AlGaAs/GaAs Terahertz Quantum Cascade Laser with Gold-Based Metal - Metal Waveguide

In this chapter, we report the fabrication of Al0.15Ga0.85As/GaAs similar to 3 THz frequency quantum cascade laser (QCL). Its operation is based on 3-quantum-well (3QW) modules, where the GaAs QWs are separated by Al0.15Ga0.85As barriers. The laser's active region is build by stacking the 228 modules. The lasers were fabricated as gold-gold waveguide devices and were gold-gold mounted on GaAs receptor wafers. The 300 nm Au/5 nm Ti claddings were made by sputtering, for which we used 8 x 10(-3) mbar pressure level and 50 W generator power. The wafer-bonding process was performed in the temperature range 350-400 degrees C. The structures were wet etched into ridges with widths in the range 50-160 microns and lengths 1.8 mm. The lasers operated with threshold current densities similar to 650 A/cm(2) at 77 K, when fed by 100-300 ns current pulses supplied with 300-1000 Hz repetition frequencies.