A method is presented for forming a monolithically integrated semiconductor device. The method includes forming a first device including first hydrogenated silicon-based contacts formed on a first portion of a semiconductor material of an insulating substrate and forming a second device including second hydrogenated silicon-based contacts formed on a second portion of the semiconductor material of the insulating substrate. Source and drain contacts of the first device are formed before a gate contact of the first device and a gate contact of the second device is formed before the emitter and collector contacts of the second device. The first device can be a heterojunction field effect transistor (HJFET) and the second device can be a (heterojunction bipolar transistor) HBT. The HJFET and the HBT are integrated in a neuronal circuit and create negative differential resistance by forming a lambda diode.