Study and analysis of the optical absorption cross section and energy states broadenings in quantum dot lasers

Abstract

In this report, we measured experimentally the modal absorption spectra of the InP and InAsP quantum dot (QD) lasers using multi-section device technique. The optical absorption cross section ( ${\text{σ}}_0$ ) and inhomogeneous broadening for the ground state (GS) and excited state (ES) were analyzed and calculated theoretically from the absorption spectra. The results showed that the InP QD laser exhibited ${\text{σ}}_0$ to be $1.347\times {10}^{-14}{\text{cm}}^2.\text{eV}$ and $3.016\times {10}^{-14}{\text{cm}}^2\text{eV}$ for GS and ES respectively, whereas for the InAsP QD material it was found as $0.511\times {10}^{-14}{\text{cm}}^2\text{eV}$ and $3.099\times {10}^{-14}{\text{cm}}^2.\text{eV}$ for GS and ES respectively. Moreover, the inhomogeneous broadening in the GS increases from 35.6 eV to 63.6 eV when As was added to InP QD, similarly, the inhomogeneous broadening of ES increases from 46.9 eV to 103.8 eV. The alloying InP QDs with arsenic decreases the ${\text{σ}}_0$ of the ground state (lasing state) and increases both inhomogeneous and linewidth broadenings. This finding may help the grower to control the growth conditions and the molecule fractions of the crystal to improve the spectral properties of the optoelectronics devices.

Keywords: Absorption cross section; Inhomogeneous broadening; Linewidth broadening; Quantum dot laser.