What is the Difference Between Forward Bias and Reverse Bias?

With the evolution of technology, electronics manufacturers continue to make choices between devices and methods to enable certain processing functions in their products. The need for these specific functionalities also drives development within other electronics industry areas. To better understand these effects on how a diode functions and its bias, one must first ask: what is forward bias and reverse bias, and what’s the difference between a forward-biased diode and reverse biased diode? That’s the question this post will seek to answer in greater detail.

What Is Forward Bias and Reverse Bias?

Before comparing the difference between forward bias and reverse bias, it’s essential to understand the characteristics of each. Essentially, bias or biasing is a method of establishing the voltages or currents along an electronic circuit’s various points so that an electronic component’s effective functions can be adequately established. A typical diode operates similarly to a one-way street, allowing current flow in only one direction, while voltage is oriented as forward biasing. However, when voltage moves in the other direction, this orientation is referred to as reverse bias. This is the primary difference between forward and reverse bias, which limits or blocks the current flow, much like a valve in larger mechanical equipment.

What is Forward Bias and Reverse Bias for Semiconductor Diodes?

Within many modern electronic devices are electrical components called diodes, which control the current flow so that it flows in only one direction. The most common types of diodes use an interface called the p-n junction, which utilizes two different materials. These are known as either p-type or n-type semiconductors.

One material touches the other material to carry a charge, while at the interface between the two materials, a depletion region forms to diffuse electrons on the p-side. This halts the flow of current. When electrons move across this junction, current flows through the diode, which has a positive voltage that allows current to flow. When the depletion region grows wider, the junction becomes reverse-biased, with a negative voltage applied to the p-side, along which electrons can’t easily move. 

The difference between a forward-biased diode and reverse biased diode is inherently simple. The forward bias connects the semiconductor’s p-type with a positive terminal, whereas the semiconductor’s n-type connects with the negative terminal. To alter the bias of a diode, a direct current voltage must be applied across it. The forward bias and reverse bias diode act in opposing ways, with forward bias allowing current to flow through the p-n junction, while reverse bias prevents this current flow through the diode.

Comparing Functionality in Forward Bias and Reverse Bias Diodes

Forward bias creates an electrical field across the potential barrier, reducing its strength, while reverse bias strengthens the potential barrier, restricting the movement of electrons across the p-n junction. Regarding how the current moves through a forward biasing diode, it’s important to look at the region around this junction, known as the depletion layer, since free charge carriers become depleted. Forward biasing diodes form a very thin layer, allowing these carriers to easily pass through without being depleted. In contrast, when a diode is reverse-biased, these free charge carriers tend to become depleted.

To properly operate, diodes must also go through a process known as doping. When a semiconductor is doped with materials, it facilitates an overabundance of displaced electrons. These are referred to as the n-type or negative region, which is alternatively referred to as a cathode. The p-type or positive region –known as an anode – can also undergo doping to arrange an abundance of holes that instead absorb the electrons rather than displace them.

A diode’s operation is facilitated over very short distances of less than a millimeter, reacting to the variance between the materials and how they interact. Yet a diode only becomes functional when the two materials are merged. This merger between p-side and n-side materials forms the p-n junction, with the area in between known as the depletion region.

When it comes to the proper functionality of a diode, the difference between forward bias and reverse bias diodes is the voltage they produce. The minimum voltage for forward-biased diodes is about .7 volts, while only a tiny amount of current – termed leakage current – passes through reverse-biased diodes. When sufficient voltage is employed, it facilitates the diode’s electronic breakdown, causing current to flow reverse through the diode.

Some Key Differences Between Forward Bias and Reverse Bias

The difference between a forward-biased diode and a reverse-biased diode essentially involves the flow of electrical current. Standard diodes permit this current to flow in one direction when in a forward-biased state, while voltage goes in the opposite direction when in a reverse-biased state. Reverse biasing, however, doesn’t result in any significant flow of current. In fact, this difference between forward-biased diode and reverse biased diode proves beneficial when transforming alternating current into direct current.

Comparing forward bias and reverse bias diodes differ in how they’re applied. With forward bias, the external voltage reduces the potential barrier and eases current flow across the p-n diode; the battery’s positive terminal thus connects with the device’s p-type semiconductor while the negative terminal connects to the n-type semiconductor. With reverse bias, the external voltage is directed to increase this potential barrier to prevent current flow across the p-n junction; in this case, the negative terminal connects to the p-region, whereas the positive terminal connects to the n-type semiconductor.

Other differences between forward-biased diodes and reverse biased diodes include the following: 

  • Forward bias diodes reduce the potential barrier, while reverse bias diodes strengthen it.
  • With forward bias diodes, an anode has a greater voltage than a cathode, whereas, in reverse bias diodes, this situation is reversed.
  • Forward-biased diodes permit large amounts of forward current, with reverse biased diodes permitting only a small amount.
  • The depletion layer difference between forward bias and reverse bias diodes is thinner for the former and thicker for the latter.
  • Low resistance occurs in forward-bias diodes, while reverse biased diodes feature high resistance.
  • Reverse-biased diodes prevent current from passing, though forward-biased diodes allow current to flow.
  • Regarding the current’s magnitude, reverse biased diodes allow none, but forward-biased diodes depend on the amount of forward current.
  • While reverse-bias diodes act as insulators, forward-biased diodes act as conductors.

The difference between a forward-biased diode and a reverse biased diode is that the former promotes the current flow while the latter inhibits it. When it comes to its capabilities, a diode’s ability to function as two separate yet efficient mechanisms makes it particularly adaptive for a range of electronic applications. Biasing affects how a diode functions, providing circuit designers with a powerful tool for controlling a device’s functions. This difference between diodes makes them so useful as components within a wide array of electronic equipment.  

To learn more about the electronic components we manufacture and distribute, don’t hesitate to contact us at Solid State Inc. today.