which can be divided into germanium diodes (Ge tubes) and silicon diodes (Si tubes) according to the semiconductor materials used. According to its different USES, it can be divided into detector diode, rectifier diode, stable diode, switch diode and so on. According to the core structure, it can be divided into point-contact diode, surface contact diode and planar diode. Point-contact diode is a very thin wire pressure on the surface of the semiconductor wafer that is bright and clean, with pulse current, touched the wire end firmly sintering together with chip, forming a p-n junction. Due to the point contact, only small current (no more than a few tens of milliampere) is allowed, which is suitable for high-frequency small current circuits, such as radio detection.
The "PN junction" of the surface contact diode is larger and allows for a larger current (a few to a few tens), which is mainly used to convert alternating current into direct current "rectifier" circuit.
Planar diode is a kind of special silicon diode, which can not only pass large current, but also have stable and reliable performance, which is used in switches, pulses and high-frequency circuits.
How diodes work.
The crystal diode is a p-n junction formed by p-type semiconductor and n-type semiconductor, forming a space charge layer on both sides of the interface, and a self-built electric field is built. When there is no external voltage, the drift current caused by the difference of carrier concentration between the p-n junction and the self-built electric field is equal to the electric balance state.
When the external voltage is offset, the interaction between the external electric field and the self-built electric field increases the diffusion current of the carrier and causes the forward current.
When there is a reverse voltage offset, the external electric field and the self-built electric field are further strengthened, and the reverse saturation current I0, which is independent of the reverse bias voltage, is formed in a certain reverse voltage range.
When coupled with reverse voltage high enough, the p-n junction electric field intensity in the space charge layer reaches the critical value of carrier multiplication process, produce a large number of electron hole pair, produced great reverse breakdown current value, called the diode breakdown phenomenon.
The conductivity of a diode.
The most important characteristic of a diode is the unidirectional conductivity. In the circuit, the current can only flow from the positive pole of the diode, the negative outflow. The forward and reverse characteristics of diodes are demonstrated by simple experiments.