JP2006251086A - Electromagnetic wave generating element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electromagnetic wave generating element for manifesting a quasi phase matching effect by a small number of semiconductor wafers and generating efficient difference frequency light with a high parallelism of a direction inversion axis. <P>SOLUTION: The electromagnetic wave generating element has an optical waveguide composed of either a group III-V or a group II-VI compound semiconductor wafer of zincblende structure on a substrate. The optical waveguide is fabricated by joining a plurality of sheets of compound semiconductor wafers taking [110] surfaces as lamination planes in such a way that either [111] axis directions or crystallographically equivalent axis directions are mutually anti-parallel. In the shape of the optical waveguide, periodic passing of an optical waveguide with a starting point on one wafer through the other wafer and subsequent passing thereof through the original wafer is repeated. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electromagnetic wave generating element, and more particularly to an electromagnetic wave generating element that can generate an electromagnetic wave of 0.1 to 10 THz with high efficiency.

  In recent years, research on electromagnetic waves (light) in the optical communication wavelength band and electromagnetic waves (radio waves) in the millimeter wave or submillimeter wave band has progressed steadily, resulting in ultra-high-speed and large-capacity signal propagation in communication trunk lines and mobile communication networks. Has been successful.

  However, research and development of electromagnetic wave generation of 0.1 to 10 THz in the middle region between light and radio waves is in the process of development, and various studies are being conducted today. The search for application fields is also very active. Light having a frequency of around 100 THz is well known as mid-infrared light, and can be easily generated by combining a readily available dielectric material (or semiconductor nonlinear optical material) and a semiconductor light source for communication. It has become like this. In addition, by performing spectrum analysis using this, we are proceeding to interesting applications such as atmospheric gas type identification and moisture measurement in gas.

  On the other hand, an electromagnetic wave having a frequency of 0.1 to 10 THz has a wavelength longer than that of mid-infrared light, and therefore has a high material permeability and a wavelength resolution higher than that of radio waves. Application to non-destructive inspection is highly expected. In addition, since many toxic and explosive constituent molecules have characteristic vibration spectra in the 0.1 to 10 THz band, enabling spectrum analysis in the 0.1 to 10 THz band detects dangerous substances. It is thought that it is very useful for things. As described above, the electromagnetic waves in the 0.1 to 10 THz band are considered to be extremely important in fields such as non-invasive inspection and dangerous substance detection.

  FIG. 9 shows a configuration of a periodic orientation inversion structure in a conventional electromagnetic wave generating element. Several proposals have already been made for the generation of electromagnetic waves in the 0.1 to 10 THz band, and FIG. 9 shows a conventional example. A conventional electromagnetic wave generating element has a structure in which a large number of semiconductor wafers, which are nonlinear optical materials, are bonded by a semiconductor direct bonding technique while periodically inverting the crystal orientation. When this electromagnetic wave generating element is used, two light waves having different wavelengths are incident in a direction having periodicity, and are generated by a pseudo phase matching method and a difference frequency generating method. This electromagnetic wave generating element is considered promising because it is overwhelmingly superior to other methods in terms of output efficiency. High efficiency of the difference frequency light using the above structure has already been realized in the mid-infrared region (see Non-Patent Document 1), but the technology for realizing this in the frequency band of 0.1 to 10 THz is applied to industrial applications. From the viewpoint of

  The difference frequency generation method means that the electric polarizability P is relative to the electric field E of incident light.

Of the nonlinear optical material that responds as (ε ₀ : dielectric constant in vacuum), a material having a large secondary response χ ⁽²⁾ is used and light of frequencies ω ₃ and ω ₂ is incident, and the frequency ω ₁ = This is a method for generating converted light having ω ₃ −ω ₂ .

  However, as is well known, the refractive index n of a substance generally has frequency dependence (this is called material dispersion). Therefore, wave number k is

(C: speed of light) and the wave number mismatch amount of the difference frequency light

Does not become 0 except in a vacuum. When Δk ≠ 0, the intensity of the difference frequency light is

It is a big problem to decrease in Here, L is the length of the substance. In order to solve this, crystal momentum can be imparted to Δk by producing a periodic orientation inversion structure 15 in which the polarizability χ ⁽²⁾ is periodically inverted as shown in FIG. 9, so that Δk = 0 can be realized. it can. This has been proven effective in experiments. The above method is known as a quasi phase matching method. Thereby, highly efficient generation of difference frequency light can be realized.

  However, when creating a quasi-phase matching structure by joining a number of semiconductor wafers that are nonlinear optical materials periodically by reversing the crystal orientation and using semiconductor direct joining technology so that the crystal orientation is antiparallel, The time required for the pasting operation increases in proportion to the increase in the number of wafers, and it becomes difficult to keep the orientation reversal axes of the wafers in parallel.

D. Zheng, A. Gordon, YS Wu, RS Feigelson, MM Fejer, RL Byer, KL Vodopyanov, “16-μm infrared generation by difference-frequency mixing in diffusion-bonded-stacked GaAs”, Optics Letters, 1998, Vol. 23, Issue 13, pp.1010-1-12.

  However, when a conventional electromagnetic wave generating element is manufactured by the above-described method, it is necessary to increase the number of wafers constituting the quasi phase matching structure in order to increase the nonlinear optical effect. As a result, in proportion to the increasing number of wafers, there is a problem that the time required for bonding the semiconductor wafers so that the crystal orientation is antiparallel while the crystal orientation is periodically reversed is increased. In addition, there is a problem that it is difficult to keep the azimuth reversal axes of each wafer in parallel.

  An object of the present invention is to generate a high-efficiency difference frequency light that exhibits a quasi-phase matching effect equivalent to the case where a large number of semiconductor wafers are bonded with a small number of wafers, and that has a high parallelism of azimuth reversal axes. The object is to provide an electromagnetic wave generating element.

  In order to achieve such an object, the present invention according to claim 1 comprises, on a substrate, a compound semiconductor of either a group III-V or a group II-VI of a zinc blende structure. A plurality of compound semiconductor wafers are bonded with the {110} plane as a laminated surface so that either the [111] axial direction or the crystallographically equivalent axial direction is antiparallel to each other. The optical waveguide having the starting point on one wafer passes through the other wafer and has a shape that periodically repeats passing through the original wafer.

  The invention according to claim 2 comprises an optical waveguide made of a compound semiconductor of either III-V group or II-VI group having a wurtzite structure on a substrate, and the optical waveguide has a [0001] axial direction and Multiple compound semiconductor wafers are placed so that one of the crystallographically equivalent axial directions is antiparallel to each other.

Face and

One of the surfaces is bonded as a laminated surface, and an optical waveguide having a starting point on one wafer passes through the other wafer and has a shape that periodically repeats passing through the original wafer .

  According to a third aspect of the present invention, in the electromagnetic wave generating element according to the first or second aspect of the invention, the angle of the optical waveguide with respect to the normal of the wafer end surface of the optical waveguide is set to be larger than the total reflection angle. And

  According to a fourth aspect of the present invention, in the electromagnetic wave generating element according to the first or second aspect, the optical waveguide includes one of a dielectric multilayer mirror and a metal mirror at a bent portion.

  According to a fifth aspect of the present invention, in the electromagnetic wave generating element according to the first aspect, the III-V compound semiconductor is one of GaAs, GaP and InP.

The invention according to claim 6 is the electromagnetic wave generating element according to claim 1, wherein the III-V group compound semiconductor is In _x1 Al _x2 Ga _1-x1-x2 N _y1 As _y2 P _1-y1-y2 (0 <= X ₁ , x ₂ , y ₁ , y ₂ <= 1, 0 <= 1−x ₁ −x ₂ <= 1, 0 <= 1−y ₁ −y ₂ <= 1) To do.

  A seventh aspect of the present invention is the electromagnetic wave generating element according to the first aspect, wherein the II-VI group compound semiconductor is one of ZnSe and CdTe.

The invention according to claim 8 is the electromagnetic wave generating element according to claim 1, wherein the II-VI group compound semiconductor is Zn _x1 Cd _x2 Hg _1-x1-x2 S _y1 Se _y2 Te _1-y1-y2 (0 <= X ₁ , x ₂ , y ₁ , y ₂ <= 1, 0 <= 1−x ₁ −x ₂ <= 1, 0 <= 1−y ₁ −y ₂ <= 1) And

  A ninth aspect of the present invention is the electromagnetic wave generating element according to the second aspect, wherein the III-V compound semiconductor is GaN.

According to a tenth aspect of the present invention, in the electromagnetic wave generating element according to the second aspect, the group III-V compound semiconductor is In _x1 Al _x2 Ga _1-x1-x2 N _y1 As _y2 P _1-y1-y2 (0 <= X ₁ , x ₂ , y ₁ , y ₂ <= 1, 0 <= 1−x ₁ −x ₂ <= 1, 0 <= 1−y ₁ −y ₂ <= 1) And

  The invention according to claim 11 is the electromagnetic wave generating element according to claim 2, wherein the II-VI group compound semiconductor is ZnS.

The invention according to claim 12 is the electromagnetic wave generating element according to claim 2, wherein the II-VI group compound semiconductor is Zn _x1 Cd _x2 Hg _1-x1-x2 S _y1 Se _y2 Te _1-y1-y2 (0 <= X ₁ , x ₂ , y ₁ , y ₂ <= 1, 0 <= 1−x ₁ −x ₂ <= 1, 0 <= 1−y ₁ −y ₂ <= 1) And

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the electromagnetic wave generating element which produces | generates highly efficient difference frequency light whose frequency | count of wafer sticking is 1 time and whose parallelism of a direction inversion axis | shaft is high.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(Embodiment 1)
FIG. 1 shows a configuration of an optical waveguide according to Embodiment 1 of the present invention. Group III-V or II-VI group compound semiconductor wafers 9 and 10 of zinc blende structure (or wurtzite structure) are bonded by a semiconductor direct bonding technique so that the crystallographically equivalent axial directions are antiparallel to each other. To do. Anti-parallel refers to a state in which the directions of the axes are opposite and the axes are parallel. The bonded wafer is stuck on the substrate.

  A portion indicated by a dotted line in FIG. The shape of the optical waveguide is a shape that periodically moves between the wafers 9 and 10. By processing by a normal dry etching or wet etching method, an optical waveguide having a periodic orientation inversion structure can be manufactured (FIG. 1- (b)). When the wafer thickness is d and the angle with respect to the normal of the wafer end face of the optical waveguide is θ, the direction inversion period Λ is

It becomes. The bent portion f of the optical waveguide utilizes the fact that light is reflected by the wafer end face. Therefore, the angle θ is set to be larger than the total reflection angle so that light does not leak out of the optical waveguide. Alternatively, if a dielectric multilayer film mirror or a metal mirror is provided at the bent portion, the angle θ can be made sufficiently smaller than the total reflection angle.

(Embodiment 2)
In FIG. 2, the structure of the optical waveguide in Embodiment 2 of this invention is shown. The shape of the optical waveguide is a shape that periodically moves between the wafers 9 and 10. Group III-V or II-VI group compound semiconductor wafers 9 and 10 of zinc blende structure (or wurtzite structure) are bonded by a semiconductor direct bonding technique so that the crystallographically equivalent axial directions are antiparallel to each other. To do. The bonded wafer is stuck on the substrate.

  A portion indicated by a dotted line in FIG. By processing by dry etching or wet etching, an optical waveguide having a periodic orientation inversion structure can be manufactured (FIG. 2- (b)). In the second embodiment, either one of the dielectric multilayer mirror and the metal mirror is installed at the bent portion f. Thereby, the azimuth inversion period Λ is a, and the angle θ can be set smaller than the total reflection angle 4d / cos θ, which greatly increases the degree of freedom in design.

  The electromagnetic wave generating element 3 is produced by the following method.

  FIG. 6 shows a semiconductor wafer bonding method according to an embodiment of the present invention. The group 9-V or II-VI group compound semiconductor wafers 9 and 10 having a zinc blende structure (or wurtzite structure) are bonded by a semiconductor direct bonding technique without using an adhesive or the like. Thus, the elements produced from the bonded wafers are integrated with no difference in refractive index. If the wafer to be bonded is a compound semiconductor having a zinc blende structure, the [111] axes (or crystallographically equivalent axes) are bonded to each other with the {110} plane as the laminated surface. The Or, if the wafer to be bonded has a wurtzite structure,

Face or

Any one of the surfaces is laminated so that the [0001] axial directions (or crystallographically equivalent axial directions) are antiparallel to each other. This bonded wafer is referred to as a bonded wafer 11. As a result, the maximum component of the tensor of the second-order nonlinear optical constant can be used.

Examples of the III-V compound semiconductor include GaAs, GaP, AlAs, AlP, InAs, InP, GaN, InN, and mixed crystals thereof, that is, In _x1 Al _x2 Ga _1-x1-x2 N _y1 As _y2 P _{1- y1-y2 (0 <= x} 1, x 2, y 1, y 2 <= 1,0 <= 1-x 1 -x 2 <= 1,0 <= 1-y 1 -y 2 <= 1) Can be used.

In addition, examples of the II-VI compound semiconductor include ZnSe, CdTe, HgTe, ZnS, and mixed crystals thereof, that is, Zn _x1 Cd _x2 Hg _1-x1-x2 S _y1 Se _y2 Te _1-y1-y2 (0 < _{= x 1, x 2, y} 1, y 2 <= 1,0 <= 1-x 1 -x 2 <= 1,0 <= 1-y 1 -y 2 <= 1) may be used .

Accordingly, the second-order nonlinear optical constant d ₁₄ is much larger than dielectric materials such as LiNbO ₃ and LiTaO ₃ that are usually used in nonlinear optical wavelength conversion elements. In addition, since light absorption in the 0.1 to 10 THz band is also small, highly efficient electromagnetic waves can be generated in that frequency band.

  FIG. 7 shows a dicing method for bonded semiconductor wafers according to an embodiment of the present invention. In order to make the bonded wafer 11 into an optical waveguide, a part is cut by the dicing apparatus 12.

  FIG. 8 shows a method for polishing a bonded semiconductor wafer in an embodiment of the present invention. In the case of a compound semiconductor having a zinc blende structure, this is adhered to the substrate 13 with an adhesive A so that the [111] direction is directed vertically. In the case of a wurtzite structure, it is pasted so that the [0001] direction faces up and down (FIG. 8- (a)). By this adhesion, when the upper surface of the cut bonded wafer 11 is polished, a normal large area wafer polishing apparatus can be used. Also, the scattering of light above and below the optical waveguide can be significantly reduced by polishing.

  After polishing, the substrate 14 is attached with an adhesive B from above (FIG. 8- (b)). As the adhesive B, an adhesive that is insoluble in the solvent C is used as the adhesive B while the adhesive A is dissolved by the solvent C. As a result, the substrate 13 is peeled off, and the surface which is the lower surface in FIGS. 8A and 8B can be polished again by the polishing apparatus (FIGS. 8C and 8D). By passing through the above steps, a bonded wafer in which upper and lower interface scattering is greatly reduced can be produced.

  As the adhesive A, an alkyl adhesive such as wax or wax, or an acrylic resin adhesive such as PMMA can be used. As the adhesive B, water glass or the like can be used. In this case, by using an organic solvent insoluble in the adhesive B such as alcohol or acetone as the solvent C, it is possible to dissolve only the adhesive A and achieve polishing of the upper surface and the lower surface.

  When the compound semiconductor material does not contain Al, water glass is used as the adhesive A, and the adhesive B is not used. A compound semiconductor substrate 14 having a refractive index smaller than that of the bonded wafer 11 is bonded to the bonded wafer 11 by a semiconductor direct bonding technique. By using a hydrofluoric acid-based etching solution as the solvent C, the adhesive A can be dissolved and polishing of the upper surface and the lower surface can be achieved.

If a wafer is bonded by the method as described above to produce an optical waveguide, an element that generates high-efficiency difference frequency light with a high degree of parallelism of the direction inversion axis can be produced. That is, when the deviation angle of the azimuth reversal axis is φ, the conversion efficiency to the difference frequency light is cos ² φ. Therefore, in the case of the element as shown in FIG. However, since the above-described element has one pasting operation, such a decrease in efficiency can be minimized.

(Embodiment 3)
In FIG. 3, the structure of the electromagnetic wave generator in Embodiment 3 of this invention is shown. As one embodiment of the present invention, an electromagnetic wave generating element can be applied to an electromagnetic wave generating device. The electromagnetic wave generator includes a laser generator 1, a wavelength tunable device 2, an electromagnetic wave generator 3, a beam splitter 4, and a mirror 5. As the laser generator 1, a Q switch YAG laser or the like can be used. An optical parametric oscillator or the like can be used as the wavelength tunable device 2.

  The light emitted from the laser generator 1 is separated into two components by the beam splitter 4, one of the light is incident on the wavelength tunable device 2, the wavelength is changed, and then passes through the other optical path separated by the beam splitter 4. The light is combined with the light and enters the optical waveguide of the electromagnetic wave generating element 3. As a result, excitation light having two different wavelengths necessary for differential frequency generation can be generated and input to the electromagnetic wave generating element.

(Embodiment 4)
In FIG. 4, the structure of the electromagnetic wave generator in Embodiment 4 of this invention is shown. In the second embodiment, a wavelength tunable device 2 is provided on each of two optical paths separated by a beam splitter. According to this configuration, even when the wavelength of the light emitted from the laser generator 1 deviates from a desired value, the wavelengths can be adjusted by using the two wavelength variable devices 2.

(Embodiment 5)
In FIG. 5, the structure of the electromagnetic wave generator in Embodiment 5 of this invention is shown. The two laser generators 1 and the input end of the coupler 7, and the output end of the coupler 7 and the electromagnetic wave generating element 3 are coupled by an optical fiber 8. According to this configuration, since the two laser generators 1 are provided, the wavelength tunable device 2 can be omitted. However, since the wavelength variability in this configuration is determined by the variable range of the laser generator 1, the wavelength variability is smaller than the former two.

It is a figure which shows the structure of the electromagnetic wave generating element in Embodiment 1 of this invention. It is a figure which shows the structure of the electromagnetic wave generator in Embodiment 2 of this invention. It is a figure which shows the structure of the electromagnetic wave generator in Embodiment 3 of this invention. It is a figure which shows the structure of the electromagnetic wave generator in Embodiment 4 of this invention. It is a figure which shows the structure of the electromagnetic wave generator in Embodiment 5 of this invention. It is a figure explaining the semiconductor wafer bonding method in one Embodiment of this invention. It is a figure explaining the dicing method of the joined semiconductor wafer in one Embodiment of this invention. It is a figure explaining the grinding | polishing method of the joined semiconductor wafer in one Embodiment of this invention. It is a figure which shows the structure of the periodic azimuth | direction inversion structure in the conventional electromagnetic wave generator.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laser generator 2 Wavelength variable device 3 Electromagnetic wave generating element 4 Beam splitter 5 Mirror 6 Optical path 7 Coupler 8 Optical fiber 9 Semiconductor wafer 10 Semiconductor wafer 10 direction reversed 12 Dicing apparatus 13 Substrate 14 Substrate 15 Periodic direction reversal structure a Directional reversal period f Bent part

Claims (12)

  An optical waveguide made of a compound semiconductor of either a group III-V or a group II-VI having a zinc blende structure is provided on a substrate, and the optical waveguide has a [111] axial direction and a crystallographically equivalent axial direction. A plurality of compound semiconductor wafers are bonded with the {110} plane as a laminated surface so that either one of them is antiparallel to each other, and an optical waveguide having a starting point on one wafer passes through the other wafer, An electromagnetic wave generating element characterized by having a shape that periodically passes through a wafer. An optical waveguide made of a compound semiconductor of either III-V or II-VI having a wurtzite structure is provided on a substrate, and the optical waveguide has a [0001] axial direction and a crystallographically equivalent axial direction. Multiple compound semiconductor wafers so that either one is antiparallel to each other

Face and

One of the surfaces is bonded as a laminated surface, and an optical waveguide having a starting point on one wafer passes through the other wafer and has a shape that periodically repeats passing through the original wafer Electromagnetic wave generating element.   3. The electromagnetic wave generating element according to claim 1, wherein the angle of the optical waveguide with respect to the normal of the wafer end surface of the optical waveguide is set to be larger than a total reflection angle.   3. The electromagnetic wave generating element according to claim 1, wherein the optical waveguide includes either one of a dielectric multilayer mirror and a metal mirror at a bent portion.   2. The electromagnetic wave generating element according to claim 1, wherein the III-V compound semiconductor is one of GaAs, GaP, and InP. 2. The electromagnetic wave generating element according to claim 1, wherein the III-V group compound semiconductor is In _x1 Al _x2 Ga _1-x1-x2 N _y1 As _y2 P _1-y1-y2 (0 <= x ₁ , x ₂ , y ₁ , y ₂ <= 1, 0 <= 1−x ₁ −x ₂ <= 1, 0 <= 1−y ₁ −y ₂ <= 1).   2. The electromagnetic wave generating element according to claim 1, wherein the II-VI group compound semiconductor is one of ZnSe and CdTe. 2. The electromagnetic wave generating element according to claim 1, wherein the II-VI group compound semiconductor is Zn _x1 Cd _x2 Hg _1-x1-x2 S _y1 Se _y2 Te _1-y1-y2 (0 <= x ₁ , x ₂ , y ₁ , y ₂ <= 1, 0 <= 1−x ₁ −x ₂ <= 1, 0 <= 1−y ₁ −y ₂ <= 1).   3. The electromagnetic wave generating element according to claim 2, wherein the III-V group compound semiconductor is GaN. 3. The electromagnetic wave generating element according to claim 2, wherein the group III-V compound semiconductor is In _x1 Al _x2 Ga _1-x1-x2 N _y1 As _y2 P _1-y1-y2 (0 <= x ₁ , x ₂ , y ₁ , y ₂ <= 1, 0 <= 1−x ₁ −x ₂ <= 1, 0 <= 1−y ₁ −y ₂ <= 1).   3. The electromagnetic wave generating element according to claim 2, wherein the II-VI group compound semiconductor is ZnS. 3. The electromagnetic wave generating element according to claim 2, wherein the II-VI group compound semiconductor is Zn _x1 Cd _x2 Hg _1-x1-x2 S _y1 Se _y2 Te _1-y1-y2 (0 <= x ₁ , x ₂ , y ₁ , y ₂ <= 1, 0 <= 1−x ₁ −x ₂ <= 1, 0 <= 1−y ₁ −y ₂ <= 1).

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