the current blocking layer 36 is made of GaAs, but GaAs has a band gap large enough to absorb the oscillated laser beam. Therefore, the semiconductor laser 30 has an optical loss waveguide structure in which light is absorbed by the current blocking layer 36, and high output cannot be obtained due to the absorption of light by the current blocking layer 36.

The present invention has been made to solve the above problems, and its purpose is to (1) provide a II-VI group semiconductor laser having a small threshold current value and capable of single transverse mode oscillation. Providing, and (2) providing a manufacturing method thereof.

[0019]

A semiconductor laser according to the present invention comprises an active layer made of a II-VI group compound semiconductor material, and first and second active layers provided so as to sandwich the active layer from above and below. And a ZnMgSS provided on the second clad layer and having an opening for passing a current.
and a third cladding layer provided in the opening of the light confinement layer, the light confinement layer having a high resistance or the third confinement layer. Has a conductivity type opposite to that of the clad layer,
Clad layer of ZnMgSSe, and the composition of Mg and S of the optical confinement layer is M of the second and third clad layers.
It is larger than the composition of g and S, thereby achieving the above object.

In one embodiment, the opening of the light confinement layer is narrower on the side closer to the active layer.

Preferably, it further comprises an optical guide layer provided between the active layer and the first cladding layer and between the active layer and the second cladding layer.

Preferably, the refractive indices of the second and third cladding layers are larger than the refractive index of the light confining layer.

Preferably, a contact layer provided on the third cladding layer and an electrode provided on the contact layer are further provided, and the electrode and the contact layer contact each other in the element area. are doing. More preferably, the contact layer comprises at least ZnSe.

In another embodiment, an etching stop layer provided between the second cladding layer and the optical confinement layer is further provided.

A method of manufacturing a semiconductor laser according to the present invention comprises a step of growing a laminated structure including at least a first cladding layer, an active layer, a second cladding layer and an optical confinement layer on a substrate, and the optical confinement layer. A step of selectively forming a mask on the optical confinement layer, a step of etching the optical confinement layer using the mask until the second cladding layer is exposed, and forming an opening in the optical confinement layer; A step of growing a third cladding layer in the opening of the confinement layer to fill the opening, and a step of growing a contact layer on the third cladding layer, wherein the active layer is II. Formed of a group VI compound semiconductor material, the optical confinement layer has a high resistance or has a conductivity type opposite to that of the third cladding layer, and the second and third The cladding layer and the optical confinement layer are made of ZnMgSSe. Made which have the composition of Mg and S of the light confining layer is greater than the composition of Mg and S of the second and third cladding layers, the above-mentioned object can be achieved by it.

Preferably, the etching of the light confinement layer stops at least in the second cladding layer.

Preferably, the opening of the optical confinement layer is formed so that the side close to the second cladding layer is narrowed.

Preferably, the step of growing the third cladding layer is performed by regrowth, and the third cladding layer is subjected to a thermal history only once.

In one embodiment, a step of growing an etching stopper layer for stopping the etching of the optical confinement layer between the second cladding layer and the optical confinement layer, and exposing the optical confinement layer by etching. Cleaning the surface of the etch stop layer, further comprising growing the third cladding layer after the cleaning step. Preferably, the etch stop layer is III-V.
The etching stop layer is formed of a group compound semiconductor material, and the step of cleaning the etching stop layer includes the step of irradiating the exposed surface of the etching stop layer with plasma containing hydrogen.

The operation will be described below.

In the semiconductor laser of the present invention having the above-described structure and the method for manufacturing the same, since the semiconductor laminated structure for laser oscillation is formed by crystal growth, the optical confinement layer and the cladding layer included in the laminated structure are formed. The thickness can be set to a predetermined value by controlling the crystal growth process instead of controlling the etching process. Therefore, it is possible to reproducibly form an optical confinement structure having desired design parameters.

Further, since the opening of the light confinement layer is formed so as to be narrower on the side closer to the active layer, the width of the mask used for forming the opening is set to an effective mesa related to current confinement. It may be wider than the width of the stripe. For this reason,
A narrow mesa stripe can be easily formed.

Further, the third clad layer, the contact layer and the electrode are in contact with each other not by the width of the mesa stripe but by the element area. Therefore, the resistance generated between the electrode and the clad layer is significantly reduced.

The etching for forming the opening in the optical confinement layer may be stopped at least in the second cladding layer. Therefore, it is easy to control this etching process.

Alternatively, if an etching stopper layer is provided between the second cladding layer and the optical confinement layer, the etching process for forming the opening can be controlled more easily. Furthermore, if the etching stop layer is formed of a III-V semiconductor material, the etching surface exposed by the etching for forming the opening can be easily cleaned and smoothed, and the third surface can be formed on the surface. The clad layer can be easily regrown. If hydrogen plasma is used for cleaning and smoothing the surface of the etching stopper layer prior to the above-mentioned re-growth, the cleaning and planarizing treatment should be performed at a temperature relatively lower than the growth temperature of the third cladding layer. You can Therefore, the influence of heat on the semiconductor laminated structure can be reduced.

If the third cladding layer is formed by regrowth,
The influence of carrier inactivation of the p-type cladding layer due to heat can be reduced.

Further, since the optical confinement layer for current confinement is a single crystal layer continuously formed in the semiconductor laminated structure, there is a possibility that operating characteristics are adversely affected such as generation of unnecessary leak current. The likelihood that a phenomenon will occur is reduced.

Further, in the semiconductor laser of the present invention, the optical confinement layer that also functions as a current blocking layer is 4
It is composed of ZnMgSSe, which is an original mixed crystal II-VI compound semiconductor material. Since this material has a large band gap as compared with the wavelength of the oscillating laser light, it does not absorb the oscillating laser light, and a refractive index guided laser structure is realized. Therefore, the threshold current can be reduced to the extent that absorption of laser light does not occur, and laser oscillation up to a high output range can be achieved.

Further, as compared with the refractive index of the light confinement layer, the second
By increasing the refractive index of the third clad layer, the effective refractive index difference Δn in the horizontal direction can be provided in the active layer. In the semiconductor laser of the present invention, single transverse mode oscillation is realized by appropriately controlling this effective refractive index difference Δn. At this time, the cladding layer and the optical confinement layer are formed of a quaternary mixed crystal semiconductor material, but the quaternary mixed crystal semiconductor material has many compositions that are lattice-matched to the substrate. Therefore, it is possible to easily select and set the composition (material) that is lattice-matched to the substrate and provides an appropriate difference in effective refractive index, and thus the degree of freedom in designing the semiconductor laser is large.

[0040]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of a semiconductor laser according to the present invention and a method of manufacturing the same will be described with reference to the drawings.

FIGS. 3A to 3C are sectional views showing the structure and manufacturing process of the semiconductor laser 100 according to an embodiment of the present invention.

In manufacturing the semiconductor laser 100,
First, as shown in FIG. 3A, an n-type GaAs buffer layer 102 and an n-type ZnSe buffer layer 1 are formed on an n-type GaAs substrate 101.
03, n-type ZnMgSSe first cladding layer 104, ZnSSe first optical guide layer 105, multiple quantum well layer (active layer) 106, Zn
The SSe second optical guide layer 107, the p-type ZnMgSSe second cladding layer 108, and the ZnMgSSe optical confinement layer 109 are sequentially laminated. Specifically, a molecular beam epitaxy (MBE) method is used to sequentially epitaxially grow the above layers on the substrate 101. As a raw material for this MBE growth, for example, a ZnSe compound source, a ZnS compound source, a ZnTe compound source, and a Mg metal source are used. The purity of each is, for example, 99.9999% or more.

Next, as shown in FIG. 3B, a mask 110 is selectively formed on this laminated structure. Mask 11
0 has an opening at a position corresponding to the groove 111 formed below.

Further, the optical confinement layer 109 is etched using this mask 110 to form a groove 111. The material of the mask 110 can be, for example, a resist film, a silicon oxide film, or a silicon nitride film. The mask 110 is formed by forming these films into a predetermined stripe shape. Further, the etching for forming the groove 111 is performed using, for example, a dichromic acid type etchant or a saturated bromine water type etchant. here,
The dichromic acid type etchant is a mixed liquid of an aqueous solution of dichromic acid and concentrated sulfuric acid, and the mixing ratio thereof is, for example, 2: 1.
Further, the saturated bromine water-based etchant is a mixed liquid of saturated bromine water, water and phosphoric acid, and the mixing ratio thereof is, for example, 2: 15: 1.
It is.

Since the above etchant is an anisotropic etchant, the groove 111 is formed in a regular mesa shape. That is, the area of the bottom of the groove 111 near the active layer 106 (or the second cladding layer 108) is smaller than the area of the top of the groove 111 corresponding to the opening of the mask 110. Groove 1
The etching for forming 11 is p-type ZnMgSSe second
It may be stopped anywhere within the range of the thickness of the clad layer 108.

Next, the mask 110 is removed and the p-type ZnMgSS is removed.
e The third clad layer 112 is formed on the second clad layer 108 and the optical confinement layer 109 so as to fill the groove 111. Further, on the third cladding layer 112, p-type
ZnSSe cladding layer 113 and p-type ZnSe contact layer 11
4 are sequentially laminated. The third clad layer 112, the clad layer 113, and the contact layer 114 are all the second clad layer.
It is made of a material having the same composition as or close to that of the clad layer 108, and is crystal-grown by using an MBE apparatus.

After that, the p-type electrode 115 is formed on the p-type contact layer 114 by, for example, vapor deposition. The p-type electrode 115 can be composed of Pd / Au or Cr / Au. On the other hand, the n-type electrode 116 is formed on the back surface of the n-type GaAs substrate 101. The n-type electrode 116 can be an In electrode or a Ni / AuGe / Ni / Au electrode.

As a result, the semiconductor laser 100 of this embodiment having the structure shown in FIG. 3C is completed.

In the structure of the semiconductor laser 100 described above, Cl is used as the n-type dopant for the n-type ZnSe buffer layer 103 and the n-type ZnMgSSe first cladding layer 104, for example. This Cl doping has, for example, a purity of 9
It is possible to use 9.9999% ZnCl ₂ as a raw material. On the other hand, the p-type ZnMgSSe second cladding layer 108, the p-type ZnMgSSe third cladding layer 112, the p-type ZnSSe cladding layer 113, and the p-type ZnSe contact layer 114 are doped with p-type impurities by, for example, crystallizing in the form of N ₂ plasma. This can be done by introducing N during the growth step.

The etching for forming the groove 111 in the optical confinement layer 109 is performed until the second cladding layer 108 is exposed. Specifically, as described above, the etching is stopped in the second cladding layer 108. Good. Alternatively, the second cladding layer 108 may be used to further facilitate the control of etching.
An etching stop layer may be stacked between the light trapping layer 109 and the light confinement layer 109. The etching stop layer in this case is, for example,
Impurity concentration is about 1 × 10 ^-3 cm ^-3 and thickness is about 10n
It can be formed of p-type GaAs which is m. Alternatively, the etching stop layer may be, for example, p-type AlGaAs or p-type InGaAs.
It is also possible to use

Next, each semiconductor layer included in the semiconductor laser 100 will be described in more detail below.

The n-type ZnSe buffer layer 103 is made of sulfur (S) or magnesium (M) at the initial stage of the crystal growth process.
g) is introduced to prevent it from directly adhering to the GaAs substrate 101 and deteriorating the surface of the crystal obtained by growth. The thickness of the ZnSe buffer layer 103 is ZnSe and GaAs.
The critical thickness determined in relation to the lattice mismatch with
0 Å) Set below. Alternatively, the ZnSe buffer layer 103
Need not be provided.

When the composition of the n-type ZnMgSSe first cladding layer 104 is expressed as Zn _1-x Mg _x S _y Se _1-y , x = 0.10 to 0.26
In addition, y is within the range of 0.1 to 0.28, and the lattice constant of ZnMgSSe matches the lattice constant of GaAs, and the doping concentration and the band gap are set to optimum values. For example, x = 0.17 and y = 0.20.
The thickness of the first cladding layer 104 is set to about 2 μm or less, for example, about 1 μm. On the other hand, the impurity concentration is
The difference between the donor concentration Nd and the acceptor concentration Na is, for example, about
It is set to be 4x10 ¹⁷ cm ^-3 .

The ZnSSe first light guide layer 105 has a thickness of, for example, about 700Å. In addition, its composition is selected so that the lattice constant of ZnSSe matches the lattice constant of GaAs,
For example, when expressed as ZnS _z Se _1-z , z = 0.06.

The active layer 106 is made of, for example, Zn having a thickness of about 70Å.
The CdSe layer is used as a well layer and the thickness is, for example, about 100Å
It has a multiple quantum well structure using the ZnSe layer as a barrier layer. The number of well layers which are repeatedly formed by being sandwiched between the barrier layers is, for example, five. Alternatively, the structure may include only one well layer. Furthermore, as another structure,
A multiple quantum well structure using a ZnSe layer as a well layer and a ZnMgSSe layer as a barrier layer can also be used. With this ZnSe layer
Oscillation wavelength of about 450 nm when combined with ZnMgSSe layer
And the oscillation wavelength can be made shorter than in the case of using the ZnCdSe layer.

The thickness of the ZnSSe second light guide layer 107 is, eg, about 700Å. The composition is ZnS.
The lattice constant of Se is selected so as to match the lattice constant of GaAs. For example, when expressed as ZnS _z Se _1-z , z = 0.06.

The composition of the second cladding layer 108 made of p-type ZnMgSSe is, for example, x = 0.17 and y = 0.20 when expressed as Zn _1-x Mg _x S _y Se _1-y . The thickness is set to about 0.2 μm or less, for example, about 0.1 μm.
On the other hand, the impurity concentration is, for example, about 1 × 10 ¹⁷ cm ⁻³ .

For the ZnMgSSe optical confinement layer 109, as described above, the groove (that is, the opening) 1 is formed by using the mask 110 made of a stripe-shaped resist film or SiO ₂ film.
11 is formed. The width of the upper portion of the opening 111, that is, the stripe width of the mask 110 used to form the groove (opening) 111 is, eg, about 5 μm. Further, the depth to be dug in the etching step for providing the groove (opening) 111 when the etching stopper layer is not used is equal to or larger than the thickness of the ZnMgSSe optical confinement layer 109, and the bottom surface of the groove 111 is p. The ZnMgSSe type is set to remain in the second cladding layer 108. Therefore, it is not necessary to strictly control the etching process.

The ZnMgSSe optical confinement layer 109 may have high resistance without being doped at all. Alternatively, it may have an n-type opposite to the conductivity type (p-type) of the third cladding layer 112. The carrier concentration in the case of n-type doping is, for example, about 1 × 10 ¹⁸ cm ⁻³ .

The p-type ZnSe contact layer 114 has an impurity concentration of about 4 × 10 ¹⁷ cm ⁻³ and a thickness of about 0.8 μm, for example.

It is also possible to provide a p-type ZnTe contact layer in addition to the p-type ZnSe contact layer 114 so that the contact layer has a multi-layer structure. In such a multilayer contact structure, contact resistance is reduced. In that case,
First, the p-type ZnSe contact layer 114 is formed so that the impurity concentration is, for example, about 1 × 10 ¹⁸ cm ⁻³ and the thickness is, for example, about 0.3 μm, and the p-type ZnSe / ZnTe multiple quantum well layer (MQW) is further formed thereon. Layer and impurity concentration is, for example, about 5 × 10 ¹⁸ cm
^The p-type ZnTe second contact layer (none of which is shown) having a thickness of about ⁻³ at ⁻³ is MBE-grown. Then, the p-type electrode 115 is vapor-deposited on the second contact layer. P for the p-type ZnTe / ZnSe multiple quantum well layer and p-type ZnTe second contact layer additionally provided as described above
The doping of the type impurities can be performed by introducing N during the crystal growth process in the form of N ₂ plasma, for example.

The semiconductor laser 100 described above is used.
In, in place of ZnMgSSe, the same ZnSSe as the light guide layer can be used as the constituent material of the cladding layer.
Alternatively, omitting the light guide layer composed of ZnSSe, ZnM
It is also possible to have a structure in which the active layer is sandwiched only by the clad layer composed of gSSe.

The semiconductor laser 10 of the present invention described above
Zero can be configured to have a refractive index guided configuration. To this end, the ZnMgSSe optical confinement layer 109
The composition of Zn _0.81 Mg _0.19 S _0.22 Se _0.78 ,
p-type ZnMgSSe second clad layer 108 and p-type ZnMgSSe third
The composition of the clad layer 112 is, for example, Zn _0.83 Mg
_0.17 S _0.2 Se _0.8 As a result, the effective refractive index difference Δn sensed by the active layer 106 in the horizontal direction, that is, the groove (opening) 11 of the optical confinement layer 109 in the active layer 106.
The difference between the effective refractive index in the region corresponding to 1 and the effective refractive index in the other regions of the active layer 106 is about 4 × 10 ⁻³ ,
A refractive index guided structure is realized. In such a refractive index guided structure, a single transverse mode oscillation is possible and a current narrowing structure is realized. Further, the heat generated in the active layer 106 can be absorbed by the third cladding layer 112 filling the opening 111 of the light confinement layer 109.

The effective refractive index difference Δn is equal to the second and third
Refractive index of cladding layers 108 and 112 and optical confinement layer 1
09 and the thickness of the second cladding layer 108 left between the optical confinement layer 109 and the active layer 106 (hereinafter, referred to as “remaining thickness t”). Is determined by the ratio of thickness to thickness. According to the present invention, the second and third cladding layers 108 and 112
The thickness of the light confinement layer 109 is determined by the crystal growth process, not the etching process. Therefore, it is possible to realize a semiconductor laser in which the thicknesses thereof can be strictly controlled, which is highly accurate and has good reproducibility, and which can perform single transverse mode oscillation.

Here, in order to realize the single transverse mode oscillation in the refractive index guiding structure, the above effective refractive index difference Δn
Is preferably set within the range of 5 × 10 ⁻³ to 1 × 10 ⁻² . This is the second and third cladding layers 108 and 1
The composition of 12 is set in the range of x = 0.06 to 0.1 and y = 0.14 to 0.28 in Zn _1-x Mg _x S _y Se _1-y so that the band gap ΔEg becomes about 2.8 eV, On the other hand, the composition of the optical confinement layer 109 which also has a function as a current blocking layer is set so that x = 0.09 to 0.15 in Zn _1-x Mg _x S _y Se _1-y so that the band gap ΔEg becomes about 3.0 eV. And y =
It is set within the range of 0.18 to 0.28, and the second cladding layer 1
This is a typical value of the effective refractive index difference Δn when the remaining thickness t of 08 is set in the range of about 0.1 μm to about 0.5 μm.

The ZnMgSSe cladding layer having a bandgap ΔEg of about 2.8 eV can sufficiently perform p-type and n-type impurity doping in the structure of the II-VI group compound semiconductor laser and has a vertical direction. It is a general clad layer that can realize optical confinement.

On the other hand, generally, it is necessary to increase the composition of Mg in order to increase the band gap of the ZnMgSSe layer, but the doping efficiency deteriorates as the content of Mg increases. However, the band gap ΔEg is about 3.0 eV
Since the ZnMgSSe optical confinement layer is a layer that does not require doping, it can be formed relatively easily.

By combining the clad layer and the optical confinement layer each having the above composition and setting the effective refractive index difference Δn of the active layer to a value within the above range, a refractive index guided type (real index guide) is obtained. Single transverse mode lasing in a (type) structure is realized.

Active layer 1 for realizing single transverse mode oscillation
In order to set the effective refractive index difference Δn of 06 to a value within the above range, the thickness h of the light confinement layer 109 needs to be about 0.1 μm or more. On the other hand, if the thickness h of the light confinement layer 109 is thicker than about 1.0 μm, the step difference in the groove 111 becomes too large, and a crystal is regrown on the light confinement layer 109 so as to fill the groove 111. It deteriorates the crystallinity of the layer. Furthermore, since the step is too large, a relatively large concave portion is formed on the outermost surface of the semiconductor laser element formed, and a gap exists when the semiconductor laser element is mounted on the chip carrier. As a result, problems such as deterioration of heat dissipation characteristics and difficulty of bonding occur.

The second one, which is composed of ZnMgSSe
The third cladding layers 108 and 112 preferably have the same composition, but are not limited thereto.

The optical confinement layer 109 and p-type ZnMgSSe corresponding to the remaining thickness of the cladding layer in the ordinary laser structure.
The second cladding layer 108 is formed by the first crystal growth. Therefore, their thickness is more rigorously determined than when determined by etching.

In the embedded semiconductor laser 100 of the present invention having the structure described with reference to FIGS. 3A to 3C, the groove (opening) 11 provided in the optical confinement layer 109.
1, the current confinement is performed. Therefore, the p-type electrode 115 and the p-type ZnSe contact layer 114, the p-type ZnSe contact layer 114 and the p-type ZnSSe cladding layer 113, and the p-type ZnSSe
Clad layer 113 and p-type ZnMgSSe third clad layer 112
However, they are in contact with each other in the element area. As a result, the resistance in the vertical direction (that is, the direction between the electrodes) generated in the semiconductor laminated structure is much lower than that in the structure of the prior art.

In order to obtain a sufficient current constriction effect, the remaining thickness t, which is the thickness of the second cladding layer below the optical confinement layer 109, must be about 0.5 μm or less. . When the remaining thickness t is larger than about 0.5 μm,
The distance between the bottom surface of the groove 111 and the active layer 106 becomes too long, and the current spread at that portion becomes too large. If the remaining thickness t becomes too small, the active layer 1
There is a possibility that the effective refractive index difference Δn at 06 becomes too large and it becomes difficult to control the transverse mode laser oscillation. However, this problem is caused by the composition of ZnMgSSe constituting the optical confinement layer 109 and the optical confinement layer 109. This can be overcome by setting the thickness h of the above to an appropriate value within the above range.

4 and 5, the composition of the second and third clad layers 108 and 112 is Zn _1-x Mg _x S _y Se _{1-y where} x = 0.08 and y = 0.18, while the optical confinement is performed. Layer 109
The composition of Zn _1-x Mg _x S _y Se _1-y is x = 0.11 and y =
A graph showing the relationship between the thickness of the optical confinement layer and the threshold current for laser oscillation when the value is 0.24 (Fig. 4), and the remaining thickness of the second cladding layer and the threshold for laser oscillation. It is a graph (FIG. 5) which shows the relationship with an electric current.

In FIG. 4, Mg of the optical confinement layer 109 is
When the composition is increased to increase the band gap ΔEg and the effective refractive index difference Δn in the active layer 106 is increased, the characteristics change from what is drawn by the solid line to what is drawn by the broken line. In this case, since the refractive index of the light confinement layer 109 becomes small, even if the thickness of the light confinement layer 109 is thinner, a sufficient effective refractive index difference Δn can be obtained. As a result, the threshold current for laser oscillation becomes low.

On the other hand, also in FIG. 5, the optical confinement layer 10
When the Mg composition of No. 9 is increased to increase the band gap ΔEg and the effective refractive index difference Δn in the active layer 106 is increased, the characteristics change from what is drawn by the solid line to what is drawn by the broken line. In this case, since the refractive index of the light confinement layer 109 is small, even if the remaining thickness of the second cladding layer 108 is increased, a sufficient effective refractive index difference Δn can be obtained. However, if the remaining thickness is too thin, the effective refractive index difference Δn becomes too large, and it becomes difficult to control the transverse mode laser oscillation, and the threshold current for laser oscillation increases.

Next, regarding the difference in contact area between the p-type electrode and the p-type contact layer and the difference in current path between the semiconductor laser according to the present invention and the semiconductor laser according to the prior art, FIGS. This will be described with reference to b).

FIG. 6A is a sectional view showing the structure of a semiconductor laser 300 formed by the conventional technique.
1B is a cross-sectional view showing the configuration of the semiconductor laser 100 of the present invention described above with reference to FIGS. 1A to 1C. Of these, in FIG. 6B, the same reference numerals are given to the same constituent elements as before, and the description thereof will be omitted. On the other hand, in the conventional semiconductor laser 300 of FIG.
On the GaAs substrate 301, n-type GaAs buffer layers 302, n
-Type ZnSe buffer layer 303, n-type ZnMgSSe first cladding layer 304, ZnSSe first optical guide layer 305, CdZnSe active layer 3
06, the ZnSSe second optical guide layer 307, the p-type ZnMgSSe second cladding layer 308, and the p-type contact layer 309 are sequentially stacked, and then the p-type ZnMgSSe second cladding layer 308 and p
The mold contact layer 309 is etched to form a mesa stripe. After that, apply the mesa stripe to the ZnMgSSe layer 3
10 and then p on the buried layer 310.
The mold electrode 311 is formed. On the other hand, the n-type electrode 312 is formed on the back surface of the n-type GaAs substrate 301. by this,
The semiconductor laser 300 is completed.

The semiconductor laser 300 according to the prior art as described above and the semiconductor laser 100 according to the present invention have a side length parallel to the groove 111 (hereinafter, referred to as “stripe”) of the mesa stripe or the optical confinement layer 109. Is about
350 μm, the length of one side perpendicular to the stripe is about 700
The structures of the two are compared, assuming that the device area occupies the width of μm and the width of the stripe is about 5 μm.

At this time, in the structure of the semiconductor laser 300 according to the prior art shown in FIG. 6A, the p-type electrodes 311 and p
The contact area with the mold contact layer 309 is about 1750 μm ² . On the other hand, in the structure of the semiconductor laser 100 according to the present invention shown in FIG. 6B, the contact area between the p-type electrode 115 and the p-type contact layer 114 is about 245000 μm ² , which is about 140 times the value of the prior art. is there. Therefore, according to the present invention, the resistance generated between the p-type electrode and the p-type contact layer is set to about 1/140 of the value in the semiconductor laser 300 having the corresponding structure formed by the conventional technique. You can Further, the vertical resistance generated between the p-type contact layer and the p-type cladding layer is also significantly reduced.

Further, in the semiconductor laser 300 according to the prior art shown in FIG. 6A, the current (shown by the broken line) flowing from the p-type electrode 311 to the n-type electrode 312 spreads over the entire element region. On the other hand, in the semiconductor laser 100 of the present invention, as shown in FIG.
The current (shown by the broken line) flowing from the optical confinement layer 10
And the active layer 106 is narrowed by the groove (opening) 111
Flows into. Therefore, in the active layer 106, the region where current actually flows does not extend beyond the width of the stripe, that is, the mask used for forming the groove 111 of the optical confinement layer 109. This is very effective in reducing the threshold current for laser oscillation.

[0082]

As described above, in the semiconductor laser and the method of manufacturing the same according to the present invention, since the semiconductor laminated structure for laser oscillation is formed by crystal growth, the optical confinement layer and the clad included in the laminated structure are formed. The layer thickness can be set to a predetermined value by controlling the crystal growth process rather than the etching process. Therefore, it is possible to reproducibly form an optical confinement structure having desired design parameters.

Further, in the semiconductor laser of the present invention, the optical confinement layer is formed by crystal growth and is not a polycrystalline layer or an amorphous layer. Therefore, crystal grain boundaries do not exist in the optical confinement layer and impurities are not captured at the boundary between the laminated structure for laser oscillation and the optical confinement layer, which causes leakage current. Therefore, the operating characteristics are not adversely affected.

Further, since the opening of the light confinement layer is formed so as to be narrower on the side closer to the active layer, the width of the mask used for forming the opening is set to be an effective mesa related to current confinement. It may be wider than the width of the stripe. For this reason,
A narrow mesa stripe can be easily formed.

Further, the third clad layer, the contact layer and the electrode are in contact with each other not by the width of the mesa stripe but by the element area. Therefore, the resistance generated between the electrode and the clad layer is significantly reduced.

The etching for forming the opening in the light confining layer may be stopped at least in the second cladding layer. Therefore, it is easy to control this etching process.

Alternatively, if an etching stop layer is provided between the second cladding layer and the optical confinement layer, the etching process for forming the opening can be controlled more easily. Furthermore, if the etching stop layer is formed of a III-V semiconductor material, the etching surface exposed by the etching for forming the opening can be easily cleaned and smoothed, and the third surface can be formed on the surface. The clad layer can be easily regrown. If hydrogen plasma is used for cleaning and smoothing the surface of the etching stopper layer prior to the above-mentioned re-growth, the cleaning and planarizing treatment should be performed at a temperature relatively lower than the growth temperature of the third cladding layer. You can Therefore, the influence of heat on the semiconductor laminated structure can be reduced.

If the third cladding layer is formed by regrowth,
The influence of carrier inactivation of the p-type cladding layer due to heat can be reduced.

Further, since the optical confinement layer for current confinement is a single crystal layer continuously formed in the semiconductor laminated structure, there is a possibility that operating characteristics are adversely affected such as generation of unnecessary leak current. The likelihood that a phenomenon will occur is reduced.

Further, in the semiconductor laser of the present invention, the optical confinement layer which also functions as the current blocking layer is 4
It is composed of ZnMgSSe, which is an original mixed crystal II-VI compound semiconductor material. Since this material has a large band gap as compared with the wavelength of the oscillating laser light, it does not absorb the oscillating laser light, and a refractive index guided laser structure is realized. Therefore, the threshold current can be reduced to the extent that absorption of laser light does not occur, and laser oscillation up to a high output range can be achieved.

The second refractive index of the light confinement layer is higher than that of the second refractive index.
By increasing the refractive index of the third clad layer, the effective refractive index difference Δn in the horizontal direction can be provided in the active layer. In the semiconductor laser of the present invention, single transverse mode oscillation is realized by appropriately controlling this effective refractive index difference Δn. At this time, the cladding layer and the optical confinement layer are formed of a quaternary mixed crystal semiconductor material, but the quaternary mixed crystal semiconductor material has many compositions that are lattice-matched to the substrate. Therefore, it is possible to easily select and set the composition (material) that is lattice-matched to the substrate and provides an appropriate difference in effective refractive index, and thus the degree of freedom in designing the semiconductor laser is large.

As described above, according to the present invention, it is possible to manufacture a semiconductor laser having excellent laser oscillation operation characteristics and reliability and having a small variation in laser oscillation operation characteristics among samples with good reproducibility.

[Brief description of drawings]

FIG. 1 is a sectional view showing a structure of a semiconductor laser according to a conventional technique.

FIG. 2 is a sectional view showing the configuration of another semiconductor laser according to the related art.

3A to 3C are cross-sectional views showing a structure of a semiconductor laser of the present invention and a manufacturing process thereof.

FIG. 4 is a graph showing the relationship between the thickness of the optical confinement layer and the threshold current for laser oscillation.

FIG. 5 is a graph showing the relationship between the remaining thickness of the second cladding layer and the threshold current for laser oscillation.

FIG. 6 is a cross-sectional view for schematically explaining a contact area between a contact layer and an electrode and a current path in a semiconductor laser according to a conventional technique and a semiconductor laser of the present invention,
(A) is a cross-sectional view showing a structure of a semiconductor laser according to a conventional technique, and (b) is a cross-sectional view showing a structure of a semiconductor laser according to the present invention.

[Explanation of symbols]

 101 n-type GaAs substrate 102 n-type GaAs buffer layer 103 n-type ZnSe buffer layer 104 n-type ZnMgSSe first cladding layer 105 ZnSSe first optical guide layer 106 multiple quantum well layer (active layer) 107 ZnSSe second optical guide layer 108 p Type ZnMgSSe second clad layer 109 ZnMgSSe optical confinement layer 110 mask 111 groove (opening) 112 p-type ZnMgSSe third clad layer 113 p-type ZnSSe clad layer 114 p-type ZnSe contact layer 115 p-type electrode 116 n-type electrode

Claims (13)

[Claims] 1. An active layer formed of a II-VI group compound semiconductor material, and a first layer provided so as to sandwich the active layer from above and below.
And a second cladding layer, an optical confinement layer formed of ZnMgSSe, which is provided on the second cladding layer and has an opening through which a current flows, and the opening of the optical confinement layer. And a third cladding layer provided on the optical waveguide, the optical confinement layer having a high resistance or having a conductivity type opposite to that of the third cladding layer. A semiconductor laser in which the second and third cladding layers are formed of ZnMgSSe, and the composition of Mg and S of the optical confinement layer is larger than the compositions of Mg and S of the second and third cladding layers. 2. The semiconductor laser according to claim 1, wherein the opening of the light confinement layer is narrowed on the side close to the active layer. 3. The light guide layer according to claim 1, further comprising an optical guide layer provided between the active layer and the first cladding layer and between the active layer and the second cladding layer, respectively. Semiconductor laser. 4. The semiconductor laser according to claim 1, wherein the refractive indices of the second and third cladding layers are higher than the refractive index of the light confinement layer. 5. A contact layer provided on the third cladding layer, and an electrode provided on the contact layer, the electrode and the contact layer contacting each other in an element area. The semiconductor laser according to claim 1, wherein 6. The semiconductor laser according to claim 5, wherein the contact layer contains at least ZnSe. 7. The semiconductor laser according to claim 1, further comprising an etching stop layer provided between the second cladding layer and the optical confinement layer. 8. A step of growing a laminated structure including at least a first clad layer, an active layer, a second clad layer and a light confinement layer on a substrate, and a mask selectively on the light confinement layer. Forming an opening in the optical confinement layer by etching the optical confinement layer using the mask until the second cladding layer is exposed, and the opening in the optical confinement layer. A step of growing a third clad layer on the third clad layer to fill the opening, and a step of growing a contact layer on the third clad layer, wherein the active layer is a II-VI group compound semiconductor. Formed of a material, the light confinement layer has a high resistance, or
Has a conductivity type opposite to that of the clad layer, and the second and third clad layers and the optical confinement layer are ZnMg.
A method of manufacturing a semiconductor laser, which is formed of SSe, wherein the composition of Mg and S of the light confinement layer is larger than the compositions of Mg and S of the second and third cladding layers. 9. The method of claim 8, wherein the etching of the light confinement layer stops at least in the second cladding layer. 10. The opening of the light confinement layer is formed so that the side close to the second cladding layer is narrowed.
The method of claim 8. 11. The method of claim 8, wherein the step of growing the third cladding layer is performed by regrowth, the third cladding layer undergoing a thermal history only once. 12. A step of growing an etching stop layer for stopping the etching of the light confinement layer between the second cladding layer and the light confinement layer, and the etching exposed by the etching of the light confinement layer. 9. The method of claim 8, further comprising cleaning the surface of the stop layer, the third cladding layer being grown after the cleaning step. 13. The etching stopper layer is formed of a III-V compound semiconductor material, and the step of cleaning the etching stopper layer includes a step of irradiating the exposed surface of the etching stopper layer with plasma containing hydrogen. 13. The method according to claim 12.