Overheating of an optically triggered SiC thyristor during switch-on and turn-on spread

A simple adiabatic model of the switch-on and turn-on spread in an optically triggered SiC thyristor has been developed. The model makes it possible to evaluate the overheating of the structure with consideration for the switched current $I_{\mathrm{max}}$, the rate of current increase $dI/dt$, the power/energy of the UV light source used for switching, the area initially switched-on by light, and the switch-on time constant $\tau$ of the thyristor. The applicability of the adiabatic approximation to evaluation of the device overheating is substantiated. It is shown that the instantaneous maximum power density is approximately inversely proportional to the area of the initially switched-on portion of the thyristor. The estimates obtained demonstrate that, to preclude the inadmissible overheating of the structure, the maximum current density during switch-on, $j_{\mathrm{max}}$, should not exceed $\sim$(2–3) $\sim$ 10$^4$ A cm$^{-2}$. With $j_{\mathrm{max}}\approx I_{\mathrm{max}}/\pi r^2_0\approx U_0/\pi r^2_0R_l$ taken for estimation, it is possible to estimate the radius of the optical window $r_0$ for a given voltage $U_0$ at which the structure is switched on and a chosen load resistance $R_l$.