An Overview on Different Types of Diodes and Their Uses

A diode is a two-terminal electrical device, that allows the transfer of current in only one direction. The diode is also known for its unidirectional current property, where the electric current is permitted to flow in one direction. A diode is used for rectifying waveforms, within radio detectors or within power supplies. They can also be used in various electrical and electronic circuits where the ‘one-way’ result of the diode is required. Most of the diodes are made from semiconductors such as Si (silicon), but in a few cases, Ge (germanium) is also used. It is sometimes beneficial to summarize the different types of diodes are existing. Some of the types may overlap, but the various definitions may benefit to narrow the field down and offer an overview of the various types of diodes.

What are Different Types of Diodes?

There are several types of diodes and those are available for use in electronics design, namely; a Backward diode, BARRITT diode, Gunn Diode, Laser diode, Light emitting diodes, Gold doped diodes, crystal diode, PN Junction, Shockley diode, Step recovery diode, Tunnel diode, Varactor diode, and a Zener diode.

Detailed Explanation of Types of Diodes

Let us talk in detail about the working principle of the diode.

Backward Diode

This type of diode is also called the back diode, and it is not extremely implemented. The backward diode is a PN-junction diode that has a similar operation to a tunnel diode. The scenario of quantum tunneling holds important responsibility in the conduction of the current mainly reverse path. With the energy band picture, the exact working of the diode can be known.

The band that lies at the uppermost level is termed the conduction band whereas the lower level band is termed the valency band. When there is an application of energy to the electrons, they tend to gain energy and move towards the conduction band. When the electrons enter from valency to the conduction band, their place of them in the valency band is left with holes.

In the zero-biasing condition, the occupied valency band is in opposition to that of the occupied conduction band. Whereas in the reverse bias condition, the P-region has a movement towards the upside corresponding to N-region. Now, the occupied band in the P-section is in contrast to the vacant band at N-section. So, the electrons start tunneling from the occupied band in the P-section to the vacant band in N-section.

So, this signifies that current flow happens also in reverse biasing. In the forward bias condition, the N-region has a movement towards the upside corresponding to P-region. Now, the occupied band in the N-section is in contrast to the vacant band at P-section. So, the electrons start tunneling from the occupied band in the N-section to the vacant band in P-section.

In this type of diode, the negative resistance region is formed and this is employed mainly for the working of the diode.

BARITT Diode

The extended term of this diode is Barrier Injection Transit Time diode which is BARRITT diode. It is applicable in microwave applications and allows many comparisons to the more widely used IMPATT diode. This link shows a clear description of what is a BARRITT Diode and its working and implementations.

Gunn Diode

Gunn diode is a PN junction diode, this sort of diode is a semiconductor device that has two terminals. Generally, it is used for producing microwave signals. Please refer to the below link for Gunn Diode Working, Characteristics, and its Applications.

Laser Diode

The laser diode does not have a similar process as that of ordinary LED (light-emitting diode) because it produces coherent light. These types of diodes are extensively utilized for various purposes such as  DVDs, CD drives, and laser light pointers for PPTs. Although these diodes are more inexpensive than other types of laser generators, they are much more expensive than LEDs. They also have a partial life.

Light Emitting Diode

The term LED stands for light-emitting diode, is one of the most standard types of the diode. When the diode is connected in forwarding bias, then the current flows through the junction and generates the light. Many new LED developments are changing they are LEDs and OLEDs. One of the main concepts to be aware of the LED is its IV characteristics. Let us go through the characteristics of LED in detail.

Before a LED emits light, it requires the flow of current through the diode because this is a current-based diode. Here, the amount of light intensity has a direct proportion to that of the forward direction of the current that flows across the diode.

When the diode conducts current in the forward bias, then there has to be a current limiting series resistor to safeguard the diode from the additional flow of current. It has to be noted down that there has to be no direct connection between the power supply to the LED where which causes instant damage because this connection allows an extreme amount of current flow and burns the device.

Every type of LED device holds its forward voltage loss through the PN junction and this constraint is known by the type of semiconductor that is used. This determines the amount of voltage drop for the corresponding amount of forwarding current generally for a current value of 20mA.

In most of the scenarios, LED’s function from minimal voltage levels having a resistor in series connection, Rs is employed for the restriction of the forward amount of current to a protected level which is in general 5mA to 30mA when there is a requirement of enhanced brightness.

Various LEDs generate light in the corresponding regions of the UV spectrum and so they generate different levels of light intensities. The specific selection of the semiconductor can be known by the entire wavelength of the photon emissions and so corresponding light s produced. The colors of the LED are as follows:

Type of Semiconductor	Wavelength Distance	Color	Forward Voltage at 20mA
GaAs	850-940nm	Infra-Red	1.2v
GaAsP	630-660nm	Red	1.8v
GaAsP	605-620nm	Amber	2.0v
GaAsP: N	585-595nm	Yellow	2.2v
AIGaP	550-570nm	Green	3.5v
SiC	430-505nm	Blue	3.6v
GalnN	450nm	White	4.0v

So the exact color of the LED is known by the distance of emitted wavelength. And the wavelength is known by the specific semiconductor composition that is employed in the PN junction at the time of its manufacturing process. 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. With the combination of various semiconductor, gaseous, and metal substances, the below LED’s can be generated and those are:

• Gallium Arsenide (GaAs) which is infra-red
• Gallium Arsenide Phosphide (GaAsP) ranges from red to infra-red and orange
• Aluminium Gallium Arsenide Phosphide (AlGaAsP) has increased bright red, orange type of red, orange, and yellow colors.
• Gallium Phosphide (GaP) exists in red, yellow, and green colors
• Aluminium Gallium Phosphide (AlGaP) – mostly in green color
• Gallium Nitride (GaN) is available in green and emerald green
• Gallium Indium Nitride (GaInN) close to ultraviolet, the mixed color of blue and green and blue
• Silicon Carbide (SiC) available as a blue a substrate
• Zinc Selenide (ZnSe)exists in blue
• Aluminium Gallium Nitride (AlGaN) is ultraviolet

Photodiode

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 types of diodes can also be used to produce electricity.

There are two kinds of Photodiodes – PN and PIN photodiodes. The difference is in their performance. The PIN photodiode has an intrinsic layer, so it must be reverse biased. As a result of reverse biasing, the width of the depletion region increases, and the capacitance of the p-n junction decreases.

This allows the generation of more electrons and holes in the depletion region. But one disadvantage of reverse biasing is that it generates noise current that may reduce the S/N ratio. So reverse biasing is suitable only in applications that require higher bandwidth. The PN photodiode is ideal for lower light applications because the operation is unbiased.

The photodiode works in two modes namely Photovoltaic mode and Photoconductive mode. In the photovoltaic mode (also called Zero bias mode), the photocurrent from the device is restricted and a voltage builds up. The photodiode is now in the Forward biased state and a “Dark current” starts flowing across the p-n junction.

This flow of dark current occurs opposite to the direction of the photocurrent. The dark current generates in the absence of light. The dark current is the photocurrent induced by the background radiation plus the saturation current in the device.

The Photoconductive mode occurs when the photodiode is reverse biased. As a result of this, the width of the depletion layer increases and leads to a reduction in the capacitance of the p-n junction. This increases the response time of the diode. Responsivity is the ratio of the photocurrent generated to the incident light energy.

In the Photoconductive mode, the diode generates only a small current called Saturation current or back current along its direction. The photocurrent remains the same in this condition. The photocurrent is always proportional to the luminescence. Even though the Photoconductive mode is faster than the Photovoltaic mode, the electronic noise is higher in the photoconductive mode. Silicon-based photodiodes generate less noise than germanium based photodiodes since silicon photodiodes have a greater bandgap.

PIN Diode

This type of diode is characterized by its construction. It has the standard P-type & N-type regions, but the area between the two regions namely the intrinsic semiconductor has no doping. 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 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. This is the cause that heavily electric charged “I” region will not have sufficient time to discharge at the time of quick cycles. And at minimal frequency levels, the diode operates as a rectifier diode where it has sufficient time for discharging and turning off.

PN Junction Diode

A P-N junction is a semiconductor device, which is formed by P-type and N-type semiconductor material. P-type has a high concentration of holes and N-type has a high concentration of electrons. Holes diffusion is from p-type to n-type and electron diffusion is from n-type to p-type.

The donor ions in the n-type region become positively charged as the free electrons move from the n-type to p-type. Hence, a positive charge is built on the N-side of the junction. The free electrons across the junction are the negative acceptor ions by filling in the holes, then the negative charge established on the p-side of the junction is shown in the figure.

 An electric field is formed by the positive ions in the n-type region and negative ions in p-type regions. This region is called the diffusion region. Since the electric field quickly sweeps free carriers out, hence the region is depleted of free carriers. The functional diagram of P-N Junction Diode is shown below.

• Forward bias – Here, the positive and negative terminals are connected to the P and N types of the diode.
• Reverse bias – Here, the positive and negative terminals are connected to the N and P types of the diode.
• Zero bias – This is called ‘0’ bias because no external voltage is applied to the diode.

Forward Bias of PN Junction Diode

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 a minimal resistive path and a thinner depletion area. The resistance of the depletion region becomes negligible when the value of the applied voltage is more. For instance, in the silicon semiconductor, when the applied voltage value is 0.6V, then the depletion layer’s resistance value becomes entirely negligible and there will be an unobstructed flow of current across it.

Reverse Bias of PN Junction Diode

Here, the connection is that the battery’s 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.

V-I Characteristics of PN Junction Diode

In addition, it is even more crucial to be aware of the V-I characteristics of the PN junction diode.

When the diode is operated under the ‘0’ bias condition it means that there is no application of external voltage to the 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 types of diodes, when the voltage value is 0.7V and in the germanium types of diodes when the voltage value is 0.3V, then the width of the potential barrier gets reduced and this allows for the current flow through the diode.

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. At this stage, the diode breakdown happens and this might lead to the diode getting damaged.

Applications of P-N Junction Diode

P-N junction diode is a two-terminal polarity sensitive device, the diode conducts when in forwarding bias and diode not conducts when reverse bias. Due to these characteristics, the P-N junction diode is used in many applications like

1. Rectifiers in DC power supply
2. Demodulation circuits
3. Clipping and clamping networks

Schottky Diode

The Schottky diode has a lower forward voltage drop than ordinary Si PN-junction diodes. At low currents, the voltage drop may be between 0.15 & 0.4 volts as opposed to 0.6 volts for an a-Si diode. To attain this performance they are designed in a different way to compare with normal diodes having a metal to semiconductor contact. These types of diodes are extensively used in rectifier applications, clamping diodes, and also in RF applications.

Step Recovery Diode

A step recovery diode is a type of microwave diode used to generate pulses at very HF (high frequencies). These diodes depend on the diode which has a very fast turn-off characteristic for their operation.

Tunnel Diode

The tunnel diode is used for microwave applications where its performance surpassed that of other devices of the day.

In the electrical domain, tunneling signifies that it is the direct movement of electrons through the minimal width of the depletion region from the conduction band to the valency band. In the PN junction diode, the depletion region is developed because of both electrons and holes. Because of these positive and negative charge carriers, the internal electrical field is developed in the depletion region. This creates a force in the opposite path of an external voltage.

With the tunneling effect, when there is minimal forward voltage value, then the forward current value will be more. It can be functioned both in forward and reverse biased conditions. Because of the high level of doping, it can function in reverse biasing also. With the decrement of barrier potential, the breakdown voltage in reverse direction also gets decreased and reaches nearly to zero. With this minimal reverse voltage, the diode may reach to breakdown condition. Because of this negative resistance region is formed.

Varactor Diode or Varicap Diode

A varactor diode is one sort of semiconductor microwave solid-state device and it is used in where the variable capacitance is chosen which can be accomplished by controlling voltage. These types of diodes are also called as variceal diodes. Even though the o/p of the variable capacitance can be exhibited by the normal PN-junction diodes. But, this diode is chosen for giving the preferred capacitance changes as they are different types of diodes. These diodes are precisely designed and enhanced such that they allow a high range of changes in capacitance.

Zener Diode

The Zener diode is used to provide a stable reference voltage. As a result, it is used in vast amounts. It works under reverse bias condition and found that when a particular voltage is reached it breaks down. If the flow of current is limited by a resistor, it activates a stable voltage to be generated. This type of diode is widely used to offer a reference voltage in power supplies.

There exist various methods in the package of a Zener diode. Few of those are employed for increased levels of power dissipation whereas others are utilized for edge mount designs. The general type of Zener diode is comprised of minimal glass covering. This diode has a band on one edge that marks it as the cathode.

Zener diode functions in a similar way as of diode when operated in forwarding bias condition. Whereas in reverse bias, there will be an occurrence of minimal leakage current. When there is an increase in the reverse voltage up to the breakdown voltage, then this creates current flow across the diode. The current value will be reached to maximum and this is captured by a series resistor.

Zener diode is a type of Diode that allows the flow of current in the forward direction similar to a rectifier diode but at the same time, it can permit the reverse flow of current also when the voltage is above the breakdown value of the Zener. This is typically one to two volts higher than the rated voltage of the Zener and is known as the Zener voltage or Avalanche point.

The Zener was named so after Clarence Zener who discovered the electrical properties of the diode. Zener diodes find applications in voltage regulation and protect semiconductor devices from voltage fluctuations. Zener diodes are widely used as voltage references and as shunt regulators to regulate the voltage across circuits.

The Zener diode uses its p-n junction in the reverse bias mode to give the Zener Effect. During the Zener effect or Zener breakdown, the Zener holds the voltage close to a constant value known as the Zener voltage. The conventional diode also has the property of reverse bias, but if the reverse bias voltage is exceeded, the diode will be subjected to high current and it will be damaged.

The Zener diode, on the other hand, is specially designed to have a reduced breakdown voltage called Zener voltage. The Zener diode also exhibits the property of a controlled breakdown and allows the current to keep the voltage across the Zener diode close to the breakdown voltage. For example, a 10 volt Zener will drop 10 volts across a wide range of reverse currents.

When the Zener diode is reverse biased, its p-n junction will experience an Avalanche breakdown and the Zener conducts in the reverse direction. Under the influence of the applied electric field, the valance electrons will be accelerated to knock and release other electrons. This ends in the Avalanche effect. When this occurs, a small change in the voltage will result in a large current flow. The Zener breakdown depends on the applied electric field as well as the thickness of the layer on which the voltage is applied.

The Zener diode requires a current limiting resistor in series to it to restrict the current flow through the Zener. Typically the Zener current is fixed as 5 mA. For example, if a 10 V Zener is used with a 12 volt supply, a 400 Ohms (Near value is 470 Ohms) is ideal to keep the Zener current as 5 mA.

If the supply is 12 volts, there are 10 volts across the Zener diode and 2 volts across the resistor. With 2 volts across the 400 ohms resistor, then the current through the resistor and Zener will be 5 mA. So as a rule 220 Ohms to 1K resistors are used in series with the Zener depending upon the supply voltage. If the current through the Zener is insufficient, the output will be unregulated and less than the nominal breakdown voltage.

The following formula is useful to determine the current through the Zener:

Zener = (VIn – V Out) / R Ohms

The value of the Resistor R must satisfy two conditions.

1. It must be a low value to permit sufficient current through the Zener
2. The power rating of the resistor must be high enough to protect the Zener.

Applications of Zener Diode

There are extensive applications of a Zener diode and a few of those are:

• It is used as a voltage limiter to regulate voltage levels across the minimal value of loads
• Employed in the applications those need over-voltage safeguarding
• Used in clipping circuits

A few of the other types of diode crucially implemented in various applications are as below:

• Laser Diode
• Avalanche Diode
• Transient Voltage Suppression Diode
• Gold Doped type of diode
• Constant Current type of diode
• Peltier Diode
• Silicon Controlled Rectifier diode

Every diode has its own benefits and applications. Few of those are widely used in various applications across multiple domains, whereas few are employed only in a few applications. Thus, this is all about different types of diodes and their uses. We hope that you have got a better understanding of this concept or to implement electrical projects please give your valuable suggestions by commenting in the comment section below. Here is a question for you, What is the function of a diode?