Patent Grant
6861342
1. Field of the Invention
This invention relates to a zinc blende type CrSb compound, a method for fabricating a zinc blende type CrSb compound and a multilayered structure including a zinc blends type CrSb compound as a ferromagnetic layer.
2. Related Art
With the development of crystal growth technique such as molecular beam epitaxy (MBE method), a different kind of metallic element can be doped into a semiconductor. Particularly, a magnetic semiconductor which is made by doping a magnetic element into a semiconductor has been intensely researched and developed. If a ferromagnetic film is epitaxially grown on a semiconductor, a much higher performance composite device than a conventional one can be provided because conventional semiconductor electronics technique is combined with ferromagnetic properties.
A CrSb compound has been expected as a ferromagnetic material to constitute a ferromagnetic layer of the composite device. With normal epitaxial growth technique, however, only CrSb compound of NiAs type crystal structure can be fabricated. Then, the CrSb compound exhibits anti-ferromagnetic properties at room temperature. Moreover, such an attempt is made as to fabricate a CrSb/Sb super lattice structure and thus, to create ferromagnetic properties in the structure, but, as of now, can not be realized at room temperature.
It is an object of the present invention to provide CrSb to exhibit ferromagnetic properties at room temperature and a method for fabricating the CrSb.
In order to achieve the above object, this invention relates to a zinc blende type CrSb compound.
This invention also relates to a method for fabricating a zinc blende type CrSb compound, comprising the steps of:
The inventors had been intensely studied to achieve the above object. As a result, they found out that the zinc blende type CrSb compound can be fabricated by forming an underlayer made of a III-V semiconductor compound on a given substrate and epitaxially growing a CrSb layer on the underlayer by means of a MBE method, according to the fabricating method of the present invention. In this case, the CrSb layer itself has the zinc blende type crystal structure. The zinc blende type CrSb compound has a much larger ferromagnetic transition temperature than room temperature, and then, can exhibit ferromagnetic properties at room temperature.
That is, if a given CrSb layer is formed according to the present invention, a zinc blende type CrSb compound to exhibit ferromagnetic properties at room temperature can be provided, as mentioned above. Therefore, if a ferromagnetic layer of a given composite device is made of the zinc blende type CrSb compound, the composite device can exhibit extreme device performances.
A multilayered structure according to the present invention can be obtained by performing the fabricating method of the present invention, and then, comprises a given substrate, an underlayer made of a III-V semiconductor compound and formed on the substrate, and a CrSb compound layer having a zinc blende type crystal structure and formed on the underlayer.
In the multilayered structure, the CrSb layer is formed as a ferromagnetic layer on the III-V semiconductor compound layer as an underlayer, so the multilayered structure has a stacking structure of semiconductor layer/ferromagnetic layer. Therefore, the multilayered structure may be preferably employed for the composite device.
For better understanding of the present invention, reference is made to the attached drawings, wherein
This invention will be described in detail with reference to the accompanying drawings. In the present invention, an underlayer made of a III-V semiconductor compound is formed on a given substrate, and then, a CrSb layer is epitaxially grown on the underlayer by means of a MBE method. The CrSb layer results in having zinc blende crystal structure.
The thickness of the underlayer is not restricted only if the zinc blende type CrSb compound can be fabricated by means of a MBE method. However, the thickness of the underlayer is preferably set within 2-1000 nm, particularly within 40-400 nm.
The underlayer may be made of a binary, ternary or quaternary III-V semiconductor compound. Particularly, the underlayer is preferably made of a semiconductor compound having a composition of AlXGa1−XAs (0≦X≦1) or AlXGa1−XSb (0≦X≦1). In this case, the zinc blende type CrSb compound can exhibit large magnetization at room temperature, and thus, good ferromagnetic performances at room temperature. The underlayer may be made by means of a conventional film-forming method such as a MBE method.
In forming the CrSb layer on the underlayer made of a III-V semiconductor compound, the epitaxial growth temperature is preferably set within 200-600° C., particularly within 250-450° C.
Also, the epitaxial growth rate is preferably set within 3-50 nm/minute, particularly within 8-20 nm/minute.
With the above-mentioned fabricating process, the CrSb layer can exhibit ferromagnetic properties at room temperature because the ferromagnetic transition temperature is 400K or over. The thickness of the CrSb layer is preferably set within 0.3-300 nm. The CrSb layer has zinc blende crystal structure, so the zinc blende type CrSb compound can be obtained from the CrSb layer, and thus, has a layered shape.
It is desired that a buffer layer made of a III-V semiconductor compound is formed between the substrate and the underlayer. In This case, the lattice strain caused by the difference in lattice constant between the substrate and the underlayer can be relaxed effectively. As a result, the ferromagnetic properties of the CrSb layer and thus, the zinc blende type CrSb compound can be developed.
Concretely, in the case of making the underlayer of a semiconductor compound having a composition of AlXGa1−XAs (0≦X≦1), the buffer layer is preferably made of a similar composition material of AlYGa1−YAs (0≦Y≦1). In the case of making the underlayer of AlXGa1−XSb (0≦X≦1), the buffer layer is preferably made of a similar composition material of AlYGa1-YSb (0≦Y1).
More concretely, in the case of making the underlayer of AlXGa1−XAs (0≦X≦1), the buffer layer is preferably made of GaAs. In the case of making the underlayer of AlXGa1−XSb (0≦X≦1), the buffer layer is preferably made of AlSb. The thickness of the buffer layer is appropriately set on the kind of the substrate, the material kind and the thickness of the underlayer.
The buffer layer may be constructed as a multilayered structure which is composed of two or over III-V semiconductor layers. In this case, the lattice strain caused by the difference in lattice constant between the substrate and the underlayer can be relaxed effectively, so that the crystallinity of the CrSb layer and thus, the zinc blende type CrSb can be more enhanced. As a result, the magnetic properties of the zinc blende type CrSb compound can be more enhanced.
The buffer layer may be formed by means of a conventional film-forming method such as a MBE method.
The kind of the substrate to be employed is not restricted, but in view of the epitaxial growth of the underlayer and the buffer layer which are made of III-V semiconductor compounds, the substrate is preferably made of a IIIV-semiconductor compound.
The present invention will be described concretely, with reference to Examples.
In this Example, a multilayered structure including a zinc blende type CrSb compound shown in
Then, the GaAs substrate was cooled down while the Sb beams were irradiated. The irradiation of the Sb beams was stopped when the GaAs substrate was cooled down to 400° C. Then, Cr beams and Sb beams were irradiated simultaneously onto the GaAs underlayer, to form a CrSb layer in a thickness of 0.6 nm on the GaAs underlayer while the GaAs substrate was held at 250° C.
In this case, the forming rate of the CrSb layer was set to 6 nm/sec. When the crystallinity of the CrSb layer was investigated by means of reflection high-energy electron diffraction (RHEED), it was turned out that the CrSb layer has zinc blende type RHEED pattern.
In this Example, a multilayered structure including a zinc blende type CrSb compound shown in
Then, a CrSb layer was formed in a thickness of 0.6 nm on the GaSb underlayer in the same manner as in Example 1. When the crystallinity of the CrSb layer was investigated by means of reflection high-energy electron diffraction (RHEED), it was turned out that the CrSb layer has zinc blende type RHEED pattern.
In this Example, a multilayered structure including a zinc blende type CrSb compound shown in
Then, a CrSb layer was formed in a thickness of 0.3 nm on the AlGaSb underlayer in the same manner as in Example 1. When the crystallinity of the CrSb layer was investigated by means of reflection high-energy electron diffraction (RHEED), it was turned out that the CrSb layer has zinc blende type RHEED pattern.
Also, the magnetization of the CrSb layer provided in Example 2 or 3 is larger than the one of the CrSb layer provided in Example 1 because the CrSb is formed on the GaSb underlayer or the AlGaSb underlayer, instead of the GaAs underlayer. Moreover, the magnetization of the CrSb layer formed on the AlGaSb underlayer in Example 3 is larger than the one of the CrSb layer formed on the GaSb underlayer in Example 2.
Although the present invention was described in detail with reference to the above examples, this invention is not limited to the above disclosure and every kind of variation and modification may be made without departing from the scope of the present invention. For example, in the above embodiments, only one underlayer and only one CrSb layer are prepared, but plural underlayers and plural CrSb layers may be prepared and alternately stacked on the GaAs substrate.
As mentioned above, a zinc blende type CrSb compound to exhibit ferromagnetic properties at room temperature, a method for fabricating the zinc blende type CrSb compound can be provided, according to the present invention. Also, a multilayered structure including the zinc blende type CrSb compound can be provided. Therefore, a composite device composed of semiconductor element and ferromagnetic element can be realized.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2001-189191 | Jun 2001 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5464990 | Shiratsuki et al. | Nov 1995 | A |
| 5563019 | Blanchet-Fincher | Oct 1996 | A |
| 6294308 | Caspar et al. | Sep 2001 | B1 |
| Number | Date | Country | |
|---|---|---|---|
| 20030003704 A1 | Jan 2003 | US |
