What type of diode

So, it was clear that the light emission color from LED is not because of the cloured plastics that are used. But also they enhance the light brightness when not illuminated by the supply of current. The photodiode is used to detect light. It is found that when light strikes a PN-junction it can create electrons and holes.

Typically, photodiodes operate under reverse bias conditions where even a small amount of flow of current resulting from the light can be simply noticed. These diodes can also be used to produce electricity.

This type of diode is characterized by its construction. The region of the intrinsic semiconductor has the effect of increasing the area of the depletion region which can be beneficial for switching applications.

The negative and positive charge carriers from N and P-type regions correspondingly have a movement to the intrinsic region. When this region is completely filled up with electron-holes, then the diode initiates to conduct. While in reverse bias condition, the broad intrinsic layer in the diode might prevent and bear high voltage levels. At increased frequency levels, the PIN diode will function as a linear resistor. It functions as a linear resistor because this diode has inadequate reverse recovery time.

And at minimal frequency levels, the diode operates as a rectifier diode where it has sufficient time for discharging and turning off.

The standard PN junction may be thought of as the normal or standard type of diode in use today. This is the most prominent of various types of diodes that are in the electric domain.

But, these diodes can be applied as small-signal types for use in RF radio frequency , or other low current applications which may be called signal diodes. Other types may be planned for high voltage and high current applications and are normally named rectifier diodes. In a PN junction diode, one has to be clear of biasing conditions. There are mainly three biasing conditions and this is dependent on the applied level of voltage.

In the forward bias condition, PN junction is developed when the battery positive and negative edges are connected to P and N types. When the diode functions in forwarding bias, then the internal and applied electric fields at the junction are in opposite paths.

When these electric fields are summed up, then the magnitude level of consequential output is less than that of the applied electric field. This connection results in the minimal resistive path and a thinner depletion area. The resistance of the depletion region becomes more negligible when the value of the applied voltage is more. For instance, in the silicon semiconductor, when the applied voltage value is 0.

Here, the connection is that the battery positive and negative edges are connected to N-type and P-type regions, This forms the reverse-biased PN junction.

In this situation, applied and the internal electric fields are in a similar direction. When both the electric fields are summed up, then the resultant electric field path is similar to that of the internal electric field path.

This develops a thicker and enhanced resistive depletion region. The depletion region experiences more sensitivity and thickness when the applied level of voltage is more and more. In addition, it is even more crucial to be aware of the V-I characteristics of the PN junction diode. This signifies that the potential barrier restricts the current flow.

Whereas when the diode operates in forwarding bias conditions, there will be a thinner potential barrier. In silicone type of diodes, when the voltage value is 0.

In this, there will be a gradual increase in the current value and the resultant curve is non-linear where because the applied voltage level surmounts the potential barrier. When the diode surmounts this potential barrier, the diode functions in normal condition, and the shape of the curve gradually gets sharp gets to linear shape with the rise of the voltage value.

Where when the diode operates in reverse bias condition, there will be an increased potential barrier. As there will be the presence of minority charge carriers in the junction, this allows for the flow of reverse saturation current. When there is an increased level of applied voltage, the minority charge carriers possess risen kinetic energy that shows an impact on the majority charge carriers.

The cathode terminal of the diode is indicated by a red or black band on one side. As these diodes have minimal current carrying capacity, their power rating is also very low.

A small signal diode with a current rating of mA may have only mW of power rating. Small signal diodes are used in high-frequency or pulsating, low-current applications like radio, television, digital logic circuits, clipper and clamper circuits, high-speed switching, and parametric amplifiers.

Large signal diodes are different from small signal diodes in the area of their p-n junction. Large signal diodes have a large p-n junction area.

This increases the current carrying capacity as well as the peak inverse voltage. These have a very low forward resistance to reverse resistance ratio, with the forward resistance typically a few ohms while the reverse resistance is in megaohms. That is why these diodes are not suitable for high-frequency circuits. They have a large PIV rating, small forward resistance, and large current carrying capacity. These are generally used for AC-to-DC voltage rectification or to suppress high peak voltages.

In fact, large signal diodes are mostly rectifier diodes. Zener diodes are semiconductor diodes designed with heavy doping to utilize Zener breakdown in their operation. When a normal diode is an applied reverse voltage higher than its PIV rating, it is permanently damaged and goes open circuit.

A Zener diode has a controlled breakdown in the reverse region. It is mostly used as a voltage rectifier in DC applications. Various Zener diodes have Zener voltage in the range of 2V to V. These diodes are also used as protection diodes in several semiconductor circuits.

Zener diode has the following symbol. Light emitting diodes are special diodes that emit visible light when forward biased. In reverse bias, like a normal diode, they are in a state of non-conduction and do not emit any light. These are semiconductor diodes made up of gallium arsenide and similar semiconductor substrates with a high-energy bandgap between their conduction and valance bands. Due to the high energy bandgap, when electrons and holes combine near the p-n junction, the radiated energy is in the form of visible light or infrared light instead of heat.

There are many different kinds of LEDs. They are generally classified by the light they transmit. LEDs of different colors have different semiconductor substrates, cut-in voltage, and reverse voltage ratings. It is important to look out maximum forward voltage, PIV rating, and maximum forward current of an LED before using it as an application.

LEDs are quite sensitive and may easily get damaged. The PIV ratings of LEDs, like signal diodes, are usually in tens of volts, while the maximum forward voltage is only a few volts.

LEDs have the following symbol. Schottky diodes are different from typical p-n diodes. A Schottky diode is constructed by forming a junction between N-type semiconductor material and metal like Platinum, Chromium, or Tungsten. Due to metal-semiconductor junction, these diodes have a high current carrying capacity and fast switching time.

The metal junction also reduces the cut-in voltage and improves the power efficiency of the diode. Because of all these benefits, Schottky diodes are used for high-frequency rectification and high-frequency switching applications. A Schottky diode has the following symbol.

Just as a generic diode has two layers, Shockley diode has four. It is also called the PNPN diode. It is similar to a thyristor without a gate terminal. It is identified as a diode as it has only two terminals, and there are two electrical states of the device — conduction and non-conduction. It can go in conduction state only when a forward voltage is applied to it. The other transistor conducts when there is sufficient voltage to bias the first one.

Therefore, a PNPN diode requires a sufficient forward voltage to go in a conduction state. If the forward voltage is dropped or reverse voltage is applied, the Shockley goes in a non-conduction state. The two most common applications of Shockley diode are trigger switch for SCR and relaxation oscillator or saw tooth oscillator.

These diodes are used in audio amplifier circuits. Following is the electrical symbol of Shockley Diode. Tunnel diodes are heavily doped semiconductor diodes — times more than a large signal diode. These diodes use a quantum phenomenon called resonant tunneling. These diodes exhibit strange negative resistance in their forward characteristics. When forward biased, the current increases with voltage and reaches a peak. This is called peak current, and the voltage at this point is called peak voltage.

Then, with the increase in voltage, the current decreases and drops to a low point called valley current. The voltage at this point is called valley voltage. On increasing the applied voltage beyond valley voltage, the current rises exponentially without any further drop. These diodes have a very fast switching time of the order of nano-seconds. Their transient response is only limited by the junction capacitance and stray wire capacitance. Tunnel diodes are used as high-speed switches in microwave oscillators and amplifiers.

It is possible to tune these diodes both electrically as well as mechanically. The following is the electrical symbol of the tunnel diode. Varactor diodes work like a variable capacitor which is why these diodes are also called varicap diodes. They are connected via a reverse bias in a constant-voltage circuit. Their specialty is that their depletion layer can be increased or decreased by varying the applied reverse voltage.

The change in the depletion layer changes the capacitance of the diode. The capacitance of a varactor diode can be varied to very high values. The constant current diode symbol is shown below.

In this type of diode, the junction is formed by contacting the semiconductor material with metal. Due to this, the forward voltage drop is decreased to a minimum. The semiconductor material is N-type silicon, which acts as an anode and metals such as Chromium, Platinum, Tungsten etc.

Due to the metal junction, these diodes have high current conducting capability and hence the switching time is reduced. So, Schottky Diode has greater use in switching applications. Mainly because of the metal — semiconductor junction, the voltage drop is low, which in turn increases the diode performance and reduces power loss. So, these are used in high frequency rectifier applications. The symbol of Schottky diode is as shown below.

It was one of the first semiconductor devices to be invented. Shockley Diode has four layers. It is also called as PNPN diode. It is equal to a thyristor without a gate terminal, which means the gate terminal is disconnected. As there is no trigger input, the only way the diode can conduct is by providing forward voltage. The diode has two operating states conducting and non-conducting. In non-conducting state the diode conducts with less voltage.

It is also called as snap-off diode or charge-storage diode. These are the special type of diodes which stores the charge from positive pulse and uses in the negative pulse of the sinusoidal signals. The rise time of the current pulse is equal to the snap time.

Due to this phenomenon, it has speed recovery pulses. The applications of these diodes are in higher order multipliers and in pulse shaper circuits. The cut-off frequency of these diodes is very high which are nearly at Giga hertz order.

As multiplier, this diode has the cut-off frequency range of to GHz. In the operations which are performing at 10 GHz range, these diodes play a vital role. The efficiency is high for lower order multipliers. The symbol for this diode is as shown below. It is used as high-speed switch, with switching speed in the order of few nano-seconds. Due to tunneling effect it has very fast operation in microwave frequency region. It is a two-terminal device in which concentration of dopants is too high.

The transient response is being limited by junction capacitance plus stray wiring capacitance. Mostly used in microwave oscillators and amplifiers. It acts as most negative conductance device.

Tunnel diodes can be tuned both mechanically and electrically. The symbol of tunnel diode is as shown below. These are also known as Varicap diodes.

It acts like the variable capacitor. Operations are performed mainly at reverse bias state only. These diodes are very famous due to its capability of changing the capacitance ranges within the circuit in the presence of constant voltage flow. They can be able to vary capacitance up to high values. In varactor diode, we can decrease or increase the depletion layer by changing the reverse bias voltage. These diodes have many applications as voltage-controlled oscillator for cell phones, satellite pre-filters etc.

The symbol of varactor diode is given below. Similar to LED in which active region is formed by p-n junction. Electrically laser diode is P-I-N diode in which the active region is in intrinsic region. In semiconductor devices, transients will occur due to the sudden change in the state voltage.

To overcome this problem, Voltage Suppression Diodes are used. The operation of voltage suppression diode is similar to Zener diode operation. The operation of these diodes is normal as p-n junction diodes but at the time of transient voltage its operation changes.

In normal condition, the impedance of the diode is high. When any transient voltage occurs in the circuit, the diode enters in to the avalanche breakdown region in which a low impedance is provided. It is very spontaneously because the avalanche breakdown duration ranges in Pico seconds. Transient voltage suppression diode will clamp the voltage to the fixed levels, mostly its clamping voltage is in minimum range.

These are having applications in the telecommunication fields, medical, microprocessors and signal processing. It responds to over voltages faster than Varistors or gas discharge tubes. In these diodes, Gold is used as a dopant.