Semiconductor device and method for manufacturing the same

Abstract

A semiconductor device is obtained using a highly oriented Mg3Sb2 pn junction. [Solution] The substrate 10 is made of n-type silicon, and a p-type Mg3Sb2 thin film 2 is formed on it by epitaxial growth. The surface of the substrate 10 (substrate surface 10A) is the (001) plane. The thickness of the Mg3Sb2 thin film 2 can be, for example, 200 nm. By forming electrodes (ohmic electrodes) 3 on the substrate 10 and the Mg3Sb2 thin film 2, this semiconductor device 1 can be used as a diode. Also, in Figure 1, light incident from the upper side of the figure can be detected as a photocurrent.

Description

Technical Field

[0001] The present invention relates to a semiconductor device using an Mg3Sb2 thin film and a method for manufacturing the same.

Background Art

[0002] Mg3Sb2, which is a Zintl phase material, is known as a semiconductor and a high-performance thermoelectric conversion material, for example, as described in Patent Document 1. As a manufacturing method thereof, for example, there is a firing method as described in Patent Document 2. In the firing method, bulk Mg3Sb2 is obtained as a sintered body (polycrystalline).

[0003] Further, Non-Patent Documents 1 and 2 describe that a highly oriented Mg3Sb2 thin film can be formed on sapphire by epitaxial growth, and a high-performance thermoelectric conversion material can be obtained using this.

[0004] Since Mg3Sb2 can be obtained in n-type and p-type by doping, if a pn junction of Mg3Sb2 can be realized, it is expected that a semiconductor device such as a diode using this can be realized. Since the bandgap of Mg3Sb2 is about 0.5 eV, an infrared detector (photodetector) corresponding to this energy can also be obtained using this. This is the same even in a heteropn junction in a form combining Mg3Sb2 and other materials, rather than a pn junction of Mg3Sb2.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0006]

Non-Patent Document 1

[0007] To improve the performance of semiconductor devices and photodetectors using Mg3Sb2 as described above, it is desirable that the Mg3Sb2 used has high crystallinity; that is, that it is a single crystal or a highly oriented crystal rather than a polycrystalline one. However, semiconductor devices using pn junctions of single crystal or highly oriented crystals of Mg3Sb2 have not been realized until now.

[0008] Although highly oriented Mg3Sb2 has been obtained in the technologies described in Non-Patent Documents 1 and 2, the sapphire used as the substrate is an insulator, not a semiconductor. Therefore, while thermoelectric conversion elements can be obtained, semiconductor devices utilizing pn junctions as described above cannot.

[0009] This invention has been made in view of the above-mentioned problems, and aims to provide an invention that solves the above-mentioned problems. [Means for solving the problem]

[0010] In order to solve the above problems, the present invention has the following configuration. The semiconductor device of the present invention is characterized by comprising a substrate having a substrate surface composed of the (001) plane of silicon of a first conductivity type, and a Mg3Sb2 thin film formed on the substrate surface, which has a second conductivity type opposite to the first conductivity type and is c-axis oriented. The semiconductor device of the present invention is characterized by comprising a c-axis oriented Mg3Sb2 thin film formed on a substrate surface composed of a silicon (001) plane. In the present invention, the first conductivity type is characterized by being n-type. The present invention relates to a method for manufacturing a semiconductor device comprising a Mg3Sb2 thin film, characterized by comprising a growth step of growing a c-axis oriented Mg3Sb2 thin film on a substrate surface composed of the (001) plane of silicon by epitaxial growth. The present invention is characterized in that, in the growth process, the Mg3Sb2 thin film is grown by supplying Mg and Sb as molecular beams to the substrate surface in a vacuum while the substrate temperature is in the range of 400°C to 500°C. [Effects of the Invention]

[0011] As described above, the present invention can be configured to obtain a semiconductor device using a highly oriented Mg3Sb2 pn junction. [Brief explanation of the drawing]

[0012] [Figure 1] This is a cross-sectional view showing the structure of a semiconductor device according to an embodiment of the present invention. [Figure 2] This figure schematically shows the apparatus configuration in the growth process of the manufacturing method according to an embodiment of the present invention. [Figure 3] This is the X-ray diffraction pattern of the sample after the growth process at a substrate temperature of 500°C. [Figure 4] This figure compares the X-ray diffraction patterns of samples after the growth process when the substrate temperature was set to 400°C, 500°C, and 550°C. [Figure 5]These are the results of measuring the current-voltage characteristics of the semiconductor device serving as an example. [Figure 6] These are the results of measuring the optical response characteristics of the semiconductor device serving as an example.

Embodiments for Carrying Out the Invention

[0013] A semiconductor device and a method for manufacturing the same according to an embodiment of the present invention will be described. This semiconductor device is composed of a substrate made of single-crystalline silicon (Si), and a heterojunction of a Mg3Sb2 thin film formed thereon by epitaxial growth.

[0014] FIG. 1 is a cross-sectional view schematically showing the structure of this semiconductor device 1. Here, the substrate 10 is made of n-type (first conductivity type) silicon, and a p-type (second conductivity type) Mg3Sb2 thin film 2 is formed thereon by epitaxial growth. As will be described later, the surface (substrate surface 10A) of the substrate 10 is a (001) plane. The thickness of the Mg3Sb2 thin film 2 can be, for example, 200 nm. By forming electrodes (ohmic electrodes) 3 on the substrate 10 and the Mg3Sb2 thin film 2 sides, respectively, this semiconductor device 1 can be used as a diode. Also, in FIG. 1, light incident from the upper side in the figure can be detected as a photocurrent.

[0015] Here, when the Mg3Sb2 thin film 2 is grown as p-type, if the substrate 10 is n-type Si, a hetero pn junction of Mg3Sb2 and Si can be obtained, and as will be described later, the diode characteristics and the like are actually obtained.

[0016] By the technique described in Non-Patent Document 1, a highly oriented Mg3Sb2 thin film could be obtained on sapphire. In contrast, here, by forming a Mg3Sb2 thin film 2 having the same high orientation on an n-type Si single crystal, a semiconductor device with the above-described hetero pn junction can be obtained. That is, the Mg3Sb2 thin film 2 can be used in more modes than the technique described in Non-Patent Document 1.

[0017] Figure 2 is a schematic diagram showing the apparatus configuration in the growth process for growing a Mg3Sb2 thin film 2 on a substrate 10 in this manufacturing method. The configuration is the same as that described in Non-Patent Document 1, except for the substrate 10. In this manufacturing method, the well-known molecular beam epitaxy (MBE) method is used. The substrate surface of the substrate 10 used here is the (001) plane of Si.

[0018] Furthermore, the substrate 10 was treated with organic cleaning, piranha solution cleaning, and hydrofluoric acid treatment to remove the oxide layer before growth. Subsequently, a Si buffer layer was formed, and a 2×1 surface reconstruction structure was confirmed by RHEED (reflection high-energy electron diffraction). This confirmed that a clean Si surface was obtained on the substrate 10 before the growth of Mg3Sb2.

[0019] The substrate 10 is fixed to the substrate holder 20 in the vacuum chamber 100, and an Mg source 21, which is a source of Mg (magnesium), and an Sb source 22, which is a source of Sb (antimony), are installed facing the substrate surface. Although not shown in the figure, the vacuum chamber 100 is evacuated by a vacuum pump, and the vacuum level is, for example, 10 -7 Pa~10 -8 The temperature range is Pa. In addition, a heater and a temperature sensor (not shown) for resistance heating are installed in the substrate holder 20, so that the temperature of the substrate 10 can be controlled during or before growth. When growing Mg3Sb2, a temperature of 400°C to 500°C is particularly preferred, and a particularly crystallinity Mg3Sb2 thin film can be obtained within this range.

[0020] High-purity Mg and Sb are packed inside the Mg source 21 and Sb source 22, respectively, and their temperatures are controlled by resistance heating. The temperature of the Mg source 21 is set to, for example, 250°C to 350°C, and the temperature of the Sb source 22 is set to, for example, 400°C to 500°C. By irradiating the substrate surface with molecular beams of these materials, a thin film of Mg3Sb2 is grown on the substrate 10. Here, since the vapor pressure of Mg is higher than the vapor pressure of Sb, a thin film of Mg3Sb2 is obtained by making the Mg content an excess (for example, Mg:Sb=4:1) compared to the stoichiometric composition of Mg3Sb2 (Mg:Sb=3:2). The above configuration is similar to that of a well-known molecular beam epitaxy apparatus.

[0021] In Mg3Sb2, the high vapor pressure of Mg makes it easy for Mg vacancies to form, and these Mg vacancies are known to function as acceptors. For this reason, in the above manufacturing method, if no intentional doping is performed, p-type Mg3Sb2 is generally easily obtained.

[0022] Figure 3 shows the X-ray diffraction (XRD) results of a sample in which a Mg3Sb2 thin film 2 was grown at a substrate temperature of 500°C. Here, peaks originating from the (004) plane of Si on the substrate 10 (corresponding to the substrate surface, which is the (001) plane of Si) and peaks originating from the grown Mg3Sb2 thin film 2 are visible. In particular, peaks on the (0002), (0004), and (0005) planes of Mg3Sb2 are visible, with the peak on the (0002) plane being especially prominent. This indicates that the Mg3Sb2 thin film 2 is strongly c-axis oriented. In other words, under the above conditions, strongly c-axis oriented Mg3Sb2 can be obtained on the (001) plane of Si.

[0023] On the other hand, when the substrate temperature was room temperature, a Debye ring-like diffraction pattern was obtained in the RHEED pattern of the sample. This indicates that in this case, polycrystalline Mg3Sb2 without orientation in a specific direction was obtained. Figure 4 also simultaneously shows the X-ray diffraction results when the substrate temperature was 400°C, 500°C, and 550°C. From these results, c-axis oriented Mg3Sb2 was obtained at a substrate temperature of 400°C, similar to the case at 500°C. However, when the substrate temperature was 550°C, only the Si peak shown in Figure 3 was obtained in the X-ray diffraction result, and the Mg3Sb2 peak could not be recognized. This indicates that Mg3Sb2 did not grow at this substrate temperature. Therefore, c-axis oriented Mg3Sb2 can be obtained at least between substrate temperatures of 400°C and 500°C, and not at a substrate temperature of 550°C.

[0024] Unlike the case where sapphire is used as the substrate as described in Non-Patent Literature 1, in this case, as shown in Figure 1, electrodes 3 can be formed on both the substrate 10 side and the Mg3Sb2 thin film 2 side to measure the current-voltage characteristics. Figure 5 shows an example of the current-voltage characteristics of this structure obtained in this way. In this case, the voltage V is the voltage on the Mg3Sb2 thin film 2 side relative to the substrate 10 (n-type Si) side. From these characteristics, the rectification characteristics of a pn junction with the Mg3Sb2 thin film 2 as the p side and the substrate 10 as the n side are obtained. That is, it can be confirmed that this structure functions as a diode.

[0025] Next, we applied a reverse bias (with V as the negative side) as shown in Figure 5 and measured the change in current (photoresponse characteristics) when pulsed light was irradiated onto a Mg3Sb2 thin film. Here, the wavelength of the light was set to 1450 nm (energy 0.85 eV). The measurement results are shown in Figure 6. A reverse current (photocurrent) that increases with the activation of the light can be observed. Therefore, it was confirmed that the structure in Figure 1 operates as a photodetector for light of this wavelength (energy).

[0026] In the above example, the substrate 10 side was made n-type and the Mg3Sb2 thin film 2 side was made p-type. However, the Mg3Sb2 thin film 2 side may also be made n-type by doping it with a donor during its growth. In this case, the substrate 10 side can be made p-type to form a pn diode.

[0027] Alternatively, in the semiconductor device 1 shown in Figure 1, both the substrate 10 and the Mg3Sb2 thin film 2 were used as semiconductor layers (n-type layer, p-type layer) constituting the semiconductor device. However, the substrate 10 may be used only as a substrate for epitaxial growth and not as a semiconductor layer constituting the semiconductor device. In this case as well, it can be used, for example, as a thermoelectric conversion element, similar to the Mg3Sb2 thin film described in Non-Patent Literature 1. In this case, a semi-insulating material can be used as the substrate 10 (Si).

[0028] Furthermore, in the above example, MBE was used in the growth process. However, it is clear that the above substrate surface configuration is valid even when other growth methods are used, as long as Mg3Sb2 can be similarly epitaxially grown on the (001) plane of Si.

[0029] Furthermore, although the above example assumes that the substrate 10 is made of n-type single-crystal silicon, the internal structure of the substrate is arbitrary as long as it has a similar (001) surface. For example, various structures may be formed within the substrate depending on the structure of the semiconductor device being manufactured.

[0030] The present invention has been described above based on embodiments. These embodiments are illustrative, and it will be understood by those skilled in the art that various modifications are possible in the combination of these components, and that such modifications also fall within the scope of the present invention. [Explanation of symbols]

[0031] 1 Semiconductor device 2 Mg3Sb2 thin film 3 electrodes (ohmic electrodes) 10 circuit boards 20 PCB holders 21 mg source 22 Sb source 100 Vacuum Chamber

Claims

1. A substrate having a substrate surface composed of the (001) surface of a first-conductivity type silicon, A second conductivity type, which is the opposite of the first conductivity type, and is c-axis oriented, is formed on the substrate surface. ３ Sb ２ Thin film and A semiconductor device characterized by comprising the following:

2. c-axis oriented Mg formed on a substrate surface composed of a silicon (001) plane. ３ Sb ２ A semiconductor device characterized by comprising a thin film.

3. The semiconductor device according to claim 1, characterized in that the first conductivity type is n-type.

4. Mg ３ Sb ２ A method for manufacturing a semiconductor device comprising a thin film, Mg c-axis oriented by epitaxial growth on a substrate surface composed of the (001) plane of silicon ３ Sb ２ A method for manufacturing a semiconductor device, characterized by comprising a growth process for growing a thin film.

5. In the aforementioned growth process, In a vacuum, by supplying Mg and Sb as molecular beams to the substrate surface while setting the temperature of the substrate within the range of 400°C to 500°C, the Mg ３ Sb ２ A method for manufacturing a semiconductor device according to claim 4, characterized by growing a thin film.

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