OXIDE SEMICONDUCTOR AND SEMICONDUCTOR DEVICE

Abstract

Provided are an oxide semiconductor excellent in transparency, mobility, and weatherability, etc., and a semiconductor device having the oxide semiconductor, a p-type semiconductor being realizable in the oxide semiconductor. The oxide semiconductor consists of a composite oxide, which has a crystal structure including a foordite structure and contains Nb and Sn elements, and its holes become charge carriers by the condition that Sn.sup.4+/(Sn.sup.2++Sn.sup.4+) which is a ratio of Sn.sup.4+ to a total amount of Sn in the composite oxide is 0.006Sn.sup.4+/(Sn.sup.2++Sn.sup.4+)0.013.

Claims

1. An oxide semiconductor comprising: a composite oxide having a crystal structure and containing Nb and Sn elements, the crystal structure including a foordite structure, wherein Sn.sup.4+/(Sn.sup.2++Se) that is a ratio of Sn.sup.4+ to a total amount of Sn in the composite oxide is 0.006Sn.sup.4+/(Sn.sup.2++Se)0.013, and its holes become charge carriers.

2. The oxide semiconductor according to claim 1, wherein the composite oxide is an oxide representing AB.sub.2O.sub.6 (A is Sn, and B is Nb) by a general chemical formula.

3. The oxide semiconductor according to claim 1, wherein at least one or more kinds of elements selected from a group composed of W, Zr, V, Mn, Ti, Ga, Hf, and Mo is added as additive element.

4. The oxide semiconductor according to claim 3, wherein a total amount of the additive element is 0.001 atom % or more and 10 atom % or less.

5. A semiconductor device including the oxide semiconductor according to claim 1.

6. The oxide semiconductor according to claim 2, wherein at least one or more kinds of elements selected from a group composed of W, Zr, V, Mn, Ti, Ga, Hf, and Mo is added as additive element.

7. The oxide semiconductor according to claim 6, wherein a total amount of the additive element is 0.001 atom % or more and 10 atom % or less.

8. A semiconductor device including the oxide semiconductor according to claim 2.

9. A semiconductor device including the oxide semiconductor according to claim 3.

10. A semiconductor device including the oxide semiconductor according to claim 4.

11. A semiconductor device including the oxide semiconductor according to claim 6.

12. A semiconductor device including the oxide semiconductor according to claim 7.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] FIG. 1 is a drawing showing X-ray diffraction patterns in a case of oxide composite SnNb.sub.2O.sub.6 (data of sample numbers 1-4 and ICDD) in a first embodiment;

[0030] FIG. 2 is a drawing showing, in the first embodiment, .sup.119Sn Mossbauer spectrum (solid line) measured at 300 K in the case of oxide composite SnNb.sub.2O.sub.6 (sample numbers 1-3), and .sup.119Sn Mossbauer spectrum measured at 300 K in a case of oxide composite SnNb.sub.2O.sub.6 (sample number 4) represented by a thin line indicating that Sn.sup.4+ hardly exists;

[0031] FIG. 3 is a drawing showing .sup.119Sn Mossbauer spectrum at each measurement temperature of 300 K and 78 K in the case of oxide composite SnNb.sub.2O.sub.6 (sample number 1) in the first embodiment; and

[0032] FIG. 4 is a drawing showing a crystal structure of oxide composite SnNb.sub.2O.sub.6 representing a foordite structure.

DETAILED DESCRIPTION

[0033] Embodiments of the present invention will be described below.

[0034] The inventors of the present invention have: paid attention to, in an oxide composite with a foordite structure, an influence on semiconductor characteristics exerted in accordance with a ratio [Sn.sup.4+/(Sn.sup.2++Sn.sup.4+)] of Sn.sup.4+ to the total amount of Sn in an oxide composite; researched and developed the oxide composite; and obtained an oxide semiconductor having excellent semiconductor characteristics and p-type semiconductor characteristics.

[0035] An oxide semiconductor according to an embodiment of the present invention is a semiconductor: enhancing ionicity of bonding by forming a double oxide with Nb.sub.2O.sub.5 with respect to SnO having a small band gap, a top of whose valence band is composed of a 5s orbital of Sn; mainly having a foordite structure as a crystal structure about composition formula SnNb.sub.2O.sub.6 that realizes a band gap made wide; and indicating that a ratio Sn.sup.4+/(Sn.sup.2++Sn.sup.4+) of Sn.sup.4+ to the total amount of Sn is 0.006Sn.sup.4+/(Sn.sup.2++Sn.sup.4+)0.013.

[0036] Additionally, the oxide semiconductor according to the embodiment of the present invention is found to be a semiconductor that: is described in a simplified manner by a general formula of SnNb.sub.2O.sub.6 as a stoichiometric composition; and has a structural defect in which a part of Sn.sup.2+ contained to forms holes serving as p-type charge carriers is oxidized to Sn.sup.4+ and a part of an Nb.sup.5+ site is substituted, such a structural defect being represented as Sn.sub.Nb by the Kroger-Vink notation that is a notation of a structural defect.

[0037] Sn can change its valence relatively easily, and take Sn.sup.0 and Sn.sup.4+ in addition to Sn.sup.2+. For example, Sn.sub.2Nb.sub.2O.sub.7, which is an oxide composite containing Sn.sup.2+ and Nb.sup.5+ similarly to SnNb.sub.2O.sub.6, has been reported as described in the background art. That is, known has been that Sn.sub.2Nb.sub.2O.sub.7 has a structural defect as represented by Sn.sub.2-p(B.sub.2-qSn.sub.q)O.sub.7-p-0.5q (see M. A. Subramanian, G. Aravamudan, G. V. Subba Rao, Progress in Solid State Chemistry 15, 55 (1983)). Here, the above-mentioned defect is such a structural defect that a defect Sn.sub.Nb, in which Sn.sup.4+ corresponding to q is substituted for Nb.sup.5+, exists in addition to V.sub.Sn which is a Sn deficiency corresponding to p and any of both cases brings generation of holes. Therefore, the generation of those defects to SnNb.sub.2O.sub.6 is found to become a center of the structural defect that leads to the generation of holes in any case.

[0038] Here, the ratio Sn.sup.4+/(Sn.sup.2++Sn.sup.4+) of Sn.sup.4+ to the total Sn amount of (Sn.sup.2++Sn.sup.4+) indicates that the defect Sn.sub.Nb, in which the Nb.sup.5+ site is substituted for Sn.sup.4+, is reflected as long as precipitation of SnO.sub.2 is not recognized.

[0039] Meanwhile, reported has been that a natural mineral foordite contains Sn.sup.4+ although its content is less than 3% (see P. Cerny, A-M. Fransolet, T. S. Ercit, R. Chapman, The Canadian Mineralogist 26, 889 (1988)). On the other hand, foordite synthesized from reagents does not contain Sn.sup.4+ (see L. P. Cruz, J.-M. Savariult, J. Rocha, J.-C. Jumas, J. D. Pedrosa, Journal of Solid State Chemistry 156, 349 (2001)). A difference between these is considered as follows: the natural mineral contains impurity components having valences other than valences of A.sup.2+ and B.sup.5+ in general chemical formula AB.sub.2O.sub.6, and a part of Sn easily variable in valences has indicated tetravalent in order to balance charges with these impurities. None of oxide composites of foordite structures each containing Sn have conventionally exhibited p-type semiconductor characteristics including P. Cerny, A-M. Fransolet, T. S. Ercit, R. Chapman, The Canadian Mineralogist 26, 889 (1988) and L. P. Cruz, J.-M. Savariult, J. Rocha, J.-C. Jumas, J. D. Pedrosa, Journal of Solid State Chemistry 156, 349 (2001). This is considered as follows: conditions for generating an appropriate amount of Sn.sup.4+, a defect Sn.sub.Nb substituting a B site, and a defect V.sub.Sn lacking Sn.sup.2+ have not been found and, additionally thereto, the generations of a minus monovalent defect Sn.sub.Nb and a minus divalent defect V.sub.Sn simultaneously brings the generation of plus divalent oxygen deficiency V.sub.O, so that expression of p-type conduction due to the generation of holes cannot be obtained for charge compensation. Amounts of generations of the structural defects Sn.sub.Nb, V.sub.Sn, and V.sup..sub.O considered here are considered to depend on temperature and atmosphere gas conditions at a time of producing the oxide composite. In the present invention, appropriately controlling the temperature and atmosphere gas conditions at a time of sample preparation brings a discovery of the optimum condition that Sn.sub.Nb is generated and V.sup..sub.O is hardly generated. Such a discovery is considered to lead to the expression of the p-type semiconductor characteristics. The p-type semiconductor characteristics are expressed also in the form of bulk or thin film.

[0040] An oxide of the present invention, which has the crystal structure including the foordite structure, only has to mainly include a crystal structure of a foordite structure. Incidentally, the term mainly refers to, for example, more than 50 weight % of the whole. Of course, the entire crystal structure is preferably composed of foordite structures. However, the oxide can be permitted to be composed of a crystal structure slightly having a structure other than the foordite structure, and it is preferable that the crystal structure is substantially composed of the foordite structures. The term substantially means, for example, 80 weight % or more.

[0041] Exemplified as a semiconductor device according to the present invention is a pn junction element in which a pn junction is formed by a p-type semiconductor of the present embodiment and an n-type semiconductor. Given as the n-type semiconductors suitable for the pn junction element are: In.sub.2O.sub.3, ZnO, and SnO.sub.2; Sn-added In.sub.2O.sub.3, Al-added ZnO, Ga-added ZnO, Sb-added SnO.sub.2, and F-added SnO.sub.2 in which impurities are added to those host materials; and the like. Particularly, ZnO is preferable in that it has a feature capable of production from an insulator to a semiconductor due to easiness of control of carrier concentration and, additionally thereto, is capable of easy etching in patterning and has no problem of using a rare raw material.

First Embodiment

[0042] In the present embodiment, explained will be an oxide semiconductor containing Sn and Nb and including an oxide composite that has a crystal structure including a foordite structure. Examined in an oxide composite having a foordite structure consisting of Sn, Nb and oxygen have been characteristics corresponding to a ratio Sn.sup.4+/(Sn.sup.2++Sn.sup.4+) of Sn.sup.4+ to an amount of (Sn.sup.2++Se). As described below, when Sn.sup.4+/(Sn.sup.2++Sn.sup.4+) satisfies 0.006Sn.sup.4+/(Sn.sup.2++Se)0.013, p-type semiconductor characteristics in which holes are used as charge carriers lead to expression.

[Production of Oxide Composite with Crystal Structure Containing Sn and Nb and Including Foordite Structure]

[0043] 2.030 g of SnO powder (High purity Materials KOJUNDO CHEMICAL LABORATORY CO. LTD, 99.5% purity), and 3.992 g of Nb.sub.2O.sub.5 powder (High purity Materials KOJUNDO CHEMICAL LABORATORY CO. LTD, 99.9% purity) were weighed, and the weighed powders were placed in a mortar made of agate and were wet-mixed for about 1 hour while ethanol (Wako Pure Chemical Corporation, special grade) was added thereto. At this time, SnO and Nb.sub.2O.sub.5 were mixed so that a ratio (Sn/Nb) of Sn to Nb was 0.50 in atomic ratio.

[0044] Thereafter, the mixture was left overnight at room temperature to dry the ethanol, and was divided into 6 powder groups approximately equal to one another. Each power group was uniaxially pressurized (15 mm in diameter, 170 MPa) to produce six disk-shaped green compacts. The green compacts were placed on an alumina boat, put in an electric furnace having an alumina core tube whose diameter is 50 mm and whose length is 800 mm, and were temporarily calcined at 1173 K for 4 hours while nitrogen gas was caused to flow therein at a flow rate of 150 ml/minute. The temporarily calcined green compacts were crushed in the agate mortar, were mixed with ethanol after addition of a polyvinyl alcohol aqueous solution as a binder to a sample by 2 wt. %, and were left overnight at room temperature for drying. Then, the dried samples were sifted so that each of their particle size is adjusted to 212 m or less, and were subjected to hydrostatic molding (285 MPa) after their uniaxially pressurization (15 mm in diameter, 170 MPa). Consequently, compacts each having a diameter of about 15 mm and a thickness of about 1.2 mm were produced. The obtained compacts were placed on an alumina boat, and were subjected to main calcination within a range of 1053 K to 1473 K for 4 hours while nitrogen gas is caused flow (flow rate: 50 ml/min). Main calcination temperature of each sample is shown in Table 1 described later.

[Percentage of Sn Valence and Electric Characteristics]

[0045] Identification of crystal structures of the obtained samples were performed by using an X-ray diffractometer (PANalytical, X' Pert Pro MRD). A composition ratio of (Sn/Nb) after the calcination was estimated by using a wavelength dispersion type fluorescence X-ray analyzer (Rigaku, ZSX). Electrical characteristics of the samples were evaluated by using a Hall effect measuring device (TOYO Corporation, Resitest 8310) through a Van der Pauw placement after a sample in which gold electrodes were deposited on four corners of a circular sample was prepared. Seebeck coefficients of the samples were evaluated by using a thermoelectric characteristic evaluation device (ADVANCE RICO, inc., ZEM-3). The measurements of the X-ray diffraction, fluorescence X-ray, and the Hall effect measurements were performed at 300 K, and the Seebeck measurements were performed at 323 K. The estimation of Sn contents of Sn.sup.4+ and Sn.sup.2+ in each sample was made by a Mossbauer spectroscopy through a transmission method. Measurements were made at two points of room temperature (300 K) and liquid nitrogen temperature (78 K). The obtained .sup.119Sn Mossbauer spectrum was subjected to least squares fitting using the Lorentz curve, and integrated intensity of absorption peaks, that is, integrated absorption intensity was found. Here, since a tetravalent Sn site and a bivalent Sn site are different in temperature dependence of recoil-free fraction f (Debye temperatures are different), there are tendencies to underestimate an amount of divalent Sn and to overestimate an amount of tetravalent Sn if a value of a ratio of peak integrated absorption intensity of data at relatively high temperature (room temperature) is used as it is. Therefore, f was corrected by: fitting, by high-temperature approximation of the Debye model, the temperature dependence of absolute integrated absorption intensity for each site; and finding the Debye temperature for each site. Specifically, High-temperature Approximation Equation (1) of the Debye model was applied to the temperature dependency of the normalized integrated absorption intensity, and the Debye temperature was determined (found) for each sample and each site.

In f=(6E.sub.R/k.sub.B.sub.D.sup.2)T(1)

E.sub.R=E.sub..sup.2/2Mc.sup.2(2)

A=const.f(3) [0046] f: Recoil-free fraction [0047] T: Measurement temperature [0048] .sub.D: Debye temperature [0049] k.sub.B: Boltzmann constant [0050] E.sub.R: Recoil energy [0051] E.sub.: Mossbauer gamma ray energy (23.87 keV) [0052] M: Recoil nuclear mass (118.90331 u) [0053] c: Light velocity [0054] A: Integrated absorption intensity

[0055] The obtained Debye temperatures were used to find the recoil-free fraction at each temperature by Equation (1) and correct the integrated absorption intensity and, then, an integrated absorption intensity ratio of tetravalent and divalent Sn sites was found. A value obtained from this ratio was set as a quantitative value independent of temperature.

[0056] FIG. 1 shows an X-ray-diffraction-pattern change in main calcination temperatures about each sample of SnNb.sub.2O.sub.6. A horizontal axis in FIG. 1 indicates a diffraction angle 2 to an incident angle using a CuK ray. The figure also shows X-ray diffraction patterns of SnNb.sub.2O.sub.6 foordite (98-020-2827) from ICDD (International Center for Diffraction Data) which is an X-ray database. The X-ray diffraction pattern in each case represents only a peak belonging to SnNb.sub.2O.sub.6 that has a foordite structure belonging to a monoclinic system. Understood from this can be that each of the sample numbers 1-4 in SnNb.sub.2O.sub.6 has a crystal structure having the foordite structure belonging to the monoclinic system regardless of a difference in the main calcination temperature.

[0057] FIG. 2 shows, by solid lines, a change in .sup.119Sn Mossbauer spectra at each main calcination temperature about the sample numbers 1-3 of SnNb.sub.2O.sub.6. Figure shows, by thin lines, a spectrum of SnNb.sub.2O.sub.6 (sample number 4) in which Sn.sup.4+ hardly exists. Incidentally, measurement temperature of the spectrum is 300 K. A horizontal axis in FIG. 2 is the Doppler velocity. Three absorption peaks are observed in all the spectra. One weak peak near 0 mm/s is a peak due to Sn.sup.4+, and two peaks at 2 to 6 mm/s are peaks due to Sn.sup.2+. Therefore, coexistence of Sn.sup.4+ and Sn.sup.2+ in all the sample numbers 1-3 is understood.

[0058] Here, a ratio Sn.sup.4+/(Sn.sup.2++Sn.sup.4+) of Sn.sup.4+ to the total Sn amount (Sn.sup.2++Sn.sup.4+) is found from .sup.119Sn Mossbauer spectrum. As described above, when the ratio is simply obtained from integrated absorption intensity ratios of these peaks, there are tendencies to underestimate the amount of divalent Sn and overestimate the amount of tetravalent Sn. Therefore, the integrated absorption intensity is corrected. The sample number 1 will be concretely described as an example.

[0059] FIG. 3 shows, by solid lines, .sup.119Sn Mossbauer spectra of the sample number 1 measured at 300 K and 78 K. Incidentally, for reference, the figure shows, by thin lines, spectra of SnNb.sub.2O.sub.6 (sample number 4) in which Sn.sup.4+ hardly exists. First, a peak area (corresponding to integrated absorption intensity A) at each temperature is found. Since the integral absorption intensity A and the recoil-free fraction f have a relationship of Equation (3), a parenthesis on the right side of Equation (1) corresponds to an inclination representing a relationship (InA vs. T) between natural logarithm (InA) of the integrated absorption intensity and temperature T. Debye temperature .sub.D was found from this inclination. Next, Equation (1) was used to find recoil-free fractions fat 300 K and 78 K from the found Debye temperature .sub.D. From a relationship between the obtained recoil-free fraction f at each temperature and the integrated absorption intensity A at the temperature, corrected integrated absorption intensity A.sub.corr when it is assumed that the recoil-free fraction f is equal to 1 (f=1) was calculated as a quantitative value independent of measurement temperature.

[0060] Integrated absorption intensity A at the measurement temperature of 78 K was 0.004504 from the peak due to Sn.sup.4+, and was 0.301744 from the peak due to Sn.sup.2+. Integrated absorption intensity A at the measurement temperature of 300 K was 0.003433 from the peak due to Sn.sup.4+ and was 0.148438 from the peak due to Sn.sup.2+. The inclination (lnA/T) (0.00122 at Sn.sup.4+ and 0.00320 at Sn.sup.2+) was obtained from these integrated absorption intensities, and the Debye temperature .sub.D (387 K at Sn.sup.4+, and 237 K at Sn.sup.2+) was obtained from these inclinations. From these Debye temperatures OD, Equation (1) was used to find recoil-free fraction f at 78 K (0.9092 at Sn.sup.4+ and 0.7791 at Sn.sup.2+), and recoil-free fraction f at 300 K (0.6935 at Sn.sup.4+ and 0.3829 at Sn.sup.2+) was obtained. Next, the corrected integrated absorption intensity A.sub.corr when it is assumed that the recoil-free fraction ratio f is equal to 1 (f=1) was found so that Sn.sup.4+ is 0.0050 and Sn.sup.2+ is 0.3877 at both of the measurement temperatures of 78K and 300K. Then, the corrected integrated absorption intensity A.sub.corr was calculated as a quantitative value independent of the measurement temperature. When this is expressed as an intensity ratio (sum is 1), the expression was calculated so that Sn.sup.4+ is 0.013, Sn.sup.2+ is 0.987, and Sn.sup.4+/(Sn.sup.2++Sn.sup.4+) is 0.013.

[0061] Table 1 collectively shows Sn.sup.4+/(Sn.sup.2++Sn.sup.4+) and electric measurement results (specific resistance, concentration of charge carriers, mobility, and Seebeck coefficient), which are found from .sup.119Sn Mossbauer spectra, about samples different in main calcination temperature of SnNb.sub.2O.sub.6.

TABLE-US-00001 TABLE 1 Production Conditions Measurement Results Main Calcination Specific Concentration Seebeck Sample Temperatures Sn.sup.4+/ Resistance of Charge Mobility Coefficients Nos. (K) (Sn.sup.2+ + Sn.sup.4+) ( cm) Carriers (cm.sup.3) (cm.sup.2V.sup.1s.sup.1) (VK.sup.1) 1 1053 0.013 4.5 10.sup.0 3.7 10.sup.18 3.8 10.sup.1 +5.0 10.sup.5 2 1103 0.006 3.6 10.sup.4 +3.0 10.sup.6 3 1173 0.004 4 1473 0 9.0 10.sup.1 1.3 10.sup.16 5.2 7.7 10.sup.6

[0062] In Table 1, the sample numbers 1-4 differ only in the main calcination temperature under production (preparation) conditions of SnNb.sub.2O.sub.6, so that electric characteristics like the samples (sample numbers 1-2) showing p-type conduction, the sample (sample number 3) showing insulating properties, and the sample (sample number 4) showing n-type conduction are different through the main calcination temperature are found to be different. Sn.sup.4+/(Sn.sup.2++Sn.sup.4+) in these samples is found indicating that each of the samples (sample numbers 1-2) showing the p-type conduction has a value higher than that of the sample (sample number 3) showing the insulating properties. Further, the samples (sample numbers 1-2) showing the p-type conduction are found indicating that the sample (sample number 1) with high concentration of charge carriers has a higher value of Sn.sup.4+/(Sn.sup.2++Sn.sup.4+) than that of the sample (sample number 2) with low concentration thereof. Namely, concentration of the holes which are charge carriers exhibiting p-type depends on a ratio of Sn.sup.4+, and shows high concentration of the holes when the ratio of Sn.sup.4+ is high. In other words, this means to have some relationship with the amount of structural defect SnB that produces the holes. Further, a case of at least 0.006Sn.sup.4+/(Sn.sup.2++Sn.sup.4+)0.013 is found indicating (meaning) p-type conduction from the sample numbers 1-2.

Second Embodiment

[0063] Explained in the present embodiment will be a case of the oxide composite of the first embodiment to which a trace of element other than Sn and Nb is added. Even if the trace of elements is added, the added oxide composite exhibits p-type semiconductor characteristics similarly to those of the first embodiment when its crystal structure is a foordite structure.

[Production of Oxide Composite with Crystal Structure that Includes Foordite Structure Containing Sn and Nb and Having Other Elements as Additional Elements]

[0064] Similarly to the production of the oxide composite in the first embodiment, SnO powder (High purity Materials KOJUNDO CHEMICAL LABORATORY CO. LTD, 99.5% purity) and Nb.sub.2O.sub.5 powder (High purity Materials KOJUNDO CHEMICAL LABORATORY CO. LTD, 99.9% purity) were weighed; WO2 powder (Wako Pure Chemical Corporation, special grade) of 1.5 to 5.0 atom % was added to the weighed powders; and the added powders were placed in a mortar made of agate and were wet-mixed for about 1 hour while ethanol (Wako Pure Chemical Corporation, special grade) was added thereto.

[0065] Thereafter, the mixture was left overnight at room temperature to dry the ethanol, and was divided into 6 powder groups approximately equal to one another. Each power group was uniaxially pressurized (15 mm in diameter, 170 MPa) to produce six disk-shaped green compacts. The green compacts were placed on an alumina boat, put in an electric furnace having an alumina core tube whose diameter is 50 mm and whose length is 800 mm, and were temporarily calcined at 1173 K for 4 hours while nitrogen gas was caused to flow therein at a flow rate of 150 ml/minute. The temporarily calcined green compacts were crushed in the agate mortar, were mixed with ethanol after addition of a polyvinyl alcohol aqueous solution as a binder to a sample by 2 wt. %, and were left overnight at room temperature for drying. Then, the dried samples were sifted so that each of their particle size is adjusted to 212 m or less, and were subjected to hydrostatic molding (285 MPa) after their uniaxially pressurization (15 mm in diameter, 170 MPa). Consequently, compacts each having a diameter of about 15 mm and a thickness of about 1.2 mm were produced. The obtained compacts were placed on an alumina boat, and were subjected to main calcination at 1053 K for 4 hours while nitrogen gas is caused flow (flow rate: 50 ml/min).

[Additional Elements and Electric Characteristics]

[0066] Table 2 collectively shows electric measurement results (specific resistance, concentration of charge carriers, mobility, and Seebeck coefficient) about samples in each of which 1.5 to 5.0 atom % of WO2 is added as an additive compound.

TABLE-US-00002 TABLE 2 Measurement Results Concentration Additive Specific of Charge Seebeck Sample Amount Resistance Carriers Mobility Coefficients Nos. (atm %) ( cm) (cm.sup.3) (cm.sup.2V.sup.1s.sup.1) (VK.sup.1) 5 1.5 1.7 10.sup.1 2.1 10.sup.18 1.7 10.sup.1 +5.8 10.sup.6 6 2.5 1.8 10.sup.1 2.3 10.sup.18 1.6 10.sup.1 +5.6 10.sup.6 7 3.5 2.2 10.sup.1 2.0 10.sup.18 1.4 10.sup.1 +4.8 10.sup.6 8 5.0 3.4 10.sup.1 1.7 10.sup.18 1.1 10.sup.1 +1.8 10.sup.6

[0067] In Table 2, SnNb.sub.2O.sub.6, to which 1.5 to 5.0 atom % of WO2 were added, was found to be p-type semiconductor since its Seebeck coefficient took a positive value in each sample. Further, in each sample of the sample numbers 5-8, a peak due to SnNb.sub.2O.sub.6 was observed from X-ray diffraction measurements. In the sample of the sample number 8, a different phase due to an additive compound such as WO3 was slightly observed in addition to the peak due to SnNb.sub.2O.sub.6. It is understood from this that the additive element is most preferably 3.5 atom % or less, but is also preferably 5 atom % or less since its Seebeck coefficient is found to take a positive value. If the additive element is 10 atom % or less, its impurities increase. However, since SnNb.sub.2O.sub.6 therein is a main crystal phase, a p-type semiconductor can be realized even if any different phases due to the additive element are slightly observed.

[0068] Although a concrete example of W has been shown as an additive element, an ion radius of W is 0.066 nm (W.sup.4+) and is smaller 3.1% (W.sup.4+) in difference than an ion radius (0.064 nm) of Nb.sup.5+. Generally, it is said that a difference in size between an ion to be substituted and an ion of an additive element is within 15% to form a substitution type solid solution. Therefore, ion radii of Zr, V, Mn, Ti, Ga, Hf and Mo are also 0.072 nm (12.5% in difference), 0.064 nm (0.0% in difference), 0.065 nm (1.5% in difference), 0.061 nm (4.7% in difference), 0.062 nm (3.1% in difference), 0.071 nm (10.9% in difference), and 0.065 nm (1.5% in difference), respectively. As with W, since the difference therebetween is within 15%, the substitution type solid solution can be formed to a foordite structure. Namely, in addition to the above-mentioned defect in which Sn.sup.4+ has substituted Nb.sup.5+, defects in which any of these additional elements have been substituted for Nb are also considered as defects that generate holes, so that the p-type can be realized even when an almost equal amount of additive elements is added.

[0069] As described above, from the identification of the crystal phase by the X-ray diffraction, the evaluations of the electric characteristics by the Hall effect measurement and thermoelectric characteristic measurement, and the results of Sn.sup.4+/(Sn.sup.2++Sn.sup.4+) by the Mossbauer spectrum measurement, a compound represented by SnNb.sub.2O.sub.6 in a general chemical formula demonstrably has the crystal structure including the foordite structure and expresses the p-type semiconductor characteristics using holes as charge carries when the ratio Sn.sup.4+/(Sn.sup.2++Sn.sup.4+) of Sn.sup.4+ to the total amount of Sn in a substance is 0.006Sn.sup.4+/(Sn.sup.2++Se)0.013. Further, the oxide semiconductor of the present invention can demonstrably realize the p-type oxide semiconductor even when having, as an additive element, at least one or more kinds of elements selected from a group composed of W, Zr, V, Mn, Ti, Ga, Hf, and Mo. The p-type oxide semiconductor can be realized even when the amount of the additive elements is 0.001 atom % or more and 10 atom % or less. Additionally, the total amount of the additive elements is preferably 0.001 atom % or more and 5 atom % or less, more preferably 0.001 atom % or more and 3.5 atom % or less.

[0070] Although a case of the bulk-like composite is exemplified by a producing method of the above-mentioned oxide composite, almost the same p-type characteristics are acquired also in thin film form. Thin-film oxide semiconductors can be produced by oxide thin-film producing techniques such as a spin coating method and a spray coating method that use a solution as a starting material in addition to vacuum deposition techniques such as a sputtering method, an evaporation method by heating or electron beams, and an ion plating method.

[0071] Incidentally, the examples shown in the above-described embodiments etc. are described to make the invention easily understood, and so the present invention is not limited to such embodiments.

[0072] Since the oxide semiconductor of the present invention can realize the p-type semiconductor, the pn junction can be realized by the transparent n-type and p-type semiconductors in the visible light region, is widely usable in devices such as transmissive type displays and transparent transistors, and is industrially useful.

[0073] While the present disclosure has been illustrated and described with respect to a particular embodiment thereof, it should be appreciated by those of ordinary skill in the art that various modifications to this disclosure may be made without departing from the spirit and scope of the present disclosure.