Graded InGaAs/GaAs strained-layer single quantum well laser

Abstract

A new graded InxGa(1−x)As/GaAs/AlGaAs strained-layer single quantum well (QW) laser diode has been proposed and experimentally characterized. Bias-dependencies of valence subbands and maximum optical gains of the InGaAs QW on the external bias are calculated taking into account the effects of the valence band mixing and intraband relaxation. Electron distributions in the conduction bands at threshold bias are also calculated by solving the Poisson and Schrödinger equation self-consistently. By a two-step grading of the InGaAs QW compositions, the higher peak value and smaller full width at half maximum of electron distributions can be obtained around the QW center even at the large external bias. Moreover, the electron-hole spatial separation is substantially reduced in the graded QW. A graded InxGa(1−x)As/GaAs strained-layer single QW laser diode with x=0.17–0.33 shows lower threshold current densities by 15% than those of the conventional In0.25Ga0.75As laser.