The anode and cathode of the electron tube are disconnected, similar to the positive and negative poles of a battery pack. There is a heating filament at the cathode. When it is working, the filament starts to heat the cathode. When the cathode atoms are heated to an excited state, the cathode starts to emit electrons to the anode, and the circuit is turned on. On the contrary, when voltage is applied to the anode, the circuit cannot be turned on, and unidirectional conductivity is obtained.
The transistor is composed of a P-type semiconductor connected to an N-type semiconductor. The P-type semiconductor is made of pure tetravalent elements doped with trivalent elements, and contains more positively charged carriers—holes; N-type semiconductors are made of pure It is made of tetravalent elements doped with pentavalent elements, and contains more negatively charged carriers-electrons. But these two are electrically neutral separately. After the two are connected, due to diffusion, part of the positive charge carriers of the P-type semiconductor goes to the N-type side, and part of the negative charge carriers of the N-type semiconductor goes to the N-type side. The P-type is over there. In this way, a PN junction is formed at the junction. One side is positively charged and the other is negatively charged, forming an internal electric field. Such an electric field prevents further diffusion of holes and electrons. When the transistor is connected to a positive or negative voltage, it will cause the PN junction to widen or narrow, thereby forming a weaker or stronger internal electric field, and the diode is turned on or off. In this way, unidirectional conductivity is obtained.
