Optical EngineeringTemperature insensitivity of the threshold current density in exciton-dominated wide energy gap quantum wire lasers
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We present simulations on temperature dependence of the threshold current density (Jth) in InGaN-AlGaN and ZnCdSe-ZnMgSSe quantum wire lasers having exciton transitions. We find that Jth in a quantum wire laser is insensitive to temperature variation when exciton binding energies are in the range of 30 to 50 meV. This behavior is similar to quantum dot lasers having free carrier transitions. We show that the temperature dependence of the threshold current density is greatly reduced in lasers having exciton transitions in comparison to the ones having free carrier transitions. The reduced dependence of Jth on the temperature is attributed to the inherent confinement of electron-hole pairs within the exciton radius along the wire axis, whereas the quantum wire cross section provides confinement of carriers in the plane perpendicular to the wire axis. The large exciton binding energies give rise to high exciton density of states and narrow spectral line width, thus confining the carriers into a pseudoquantum dot-like structure. The effect of exciton localization due to the randomness in quantum wire fabrication, causing exciton inhomogeneous line broadening, is also discussed.