Theoretical analysis of the influence of the barrier composition on properties of GaInAs/GaInAsP/GaInP laser diodes

Recently 980 nm separate confinement heterostructure (SCH) InGaAs/GaInAsP/GaInP lasers have become of great interest because of potential improvements in threshold current and optical far field divergence over SCH InGaAs/GaAs/GaInP lasers. The authors report the first theoretical study on the influence of barrier composition on threshold current density and the optical far field of GaInAs/GaAs/GaInP and GaInAs/GaInAsP/GaInP SCH lasers. The paper presents the CADILAC model for computer-aided design of aluminium-free GaInAs strained quantum well lasers taking into account in particular the effects of strain on modification of the well band structure. A comparison between theoretical and experimental results is reported. The variations of the threshold current density and the transverse far field divergence versus energy bandgap of the SCH layer in multiple quantum well GaInAs/GaAs/GaInP and GaInAs/GaInAsP/GaInP SCH laser emitting at 980 nm are analysed. It is found that the increase of the bandgap energy of the barrier layer causes only a slight degradation of the radiative current density and a reduction of the far field divergence due to the refraction index decrease of the GaInAsP material and to well broadening in order to allow for the emission at 980 nn. Expecting the decrease in barrier current resulting from better confinement of the carriers in GaInAs/GaInAsP wells, these results tend to confirm the superiority of the InGaAs/GaInAsP/GaInP laser as a candidate for the pump sources of erbium-doped fibre optic amplifiers.