High-brightness blue- and green-LEDs and high-power violet LDs have been achieved. In these devices, GaInN-based QWs are usually used as an active layer grown on a thick GaN template layer. However, the efficiency of green LEDs is not satisfactory and green LDs have not been realized yet. Many reports have been published on LEDs grown on nonpolar nitride planes, such as a- and m-plane, because the problem of the internal electric field can be solved in principle. However, regarding the efficiency of green LEDs and the realization of green LDs, the generation of mismatch-induced defects is another severe problem. In this report, we discuss about the importance of the strain control in GaInN/GaN MQWs for achieving high-performance green-light emitters. We fabricated GaInN/GaN MQWs on a high-crystalline-quality thick m-plane GaInN underlying layer, and the integral PL intensity was compared with that of identical GaInN/GaN MQWs on a high-crystalline-quality m-plane GaN underlying layer. The dislocation and stacking fault densities of thick GaInN on m-plane grooved GaN and m-plane GaN are of the same order: 10⁷ cm^-2 and 10⁴ cm^-1, respectively. The light emission wavelengths from the MQWs were violet (~396 nm), blue (~450 nm), and green (~535 nm). The integral PL intensities obtained from the GaInN/GaN violet, blue, and green MQWs on the high-quality thick GaInN underlying layer were 1.1, 1.5, and 2.1 times higher than these obtained from the MQWs on the m-plane GaN underlying layer, respectively. This result clearly shows that the use of an almost perfectly relaxed GaInN template is essential for improving the PL efficiency in the long-wavelength (green) region, which is expected to lead to the improved performance of green-light emitters.

Acknowledgement: This study was partly supported by the Knowledge Cluster Initiative (2nd stage), Tokai region and the Ministry of Education, Culture, Sports, Science and Technology (Grant-in-Aid for Young Scientists (A), # 21686034).

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