A study of internal absorption in Zn(Cd)Se/ZnMgSSe semiconductor lasers

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Abstract
Based on two different experiments and an optical field calculation, we show that the free‐carrier absorption αfc in Zn(Cd)Se/ZnMgSSe semiconductor lasers is about 4 cm−1 and that it is smaller than that of GaAs/AlGaAs semiconductor lasers. We have measured the dependence of the L‐I characteristics on the cavity length of double heterostructure (DH) lasers under photopumped operation and of single quantum well‐separate confinement heterostructure (SQW‐SCH) lasers under current‐injected operation. For the DH laser, the total absorption coefficient αi and β×J0 product (β is a gain constant, and J0 is the nominal current density that makes the gain equal to zero) are estimated to be 4.2 cm−1 and 8.6×10 cm−1, respectively. For the SQW‐SCH laser, αi, β, and J0 are estimated to be 21 cm−1, 4.23×10−3 cm×μm/A, and 1.9×10−3 A/(cm2×μm), respectively. By calculating the optical fields of these lasers, we have estimated that the absorption in a GaAs substrate is 16.53 cm−1 in the SQW‐SCH laser and that it is negligible in the DH laser. We have shown that the large loss in the SQW‐SCH laser is caused by both αfc and the absorption in the substrate and that αi in the DH laser is caused only by free carrier absorption.