Emitter injection efficiency formula

If recombination lifetime reduces to determine the collector current density beyond which the current gain will be practically constant. Solution : (a) The different current gain components are so that the current gain is primarily determined by emitter injection efficiency . This requires that the SCR limited current gain . The factors affecting the common emitter current gain (β) in InAs bipolar junction transistors (BJTs) have been studied by estimating the base transport factor (αT) and the emitter injection efficiency (γ). T, γ, and the minority carrier .

To solve this problem we need to calculate the neutral base width in the device.

Also note that since the emitter thickness is small compared to the carrier diffusion length in the emitter , we will use the narrow diode theory to calculate the emitter efficiency.

Using the parameters given, the built in voltage it the BCJ is. Lb increases the properties of the transistor start to degrade. It is also desired that the emitter injection efficiency be at least.

SOME IMPORTANT ISSUES DISCUSSED THIS WEEK. This week we have finished our discussions on the the operation of the bipolar junction transistor. Bipolar Junction Transistor Fundamentals. Narrow Base controls number of holes emitted. Collector “collects” holes emitted by the emitter.

Emitter Efficiency : Characterizes how effective the large hole current is controlled by the small . All bipolar devices including LEDS and solar cells have emitter layers which injects minority carriers into adjacent base region. According to the Shockley theory , the emitter is characterized by an injection efficiency which is the ratio of the current injected from the emitter into the base to the sum of this current and the back . Consider an NPN BJT with the following parameters: I. Determine the base transport factor, αT. Show that the injection efficiency of the emitter , defined as. Emitter current due to minority carriers injected into the base. Parasitics exists in the structure.

From (25) and (26), we can calculate directly . The emitter injection efficiency is defined as. Equation (.12) illustrates that the base Gummel number is basically proportional to the base dopant density per area. The higher the base dopant density is, the lower. An exact solution to the 1D diffusion equation can be obtained for the narrow- base diode, but that approach.

Simplified models and classifications are needed to speed up the hand- calculation analysis . The small signal, or sinusoidal, common base current gain is defined as. Contacts are made to all three regions, the two outer regions called the emitter and collector and the middle region called the base. The structure of an npn bipolar transistor is shown in Figure 5. Base Transport Factor: – Decrease (1) relative to (2) to increase transport factor.

In the more traditional BJT, also referred to as homojunction BJT, the efficiency of carrier injection from the emitter to the base is primarily determined by the doping ratio between the emitter and base, which means the base must be lightly doped to obtain high injection efficiency , making its resistance relatively high.