JPH0233134A - Optical switch - Google Patents

Abstract

PURPOSE:To form a p-n junction between a core layer and a semiconductor layer as a continuous growth surface and to suppress a diffusion to the core layer side of n type impurities by forming a p type semiconductor layer positioned on the upper face of an n type semiconductor core layer by epitaxial growth. CONSTITUTION:On an n type semiconductor substrate 1 on which the lower electrode 11 has been formed, an n type semiconductor lower clad layer 13 and an n type semiconductor core layer 14 are laminated successively. On this core layer 14, a p type semiconductor thin layer 15 is formed, and also, the upper clad layer 16 and a p type semiconductor cap layer 17 whose refractive index is the same as that of the thin layer 15 are brought to continuous growth. Subsequently, by executing photolithography and a wet etching processing, a ridge corresponding to waveguides A-D is formed, and thereafter, an insulating thin film 18 is formed and covered thereon. In the end, a window 18a is pierced in a prescribed part of the insulating thin film 18, and by diffusing Zn from this window 18a by a vapor phase diffusing method, a p type impurity area 10 is formed in a part of the clad layer 16 and the cap layer 17, and the continuity of a p-n junction surface is secured.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a waveguide crossing type optical switch, and more particularly to a current injection type optical switch using a semiconductor as a material.

(Prior Art) In the field of optical communications, optical switches that can electrically change optical paths are considered important.

In particular, semiconductor optical switches have attracted much attention because they can be monolithically integrated together with active elements such as semiconductor lasers and photodiodes.

As one such semiconductor optical switch, a waveguide crossing type current injection type optical switch is known. This optical switch forms a current injection region at the intersection of the waveguides,
From here, by injecting a predetermined value of current, a plasma dispersion effect and/or band filling effect is caused at this intersection, reducing the refractive index of that area, resulting in total reflection of the guided light and its propagation. By changing the direction, the waveguide through which the light propagates is changed to cause a switching effect. Among such switches, the 51st example of the IXZ optical switch is shown as a perspective view!
1, and a sectional view taken along the line Vl--Vl in FIG. 5 is shown in FIG.

First, in FIG. 6, a substrate 62 made of an n-type semiconductor such as n''G, A, etc. is formed on a lower electrode 61 with ohmic contact.

On the upper surface of the substrate 62, a lower cladding layer 63 made of an n-type semiconductor and a core layer 64 also made of an n-type semiconductor are sequentially laminated. In this case, the lower cladding layer 63 is
It is necessary that its refractive index be smaller than that of the core layer 64. For this reason, for example, the lower cladding layer 63 has n −A j! G a A *, and the core layer 64 is composed of n - G a A *.

On this core layer 64, as shown in FIG. 5, waveguides A, B, C, and D are formed in a ridge shape, intersecting each other at a predetermined intersection angle.

The waveguide has a refractive index lower than that of the core layer 64, for example n
- An upper cladding layer made of an n-type semiconductor such as A
, A, and a cap layer 66 made of a p-type semiconductor such as A.

Along the waveguide length direction at the intersection of each waveguide (
On both sides, an insulating thin film 67 made of an insulating material such as S + Ot is formed. A window 67a that reaches the cap layer 66 is formed in the insulating thin film 67 in the waveguide length direction.

Through this window 67a, a p-type impurity region 6 is formed by diffusing a p-type impurity such as Zn into the cap layer 66 and upper cladding layer 65 described above by, for example, vapor phase diffusion.
B is formed.

Then, the window 67a is sealed and the upper electrode 69 is formed in contact with the cap layer 66.

When a voltage is applied between the upper electrode 69 and the lower electrode 61 and a predetermined amount of current is injected between the two electrodes, a plasma dispersion effect is exhibited at the interface between the p-type impurity region 68 and the upper cladding layer 65. The refractive index of the part decreases, turning it into a reflective surface. Therefore, for example, light introduced from waveguide A propagates in the direction of waveguide C using the low refractive index portion generated at the intersection as a reflection surface. That is,
A switching effect occurs.

FIG. 7 is a plan view illustrating another type of optical switch,
FIG. 8 illustrates a cross-sectional view taken along the line ■-■.

In the case of this type of optical switch, a substrate 82, such as n-type 1nP, is formed on the lower electrode 81 with ohmic contact. A ridge groove 83a extending in the waveguide length direction at the intersection portion is carved on the upper surface of the substrate 82.
Here is n type 1. A core layer 83 such as GaAsP is formed.

On the upper surface of the core layer 83, on one side of the intersection of the waveguides as shown by diagonal lines in FIG.
A current injection region 84 is formed by forming a cap layer 84b made of ``'' type 1*GaAsP.

A buried layer 85 made of, for example, InP and having a higher resistance value than the current injection region is formed at a location other than the current injection region 84.

A 5108 insulator 11111186 having a window 86a at a portion corresponding to a part of the cap layer 84b is formed on the upper surface of the cap layer 84b and the buried layer 85, and the cap layer 84b is formed on the upper surface of the cap layer 84b through the window 86a. A contacting upper electrode 87 is formed.

In the case of this type of optical switch, the above-described current injection region 84 and buried layer 85 are formed as follows.

That is, the semiconductor constituting the current injection region is epitaxially grown on the entire upper surface of the core layer 83 to a predetermined thickness, and then the portion where the buried layer is to be formed is removed by etching. Then, a high-resistance semiconductor constituting the buried layer is epitaxially grown at this buried layer formation position.

(Problems to be Solved by the Invention) Among these optical switches, the former type of optical switch in which a p-type impurity region 68 is formed has the following problems. That is, when forming p-type impurity region 68, upper cladding layer 65 and this p-type impurity region 6
In some cases, the Pn bonding surface between the front surface 68a and the core layer 64 may not be clearly formed.
The problem is that it is difficult to control the gap width between the two.

The switching function is better if the pn junction surface is clearly formed at -a. Further, if an impurity region exists near the core layer, loss due to light absorption increases. Therefore, from the point of view of optical operation, it is advantageous to increase the gap width between the impurity region and the core layer. On the other hand, when current flows into the impurity region, the current spreads within the cladding layer. In order to suppress this radio wave distortion, it is advantageous to reduce the gap width between the impurity region and the core layer.

Therefore, in the case of this type of optical switch, in order to enhance its switching function, it is first necessary to strictly control the gap width between the front surface 68a of the p-type impurity region and the core layer 64 to be appropriate. This is necessary.

However, when the p-type impurity is diffused into the upper cladding N65 by the vapor phase diffusion method described above, the concentration gradient of the impurity due to diffusion becomes exponential, so the depth of diffusion is set to a predetermined value, that is, the diffusion depth is Front face of area 6
It is extremely difficult to form 8a at an appropriate position from the top surface of the core layer 64.

For the latter type of optical switch, p at the ridge
The n-junction is clearly formed because it is formed by epitaxial growth of each layer. 84 and core layer 8
A problem arises in that the crystallinity of the buried layer 85 deteriorates at the interface with the buried layer 85. Furthermore, the number of steps increases, and it cannot be said to be advantageous from an economic point of view.

An object of the present invention is to provide an optical switch that solves the above-mentioned problems in conventional current injection type optical switches.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a lower electrode; an n-type semiconductor substrate formed on the lower electrode;
an n-type semiconductor lower cladding layer formed on the n-type semiconductor substrate; an n-type semiconductor core layer formed on the n-type semiconductor lower cladding layer; and an n-type semiconductor core layer formed on the n-type semiconductor core layer. a p-type semiconductor thin layer, an n-type semiconductor upper cladding layer formed on the p-type semiconductor thin layer, and a semiconductor cap layer formed on the n-type semiconductor upper cladding layer; a ridge partially formed with the p-type semiconductor thin layer or a p-type impurity region extending into the thin layer; covering the upper surface of the semiconductor cap layer and a part of the n-type semiconductor core layer; A cross-waveguide optical switch is provided, comprising: an insulated thin film in which a window reaching a semiconductor cap layer is formed; and an upper electrode formed at least on the window.

The optical switch of the present invention has a p-type semiconductor thin layer of a predetermined thickness between the n-type semiconductor core layer 64 and the n-type semiconductor upper cladding 7165 in the conventional optical switch shown in FIGS. 5 and 6. Also, p-type impurity region 6
The front surface 68a of No. 8 is characterized by having a small ridge (both of which remain within the P-type semiconductor thin layer).

Here, it is preferable that the composition of the p-type semiconductor yIN is determined so that it has the same refractive index as the upper cladding layer formed on its upper surface, and when forming this thin layer,
A p-type semiconductor of a predetermined composition may be epitaxially grown on the upper surface of the core layer by, for example, MOCVD. In this case, the layer thickness is not particularly limited, but is usually 0.05 to 0.
．． It is about 5 μm.

The p-type impurity region may have any depth as long as the diffusion depth does not pass through the p-type semiconductor TiIN and reach the underlying core layer. However, in view of the above-mentioned current diffusion problem, the vicinity of the interface between the above-mentioned thin layer and the upper cladding layer is appropriate.

(Function) In the optical switch of the present invention, the p-type semiconductor thin layer located on the n-type semiconductor core layer is an epitaxially grown layer of a predetermined thickness, so that the p-n junction between the two is a continuous growth surface. This will clearly improve the switching function.

In addition, since this thin layer has a predetermined thickness and is a p-type semiconductor, the diffusion of p-type impurities from the window into the upper cladding layer toward the core layer side is suppressed to some extent. . Therefore, the presence of this thin layer facilitates control when forming the p-type impurity region.

(Embodiments of the Invention) A switch according to an embodiment of the present invention will be described below with reference to the accompanying drawings.

Example 1 A 1×2 optical switch of the waveguide crossing type was manufactured as follows, as shown in Fig. 1, a perspective view, and Fig. 2, a cross-sectional view of the waveguide crossing portion along the line ■-■. did.

That is, first, on the n9 type G, A, and the substrate 12, the MO
By the CVD method, the lower cladding layer 13 of the n-type AIG, As, the core layer 14 of the n-type G,A, the thin layer 15 of the p-type AIG, A, and the thin layer 15 are sequentially formed. Upper cladding layer 16 of n-type A f G, A, and P with the same refractive index
Cap layers 17 of type 9 G and A were continuously grown.

Then, photolithography and wet etching were performed to form the waveguide A as shown in FIG.

After forming the ridges corresponding to B, C, and D, the upper surface is coated with an insulating Tll film 1 of S t Ox by sputtering method.
8. Thereafter, windows 1 are formed at predetermined locations on the insulating thin film 18 by photolithography and wet etching.
8a was drilled.

Zn was diffused from this window lea by a vapor phase diffusion method to form a p-type impurity region 19 in part of the upper cladding layer 16 and the cap 1117.

At this time, the front surface of the diffusion region 19 was controlled to be in contact with the thin layer 15.

Finally, by vacuum evaporation method or sputtering method,
The upper electrode 2o was formed using Cr/Au, and the lower electrode 11 was formed using AuGeNi/Au by vacuum evaporation. In the above embodiment, the p-type impurity region 19 was formed by a diffusion method, but the p-type impurity region may also be formed by an ion implantation method.

Example 2 A 2×2 optical switch as shown in the perspective view of FIG. 3 and the cross-sectional view of the waveguide intersection along line IV-IV in FIG. 3 was manufactured in the same manner as in Example 1.

In the case of this optical switch, since it is a 2×2 switch, a window for current injection is formed at the center of the intersection of each waveguide. Therefore, the p-type impurity region is formed at the center of the beam.

This optical switch also exhibited the same switching function as the optical switch of Example 1.

(Effects of the Invention) As is clear from the above explanation, in the case of the optical switch of the present invention, the p-type semiconductor thin layer located on the upper surface of the n-type semiconductor core layer is formed by epitaxial growth. Since the junction is a continuous growth surface,
The performance is higher than that of a pn junction formed by an impurity diffusion method.

In addition, in this p-type semiconductor thin layer, the p-type impurity diffusion rate is slightly slower than in other parts, so it is difficult to control the depth of the front surface when forming the p-type impurity region for current injection in the upper cladding layer. It becomes easier to do.

In addition, in the case of the optical switch of the present invention, crystal regrowth for forming the current conductive part is not required, and compared to a buried layer forming type optical switch, there is no deterioration of crystallinity at the buried layer interface. In addition, the number of steps is reduced, which has great industrial merits.

[Brief explanation of the drawing]

Figure 1 is a perspective view of a 1x2 optical switch according to an embodiment of the present invention, Figure 2 is a sectional view taken along the line ■-■ in Figure 1, and Figure 3 is a 2x2 optical switch.
FIG. 4 is a sectional view taken along the line ■-IV of FIG. 3, FIG. 5 is a perspective view of a conventional 1×2 switch, and FIG. 7 is a plan view of another conventional example, and FIG. 8 is a cross-sectional view along the line V[-Vl.
It is a cross-sectional view along the -■ line. 11... Lower electrode, 12... N-type semiconductor substrate, 13
... n-type semiconductor lower cladding layer, 14 ... n-type semiconductor core layer, 15 ... p-type semiconductor thin layer, 16 ... n-type semiconductor upper cladding layer, 17 ... p-type semiconductor cap layer , 18... Insulating thin film, 18a... Window, 19...
p-type impurity region, 20...upper electrode;

Claims (4)

[Claims] (1) a lower electrode; an n-type semiconductor substrate formed on the lower electrode; an n-type semiconductor lower cladding layer formed on the n-type semiconductor substrate; and an n-type semiconductor lower cladding layer formed on the n-type semiconductor lower cladding layer. an n-type semiconductor core layer formed on the n-type semiconductor core layer; a p-type semiconductor thin layer formed on the n-type semiconductor core layer; an n-type semiconductor upper cladding layer formed on the p-type semiconductor thin layer; and the n-type semiconductor thin layer formed on the p-type semiconductor thin layer; a ridge consisting of a semiconductor cap layer formed on a semiconductor upper cladding layer, in which a p-type impurity region extending from the upper surface of the semiconductor cap layer to the p-type semiconductor thin layer or into the thin layer is formed; an insulating thin film that covers the upper surface of the semiconductor cap layer and a part of the n-type semiconductor core layer, and in which a window reaching the semiconductor cap layer is formed; and an upper electrode formed at least on the window. A cross-waveguide optical switch characterized by: (2) The waveguide crossing optical switch according to claim 1, wherein the p-type impurity region is formed by a diffusion method and/or an ion implantation method. (3) The waveguide crossing type optical switch according to claim 1, wherein the semiconductor is a compound semiconductor composed of elements of groups III and V of the periodic table. (4) The waveguide crossing optical switch according to claim 1, wherein the semiconductor is silicon.