0
The maximum base thickness in a BJT is dependent on a number of variables and parameters (or call them "constraints").
You could create a base region with thickness ranging from a few layers of atoms up to the point where the "base" region responds to the models of bulk semiconductor by messing with the process parameters. But why?
If the base is too thick then with the transistor biased into the 'active' region (i.e., B-E junction forward biased & B-C junction reverse biased), the transistor 'alpha' (the ratio of carriers collected by BC to those generated in BE) will be hopelessly low and the transistor will not exhibit the high current gain that you expect from BJTs.
That's because a thick base provides too much opportunity for large numbers of forward current charge carriers to be recaptured by the crystal matrix or lost to the collector current in other ways.
Add your answer:
Earn +20 pts
How do you calculate the current gain of a transistor?
Bipolar transistor current gain is also called "Beta," or the h-parameter "hfe." beta = current_out / current_in The beta of a BJT is mostly determined by the thickness of the Base region, and by the excess doping in the Emitter relative to the Base. A thin Base and a heavily-doped Emitter leads to a high value for current gain. In a BJT, beta = Ic / Ib In a FET, beta is usually taken as infinity, since no current flows in or out of the gate. Beta is an impirical number. It means nothing unless the Ic is known or the load. It can have a beta from 1000 to 10 it all depends on the load.
What is the main advantage of an fet transistor over a bjt transistor?
BJT & FET parameters are temperature dependent. In BJT the collector junction resistance decreasing ( collector current increasing) with temperature raise.Due to the highe temperature & current transistor will damage quickly. In FET drain resistance increasing (drain current decreasing ) with increasing temperature.Due to this property it will not damage easily. We can say from the above two statements FET is more temperature stable.FET can use in highe temperature applications.
Why use a npn transistor in a common emitter bjt single stage amplifier circuit?
You can use an npn or a pnp bjt in a common emitter amplifier circuit. The decision of which one to use is based on whether you want the collector and base to be more positive (npn) or more negative (pnp) than the emitter.
What is the deffbetween forward and reverse biased?
Asking about biasing of the emitter alone does not make sense. When you talk about bias, you talk about a junction, such as emitter-base or emitter-collector or base-collector. In a bipolar junction transistor (BJT) both the emitter-base and emitter-collector need to be forward biased, otherwise you are operating the BJT in cutoff mode. Certainly, if you intend to operate the BJT as a switch, then reverse bias for emitter-base (actually, zero bias) could well be one of the valid states, corresponding to a cutoff condition for emitter-collector. However, operation in linear mode, the other normal way to use a BJT, requires that both the emitter-base and the emitter-collector be forward biased. Of course, depending on the ratio of emitter-base to emitter-collector versus hFe, you could also be saturated, which is a non-linear mode, i.e. an on switch.
What is the difference between jfet and mosfet?
1-BJT is bipolar while JFET is unipolar. 2-BJT has low input impedence while JFET has high input impedence. 3-JFET has low power discipation as compared to BJT. 4-JFET has low noise as compared to BJT. 5-BJT is current controlled while JFET is voltage controlled. 6-JFET is mostly used in digital circuits.
What are the three element of a transistor?
For a BJT transistor the three basic elements are collector, base and emitter. For a FET transistor are drain, gate and source which are analogous for the BJT parts mentioned before.
What are the three element of transistor?
For a BJT transistor the three basic elements are collector, base and emitter. For a FET transistor are drain, gate and source which are analogous for the BJT parts mentioned before.
What separates the three regions in a BJT?
Two junctions namely emitter-base junction and collector-base junction separates regions in a transistor.
What are the example current controlled device?
Bipolar junction transistor(BJT)
What is bjt and jfet?
BJT is Bipolar junction transistor FET is Field effect Transistor It is a current controlled device It is voltage controlled device
Difference between bjt and ujt?
UJT is the voltage controlled device.in which only one mejority carriers are responsible for current flowing. UJT is one junction transistor and it is three terminal emitter and two base. BJT is the current controlled device. in which both mejority and minority carrier are responsiblefor current flowing. this type of transistor consists of two junction and three terminal these are : emitter , base , collector.
What is the difference between the UJT and BJT transistors?
UJT (UniJunction Transistor): It is a transistor with only one junction and three terminals: an emitter (E) and two bases (B1 and B2). BJT (Bipolar Junction Transistor): This type of transistor consists of two junctions and three terminals, namely Emitter "E", Base "B" and Collector"C". There are two types of BJT, i) PNP and ii) NPN.
Can UJT replace BJT?
No. A unijunction transistor (UJT) is entirely different in design and application than a bipolar junction transistor (BJT). The UJT works on the principle of voltage modulation of the effective substrate resistance, while the BJT works on the principle of current amplification from one junction to the other, usually base-emitter to collector-emitter.
How do you make common base transistor or circuit?
it is one of the configuration of BJT ,which is achieved by making the BASE grounded(i.e common base).Here the emmiter serves as the input and collector as the output.
How works bjt transistor as a sram device?
Define BJTSRAM?
Why CE configuration of BJT transistor gives 180 phase shift?
when the switch the emitter-base junection is an opnd circut and heance the value of input or base curent is zero.
What types of transistors are the following - BJT PCT UJT SBT FET GJT AJT DFT?
The BJT is the bipolar junction transistor, the PCT is the point contact transistor, the UJT is the uni-junction transistor, the SBT is the surface barrier transistor, the FET is the field effect transistor, the GJT is the grown-junction transistor, the AJT is the alloy-junction transistor, and the DFT is the drift field-junction transistor.
