Schottky Diode

Between the mid-1950s and the late 1960s, the healthcare industry was on verge of a massive transition with the developing research on x-rays and gamma rays. However, the complication of developing a commercial detector was much more difficult than the theoretical analysis. CdTe crystals showed a very fluctuating result until the introduction of Schottky Diode as a surface barrier. Nevertheless, Takahashi created an enhanced version by adding stacked detectors to the Diodes.  In fact, this was how Schottky Diode became an integral part of the X-ray detectors. Cat’s whisker demodulator used in the extraction of audio modulations during the early 20th century is believed to be the predecessor of the modern-day Schottky Diode.

Introduction to Schottky Diode

Schottky Diode is a type of semiconductor diode with low forward voltage drop which helps in providing high switching action speed. Moreover, we prefer Schottky Diode conventional silicon PN-junction diodes because of this reason.

For example, the typical P-N diode has a relatively higher forward voltage ranging between 600 to 700 mV. In the case of Schottky Diode, the forward voltage is dropped by over 70 per cent. On average, the general forward voltage produced by Schottky DIode ranges between only 150 mV to 300 mV at the maximum.

Understanding the Working Principle of Schottky Diode

Schottky Diode is primarily known for the fast rate of switching and reduced forward voltage drop. Additionally, the junction between the metal electrode and the semiconductor does not have a depletion layer which makes it impossible for the diode to store additional charges at the junction like in case of P-N diodes. Hence the current flow through the diodes directly each time there is a voltage drop. 

Structure of a Schottky Diode

Schottky Diode is constructed out of metallic electrodes that are connected to an N-type semiconductor. As mentioned above, rather than the conventional P and N-type types, these metal electrodes prevent depletion of layers. Henceforth, this creates a stable unipolar device which is far more stable structurally than the conventional Bipolar devices.

We denote the metallic end as Anode and the N-type semiconductor as the Cathode. Furthermore, this creates a single pathway of current flow from the Anode (metal) to the Cathode ( semiconductor) with no backflow at all.

The semiconductor used is a compound created by combining Silicon and Metal results in the highly conductive end product called Silicide. In fact, the highly conductive ability of Silicide results in a very low Ohm resistance value, which increases the flow of current. 

However, the higher current flow produces a very small forward voltage drop of Vf less than 0.3 to 0.45 V.

The forward voltage drop of every metal-silica compound differs from each other on the basis of the conductivity of the said metal. It generally fluctuates between 0.3 Volts to 0.5 Volts.

Working Principle of  Schottky Diode

We know that an atom which receives an extra electron becomes a negative ion while the atom that loses an electron becomes a positive ion. Similarly, in case of a Schottky Diode, the free electrons in the semiconductor move towards the metal anode to create a balance between both the operation ends. 

The loss of electron at the n- Junction causes it to change to Positive ion, while the gain of an electron at the metal junction causes it to change to Negative ion. Moreover, this region of positive and negative ion are both at the junction, we refer to them as Depletion region.

The larger volume of free electrons in the metal end restricts the width movement of the electron.  Therefore, the built-in voltage is absent in the metal junction but abundant in the n-type Cathode or n-type semiconductor. The built-in voltage creates a barrier that prevents electrons from flowing backwards from the semiconductor to the metal end.

Advantages and Disadvantages of Using Schottky Diode

Advantages

• Minimal to zero depletion results in low capacitance in the diodes
• Recovery time reduces greatly, especially in a reversed state. The switch on to shut down time lapse is very small.
• The density of the current flow is higher due to the absence of the depletion layer.
• Easily operational in areas of High frequency

Disadvantage

• Reverse saturation of the current flow is very large

Application of Schottky Diode

We use it widely in the Electronics and Electrical appliances, we regard it as one of the key inventions of this era. Some of the most common use of the Schottky Diode includes –

1. Voltage Clamping to prevent saturation in the transistor
2. Digital device TTL like computers and laptops  for its fast switching mechanism
3. As rectifier in the power supply of solar Panels
4. Power divider in OR circuit
5. As RF mixer for its ability to switch speed

FAQ on Schottky Diode

Question 1: What is the difference between Schottky Diode and PN diode?

Answer 1:

Schottky Diode	PN Diode
The current movement in the forward direction is caused by the Thermionic Emission	The forward current movement occurs due to diffusion current.
The junction lies between the metallic electrode and the n-type semiconductor	The junction lies between P-type and N-type semiconductor
Temperature dependency is minimal to nil	Temperature dependency is very essential
Smaller cut in voltage produced of up to 0.3 V	The large cut-in voltage produced up to 0.7 V
High Switching speed	Switching speed is limited and varies depending on various external factors
Unipolar	Bipolar

Question 2: Why do we call the Schottky diode a hot-carrier diode?

Answer 2: In a neutral rest phase of the Schottky Diode, the electrons on the semiconductor end have very low energy emission when we compare it to that of the electrons on the metallic end. Therefore, we refer to the Schottky diode as Hot -carrier Diode in its unbiased state.

Question 3: What are the uses of a Schottky Diode?

Answer 3: Schottky Diodes are primarily used as RF mixers, Power rectifiers etc. the primary characteristic feature of Schottky Diode is its ability to reverse from a state of conduction to a state of blocking. Therefore, this makes it very useful in areas of low turn-on voltage.

Question 4: What is a Schottky Rectifier?

Answer 4: Schottky Rectifier is a semiconductor diode primarily consisting of a metal and semiconductor combination junction. Further, the low forward voltage drop combined with the fast switching speed makes it one of the most preferred and reliable rectifiers used.