Characteristics and Applications of Diodes

Operating Principle of Diode

Crystal diode is a p-n junction formed by p-type semiconductor and n-type semiconductor. Space charge layer is formed on both sides of its interface and self-built electric field is built. When there is no applied voltage, the diffusion current caused by carrier concentration difference on both sides of the p-n junction is equal to the drift current caused by the built-in electric field, so it is in the state of electric equilibrium.

When there is a positive voltage bias, the interaction between the external electric field and the self-built electric field causes the increase of carrier diffusion current and the positive current.

When there is reverse voltage bias, the external electric field and the self-built electric field are further strengthened, and the reverse saturated current I0 independent of the reverse bias voltage is formed in a certain range of reverse voltage.

When the applied reverse voltage is high to a certain extent, the electric field intensity in the space charge layer of p-n junction reaches the critical value, resulting in the multiplying process of carriers, a large number of electron hole pairs and a large number of reverse breakdown currents, which are called diode breakdown phenomena.

Types of Diodes

There are many kinds of diodes. According to the semiconductor materials used, they can be divided into germanium diode (Ge tube) and silicon diode (Si tube). According to its different uses, it can be divided into detector diode, rectifier diode, regulator 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. The point contact diode is a kind of semiconductor wafer with a very thin wire pressed on the surface of the wafer, and connected with a pulse current, so that one end of the contact wire and the wafer are firmly sintered together, forming a "PN junction". Because of point contact, only small currents (no more than tens of milliamperes) are allowed to pass through, which is suitable for high frequency low current circuits, such as radio detection.