Performance Modeling of Silicon Carbide Photoconductive Switches for High-Power and High-Frequency Applications

In this article, we focus on the physical modeling of the nonlinear operation of intrinsic photoconductive semiconductor switches (PCSS) based on 4H-SiC using coupled electrical and optical simulations to provide performance bounds of the switch as a function of material and geometry parameters, as well as applied bias. We also conduct a full design-space exploration to identify the optimal operating and design conditions to maximize the compound metric f
_op
P
_out
, where f
_op
is the maximum operating frequency, and Pout is the maximum output power the switch can provide. We quantify that a 10-μm long and 5-μm thick 4H-SiC PCSS can deliver output power density greater than 2W/mm at 150 GHz when triggered by a 0.325-μm laser with intensity of 3 kW/cm
²
. The output power density can be significantly enhanced by increasing the optical generation rate as well as by using thicker SiC to improve its absorption characteristics. A brief discussion of signal distortion and electrostatic screening effects at high optical bias is included. Finally, we present an analytic model of charge cloud propagation and the frequency of operation based on the physics, material parameters, and geometry of the PCSS. The model accurately captures f
_op
of 4H-SiC PCSS over a broad range of laser spot size, device length, and electrical bias applied at the contacts.