The silicon controlled rectifier (SCR) is a member of which family?

The Silicon Controlled Rectifier (SCR) belongs to a broad class of solid-state semiconductor devices known as thyristors. Thyristors are characterized by their four-layer (PNPN) construction and their ability to act as high-speed, heavy-duty electronic switches. Varistors are voltage-dependent resistors used for surge protection, and varactors are diodes used as voltage-controlled capacitors. Neither shares the four-layer switching characteristics of an SCR. A phase-locked loop (PLL) is an entire electronic circuit or system used for frequency control, not a family of individual discrete semiconductor components like the thyristor family.