Electronic Devices - BJT Devices - Discussion

3 layers.

Silicon dioxide sio2 insulating layer and gate layer/conducting layer.

Layers means?

The doping results in a material that either adds extra electrons to the material (which is then called N-type for the extra negative charge carriers) or creates "holes" in the material's crystal structure (which is then called P-type because it results in more positive charge carriers). The transistor's three-layer structure contains an N-type semiconductor layer sandwiched between P-type layers (a PNP configuration) or a P-type layer between N-type layers (an NPN configuration).

What does it mean the word of (layer) ?

Three layers are amorphous silicon, dielectric/insulator and gate material.

I dont know what is meant by a layer in the device. As far as i know, emitter,collector anb base are the three terminals of a bjt device.

Emitter, base, collector.