BARITT Diode or commonly referred to as Barrier Injection Transit-Time Diode has many Similarities to the more widely used IMPATT DIODE. BARITT Diode is usually used for Microwave Signal Generations of frequencies up to 25Ghz for Silicon (Si) Material and 90GHz for Gallium-Arsenide (GaAs).
The main difference between BARITT Diode and other Diode is that BARITT uses thermionic emission whereas other diode works on avalanche multiplication. BARITT diode can produce low noise microwave signal because it works on the thermionic emission process.
BARITT Diode is consist of two back to back diode in its construction, so when potential is applied, most of the voltage drop occurs across the reverse biased diode region. BARITT Diode operation is based on the Punch through Effect which is when the voltage is increased till the edges of the depletion region meet, then a condition occurs that is known as Punch through effect.
Basic Structure of BARITT Diode:
BARITT Diode is two terminal and three-layer device (P-N-P Layer). The major difference between its layers is that Emitter region is 5% less than the size of Collector region whereas the N-region is larger one compared to both P-type regions the reason behind that, the Punch through effect occurs in between this region.
When Emitter terminal is connected with a positive terminal of the battery and collector is connected with a negative terminal of the battery the BARITT Diode is said to be in a forward bias. In a Forward bias mode, Emitter-base junction will be in forward bias and collector-base junction will be reverse bias and as we increase forward bias voltages E-B will be in conduction mode and C-B junction will be reverse bias hence depletion region will increase as shown in above figure. The corresponding effect of an electric field inside the BARITT diode is shown in the above figure.
VI Characteristic Curve of BARITT Diode:
It can be seen within the above diagram that the punch-through voltages are different for the two directions. In the Forward bias direction punch-through voltages are positive and in reverse bias direction, the Punch-through voltages are negative. This difference behavior results from asymmetry in the two junctions of BARITT Diode and it can be controlled during the manufacture stages of the diode.
Working of BARITT Diode:
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After a terminal charge is injected, it travels to the base material of the device (Substrate) with the saturation velocity.
As seen from the above diagram, it can be seen that the injection current and RF voltage waveform are both in phase with each other. This results in a non-ideal current waveform situation, which flows in the positive resistance region and due to the positive resistance region BARITT diode encounter more losses compared to an IMPATT Diode.
The width of the terminal current pulse is determined by the (ON Time) transit time which is L/Vsat (Here L means the electrodes are spaced L(Distance) apart and Vsat means saturation velocity). This constitutes till three-quarters of the cycle. In BARITT diode, the power capability decreases close to as the square of the frequency because higher frequencies need a smaller separation between the electrodes and this successively limits the voltages that may be used. Also, the potency falls away with increasing frequency. For low-frequency operation, it’s going to be around 5% or a bit a lot.