Dynamic modulation and impedance characteristics of a terahertz quantum cascade laser

The modulation and impedance properties of a terahertz (THz) quantum cascade laser (QCL) are investigated theoretically based on a three-level rate equation model. The effect of different device parameters, namely, facet reflectivity, injection efficiency, spontaneous emission factor, and operating current, on the modulation and impedance characteristics of the QCL is analyzed in detail. The device shows a maximum modulation bandwidth (f(3dB)) of 21 GHz and an intrinsic impedance of 3.8 m? when operating under the designed conditions. The modulation bandwidth and impedance increase with the increase in facet reflectivity and injection efficiency. However, the modulation bandwidth increases but the impedance decreases with the increase in operating current. The spontaneous emission factor has no effect on both the modulation bandwidth and impedance. The theoretical model will aid in the design of THz QCLs requiring a large modulation bandwidth and the external circuit design to match the standard 50 ? source for reducing reflections and improving the coupling efficiency.