JPH04361239A - Single crystalline thin film and produciton thereof - Google Patents

Abstract

PURPOSE:To provide the single crystalline thin-film suitable for obtaining a high-performance SHG element. CONSTITUTION:Metal oxides Li2O, Nb2O5, Ta2O5, and MOz (z is arbitraty) are respectively previously prepd. as targets TG1, TG2, TG3, TG4 for laser abrasion. The laser beam BM from an excimer laser 1 is thereafter made incident successively in prescribed sequence on the respective targets TG1, TG2, TG3, TG4 to successively epitaxially grow the abraded metal oxides from the surfaces of the respective targets on LiTaxNb1-xO3 (0gammax<=1) as a single crystalline substrate 2 to form LiTayNb1-yO3:M as the single crystalline thin-film 3.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a unit having a nonlinear optical effect formed on a predetermined substrate in order to realize a wavelength conversion element such as a second harmonic generation element (SHG element) used in an optical disc. This invention relates to a crystalline thin film and its manufacturing method.

0002

[Prior Art] Conventionally, LiNb having a nonlinear optical effect
To form oxides such as O3 and LiTaO3 as a single crystal thin film on a given substrate, for example, RF sputtering method, CVD method, or 1975
The document “Journal of Crysta” published in
Methods such as the LPE method (liquid phase epitaxial method) disclosed in "L Growth 29, pp. 289-295" are known, and a single crystal thin film on a substrate created by these methods is used to form an optical waveguide. It can function as

Among these methods, in the LPE method, Li
A thin film of LiNbO3 with a film thickness of 1 to 10 μm can be epitaxially grown on a TaO3 substrate using the LPE method with good crystallinity, and the optical propagation loss can be reduced to 1 to 5 dB/cm.
In addition, the electro-optical constant r33 is set to (28.5/
1012) It was possible to make m/V almost the same level as in the bulk case.

0004

[Problems to be Solved by the Invention] Generally, when a single-crystalline thin film of, for example, LiNbO3 formed on a substrate is used as an optical waveguide for a waveguide-type SHG element, it is generally necessary to use a single-crystalline thin film formed on a substrate as a light source for driving the SHG element. When fundamental wave light with a wavelength of 830 nm is incident from a semiconductor laser, LiN
Ordinary refractive index n0 of fundamental wave light in bO3 single crystal thin film
(ω), the extraordinary refractive index ne(2ω) of the second harmonic light is different from “2.253” and “2.282”, respectively.
Conditions n0(
ω)=ne(2ω) is not satisfied.

In order to enable phase matching between the fundamental wave light and the second harmonic light and to generate the second harmonic light efficiently, it is necessary to
For example, by epitaxially growing a single crystalline thin film LiNbO3 doped with MgO on an iTaO3 substrate, the refractive indexes of both of the above are n0(ω) and ne(2ω).
It would be better if they were approximately the same.

However, in the above-mentioned LPE method for manufacturing a single crystalline thin film, when forming an MgO-doped single-crystalline thin film LiNbO3:Mg-doped by liquid phase epitaxial growth, the amount of MgO dopant is limited to 5%. It was getting worse. In addition, in the LPE method, dopants that can be used other than Mg, that is, metal elements, include Fe, Zn,
It was limited to a few types such as V. For this reason, in application to SHG elements, a certain type of semiconductor laser is used as a light source, and for the fundamental wave light of a predetermined wavelength from this laser, the refractive index of n0 (ω) and ne (2ω) is set to the same level. Even if it were possible to create a single-crystalline thin film that would make it possible to obtain a single-crystal thin film, another semiconductor laser would be used as a light source, and the wavelength of its fundamental wave light would be different from the above, for example, if the amount of MgO dopant was reduced by 10%. If the refractive indexes of n0 (ω) and ne (2ω) cannot be made to the same level unless the above conditions are met, a single-crystalline thin film that makes both refractive indexes similar by limiting the dopant composition and type of dopant may be used. There was a problem that it was not possible to create .

[0007] As described above, in the production method using the LPE method, the dopant composition and dopant type are limited, and furthermore, precise film thickness control cannot be performed.
High-performance S
It has been extremely difficult to realize an HG element.

An object of the present invention is to provide a single-crystalline thin film suitable for realizing a high-performance SHG element and a method for manufacturing the same.

[0009]

[Means for Solving the Problems] The present invention provides a single crystalline thin film made of mixed crystal LiTa doped with a desired amount of an arbitrary metal element M.
yNb1-yO3:M-doped (0≦y≦1) single-crystalline thin film, which is characterized by being formed by laser ablation.

More specifically, as shown in FIG. 1, laser ablation targets TG1, TG2, TG3
, TG4, metal oxides Li2O, Nb2O5, T
Each of a2O5 and MOz (z is arbitrary) is prepared in advance. After that, for example, the laser beam BM from the excimer laser 1 is directed to each target TG1, TG2, TG3,
The metal oxide is ablated from the surface of each target by sequentially injecting it into the TG4 in a predetermined order, and the metal oxide ablated from the surface of each target is transferred to LiTaxNb1 as the single crystal substrate 2.
-xO3 (0≦x≦1) is sequentially epitaxially grown to form a single crystal thin film 3 having a structure as shown in FIG. 2, for example, ie, LiTayNb1-yO3:M. However, FIG. 2 is simplified for convenience of explanation.

When the above structure is an illuminite structure, the characteristics of the illuminite structure are that the first layer L1 is a layer containing element A, the second layer L2 is a layer containing element B, and the third layer L3 is a layer containing element B.
It consists of a layer containing the same element A as the layer L1. Therefore, when trying to create a mixed crystal of LiTayNb1-yO3, element A is changed to Li, element B is changed to Ta or Nb, a layer of Li2O is formed in the first layer L1, and then a layer of Li2O is formed in the second layer L2. A layer of Ta2O5 or a layer of Nb2O5 is formed as the third layer L3, and then a layer of Li2O is formed as the third layer L3.

[0012] In order to form such a mixed crystal to a predetermined thickness, the above-mentioned layers are regularly and repeatedly laminated in the thickness direction. At this time, the third layer L3 functions as the first layer L1, It can be considered that a layered structure that is essentially a combination of two layers, the first layer L1 and the second layer L2, is repeatedly formed in the thickness direction. In addition, when creating the above-mentioned mixed crystal, when y is set to, for example, "0.5" and the composition ratio of Ta and Nb is to be set to 1:1, a layered structure of the first layer L1 and the second layer L2 is required. By repeating this in the thickness direction, layers of Ta2O5 and layers of Nb2O5 may be alternately formed in the second layer L2.

[0013] Further, the doping of the metal element M into the above-mentioned mixed crystal can be carried out by forming a layer of Li2O in the first layer L1 or the second layer L2.
Alternatively, instead of forming a layer of Ta2O5 or Nb2O5, a layer of MOz may be formed. At this time, the doping amount of the metal element M is MO in the thickness direction.
It is naturally determined by how many layers of z are included.

Therefore, by the laser ablation method, a single crystalline thin film LiTayNb1-yO3:M (for example, y
to "0.5"),
Basically, the laser beam BM from excimer laser 1
is incident on the target TG1, and Li2O from the target TG1 is laminated on the substrate 2 to form the first layer L1,
Next, the laser beam BM is directed to the target TG2 (or T
G3) to deposit Ta2O5 (or Nb2O5) from the target TG2 (or TG3) on the first layer L1 to form the second layer L2, and then make the laser beam BM enter the target TG1 to deposit Li2O on the first layer L1. 2 layer L
A third layer L3 (substantially the first layer L1) is laminated on top of 2.
and then direct the laser beam BM to target TG3
(or TG2) to inject Nb2O5 (or Ta2O5) from target TG3 (or TG2) into the third
It is laminated on top of layer L3.

[0015] By repeating the layer forming process using such a laser ablation method, a mixed crystal LiTayNb1-yO3 (y = "0.5") can be created on the substrate 2, but in this repeating process, 1st
When forming layer L1 (third layer L3) or second layer L2, basically target TG1 or target TG
2. By selectively making the laser beam BM incident on TG3 incident on the target TG4 and emitting MOz from the target TG4, the first layer L1 (third layer L3) and the third layer laminated in the thickness direction are Some of the two layers L2 can be MOz layers, making it possible to create a mixed crystal doped with the metal element M as a single crystalline thin film.

[0016] A single crystalline thin film is constructed of the mixed crystal LiTayNb1-yO3 in a state in which the metal element M as an impurity is not doped, thereby realizing a waveguide type SHG element, and the single crystalline thin film is used as an SHG element. When functioning as a waveguide, as mentioned above, the ordinary refractive index n0 (ω) of the fundamental wave light and the extraordinary refractive index ne (2ω) of the second harmonic light in this single crystal thin film are generally different, and the fundamental wave light Phase matching cannot be achieved between the second harmonic light and the second harmonic light, and the second harmonic light cannot be efficiently generated.

On the other hand, when a single-crystalline thin film is composed of the mixed crystal LiTayNb1-yO3:M doped with a predetermined amount of the metal element M, the ordinary refractive index n0(ω) of the fundamental wave light is
, the extraordinary refractive index ne(2ω) of the second harmonic light can be made to be approximately the same. In this case, the fundamental wave light and the second harmonic light can be phase matched, and the second harmonic light can be efficiently generated.

By the way, in the present invention, the laser beam BM
For example, a single crystalline thin film having an illuminite structure is sequentially formed layer by layer by selectively controlling such that it is incident on any one of the targets TG1 to TG4. By controlling the power, number of shots, or irradiation time of the laser beam BM to the targets TG1 to TG4,
, Nb2O5, by controlling the number and deposition speed of MOz,
It becomes possible to arbitrarily and precisely control the composition of each layer. That is, target TG2 with respect to target TG3
By changing the power of the laser beam BM, the number of shots, or the irradiation time, the ratio of y can be changed arbitrarily and precisely. Also, target TG1
By changing the power, number of shots, or irradiation time of the laser beam BM to the target TG4 for TG3, it is possible to precisely dope any desired amount of the metal element M, thereby changing the ordinary refractive index of the fundamental wave light. n0(ω) and the extraordinary refractive index ne(2ω) of the second harmonic light
It becomes possible to easily create a single-crystal thin film doped with the metal element M in an amount necessary to make the values almost the same.

Furthermore, by sequentially forming single-crystalline thin films layer by layer, precise film thickness control, which could not be achieved with conventional LPE methods, becomes possible. In other words, restrictions on the type of metal element M can be eliminated.

[0020] In the above explanation, the case of creating a single crystalline thin film with an illuminite structure was taken as an example, but when creating a single crystalline thin film with a perovskite structure,
This can be created using a similar laser ablation manufacturing process.

Furthermore, in the above explanation, it was assumed that four targets TG1, TG2, TG3, and TG4 were prepared and each layer of four types of metal oxides Li2O, Ta2O5, Nb2O5, and MOz was formed in a predetermined order. ,
Only two targets consisting of two types of metal oxides LiTayNb1-yO3 and MOz were prepared, and the metal oxide LiTa was deposited on the substrate using the same laser ablation method.
A layer of yNb1-yO3 and a layer of metal oxide MOz may be formed in a predetermined ratio, thereby creating a single crystalline thin film LiTayNb1-yO3:M doped with the metal element M.

[0022]

EXAMPLES The present invention will be explained in more detail below using examples.

Example 1 In Example 1, LiTaO3 is used for the substrate 2,
On this substrate 2 is formed a single crystal thin film LiNb doped with magnesium Mg as the metal element M with a y ratio of “0”.
O3:Mg was created. That is, first, LiTaO3
Set the board 2 in the board holder and set the board temperature to 300℃.
Keep it. Next, in this case, three types of targets T
G1, TG3, TG4 (Li2O, Nb2O5, M
gO) is controlled by a computer, a laser beam BM with a wavelength of 193 nm from an ArF excimer laser is sequentially incident on targets TG1 and TG3 at 100 pulses each, and layers of Li2O and Nb2O5 are formed by ablation of 10 Å each from targets TG1 and TG3. Formed. Thereafter, this laser beam BM was made incident on the target TG4, and a 20 Å layer of MgO was formed by ablation from the target TG4. By repeating such irradiation to targets TG1, TG3, and TG4, MgO becomes 10% in LiNbO3.
A doped single crystalline thin film with a thickness of 3 μm could be formed. In addition, each target TG1, TG3, TG
When the laser beam BM from the ArF excimer laser is incident on 4, this laser beam BM is focused to 56 μm,
The energy was 0.2 J/cm2. At this time, the ablation rate is the target TG1, TG3.
Both were 1 Å with 10 pulses.

[0024] After creating a 3 μm thick monocrystalline thin film LiNbO3:MgO doped with 10% in this manner, this was annealed at a temperature of 600°C for 1 hour in an oxygen gas O2 atmosphere to improve crystallinity. I did this.

When this single-crystalline thin film is used as a waveguide of a waveguide-type SHG element and a fundamental wave light having a wavelength of about 830 nm is incident on it from a semiconductor laser as a driving light source, the ordinary refractive index of the fundamental wave light n0 ( ω) is “2.266
”, and the extraordinary refractive index ne (2ω) of the second harmonic light is “2.
263'', n0(ω) and ne(2ω) can be made almost the same, phase matching is possible, and 41
Second harmonic light with a wavelength of 5 nm could be efficiently generated.

As can be seen from Example 1, in the present invention, when forming a single crystalline thin film, the thickness of each layer, in other words, the thickness of the thin film, can be precisely controlled on the order of Å, and the metal element M The amount of doping can be precisely controlled to any desired amount (10% in the above example), thereby making it possible to realize a high-performance SHG element. Also, when using a semiconductor laser that emits fundamental wave light of a wavelength other than 830 nm, metal elements are used to make the refractive index of the fundamental wave light and the second harmonic light similar depending on the wavelength. Since the amount and type of M doping can be freely set without any restrictions, it becomes possible to easily realize a high-performance SHG element.

In Example 1, magnesium Mg was used as the metal element M, but any other metal may be used. Furthermore, although the temperature of the substrate 2 was set at 300° C. during film formation, a single crystalline thin film with good crystallinity can be created by appropriately controlling the temperature of the substrate within the range of 0° C. to 1100° C. Furthermore, in this Example 1, after forming a single crystalline thin film by laser ablation, this was treated with oxygen gas O2.
Although annealing was performed in an atmosphere, the annealing is not limited to an oxygen gas O2 atmosphere, but any oxidizing gas atmosphere such as O3, NO, NO2, N2O, etc. may be used.

In this case, by exposing each layer to an oxidizing gas atmosphere including O2, it is possible to reduce the O (oxygen)-vacant lattice points generated during the formation of each layer, resulting in a monomer with better crystallinity. Crystalline thin film LiTayNb1-yO3
:M dope can be created.

[0029]

Effects of the Invention As explained above, the single crystal thin film of the present invention is a single crystal thin film doped with any metal element M in any desired amount.
Since y≦1), high-performance S
An HG element can be easily realized.

[0030] Furthermore, in the present invention, such a single-crystalline thin film is created by a laser ablation method, so that it is possible to add any dopant M in any amount, and furthermore, it is possible to add any dopant M in any amount. It became possible to control the film thickness and obtain a single-crystalline thin film capable of realizing a high-performance SHG element.

[0031] Furthermore, LiTaxNb1-xO3 (
0≦x≦1), and the temperature of this substrate is from 0℃ to 1100℃.
By appropriately controlling the temperature within the range of 0.degree. C., a single crystalline thin film with good crystallinity can be created.

[0032] Furthermore, four targets each having four types of metal oxides Li2O, Ta2O5, Nb2O5, and MOz as basic base materials were used, and on the substrate,
Metal oxides Li2O, Ta2O5, Nb2O5, MOz
By forming each layer by laser ablation to create a single-crystalline thin film, each layer can be formed precisely to the desired thickness, and it is also possible to precisely dope the dopant M in any desired amount. At the same time, the ratio of y, that is, the composition ratio of Ta and Nb, could be precisely set to any desired value.

[0033] Also, two targets each having two types of metal oxides LiTayNb1-yO3 and MOz as basic base materials were used, and each layer of metal oxides LiTayNb1-yO3 and MOz was formed on the substrate to form a single layer. By forming a crystalline thin film, it was possible to precisely dope any desired amount of dopant M through a simple manufacturing process.

[0034] Furthermore, by further annealing the LiTayNb1-yO3:M-doped single crystal thin film produced by the laser ablation method in an oxidizing gas atmosphere, the crystallinity of the single crystal thin film can be further improved. We were able to.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining an example of the method for manufacturing a single crystalline thin film of the present invention.

FIG. 2 is a diagram for explaining an illuminite structure or a perovskite structure.

[Explanation of symbols]

1 Excimer laser 2 Substrate 3
Single crystal thin film TG1
~TG4 target

Claims (6)

[Claims] [Claim 1] LiTayNb1-yO3 doped with a predetermined amount of an arbitrary metal element M: M doped (0≦y≦1)
When using the single crystalline thin film as an optical waveguide of a second harmonic element, the amount of doping of the metal element M is determined to A single-crystalline thin film characterized by having an amount that makes the refractive index the same. 2. A predetermined target is selectively irradiated with a laser beam from a laser, and by ablation from the target, an arbitrary metal element is deposited with M on a predetermined substrate.
iTayNb1-yO3: A method for producing a single crystalline thin film, characterized in that a M-doped (0≦y≦1) single crystalline thin film is produced. 3. The substrate includes LiTaxNb1-x
A single crystal substrate made of O3 (0≦x≦1) is used,
3. The single crystal according to claim 2, wherein the temperature of the substrate is appropriately controlled within a range of 0° C. to 1100° C. when forming the single crystalline thin film on the substrate. method for producing a synthetic thin film. 4. The targets used include four types of metal oxides Li2O, Ta2O5, Nb2O5, and MOz (M is a metal element, and the value of z is arbitrary) as basic base materials, respectively. By selectively irradiating four targets with a laser beam and causing ablation, metal oxides Li2O, Ta2O5,
Each layer of Nb2O5 and MOz is formed, and LiTayNb1
3. The method of manufacturing a single crystalline thin film according to claim 2, wherein a single crystalline thin film doped with -yO3:M (0≦y≦1) is produced. 5. The target contains two types of metal oxides LiTayNb1-yO3 (0≦y≦1), MOz(
Two targets are used, each of which has a base material of (M is a metal element and the value of z is arbitrary), and by selectively irradiating the two targets with a laser beam and causing ablation, metal oxide is formed on the substrate. ThingsLiTayNb
A layer of 1-yO3 and a layer of metal oxide MOz are formed at a predetermined ratio, and LiTayNb1-yO3:M doped (0≦y
3. The method for producing a single crystalline thin film according to claim 2, wherein a single crystalline thin film having a condition of ≦1) is produced. 6. LiTayNb1-yO3:M doped (0≦y≦
A method for producing a single crystalline thin film, characterized in that the single crystalline thin film of 1) is further annealed in an oxidizing gas atmosphere.