Fig. 1. Structure schematic and COMSOL simulation results. (a) Schematic of semi-insulated surface-plasmon buried grating first-order distributed feedback terahertz quantum cascade laser; (b) schematic of buried grating in cross section(x-y plane); (c) distribution of calculated electric field E_y of the high-frequency mode and low-frequency mode along the cross-section of laser (x-y plane); (d) impact of the etching depth on loss and the frequency of high-fr

Fig. 2. Simulation results of two band-side modes. (a) High-frequency mode and (b) low-frequency mode changes in longitudinal distribution of real part of E_y with different corrosion depths; (c) high-frequency and low-frequency modes loss caused by n⁺ GaAs layer with different corrosion depths

Fig. 3. Simulated |E_y| distribution of low frequency mode and high frequency mode in the x-y plane, when N_slit=200, d_etch=600 nm

Fig. 4. Simulation results of the mode in the x-y plane. (a) Normalized distribution of |E_y|² of longitudinal fundamental mode of buried grating at the center of active region of high-band side mode with different etching depths along the length of laser cavity; (b) power flow distribution along the x direction in the resonant cavity when d_etch=400 nm, 600 nm, 800 nm, and 1000 nm

Fig. 5. SEM pictures and test results of the devices. (a) SEM pictures of 1st-DFB-THz-QCL semi-insulated surface-plasmon buried grating; (b) emission spectrum of a typical buried grating 1st-DFB-THz-QCL, the grating period is 12.4 μm, N_slit=200, and the driving current is 2.16 A; (c) Linear relationship between different grating periods and laser wavelength; (d) emission spectrum of a typical single-mode laser under different driving currents in the dynamic range

Fig. 6. Test results of the devices. (a) Test results of voltage-current-power characteristics of single-metal waveguide F-P cavity laser (illustration shows the spectrum of the laser at the maximum pump current); (b) test results of voltage-current-power characteristics of buried grating single-mode devices (illustration shows the spectrum of the laser under different pump currents)