JPH04107428A - Substrate type optical switch - Google Patents

Abstract

PURPOSE:To reduce the absorption loss of free carriers by providing a current confinment layer above a compound semiconductor substrate and an optical waveguide layer above the current confinment layer, and composing the current confinment layer of a crystal layer where a current confinment part is selectively removed. CONSTITUTION:The current confinment layer 32 is provided above the compound semiconductor substrate 22, a 1st semiconductor layer which is not doped is provided above the current confinment layer 32, and the optical waveguide layer 34 is provided above the 1st semiconductor layer. In this case, the current confinment layer is composed of the crystal layer where the current confinment part is selectively removed and the current confinment part consists of the current confinment layer 32 and an opposite conduction type 2nd semiconductor layer. Consequently, carriers which are injected into a waveguide type optical switch flow as a narrow laminar current across the optical waveguide layer 34 toward the current confinment part, so that carriers are concentrated on only the part of the current confinment part which is required for switching. Therefore, the current confinment part confines the injected current effectively to an inflow and outflow area without outward dispersion. Consequently, the absorption loss of the free carriers can be decreased.

Description

[Detailed Description of the Invention] [Field of Application in Industry-1-] This invention relates to a substrate type optical switch used as a power device in optical communication, optical information processing system, etc. The present invention relates to a carrier injection type substrate type optical switch having a buried structure.

[Prior Art] Conventionally, it has been known that a direct transition type semiconductor +Af-1 does not exhibit a large nonlinear refractive index due to the Hunt-filling effect. This effect (resulting from the fact that electrons are filled from near the band gap due to J1 optical absorption, and the absorption spectrum is knotted toward the short wavelength side).As an example of effectively using this hunt-filling effect, A total internal reflection type substrate type optical switch as shown in FIG. 5 and FIG. 5 is provided.

This substrate type optical switch 1 has a compound semiconductor monthly rate n
type indium phosphide (hereinafter referred to as n-1nP) substrate 2
On top, tope-free inium gallium arsenide phosphide (hereinafter referred to as
Compound semiconductor R24 such as u-1nGaAsP)
Two optical waveguides 3.4 are formed to intersect in an X-shape on a plane, and electrodes 6 are provided on two sides of this intersection 5, and n-rnPnP2O below this intersection 5.
Electrodes 7 are formed on each of the five sides.

Next, a method for manufacturing the substrate type optical switch 1 will be explained with reference to FIG.

First, as shown in FIG. 7(a), an n-InP buffer layer 11 is formed by liquid phase epitaxy (LPE) on an 11nP substrate 2 on which one electrode 7 has been formed on the bottom surface in advance.
, u-1nGaΔsP optical waveguide layer I2, and nTnP cladding layer I3 are sequentially grown in multiple layers.

Next, as shown in the same figure (b), 111nP
The crat layer 13 is etched to have a rectangular cross-section and an X-shape in plan to form a rib-shaped optical waveguide 3 (4). Next, n-
Current confinement part of 1nP crat layer I3? Using this selective zinc (Zn) diffusion, p-type indium phosphide (hereinafter p-
A current confinement layer I4 (referred to as 1nl') is formed. Next, a silicon dioxide (hereinafter referred to as "Sin") insulating layer 15 is formed on the u-1nGa 8sP layer 12 on the upper part of the waveguide layer 12 and on the parts other than the two surfaces of the intersection 5 of the rib-shaped optical waveguide 3 (4). An electrode 6 is formed on the p-InP current confinement layer I4.
form.

The substrate 4-0 optical switch I changes the refractive index of the intersection 5 by applying a voltage between the electrodes 6 and 7, thereby causing total reflection of the incident light and changing the direction of the emitted light.

For example, as shown in FIG. 4, light incident from the end 3a of the optical waveguide 3 will be output as is from the other end 3b of the optical waveguide 3 if the current at the intersection 5 is in the OFF state; When the ON state is reached, the optical waveguide 3 is transferred to the optical waveguide 4, and the output "4" is output from the other end 4a of the optical waveguide 4.

That is, it operates as an optical switch.

As described above, the substrate-type optical switch l described in "-" has the characteristics of having a large nonlinear refractive index due to the bandpass link effect, and is fabricated by the liquid-liquid 11 epitaxial growth (LP II) method on the n-1nP substrate 2. It is an optical switch that has the advantage of being able to be created using only the first stage of growth.

[Problem to be solved by the invention] By the way, in the above-mentioned one-plate optical switch 1, i, J:, I
Since selective zinc (Zn) diffusion is used to confine E carriers, there is a problem in that it is very difficult to control the concentration of Zn, which is a p-type dopant, in the depth direction. Because the carrier density in the transition region fluctuates significantly due to the dispersion of the Zn concentration in the direction of the diffusion depth, the switch drive current varies greatly, and free carrier absorption loss due to Zn occurs, resulting in an optical transmission loss. is making it very big.

Also, is it possible to selectively diffuse p-type 1・-pan)・?
Since p-type dopants generally cannot be selectively diffused, there is also the problem that it is very difficult to create an optical switch using a p-type substrate.

This invention ('','') was made in view of the circumstances listed below.
In addition to effectively solving the following two problems, the current confinement for switching can be selected without performing zinc (Zn) diffusion.1. Another object of the present invention is to provide a substrate type optical switch which can be easily and efficiently operated and which can reduce absorption loss of free carriers.

Means for Solving Problem 1] In order to solve problem 2, the present invention employs the following substrate type optical switch. Zunawa, in a carrier injection type substrate optical switch using a compound semiconductor material as an optical waveguide, a current confinement layer is provided at a partial position of a compound semiconductor foil plate, and a current confinement layer is provided at a position above the current confinement layer. - an optical waveguide layer is provided at a partial position of the first semiconductor layer; The current confinement layer is characterized by being comprised of a second semiconductor layer of a conductivity type opposite to that of the current confinement layer.

[Function] In this invention, by forming a current confinement part in the current confinement layer, carriers injected into the substrate type optical switch flow as a narrow laminar flow across the optical waveguide layer toward the current confinement part, In the optical waveguide layer, carriers are concentrated only in the parts necessary for switching. therefore,
The current confinement effectively confines the injected current within the inflow and outflow regions without dissipating it outwardly.

The first semiconductor layer and the optical waveguide layer provided independently above the current confinement layer effectively prevent incident light from being dissipated to the outside of the optical waveguide layer. propagate. In this optical waveguide layer, the carriers -1- effectively change the refractive index of this optical waveguide layer, causing total reflection of the incident light and changing the direction of the outgoing light. It also reduces absorption of injected carriers and reduces free carrier absorption loss.

The current confinement section, which is composed of a second semiconductor layer having a conductivity type opposite to that of the current confinement layer, more effectively prevents the carriers injected into the current confinement layer from dissipating outward, and prevents the carriers injected into the current confinement layer from dissipating outward. to be confined in

[Embodiment] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

1 to 3 are diagrams that do not show the substrate type optical switch 21 according to the present invention.

This substrate type optical switch 2I has a p-InP substrate 221- which is a compound semiconductor substrate, and two optical waveguides 23.2/l made of a compound semiconductor material 23.2/l have a rectangular cross section and intersect in an X-shape on a plane. 4, and this intersection 2
An n-electrode 26 is located on the -1- plane of 5, and this intersection 25
A p-electrode 27 is formed on the lower surface of the p-ITIP substrate 22 below.

On this p-■nP substrate 22, as shown in FIG.
, n-InP current confinement layer 32, undoped l nP
(u −1nP )Hasopha layer (first semiconductor layer) 33,
U-TnGaAsP optical waveguide layers 34 are sequentially laminated. However, the symbol (n+) (or (n-1-)) means p-type (or (Jn-type)) containing a high concentration of impurities.

A current confinement portion 3 is selectively removed by etching in a portion of the n-1nP current confinement layer 32 that confines current.
5 is formed, and this current confinement portion 35 contains impurities (
p-1, which is a TnP layer converted to p-type by Zn) diffusion
An nP layer (second semiconductor layer) 36 is formed. Also,
The (n+)-InP buffer layer 31 formed below this n-TnP current confinement layer 32 and the u-TnP/<Tfa layer 33 formed above are communicated by a current confinement portion 35.

of the optical waveguide portion of the u-TnG'aΔsP optical waveguide layer 34
In part, there is an n-TnP layer 37 and a (1+)-T
nGaA sP contact layers 38 are sequentially stacked.

And u −1′ nGaA sP optical waveguide layer 34
A 5iO7 insulating layer 3 is formed on the upper part of the (n+)-1nGaΔsP contact layer 38 except for the upper surface of the intersection 25.
An n-electrode 26 is formed on the intersection 25-1- plane of the (n+)-1nGa aΔsP contact layer 38.
is formed.

Next, referring to FIG. 3, the above substrate type optical switch 2I
The manufacturing method will be explained.

■ [See Fig. 3(a)] A p-1nPP plate 2 with a p-electrode 27 formed at the bottom of the tack by liquid phase epitaxy (LPE) method.
2" Second, as the first stage of crystal growth, (pl-) -
I nP Hasofa layer 31 3 lim, n-I
The nP current filling layer 32 is I μm, u −1 nGa
The ΔsP processing mask layer 41 is sequentially grown in multiple layers to a thickness of 03 μm.

(2) [See FIG. 3(b)] Etching windows 42 are formed at positions corresponding to the current confinement portions of the u-1nGaAsP processing mask layer 41 by photolithography. Next, with aqueous hydrochloric acid solution, n-T
The nP current confinement layer 32 is etched to form a V-groove 43 with a depth of 15 μm which will become the current confinement portion 35. After forming this V groove/I3, the u-1nGaAsP that became unnecessary
Processing mask layer 41 is removed from n-InP current confinement layer 32.

■ [See Figure 3(c)] The n-1nP current confinement layer 32 and V groove 4 in Figure 3(b) described above are made by liquid phase epitaxial growth (LPE).
As the second stage of crystal growth, u-T
The nP buffer layer 33 has a thickness of 2 μm and is made of u-InGaA sP.
P waveguide layer 34 is 1.5 μm, n −1nP crat layer 37 is I, 5 μm, (n+) −1nGaΔ
The sP contact layer 38 is sequentially grown in multiple layers of 0 and 7 It m.

During this second stage of crystal growth, the p-type dopant 7,n diffuses from the (n+)-TnP buffer layer 31 toward the u-TnP buffer layer 33, and the current confinement portion 3
A p-1nP layer 36, which is an InP layer converted to p-type, is formed around the p-1nP layer 36. Optical waveguide 2 of this p-1nP layer 36
3. Length (Q) along intersection 25 of 24 (see Figure 1)
is at most a hundred and several tens of meters per meter.

■ [See Figure 3 (1)] (n±) -1nG aA sP contact layer 38 -
1. 810. is formed in a part of the optical waveguide 23 (24) forming part. A mask layer 44 is formed, and the n-1nP crystal layer 37 and (nf
-) -InG aAsP contact layer 38 is etched into the shape of all 38 to form a rib-shaped optical waveguide 23 (24) having a rectangular cross section and an X-shape in plane. This optical waveguide 23
(24) Si○, mask layer 44 that is no longer needed after formation
is removed from the (n+) 1nGaΔsP contact IL 38.

■[Refer to FIG. 3(e)] S+ is applied to the part of the u-1nG aA sP optical waveguide layer 34 and the upper surface of the intersection 25 of the optical waveguide 23 (24).
After forming the O3 insulating layer 39, the optical waveguide 23 (24) is formed.
An n-electrode 26 is formed on the plane of the intersection 25 of the substrate type optical switch 21.

n- of the substrate type optical switch 21 configured as described in -1-
When a predetermined voltage is applied between the electrode 2G and the p~electrode 27,
The contact layer 1' injected from the n-electrode 26 is (n0)-''InGaA sP contact layer 38, n-
It crosses the 1nP cladding layer 37 and the u-1nGaΔsP optical waveguide layer 34 (p+) and flows into the rnp buffer layer 31.

n-InPYJl flow confinement/i32 is 1)-11I
Since the current confinement part 35 made of the P layer 36 is formed, the injected carriers become a narrow laminar flow from the electrode 26 toward the current confinement part 35, and the u-1nGa 8s
In the P waveguide layer 34, carriers are concentrated only in the portion necessary for switching. Therefore, this carrier effectively changes the refractive index of the intersection 25, causing total reflection of the incident light and changing the direction of the emitted light. For example, as shown in FIG. 1, light incident from one end 23a of the optical waveguide 23 will be output as is from the other end 231) of the optical waveguide 23 if the current at the intersection 25 is OFF; When the ON state is reached, the optical waveguide 23 is transferred to the optical waveguide 24, and the other end 24a of this optical waveguide 24 is turned on.
It will be output from. It operates as an optical switch.

Here, the results of a test conducted by the inventors to confirm the effectiveness of the substrate type optical switch 21 will be explained.

Table I compares the 2×2 substrate type optical switch 2I of this embodiment with an element length of 2 mm and the conventional substrate type optical switch 1.

”-, the substrate-type optical switch 21 can perform switching operation with approximately 1/2 the drive current compared to the conventional substrate-type optical switch I, and the insertion loss is also 6 (1/2).
A drop of 3 or more is a problem. Among these, the waveguide loss is I
(113/cm), and most of the reduced insertion loss is due to a decrease in free carrier absorption.Also, the extinction ratio is +5 (113/cm), which is the same as the conventional one, and there are no particular changes in other characteristics. From this, it can be seen that this substrate type optical switch 21 performs a switching operation with a drive current of 80 mA and has good switching characteristics.

As described in detail above, according to the substrate type optical switch 21 of the embodiment described in Section 2, the n-1nP current confinement layer 3 made of a compound semiconductor crystal is formed on the p-InP substrate 22.
2 is formed, and a current confinement portion 35 selectively removed by etching is formed in the current confinement portion of this n-T nP current confinement layer 32. formed p-
The n-junction structure effectively injects carriers, while
Excluding current confinement portion 35<n-TnP current confinement layer 3
2 always maintains a high resistance state (current OFF state) well against applied voltages below the reverse breakdown voltage, and effectively directs the injected current within the inflow and outflow region without dissipating it outward. can be confined to. therefore,
The spread of the carriers flowing into the optical waveguide 23 (24) becomes smaller, and the carrier density in the switching part increases, so the refractive index of the switching part can be lowered with a low drive current. In addition, the formation of the n-1nP current confinement layer 32 and the current confinement portion 35 can be performed using the crystal growth method described in 5. controllability is improved, free carrier absorption loss can be reduced, and increase in insertion loss can be suppressed. Therefore, it is possible to provide a substrate type optical switch which can perform switching operation with a low drive current, has good loss characteristics, high efficiency, and the like.

In addition, u-
■nP haphazard layer 33, uTnGaΔsP optical waveguide layer 3
4 were stacked sequentially, so the incident light was
The injected carriers can be effectively propagated outside the optical waveguide layer 34 without being dissipated.
The refractive index of the Ga/\sP optical waveguide layer 3/I can be effectively changed, and the direction of emitted light can be effectively changed with a low driving current. Furthermore, absorption of free carriers can be reduced, and absorption loss of pewter carriers can be reduced.

Furthermore, since the pInr' layer 36 is layered in the current confinement section 35, the carriers injected into the current confinement section 35 are more effectively confined within the current inflow/outflow region without being dissipated outward. be able to.

In the above embodiment, the n-TnP current confinement layer 32 is formed on the InP substrate 22 (I), but this structure can also be applied to compound semiconductor substrates other than p-type. , for example, p-TnP on an n-1nP substrate.
Various configurations are possible, such as a configuration in which a current confinement layer is formed or a configuration in which a 5T-rnP current confinement layer is formed on a TnP substrate.

[Effects of the Invention] As described in detail below, according to the present invention, in a carrier injection type substrate type optical switch using a compound semiconductor material as an optical waveguide, a current confinement layer is provided at an upper position of the compound semiconductor substrate. An optical waveguide layer is provided 51 above the current confinement layer, and the current confinement layer is composed of a crystal layer from which the current confinement portion is selectively removed.
J carriers can be injected effectively in this part of the current confinement region, while the upper part of the current confinement layer excluding the current confinement region is always in a high resistance state for applied voltages below the reverse breakdown voltage. (current OFF condition fQ) is maintained well, and the injected current can be effectively confined within the inflow and outflow region without dissipating outward. Since the spread of the carriers caused by the oscillation is reduced and the carrier density flowing into the switching portion is increased, efficient switching operation can be achieved with a low drive current.

In addition, since the current confinement portion can be freely formed at any position on the compound semiconductor substrate, the dopant concentration of the current confinement layer and the current confinement portion can be well controlled. Better loss characteristics can be obtained compared to conventional ones.

In addition, since a non-toped first semiconductor layer was provided at a part of the current confinement layer (J), an optical waveguide layer was provided at a part of the first semiconductor layer. The injected carriers can effectively change the refractive index of the optical waveguide layer, and the direction of the emitted light can be effectively changed with a low driving current. In addition, the absorption of free carriers can be reduced, and the absorption loss of free carriers can be reduced.

Furthermore, since the current confinement section is composed of a second semiconductor layer having a conductivity type opposite to that of the current confinement layer, the carriers injected into the current confinement section do not dissipate outward, and the current flows into and out of the region. can be more effectively confined within.

As a result of the above, the absorption loss of free carriers can be reduced, and a highly efficient substrate type optical switch with good loss characteristics can be provided.

[Brief explanation of the drawing]

1 to 3 are diagrams showing one embodiment of the present invention, in which FIG. 1 is a perspective view of a substrate type optical switch, and FIG. 2 is a sectional view taken along the IT-n line in FIG. 1. , Figure 3(a)-(e
) is a process diagram for explaining the manufacturing method of a substrate type optical switch, FIGS. 4 and 5 are diagrams showing a conventional substrate type optical switch, and FIG. 4 is a perspective view of the substrate type optical switch. Fifth
Figures (a) and (b) are process diagrams for explaining the manufacturing method of a substrate type optical switch. 2]...22...Substrate type optical switch, -p-1nP substrate, -optical waveguide, -intersection, 26...n...p-electrode/(p+)-1nP buffer layer , n-InP current confinement layer, u-1nP buffer layer, u-TnGaΔsP optical waveguide layer, current confinement section, electrode, p-1nP layer, n-1nP cladding l〆, (n+) -r nc; aA sP contact S10
．． insulation layer.

Claims (1)

[Claims] In a carrier injection type substrate type optical switch using a compound semiconductor material as an optical waveguide, a current confinement layer is provided at an upper position of the compound semiconductor substrate,
An undoped first semiconductor layer is provided above the current confinement layer, an optical waveguide layer is provided above the first semiconductor layer, and the current confinement layer is composed of a crystal layer from which a current confinement portion is selectively removed. . A substrate type optical switch, wherein the current confinement section is composed of a second semiconductor layer having a conductivity type opposite to that of the current confinement layer.