Direct comparison of optical properties and carrier dynamics of InGaN multiple quantum well (MQW) laser diode structures grown on pendeo epitaxial (PE)-GaN and sapphire substrates is reported. A strong increase in quantum efficiency and a dramatic reduction in stimulated emission threshold are observed for InGaN MQWs on PE-GaN substrates as compared to MQWs on sapphire substrates. Based on temperature-dependent time-resolved optical analysis, the authors find that a significant increase in nonradiative lifetime due to suppressed dislocation density plays an important role in enhancing optical properties of InGaN MQWs grown on PE-GaN substrates, resulting in radiative-process dominant emission even at room temperature. (c) 2007 American Institute of Physics.