Numerical simulation of multiquantum barriers in 630nm laser diodes.

Red-emitting quantum well (QW) 630nm laser diodes have many potential applications in industry and medicine. The main profiteers would be in areas such as the development of critical memory, barcode readers and in the treatment of cancer. The limitation of the low inherent band offsets of the materials used to create such devices, gives rise to a high percentage of electron leakage via thermal activation in the QW active region. However, implementation of Multiquantum Barrier (MQB) into the p-type cladding region of the device enhances the effective conduction band discontinuity, thus increasing the reflection probability of carriers back into the device active region, consequently elevating output power of the laser device. A study of (Al[0.7].Ga[0.3])[0.5]ln[0.5]P/(Al[0.3]Ga[0.7])[0.5]ln[0.5]P (barrier/well) MQB has been investigated as a feasible material structure to enhance electron confinement within laser diodes in the 630nm regime. The structure was optimised theoretically based on the Gamma-X transport mechanisms, using an effective mass approximation and the transfer matrix technique. To accurately model such structures it is important to include possible distortion to the conduction band profiles induced by the different positions of the Fermi level with respect to the vacuum level. Thus, a dual-band device simulator was developed to model the band bending features, of both the Gamma and X minima. This novel simulator simultaneously solves the constituent expressions making up the drift-diffusion equation set, which is then solved iteratively with Schrodinger's equation to yield a self-consistent solution. Using these two simulation models a novel MQB structure is proposed which inhibits electron transmission across it in both the Gamma and X bands. Subsequently, this MQB structure predicts a theoretical effective enhancements of 50% the height of the intrinsic conduction band offset