Effect of active layer thickness on differential quantum efficiency of 1.3 and 1.55 μm InGaAsP injection lasers

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Abstract
The dependence of differential quantum efficiency (ηd) on active layer thickness (d) for 1.3 and 1.55 μm InGaAsP buried crescent (BC) injection lasers has been measured. A comparison of the results shows that ηd for 1.55 μm lasers increases more rapidly with decreasing d than ηd for 1.3 μm lasers. The significantly different dependence of ηd on d in BC lasers suggests that the optical absorption in the active region of InGaAsP lasers is strongly wavelength dependent. This gives the important practical conclusion that the ηd for 1.55 μm lasers can be significantly improved by reducing d, whereas the ηd for 1.3 μm lasers can only be slightly improved by reducing d. As a result of ηd vs d investigation, we have obtained high performance 1.3 and 1.55 μm BC lasers which exhibit threshold currents as low as 9 mA at 25 °C, high‐temperature operation (up to 100 °C), and ηd over 65% (1.3 μm) and 45% (1.55 μm).