Si-Sam Park

Comparative investigation of InGaN quantum well laser diode structures grown on freestanding GaN and sapphire substrates

Comparative analysis of optical characteristics of In0.08Ga0.92N∕In0.03Ga0.97N multiquantum well (MQW) laser diode structures grown on freestanding GaN and on sapphire substrates is reported. Higher quantum efficiency, higher thermal activation energy, smaller Stokes-like shift, and shorter radiative lifetime are observed for InGaN MQWs on GaN substrate than those of the same MQWs on sapphire substrate. From time-resolved optical analysis, we find that not only an increase in nonradiative lifetime due to reduced dislocation density but also a decrease in radiative lifetime caused by suppressed piezoelectric field play an important role in enhancing optical properties of InGaN MQWs on GaN substrates.

Intervalley splittings of Si quantum wells

Intervalley splittings of Si quantum wells are studied using a multivalley effective mass theory and a finite element method. It is found that the contributions to the valley splitting mainly come from the quantum well interfaces and the external field. Especially the derivatives of the confinement potential which appears in the valley coupling Hamiltonian cause the periodic oscillation of the splitting with the well width. Theoretical predictions are in reasonably good agreement with the recent experimental observation of valley splitting in a SiO2/Si/SiO2 quantum well, which proves the validity of our approach.