| Research Abstract |
In the growth of group III nitride on sapphire substrate by metalorganic vapor phase epitaxy, low temperature buffer layer technique, which was established by us in 1986, is commonly used. High-brightness blue and green light emitting diodes and violet laser diode have been commercialized based on the low temperature buffer layer technique. In these devices, GaInN is used as the active layer. Compositional fluctuation of the GaInN is thought to form by the difference of the surface energy. The size of each domains formed by the compositional fluctuation is thought to be a few nm to tens of nm range. High In compositional domain formed by this fluctuation is thought to act as a hole capture center, thereby screening the effect of high density threading dislocations. This domain structure is thought to be effective to fabricate high-efficiency light emitting diode. However, this domain seriously affects the performance of the laser diode by widening the gain spectrum, thud decreasing the peak gain. Large piezoelectric field which separates electrons and holes inside the well layer also prohibits realization of green laser diode based on nitride semiconductors.
In the first fiscal year, luminescent property of GaInN based multi quantum well structure was studied in detail. We found that no compositional fluctuation occurred in our sample. In the second fiscal year, we found that luminescent property of GaInN-based multi quantum well was not affected by the compositional fluctuation, but was affected by the surface depletion. This new finding is very important as a mile stone of the fabrication of green laser diode based on group III nitride semiconductors.
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