Silver-Based Double Metal Waveguide For Terahertz Quantum Cascade Laser

We have designed and fabricated terahertz quantum cascade lasers (THz QCLs) with double metal waveguide (DMW) based on three and four-quantum well GaAs/Al0.15Ga0.85 As active module with resonant-phonon depopulation scheme. Three-well and four-well THz QCLs have a lasing frequencies of 3.2 THz and 2.3 THz, respectively. We investigate the dependence of threshold current and lasing output power on temperature for fabricated THz QCL. We propose to use DMW based on silver (Ag) for reducing the losses of the waveguide. The spectra of the loss coefficient of the DMW based on Au and Ag are calculated. It is shown, that the use of Ag-based DMW allows to reduce losses by 2-4 cm(-1) in comparison with Au-based DMW. Taking into account the absorption of THz radiation by free carriers and optical phonons, the spectrum of total mode losses has a wide minimum in the region of 3-6 THz, which shifts to the high-frequency region of the spectrum with increasing temperature. The postgrowth processing for THz QCL with Ag-Ag DMW are studied.