Effect of doping profile on the output power of broadly tuneable InGaAsP/InP asymmetric multiple quantum well lasers: finite element method simulations and experimental results

Broadly tuneable InGaAsP/InP asymmetric multiple quantum well (AMQW) ridge waveguide laser diodes suffer from low output power. Theoretical and experimental studies to understand the effect of doping profile on the laser output power and to solve the output power problem without affecting the tuning range of the laser are reported. A commercially available partial differential equation solver, FlexPDE, was used to solve the main equations for flow of current and hence simulate the AMQW devices. The simulations, which were validated with published data, showed poor current injection efficiency to the centre of the active region. The simulations identified the ridge structure as the main reason for this poor current injection efficiency. Since the ridge structure is an essential part of this type of laser diode, effort was put forth to reduce the effect of the ridge structure on the current injection efficiency by optimising the doping profile of the device. Both simulation and experimental data showed that extending the doping profile closer to the active region would improve significantly the current injection efficiency consequently, the output power without affecting the tuning range of the device. Over all, the Flex PDE solver showed potential to handle laser diode design problem.