Cavity length and temperature dependent characteristics of compressively strained InGaAsP MQW BH lasers with a two-step compositional SCH structure

Abstract

We investigated the cavity length and temperature dependence of the device characteristics for 1.5 µm InGaAsP/InGaAsP multiple quantum well lasers with a two-step compositional separate confinement heterostructure by eptiaxial regrowth. The device parameters, such as internal optical loss, internal quantum efficiency, transparency current density and modal differential gain, were estimated by fittings to experimental values of threshold current density and slope efficiency as a function of cavity length. Under continuous wave (CW) mode at 25 °C, the uncoated 600 µm long laser emitted a maximum output power of 22 mW with a threshold current of 9.3 mA and a slope efficiency of 0.17 mW mA−1, and it operated up to 97 °C. The full-width at half-maximum values of far-field patterns with a single lobe remained almost constant, indicating ∼18.7° (horizontal) × 24° (vertical) at 25 °C over a wide range of injection current. In terms of maximum CW operating temperature, the optimum cavity length is governed by the trade off between emitting volume and internal temperature of lasers, leading to a temperature of 116 °C at a cavity length of 900 µm. By applying a high-reflectivity coating, based on an Au/Ti metallic mirror with an insulation layer of SiO2, on the rear facet of lasers, the device performance was significantly improved due to the reduced mirror loss without degradation of electrical properties, resulting in a high output power of 36 mW and a low threshold current of 7.8 mA and with a slope efficiency of 0.263 mW mA−1 under CW mode at 25 °C for the 600 µm long cavity.