JPH0695044A - Optical modulator element - Google Patents

Abstract

PURPOSE:To provide the optical modulator element for TE-like mode which is formed by using an inexpensive Si and Ge single crystalline substrate and has sufficient element characteristics. CONSTITUTION:The single crystalline substrate contg. at least one kind of Si and Ge elements is provided therein with at least a pair of lower electrode parts electrically separated from other regions by respective p-n junctions facing each other apart a prescribed spacing. One or plural layers of epitaxially grown buffer layers are provided on the single crystalline substrate and an epitaxially grown film consisting of the composite oxide of a perovskite structure contg. Pb is provided on the buffer layer. An optical waveguide of the propagation direction of light parallel with the longitudinal direction of the spacing between a pair of the lower electrodes is provided of a part or the whole of the multi component oxide right above the spacing. At least a pair of upper electrodes are provided in the positions facing the lower electrodes via the buffer layer and the multi component oxide layer. A mechanism to electrically connect the upper electrodes and lower electrodes facing each other via the film is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical modulator device useful for printers, light emitting devices, optical communications, optical computers and the like.

[0002]

2. Description of the Related Art (Pb, La) (Zr, Ti) O ₃ ,
A complex oxide having a perovskite structure containing a Pb element such as (Pb, La) TiO ₃ has an excellent electro-optic effect, and these materials can be thinned to be applied to an optical waveguide type optical modulator and an optical switch element. Widely tried.

Since the optical switch is considered to be a kind of optical modulator in a broad sense, the optical modulator in the following description also includes an optical switch.

In the optical modulator device using these materials, the thin film made of the complex oxide needs to be a single crystal in order to obtain sufficient device characteristics. In a polycrystalline body, it is difficult to obtain sufficient device characteristics due to light scattering by grain boundaries.

Conventionally, optical modulators using these composite oxide thin films have been prototyped using an epitaxial film on an alumina single crystal substrate [J. J. Appl. Phys. ，
24, Suppl. 24-2, 284 (1985)].
However, an oxide single crystal substrate such as alumina is expensive.
Furthermore, in order to meet recent demands for miniaturization and high integration of electronic devices, it has been attempted to fabricate an optical modulator using the above-mentioned composite oxide thin film on a Si, Ge single crystal substrate ( JP-A-62-39825, JP-A-63-551
98, JP-A-60-161635).

[0006]

However, when the Si, Ge single crystal substrate is used, the following problems to be solved occur.

The first problem is that when an optical waveguide is provided on a Si, Ge single crystal substrate, the refractive index of the composite oxide is
However, since Si and Ge have a refractive index of 4.0 and 5.3, respectively, in order to confine light in the waveguide, a Si and Ge single crystal substrate and a complex oxide are used. A complex oxide and a buffer layer having a refractive index smaller than that of the waveguide are required between the waveguides.

Further, this buffer layer must be a film epitaxially grown on the underlying layers, Si and Ge, in order to obtain an epitaxial film of complex oxide.

As such a buffer layer, MgAl
₂ O ₄ and MgO have been proposed, but since the fabrication process conditions are as severe as about 950 ° C., when aiming for device integration, it is possible to use a drive circuit already fabricated in a Si or Ge single crystal substrate. There is limited damage and can only be used.

The second problem will be described.

In the case of an optical waveguide modulator using an anisotropic material such as the complex oxide, the main component of the electric field of light is directed in the in-plane direction of the film in a plane perpendicular to the light propagation direction. The waveguide configuration is such that it is in the open mode (TE-like mode) or in the mode perpendicular to the film surface (TM-like mode).

The complex oxide has an electro-optical effect in which the refractive index is changed by an electric field applied from the outside, but the light propagating in the complex oxide has a polarization state in which the electric field plane is parallel to the applied electric field direction. In some cases, it is most strongly affected by changes in refractive index.

Therefore, in the TE-like mode, it is necessary to apply an electric field perpendicular to the propagation direction of guided light and in the in-plane direction of the film. In an example in which an optical switch is manufactured using an oxide single crystal substrate, such an electric field is applied using a planar electrode (FIG. 2).

However, in the case of a Si / Ge single crystal substrate, charges of opposite polarity are induced in the Si / Ge single crystal substrate under each electrode in the inner surface of the buffer layer. An electric field of effective strength is not generated in the film in the film in-plane direction (FIG. 3).

The object of the present invention is to solve these problems,
It is possible to fabricate a TE-like mode optical / modulator element having sufficient element characteristics on an inexpensive Si / Ge single crystal substrate, and further, a mature integrated circuit using a conventional Si / Ge single crystal. By using the technology, it is possible to realize high integration and multifunction of the optical modulator element.

[0016]

As a result of extensive studies, the present invention has led to the present invention.

That is, according to the present invention, in a single crystal substrate containing at least one of Si and Ge elements, a lower portion which is electrically separated from other regions by PN junctions facing each other with at least one pair of constant gaps. An electrode portion is provided, one or more buffer layers epitaxially grown on the single crystal substrate are provided, and an epitaxial growth film made of a complex oxide having a perovskite structure containing Pb is provided on the buffer layer. An optical waveguide whose light propagation direction is parallel to the longitudinal direction of the gap is provided directly above the gap between the pair of lower electrodes in a part or all of the film, and the lower electrode, the buffer layer, and the complex oxide layer are provided. At least one pair of upper electrodes are provided at positions facing each other through the film, and the electrodes of the upper electrode and the lower electrode facing each other through the film are optical modulator elements provided with a mechanism to be electrically connected.

FIG. 1 shows the basic structure of the optical modulator element of the present invention.

The substrate used in the present invention is made of Si, Ge, S.
A single crystal substrate containing at least one of Si and Ge elements such as i _(1-X) Ge _X (hereinafter referred to as Si and Ge single crystal substrate). These substrates have a plane orientation of (100) or (111)
And substrates that are offset within ± 10 ° of their orientation are desirable. Further, the single crystal substrate referred to here is Si, G formed on an amorphous substrate or a polycrystalline substrate.
It also includes a substrate obtained by melting and recrystallizing the e, Si _1-x , Ge _x film by lamp heating or laser heating.

In the optical modulator element of the present invention, the S
In the i, Ge single crystal substrate, at least one pair of opposing lower electrode portions that can be electrically separated from the contact area by a PN junction is provided.

The gap between the pair of lower electrode portions is 500 to
90,000,000Å and 5000 to 5,000,000
0Å is desirable.

On the Si, Ge single crystal substrate, one or a plurality of epitaxially grown buffer layers are also provided. This buffer layer is composed of SrO, BaO, CeO ₂ ,
It is composed of oxides such as ZrO ₂ , TiO ₂ , Al ₂ O ₃ , MgO and MgAl ₂ O ₄ . The thickness of this buffer layer is 1
0 to 8,000,000Å, preferably 500 to 50000Å.

Further, on the buffer layer (Pb, La)
One or a plurality of epitaxial growth films of a complex oxide having a perovskite structure containing Pb such as TiO ₃ and (Pb, La) (Zr, Ti) O ₃ are provided. (Hereinafter, referred to as a complex oxide film). The film thickness is 500 to 5,000,000Å, 80
0-200000Å is desirable. Then, in this composite oxide film, a waveguide is provided between the gaps of the pair of lower electrodes or including the gap and passing in parallel with the gap.

The dimension of the optical waveguide in the in-plane direction of the film perpendicular to the light propagation direction is 1000 to 90000000Å
Therefore, 3000 to 50000000Å is desirable.

A pair of Al, Au, Cr, Pt, at least one pair of Al, Au, Cr, Pt, is provided on the optical waveguide or sandwiching the optical waveguide and facing the lower electrode through the buffer layer and the complex oxide layer.
An upper electrode made of poly-Si or the like is provided.

Finally, the upper electrode and the lower electrode, which face each other with the buffer layer and the complex oxide layer in between, are formed on the device by Al, A
A film of u, Cr, Pt, poly-Si, etc.
Electrical connection is made by bonding lead wires such as u and Al.

Next, the manufacturing method and detailed structure will be described in more detail.

The lower electrode can be manufactured by a usual Si or Ge wafer process technique. That is, pattern formation is performed by a lithography process using a resist and a dry or chemical etching process, and impurity introduction is performed by a solid phase and vapor phase diffusion process or an ion implantation process. As a detailed configuration example, (1) two P-type lower electrodes are provided in an n-type substrate (FIG. 5).

(2) Two n-type lower electrodes are provided in the P-type substrate (FIG. 6).

(3) P well is provided in the n-type substrate, and P well
An n-type lower electrode is provided in the well, and a P-type lower electrode is provided in a portion other than the P well (FIG. 7).

(4) An n well is provided in a P-type substrate, and n
A P-type lower electrode is provided in the well, and an n-type lower electrode is provided in a portion other than the n-well (FIG. 8).

(5) Si is epitaxially grown in an n-type or P-type substrate by using SiH ₄ gas or the like, a P well and an n well are provided in the epitaxial Si film, and an n type lower electrode, A P-type lower electrode is provided in the n-well (FIG. 9).

5 to 9, 1 and 2 are lower electrodes, and 3 is a Si, Ge single crystal substrate.

The epitaxial buffer layer is made of Si, Ge.
The surface of the single crystal substrate is cleaned by HF treatment, HCl boil treatment, high temperature flash method, Ga beam irradiation method, etc.
After removing the oxide film on the surface of the i, Ge single crystal substrate, MB
It is formed by E (molecular beam epitaxial) method, ALE (atomic layer epitaxial) method, MOCVD (metal organic chemical vapor deposition) method, CVD method, sputtering method, vapor deposition method, or the like.

In order to obtain a good epitaxial growth film or to provide a light absorption layer, SrTiO ₃ , BaTiO ₃ , or between the buffer layers and between the buffer layer and the Si, Ge single crystal substrate, SrF ₂ , CaF ₂ , Z
An epitaxial layer such as nS, ZnSe or GaP may be provided.

Next, the composite oxide film is formed by MBE method and ALE.
Method, MOCVD method, CVD method, sputtering method vapor deposition method.

In the optical waveguide, a complex oxide film is formed into a ridge type by RIE (reactive ion etching) method or chemical etching method, or Ta ₂ O ₅ , SiO ₂ , Al _{2 is formed.}
There is a method of patterning an upper dielectric film such as O _{3 and} a method of forming a facing metal film, but the shape of the optical waveguide is not limited.

In some cases, the upper electrode is provided on the composite oxide film via the upper buffer layer.

Further, the structure of the optical modulator is not limited to any structure other than that of the optical waveguide type, and a total reflection type optical switch, a directional coupler type optical switch,
It also includes a branch type optical switch.

SrO, BaO, CeO ₂ , ZrO ₂ , Ti
The buffer layer material such as O ₂ , Al ₂ O ₃ , MgO, and MgAl ₂ O ₄ has a crystal plane having an atomic arrangement that substantially matches Si, Ge, Si _1-x , Ge _x and the complex oxide. Therefore, the composite oxide is epitaxially grown by reflecting the crystal structure of the Si, Ge single crystal substrate. In addition, these buffer layers can be made to be a single layer or a plurality of layers so that the total refractive index can be made smaller than that of the complex oxide, and therefore, if the film thickness is appropriately selected, light can be well confined in the complex oxide waveguide. .

When a voltage is applied to the structure of only the planar type upper electrode, electric charges of opposite polarities to those of the upper electrode are induced at the Si / Ge single crystal interface immediately below the electrodes at each electrode, so that the optical waveguide An electric field is not effectively generated in the in-plane direction of the film,
A sufficient change in refractive index does not occur in the complex oxide waveguide.

When the upper electrode and the lower electrode of the present invention are used together, an electric field is effectively generated in the optical waveguide film, and good light modulation characteristics are obtained.

[0043]

【Example】

Example 1 A (100) n-type Si substrate surface having a resistance value of 1 to 0.1 Ω / cm was used, and about 200 was formed at two locations by a Si wafer process.
A lower electrode in a P-type region having a length of 10 mm is formed by B ion implantation at intervals of 000Å. Next, this substrate is RCA
After washing, it was dipped in HF / H ₂ O (1/100) and placed in an MBE apparatus. After exhausting to 10 ⁻¹¹ Torr, SrO pellets are vapor-deposited by electron beam heating,
An SrO film having a film thickness of about 500Å is prepared. Next, the MgO pellet is grown by electron beam heating to about 5000Å.
The sample is taken out and put in the MOCVD equipment, and Pb (C
₂ H ₅ ) ₄ , La (DPM) ₃ , Ti (OC ₃ H ₇ ) ₄ and O ₂
Using gas as a raw material, a (Pb, La) TiO ₃ (100) oriented epitaxial film is grown to a film thickness of about 4000Å.

Next, an Al ₂ O ₃ —SiO ₂ film is grown by electron beam heating vapor deposition to about 500 Å. Next, the above 2
Place Al so that it is located right above the gap area of the lower electrode.
RIE etching is performed on the ₂ O ₃ —SiO ₂ film. Next, the film thickness 2
A 000Å Al electrode is formed with a pattern of 10 mm in length at intervals of about 200,000Å. Next, a contact hole reaching the lower electrode is formed by RIE and then connected by an Al metal film.

TE mode light having a wavelength of 633 mm is incident on this optical switch element by using a prism, and one upper-lower electrode has -0.5 V and the other upper-lower electrode has -20 V.
When applied, the intensity of emitted light was reduced by 25% as compared with the case where no voltage was applied.

In the case of the optical switch element having the same structure except that the lower electrode was not formed, the effect of voltage application was not confirmed when measured under the same conditions. Note that FIG. 10 is an explanatory diagram of the optical modulator element of the first embodiment.

[0047]

EFFECTS OF THE INVENTION A buffer layer having a refractive index smaller than that of the composite oxide as a whole has a crystal plane having an atomic arrangement that substantially matches the Si and Ge single crystals and the composite oxide, respectively. Since the composite oxide film used is an epitaxial film with few crystal grain boundaries, the optical waveguide loss deficiency is small, and the anisotropy of the material can be remarkably exhibited.
An optical switch element having higher characteristics can be manufactured on the substrate.

Further, by forming the lower electrode,
Since a sufficient electric field can be generated in the composite oxide film, the light modulation characteristics can be further improved.

Furthermore, since it becomes possible to fabricate an optical switch element on a Si or Ge single crystal, the optical modulator element can be highly integrated and multifunctional.

[Brief description of drawings]

FIG. 1 is a sectional view showing the basic configuration of an optical modulator device according to the present invention.

FIG. 2 is a cross-sectional explanatory diagram of an optical switch using an oxide single crystal substrate.

FIG. 3 is an explanatory cross-sectional view of an optical switch using a Si, Ge single crystal substrate.

FIG. 4 is a cross-sectional explanatory view of an optical switch in which a lower electrode is added to a Si / Ge single crystal substrate.

FIG. 5 is a structural example of a lower electrode in the optical modulator element of the present invention.

FIG. 6 is another example of the configuration.

FIG. 7 shows another example of the configuration.

FIG. 8 shows another example of the configuration.

FIG. 9 shows another example of the configuration.

FIG. 10 is a structural example of an optical modulator device of the present invention according to an embodiment.

Claims (1)

[Claims] 1. A single crystal substrate containing at least one of Si and Ge elements is provided with lower electrode portions electrically opposed to other regions by PN junctions facing each other with at least one pair of constant gaps. A single or a plurality of buffer layers epitaxially grown on the single crystal substrate, and an epitaxial growth film made of a complex oxide having a perovskite structure containing Pb on the buffer layer, and a part of the complex oxide film. Or, at a position directly above the gap between the pair of lower electrodes, an optical waveguide whose light propagation direction is parallel to the longitudinal direction of the gap is provided, and the optical waveguide is opposed to the lower electrode via the buffer layer and the complex oxide layer. At least one pair of upper electrodes are provided in the
An optical modulator element provided with a mechanism to be electrically connected.