Direct texture transparent conductive oxide served as electrode or intermediate layer for photovoltaic and display applications

Abstract

The present invention provides transparent semiconducting films for constructing a translucent electrode that possess a high transparency and low sheet resistance. Further, the transparent semiconducting films have a high light diffusion property, which is capable to be a translucent front/back electrode in a light-emitting device for improving the light emission efficiency and a front/intermediate/back electrode in a multi-junction solar cell for improving the light trapping effect. Related fabrication method and how they are applied in different fields are also provided in the present invention.

Claims

1. A transparent semiconductor comprising: at least a bottom layer and at least a top layer sequentially deposited on a base substrate, wherein said bottom layer and top layer are made of at least two different metal oxides having two different crystalline temperatures, wherein said top layer is direct textured to form a plurality of pyramid-like structures on the surface thereof having only an orientation peak at 340.4 degrees two theta in a XRD pattern thereof.

2. The transparent semiconductor according to claim 1, wherein one of the at least two metal oxides is selected from indium oxide (In.sub.2O.sub.3), SnO.sub.2, ZnO, CdO, InO.sub.1.5, GaO.sub.1.5, NiO, or CuMO.sub.2, where M is Al, Ga, In, Sc, Cr, Y, or B; and the other of the at least two metal oxides is zinc oxide (ZnO) or tin oxide (SnO.sub.2) sequentially deposited on said base substrate.

3. The transparent semiconductor according to claim 2, wherein said indium oxide based bottom layer is doped with a metal oxide selected from the group consisting of titanium oxide (TiO.sub.2), cerium oxide (CeO.sub.2), tungsten oxide (WO.sub.3) and tin oxide (SnO.sub.2).

4. The transparent semiconductor according to claim 2, wherein the zinc oxide based top layer is doped with a metal oxide selected from the group consisting of gallium oxide (Ga.sub.2O.sub.3), aluminum oxide (Al.sub.2O.sub.3) and boron oxide (B.sub.2O.sub.3).

5. The transparent semiconductor according to claim 2, wherein the tin oxide based top layer is doped with a metal oxide selected from the group consisting of gallium oxide (Ga.sub.2O.sub.3), aluminum oxide (Al.sub.2O.sub.3) and antimony oxide (Sb.sub.2O.sub.3).

6. The transparent semiconductor according to claim 3, wherein the titanium oxide has a weight ratio from 1% to 5% with respect to the total weight of said indium oxide based bottom layer doped with said titanium oxide (ITiO).

7. The transparent semiconductor according to claim 3, wherein the cerium oxide has a weight ratio of 10% with respect to the total weight of said indium oxide based bottom layer doped with said cerium oxide (ICO).

8. The transparent semiconductor according to claim 3, wherein the tungsten oxide has a weight ratio of 1% with respect to the total weight of said indium oxide based bottom layer doped with said tungsten oxide (IWO).

9. The transparent semiconductor according to claim 3, wherein the film thickness of said bottom layer is 150 nm to 600 nm.

10. The transparent semiconductor according to claim 4, wherein the film thickness of said top layer is 150 nm to 2,200 nm.

11. A method for fabricating a transparent semiconductor on a base substrate comprising: sequentially depositing a first metal oxide and a second metal oxide having two different crystalline temperatures forming at least two semiconducting layers on said base substrate by at least two rounds of sputtering under a first processing temperature and a second processing temperature, respectively; and controlling thickness for each of said layers during said sequential depositing, wherein a top layer of said at least two semiconducting layers is direct textured by said sputtering to form a plurality of pyramid-like structures on the surface thereof.

12. The method according to claim 11, wherein said first metal oxide is selected from indium oxide (In.sub.2O.sub.3), SnO.sub.2, ZnO, CdO, InO.sub.1.5, GaO.sub.1.5, NiO, or CuMO.sub.2, where M is Al, Ga, In, Sc, Cr, Y, or B; and said second metal oxide is zinc oxide (ZnO) or tin oxide (SnO.sub.2).

13. The method according to claim 11, wherein the first processing temperature for depositing the first metal oxide based semiconducting layer is at about 25 C., room temperature, or a temperature below the crystalline temperature of any of said metal oxides.

14. The method according to claim 11, wherein the second processing temperature for depositing the second metal oxide based semiconducting layer is from 25 C., room temperature, or a temperature below the crystalline temperature of any of said metal oxides to 350 C.

15. The method according to claim 11, wherein the thickness of the first metal oxide based semiconducting layer is from 150 nm to 600 nm.

16. The method according to claim 11, wherein the thickness of the second metal oxide based semiconducting layer is from 150 nm to 2,200 nm.

17. The method according to claim 12, wherein said indium oxide (In.sub.2O.sub.3) is doped with a metal oxide selected from the group consisting of titanium oxide (TiO.sub.2), cerium oxide (CeO.sub.2), tungsten oxide (WO.sub.3) and tin oxide (SnO.sub.2).

18. The method according to claim 12, wherein said zinc oxide (ZnO) is doped with a metal oxide selected from the group consisting of gallium oxide (Ga.sub.2O.sub.3), aluminum oxide (Al.sub.2O.sub.3) and boron oxide (B.sub.2O.sub.3).

19. A multi-junction solar comprising a surface electrode, stacks of a photovoltaic semiconducting layer, an intermediate layer, and a backside electrode, being sequentially formed on a base substrate, wherein said intermediate layer is the transparent semiconductor according to claim 1.

20. A nitride-based light-emitting device comprising a buffer layer, n-doped nitride based semiconducting layer, a nitride based quantum-well layer, a p-doped nitride based semiconducting layer, a transparent conducting electrode, being sequentially formed on a base substrate, wherein said transparent conducting electrode is the transparent semiconductor according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the present invention are described in more detail hereinafter with reference to the drawings, in which:

(2) FIG. 1 is the cross-sectional view showing the constitution of a bi-layer transparent semiconducting thin film structure on a substrate according to an embodiment of the present invention;

(3) FIG. 2 is the scanning electronic microscopy (SEM) images illustrating the surface morphology of transparent semiconducting films according to two embodiments of the present invention;

(4) FIG. 3 is the X-Ray diffraction patterns of transparent semiconducting bottom film according to an embodiment of the present invention;

(5) FIG. 4 is the X-Ray diffraction patterns of transparent semiconducting top film according to an embodiment of the present invention;

(6) FIG. 5 is the cross-sectional view showing a manufacturing method for a nitride-based light-emitting device according to the first implementation embodiment of the present invention;

(7) FIG. 6 is the cross-sectional view showing a manufacturing method for a multi-junction solar cell according to the second implementation embodiment of the present invention.

DETAILED DESCRIPTION OF INVENTION

(8) In the following description, the present bi-layer semiconductor and method of fabrication thereof under different parameters are set forth as preferred examples. It will be apparent to those skilled in the art that modifications, including additions and/or substitutions, may be made without departing from the scope and spirit of the invention. Specific details may be omitted so as not to obscure the invention; however, the disclosure is written to enable one skilled in the art to practice the teachings herein without undue experimentation.

(9) FIG. 1 is the cross-sectional view showing the constitution of a thin film according to a preferred embodiment of the present invention. The thin film has a bottom film 2 and a pyramid shaped top film 3 grown on a substrate 1 sequentially.

(10) The substrate 1 can be opaque or transparent substrate. For light transmitting purpose, transparent glass with good visible transmittance is preferable as the substrate 1 for thin films grown on top. Extended to the near infrared (NIR) transmission, low-iron glass as the substrate 1 can be an example.

(11) The transparent semiconducting films formed on the substrate 1 comprising of a bottom film 2 of an indium oxide (In.sub.2O.sub.3) based semiconducting layer and a pyramid shaped top film 3 of a zinc oxide (ZnO) based semiconducting layer, possesses a sheet resistance less than 15 ohm/sq and a transmittance not less than 85%.

(12) The bottom film 2 of the indium oxide based semiconducting layer doped with the metal oxide selected from the group consisting of titanium oxide (TiO.sub.2), cerium oxide (CeO.sub.2), tungsten oxide (WO.sub.3) or tin oxide (SnO.sub.2). The indium oxide doped with cerium oxide, namely ICO, for example, may be used. The ICO film has a high refractive index of 2.1 which is able to reduce the refractive index difference with some high refractive index substrates, like nitride-based semiconductor. Other examples, the indium oxide either doped with titanium oxide or tungsten oxide, namely of ITiO and IWO, may be used. The ITiO and IWO have a high transmission at NIR range, which are able to use in NIR related device.

(13) The bottom film 2 of the indium oxide based semiconducting layer as the bottom film 2 can assist the texture formation of the top film 3 of the zinc oxide (ZnO) based semiconducting layer, thereby improves the surface roughness. The thickness of the bottom film 2 is preferably within 250 to 400 nm. If the film thickness is below 250 nm, the surface roughness is reduced and the haze effect is not pronounced. If the film thickness is more than 400 nm, the light transmittance is reduced.

(14) The top film 3 of the zinc oxide (ZnO) based semiconducting layer doped with the metal oxide selected from the group consisting of gallium oxide (Ga.sub.2O.sub.3) and aluminum oxide (Al.sub.2O.sub.3). The surface roughness of the top film 3 can be governed the film thickness. The thickness of the top film 3 is preferably within 1000 to 2000 nm. If the film thickness is below 1000 nm, the surface roughness is reduced and the haze effect is not pronounced. If the film thickness is more than 2000 nm, the light transmittance is reduced.

(15) In addition to the surface roughness, the processing temperature of the top film 3 can change the surface morphology and thereby changes the haze effect. The processing temperature of the top film 3 is preferably at 300 C. or above, to form a pronounced pyramid shape on the film surface. If the processing temperature is less than 300 C., it would form a less pronounced pyramid surface and reduce the haze effect.

(16) The preparation method of the transparent semiconducting texturing films will now be described. The bottom film 2 and the top film 3 are sequentially deposited on the substrate 1 by the RF magnetron sputtering method (e.g. vacuum sputtering by oxide based targets or using reactive sputtering by metallic targets), according to the constitution of a thin film structure shown in FIG. 1. The substrate 1 is sequentially cleaned by acetone, isopropanol and deionized water before loading in a vacuum sputtering chamber for the thin film deposition. The bottom film 2 is formed on the substrate 1 by sputtering a 4 inches indium oxide based target doped with the metal oxide consisting of titanium oxide (TiO.sub.2) and tin oxide (SnO.sub.2). The target is sputtered by a mixture gas of argon and oxygen (in a ratio of 99 to 1) at a RF power of 200 W and an operating pressure of 3.0 mTorr. Afterwards, the top film 3 is formed on the bottom film 2 by sputtering a 4 inches zinc oxide (ZnO) based target doped with the metal oxide consisting of gallium oxide (Ga.sub.2O.sub.3) and aluminum oxide (Al.sub.2O.sub.3). The target was sputtered by a pure gas of argon at a RF power of 400 W and an operating pressure of 3.0 mTorr. The substrate 1 is annealed at a set temperature during the film 3 deposition. The thicknesses of film 2 and 3 are monitored by a calibrated crystal quartz sensor. It is possible to substitute ZnO with tin oxide (SnO.sub.2) as the base material for top film 3, and the corresponding metal oxide dopant is selected from gallium oxide (Ga.sub.2O.sub.3), aluminum oxide (Al.sub.2O.sub.3), or antimony oxide (Sb.sub.2O.sub.3).

(17) The transparent semiconducting films formed on the substrate 1 is then measured by different techniques to obtain the optical, surface and electrical characteristics. The optical transmittance is measured by an integrated sphere equipped in the UV-VIS-NIR spectrometer. The sheet resistance is probed by a Hall-effect measurement system. The surface morphology and roughness are inspected by the scanning electronic microscopy (SEM) and atomic force microscopy (AFM).

EXAMPLES

(18) The embodiments of the present invention will now be described with several examples. Examples 1.1-1.5, 2.1-2.3 and 3.1-3.5 are, respectively, working examples demonstrating the effect of different processing temperature and/or different thickness of the bottom film 2 and the top film 3 thickness on forming the transparent semiconducting films. The comparative examples 1.1 and 1.2 are the counter examples to illustrate the function of the bottom film 2 in assisting the surface-texturing on the top film 3. The parameters of optical, electrical and surface characteristics from the examples are summarized in TABLE 1.

Example 1.1

(19) A transparent semiconducting film was fabricated as the above described process and the constitution as shown in FIG. 1. The bottom film 2 and the top film 3 were made in a thickness of 350 nm and 1650 nm, respectively. The processing temperature of the top film 3 was at 25 C. Its optical, electrical and surface properties were characterized. An average total transmittance (TT), which measured from 400 nm to 1200 nm, was found to be 87.3%. A peak haze of 11.7% was found at 456 nm. A mean surface roughness (Ra) and a root mean square surface roughness (Rms) were found to be 25.4 nm and 31.7 nm, respectively. The sheet resistance was found to be 216 ohm/sq. An SEM image illustrating the surface morphology of the top film 3 is shown in FIG. 2 (left panel).

Example 1.2

(20) A transparent semiconducting film was fabricated as the above described process and the constitution as shown in FIG. 1. The bottom film 2 and the top film 3 were made in a thickness of 350 nm and 1650 nm, respectively. The processing temperature of the top film 3 was at 200 C. Its optical, electrical and surface properties were characterized. An average total transmittance (TT), which measured from 400 nm to 1200 nm, was found to be 87.0%. A peak haze of 14.9% was found at 452 nm. A mean surface roughness (Ra) and a root mean square surface roughness (Rms) were found to be 27.3 nm and 33.9 nm, respectively. The sheet resistance was found to be 61.7 ohm/sq.

Example 1.3

(21) A transparent semiconducting film was fabricated as the above described process and the constitution as shown in FIG. 1. The bottom film 2 and the top film 3 were made in a thickness of 350 nm and 1650 nm, respectively. The processing temperature of the top film 3 was at 250 C. Its optical, electrical and surface properties were characterized. An average total transmittance (TT), which measured from 400 nm to 1200 nm, was found to be 83.2%. A peak haze of 14.9% was found at 436 nm. A mean surface roughness (Ra) and a root mean square surface roughness (Rms) were found to be 25.5 nm and 32.0 nm, respectively. The sheet resistance was found to be 17.6 ohm/sq.

Example 1.4

(22) A transparent semiconducting film was fabricated as the above described process and the constitution as shown in FIG. 1. The bottom film 2 and the top film 3 were made in a thickness of 350 nm and 1650 nm, respectively. The processing temperature of the top film 3 was at 300 C. Its optical, electrical and surface properties were characterized. An average total transmittance (TT), which measured from 400 nm to 1200 nm, was found to be 85.5%. A peak haze of 15.2% was found at 432 nm. A mean surface roughness (Ra) and a root mean square surface roughness (Rms) were found to be 25.3 nm and 31.8 nm, respectively. The sheet resistance was found to be 14.2 ohm/sq.

Example 1.5

(23) A transparent semiconducting film was fabricated as the above described process and the constitution as shown in FIG. 1. The bottom film 2 and the top film 3 were made in a thickness of 350 nm and 1650 nm, respectively. The processing temperature of the top film 3 was at 350 C. Its optical, electrical and surface properties were characterized. An average total transmittance (TT), which measured from 400 nm to 1200 nm, was found to be 88.3%. A peak haze of 18.3% was found at 428 nm. A mean surface roughness (Ra) and a root mean square surface roughness (Rms) were found to be 25.4 nm and 31.8 nm, respectively. The sheet resistance was found to be 12.8 ohm/sq. An SEM image illustrating the surface morphology of the top film 3 is shown in FIG. 2 (right panel).

(24) It can be seen from examples 1.1-1.5, which the film thicknesses are the same and the processing temperature is varied from 25 C. to 350 C., the peak haze is gradually increased from 11.7% to 18.3%. But there are no sharp changes in the average total transmittance (TT), which are just 85%. In addition, there are also no enhancement on the surface roughness, which kept at the values of 25 nm (Ra) and 32 nm (Rms), even the processing temperature is elevated.

(25) FIG. 2 depicts the SEM images of the film surface captured from example 1.1 and 1.5. A pronounced pyramid sharp can be observed on the film surface, particularly at 350 C. (example 1.5). It demonstrates that the elevation of the processing temperature just changes the surface morphology rather than the surface roughness, and thereby enhances the haze effect. Furthermore, it is found that the sheet resistance is lowered from 212 ohm/sq to 12.8 ohm/sq with the elevated temperature. FIG. 3 and FIG. 4 are, respectively the XRD patterns of the bottom film 2 and the top film 3. At a high processing temperature, for example 350 C., the films demonstrate strong (002) and (400) peaks. It can be the evident to explain the improvement of the electrical conductivity at high processing temperature due to the well-crystallized phase.

Example 2.1

(26) A transparent semiconducting film was fabricated as the above described process and the constitution as shown in FIG. 1. The bottom film 2 and the top film 3 were made in a thickness of 150 nm and 1950 nm, respectively. The processing temperature of the top film 3 was at 350 C. Its optical, electrical and surface properties were characterized. An average total transmittance (TT), which measured from 400 nm to 1200 nm, was found to be 85.9%. A peak haze of 13.1% was found at 424 nm. A mean surface roughness (Ra) and a root mean square surface roughness (Rms) were found to be 16.8 nm and 21.3 nm, respectively. The sheet resistance was found to be 21.1 ohm/sq.

Example 2.2

(27) A transparent semiconducting film was fabricated as the above described process and the constitution as shown in FIG. 1. The bottom film 2 and the top film 3 were made in a thickness of 250 nm and 1950 nm, respectively. The processing temperature of the top film 3 was at 350 C. Its optical, electrical and surface properties were characterized. An average total transmittance (TT), which measured from 400 nm to 1200 nm, was found to be 86.8%. A peak haze of 19.9% was found at 424 nm. A mean surface roughness (Ra) and a root mean square surface roughness (Rms) were found to be 23.0 nm and 28.9 nm, respectively. The sheet resistance was found to be 11.1 ohm/sq.

Example 2.3

(28) A transparent semiconducting film was fabricated as the above described process and the constitution as shown in FIG. 1. The bottom film 2 and the top film 3 were made in a thickness of 400 nm and 1950 nm, respectively. The processing temperature of the top film 3 was at 350 C. Its optical, electrical and surface properties were characterized. An average total transmittance (TT), which measured from 400 nm to 1200 nm, was found to be 86.6%. A peak haze of 19.9% was found at 424 nm. A mean surface roughness (Ra) and a root mean square surface roughness (Rms) were found to be 23.6 nm and 29.9 nm, respectively. The sheet resistance was found to be 11.2 ohm/sq.

(29) It can be seen from examples 2.1-2.3, which the thickness of the bottom film 2 is varied from 150 to 400 nm and the thickness of the top film 3 is made at 1950 nm processing at the temperature of 350 C., the peak haze is gradually increased from 13.1% to 19.9%. There are no sharp changes in the average total transmittance (TT), which are kept at 86%. However, there is obviously enhancement on the surface roughness, which comes saturated for film 2 thickness over 250 nm. In addition, the sheet resistance is lowered from the 21.1 ohm/sq to 11.1 ohm/sq and saturated for film thickness over 250 nm. It can be known that the bottom film 2 also contributes to the electrical conductivity even a thick layer of film 3 is formed on top. In short, the thickness of the bottom film 2 is preferably at 250 nm to 400 nm.

Example 3.1

(30) A transparent semiconducting film was fabricated as the above described process and the constitution as shown in FIG. 1. The bottom film 2 and the top film 3 were made in a thickness of 350 nm and 150 nm, respectively. The processing temperature of the top film 3 was at 350 C. Its optical, electrical and surface properties were characterized. An average total transmittance (TT), which measured from 400 nm to 1200 nm, was found to be 91.8%. No haze effect was found from the spectrum. A mean surface roughness (Ra) and a root mean square surface roughness (Rms) were found to be 3.8 nm and 4.8 nm, respectively. The sheet resistance was found to be 22.3 ohm/sq.

Example 3.2

(31) A transparent semiconducting film was fabricated as the above described process and the constitution as shown in FIG. 1. The bottom film 2 and the top film 3 were made in a thickness of 350 nm and 1400 nm, respectively. The processing temperature of the top film 3 was at 350 C. Its optical, electrical and surface properties were characterized. An average total transmittance (TT), which measured from 400 nm to 1200 nm, was found to be 87.7%. A peak haze of 10.5% was found at 432 nm. A mean surface roughness (Ra) and a root mean square surface roughness (Rms) were found to be 18.9 nm and 23.7 nm, respectively. The sheet resistance was found to be 12.4 ohm/sq.

Example 3.3

(32) A transparent semiconducting film was fabricated as the above described process and the constitution as shown in FIG. 1. The bottom film 2 and the top film 3 were made in a thickness of 350 nm and 1650 nm, respectively. The processing temperature of the top film 3 was at 350 C. Its optical, electrical and surface properties were characterized. An average total transmittance (TT), which measured from 400 nm to 1200 nm, was found to be 88.3%. A peak haze of 18.3% was found at 428 nm. A mean surface roughness (Ra) and a root mean square surface roughness (Rms) were found to be 25.4 nm and 31.8 nm, respectively. The sheet resistance was found to be 12.8 ohm/sq.

Example 3.4

(33) A transparent semiconducting film was fabricated as the above described process and the constitution as shown in FIG. 1. The bottom film 2 and the top film 3 were made in a thickness of 350 nm and 1950 nm, respectively. The processing temperature of the top film 3 was at 350 C. Its optical, electrical and surface properties were characterized. An average total transmittance (TT), which measured from 400 nm to 1200 nm, was found to be 86.6%. A peak haze of 20.0% was found at 428 nm. A mean surface roughness (Ra) and a root mean square surface roughness (Rms) were found to be 24.8 nm and 31.2 nm, respectively. The sheet resistance was found to be 11.2 ohm/sq.

Example 3.5

(34) A transparent semiconducting film was fabricated as the above described process and the constitution as shown in FIG. 1. The bottom film 2 and the top film 3 were made in a thickness of 350 nm and 2300 nm, respectively. The processing temperature of the top film 3 was at 350 C. Its optical, electrical and surface properties were characterized. An average total transmittance (TT), which measured from 400 nm to 1200 nm, was found to be 83.5%. A peak haze of 27.8% was found at 436 nm. A mean surface roughness (Ra) and a root mean square surface roughness (Rms) were found to be 27.7 nm and 34.4 nm, respectively. The sheet resistance was found to be 8.7 ohm/sq.

(35) As shown in example 3.1-3.5, when the thickness of film 3 was varied from 150 nm to 2300 nm and the thickness of film 2 was kept at 350 nm, the peak haze was sharply increased from nothing to 27.8%. However, the average total transmittance (TT) was gradually decreased from 91.8% to 83.5%. In addition, the surface roughness was also significantly improved, for example, Ra was increased from 3.8 nm to 27.7 nm. It can be clearly seen that the thickness of film 3 can govern the surface roughness and optical transmittance. A relatively thicker film can introduce a rougher film surface and thereby improves the haze effect, but reduces the average total transmittance (TT). Thus, there is a trade-off between the optical transmittance and haze effect. For retaining a good transmittance (i.e. >85%) and a good haze effect (i.e. >15%), the thickness of top film 3 is preferable from 1500 nm to 2000 nm.

Comparative Example 1.1

(36) A transparent semiconducting film was fabricated according to the process as described herein and the constitution as shown in FIG. 1. The bottom film 2 and the top film 3 were made in a thickness of 350 nm and 0 nm, respectively. The processing temperature of the bottom film 2 was at 350 C. Its optical, electrical and surface properties were characterized. An average total transmittance (TT), which measured from 400 nm to 1200 nm, was found to be 91.1%. No haze effect was found from the spectrum. A mean surface roughness (Ra) and a root mean square surface roughness (Rms) were found to be 1.8 nm and 2.5 nm, respectively. The sheet resistance was found to be 33.6 ohm/sq.

Comparative Example 1.2

(37) A transparent semiconducting film was fabricated as the above described process and the constitution as shown in FIG. 1. The bottom film 2 and the top film 3 were made in a thickness of 0 nm and 1650 nm, respectively. The processing temperature of the top film 3 was at 350 C. Its optical, electrical and surface properties were characterized. An average total transmittance (TT), which measured from 400 nm to 1200 nm, was found to be 91.7%. A peak haze of 10.9% was found at 424 nm. A mean surface roughness (Ra) and a root mean square surface roughness (Rms) were found to be 15.3 nm and 20.0 nm, respectively. The sheet resistance was found to be 74.6 ohm/sq.

(38) Comparative example 1.1 is a single film 2 only. It is seen that the bottom film 2 is a flat layer. There is no haze effect that can be observed. The Ra and Rms are just 1.8 nm and 2.5 nm, respectively, which are ten times less than the surface roughness of example 1.5. Thus, the ups and downs surface feature of film 3 is not contributed by the surface topography of film 2.

(39) On the other hand, a sole film 3 is made in comparative example 1.2. Without the bottom film 2, the film 3 can exhibit a peak haze of 10.9% and a surface roughness Ra of 15.3 nm. However, it is still 2 times less than the dual film 23 shown in example 1.5. It demonstrates that a high texture surface cannot be formed on a sole film. In short, the bottom film 2 cannot offer a ups and downs surface texture but can assist the growth of the top film 3 in forming a high degree of roughness on the film surface.

(40) TABLE-US-00001 TABLE 1 Optical Electrical Films formation conditions characteristics Surface property Film 2 Film 3 Process. Peak roughness Sheet thickness thickness temp. TT haze Ra Rms resistance (nm) (nm) ( C.) (%) (%) (nm) (nm) (ohm/sq) Ex. 1.1 350 1650 25 87.3 11.7 25.4 31.7 216 Ex. 1.2 350 1650 200 87.0 14.9 27.3 33.9 61.7 Ex. 1.3 350 1650 250 83.2 14.9 25.5 32.0 17.6 Ex. 1.4 350 1650 300 85.5 15.2 25.3 31.8 14.2 Ex. 1.5 350 1650 350 88.3 18.3 25.4 31.8 12.8 Ex. 2.1 150 1950 350 85.9 13.1 16.8 21.3 21.1 Ex. 2.2 250 1950 350 86.8 19.9 23.0 28.9 11.1 Ex. 2.3 400 1950 350 86.6 19.9 23.6 29.9 11.2 Ex. 3.1 350 150 350 91.8 3.8 4.8 22.3 Ex. 3.2 350 1400 350 87.7 10.5 18.9 23.7 12.4 Ex. 3.3 350 1650 350 88.3 18.3 25.4 31.8 12.8 Ex. 3.4 350 1950 350 86.6 20.0 24.8 31.2 11.2 Ex. 3.5 350 2300 350 83.5 27.8 27.7 34.4 8.7 Comp. 350 0 350 91.1 1.8 2.5 33.6 Ex. 1.1 Comp. 0 1650 350 91.7 10.9 15.3 20.0 74.6 Ex. 1.2

First Implementation EmbodimentApplication in Light-Emitting Device

(41) This embodiment is to use the transparent semiconducting texturing films as the front/back electrode in forming a light-emitting device, preferably in a nitride-based light-emitting device, for improving the light extraction.

(42) As shown in FIG. 5, it is the cross-sectional view showing a manufacturing method for a nitride-based light-emitting device, according to the embodiment of the present invention. The nitride-based light-emitting device consisting of a buffer layer 5, n-doped nitride based semiconducting layer 6, a nitride based quantum-well layer 7, a p-doped nitride based semiconducting layer 8, and a transparent conducting electrode 23, are sequentially formed on a base substrate 4. The transparent conducting electrode 23 is made of stacked indium oxide (In.sub.2O.sub.3) based semiconducting layer and zinc oxide (ZnO) based semiconducting layer according to the first embodiment as shown in FIG. 1.

(43) The film 2 may preferably consist of cerium oxide (CeO.sub.2). The indium oxide doped with cerium oxide, namely ICO, has a high refractive index of 2.1. It may suppress the refractive index mismatch with the nitride based semiconducting layer 8, which has refractive index of 2.5, for improving the light extraction. The texturing film 3 may further relax the light trapped in the device due to the total internal reflection.

(44) In short, this embodiment uses the features of the transparent semiconducting texturing films, like the high refractive index and texturing surface, for reducing the light trapping and enhancing the light extraction capability in the nitride-based light-emitting device.

Second Implementation EmbodimentApplication in Multi-Junction Solar Cell

(45) This embodiment is to use the transparent semiconducting texturing films as the front/intermediate/back electrode in forming a multi-junction solar cell for improving the light trapping effect.

(46) As shown in FIG. 6, it is the cross-sectional view showing a manufacturing method for a multi-junction solar cell, according to the embodiment of the present invention. The multi-junction solar cell consisting of a surface electrode 10, stacks of a photovoltaic semiconducting layer 11 and 12, an intermediate layer 23, and a backside electrode 13, are sequentially formed on a base substrate 9. The intermediate layer 23 is made of stacked indium oxide (In.sub.2O.sub.3) based semiconducting layer and zinc oxide (ZnO) based semiconducting layer according to the first embodiment as shown in FIG. 1.

(47) The film 2 may preferably consist of titanium oxide (TiO.sub.2) or tungsten oxide (WO.sub.3). The indium oxide doped with titanium oxide (TiO.sub.2), namely ITiO, or doped with tungsten oxide (WO.sub.3), namely IWO, either has strong light transmittance at NIR range. It may improve the light transmission to stacks of the photovoltaic semiconducting layer 11 which has low energy absorption. The texturing film 3 may further enhance the light trapped in layers 11 and 12 due to the total internal reflection, which the optical path is now rearranged by the texturing surface at the interface of layer 3 and layer 12.

(48) In short, this embodiment uses the features of the transparent semiconducting texturing films, like the high NIR transmittance and texturing surface, for enhancing the light trapping and improving the light absorption capability in the multi-junction solar cell.

(49) The foregoing description of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations will be apparent to the practitioner skilled in the art.

(50) The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, thereby enabling others skilled in the art to understand the invention for various embodiments and with various modifications that are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalence.

INDUSTRIAL APPLICABILITY

(51) The present invention is useful in photovoltaic, display and solid-state lighting industries which require a semiconducting material with good electrical conductivity, optical transparency and good interfacial adhesion. The simple two-step sputtering process of the present invention is also easy to practice and be optimized in order to form surface-textured TCO with high haze, e.g., over 50%, by varying the thickness of the layer(s) and/or corresponding processing conditions during sputtering.