For a p-n-p BJT with NE>NB>NC, show the dominant current...

For a $\mathrm{p}-\mathrm{n}-\mathrm{p} \mathrm{BJT}$ with $N_{E}>N_{B}>N_{C}$, show the dominant current components, with proper arrows, for directions in the normal active mode. If $I_{E p}=10 \mathrm{~mA}$, $I_{E_{n}}=100 \mu \mathrm{A}, I_{C p}=9.8 \mathrm{~mA}$, and $I_{C n}=1 \mu \mathrm{A}$, calculate the base transport fac- tor, emitter injection efficiency, common-base current gain, common-emitter current gain, and $I_{C B O}$. If the minority stored base charge is $4.9 \times 10^{-11} \mathrm{C}$, calculate the base transit time and lifetime.

For a $\mathrm{p}-\mathrm{n}-\mathrm{p} \mathrm{BJT}$ with $N_{E}>N_{B}>N_{C}$, show the dominant current components, with proper arrows, for directions in the normal active mode. If $I_{E p}=10 \mathrm{~mA}$, $I_{E_{n}}=100 \mu \mathrm{A}, I_{C p}=9.8 \mathrm{~mA}$, and $I_{C n}=1 \mu \mathrm{A}$, calculate the base transport fac-
tor, emitter injection efficiency, common-base current gain, common-emitter current gain, and $I_{C B O}$. If the minority stored base charge is $4.9 \times 10^{-11} \mathrm{C}$, calculate the base transit time and lifetime.

Key Concepts

Active Mode of BJTs

In active mode, one junction (typically the emitter-base junction) is forward-biased while the other (the base-collector junction) is reverse-biased. This biasing allows the majority carriers to be injected from the emitter into the base, where most of them diffuse across to be collected at the collector, thus enabling amplification.

Carrier Injection Efficiency (Emitter Injection Efficiency)

Carrier injection efficiency measures how effectively the emitter injects its majority carriers into the base compared to any unwanted minority carriers injected in the opposite direction. It is a key factor in determining the overall performance of the transistor, as high efficiency ensures that most of the emitter current contributes to the desired conduction process.

Base Transport Factor

The base transport factor is defined as the fraction of carriers injected into the base that successfully diffuse across it and are collected by the collector. It is heavily influenced by the recombination processes in the base and the width of the base, and it is crucial in determining the magnitude of the collector current relative to the emitter current.

Common?Base and Common?Emitter Current Gains

The common-base current gain (alpha) represents the ratio of the collector current to the emitter current, reflecting the efficiency of carrier transmission across the base. The common-emitter current gain (beta) is related to alpha by the relationship beta = alpha/(1 - alpha) and indicates the overall amplification capability of the transistor in common-emitter configuration.

Leakage Currents in BJTs

Leakage currents, such as the collector-base leakage current (I_CBO), are the small currents that flow due to minority carriers even when a junction is reverse-biased. These currents can influence the biasing conditions and performance of a transistor, particularly under high temperature or low-signal conditions.

Minority Stored Base Charge, Base Transit Time and Carrier Lifetime

The minority stored base charge is the amount of charge stored in the base due to minority carriers that have been injected from the emitter. The base transit time is the time taken by these carriers to traverse the base, and the carrier lifetime is the average time before recombination occurs. Together, these parameters determine the speed and frequency response of a transistor.

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