Current flow through an InGaN/GaN/AlGaN multi-quantum well (MQW) laser diode is simulated. We found that electron overflow to the AlGaN p-cladding layer is very large, which prevents the current injection into the MQW layers. We clarified that the electron overflow occurs easily in nitride lasers because of three intrinsic reasons; poor hole injection due to the small hole mobility and thermal velocity, the small conduction band offset for InGaN/GaN, and the high threshold carrier density. We show that the Al composition and the p-doping of the AlGaN p-cladding layer is of critical importance to obtain laser oscillation by current injection.

We investigated the growth rate enhancement in selective area metalorganic vapor phase epitaxy with a new surface boundary condition for the vapor phase concentration of source materials. In our model, the growth rate is proportional to the vapor phase concentration at a distance of the vapor phase mean-free path of source materials from the substrates, and the vapor phase concentration is laterally uniform at the top of the stagnant layer. This model predicts that the growth rate modulation produced by mask-patterning disappears at a specific pressure at which the vapor phase mean-free path reaches the stagnant layer thickness. We controlled the vapor phase mean-free path of trimethylindium in InP growth by varying the growth pressure from 6 to 180 Torr with a fixed total inlet gas flow rate to the reactor. Experiments showed a great reduction of the growth rate enhancement with the decrease in the growth pressure and the growth rate enhancement virtually disappeared at the lowest pressure. We also investigated the dependence of the stagnant layer thickness on the mask design. The experimental stagnant layer thickness related to the typical surface length, such as the period of mask-patterning.