WO2003034510A1

WO2003034510A1 - P-type zinc oxide thin film, compound semiconductor using the same and method for producing the same

Info

Publication number: WO2003034510A1
Application number: PCT/KR2002/001952
Authority: WO
Inventors: Jae-Min Myoung
Original assignee: BLUETRON Inc
Current assignee: BLUETRON Inc
Priority date: 2001-10-19
Filing date: 2002-10-18
Publication date: 2003-04-24
Anticipated expiration: 2004-04-19
Also published as: KR20030033228A

Abstract

There is provided a zinc oxide semiconductor device having a hole concentration higher than 1019/cm3 produced by dual-doping a group III element and a group V element, Ga and As, into a zinc oxide thin film so that Madelung energy is reduced by the introduction of an n-type dopant, a group III element, and the incorporation with a p-type dopant, a group V element is made easy to enhance the local energy level of As inside a band gap.

Description

P-TYPE ZINC OXIDE THIN FILM, COMPOUND SEMICONDUCTOR USING THE SAME AND METHOD FOR PRODUCING

Technical Field

The present invention relates to a p-type zinc oxide thin film, an optoelectronic power compound semiconductor using the same, and a manufacturing method thereof, and more particularly, to a p-type zinc oxide thin film having a hole concentration higher than 10¹⁹/cm³ produced, in which a p-type dopant, Group N element of As and an n-type dopant, Group III element of Ga are dual-doped to control the concentration of the two elements appropriately. Further, the present invention is directed to a- manufacturing method of a zinc oxide thin film having a hole concentration higher than 10¹⁹/cm³ produced by depositing a zinc oxide thin film to a predetermined thickness on a substrate made of the elements to be doped and thermally annealing the resulting substrate so that a doping material is dual-doped into the zinc oxide thin film to a predetermined concentration. Background Art

Generally, zinc oxide is a material that many studies are being made for the past several decades because of its good electrical, optical and piezoelectric characteristics, and has a high possibility to be useful in a surface acoustic device, a transparent electrode, and an optical device, etc.

In particular, the zinc oxide has a characteristic of a wide band gap of 3.37 eV, and may change the band gap as high as 4 eV by addition of Mg or the like. Accordingly, the zinc oxide is regarded as a material of an optical device for next generation, being capable of oscillating a laser corresponding to the frequency range of ultraviolet rays . In addition, the development of a quantum well structure by minimization of nanometer unit is known to greatly improve the optical characteristics.

In the meantime, the optical device for a Group D nitride compound such as GaN is now in a step of practical uses. However, most of the nitride compounds, which GaN is representative of, require a high temperature higher than 1000 °C during a growing step of a thin film, so that limitation still remains in selecting an appropriate substrate, and therefore, it is found that the growth of a high quality of an epitaxial thin film in the Si-substrate which is used most availably in manufacturing processes is difficult.

In the meantime, a zinc oxide semiconductor has a 60 meV of exciton binding energy at a room temperature which is much greater compared with the case of 28 meV of GaN to maximize the efficiency of an optical device operatable at a room temperature and a high temperature. In addition, since the zinc oxide can be used to grow a high quality of an epitaxial thin film even at a comparably low temperature of about 500 °C, it is found to be possible and easy to grow an epitaxial film on a Si-substrate compared with the case of GaN, and therefore, the zinc oxide is much more advantageous for practical uses. Owing to advantages of the material characteristic, many experiments have been made to produce a high quality of a zinc oxide epitaxial thin film since 1990s. Early experiments for a zinc oxide thin film have been mostly focused on the experiments for applications of a transparent electrode to replace ITO (Indium Tin Oxide) , and a sputtering method was used in a deposition process and the quality of a produced product was considerably bad. Since then, by activation of the optical device development based on GaN, experiments for a high quality of an epitaxial thin film have been begun since the later part of the 1990s.

The research group in Tokyo university of technology succeeded in ultraviolet stimulated emission at a room temperature by using a LMBE (laser molecular beam epitaxy) in 1998. Further, Ohotomo et al . of the group observed the blue shift by the quantum effect in PL (photo luminescence) analysis from the manufacturing of superlattice structure of ZnO/Zn₁__xMg_xO. Also, they reported that a high quality of an epitaxial thin film was made with 100 cm²/V of a high electron mobility and 10¹⁵/cm³ of a low remaining electron concentration by using a ScAlMg0₄ substrate of about 0.09% of a lattice constant difference. Recently, they announced the controlling possibility of a band gap in a manufacturing method of a Zn₁__xMn_xO epitaxial thin film by addition of Mn.

Ko et al. in the Japanese Dongbuk university reported the manufacturing of a high quality of ZnO epitaxial thin film having a good optical characteristics by using a CaF₂ substrate which has a small lattice mismatch compared with a conventional sapphire substrate, and effectively compensates the co pressive stress caused by thermal expansive coefficient difference with tensile stress achieved by the lattice mismatch. In addition, they made a flat thin film in its surface shape far into atomic level in an initial growing step by introducing an MgO buffer layer.

In the meantime, Vispute et al. in US introduced GaN as a buffer layer in manufacturing a ZnO optical device by using the property that ZnO and GaN have a similar lattice constant. Iwata et al. tried to manufacture a p-type thin film by adding N during the growth of a zinc oxide thin film, but in its result, they reported that the conversion to the p-type was not observed. Up to now, it is known that p-type doping of zinc oxide is difficult.

In the meantime, domestic experiment reports on the above studies are hardly found except just several research groups compared with the study reports in the above countries. Recently, it was reported that a thin film was grown at 0.13° of full width at half maximum of x-ray locking curve by using a magnetron sputtering method, but other experimental reports are not successful in the quality of crystal. Therefore, many experimental developments are required for a zinc oxide epitaxial thin film for optical devices.

Generally, the applications in optical devices such as laser, etc. require a high quality material of single crystal, but zinc oxide has characteristics of difficulty in being manufactured as single crystal in bulk type up to now, and so, it should be necessarily subject to a hetero epitaxial growth process. However, since lattice constant difference between most of substrate materials (sapphire (A1₂0₃) , Si) and a grown film is great, the grown thin film has many defects, which seriously affect optical property, etc. Accordingly, it is required that the lattice constant difference should be minimized.

In addition, the zinc oxide thin film generally shows an n-type electric conductivity by Zn interstitial atoms or 0₂ vacancies, which causes a serious problem in a p-type doping. The studies for point defect of material itself greatly affecting the characteristics of optical device, interfacial defect caused by lattice mismatch, and oxygen ion effect in plasma, etc. are still far away.

An ultraviolet rays detecting device is used for military usages like guidance systems of missile and rocket, etc., industrial usages like ultraviolet rays detecting in frame, air environment research, and engine monitoring, etc., research usages of plasma examination, etc., and academic usages of astronomy, etc. In addition, the ultraviolet rays detecting device is expected to be greatly increased in its demands as an optical detecting device of high speed communication network because it is used for signal detecting of optical communication, and signal detecting for communication between the Earth and satellite, and between satellites, and also, as communication detecting device in the atmosphere of the Earth and cosmic space with the advent of the aerospace time. At the present, an optical amplifier or a silicon optical diode is being used for an ultraviolet rays detecting device. However, the optical amplifier has disadvantages in that it requires a high voltage and its efficiency is low. The silicon optical diode also has disadvantages in that it is sensitive to visible rays and infrared rays and a band control filtering device should be added, so that the bulk of the detecting device becomes big, and its structure is very complex. In addition, since silicon has a narrow band gap, it has a problem of thermal stability, and further in a bad environmental condition, it shows a disadvantage of chemical unstableness . To solve the above disadvantages, it should be necessary to use a semiconductor which is stable thermally and chemically, and has low sensitivity to the ranges of visible rays and infrared rays. A zinc oxide compound becomes an object for many experimental researches as a material effectively to replace the material of a conventional ultraviolet detecting device since it has many advantages of chemical and thermal stability, high mobility, high quantum effect, and selectivity of specific wave length according to the molar fraction control of added Mg, etc. as a maximum band gap semiconductor of direct transition type. However, even though the zinc oxide has many advantages as above, it is difficult to form a zinc oxide thin film having a hole concentration higher than 10¹⁹/cm³ effectively by the conventional technology.

In addition, a zinc oxide thin film used as an optical material is required to have a high quality of crystallinity and uniformity. As efforts to comply with the requirement, MOCVD (metal organic CVD) , molecular beam epitaxy and pulse laser deposition method, etc. have been used, but all of them have a disadvantage of being very costly.

Disclosure of the Invention

Accordingly, the present invention is directed to a p-type zinc oxide thin film having a hole concentration higher than 10^x/cm³ that substantially obviates one or more problems due to limitations and disadvantages of the related art.

An object of the present invention is to provide a method of manufacturing an optical power compound semiconductor device formed by dual-doping a material of a substrate into a zinc oxide thin film which is deposited on the substrate, and is made of different dopant materials from the material of the substrate. Another object of the present invention is to provide a p-type zinc oxide thin film manufactured by using a sputtering method to decrease production cost, and a manufacturing method thereof.

Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims thereof as well as the appended drawings .

To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, an optoelectronic oxide semiconductor device includes a substrate, and a film of

^Zn0ι-χ (0 — X — 1) formed on the substrate, and a p-type dopant level obtained inside the zinc oxide thin film is enough to form a p-n junction which is useful in an electric device or an electric field light-emitting device. The film of ZnO^.. (O≤X≤l) of the present invention contains a p-type dopant and an n-type dopant, and has a hole concentration higher than at least 10¹⁹/cm³. In addition, preferably, the film has a mobility higher than 12 cm²/V-sec, and a resistivity lower than 0.012 Ω-cm.

The p-type dopant is selected from the group N elements, and preferably contains As. In addition, the n- type dopant is selected from the group IE elements, and preferably includes Ga . The substrate may be made of GaAs. The thickness of the film of ZnO^ (0<X<1) is greater than 0.3 β , and the molar ratio of the Ga and the As contained in the film is controlled to be in a range of 0.0001 - 0.1.

The p-type zinc oxide thin film of the present invention may be used in a p-n junction, an electric field transistor, a light-emitting diode, a laser diode or a light-detecting diode.

In another aspect of the present invention, a manufacturing method of a p-type zinc oxide thin film may be performed by loading a GaAs substrate into a reaction chamber under a vacuum condition, depositing a zinc oxide thin film on the GaAs substrate to a predetermined thickness, thermally annealing the substrate on which the zinc oxide thin film is deposited so that the Ga atom and the As atom of the GaAs substrate are dual-doped into the zinc oxide thin film to control a concentration of the thin film.

The deposition and the thermal-annealing of the zinc oxide thin film can be performed by one selected from the group consisting of MBE, MOCVD, PLD and a sputtering apparatus.

The deposition of the zinc oxide thin film can be performed by a magnetron sputtering by using a ZnO target, or by a reactive ion sputtering using a Zn target, and Ar gas and 0₂ gas are fed into the reaction chamber for a sputtering in each case.

The deposition and the thermal-annealing of the zinc oxide thin film can be performed at a room temperature or higher than that, and the thermal annealing of the zinc oxide thin film can be performed by sealing the reaction chamber at a high vacuum pressure higher than about 10^~3 Torr and thermally annealing the zinc oxide thin film in the atmospheric condition, or can be performed under an environment of a high vacuum pressure higher than about 10^" ² Torr without sealing or under an environment in which an atmosphere can be controllable.

By the thermal-annealing, the zinc oxide thin film may have a hole concentration higher than at least 10¹⁹/cm³, a mobility higher than 12 cnr/V-sec, and a resistivity not greater than 0.012 Ω-cm.

Preferably, the thermal-annealing is performed at a temperature of about 300 - 750 °C for several minutes to several hours.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.

Brief Description of the Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.

In the drawings :

FIG. 1 is a schematic diagram of a magnetron sputtering apparatus which is applied on a manufacturing method of a zinc oxide thin film in accordance with the present invention; FIG. 2 is a schematic diagram of a quartz furnace for annealing a zinc oxide thin film formed by using the apparatus of FIG. 1;

FIGs. 3a and 3b are SEM photographs of zinc oxide thin films manufactured by the method of the present invention;

FIG. 4 is a graphical representation of the analysis results by an X-ray diffraction in cases of depositing a zinc oxide thin film, and annealing after the deposition of the zinc oxide thin film formed by the manufacturing method of the present invention;

FIG. 5 is a view of the photoluminescence characteristic spectrums of zinc oxide thin films in cases of depositing a zinc oxide thin film, and annealing after the deposition of the zinc oxide thin film respectively formed by the manufacturing method of the present invention;

FIG. 6 is a view of a secondary ion mass spectrometry (SIMS) characteristic spectrum of a zinc oxide thin film formed by the manufacturing method of the present invention; and

FIG. 7 is a table showing hole concentration, mobility, and resistivity measured after forming a zinc oxide semiconductor device formed by the manufacturing method of the present invention.

Best Mode for Carrying out the Invention Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings .

FIG. 1 is a schematic diagram of a magnetron sputtering apparatus which is applied on a manufacturing method of a zinc oxide thin film in accordance with the present invention.

Referring to FIG. 1, a magnetron sputtering apparatus 100 includes a reaction chamber 110. Inside the reaction chamber 110, a substrate holder 120, on which a substrate 200 is placed, is located inside the reaction chamber 110 with adjacent to the upper surface of the reaction chamber 110, and a zinc oxide thin film is deposited on the substrate 200. A sputter gun 130 is placed on the lower side of the reaction chamber 110, and a ZnO target 210 of a high degree of purity is placed on the sputter gun 130. A pumping part 140 is connected on a predetermined portion of the reaction chamber 110 (the right side in FIG. 1) for purging the reaction chamber 110 and controlling the pressure inside the reaction chamber 110. The pumping part 140 includes a rotary pump and a diffusion pump.

A gas supplying part 150 is placed on a predetermined portion of the reaction chamber 110 (the left side in FIG. 1) for supplying reaction gases to generate plasma, and a MFC (mass flow controller) 152 is placed on a gas supplying pipe of the gas supplying part 150, for controlling the flow of supplied gas. The sputter gun 130 is connected to an RF (radio frequency) matching box 160, and the RF matching box 160 is connected to a RF power source 170. A plasma shield 180 is placed on the edge portion of the sputter gun 130, for preventing the plasma generated from the sputter gun 130 from proceeding toward the edge portion of the reaction chamber 110. First, the GaAs substrate 200 is placed on the substrate holder 120 inside the reaction chamber 110 to form a zinc oxide thin film, and the ZnO target 210 is placed on the sputter gun 130. That is, the target 210 and the substrate 200 are placed to face each other. The pumping part 140 extracts the air inside the reaction chamber 110 to maintain the pressure inside the reaction chamber 110 at 10^"3 Torr and over that.

In this embodiment, Ga and As are used as a dual- doped material into the zinc oxide thin film and thus, the GaAs substrate is used, but to dope other kinds of materials, a substrate of InP, GaN, or A1N, etc. can be used.

Then, Ar gas and 0₂ gas are fed into the reaction chamber 110 by the gas supplying part 150 through separate supplying pipes. The MFC 152 functions to control the amount of the supplied Ar gas and 0₂ gas.

If the gas supplying is completed, RF energy is supplied to the sputter gun 130 to ionize the mixture of the Ar gas and 0₂ gas to generate plasma.

Ionized Ar and 0₂ ions inside the generated plasma strike the target and sputter the target material so that a zinc oxide thin film is deposited on the substrate 200.

Then, as shown in FIG. 2, a substrate 202, which is produced with the zinc oxide thin film formed thereon as a result of the sputtering, is introduced into a quartz tube or a container which is separated from the outer atmosphere, or possibly controls its inner atmosphere for thermal- annealing. The substrate 202 is annealed at a temperature of, for example, about 300 °C or higher than that, preferably a temperature range of 300 - 750 °C with varying time intervals in accordance with an appropriate doping concentration . Even though the ZnO target is used in the above embodiment, the reason that 0₂ gas and Ar gas are supplied together is to control a stoichiometric ratio of the zinc oxide thin film which is formed on the substrate by the sputtering method from the ZnO target .

In the meantime, unlike the magnetron sputtering apparatus described in the above embodiment, in a reactive sputtering method, a Zn target is used instead of the ZnO target to separate Zn ions from the Zn target, to react the separated Zn ions with supplied 0₂ ions, and to form a zinc oxide thin film on a substrate.

In addition, the above embodiment introduces about the sputtering of the zinc oxide thin film which is performed at a room temperature as an example, but a preheating of the substrate up to a predetermined temperature can be additionally performed before the deposition of the thin film to increase the dual doping effect of Ga and As.

FIGs . 3a and 3b are SEM photographs of the zinc oxide thin films formed by the manufacturing method of the present invention wherein the photographs show the cases of supplying Ar gas only, and supplying Ar gas and 0₂ gas together respectively when using the ZnO target. With comparison of FIGs. 3a and 3b, grain size is much more precisely shown in FIG. 3b where 0₂ gas is supplied with Ar gas, than the case in FIG. 3a where Ar gas only is supplied. FIG. 4 is a graphical representation of the analysis results by an X-ray diffraction in cases of depositing a zinc oxide thin film, and annealing after the deposition of the zinc oxide thin film respectively formed by the manufacturing method of the present invention. In two cases, a peak is shown when 2 Θ is about 35°by which it is confirmed that a formed film is a zinc oxide thin film preferentially grown in the direction of c axis.

FIG. 5 is a view of the photoluminescence characteristic spectrums of zinc oxide thin films in cases of depositing a zinc oxide thin film, and annealing after the deposition of the zinc oxide thin film respectively formed by the manufacturing method of the present invention.

As shown in FIG. 5, a peak is generated at about 430 nm of wavelength in both cases by which it is confirmed that a formed film is a zinc oxide thin film.

FIG. 6 is a view of a characteristic spectrum by secondary ion mass spectrometry (SIMS) using Cs⁺ as primary ion for a zinc oxide thin film deposited by the above manufacturing method and annealed. Referring to FIG. 6, with the increase of thickness in a horizontal axis, the amount of secondary ions, Ga and As, is constant up to about 0.8 μm in thickness, but is rapidly increased at the thickness higher than 0.8 β . From the fact that the amount of Ga and As ions is rapidly increased at a thickness higher than 0.8 βm, the portion above 0.8 βm is found to be a GaAs substrate, and therefore, it is presumed that the thickness of the zinc oxide thin film formed on the GaAs substrate is about 0.8 βm. The above result apparently shows that Ga atom and As atom are diffused into the zinc oxide thin film and dual- doped during a thermal-annealing.

FIG. 7 is a table showing hole concentration, mobility, and resistivity measured on the zinc oxide thin film deposited and then, annealed by the manufacturing method of the present invention.

Referring to FIG. 7, the zinc oxide thin film (sample A~D) manufactured by the dual-doping of As and Ga ions during a thermal-annealing has a hole concentration of 1.2

x 10¹⁹/cm³ - 2 x 10²⁰/cm³, a mobility of 12 cm²/V-sec - 33 cmVV'sec, and a resistivity of 0.0018 - 0.012 Ω-cm, which is found to be a p-type zinc oxide thin film.

The above result says that a p-type zinc oxide thin film having a hole concentration above 10¹⁹/cm³ can be achieved by dual-doping a group IE element and a group N element, Ga and As, into a zinc oxide thin film because the introduction of an n-type dopant, a group III element reduces Madelung energy, and the incorporation with a p- type dopant, a group N element is made easy to enhance the local energy level of As inside a band gap.

Described as above, the p-type zinc oxide manufactured by the embodiment of the present invention is different from a p-type zinc oxide which is conventionally produced by doping As only, wherein an As doping concentration does not explain a hole concentration higher than 10¹⁸/cm³ and 10²⁰/cm³. However, the mechanism of dual doping of Ga and As according to the present invention can fully explain the above result.

Industrial Applicability

As described above, according to the manufacturing method of a zinc oxide thin film of the present invention, Ga and As atoms, components of a GaAs substrate are diffused and dual-doped into a zinc oxide thin film formed on the substrate during a thermal-annealing. As a result, a p-type zinc oxide thin film is achieved with a hole concentration higher than 10¹⁹/cm³ and characteristics of the p-type zinc oxide thin film. While the present invention has been described and illustrated herein with reference to the preferred embodiments thereof, it will be apparent to those skilled in the art that various modifications and variations can be made therein without departing from the spirit and scope of the invention. Thus, it is intended that the present invention covers the modifications and variations of this invention that come within the scope of the appended claims and their equivalents.

Claims

1. An optoelectronic compound semiconductor device comprising: a substrate; and a film of ZnO^ (O≤X≤l) formed on the substrate, the film containing a p-type dopant and an n-type dopant and having a hole concentration higher than at least 10¹⁹/cm³.

2. The optoelectronic semiconductor device of claim 1, wherein a mobility is higher than at least 12 cm²/V-sec.

3. The optoelectronic semiconductor device of claim 1, wherein a resistivity is 0.012 Ω-cm or lower than 0.012 Ω* cm.

4. The optoelectronic semiconductor device of claim 1, wherein the p-type dopant is selected from the group N elements .

5. The optoelectronic semiconductor device of claim 4, wherein the p-type dopant comprises As.

6. The optoelectronic semiconductor device of claim 1, wherein the n-type dopant is selected from the group IE elements .

7. The optoelectronic semiconductor device of claim 6, wherein the n-type dopant comprises Ga.

8. The optoelectronic semiconductor device of claim 1, wherein the substrate is made of GaAs.

9. The optoelectronic semiconductor device of claim 1, wherein the p-type dopant is As and the n-type dopant is Ga, and the substrate is made of GaAs.

10. The optoelectronic semiconductor device of claim 1, wherein the ZnO film has a thickness greater than 0.3 β m .

11. The optoelectronic semiconductor device of claim 1, wherein the ZnO film comprises Ga and As contained with a molar ratio ranged from 0.0001 to 0.1.

12. A p-type zinc oxide thin film in which a p-type dopant and an n-type dopant are dual-doped, the film having a hole concentration higher than at least 10¹⁹/cm³.

13. The p-type zinc oxide thin film of claim 12, wherein a mobility is higher than at least 12 crrr/V-sec.

14. The p-type zinc oxide thin film of claim 12, wherein a resistivity is 0.012 Ω-cm or lower than 0.012

Ω* cm.

15. The p-type zinc oxide thin film of claim 12, wherein the p-type dopant is selected from the group N elements.

16. The p-type zinc oxide thin film of claim 15, wherein the p-type dopant comprises As.

17. The p-type zinc oxide thin film of claim 12, wherein the n-type dopant is selected from the group IE elements .

18. The p-type zinc oxide thin film of claim 17, wherein the n-type dopant comprises Ga.

19. The p-type zinc oxide thin film of claim 12, wherein the p-type dopant is As and the n-type dopant is Ga.

20. The p-type zinc oxide thin film of claim 12, wherein the ZnO film has a thickness of greater than 0.3 β m .

21. The p-type zinc oxide thin film of claim 12, wherein the zinc oxide thin film is employed on a p-n junction.

22. The p-type zinc oxide thin film of claim 12, wherein the zinc oxide thin film is employed on a field effect transistor.

23. The p-type zinc oxide thin film of claim 12, wherein the zinc oxide thin film is employed on a light- emitting diode.

24. The p-type zinc oxide thin film of claim 12, wherein the zinc oxide thin film is employed on a laser diode.

25. The p-type zinc oxide thin film of claim 12, wherein the zinc oxide thin film is employed on a light- detecting diode.

26. A manu acturing method of a p-type zinc oxide thin film, the method comprising the steps of: a) loading a GaAs substrate into a reaction chamber; b) depositing a zinc oxide thin film on the substrate to a predetermined thickness; and c) thermally annealing the substrate on which the zinc oxide thin film is deposited such that Ga atom and As atom of the GaAs substrate are dual-doped into the zinc oxide thin film, to control concentration of the Ga atom and the As atom.

27. The manufacturing method of claim 26, wherein the deposition and the thermal-annealing of the zinc oxide thin film are performed by one selected from the group consisting of MBE, MOCVD, PLD, and a sputtering apparatus.

28. The manufacturing method of claim 26, wherein the deposition of the zinc oxide thin film is performed by a magnetron sputtering using a ZnO target, and Ar gas and 0₂ gas are supplied into the reaction chamber for the sputtering.

29. The manufacturing method of claim 26, wherein the deposition of the zinc oxide thin film is performed by a reaction ion sputtering using a Zn target, and Ar gas and 0₂ gas are supplied into the reaction chamber for the sputtering.

30. The manufacturing method of claim 26, wherein the deposition and the thermal-annealing of the zinc oxide thin film are performed at a room temperature or at a temperature higher than the room temperature.

31. The manufacturing method of claim 30, wherein the step of thermally annealing the zinc oxide thin film comprises the steps of: sealing the reaction chamber at a vacuum-pressure higher than 10^~3 Torr; and thermally annealing the zinc oxide thin film in the atmosphere.

32. The manufacturing method of claim 26, wherein the thermal-annealing is performed at a temperature range of 300 - 750 °C for several minutes to several hours.

33. The manufacturing method of claim 26, wherein the zinc oxide thin film has a hole concentration higher than at least 10¹⁹/cm³ by the thermal-annealing.