Improvement in threshold of InGaNGaN quantum-well lasers by p -type modulation doping

The optical properties of modulation-doped InGaNGaN laser diodes are theoretically studied with the effects of electron spillover from quantum wells considered. We use a six-band model including the strain effect for calculating valence band states. The continuous subbands are treated by a dense discretization for the electrons spilling from the quantum wells. The calculation results show that the threshold current can be significantly reduced by p -type modulation doping around the wells but not by n -type doping, supposed that the layers are of a perfect quality and the impurity-induced defects are ignored. Also, the p -type modulation doping can make the threshold current more insensitive to the cavity loss compared with other cases. An optimized threshold current density can be achieved for single-quantum-well lasers by introducing p -type dopants. However, the dopant concentration is high and may be inaccessible. For double-quantum-well lasers an optimized low threshold current can be achieved with a slighter and practicable p -type doping level.