Abstract:
The invention discloses a zinc-oxide-based semiconductor light-emitting device and the fabrication thereof. The method according to the invention, first, is to prepare a substrate. Next, by an atomic-layer-deposition-based process, a ZnO-based multi-layer structure is formed on or over the substrate where the ZnO-based multi-layer structure includes a light-emitting region.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a semiconductor light-emitting device and method of fabricating the same, and more particularly, to a ZnO-based semiconductor light-emitting device and method of fabricating the same. 
     2. Description of the Prior Art 
     Light-emitting diodes (LEDs) are semiconductor devices initially used for indicator lamps or display panels. As the emergence of white light LEDs, LEDs can also be used for illumination. Comparing with traditional light sources, LEDs have the advantages of high efficiency, long lifetime, high durability and high reliability, etc. It is renowned as revolutionary light source of the 21st century. 
     Zinc oxide (ZnO) is a II-VI group compound semiconductor with a direct bandgap energy of 3.37 eV at room temperature, and its emitted light is in the range of ultraviolet. 
     As a raw material for fabricating white light LEDs, the zinc oxide has following advantages: 
     1. Abundance and relatively low cost of raw materials. 
     2. The exciton binding energy of zinc oxide is up to 60 meV, so the light emitting efficiency is high. 
     3. Since the emission wavelength of zinc oxide is around 380 nm, it is more efficient in exciting fluorescent material than other materials (e.g. GaN) for fabricating white light LEDs. Therefore, the zinc oxide is very suitable for fabricating white light LEDs. 
     4. Zinc oxide is easier to be processed by chemical etching than other materials (e.g. GaN) for fabricating white light LEDs. 
     However, zinc oxide shows intrinsic n-type characteristics due to the presence of native defects, such as oxygen vacancies and zinc interstitials. Thus it suffers from the difficulty to prepare reliable and high-quality p-type zinc oxide. In order to realize a high-quality p-type zinc oxide, high-concentration p-type doping is needed to overcome the strong self-compensation effect resulting from the native n-type defects. Nevertheless, the solid solubility of p-type acceptors in zinc oxide is not high enough to achieve high p-type doping concentrations. Therefore, it is difficult to produce high-quality p-type zinc oxide, as well as the important structure of an LED, the p-n junction. As a result, a reliable growth technique is desired for the growth of high-quality zinc oxide. 
     Though zinc oxide is suitable for fabricating a white light LED, but owing to the limitations described above, the technology of fabricating a white light LED with zinc oxide is held up. 
     Accordingly, a scope of the invention is to provide a zinc-oxide-based semiconductor light-emitting device and a method of fabricating the same to solve aforesaid problems. 
     SUMMARY OF THE INVENTION 
     A scope of the invention is to provide a zinc-oxide-based semiconductor light-emitting device and a method of fabricating the same. 
     According to an embodiment of the invention, the method of fabricating a semiconductor light-emitting device, firstly, prepares a substrate. Then, by an atomic layer deposition based process, the method forms a ZnO-based multi-layer structure on or over the substrate, where the ZnO-based multi-layer structure includes a light-emitting region. 
     According to another embodiment of the invention, the semiconductor light-emitting device includes a substrate and a ZnO-based multi-layer structure formed on or over the substrate, where the ZnO-based multi-layer structure includes a light-emitting region. 
     Therefore, according to the invention, the method fabricates a semiconductor light-emitting device by an atomic layer deposition based process. Thereby, the method can successfully fabricate high-quality ZnO-based semiconductor light-emitting device. In addition, since the layer formed by the atomic layer deposition process has several advantages such as easy and accurate thickness control, accurate control of material composition, facile doping, abrupt interfaces, high uniformity over a large area, good reproducibility, dense and pinhole-free structures, low deposition temperatures, etc., the semiconductor light-emitting device has very high crystal quality and very low defect density. 
     The advantage and spirit of the invention may be understood by the following recitations together with the appended drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE APPENDED DRAWINGS 
         FIG. 1  shows the fabricating method according to an embodiment of the invention. 
         FIG. 2  shows the X-ray diffraction pattern of the ZnO layer grown on a sapphire substrate by an atomic layer deposition process. 
         FIG. 3  shows the spontaneous emission photoluminescence spectrum of the ZnO layer grown on a sapphire substrate by an atomic layer deposition process. 
         FIG. 4  shows the stimulated emission photoluminescence spectra of the ZnO layer grown on a sapphire substrate by an atomic layer deposition process. 
         FIG. 5  shows the relationship between the photoluminescence light emission intensity and the excitation intensity of the ZnO layer grown on a sapphire substrate by an atomic layer deposition process. 
         FIG. 6  shows a semiconductor light-emitting device according to an embodiment of the invention. 
         FIG. 7  shows the current density vs. voltage characteristics of the semiconductor light-emitting device shown in  FIG. 6 . 
         FIG. 8  shows the X-ray diffraction patterns of the ZnO layer and the GaN layer of the semiconductor light-emitting device shown in  FIG. 6 . 
         FIG. 9  shows the photoluminescence spectra of the ZnO layer and the GaN layer of the semiconductor light-emitting device shown in  FIG. 6 . 
         FIG. 10  shows the electroluminescence spectra of the semiconductor light-emitting device shown in  FIG. 6  at various injection currents. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Please refer to  FIG. 1 .  FIG. 1  shows the fabricating method according to an embodiment of the invention. According to the embodiment of the invention, the method fabricates a ZnO-based semiconductor light-emitting device by an atomic layer deposition based process. The ZnO-based semiconductor light-emitting device means that the semiconductor light-emitting device has, but not limited to, a ZnO layer, a MgxZn 1-x O layer, a BeyZn 1-y O layer, or other compound layer with ZnO. 
     As shown in  FIG. 1 . The method, firstly, prepares a substrate  10  and set the substrate  10  in a reaction chamber  20  designed for performing an atomic layer deposition (ALD) based process. In the embodiment, the substrate  10  can be a sapphire substrate, a Si substrate, a SiC substrate, a GaN substrate, AlGaN substrate, a InGaN substrate, a ZnO substrate, a ScAlMgO 4  substrate, a YSZ (yttria-stabilized zirconia) substrate, a SrCu 2 O 2  substrate, a CuAlO 2  substrate, LaCuOS substrate, a NiO substrate, a LiGaO 2  substrate, a LiAlO 2  substrate, a GaAs substrate, a glass substrate, or the like. 
     Then, by an atomic layer deposition based process, the method forms a ZnO-based multi-layer structure on or over the substrate, where the ZnO-based multi-layer structure includes a light-emitting region (not shown). In actual applications, the atomic layer deposition based process can be an atomic layer deposition process, a plasma-enhanced atomic layer deposition process, a plasma-assisted atomic layer deposition process, or combination of above processes, such as combination of the atomic layer deposition process and the plasma-enhanced atomic layer deposition process or combination of the atomic layer deposition process and the plasma-assisted atomic layer deposition process. Using the plasma-enhanced ALD process or the plasma-assisted ALD process can ionize precursors, so as to lower the deposition temperature. It is noticeable that the atomic layer deposition process is also named as Atomic Layer Epitaxy (ALE) process or Atomic Layer Chemical Vapor Deposition (ALCVD) process, so that these processes are actually the same. 
     In the embodiment, the light-emitting region can be a p-type doped ZnO/intrinsic ZnO/n-type doped ZnO structure combination, a p-type doped ZnO/intrinsic ZnO structure combination, a p-type doped ZnO/n-type doped ZnO structure combination, a p-type doped Mg x Zn 1-x O/intrinsic Mg y Zn 1-y O/n-type doped Mg z Zn 1-z O structure combination, a p-type doped Mg x Zn 1-x O/n-type doped Mg y Zn 1-y O/n-type doped Mg z Zn 1-z O structure combination, a p-type doped Mg x Zn 1-x O/p-type doped Mg y Zn 1-y O/n-type doped Mg z Zn 1-z O structure combination, a p-type doped Mg x Zn 1-x O/intrinsic ZnO/n-type doped Mg z Zn 1-z O structure combination, a p-type doped Mg x Zn 1-x O/n-type doped ZnO/n-type doped Mg z n 1-z O structure combination, a p-type doped Mg x Zn 1-x O/p-type doped ZnO/n-type doped Mg z Zn 1-z O structure combination, a p-type doped Mg x Zn 1-x O/n-type doped Mg z Zn 1-z O structure combination, a p-type doped Mg x Zn 1-x O/intrinsic Mg y Zn 1-y O structure combination, a p-type doped Mg x ZnO/intrinsic ZnO structure combination, a p-type doped Mg x Zn 1-x O/intrinsic ZnO/n-type doped ZnO structure combination, a p-type doped Mg x Zn 1-x O/p-type doped ZnO/n-type doped ZnO structure combination, a p-type doped Mg x Zn 1-x O/n-type doped ZnO structure combination, a p-type doped ZnO/intrinsic ZnO/n-type doped Mg z Zn 1-z O structure combination, a p-type doped ZnO/n-type doped ZnO/n-type doped Mg z Zn 1-z O structure combination, a p-type doped ZnO/n-type doped Mg z Zn 1-z O structure combination, an n-type doped ZnO/p-type doped the substrate structure combination, an n-type doped Mg z Zn 1-z O/p-type doped the substrate structure combination, a p-type doped Be x Zn 1-x O/intrinsic Be y Zn 1-y O/n-type doped Be z Zn 1-z O structure combination, a p-type doped Be x Zn 1-x O/n-type doped Be y Zn 1-y O/n-type doped Be z Zn 1-z O structure combination, a p-type doped Be x Zn 1-x O/p-type doped Be y Zn 1-y O/n-type doped Be z Zn 1-z O structure combination, a p-type doped Be x Zn 1-x O/intrinsic ZnO/n-type doped Be z Zn 1-z O structure combination, a p-type doped Be x Zn 1-x O/n-type doped ZnO/n-type doped Be z Zn 1-z O structure combination, a p-type doped Be x Zn 1-x O/p-type doped ZnO/n-type doped Be z Zn 1-z O structure combination, a p-type doped Be x Zn 1-x O/n-type doped Be z Zn 1-z O structure combination, a p-type doped Be x Zn 1-x O/intrinsic Be y Zn 1-y O structure combination, a p-type doped Be x Zn 1-x O/intrinsic ZnO structure combination, a p-type doped Be x Zn 1-x O/intrinsic ZnO/n-type doped ZnO structure combination, a p-type doped Be x Zn 1-x O/p-type doped ZnO/n-type doped ZnO structure combination, a p-type doped Be x Zn 1-x O/n-type doped ZnO structure combination, a p-type doped ZnO/intrinsic ZnO/n-type doped Be z Zn 1-z O structure combination, a p-type doped ZnO/n-type doped ZnO/n-type doped Be z Zn 1-z O structure combination, a p-type doped ZnO/n-type doped Be z Zn 1-z O structure combination, an n-type doped Be z Zn 1-z O/p-type doped the substrate structure combination, or the like, 0&lt;x, y, z≦1, where the p-type doped the substrate can be the substrate  10 . 
     The precursors of the ZnO structure can be a DEZn (diethylzinc, Zn(C 2 H 5 ) 2 ) precursor, a DMZn (dimethylzinc, Zn(CH 3 ) 2 ) precursor, a zinc acetate (Zn(CH 3 COO) 2 ) precursor or a ZnCl 2  precursor and a H 2 O precursor, an O 3  precursor, an O 2  precursor, or an oxygen radical. The DEZn, the DMZn, the zinc acetate or the ZnCl 2  is the source of the Zn, and the H 2 O, the O 3 , the O 2 , or the oxygen radical is the source of the O. The precursors of the Mg x Zn 1-x O structure can be a DEZn precursor, a DMZn precursor, a zinc acetate precursor or a ZnCl 2  precursor, a MgCp 2  (Bis(cyclopentadienyl)magnesium, Mg(C 5 H 5 ) 2 ) precursor, a Mg(thd) 2  (2,2,6,6-tetramethyl-heptanedionato-3,5-magnesium(II)) precursor or a Bis(pentamethylcyclopentadienyl)magnesium (C 20 H 30 Mg) precursor and a H 2 O precursor, an O 3  precursor, an O 2  precursor, or an oxygen radical. The DEZn, the DMZn, the zinc acetate or the ZnCl 2  is the source of the Zn; the MgCp 2 , the Mg(thd) 2  or the Bis(pentamethylcyclopentadienyl)magnesium is the source of the Mg; and the H 2 O, the O 3 , the O 2 , or the oxygen radical is the source of the O. 
     The precursors of the Be x Zn 1-x O structure can be a DEZn precursor, a DMZn precursor, a zinc acetate precursor or a ZnCl 2  precursor, a Be(acac) 3 (beryllium acetylacetonate, (CH 3 COCH═C(O—)CH 3 ) 2 Be) precursor or a BeCl 2  precursor and a H 2 O precursor, an O 3  precursor, an O 2  precursor, or an oxygen radical. The DEZn, the DMZn, the zinc acetate or the ZnCl 2  is the source of the Zn; the Be(acac) 3  or the BeCl 2  is the source of the Be; and the H 2 O, the O 3 , the O 2 , or the oxygen radical is the source of the O. 
     In the embodiment, the method of fabricating the p-type doped ZnO includes adding a p-type dopant during the atomic layer deposition process, where the p-type dopant can be nitrogen, phosphorous, arsenic, etc. The precursor of nitrogen as the p-type dopant is, preferable but not limited to, a NH 3  precursor, a NO precursor, a N 2 O precursor, an 1,1-Dimethylhydrazine ((CH 3 ) 2 NNH 2 ) precursor, a Tert-butylamine ((CH 3 ) 3 CNH 2 ), or a Tert-butyl hydrazine ((CH 3 ) 3 CNHNH 2 ) precursor. The precursor of phosphorous as the p-type dopant is, preferable but not limited to, a PH 3  precursor, a P 2 O 5  precursor, a Zn 3 P 2  precursor, or a Diethyl phosphite ((C 2 H 5 O) 2 P(O)H). The precursor of arsenic as the p-type dopant is, preferable but not limited to, an AsH 3  precursor. 
     In the embodiment, the method of fabricating the n-type doped ZnO includes adding an n-type dopant during the atomic layer deposition process, where the n-type dopant can be aluminum, gallium, indium, etc. The precursor of aluminum as the n-type dopant is, preferable but not limited to, a Trimethylaluminum (Al(CH 3 ) 3 ) precursor or a Triethylaluminum (Al(C 2 H 5 ) 3 ) precursor. The precursor of gallium as the n-type dopant is, preferable but not limited to, a Trimethylgallium (Ga(CH 3 ) 3 ) precursor or a Triethylgallium (Ga(C 2 H 5 ) 3 ) precursor. The precursor of indium as the n-type dopant is, preferable but not limited to, a Indium acetylacetonate (In(OCCH 3 CHOCCH 3 ) 3 ) precursor or a Trimethylindium (In(CH 3 ) 3 ) precursor. 
     As shown in  FIG. 1 , an example of forming a ZnO layer by an atomic layer deposition process is presented. In an embodiment, an atomic layer deposition cycle (ALD cycle) includes four reaction steps of: 
     1. Using a carrier gas  22  to carry DEZn molecules  24  into the reaction chamber  20 ; thereby, the DEZn molecules  24  are absorbed on the surface of the substrate  10  to form a layer of DEZn. 
     2. Using the carrier gas  22 , with assistance of the pump  28 , to purge the DEZn molecules which are not absorbed on the surface of the substrate  10 . 
     3. Using the carrier gas  22  to carry H 2 O molecules  26  into the reaction chamber  20 ; thereby, the H 2 O molecules  26  react with the DEZn radicals absorbed on the surface of the substrate  10  to form one monolayer of ZnO, where by-product are organic molecules. 
     4. Using the carrier gas  22 , with assistance of the pump  28 , to purge the residual H 2 O molecules  26  and the by-product due to the reaction. 
     In the embodiment, the carrier gas  22  can be highly pure argon gas or nitrogen gas. The above four steps is called an ALD cycle. An ALD cycle grows a thin film with a thickness of only one monolayer on the entire surface of the substrate  10 ; the characteristic is named as “self-limiting”, and the characteristic allows the precision of the thickness control of the atomic layer deposition to be one monolayer. Therefore, the thickness of the ZnO layer can be precisely controlled by the number of ALD cycles. 
     In practice, during the process of fabricating an n-type doped ZnO or a p-type doped ZnO, the doping is implemented by replacing partial ALD cycles with the ALD cycles of n-type dopant or p-type dopant, and the doping concentration is determined by the proportion of the replaced ALD cycles. Take an n-type doped ZnO with 6% Al for example, 3 of 50 ALD cycles of DEZn and H 2 O are replaced by 3 ALD cycles of TMA and H 2 O, or 6 of 100 ALD cycles of DEZn and H 2 O are replaced by 6 ALD cycles of TMA and H 2 O, etc. 
     In the embodiment, the deposition temperature is in a range of from room temperature to 800° C. However, the deposition temperature is preferably in a range of from 100° C. to 300° C. It is noticeable that since the deposition temperature is relatively low, the damage and/or malfunction probability of equipment owing to high temperature can be reduced, and the reliability of the process and the equipment availability are further enhanced. 
     In order to further decrease the defect density and improve the crystal quality, any structure of the p-type doped ZnO/intrinsic ZnO/n-type doped ZnO structure combination, the p-type doped ZnO/intrinsic ZnO structure combination, the p-type doped ZnO/n-type doped ZnO structure combination, the p-type doped Mg x Zn 1-x O/intrinsic Mg y Zn 1-y O/n-type doped Mg z Zn 1-z O structure combination, the p-type doped Mg x Zn 1-x O/n-type doped Mg y Zn 1-y O/n-type doped Mg z Zn 1-z O structure combination, the p-type doped Mg x Zn 1-x O/p-type doped Mg y Zn 1-y O/n-type doped Mg z Zn 1-z O structure combination, the p-type doped Mg x Zn 1-x O/intrinsic ZnO/n-type doped Mg z Zn 1-z O structure combination, the p-type doped Mg x Zn 1-x O/n-type doped ZnO/n-type doped Mg z Zn 1-z O structure combination, the p-type doped Mg x Zn 1-x O/p-type doped ZnO/n-type doped Mg z Zn 1-z O structure combination, the p-type doped Mg x Zn 1-x O/n-type doped Mg z Zn 1-z O structure combination, the p-type doped Mg x Zn 1-x O/intrinsic Mg y Zn 1-y O structure combination, the p-type doped Mg x Zn 1-x O/intrinsic ZnO structure combination, the p-type doped Mg x Zn 1-x O/intrinsic ZnO/n-type doped ZnO structure combination, the p-type doped Mg x Zn 1-x O/p-type doped ZnO/n-type doped ZnO structure combination, the p-type doped Mg x Zn 1-x O/n-type doped ZnO structure combination, the p-type doped ZnO/intrinsic ZnO/n-type doped Mg z Zn 1-z O structure combination, the p-type doped ZnO/n-type doped ZnO/n-type doped Mg z Zn 1-z O structure combination, the p-type doped ZnO/n-type doped Mg z Zn 1-z O structure combination, the n-type doped ZnO/p-type doped the substrate structure combination, the n-type doped Mg z Zn 1-z O/p-type doped the substrate structure combination, the p-type doped Be x Zn 1-x O/intrinsic Be y Zn 1-y O/n-type doped Be z Zn 1-z O structure combination, the p-type doped Be x Zn 1-x O/n-type doped Be y Zn 1-y O/n-type doped Be z Zn 1-z O structure combination, the p-type doped Be x Zn 1-x O/p-type doped Be y Zn 1-y O/n-type doped Be z Zn 1-z O structure combination, the p-type doped Be x Zn 1-x O/intrinsic ZnO/n-type doped Be z Zn 1-z O structure combination, the p-type doped Be x Zn 1-x O/n-type doped ZnO/n-type doped Be z Zn 1-z O structure combination, the p-type doped Be x Zn 1-x O/p-type doped ZnO/n-type doped Be z Zn 1-z O structure combination, the p-type doped Be x Zn 1-x O/n-type doped Be z Zn 1-z O structure combination, the p-type doped Be x Zn 1-x O/intrinsic Be y Zn 1-y O structure combination, the p-type doped Be x Zn 1-x O/intrinsic ZnO structure combination, the p-type doped Be x Zn 1-x O/intrinsic ZnO/n-type doped ZnO structure combination, the p-type doped Be x Zn 1-x O/p-type doped ZnO/n-type doped ZnO structure combination, the p-type doped Be x Zn 1-x O/n-type doped ZnO structure combination, the p-type doped ZnO/intrinsic ZnO/n-type doped Be z Zn 1-z O structure combination, the p-type doped ZnO/n-type doped ZnO/n-type doped Be z Zn 1-z O structure combination, the p-type doped ZnO/n-type doped Be z Zn 1-z O structure combination, and the n-type doped Be z Zn 1-z O/p-type doped the substrate structure combination can be further annealed at a temperature ranging from 400° C. to 1200° C. after deposition, and the atmosphere can be nitrogen, oxygen, argon, or mixture of nitrogen, oxygen and argon. 
     The atomic layer deposition based process can offer following advantages: 
     1. Low deposition temperatures. 
     2. Precise thickness control, to the degree of one monolayer. 
     3. Accurate control of material composition. 
     4. Facile doping to achieve high doping concentrations. 
     5. High-quality epitaxial layer with low defect density 
     6. Abrupt interface and excellent interface quality for growth of high quality heterojunctions, multiple quantum wells and so on. 
     7. Large-area and large-batch capacity. 
     8. High uniformity. 
     9. Excellent conformality and good step coverage. 
     10. Good reproducibility. 
     Please refer to  FIG. 2 .  FIG. 2  shows the X-ray diffraction pattern of the ZnO layer grown on a sapphire substrate by an atomic layer deposition process. As shown in  FIG. 2 , the ZnO layer formed by the atomic layer deposition process has excellent crystal quality. 
     Please refer to  FIG. 3  through  FIG. 5 .  FIG. 3  shows the spontaneous emission photoluminescence spectrum at room temperature of the ZnO layer grown on a sapphire substrate by an atomic layer deposition process.  FIG. 4  shows the stimulated emission photoluminescence spectra of the ZnO layer grown on a sapphire substrate by an atomic layer deposition process.  FIG. 5  shows the relationship between the photoluminescence light emission intensity and the excitation intensity of the ZnO layer grown on a sapphire substrate by an atomic layer deposition process.  FIG. 5  shows that the light emission intensity increases super-linearly with the excitation intensity, indicating that the stimulated emission occurs at a low threshold intensity of 33.3 kW/cm 2 . The occurrence of stimulated emission indicates that the ZnO layer grown by the atomic layer deposition process has very high crystal quality and very low defect density. This shows, since the atomic layer deposition process offers the advantages such as easy and accurate thickness control, accurate control of material composition, facile doping, abrupt interfaces, high uniformity over a large area, good reproducibility, dense and pinhole-free structures, low deposition temperatures, etc., the semiconductor light-emitting device fabricated by the atomic layer deposition process has very high crystal quality and very low defect density. Besides, the semiconductor light-emitting device can probably induce lasing phenomenon, so the semiconductor light-emitting device can be more extensively utilized. 
     Please refer to  FIG. 6 .  FIG. 6  shows a semiconductor light-emitting device  3  according to an embodiment of the invention. In the embodiment, the semiconductor light-emitting device  3  is a light-emitting diode fabricated by an atomic layer deposition based process. In actual applications, the atomic layer deposition based process can be an atomic layer deposition process, a plasma-enhanced atomic layer deposition process, a plasma-assisted atomic layer deposition process, or combination of above processes. As shown in  FIG. 6 , the semiconductor light-emitting device  3  includes a substrate  30 , a GaN layer  32 , a ZnO layer  34 , and electrodes  36 . In the embodiment, the substrate  30  is a sapphire substrate. In practice, the GaN layer  32  can be a GaN structure grown on the substrate  30  by a metal organic chemical vapor deposition (MOCVD) process. The ZnO layer  34  can be an intrinsic n-type ZnO layer grown on the GaN layer  32  by the atomic layer deposition process. After annealed at the temperature of 950° C. in the nitrogen atmosphere for five minutes, and then deposited with the electrodes  36  by an evaporator, an n-type ZnO/p-type GaN heterojunction light-emitting diode is finished as the semiconductor light-emitting device  3 , as shown in  FIG. 6 . 
     Please refer to  FIG. 7 .  FIG. 7  shows the current density vs. voltage characteristics of the semiconductor light-emitting device  3  shown in  FIG. 6 . From  FIG. 7 , we can see that the semiconductor light-emitting device  3  shows a rectifying characteristic. Please refer to  FIG. 8 .  FIG. 8  shows the X-ray diffraction patterns of the ZnO layer  34  and the GaN layer  32  of the semiconductor light-emitting device  3  shown in  FIG. 6 . As shown in  FIG. 8 , the full-width at half-maximum (FWHM) of the ZnO (0002) Kα1 peak and GaN (0002) Kα1 peak are 0.05° and 0.04°, respectively, suggesting that the crystal quality of the ZnO layer  34  is good and comparable to that of GaN. Please refer to  FIG. 9  and  FIG. 10 .  FIG. 9  shows the photoluminescence spectra of the ZnO layer  34  and the GaN layer  32  of the semiconductor light-emitting device  3  shown in  FIG. 6 .  FIG. 10  shows the electroluminescence spectra of the semiconductor light-emitting device  3  shown in  FIG. 6  at various injection currents. Comparing  FIG. 9  with  FIG. 10 , it can be found that as the injection current is low, electroluminescence originates mainly from the GaN layer  32 ; as the injection current increases, the light emission from the ZnO layer  34  dominates over that from the GaN layer  32 . Accordingly, it is demonstrated that the ZnO-based semiconductor light-emitting device has good light-emitting performance due to the excellent light-emitting characteristics of ZnO. 
     Comparing with prior art, the method according to the invention fabricates a semiconductor light-emitting device by an atomic layer deposition process. Thereby, the method can successfully fabricate high-quality ZnO-based semiconductor light-emitting devices. In addition, since the layer formed by the atomic layer deposition process has several advantages such as easy and accurate thickness control, accurate control of material composition, facile doping, abrupt interfaces, high uniformity over a large area, good reproducibility, dense and pinhole-free structures, low deposition temperatures, etc., the semiconductor light-emitting device has very high crystal quality and very low defect density. Moreover, by the atomic layer deposition process, the semiconductor light-emitting device can be fabricated on large area so as to be more productive, and makes the associated product move competent. Furthermore, since the deposition temperature is relatively low, the damage and/or malfunction probability of equipment owing to high temperature can be reduced, and the reliability of the process and the equipment availability are further enhanced. 
     With the example and explanations above, the features and spirits of the invention will be hopefully well described. Those skilled in the art will readily observe that numerous modifications and alterations of the device may be made while retaining the teaching of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.