bjtflow.t

Question # 1 / 11

Consider the BJT diagram shown in the Figure below.

Using the scrolling menu select the correct choice
Injected holes lost to recombination in the base
Holes reaching the reverse-biased collector junction
Thermally generated electrons and holes making up the reverse saturation current of the collector junction
Electrons supplied by the base contact for recombination with holes
Electrons injected across the forward-biased emitter junction
bjtband.t

Question # 2 / 11

Consider the pnp BJT band diagrams shown below.

Choose the correct band diagram (Figure A, B or C) for each condition.
The emitter diode is forward biased and the collector is reverse biased (Normal mode).
No voltage is applied (equilibrium).
The collector diode is forward biased and the emitter is reverse biased (Inverted mode)
In the normal active mode (the holes are the minority carrier in the base) the base width should be to increase the base transport efficiency and current gain. holeinbase.t

Question # 3 / 11

Consider the excess hole distribution in the base of pnp BJT shown below:

Assume that the current in the base can be approximated by the hole diffusion current

Calculate the following quantities:
Collector current: mA.
Current gain of the transistor: holesmode.t

Question # 4 / 11

Consider the hole distribution in the base of a pnp BJT which is sketched below:

Could you identify the excess hole distribution associated with the mode of the transistor specified.
Normal active mode
Cutoff mode
Saturation mode
Threshold between saturation and normal mode
currents.t

Question # 5 / 11

The excess carriers at the emitter and collector side of the base of pnp transistor are given by

In the active mode those equations can be approximated by:

for a biased emitter junction
and

for a biased collector junction.
Identity the correct current.

=I_B+I_C ebersmoll.t

Question # 6 / 11

Consider the Ebers-Moll model shown below:

The above model repesents a BJT.
Label corresponds to

Label corresponds to

bjtmodes.t

Question # 7 / 11

Consider the following Ebers-Moll equivalent circuit model:

Match each figure to its correct mode, and indicate the various junction biasing directions (Forward or Reverse)
Figure corresponds to the normal Active mode. The EB diode is biased. The CB diode is biased.
Figure corresponds to the normal Inverted mode. The EB diode is biased. The CB diode is biased.
Figure corresponds to the normal Saturation mode. The EB diode is biased. The CB diode is biased.
Figure corresponds to the normal cut-off mode. The EB diode is biased. The CB diode is biased. secondary.t

Question # 8 / 11

There are many secondary effect in the BJT that must be included in the study of the BJT. Refer to the figures below.

Region of Figure c) shows the Early Effect.
Region of Figure c) shows the Avalanche Breakdown effect.
The collector-base voltage in Figure a) is than the collector-base voltage in Figure b).
The increase in collector current with collector voltage in Figure a) is than in Figure b). schottkyclamped.t

Question # 9 / 11

Consider the device cross sections shown below:

Select the correct cross section.
The cross section is that of a Schottky diode clamped n-p-n transistor.
The cross section is that of a normal n-p-n transistor. hbtband.t

Question # 10 / 11

Consider the band diagrams below:

Specify which band diagrams (Figure A or B) corresponds to the transistor specified.
Figure is a homojunction bipolar transistor: BJT (qVn equal to qVp)
Figure is an heterojunction bipolar transistor HBT (qVn smaller than qVp).
Match the proper label with the corresponding band edge discontinuity.
corresponds to qVn the electron barrier
corresponds to qVp the hole barrier
corresponds to qV_EB
corresponds to qV_CB

In a npn HBT the emitter injection efficiency and therefore the current gain is inceased by selecting an emitter with a bandgap such that electron barrier qVn is and the hole barrier is . hbt.t

Question # 11 / 11

In designing heterojunction bipolar transistors (HBT's), the difference between the bandgaps at the heterojunction (

) influences the ratio of electron to hole current exponentially.

This is very useful because it allows the designers to alter the doping concentrations without greatly affecting current flow. To create a suitable high-frequency transistor, a designer could then design an HBT with a doped base to reduce base resistance and a doped emitter to reduce junction capacitance.

 
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