An apparatus includes transistor and a set of one or more serially-connected diodes coupled to the transistor. The transistor includes a gate, and first and second terminals. A first diode in the set of serially-connected diodes has a first terminal connected to the second terminal of the transistor. At least one of the diodes includes a first layer including silicon having a first type of carrier as its majority carrier, a first terminal, and a second terminal. The first terminal includes a second layer formed on the first layer, a third layer comprising amorphous hydrogenated silicon having a second type of carrier as its majority carrier formed on the second layer, and a conductive layer formed on the third layer. The second terminal includes a fourth layer comprising crystalline hydrogenated silicon of the first carrier type formed on the first layer, and a conductive layer formed on the fourth layer.