JPS62200785A - Semiconductor laser device and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a highly reliable laser device having a single basic lateral mode and capable of growing high-quality crystals on a surface having stepped portions even with mixed crystals having strict lattice-matching conditions, by utilizing the same V-family element for a current blocking layer and for a substrate. CONSTITUTION:A semiconductor laser device according to the present invention comprises a semiconductor substrate 11 having a first type of conductivity, a clad layer 14 of the first type of conductivity, an active layer 15 and clad layers 16-18 having a second type of conductivity and having a linear projection 18 thereon. A double hetero junction structure is thus formed on the semiconductor substrate 11. A current blocking layer 21 is provided on the double hetero junction structure except at least a part of the projection 18 of the clad layers having the second type of conductivity so that it performs optical waveguide and constriction of electric current. In such a semiconductor laser device, the substrate 11, he double hetero junction structure 14-18 and the current blocking layer 21 may be formed of compound semiconductors of III-V families, while the double hetero junction structure 14-18 contains a V family element different from an V-family element composing the substrate 11 and the current blocking layer 21 contains the same V-family element with the substrate 11.

Description

Detailed Description of the Invention [Objective of the Invention] (Industrial Application Field) The present invention relates to a semiconductor laser having a current confinement effect and an optical waveguide effect, and in particular to a chemical vapor deposition method (chemical vapor deposition method) using an organic metal.
The present invention relates to a semiconductor laser device suitable for manufacturing by the MOCVD method (hereinafter abbreviated as MOCVD method) and a method for manufacturing the same.

(Prior Art) In recent years, the MOCVD method has been attracting attention as a method for producing semiconductor materials for semiconductor lasers used as light sources for optical information processing, replacing the conventionally used liquid phase epitaxy method (hereinafter abbreviated as LPE method). There is. This MOCVD method has excellent uniformity in controllability of composition and film thickness, and is thought to occupy an important position in future laser manufacturing technology.

Unlike the LPE method, the MOCVD method has a drawback in that it is difficult to obtain crystals with good luminous efficiency on top of steps such as grooves, so it is necessary to planarize the area from the substrate to the active layer. M.O.
A typical laser structure using the CVD method is the fifth one.
There is one using GaA or As as a material as shown in the figure. This is a G
By regrowing aA1As, current confinement and an optical waveguide are formed in a self-aligned manner.

In addition, in the figure, 51 is an n-GaAs substrate, and 52 is an n-Ga'
A, f? As cladding layer, 53 is GaAs active layer, 54
55 is a p-GaAs cladding layer, 55 is an n-GaAs current blocking layer, and 56 is p-GaAl! As cladding layer, 57
58 and 59 indicate a p-GaAs contact layer and electrodes, respectively. However, in a laser with this structure, the layer regrown on the groove plays the role of optical confinement and current path, so there are strict requirements for the crystal quality of this regrown layer. Only prototype lasers have been reported.

By the way, as a recent technological trend, InGaAs, which can be used for longer and shorter wavelengths, is being used as a semiconductor material for long wavelength lasers for optical communication and short wavelength lasers for optical recording.
P, InGaA j7 As.

InGaANOP etc. are attracting attention. Among them, InGaANOP and I, which are composed of only one type of group V element,
This is suitable for the nGaAGaAlAs growth method. However, unlike GaA1As, these materials have strict conditions for lattice matching with the substrate crystal, making it difficult to create complex layer structures. Even a prototype has not been reported.

The present inventors have developed an InGaA film formed by MOCVD method.
iP, InGaA, f? We have been researching a semiconductor laser with a single transverse mode using As, and as a result,
It has been found that it is difficult to obtain sufficient characteristics with the element having the structure shown in FIG. 5, which has been conventionally employed in lasers using GaA and 17As. That is, in the configuration shown in FIG. 5, the substrate is made of GaAs.
In a laser in which the cladding layer is InGaP and the active layer is InGaP, the laser deteriorates rapidly in an extremely short period of about one hour, and reliability that can withstand practical use cannot be expected. In order to investigate the cause of this deterioration, we examined the striped portion of the wafer by X-ray diffraction, and found that the lattice mismatch was 0.1[
In contrast, lattice mismatch of 0.2% or more is observed in the regrown portion on the groove, and the occurrence of dislocations due to this large lattice mismatch is the main cause of rapid deterioration. it is conceivable that.

Such a phenomenon is considered to be common to mixed crystal materials in which the conditions for lattice matching are strict because the properties of the constituent group (I) elements are significantly different from those of the substrate. Therefore, in order to realize a semiconductor laser having a single fundamental transverse mode using InGaA, f'P, or InGaA-As, which is expected to have increasing demands in the future, it is necessary to
It is clear that the semiconductor laser manufacturing technology used in the above cannot be applied as is, and a completely new technology is required.

(Problems to be solved by the invention) As mentioned above, in the conventional device, InGaAiP and InG
When using a mixed crystal material with strict lattice matching conditions such as aA or As, it is difficult to grow a high-quality crystal on a surface with steps, and it is difficult to grow a high-quality crystal on a surface with steps. It has been extremely difficult to realize a semiconductor laser that operates in one fundamental transverse mode.

The present invention has been made in consideration of the above circumstances, and its purpose is to provide InGaAnoP and 1nGaAJ!
Even when using a mixed crystal material with strict lattice matching conditions such as As, a high-quality crystal can be grown on a surface with steps, and this is a highly reliable semiconductor laser with a single fundamental transverse mode. The goal is to provide equipment.

Another object of the present invention is to provide a method for manufacturing a semiconductor laser device that achieves the above object.

[Configuration of the Invention (Means for Solving Problems)] The gist of the present invention is to provide a semiconductor laser using a semiconductor material in which crystal growth is difficult due to problems such as lattice mismatch because the constituent group V elements are different from that of the substrate. In this method, a heterojunction with a different type of ■-V group semiconductor made of the same group V element as the substrate is formed around the striped convex portion provided in the cladding layer, thereby achieving current confinement and an optical waveguide structure. By creating the semiconductor material, regrowth of the semiconductor material that is difficult to grow crystals is avoided;
By switching the V group atmosphere on the crystal surface in an extremely short period of time during crystal growth, it is possible to create a heterojunction of semiconductors composed of mutually different group V elements.

That is, the present invention provides a first conductivity type semiconductor substrate, a first conductivity type cladding layer, an active layer, and a second conductivity type semiconductor substrate having a striped convex portion.
A double heterojunction structure made of a conductive type cladding layer and formed on the semiconductor substrate, and a current formed on the double heterojunction structure excluding at least a part of the convex part of a second conductive type cladding layer. In the semiconductor laser device comprising a blocking layer and performing optical waveguide and current confinement, the substrate.

The constituent materials of the double heterojunction structure and the current blocking layer are each made of a ■-V group compound semiconductor, and the group V element constituting the double heterojunction structure is different from the group V element constituting the substrate, The group V element constituting the current blocking layer is the same as the group V element constituting the substrate.

The present invention also provides a method for manufacturing a semiconductor laser device having the above structure, in which a first conductivity type cladding layer, an active layer and a second conductivity type cladding layer are formed on a first conductivity type semiconductor substrate, and a Group V element constituting the substrate is provided. A double heterojunction structure containing a group V element different from the group V element and a second conductivity type contact layer are successively grown in the above order by a chemical vapor deposition method using an organic metal, and then the second conductivity type contact layer is grown in the above order. forming an etching mask thereon, then selectively etching the contact layer using the mask, and selectively etching the second conductivity type cladding layer partway through to form striped convex portions in the cladding layer; Next, with the mask remaining or after removing the mask, a group V element, which is the same as the group V element constituting the substrate, is deposited on the double heterojunction structure and on the side surface of the contact layer by chemical vapor deposition using an organic metal. This is a method in which a current blocking layer containing elements is grown and formed.

(Function) According to the present invention, since the current blocking layer grown on the surface having steps is made of the same group V element as the substrate, the current blocking layer is grown in a high quality crystalline state. Become.

Therefore, the optical waveguide and current confinement structure are formed in a self-aligned manner using the MOCVD method. InG
aA, gP and I n G a A I! It becomes possible to realize a semiconductor laser using a mixed crystal material with strict conditions for lattice matching, such as As.

(Example) First, before describing an example, the basic principle of the present invention will be explained.

The present inventors used trimethylaluminum, trimethylgallium, and trimetatalindium, which are group (III) methyl-based metals, and arsine and phosphine, which are V-hydrogenides, as raw materials for forming each layer constituting a semiconductor laser. Using organometallic pyrolysis under subatmospheric pressure,
On InGaAnGaAlAs grown on InP substrate
#乎#=Step is formed on P and InP or I is formed on top of this.
InGaANOP or GaA grown on nGaAlAs substrate, ff
A step is formed on As and Ga is placed on top of this.
A,i? As or InGaAJ:! The experiment was repeated to re-grow P. As a result, the GaA no A formed a step.
Although regrowth of GaA, &AS on S or InGaAiP was easy, regrowth of high quality InGaAiP was difficult. Further, although it was easy to re-grow InP on InP or InGaAlAs with a step formed thereon, it was difficult to re-grow InGaA or i'As.

When these regrown layers were examined by X-ray diffraction, it was found that In
In GaAiP, InGaA, and i'As, the lattice constants were significantly different between the stepped portion and the flat portion, and many transitions were observed.

These InGaAiP and InGaAJ! AsnGaA
The difficulty in determining the lAs mixed crystal length is thought to be due to the following reasons. That is, InP, Ga
P, A, i? Because the lattice constant of P is significantly different from that of GaAs, with which this mixed crystal must be lattice-matched, and the lattice constant is sensitive to composition, this mixed crystal was regrown on a surface with steps. In this case, the difference in crystal growth between the stepped portion and the flat portion causes a compositional shift in fi, resulting in a large lattice mismatch. It is also believed that the reason why InGaA1As is difficult to re-grow on a step is based on the same reason. on the other hand,
InP and GaAlAs, which are composed of the same group III elements as the substrate that must be lattice-matched, do not have this problem with lattice matching, so if an appropriate method is used, high-quality crystals can be formed even on steps. It is considered that it is possible to grow with good reproducibility.

Hereinafter, details of the present invention will be explained with reference to illustrated embodiments.

FIG. 1 is a sectional view showing a schematic structure of a semiconductor laser according to an embodiment of the present invention. 11 in the figure is an n-GaAs substrate, and on this substrate 11 is an n-GaAs buffer layer 1.
2 and an n-InGaP buffer layer 13 are formed. On the buffer layer 13, n-InGaAl! P cladding layer 14° InGaP active layer 15 and p-1nGaA
A double heterojunction structure consisting of the cladding layer L6.17 and 1B is formed. Here, the cladding layer 17
is low A, f? This composition acts as an etching stop layer, which will be described later. Further, the cladding layer 18 is processed into a striped shape, thereby forming striped ribs in the p-cladding layer. On the cladding layer 18, p-I
An nGaA contact layer 19 and a p-GaAs contact layer 20 are formed.

An n-GaAs current blocking layer 21 is formed on the side surfaces of the double heterojunction structure and the contact layer 20. On the contact layer 20 and the current blocking layer 21, p-GaA
An s-contact layer 22 is formed.

A metal electrode 23 is attached to the upper surface of the contact layer 22, and a metal electrode 24 is attached to the lower surface of the substrate 11.

In this structure, current confinement is performed by a contact layer 20 and a current blocking layer 21, and optical waveguide is performed by a cladding layer 18 formed in a striped mesa.

Note that the buffer layer 13 is made of InGa formed on GaAs.
A. This is to improve the quality of ffP crystal.

Further, the contact layer (intermediate contact layer) 19 is intended to reduce the electrical resistance between the cladding layer 18 and the contact layer 20, and has a larger band gap than the contact layer 20, and has a larger bandgap than the cladding layer 18. It is sufficient if the band gap is small. Furthermore, the bandgap of the intermediate contact layer 19 may be made similar to the cladding layer 18 and the contact layer 20 at the portion thereof, and may be gradually changed from the cladding layer 18 to the contact layer 20.

Next, a method of manufacturing the semiconductor laser having the above structure will be described.

FIGS. 2(a) to 1' are cross-sectional views showing the manufacturing process of the example laser. First, the raw materials are metal-based group II organic metals (trimethylindium, trimethylgallium,
(trimethylaluminum) and V-hydrogenides (arsine, phosphine) under subatmospheric pressure.
By the OCVD method, the surface orientation (1
00) n-GaAs substrate jl (Si doped, 3x t
o18cIn-3) with a thickness of 0.5 [μml n-
GaAs first buffer layer 12 (Se doped, 3X 10
18n-3), thickness 0.5Ett m] n-In
GaP second buffer layer 13 (Se doped, 3x 101
8c11-3), thickness 1.5 [μ77Z] n-InGaA P first cladding 0.5 0.2
0.3 layer 13 (Se doped, IX 1018c11-3),
InGaP active layer 15 with a thickness of 0.1 [μ71L]. Thickness 0.5 0.5 0, I Cμ m co p-In
Ga A, ff PO,
50, 20, 3 Second cladding layer 10 (Mg doped, 2×to18cI1
1-3).

Thickness 0.02 [μ7 to act as etching stop layer
'IL] p-1nGaAno P third cladding 0.5
0.4 0.1 layer 17 (Mg doped, 2X 1018cII-3),
p-InGaA with a thickness of 1.4 [μ77Z]
40.5 0.2 0.3 Cladding layer 18 (Mg doped, 2x 1018cII-
3) , thickness 0.01 [μ
71′L] p-In Ga A, g P
Sequential growth of p-GaAs second contact layer 20 (Mg doped, 2X 1018 (1-3)) of first contact 0.5 0.4 0.1 layer 19 (Mg doped, 2X 10181018C and thickness 0.5Eμ7rL) Then, a 5i02 film 2G was formed on the second contact layer 20 in the form of a stripe with a width of 5 [μm] and a thickness of 0.1 [μ77Z] by thermal decomposition of silane gas and photolithography. Formed.

Next, as shown in FIG. 2(b), using the 5i02 film 26 as a mask, the second contact layer 20 is etched with a GaAs selective etchant to expose the first contact layer 19, and a GaAs film having a width of 3 [μ771] is etched. A striped mesa 27 was formed.

Next, as shown in FIG. 2(c), using the GaAs striped mesa 27 as a mask, the first contact layer 19 and the fourth contact layer 17 are etched using a selective etchant of InGaA and i'P until the third cladding layer 17 is exposed. Cladding layer 18
A striped mesa 28 was formed by etching.

By treating this wafer with a GaAs selective etchant, the second contact layer 20 was etched to narrow its width, thereby forming a striped mesa 29 having the shape shown in FIG. 2(d). Note that the selective etchant for GaAs is a mixture of 28% ammonia water, 35% hydrogen peroxide water, and water in a ratio of 1:30:9.
'C] was used.

The selected etchant for InGaA-P was sulfuric acid or phosphoric acid, and was used at a temperature of 40 to 130 ['C].

Next, by MOCVD under reduced pressure using trimethyl gallium and arsine as raw materials, an n-GaAs current blocking layer 21 (Mg-doped,
5x t018i-3) was grown to a thickness of 0.5 [μ7Il]. At this time, growth was performed by introducing diluted phosphine gas to 700 ['(l), then switching the phosphine gas flow to an arsine gas flow and waiting for about 1 second.
This was done by introducing a trimethyl gallium metal gas. As a result, no growth of GaAs was observed on the 5i02 film 26, and a wafer having the cross-sectional shape shown in FIG. 2(e) was obtained.

Next, after removing the 5i02 film 26, a p-GaAs third layer is deposited on the entire surface by MOCVD as shown in FIG.
Contact layer 22 (Mg doped.

5X to18C11-') was grown to a thickness of 3 [μm]. Thereafter, the normal electrode attachment process is performed by depositing the A u/Z n electrode 23 on the third contact layer 22 and the A u/G e electrode 24 on the lower surface of the substrate 11, as shown in FIG. A laser wafer having the structure shown was obtained.

The wafer thus obtained was cleaved to have a cavity length of 250 mm.
When a [μTL] laser device was fabricated, good characteristics were obtained, such as a threshold current of 90 [mA] and a differential quantum efficiency of 20 [%] per side. The light output is 20 [
mW] or more, showing good current-light output characteristics without kinks.

Furthermore, both the far-field image and the near-field image were unimodal, indicating that good mode control was performed.

As described above, according to this embodiment, the current confinement structure and the optical waveguide structure can be formed in a self-aligned manner, and since GaAs is used as the current blocking layer 21, current can be formed even on a stepped surface. The blocking layer 21 can be grown in a high quality crystalline state. Therefore, InGaAl! has strong demand as a light source for optical information processing! Even when using P, a semiconductor laser with a single fundamental transverse mode, small astigmatism, and stable operation even under the feedback of a large amount of externally reflected light has good reproducibility and high reliability. Together, they can be realized, and their usefulness is enormous. Furthermore, since the electrode 23 is deposited on the flat surface of the third contact layer 22, the contact resistance between the contact layer 22 and the electrode 23 can be made sufficiently small, and the deformation of the electrode 23 can be prevented. do not have. Therefore, there are advantages such as improvement in element characteristics and reliability.

Further, according to the manufacturing method of this embodiment, various difficulties that normally occur can be skillfully avoided. That is, the formation of an optical waveguide by selective etching and the creation of a current confinement structure by MOCVD under reduced pressure provide good reproducibility without using advanced microfabrication techniques. Furthermore, when forming an optical waveguide and current confinement structure by combining InGaAiP and GaAs (which may also be GaA)As as in the example, regrowth of InGaAiP and GaAs on the exposed surface at the same time is prevented. However, damage to the crystal surface due to evaporation of P and As during temperature rise is usually
a It is difficult to suppress both AnoP and GaAs at the same time. However, with the growth method adopted here,
Since the GaAs surface is covered with the 5i02 film 26, the above-mentioned problems do not occur, and good growth is achieved by raising the temperature in a P atmosphere. Furthermore, in this example, the width of the striped 5i02 film 26 is 5 [μm].
On the other hand, the width of the top of the second contact layer 20 is 3 [μ
m]. For this reason, the GaAs current blocking layer 21
The shape after growth is as shown in FIG. 2 (f'), and since the periphery of the second contact layer 20 that forms the current flow path is flat, it is easy to form an electrode thereon. There are advantages such as

Note that the present invention is not limited to the embodiments described above. For example, the third contact layer 22 may be omitted, and the third contact layer 22 may be omitted.
As shown in the figure, the electrode 23 may be directly deposited on the second contact layer 20. In addition, the third contact layer 2
2, the P-type diffusion layer 41 may be formed by diffusion or ion implantation of a P-type dopant such as Zn, as shown in FIG. Here, in the example of FIG. 4, during the growth of the current blocking layer 21 in FIG. 2(c),
The 5i02 film 26 is removed and a current blocking layer 21 is formed on the entire surface.
, and the diffusion layer 41 is formed in the portion where current confinement is to be performed.

In the example, after etching the p-1nGaAiP fourth cladding layer to form striped ribs,
Although the aAs second contact layer is re-etched, this re-etching step is not necessarily necessary. Also, p-
The second to fourth cladding layers made of InGaAsP can also be formed as a single layer. Furthermore, the p-InGaA first contact layer (intermediate contact layer) does not necessarily have to be used.

Further, the present invention can be similarly applied to lasers using materials other than those described in the embodiments.

For example, GaA AS with GaAs as a substrate.

InGaAsP or InGaA with InP as a substrate
, 7? Lasers using As, j, nGaAsP, etc. can be considered. Furthermore, in the embodiment, the first conductivity type is n type, and the second conductivity type is n type.
Although the conductivity type is p-type, it goes without saying that these may be reversed. In addition, various modifications can be made without departing from the gist of the present invention.

[Effects of the Invention] As detailed above, according to the present invention, the current blocking layer grown on the surface of the second conductivity type cladding layer having a step such as the striped convex portion is made of the same V group as the substrate. Since it is composed of elements, the current blocking layer can be grown in a high-quality crystalline state while forming the current confinement structure and the optical waveguide structure in a self-aligned manner. Therefore, InGaA, f7P
Despite using mixed crystal materials with strict conditions for lattice matching, such as InGaA and As, highly reliable semiconductor lasers with a single fundamental transverse mode were realized, and optical information It is extremely effective as a processing light source, etc.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the element structure of a semiconductor laser according to an embodiment of the present invention, FIGS. 4 is a sectional view showing a modified example, and FIG. 5 is a sectional view showing an element structure of a conventional laser. 1l-n-GaAs substrate, 12-n-GaAs buff layer, 13...n -1nGaP buffer layer, 14
... n-1 nGaA P cladding layer (first conductivity type cladding layer), ■5-I nGaP active layer, 16, 17
, l8-...p-1nGaAiP cladding layer (second conductivity type cladding layer), 19-p-1nGaAJP:
+ contact layer, 20.22-=p-GaAs contact layer, 21-...n-GaAs current blocking layer, 23
．． 24--electrode, 2G--5i02 film. Applicant's agent Patent attorney Takehiko Suzue Figure 1

Claims (8)

[Claims] (1) A double heterojunction structure formed on the semiconductor substrate, consisting of a first conductivity type semiconductor substrate, a first conductivity type cladding layer, an active layer, and a second conductivity type cladding layer having striped convex portions. and a current blocking layer formed on the double heterojunction structure excluding at least a part of the convex portion of the second conductivity type cladding layer, and performing optical waveguide and current confinement, The constituent materials of the substrate, double heterojunction structure and current blocking layer are respectively
It is a III-V group compound semiconductor, and the double heterojunction structure includes a group V element different from the group V element constituting the substrate, and the current blocking layer includes the same group V element as the substrate. Semiconductor laser device. (2) The substrate is GaAs, and the double heterojunction structure is In_xGa_1_-_x_-_yAl_yP(0
≦y≦1) The current blocking layer is Ga_1_-_zAl_z
The semiconductor laser device according to claim 1, characterized in that As (0≦z≦1). (3) The substrate is InP, and the double heterojunction structure is In_xGa_1_-_x_-_yAl_yAs(0
≦y≦1), the semiconductor laser device according to claim 1, wherein the current blocking layer is made of InP. (4) On the second conductivity type cladding layer and current blocking layer,
2. The semiconductor laser device according to claim 1, further comprising a second conductivity type contact layer. (5) Between the contact layer and the second conductivity type cladding layer, at least one second conductivity type intermediate contact layer having a larger band gap than the contact layer and a smaller band gap than the cladding layer is provided. A semiconductor laser device according to claim 4, characterized in that: (6) The intermediate contact layer has a smaller band gap closer to the contact layer and a larger band gap closer to the second conductivity type cladding layer, and the band gap gradually changes between the layers. A semiconductor laser device according to claim 5, characterized in that: (7) In a method for manufacturing a semiconductor laser device made of a III-V group compound semiconductor material, a semiconductor substrate of a first conductivity type, a cladding layer of a first conductivity type, an active layer, and a cladding layer of a second conductivity type are placed on a semiconductor substrate of the first conductivity type. a step of successively growing and forming a double heterojunction structure containing a group V element different from the constituent group V element and a second conductivity type contact layer in the above order by a chemical vapor deposition method using an organic metal; forming an etching mask on the second conductivity type contact layer, then selectively etching the contact layer using the mask, and selectively etching the second conductivity type cladding layer partway through the second conductivity type cladding layer to form a stripe on the cladding layer; a step of forming a convex portion in the shape of a shape, and then, with the mask left in place or after removing the mask, at least the double heterojunction structure portion and the side surface of the contact layer are formed by chemical vapor deposition using an organic metal. A method for manufacturing a semiconductor laser device, comprising the step of growing a current blocking layer containing the same group V element as the group V element constituting the substrate. (8) The mask is left when growing the current blocking layer, the mask is removed after the current blocking layer is formed, and then the contact layer and the current blocking layer are grown using an organic metal. 8. The method of manufacturing a semiconductor laser device according to claim 7, wherein the second conductivity type contact layer is grown again by a vapor phase growth method.