FIGS. 1 to 3 are drawing illustrating a III-nitride compound semiconductor light emitting device according to the prior art. Specifically, FIG. 1 is a cross-sectional view of the III-nitride compound semiconductor light emitting device, FIG. 2 is an energy band diagram showing that the active layer 13 has an InGaN/GaN multiple-quantum-well structure, and FIG. 3 is an energy band diagram showing that the active layer 13 has an InGaN/InGaN multiple-quantum-well structure.
Referring to FIG. 1, to fabricate a nitride compound semiconductor light emitting device according to the prior art, the buffer layer 11, the n-InxAlyGazN layer 12, the active layer 13, the p-InxAlyGazN layer 14 and the transparent electrode layer 15 are successively formed on the substrate 10. Then, mesa etching is performed in such a way to expose the n-InxAlyGazN layer 12. Next, the transparent electrode layers 16 and 17 are formed on the exposed portion of the n-InxAlyGazN layer 12 and the transparent electrode layer 12, respectively. Then, the passivation film 18 is formed on the device. In this respect, x, y and z in InxAlyGazN forming the layers 12 and 14 satisfy the following conditions: x+y+z=1, 0≦x<1, 0≦y<1, and 0<z≦1.
As shown in FIG. 2, the active layer 13 has an InGaN/GaN multiple-quantum-well structure having an alternate stacking comprising the InGaN quantum well layers 13b and the GaN barrier layers 13a. Alternatively, as shown in FIG. 3, the active layer 13 has an InGaN/InGaN multiple-quantum-well structure of an alternate stacking comprising the InGaN quantum well layers 13b and the InGaN barrier layers 13a′. In the InGaN/InGaN multiple-quantum-well structure, the barrier layers 13a′ have a lower indium (In) content than that of the quantum well layers 13b. 
The InGaN/GaN multiple-quantum-well active layer as shown in FIG. 2 has an advantage in that it is more stable in high-current operation or high-temperature operation than InGaN/InGaN. This is because the energy band gap of GaN forming the barrier layers 13a is higher than that of the barrier layers 13a′, leading to an increase in the efficiency of recombination between electrons and holes.
However, the InGaN/GaN multiple-quantum-well active layer has a limitation in that the GaN barrier layers 13a should be grown at low temperature since the growth temperature of the InGaN well layers 13b is about 200-350° C. lower than the general growth temperature of high-quality GaN. This makes it difficult to make the GaN barrier layers 13a with high quality levels. Another disadvantage is that the strain of the InGaN well layers 13b and the GaN barrier layers 13a needs to be optimized only with-the thickness of the InGaN well layers 13b and the GaN barrier layers 13a. 
In the other hand, in the case of the InGaN/InGaN multiple-quantum-well active layer as shown in FIG. 3, the barrier layers 13a′ are also made of InGaN so that the InGaN barrier layers 13a′ with high quality can be made at a growth temperature range similar to that of the InGaN well layers 13b. The InGaN barrier layers 13b made of the same material as the InGaN well layers 13b provide growth surfaces of the next well layers so that the InGaN well layers 13b with high quality can be obtained, leading to a light emitting device having high quantum efficiency.
However, the InGaN/InGaN multiple-quantum-well active layer has a disadvantage in that it has low stability in high-current or high-temperature operations as compared to the InGaN/GaN multiple-quantum-well layer. In an attempt to overcome this disadvantage, a p-AlGaN electron-blocking layer is generally formed on the active layer so as to increase the high-temperature stability and efficiency of the active layer. However, this approach has a disadvantage in that, in epitaxial growth of the nitride compound, the deposition of an aluminum (Al)-containing nitride compound, which is difficult to remove easily, occurs within a reactor. This results in a great reduction in mass production.
Another disadvantage with the InGaN/InGaN multiple-quantum-well active layer is that the performance and properties of a light emitting diode including the active layer are sensitive to a small change in, the indium composition of the InGaN barrier layer 13a′ thus making the mass production of the diode difficult.
Trimethy indium (TMIn) is mainly used as a precursor for indium. It has a melting point of 88° C. and is solid at room temperature. Thus, growing a material with the precursor maintained at a constant composition is relatively difficult compared to other precursors. Particularly, a small change in the indium composition in the barrier layers 13a′ is difficult to detect even by a nondestructive measurement system, such as a PL (photoluminescence) or XRD (X-ray Diffraction) system, and thus, causes a difficulty in quality control and has a great effect on the production of prior products.
As described above, the existing typical InGaN/GaN multiple-quantum-well layer and InGaN/InGaN multiple-quantum-well layer have advantages and disadvantages, which are contrary to each other.