Ohmic contacts for room-temperature AlGaAs/GaAs quantum cascade lasers (QCL)

This paper reports on the results of optimization of the ohmic contacts for GaAs/AlGaAs quantum cascade lasers (QCLs). Technological parameters during the optimization procedure concerned time and temperature of thermal processing as also the ratio of metallic layers thickness. The main goal of this work was to obtain stable ohmic contacts with low resistance and a smooth surface. Circular transmission line method (CTLM) was applied for the electrical characterization of the Ni/AuGe/Ni/Au and AuGe/Ni/Au metallization systems. Transmission electron microscopy (TEM) method was used for the characterization of microstructures. Elements concentration in layers was determined by the energy dispersive X-ray spectroscopy (EDXS). The best results for the specific contacts resistivity, thermal stability and morphology were obtained when the Ni/AuGe/Ni/Au and the AuGe/Ni/Au systems were processed at 440 degrees C and 400 degrees C, respectively.