Effect of active layer thickness on differential quantum efficiency of 1.55 μm InGaAsP buried crescent injection lasers

Comprehensive measurements of the differential quantum efficiency (ηd ) dependence on the active layer thickness (d) for 1.55 μm InGaAsP buried crescent (BC) injection lasers are presented. The results show that ηd increases rapidly as d decreases. The strong d dependence of ηd in 1.55 μm BC lasers suggests that a large value of optical absorption in the active region is one of the dominant mechanisms which determines the ηd of these InGaAsP lasers. The likely cause for large absorption in the active region is intervalence band absorption (IBA). Thus, by reducing the active layer thickness and hence, the effect of IBA, we have obtained 1.55 μm BC lasers which exhibit threshold currents as low as 9 mA at 25 °C, ηd over 45%, and high-temperature operation up to 100 °C.