High-power nano- and picosecond optoelectronic switches based on high-voltage silicon structures with $p$–$n$ junctions. III. Self-heating effects

The self-heating effects of optoelectronic switches based on vertical high-voltage structures with $p$–$n$ junctions (Vertical Photoactivated Semiconductor Switches, VPSS) operating in the high-frequency mode are theoretically studied for the first time. It is shown that the strong temperature dependence of the control-radiation absorbance $\kappa(T)$ is a major factor controlling the maximum switching frequency $f _{\operatorname{max}}$ and the corresponding maximum crystal temperature $T _{\operatorname{max}}$, as well as the temperature $T$ and current density $j$ distributions over the device area. Two-dimensional analysis of the simplest electrothermal model of a VPSS embedded into a double coaxial forming line shows that an increase in the switching frequency $f$ leads to current displacement to the device periphery where the temperature is minimum. However, the $T$ and $j$ distributions over the device area remain stable at $f<f_{\operatorname{max}}$ and $T<T_{\operatorname{max}}$. Certainly, $f_{\operatorname{max}}$ and $T_{\operatorname{max}}$ depend on the control-radiation pulse energy, pulse switching power, and heat-removal conditions. For the VPSS based on indirect-gap semiconductors (Si, SiC), they vary within 20–120 kHz and 120–160$^{\circ}$C which is quite sufficient for practical applications. However, VPSSs based on direct-gap semiconductors (GaAs, InP) are in fact inapplicable to operation in high-frequency modes due to the fact that the dependence $\kappa(T)$ is too sharp.