JPS63318791A - Manufacture of iii-v compound semiconductor optical waveguide element with embedded structure - Google Patents

Abstract

PURPOSE:To make it possible to manufacture a III-V compound semiconductor optical guide element having an arbitrary fine embedded structure only with one crystalline growth by a method wherein a stripe-shaped projecting section having a vertical sidewall with a specific plane orientation is formed on the surface of a specific plane orientation of substrate, and an optical guide layer and a clad layer is epitaxially grown on it. CONSTITUTION:A stripe-shaped projecting section having a vertical sidewall with plane orientation equivalent to the crystallographical plane orientation a face 01-1 and a face 0-11 or the face 01-1 and the face 0-11 is formed on the crystallographical plane orientation, a face 100 or a plane equivalent to the face 100 on a substrate 1 mainly consisting of III-V compound. Then, in a vapor phase or vacuum, at least, a crystalline layer mainly consisting of III-V compound to be an optical guide layer 3 and a crystalline layer mainly consisting of III-V compound to be a clad layers 2, 3 are epitaxially grown on the said plane. For example, after said stripe is formed on an n-type 100 plane GaAs substrate crystal 1, an n-AlGaAs lower clad layer 2, the GaAs optical guide layer 3, and the p-AlGaAs upper clad layer 4 are formed.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is a method for manufacturing an optical waveguide element with a buried structure mainly made of a ■-v group compound semiconductor, and is an optical waveguide element with a high light confinement effect. applied to the production of

[Conventional technology]

(2) Optical waveguide devices such as semiconductor lasers, optical modulators, and optical switches using group V compound semiconductors are important components in the fields of optical communication and optical information processing. Among these, an optical waveguide device with a buried structure is advantageous in terms of unifying the waveguide mode and stabilizing the device characteristics. In Figure 1, l is the substrate crystal, c is the lower cladding layer, 3 is the optical waveguide layer, ≠ is the upper cladding layer, g' is the current blocking layer, ! is the contact layer, and r is the contact. diffusion layer.

To explain the process step by step, first, a lower cladding layer 2, an optical waveguide layer 3, and an upper cladding layer are crystal-grown on a substrate crystal l, and an epitaxial wafer for an optical waveguide element with a planar structure is produced (see FIG. 11). a)). The leading wave layer 3 and the upper cladding layer of the hindlimb epitaxial wafer are processed into mesa-shaped stripes by etching or the like (FIG. 11(b)). After that, crystal growth is performed once again to form a current blocking layer lτ and a contact layer! (1st/
Figure (C)). However, this method has the disadvantage that the process is complicated and the yield is low because the buried structure is produced by performing crystal growth multiple times. Furthermore, the side surfaces of the portion of the device that will become the optical waveguide layer deteriorate due to etching, which adversely affects device characteristics.

As a method to improve this drawback, attempts have been made to fabricate a buried structure semiconductor laser by one-time crystal growth. An example thereof is shown in FIG.

In the first figure, I is the substrate crystal, C is the lower cladding layer, 3 is the optical waveguide layer, G is the upper cladding layer, ! is the contact layer. To explain the process step by step, first, the substrate crystal is chemically etched to form inverted mesa-shaped striped protrusions (Fig. 72(a)), and then the lower cladding layer is formed by organometallic chemical vapor deposition. 2. Form the optical waveguide layer 3, the upper cladding layer, and the contact layer j (Figure 1 (b)) (Japan Society of Applied Physics, Autumn Academic Conference Proceedings PIT
.

/ri J'z year). In this method, the substrate crystal is processed by chemical etching, and the striped protrusions formed have an inverted mesa shape, so even if the crystal grows on the substrate crystal, the optical waveguide formed on the top surface of the protrusions is The layer is not continuous with the waveguide layer formed on the sidewalls of the protrusions and at locations other than the protrusions on the substrate. Therefore, an optical waveguide layer with a buried structure is formed by one-time crystal growth. However, in the inverted mesa shape obtained by chemical etching as shown in Figure 1, the relationship between the stripe width W and the etching depth d is w).
(X a, and the deeper the depth, the wider the stripe width must be. Therefore, in order to fabricate a leading wave element with a thick structure, the stripe width must be widened, as shown in Fig. 72. There is a limit to the amount of buried structure KFi that can be fabricated using this method.Furthermore, due to the anisotropy of crystal growth,
Stripe width at the top of the leading wave layer “ ” ” −y7 (
t*+14), the shape of the optical waveguide layer is limited.

[Problem that the invention seeks to solve]

In order to eliminate the complexity of the process caused by multiple crystal growths and to solve the problem of poor yield, the present invention utilizes the difference in crystal growth rate depending on the crystal orientation to form a buried structure on the substrate crystal in one crystal growth. Provided is a method for forming an optical waveguide layer, and a method for realizing an m-v group compound semiconductor guided wave element in which the buried structure is not limited by the shape of the striped convex portions formed on the substrate crystal. do.

[Means for solving problems]

The present invention makes it possible to produce a ■-■ group compound semiconductor optical waveguide device having an arbitrary fine buried structure by one crystal growth.

Striped convex portions having vertical sidewalls are formed on a substrate crystal using a processing method such as reactive ion etching that provides vertical sidewalls, and crystal growth is performed on the substrate crystal. At this time, a group IV compound is used as the crystal substrate, a plane equivalent to the crystallographic plane orientation (ioo> plane or <100) plane is used as the plane on which the striped convex portions are formed, and the vertical side walls of the convex portions are formed to have crystallography. Thereafter, crystal growth is performed in a gas phase or in a vacuum to produce a ■-v group compound semiconductor guided wave element having a predetermined buried structure.

[For production]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the drawings when crystal growth is performed in a gas phase or in a vacuum using a vapor phase growth method such as an organometallic chemical vapor deposition method or a molecular beam epitaxy method.

Figure 1 shows the case of crystal growth on a substrate crystal having the crystallographic plane orientation shown in the present invention. This is a case where crystal growth is performed on a substrate crystal in which striped convex portions having different plane orientations are formed. Figures 7-9 (a) are diagrams showing the plane orientations of the substrate crystal and the striped convex parts;
Both (b) are cross-sectional views of the crystal growth layer. be.

In the crystal growth shown in FIG. 1, crystals do not grow on the side walls of the striped convex portions, but crystals grow independently on the convex portions and concave portions. Growth stops once the growth layer reaches the apex of the triangle in the convex portion, and after growth in the concave portion catches up with the apex of the triangle, growth begins, and the growth surface is flattened. As a result, the optical waveguide layers 3 formed in the convex portions and the concave portions are independent from each other, and both have a light confinement effect.

On the other hand, as shown in Figure 2, when crystals grow on a substrate crystal that has striped protrusions with (0//) and (0/I) planes on the sidewalls, crystals also grow on the sidewalls of the protrusions. , the layers grown in the convex portions and concave portions are continuous and no light confinement occurs.

As explained above, in the present invention, when forming striped convex portions on a substrate crystal, the side walls of the convex portions are formed on the (071) plane and the (0/) plane, or on the (O)/) plane and the (0/ / ) plane, an independent optical waveguide layer can be formed on the substrate crystal.

〔Example〕

(Example 1) FIG. 3 is a diagram illustrating an example of the present invention, in which (0
On a substrate crystal in which striped convex portions with (0//) planes as side walls are formed, crystal growth is performed once by metal organic chemical vapor deposition to form an optical waveguide with a buried structure. This is an example in which an optical waveguide device was fabricated. l is the substrate crystal (n-type (100) plane GaAs substrate crystal), 2 is the lower cladding layer (n-AIGaAs), and 3 is the optical waveguide layer (und
ope-GaAs), l is the upper cladding layer (p-GaAs), l is the upper cladding layer (p-GaAs),
(AlGaAs), 4AI is a current pull layer (n-A
lGaAs), j is the contact layer (p''-GaAs)
It is. In terms of crystal growth, the width W' at the top end of the optical waveguide layer is w' = w − (
t2 + t3) rr tonal.

In this embodiment, stripes having vertical sidewalls are first formed on the (100) plane of the substrate by reactive ion etching using BO1a gas. At this time, make sure it is on the screen. After that, while keeping the substrate at a temperature of 730″C and rotating at s/Orpm to obtain crystal uniformity, trimethylgallium, triethylaluminum, and arsine were used as source gases, diluted with hydrogen gas, and the growth pressure was fQTorr. , /~3 μm/hour.

(Example 2) Figure μ shows the contact layer j in the device of Example/.
is removed leaving behind a striped pattern, and an insulating layer is formed on the removed portion. t is an insulating layer (8isN4
), t is a contact diffusion layer (Zn diffusion layer). The contact layer and the upper cladding layer are in contact with the contact diffusion layer t. Contact layer for the device of this example! When a forward bias is applied through the substrate crystal l, a carrier confinement effect occurs in the waveguide layer, and when a reverse bias is applied, an electric field is applied to the optical waveguide layer.

(Example 3) Figure 5 shows an example in which electrodes were actually formed on the device of Example A, with 7 being an upper electrode (Ti-Pt-Au) and 7' being a lower electrode (Au-Go-Ni). It is. Using the element of this example, a semiconductor laser and an optical amplifier were formed as forward bias elements, and the formed semiconductor laser was capable of oscillation with a low threshold. Further, as the reverse bias element, an optical modulator, two-phase modulator, or the like is formed.

(Example Hiroshi) Figure 6 shows a contact layer directly on the upper cladding layer≠ of the device of Example 1! This structure has a structure in which the current blocking layer 6' is grown on top of the current blocking layer 6', and the current blocking layer 6' above the striped convex portion is removed by etching, and the insulating layer 6 and the electrode (upper electrode 7') are removed by etching. and a lower electrode 7'). Direct electrical contact is made between the upper electrode 7 and the contact layer j, and electrical insulation is provided between the upper electrode 7 and the current blocking layer μ' by an insulating layer B. The device of this example operates in the same way as the device of Example 3.

(Example) FIG. 7 is a diagram explaining another example, (0//)
On a substrate crystal in which striped convex portions with IIT and (oii) planes as side walls are formed, crystal growth is performed once by metal organic chemical vapor deposition to form an optical waveguide with a buried structure, and a leading wave element is formed. The feature of this example is that electrical contact is made to the optical waveguide layer formed inside the concave portion sandwiched between the striped convex portions. l is the substrate crystal (n-type (/00) plane GaA
s substrate crystal), λ is the lower cladding layer (n-GaAs)
, 3 is the optical waveguide layer (undoped GaAs), G is the upper two-layer layer (p-GaAg), and Hiro' is the current plate lf.
f7 is a layer (n-GaAs), 5 is a contact layer (p+-
t is an insulating layer (B15Na), and r is a contact diffusion layer (Zn diffusion layer). Since the optical waveguide layer 3 is made of fiGaA13, its refractive index is (
) Since it is larger than aAs and has a smaller forbidden band width, it can achieve light confinement and carrier confinement effects.

In this example, stripes having vertical sidewalls are first formed on the (ioo) plane of the substrate by reactive ion etching using BCl3 gas. At this time, the side walls of the stripes are (0//) and (0//) planes. Thereafter, the substrate was maintained at a temperature of 730''C and rotated at /Orpm to obtain crystal uniformity, while trimethylgallium, trimethylindium,
Using arsine, diluted with hydrogen gas, growth pressure 10 To
Crystal growth was performed at a growth rate of rr,/~3 μm/hour.

Further, as in this embodiment, the advantage of using an optical waveguide layer formed inside a recess formed by striped convex portions of a substrate crystal is that the width of the optical waveguide layer is formed on the substrate crystal. Since the width matches the width inside the recess, the optical waveguide layer can be formed with extremely high processing accuracy.

Furthermore, the upper part of the optical waveguide layer does not become narrower than the lower part as in Examples 1 to 1.

(Example 6) The second figure is an example in which electrodes were formed on the element of Example J. 7 is an upper electrode (Ti-Pt-Au), and 7' is a lower electrode (Au-Go-Ni). The element of this embodiment is applied as a forward bias element to a semiconductor laser and an optical amplifier, and as a reverse bias element to an optical modulator 9 phase modulator and the like.

(Example 7) FIG. 2 shows a structure in which a contact layer j is grown directly on the upper cladding layer of the device of Example j, a current blocking layer is grown on top of the contact layer j, and a recessed portion is further grown. The current blocking layer 6' on the upper part of
') is provided. Direct electrical contact is made between the upper electrode 7 and the contact layer j, and the current blocking layer
Electrical insulation is provided by an insulating layer B between the two. The device of this example operates similarly to the device of example t.

(Example t) FIG. 70 shows the device of Example 7 in which the current blocking layer ′ was not formed and the insulating layer t and electrodes (upper electrode 7 and lower electrode 7′) were directly formed. The contact layer j and the upper electrode 7 in the upper part of the recess formed by the striped convex parts are in direct electrical contact, and the other parts are electrically insulated from the insulating layer 6Vc. The device shown in this embodiment also operates in the same way as the device in embodiment B.

Among the embodiments shown above, when a substrate crystal obtained by epitaxially growing AlGaAs on GaAs is used instead of GaA3 used as the substrate crystal 1 in embodiment t-r, the lower cladding layer ko and the upper cladding layer 1 are used. is AlGaAs, and the optical waveguide layer 3 is GaAs or GaA.
A superlattice of S/AlGaAs can be used.

Moreover, although all the embodiments have been shown limited to AlGaAs-based or InGaAs-based materials, the present invention can be similarly applied to a material using an aluminum-nP substrate.

Furthermore, the crystallographic plane orientations of the stripe sidewalls do not need to match perfectly, and similar results were obtained even when the plane orientations deviated by about ±200.

〔Effect of the invention〕

As explained above, the present invention allows the side walls of the striped protrusions formed on the substrate crystal to be By making the crystal have a plane orientation equivalent to the ((:)//) plane and (0//) plane or the (0//) plane and (0/ / ) plane, one crystal growth can be achieved. This makes it possible to fabricate optical waveguide elements with arbitrary fine buried structures. As a result, the complexity of the process required for multiple crystal growths can be eliminated, and an optical waveguide element with a buried structure can be manufactured with a high yield.

By using the present invention, it becomes easy to manufacture semiconductor lasers, semiconductor laser arrays, optical amplifiers, optical amplifier arrays, optical modulators, optical switches, optical switch matrices, and the like.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating a case where a crystal is grown on a substrate crystal having the crystallographic plane orientation shown in the present invention,
L) is a diagram showing the plane orientation of the substrate crystal, and (b) is a cross-sectional diagram of the crystal growth layer. FIG. 2 is a diagram illustrating a case where a crystal is grown on a substrate crystal having a plane orientation different from the crystallographic plane orientation shown in the present invention, and (a) is a diagram showing the plane orientation of the substrate crystal. , (b) are cross-sectional views of the crystal growth layer. Figure 3 is a diagram for explaining the embodiment, Figure μ is a diagram for explaining the embodiment, and Figure ! The figure is a diagram for explaining Example 3, in which electrodes are formed on the element shown in FIG. FIG. 6 is a diagram for explaining Example 1, FIG. 7 is a diagram for explaining Example J, and FIG. R is a diagram for explaining Example t, in which electrodes were formed on the element shown in FIG. This is the case. Fig. 3 is a diagram for explaining the seventh embodiment, and Fig. io is a diagram for explaining the embodiment r. 11th
The figure shows a conventional method for manufacturing a semiconductor optical waveguide device with a buried structure, and FIG. FIG. l... Substrate crystal, 2... Lower cladding layer, 3...
Optical waveguide layer, G...upper cladding layer, D'...current blocking layer,! ... Contact layer, 6... Insulating layer, 7
...Top electrode, 7'...Bottom electrode, r...Diffusion layer for contact. -1111-37 1 ¥37 Y4-A-1-Ko-2 Tact nI 1-layer No-- Series] Working cattle 6 items 2--1 Chokei pcraper JF eyebrows--1 Mitsunjun Fake 4-m- and 7) Layer 4'-m- to 3L professional 7 layer 5--Contact) Fake J--1 Shusai-type layer 7--Kamiyoji 7'- Lower pot p Densamine Otozuma 7V θ-----Co〉7 feet Kōri λヲ0sha funeral 1TiJ Mine turn 1---Isshota Keishoken/θ times 7-φ AJ2 (phantom /Heno2 CC) Mine/Ikuni<aノ/---・慕Jg? Introduction 1 Shoulder'-t2 "7 2-°-lower 7f/eyebrow 3-・Light guide stratification ≠-・etc. acta, 1 layer 5-・-koλkuku) scraps

Claims (1)

Scope of Claims: On a crystallographic (100) plane or a plane equivalent to the (100) plane of a substrate crystal mainly composed of III-V group, forming a striped convex portion having vertical side walls with plane orientations equivalent to the @) plane and the (0@1@1) plane, or the (01@1@) plane and the (0@1@1) plane; , epitaxially growing on the surface in a gas phase or vacuum at least a crystal layer consisting mainly of III-V groups to become an optical waveguide layer and a crystal layer mainly consisting of III-V groups forming a cladding layer. 1. A method for manufacturing a III-V group compound semiconductor optical waveguide device having a buried structure, the method comprising the steps of: