JP2721869B2 - Method for manufacturing diluted magnetic semiconductor thin film - Google Patents

Description

The present invention relates to a method for producing a diluted magnetic semiconductor thin film, and more particularly, to a method for producing a diluted magnetic semiconductor thin film having a large Faraday effect at room temperature. The present invention also relates to a method for producing a single crystal thin film having a uniform crystal orientation.

(Prior Art) A compound in which a part of Cd of CdTe is replaced by Mn, that is, a compound having a zinc blende type crystal structure in which _{x in the} composition formula Cd _1-x Mn _x Te is represented by 0 <x <0.77 is semiconducting. Since it has both properties and magnetic properties, it is called a diluted magnetic semiconductor.

Due to the presence of Mn ions, the Faraday effect of this compound is larger than that of conventional II-VI group compound semiconductors such as ZnSe and ZnTe at room temperature and in the visible light wavelength region, and the light absorption coefficient is small. It is attracting attention as a material for magneto-optical elements in light.

The waveguide type is effective for reducing the size and weight of the magneto-optical element, stabilizing it, and improving its performance.

When fabricating a waveguide-type magneto-optical element using Cd _1-x Mn _x Te, a thin film having excellent surface flatness and crystallinity is required.

(Problems to be solved by the invention) So far, Cd _1-x Mn _x Te thin films have been deposited on glass substrates and GaAs substrates, hot-wall methods on GaAs substrates, and Ga.
Molecular beam epitaxy (MBE) on As or CdTe substrate, atomic layer epitaxy on CdTe substrate, and cluster ion beam (ICB) on sapphire substrate
Formed by the method. Among the thin films formed by these methods, a thin film formed on a glass substrate is polycrystalline, and has a disadvantage that the surface roughness of the thin film is large. GaAs substrate and Cd
The thin film formed on the Te substrate is a single crystal thin film with good crystallinity.

But the refractive index of GaAs is 3.6, greater than 2.8 to 3.0 which is the refractive index of Cd _1-x Mn _x Te. Therefore, when light is introduced into the Cd _1-x Mn _x Te thin film, the light leaks from the thin film to the substrate and does not propagate through the thin film.

The refractive index of CdTe is 2.8~2.9, Cd _1-x Mn _x refractive index equal to or slightly larger since the light of Te is sometimes leaks into the substrate. In addition, this compound also has a disadvantage that large crystals of good crystallinity have not been obtained. It can not be used for these reasons the GaAs and CdTe on the substrate for Cd _1-x Mn _x Te waveguide type magneto-optical element. When the sapphire substrate satisfies the guided light conditions for a refractive index of 1.8 smaller than the refractive index of Cd _1-x Mn _x Te. Until now, a single crystal has been formed on the sapphire C-plane substrate by the ICB method. However, the degree of crystallinity and the surface roughness of the thin film which affect the absorption loss and the scattering loss of guided light have not been clarified.

The present invention has been made in view of the above, provides a production method for forming the surface is flat, and a Cd _1-x Mn _x Te single crystal thin film crystal orientation are aligned on a sapphire substrate Is to do.

(Means for Solving the Problems) In order to achieve this object, a first aspect of the present invention is to provide a composition formula Cd
_{In the} method for producing a single crystal thin film having a zinc blende type crystal structure in which _{x of 1-x} Mn _x Te is 0.05 ≦ x ≦ 0.77, a sapphire C-plane substrate is preliminarily formed at a temperature of 850 ° C. or more before forming the thin film. The second invention is characterized in that it is subjected to heat treatment, the second invention keeps the heat-treated substrate at 180 ° C. to 340 ° C., and Cd, Mn and Te, or a compound containing these elements on this substrate. It is characterized in that a thin film is formed by vapor deposition in a degree of vacuum higher than 1 × 10 ⁻⁵ Pa.

 The present invention will be described in more detail.

According to the _first method for producing a diluted magnetic semiconductor thin film of the present invention, the Verdet constant representing the magnitude of the Faraday effect of the Cd _1-x Mn _x Te thin film, when the amount of Mn x is less than 0.05, room temperature and
II- such as ZnSe in the visible light wavelength range of 480 nm to 780 nm
It is smaller than the value of the group VI compound semiconductor, 0.04 deg / Oe · cm. Therefore, the Cd _1-x Mn _x Te thin film does not have an advantage as a magneto-optical thin film. On the other hand, when x is larger than 0.77, MnTe is mixed in the thin film in addition to the zinc blende type crystal, and the thin film does not become a single crystal film. Therefore, the half-width (abbreviated as FWHM) of the X-ray rocking curve, which is a measure of crystal orientation and crystallinity, is 4 °, which is almost the same as the value of a thin film formed on a glass substrate, and the crystallinity is poor. From these, 0.05 ≦ x ≦ 0.77 is effective as x.

The C-plane of sapphire, that is, (0001) is used for the substrate.

The C-plane of sapphire and the atomic arrangement of (111) in Cd _1-x Mn _x Te are the same, and the lattice constant of sapphire (4.758)
Å) is relatively close to the interatomic distance of Cd _1-x Mn _x Te (4.506Å / 4.587Å). Therefore, the Cd _1-x Mn _x Te thin film formed on this substrate is a single crystal.

Also, since the refractive index of sapphire is smaller than the refractive index of the Cd _1-x Mn _x Te thin film, it satisfies the light guiding condition for the refractive index. A substrate having a sharply polished surface is used, and heat treatment is performed before forming a thin film. The surface of the thin film formed on the substrate heat-treated at a temperature lower than 850 ° C. has a large number of circular projections and large surface roughness. When the substrate is heat-treated at a temperature of 850 ° C. or more, the surface condition is improved, such as removing the distortion of the substrate and reducing the unevenness of the surface. Therefore, the surface roughness and FWHM of the thin film formed on this substrate are 850 ° C.
It is smaller than a thin film formed on a substrate heat-treated at the following temperature, and the crystallinity is improved. The effect of the heat treatment of the substrate is seen when the substrate is heated in various atmospheres such as vacuum, air, oxygen, nitrogen, hydrogen or argon. This effect appears when the heat treatment time is several minutes or more. The above effect can be maintained even after the substrate subjected to the heat treatment undergoes a cleaning process.

The effect of the heat treatment of the substrate described above is basically not limited to a specific thin film forming method, and even if various thin film forming methods such as an evaporation method, an MBE method, and a CVD method are used,
Use of a substrate that has been heat-treated at a temperature of 0 ° C. or higher has the above effects.

Next, the formation of the second Cd _1-x Mn _x Te thin film of the present invention will be described.

According to the second method for producing a diluted magnetic semiconductor thin film of the present invention, a sapphire C-plane substrate is heated at 850 ° C. or higher before vapor deposition, and then kept at 180 ° C. to 340 ° C. By depositing Cd, Mn and Te or a compound containing these elements in a vacuum higher than 1 × 10 ^-5 Pa, a Cd _1-x Mn _x Te thin film having a zinc blende type crystal structure is formed thereon. Form.

When the substrate temperature at which the thin film is formed on the substrate after the heat treatment is lower than 180 ° C., the FWHM is about 4 ° because the formed thin film is polycrystalline. Since this value is almost the same as the value of the thin film formed on the glass substrate, there is no advantage in using the sapphire substrate. On the other hand, when the substrate temperature is higher than 340 ° C., there is a disadvantage that the surface roughness of the thin film becomes coarser than that of the thin film formed on the substrate at a lower temperature. Furthermore, from thin film
There is also a disadvantage that the re-evaporation of Cd becomes intense, and the Mn amount x in the thin film deviates significantly from the charged Mn amount. From these facts, it is appropriate that the substrate temperature is in the range of 180 ° C. to 340 ° C.

The FWHM of a thin film formed at a degree of vacuum lower than 1 × 10 ⁻⁵ Pa during vapor deposition is about 4 °, and the crystal orientation is poor. The FWHM of a thin film formed at a higher vacuum degree is smaller than 4 °, and the thin film is a single crystal. From this, it is desirable that the degree of vacuum during the deposition be higher than 1 × 10 ⁻⁵ Pa and higher.

The raw materials used in the above-described vapor deposition method include elements of Cd, Mn, and Te, or three or more of them, as long as the Cd _1-x Mn _x Te thin film can be formed so as to have the composition of the Mn amount. Various combinations of elements and compounds such as CdTe, MnTe and Cd _1-x Mn _x Te can be used.

(Example) In a vacuum deposition apparatus which was evacuated to a degree of vacuum of 1 × 10 ⁻⁵ Pa in advance, a sapphire C-plane substrate whose surface roughness was mirror-polished to 20 ° or less was heated at 600 ° C. to 1000 ° C. By simultaneously depositing CdTe and MnTe on this substrate set at a temperature between room temperature and 360 ° C, a Cd _1-x Mn _x Te
A thin film was formed. The amount of Mn during the deposition was changed by adjusting the deposition rate of each raw material by feedback from a film thickness monitor installed in each of the CdTe and MnTe evaporation sources. The degree of vacuum during vapor deposition was adjusted by opening and closing a gate valve of an exhaust device. The composition of the thin film produced by this method was determined by X-ray micro analysis.

Table 1 shows the amount of Mn, the manufacturing conditions, the Verdet constant, the full width at half maximum (FWHM) of the X-ray rocking curve, and the surface roughness of the thin film obtained by the above method.

Sample Nos. 2, 3, 6, and 15 have a substrate heat treatment temperature of 1000 ° C., a substrate temperature of 280 ° C., and a degree of vacuum of 5 × 10 ⁻⁶ Pa.
Examples of the present invention of a thin film formed by changing the Mn amount x in the range of 0.05 to 0.7 under the conditions of
Are comparative examples of the thin films of zero and 0.8, respectively. Sample N
The Verdet constants of the thin films of x. 2, 3, 6 and No. 15 where x is in the range of 0.05 to 0.7 are equal to or more than 0.04 deg / Oe · cm which is the value of II-VI group compound semiconductor such as ZnSe. And FWHM are smaller than 4 ° which is the value of a thin film formed on a glass substrate, and the surface roughness is extremely small. Further, reflection electron beam diffraction confirmed that these thin films were single crystals. The Verde constant of the thin film with zero x of sample No.1 is 0.015d
eg / Oe · cm, which is smaller than the value of the II-VI group compound semiconductor. On the other hand, the thin film of Sample No. 16 having x of 0.8 has a Verdet constant of 0.6 deg / Oe · cm, which is considerably larger than the value of the II-VI compound semiconductor. However, the thin film is polycrystalline and has a large surface roughness. This is because the thin film contains a MnTe phase in addition to the zinc blende type crystal phase. The present invention in which heterophases are mixed in a thin film with x of 0.8 is consistent with the fact that the range of x, which is a bulk zinc-blende single crystal phase, is up to 0.77. From these, _{x in the} composition formula Cd _1-x Mn _x Te is 0.
It was confirmed that 05 ≦ x ≦ 0.77 was effective.

For the thin films of Sample Nos. 5 and 6, x was 0.4, the substrate temperature was 280 ° C., and the degree of vacuum was 5 × 10 ⁻⁶ Pa. And 1000
This is an example of a thin film formed at a temperature of 100 ° C., and Sample No. 4 is a comparative example of a thin film formed at a heat treatment temperature of a substrate of 600 ° C. The thin film formed on the substrate heat-treated at 600 ° C. in the comparative example is monocrystalline, but has extremely large surface roughness. sample
The surface roughness and FWHM of the thin films formed on the substrates heat-treated at 850 ° C and 1000 ° C of No. 5 and Sample No. 6 were both 85.
The value becomes smaller than the value of the thin film formed on the substrate heat-treated at a temperature lower than 0 ° C.

Thus Cd _1-x Mn _x Te surface roughness of the film becomes smaller when the heat treatment temperature of the substrate is higher than 850 ° C., the effect of crystallinity is improved.

Sample No. 6 and Sample Nos. 8 to 11 have different substrate heat treatment temperatures.
180 ° C to 3 ° C under the condition of 1000 ° C and vacuum degree of 5 × 10 ^-6 Pa
This is an example of a thin film formed on a substrate set at different temperatures in a range of 40 ° C., and Sample No. 7 and Sample No. 12 are comparative examples of a thin film formed on a substrate at room temperature and 350 ° C., respectively.

180 ° C. to 340 ° C. of Sample No. 6 and Sample Nos. 8 to 11 in Examples
The FWHM of the thin film formed on the glass substrate is smaller than the value of 4 ° which is the value of the thin film formed on the glass substrate, and the surface roughness is 60 °.
Å Very small, below. In the example of Sample No. 11, the amount of charged Mn when forming the thin film is 0.4, but x of the thin film is slightly larger than the charged amount of Mn because Cd is re-evaporated from the thin film.
In the comparative example of sample No. 12, which was formed on a substrate set at 360 ° C., which was higher than this example, x (0.55) of the thin film was the charged Mn amount because Cd was re-evaporated from the thin film. 0.
Significantly greater than 4. The surface roughness of this thin film is 360 ° C
It is much larger than the roughness of the thin film formed on the lower temperature substrate. On the other hand, in the case of the comparative example of the sample No. 7 formed on the substrate at room temperature, the FWHM is almost equal to the value of the thin film formed on the glass substrate. From these, by evaporation, to the heat-treated substrate, the substrate temperature for the surface to form a flat and Cd _1-x Mn _x Te single crystal thin film with uniform crystal orientation is 18
0 ° C to 340 ° C is suitable.

Sample No. 6 and Sample No. 13 had x of 0.4, substrate heat treatment temperature of 1000 ° C. and substrate temperature of 280 ° C., and the degree of vacuum was 5 × 10 ⁻⁶ Pa and 10 × 10 ^{−, respectively. This} is an example of a thin film formed at ⁶ Pa, and Sample No. 14 is a comparative example of a thin film formed at 20 × 10 ⁻⁶ Pa. Samples in these thin films
The FWHMs of the thin films of No. 6 and Sample No. 13 formed in a vacuum of (5 to 10) × 10 ⁻⁶ Pa are smaller than those of the thin films formed on the glass substrate. In the comparative example of sample No. 14 formed in 2 × 10 ⁻⁵ Pa having a lower degree of vacuum than this, the thin film was polycrystalline, and the FWHM was comparable to the value of the thin film formed on the glass substrate. is there. Therefore, there is no advantage of using a sapphire substrate.
For these reasons, the degree of vacuum during vapor deposition needs to be higher than 1 × 10 ⁻⁵ Pa.

From the above Examples and Comparative Examples, in forming a thin film of a zinc blende type crystal structure in which _{x of the} composition formula Cd _1-x Mn _x Te is 0.05 ≦ x ≦ 0.77, the sapphire C-plane substrate was previously heated to 850 ° C. or higher. Cd, Mn and Te, or a compound containing these elements, is deposited on this substrate kept at 180-340 ° C in a vacuum higher than 1 × 10 ^-5 Pa By doing so, it was confirmed that a single-crystal thin film having a flat surface and excellent crystal orientation was obtained.

(Effect of the Invention) As described above, according to the method of manufacturing a semimagnetic semiconductor thin film according to the present invention, Cd having a flat and uniform crystal orientation is obtained.
Because it can produce _1-x Mn _x Te single crystal thin film on a sapphire substrate, there is an advantage that can be applied as a material for a waveguide type magneto-optical device.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location H01L 21/365 H01L 21/365

Claims (2)

(57) [Claims] A composition formula Cd _1-x Mn _x on a sapphire C-plane substrate.
In the method of manufacturing a single crystal thin film having a zinc blende type crystal structure in which x of Te is 0.05 ≦ x ≦ 0.77, the substrate is formed before the thin film is formed.
A method for producing a diluted magnetic semiconductor thin film, wherein a heat treatment is performed at a temperature of 850 ° C. or higher. 2. The composition formula Cd _{1 -x} Mn _x on a sapphire C-plane substrate.
In the method of manufacturing a single crystal thin film having a zinc blende type crystal structure in which x of Te is 0.05 ≦ x ≦ 0.77, the substrate is formed before the thin film is formed.
After performing the heat treatment at a temperature of 850 ° C. or more, the heat-treated substrate is maintained at a temperature in the range of 180 ° C. to 340 ° C., and Cd, Mn, Te, or a compound containing these elements is deposited on the substrate. A method for producing a diluted magnetic semiconductor thin film, which is formed by vapor deposition in a degree of vacuum higher than × 10 ⁻⁵ Pa.