JP5310528B2 - Silicon material structure and manufacturing method thereof - Google Patents

Description

  The present invention relates to a silicon material structure and a manufacturing method thereof.

Conventionally, a silicon material structure in which Si microcrystals having a uniform crystal orientation are embedded in SiO ₂ is known.

For example, Non-Patent Document 1 describes a method of obtaining a silicon material structure by generating highly oriented Si nanoparticles in SiO ₂ using Si molecular beam epitaxy with oxygen ion implantation. Has been. The Si nanoparticles in the silicon material structure thus obtained are widely distributed in a range of 3 to 50 nm in width and height, and have a [100] axis perpendicular to the substrate surface. Non-Patent Document 2 uses a SOI (silicon-on-insulator) substrate to produce a silicon material structure in which a Si single crystal of 2 nm thickness is embedded in a 2 nm thick SiO ₂ thin film, and its structure The results of the current-voltage characteristics of the body are described. According to this, negative resistance is observed at temperatures of 15K and 100K, but no negative resistance is observed at 150K. Non-Patent Document 3 discloses a silicon single electron transistor. According to it, negative resistance is observed at room temperature.

Thin Solid Films, 294, 227-230, 1997 Electronics Letters, 37, 1200-1201, 2001 Japanese Journal of Applied Physics, 46, 24-27, 2007

  In the silicon material structure of Non-Patent Document 1, since Si nanoparticles are too large, they do not function as a resonant tunnel diode (RTD) in the first place. The silicon material structure of Non-Patent Document 2 functions as an RTD because negative resistance is observed at extremely low temperatures (15K to 100K), but no negative resistance is observed when the temperature reaches 150K. Therefore, it does not function as an RTD. In the single electron transistor of Non-Patent Document 3, negative resistance is observed at room temperature, but leakage current is large in a low bias section from zero voltage to a peak rising voltage. Furthermore, the manufacturing method of Non-Patent Document 3 is expensive and limited to a small area.

  The present invention has been made to solve such a problem, and provides a silicon material structure in which a negative resistance is observed even at room temperature, functions as an RTD, and has a small leakage current in a low bias section. Main purpose.

In order to achieve the above-described object, a first SiO ₂ layer having a thickness of 5 to 6 nm and a Si microcrystal having a crystal orientation aligned in a predetermined orientation are embedded in a SiO ₂ thin film in a dot shape with a thickness of 5 to 5. When a silicon material structure in which a 6 nm intermediate layer and a second SiO ₂ layer having a thickness of 5 to 6 nm are laminated in this order on a Si substrate was produced, it was found that negative resistance was observed even at room temperature. The present invention has been completed.

That is, the silicon material structure of the present invention is
A first SiO ₂ layer having a thickness of 2 to 6 nm;
An intermediate layer having a thickness of 1 to 10 nm formed on the first SiO ₂ layer, in which Si microcrystals with crystal orientations aligned in a predetermined orientation are embedded in a SiO ₂ thin film in a dot shape;
A second SiO ₂ layer 2-6 nm thick formed on the intermediate layer;
It is equipped with.

In addition, the manufacturing method of the silicon material structure of the present invention,
(A) On the degenerated semiconductor substrate, the first SiO ₂ layer, the Si layer, and the second SiO ₂ layer are arranged in this order, and the first and second SiO ₂ layers have a thickness of ₂ to 6 nm, and the Si layer Laminating so that the thickness becomes 1 to 10 nm;
(B) a step of heating the laminate obtained in the step (a) in a vacuum, an inert gas atmosphere or a reducing gas atmosphere so that the Si layer becomes polycrystalline;
(C) The Si microcrystals oriented in the Si layer other than the {100} plane in the Si layer of the laminate subjected to the treatment in the step (b) are oxidized to become SiO ₂ , and the Si microcrystals oriented in the {100} plane Heating in an atmosphere containing oxygen so that at least a portion of the microcrystals remains unoxidized;
Is included.

According to the silicon material structure of the present invention, a negative characteristic is observed that negative resistance is observed even at room temperature, that is, it functions as an RTD even at room temperature. Such characteristics are obtained because the silicon material structure has an intermediate layer with a thickness of 1 to 10 nm in which Si microcrystals with crystal orientations aligned in a predetermined orientation are embedded in a SiO ₂ thin film in the form of dots. It is guessed that it is because That is, when electrodes are attached to the outside of the degenerate semiconductor substrate on which this silicon material structure is formed and the outside of the second SiO ₂ layer, respectively, and a current is applied to the silicon material structure by applying a voltage between the two electrodes, Has an effective mass m * corresponding to the crystal plane. Here, as shown in FIG. 1, since the position of the quantization level E _Rn in the quantum well region is inversely proportional to the effective mass m *, if the quantum well is oriented in a random direction where the crystal orientation is not aligned, If it is formed of a crystal, various effective masses m * exist depending on the crystal plane, and the position of the quantization level E _Rn varies. That is, the position of the quantization level E _Rn is not discrete but continuous. As a result, no negative resistance is observed. On the other hand, in the silicon material structure of the present invention, since the crystal orientation of the silicon microcrystal is aligned in a predetermined direction, the effective mass m * is also substantially constant, and the ideal quantization level E _Rn is obtained. It is considered that negative resistance is observed even at room temperature. Further, in order to function as an RTD, it is necessary that the thickness of the intermediate layer is 1 to 10 nm, but the silicon material structure of the present invention also satisfies this point. Further, the silicon material structure of the present invention has a characteristic that almost no current flows in a section from a voltage of zero to a rising voltage at the peak of the RTD, that is, the leakage current is extremely small.

  Moreover, according to the manufacturing method of the silicon material structure of this invention, the silicon material structure mentioned above can be manufactured easily. For example, as in Non-Patent Document 1, it is possible to align the crystal orientation of the Si microcrystals to a predetermined orientation by the Si molecular beam epitaxy method with oxygen ion implantation, but the molecular beam epitaxy method takes a long processing time. However, it can only be made with a small area, and it is difficult to produce it with a small thickness (several nm). On the other hand, in the method for producing a silicon material structure according to the present invention, the crystal orientation of the Si microcrystal can be easily set to a predetermined orientation only by performing vacuum heat treatment (step (b)) and oxygen heat treatment (step (c)). It can also be used for a large area and can be manufactured with a small thickness (several nm). In addition, the manufacturing cost can be reduced as compared with the conventional one.

It is explanatory drawing of the quantization level of RTD. 1 is a schematic view of a silicon material structure of Example 1. FIG. 3 is a flowchart showing a procedure for manufacturing the silicon material structure according to the first embodiment. 6 is a graph showing XRD spectra of Comparative Examples 1 and 2 and Example 1. It is a photograph of the cross-sectional TEM image of the silicon material structure of the comparative example 1 and Example 1. FIG. It is a graph showing the distribution of the reciprocal lattice point presence intensity created based on the image (FFT image) which fast-transformed the lattice image of the silicon material structure of the comparative example 1, Example 1, and the reference example, and the FFT image. It is explanatory drawing which represented the cross section of the silicon material structure typically, (a) represents before oxygen heat processing, (b) represents after oxygen heat processing. It is explanatory drawing when the graph which shows the profile of Example 1 is curve-fitted. The IV characteristic of the temperature of Example 1 with the temperature of 100K-350K is shown. It is a graph showing the characteristic with respect to the temperature change of the peak-to-valley ratio (PVR) and half value width (FWHM) of Example 1 based on FIG. The raw data of IV characteristic of the temperature of 100K-350K of Example 1 are shown. It is a graph showing the characteristic with respect to the temperature change of PVR and FWHM of Example 1 based on FIG. 2 is an explanatory diagram of a microscopic current detection microscope image of Example 1. FIG.

Silicon material structure of the present invention, a first SiO ₂ layer having a thickness of 2-6 nm, is formed on the first SiO ₂ layer, the crystal orientation of Si microcrystals aligned in a predetermined orientation SiO ₂ An intermediate layer having a thickness of 1 to 10 nm embedded in the form of dots in a thin film, and a second SiO ₂ layer having a thickness of 2 to 6 nm formed on the intermediate layer.

In the silicon material structure of the present invention, the intermediate layer has a thickness of 1 to 10 nm. If the thickness is less than 1 nm, the size of the silicon microcrystals is too small, so that it is difficult to maintain the size. On the other hand, if the thickness exceeds 10 nm, the respective quantization levels E _Rn (see FIG. 1) that can be taken by electrons are not discrete but continuous, and the RTD peak is hardly observed. In the intermediate layer, Si microcrystals with crystal orientations aligned in a predetermined orientation are embedded in the SiO ₂ thin film in the form of dots. Even if Si microcrystals with random crystal orientation are embedded in dots in the SiO ₂ thin film, various effective masses m * exist depending on the crystal plane, and each quantization level E _Rn is discrete. As a result, the RTD peak is unlikely to appear. In addition, when Si microcrystals whose crystal orientation is in a predetermined orientation are embedded in a uniform manner rather than in a dot shape, RTD peaks appear only at extremely low temperatures as in Non-Patent Document 2.

In the silicon material structure of the present invention, the first and second SiO ₂ layers each have a thickness in the range of 2 to 6 nm. If this thickness is less than 2 nm, the leakage current increases, which is not preferable. On the other hand, if the thickness exceeds 6 nm, it is difficult to flow current, which is not preferable.

In the silicon material structure of the present invention, the first SiO ₂ layer is formed on a degenerate semiconductor substrate, and the Si microcrystal has a crystal orientation in a range of ± 15 ° with respect to the normal line of the degenerate semiconductor substrate. It may be tilted. A degenerate semiconductor is a semiconductor in which the number of electrons in the conduction band is comparable to that of a metal, and includes GaAs, Si, TiO ₂ , ITO, FTO, etc. Among them, GaAs that is easy to obtain a flat surface at the atomic level. And Si are preferred. For example, the first SiO ₂ layer is formed on an n-type Si (100) substrate, and the Si microcrystal has a crystal orientation of the <100> axis, which is relative to the [100] axis of the Si substrate. You may incline in the range of +/- 15 degree. This inclination angle can be obtained as follows. That is, an image (FFT image) obtained by Fourier transforming the lattice image (TEM image) of the intermediate layer represents a reciprocal lattice space of the TEM image, and the periodic structure of the TEM image appears as spots and rings in the FFT image. Here, for the intermediate layer, a graph is created with the horizontal axis representing the normal line of the degenerate semiconductor substrate, that is, the angle from the [100] axis of the Si substrate, and the vertical axis representing the reciprocal lattice point existence intensity. For comparison, a similar graph is created for the Si (100) substrate. Then, an angle (peak position) θa formed by the [111] axis with respect to the [100] axis of the Si (100) substrate is obtained from the graph of the Si (100) substrate. On the other hand, the graph of the intermediate layer of the silicon material structure of the present invention is curve-fitted with a normal distribution, and the peak position θb and the half width FWHM of the crystal orientation <100> axis of the Si microcrystal of the intermediate layer are obtained. At this time, the <100> axis of the Si microcrystal of the intermediate layer exists in the range of angles θ1 to θ2 (see the following formula). For this reason, the <100> axis of the Si microcrystal of the intermediate layer is inclined with respect to the [100] axis of the Si (100) substrate in the range of the angle (θ1-θa) to (θ2-θa). . Here, the angle (θ1−θa) is −15 °, and the angle (θ2−θa) is + 15 °.
θ1 = θb− (FWHM / 2), θ2 = θb + (FWHM / 2)

  The silicon material structure of the present invention exhibits a negative resistance at least at a temperature of 300K. That is, it exhibits RTD characteristics at room temperature or higher. In addition, there is little leakage current in a low bias section from zero voltage to the rising voltage of the RTD peak. Furthermore, the peak voltage changes depending on the temperature.

The method for producing the silicon material structure of the present invention is as follows.
(A) On the degenerated semiconductor substrate, the first SiO ₂ layer, the Si layer, and the second SiO ₂ layer are arranged in this order, and the first and second SiO ₂ layers have a thickness of ₂ to 6 nm, and the Si layer Laminating so that the thickness becomes 1 to 10 nm;
(B) a step of heating the laminate obtained in the step (a) in a vacuum, an inert gas atmosphere or a reducing gas atmosphere so that the Si layer becomes polycrystalline;
(C) The Si microcrystals oriented in the Si layer other than the {100} plane in the Si layer of the laminate subjected to the treatment in the step (b) are oxidized to become SiO ₂ , and the Si microcrystals oriented in the {100} plane Heating in an atmosphere containing oxygen so that at least a portion of the microcrystals remains unoxidized;
Is included.

In the method for producing a silicon material structure of the present invention, in step (a), a first SiO ₂ layer, a Si layer, and a second SiO ₂ layer are formed on a degenerate semiconductor substrate such as an n-type Si (100) substrate. Are stacked in this order. The first SiO ₂ layer, Si layer, and second SiO ₂ layer may be generated by sputtering, vacuum deposition, ion plating, or chemical vapor deposition. For example, the first and second SiO ₂ layers may be generated by high frequency magnetron sputtering using SiO ₂ as a target under vacuum. The Si layer may be generated by high-frequency magnetron sputtering using non-doped Si as a target under vacuum. In order to obtain RTD characteristics, it is preferable that the thickness of the Si layer be in the range of 1 to 10 nm, and the thickness of the first and second SiO ₂ layers be ₂ to 6 nm.

In the method for producing a silicon material structure of the present invention, in step (b), the laminate obtained in step (a) is vacuum, inert gas or reducing gas atmosphere so that the Si layer becomes polycrystalline. Heat with. When this step (b) is performed in a vacuum atmosphere, it is preferable to adjust the degree of vacuum so that it is in the order of 10 ⁻⁶ Torr. When performing in an inert gas atmosphere, it is preferable to employ, for example, nitrogen, argon, or helium as the inert gas. In the case of carrying out in a reducing gas atmosphere, for example, hydrogen is preferably used as the reducing gas. The processing temperature at this time is preferably 600 to 1000 ° C., and more preferably 800 to 1000 ° C. The heating rate is preferably 10 to 20 ° C./second, more preferably 13 to 17 ° C./second. Although processing time changes also with processing temperature, what is necessary is just to set suitably in the range for 5 minutes-90 minutes, for example.

In the process for producing a silicon material structure of the present invention, in step (c), the laminated body subjected to the process (b) is oxidized into SiO ₂ by oxidizing Si microcrystals other than the {100} plane in the Si layer. Thus, the Si microcrystals on the {100} plane are heated in an atmosphere containing oxygen so that at least a part of them remains unoxidized. As a result, the layer sandwiched between the two SiO ₂ layers is in a state where Si microcrystals having crystal orientations aligned in a predetermined orientation are embedded in the SiO ₂ thin film in a dot shape. Here, Journal of Applied Phys. (J. Appl. Phys.), 36, 3770, 1965 discloses an oxidation rate of Si (100) at 600 to 850 ° C. Specifically, a graph is disclosed in which the horizontal axis represents the oxidation time (minutes) and the vertical axis represents the oxide film thickness (nm) in the range of 600 to 850 ° C. in increments of 50 ° C. Also, in “Polycrystalline Silicon for integrated Circuit Applications” by Kamins, the oxidation rate of polycrystalline silicon is [100] axis (ie, Si (100 )) Is the slowest. Therefore, based on these documents, it is possible for those skilled in the art to find an oxidation temperature and an oxidation time that satisfy the condition of step (c) without repeating excessive trial and error. Specifically, an oxidation temperature at which the oxidation rate of Si {100} is relatively moderate is set, and oxidation proceeds sufficiently except for Si {100}, but at least part of Si {100} remains unoxidized. What is necessary is just to set suitably the oxidation time which satisfy | fills these conditions. The oxidation temperature at which the oxidation rate of Si {100} is relatively moderate is preferably set in the range of 650 ° C. to less than 800 ° C., preferably 650 ° C. to 750 ° C. When the oxidation temperature is set to 700 ° C., the oxidation time is set to 20 to 40 minutes. When the oxidation temperature is set to 650 ° C., the oxidation time is set to 60 to 100 minutes and the oxidation temperature is set to 750. The oxidation time may be appropriately set such that the oxidation time is set to 3 to 15 minutes when set to ° C. On the other hand, in the step (c), the pressure is preferably set in the range of 0.01 to 1 atmosphere. Specifically, when the oxidation temperature is high (for example, 750 ° C.), the pressure is set low (for example, 0.01 or 0.1 atm), and when the oxidation temperature is low (for example, 650 ° C.), the pressure is increased. It is preferable to set (for example, 1 atm).

  The silicon material structure manufactured by the method of manufacturing the silicon material structure of the present invention has a unique characteristic that negative resistance is observed even at room temperature, that is, it functions as an RTD even at room temperature. In addition, there is also a characteristic that almost no current flows in a low bias section from the voltage zero to the rising voltage of the RTD peak, that is, the leakage current is extremely small.

[Example 1]
FIG. 2 shows a schematic view of the silicon material structure of the first embodiment. This silicon material structure is formed on a Si substrate (resistivity 0.02 Ω · cm or less) having a thickness of about 6 nm on a 500 μm-thick single crystal n-type Si wafer oriented in the (100) plane. and the SiO ₂ layer, crystal orientation <100> and the intermediate layer having a thickness of about 6nm to Si microcrystals are embedded in a dot shape to the SiO ₂ thin film having a uniform axially, a second SiO ₂ layer having a thickness of about 6nm Are stacked in this order. The first SiO ₂ layer laminated on the Si substrate, the diameter of the stack of the intermediate layer and the second SiO ₂ layer was set in the range of 60～200Myuemu.

A procedure for manufacturing the silicon material structure having the SiO ₂ / Si / SiO ₂ structure will be described below. FIG. 3 is a flowchart showing the manufacturing procedure.

First, the Si substrate was cleaned with a hydrofluoric acid aqueous solution (concentration: 10 wt%) for 5 minutes. That is, since the surface of the Si substrate was covered with SiO ₂ by air oxidation, this SiO ₂ was removed by cleaning. Then, it introduce | transduced into the high frequency magnetron sputtering apparatus, and evacuated to vacuum degree 1 * 10 < ^-7 > Torr. Next, in accordance with the conditions shown in Table 1, SiO ₂ , Si, and SiO ₂ were deposited in this order at room temperature on the Si substrate (step (a)). After that, it is introduced into a rapid heating furnace (lamp heater, MILA3000 manufactured by ULVAC-RIKO Co., Ltd.), evacuated to a vacuum degree of 1 × 10 ⁻⁶ Torr, and increased to 900 ° C. at a temperature rising rate of 15 ° C./second. It heated and heat-processed for 30 minutes at the temperature (process (b), vacuum heat treatment). And after cooling to room temperature, a mixed gas in which oxygen and argon are mixed at 0.5 LPM and 2.0 LPM respectively is introduced into a rapid heating furnace and heated to 700 ° C. at a temperature rising rate of 12 ° C./second. Heat treatment was performed for 30 minutes at a temperature (step (c), oxygen heat treatment). This step (c) was carried out at 1 atm. LPM is an abbreviation for liter / minute. In this way, a silicon material structure was produced.

[Comparative Example 1]
A silicon material structure 10 was fabricated in the same manner as in Example 1 except that the step (c), that is, the oxygen heat treatment was not performed.

[Comparative Example 2]
A silicon material structure 10 was produced in the same manner as in Example 1 except that the temperature was set to 800 ° C. in the step (c).

[Comparative Example 3]
A silicon material structure 10 was produced in the same manner as in Example 1 except that the temperature was set to 600 ° C. in the step (c).

[Structural analysis]
(1) XRD spectrum The XRD spectra of the silicon material structures of Comparative Examples 1 and 2 and Example 1 are shown in FIG. As is clear from FIG. 4, in Comparative Example 1 and Example 1, peaks related to Si, that is, (111), (220), and (311) planes were observed. In Comparative Example 2, these peaks were observed. Was not observed. This means that in Comparative Example 2, most of the Si microcrystals were oxidized. The XRD spectrum of Comparative Example 3 was not shown in FIG. This means that in Comparative Example 3, the temperature of the oxygen heat treatment was too low and the oxidation of Si microcrystals hardly proceeded.

(2) Cross-sectional TEM Image FIG. 5 shows cross-sectional TEM images of the silicon material structures of Comparative Example 1 and Example 1. As is clear from FIG. 5, in both cases, a lattice image of Si is seen in the intermediate layer, and it can be seen that this intermediate layer is sandwiched between the amorphous SiO ₂ layers from above and below. The thickness of each layer is written in FIG. In addition, the intermediate layer of Example 1 was 1.1 nm thinner than the intermediate layer of Comparative Example 1 due to the oxygen heat treatment.

(3) FFT image The image (FFT image) which carried out the fast Fourier transform of the lattice image of the silicon material structure of the comparative example 1, Example 1, and a reference example is shown on the right side of FIG. The FFT image of the reference example is an FFT image when a single crystal n-type Si wafer oriented in the (100) plane is viewed from the [110] axis. Moreover, the graph showing the distribution of the reciprocal lattice point existence intensity created based on the FFT image is shown on the left side of FIG. In the graph on the left side of FIG. 6, the [100] axis is 0 ° and a profile of one round (360 °) is taken, the horizontal axis is the angle θ from the [100] axis, and the vertical axis is the reciprocal lattice point existence intensity. Is.

  Now, the FFT image represents the reciprocal space of the TEM image, and the periodic structure of the TEM image appears as spots and rings in the FFT image. A ring is seen in the FFT image of Comparative Example 1. This ring shows the {111} plane. The fact that such a ring was observed means that the intermediate layer of Comparative Example 1 contains polycrystalline silicon. On the other hand, in the FFT image of Example 1, four bright spots are seen along the ring. These four spots indicate {111} planes. Here, similar four spots are seen in the FFT image of the reference example. Moreover, four peaks are seen in the graph representing the profile of the reference example. The profile of Example 1 is similar to the profile of this reference example, and has peaks at positions that substantially coincide with the four peak positions of the reference example. Therefore, it can be said that the intermediate layer of the silicon material structure of Example 1 has a structure in which Si microcrystals oriented in the (100) plane are embedded.

The reason for this structure is presumed as follows. 7A and 7B are explanatory views schematically showing a cross section of the silicon material structure, in which FIG. 7A shows before the oxygen heat treatment, and FIG. 7B shows after the oxygen heat treatment. As shown in FIG. 7A, the Si layer has a polycrystalline structure before the oxygen heat treatment, but oxygen molecules or oxygen atoms are diffused into the Si layer from the outside by the oxygen heat treatment, or SiO ₂ / Si Oxygen diffuses into the Si layer at the interface, and Si microcrystals with a fast oxidation rate are preferentially oxidized. Here, according to the above-mentioned Kamins document, it is described that the oxidation rate of polycrystalline silicon is the slowest [100] axis. Therefore, Si microcrystals oriented other than the (100) plane have priority. As shown in FIG. 7B, the Si microcrystals oriented to Si (100) remain. That is, the Si layer is changed to an intermediate layer having a structure in which Si microcrystals oriented to Si (100) are embedded in the SiO ₂ thin film by oxygen heat treatment.

From the graph showing the profile of the reference example, it can be read that the angle (peak position) θa formed by the [111] axis with respect to the [100] axis of the Si (100) substrate is 57 °. On the other hand, when the graph showing the profile of Example 1 was curve-fitted with a normal distribution (see FIG. 8), the peak position θb of the crystal orientation [100] axis of the Si microcrystal and the half-value width FWHM were obtained. The position θb was 61 °, and the full width at half maximum FWHM was 18 °. Therefore, the [100] axis of the Si microcrystal of the intermediate layer exists in the range of θ1 to θ2, that is, 52 to 70 ° (see the following formula), and is 52 ° with respect to the [100] axis of the Si (100) substrate. It is inclined in the range of −57 ° = −5 ° to 70 ° -57 ° = 13 °.
θ1 = 61 °-(18 ° / 2) = 52 °, θ2 = 61 ° + (18 ° / 2) = 70 °

  From the above, it can be said that the oxygen heat treatment of Example 1 has the effect of homogenizing the orientation of the silicon microcrystals in the intermediate layer.

[Characteristic]
(1) Current-voltage characteristics (IV characteristics)
Next, an Al electrode having a diameter of 60 μm and a film thickness of 300 nm was formed on the second SiO ₂ layer of the silicon material structure of Example 1 by photolithography. The same Al electrode was also formed on the entire back surface of the Si substrate. Then, a voltage was applied between both Al electrodes to measure IV characteristics. FIG. 9 shows IV characteristics at measurement temperatures of 100 K to 350 K (−173 ° C. to 77 ° C.). FIG. 10 shows the characteristics of the peak-to-valley ratio (PVR) with respect to the temperature change and the half-value width (FWHM) with respect to the temperature change. As is apparent from FIG. 9, a phenomenon (negative resistance) in which the current rapidly decreases at a specific voltage was observed in all temperature regions. In particular, negative resistance is shown even at 350K above room temperature (300K), but this is the world's first. Moreover, the negative voltage peak voltage value and peak current value both tended to decrease with increasing temperature. Furthermore, there was very little leakage current in the low bias section from the voltage zero to the peak rising voltage. As is clear from FIG. 10, PVR showed a maximum value of 4.7 at a temperature of 250K, but FWHM hardly changed regardless of the temperature. In Comparative Example 1, no RTD peak was observed even at an extremely low temperature of 5K.

  By the way, the IV characteristic in FIG. 9 is plotted by subtracting the amount (4-5 pA) considered to be the background current from the current value of the raw data. However, since the origin of the background current has not been determined, FIG. 11 shows the IV characteristics plotted based on the results. FIG. 12 shows the characteristics of the PVR produced based on the IV characteristics of FIG. 11 with respect to the temperature change and the characteristics of the FWHM with respect to the temperature change. In FIG. 12, the PVR showed a maximum value of 4.2 at a temperature of 250K.

(2) Microcurrent detection microscopic image For Example 1, microcurrent detection microscopic image data was obtained. The result is shown in FIG. This data was obtained by simultaneously probing a sample topograph (uneven image) and a current image by AFM using a conductive cantilever. As is apparent from FIG. 13, the outermost surface of Example 1, that is, the shape of the second SiO ₂ layer surface is flat at the atomic level, but current was detected locally. It seems that the black spots in the current image are paths for current flow. This suggests that the Si crystallites oriented in the {100} plane behave as isolated quantum dots, and that a tunnel current flows through the quantum dots. That is, this result supports the structural model shown in FIG.

[Others]
In Example 1, when the temperature of the oxygen heat treatment was set to 650 ° C. and 750 ° C., almost the same result as in Example 1 was obtained.

Claims (8)

A first SiO ₂ layer having a thickness of 2 to 6 nm;
An intermediate layer having a thickness of 1 to 10 nm formed on the first SiO ₂ layer, in which Si microcrystals with crystal orientations aligned in a predetermined orientation are embedded in a SiO ₂ thin film in a dot shape;
A second SiO ₂ layer 2-6 nm thick formed on the intermediate layer;
Equipped with a,
The first SiO ₂ layer, the intermediate layer, and the second SiO ₂ layer are each sheet-like and form a structure in which three layers are laminated.
Silicon material structure. The first SiO ₂ layer is formed on a degenerate semiconductor substrate, and the Si microcrystal has a crystal orientation of <100> axis and the axis is ± 15 ° with respect to the normal line of the degenerate semiconductor. Tilted in range,
The silicon material structure according to claim 1. The degenerate semiconductor is a single crystal substrate,
The silicon material structure according to claim 1 or 2. Exhibit negative resistance at least at a temperature of 300K,
The silicon material structure according to claim 1. (A) On the degenerated semiconductor substrate, the first SiO ₂ layer, the Si layer, and the second SiO ₂ layer are arranged in this order, and the first and second SiO ₂ layers have a thickness of ₂ to 6 nm, and the Si layer Laminating so that the thickness becomes 1 to 10 nm;
(B) a step of heating the laminate obtained in the step (a) in a vacuum, an inert gas atmosphere or a reducing gas atmosphere so that the Si layer becomes polycrystalline;
(C) The Si microcrystals oriented in the Si layer other than the {100} plane in the Si layer of the laminate subjected to the treatment in the step (b) are oxidized to become SiO ₂ , and the Si microcrystals oriented in the {100} plane Heating in an atmosphere containing oxygen so that at least a portion of the microcrystals remains unoxidized;
Of silicon material structure including In the step (b), heating is performed at a temperature of 600 ° C. or higher and 1000 ° C. or lower,
In the step (c), heating is performed at a temperature of 650 ° C. or higher and lower than 800 ° C.,
A method for producing a silicon material structure according to claim 5. In the step (a), the first SiO ₂ layer, the Si layer, and the second SiO ₂ layer are generated by sputtering, vacuum vapor deposition, ion plating, or chemical vapor deposition.
A method for producing a silicon material structure according to claim 5 or 6. The silicon material structure manufactured by the manufacturing method of the silicon material structure of any one of Claims 5-7.