An apparatus includes a junction field-effect transistor (JFET) and a set of one or more serially-connected diodes. The JFET includes a first layer including silicon of a first conductivity type, a gate, and first and second terminals. The gate includes a second layer formed on the first layer and including intrinsic amorphous hydrogenated silicon, a third layer formed on the second layer and including amorphous hydrogenated silicon of a second conductivity type, and a conductive layer formed on the third layer. Each of the first and second terminals includes a fourth layer formed on the first layer, the fourth layer including crystalline hydrogenated silicon of the first conductivity type, and a conductive layer formed on the fourth layer. Each of the serially-connected diodes has first and second terminals, a first of the serially-connected diodes having the first terminal connected to the second terminal of the JFET.