Semiconductors: Intrinsic, N-Type, P-Type, and PN Junctions Explained
Semiconductors: Intrinsic, N-Type, and P-Type
Intrinsic semiconductors are semiconductors with no impurities. They are characterized by having 4 electrons in the last layer of atoms and form a stable structure, binding to the neighboring atoms with covalent bonds, sharing 4 pairs of electrons.
Semiconductor N-Type
An N-type semiconductor is extrinsic, i.e., containing a number of impurities. If some atoms with 5 electrons in their last layer are added to a pure semiconductor (intrinsic), these atoms have an unbound electron in the crystal structure, which can move easily within the semiconductor to increase its conductivity, which depends on the number of impurity atoms. This will form an N-type semiconductor.
P-Type Semiconductor
A P-type semiconductor is created when atoms containing 3 electrons in the last layer are added as impurities to an intrinsic semiconductor. In the crystal structure, these atoms lack an electron to make a link, so a hole appears. This creates a P-type semiconductor.
PN Junction
A PN junction is the union of a P-type semiconductor with an N-type semiconductor. In the bonding process, some electrons move from the N-type to the P-type semiconductor and recombine with the holes in the semiconductor, creating a barrier layer in which there are no free electrons or holes.
Polarization
Direct Polarization: This involves connecting the positive terminal of the generator to the P-type semiconductor and the negative terminal to the N-type semiconductor. Due to the applied voltage being greater than the voltage, the electrons in the N-type semiconductor diffuse across the junction to the P-type semiconductor, and then pass through the conductor to the positive pole of the generator, while the negative supply provides electrons to the N-type semiconductor.
Reverse Polarization: This involves connecting the positive terminal of the generator to the N-type semiconductor and the negative terminal to the P-type semiconductor. Due to the applied voltage, the free electrons in the N-type semiconductor are attracted to the positive terminal of the battery, widening the barrier layer and practically preventing the passage of electrons through the junction. However, there is a very low current intensity through the union, due to electrons flowing from the links due to the effect of temperature.
Diode Ratings
Direct Current Rating: Max. Instant. AC. The diode can be burned by the Joule effect if the direct current flowing through it in continuous operation is over rated.
Nominal Reverse Voltage: Max. reverse voltage withstand without driving the diode. If the reverse voltage applied to the diode in continuous operation is over rated, the diode is rendered conductive, breaking the crystalline structure and deteriorating the junction.
Phase Bridge
A phase bridge consists of 2 pairs of rectifying diodes connected in parallel with the load. A central point of the 2 pairs of diodes connects the AC voltage supply. Each pair of diodes conducts current during a half period, with always two diodes being forward-biased and two reverse-biased, which is why during each alternation of the AC voltage applied by the load, a current circulates in the same way.
Transistor as a Switch
The transistor as a switch: In the transistor, a high current is achieved in the collector when a small current flows through the base terminal, indicating that the transistor is saturated. To stop the current around the base terminal, the transistor ceases to be a driver, indicating that the transistor is off. This feature can be used to operate the transistor as a switch with a load connected to the collector. The load current will flow only if bias is applied to the base-emitter junction. Disconnecting the circuit’s power base, the load electric current stops flowing.