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Diodes are the basic building blocks for most semiconductor devices. They are part of the bipolar family of devices. Diodes consist of two semiconductor materials, one doped with a deficiency of electrons called p-type material, and the other side is doped with an extra abundancy of electrons called n-type material. A process known as doping the material is what makes some parts of the diode p-type and the other parts n-type.

While growing the semiconductor crystal, a small amount of arsenic or phosporous can be mixed in with the process and dope the material. To change the type of material from p to n type, one can add some n-type chemicals to swamp out the p-type materials already in the 'substrate'. When you get done with the making of a diode, you have two types of material in direct contact with one another - this is called an abrupt pn-junction. The p-side is called the anode and collects the electrons emitted from the cathode, the n-side.

Diode's construction

Diode is made from joining one P-typed semi conductor with one N-typed semi conductor . A bipolar device of distinct polarties . Positive at the end of P-typed semi conductor and negative at the end of N-typed semi conductor . A device directs the flow of current , in the direction of the arrow pointing

+ o--[P|N]--o -

Diode's Symbol

Diode's current and voltage curve

Diode's current and voltage curve or I V Curve shows manufacturer's specification of diode's operation voltage and current

As seen in the graph above the diode actually works in both the forward region and the backward region. In the forward region the value of I and V are positive and in the backward region I and V are negative.

Diode's Operation

Ideal Diode

The real diode approaches the ideal diode in the sense that the reverse current is extremely small (less than 1fA) at least for a significant part of the characteristic, and the forward current is very high (on the order of 1mA). Although a real diode does not have the characteristics as the ideal diode, in theory it is possible to make an ideal diode if the concentrations of dopants in both the regions are infinite. However, there is no way of actually doing this and experiments do not agree.

The Shockley equation

The diode reverse (saturation) current is governed by the doping concentration. The current flowing through the device varies as the voltage applied across it changes as given by the Shockley diode equation (not to be confused with Schottky):

${\displaystyle I_{D}=I_{S}(e^{V_{D}/nV_{T}}-1)}$

${\displaystyle V_{T}}$ is defined as ${\displaystyle V_{T}=kT/q}$, where ${\displaystyle k}$ is Boltzmann's constant, ${\displaystyle T}$ is the temperature in Kelvin, and ${\displaystyle q}$ is the magnitude of the charge on an electron.

In the forward bias direction, current flows with low voltage. If one draws a characteristic for this equation, a sharp increase in current can be seen at a particular voltage called the cut-in voltage or the on-voltage.

In the reverse bias mode, the diode current is approximately ${\displaystyle -I_{S}}$. This is called the reverse saturation current because it looks like the diode is saturated with charge and cannot allow more current in the reverse bias direction than this.

Diode's Break-down

However, a break from the above equation takes place at a point called break-down voltage. One could think of it as the point where the Shockley equation breaks down and is no longer valid. There are two reasons for breakdown to occur.

Diode Types

LED (Light Emitting Diode)
Schottky diode
Zener diode
Varicap diode

Diode's Circuits

Reference

• Diode

External Links

• Rectification Basics: Electronics for Beginners