Processing of deeply etched GaAs/AlGaAs quantum cascade lasers with grating structures

Gratings in GaAs/AlGaAs mid-infrared quantum cascade lasers (QCLs) are fabricated with a structure depth of more than 10 mu n. A N-2/SiCl4 inductively coupled plasma reactive ion etching (ICP-RIE) process was employed to achieve extremely smooth sidewalls and selectivities to the SiNx etch mask of up to 70: 1. EDX spectra measured on as-etched samples show that sidewall etch inhibition is caused by a thin Si containing layer on the sidewalls that is formed simultaneously with ICP etching of GaAs at the bottom of the trenches. To demonstrate device application gratings with a pitch of 1.72 mu m are applied to long rib waveguide-based QCLs; emitting at lambda = 10.7 mu m. When etched laterally together with the rib the grating gives rise to stable single mode emission up to 295K from these QCLs. The respective grating coupling coefficient is determined to be kappa = 29 cm(-1).