You are provided a silicon npn bipolar junction transistor o

You are provided a silicon n^+pn bipolar junction transistor operating at RT. The doping in the emitter is 1 Times 10^17 cm^-3, the base is 5 Times 10^15 cm^-3, and the collector is 1 Times 10^14 cm^-3. The physical width of the base is 5 microns. Complete the table below:

Solution

emitter

base

collector

units

doping

medium

high

low

cm^-3

Minority carrier mobility

medium

low

high

cm²/s

Minority carrier diffusion coefficient

medium

high

low

Minority carrier lifetime

medium

short

high

µs

Minority carrier diffusion length

medium

short

high

µm

J_diffusion=qD_n

Where     is recombination, D_n is diffusion coefficient.

Diffusion length is the average length a carrier moves between generation and recombination. SRH(Shockley-Read-Hall recombination) recombination is the dominant recombination mechanism. The recombination rate will depend on the number of defects present in the material, so that as doping the semiconductor increases the defects in the solar cell, doping will also increase the rate of SRH recombination .Semiconductor materials that are heavily doped have greater recombination rates and consequently, have shorter diffusion lengths. Higher diffusion lengths are indicative of materials with longer lifetimes, and is therefore an important quality to consider with semiconductor material. The diffusion length is related to the carrier lifetime by the diffusivity according to the following formula:

L=sqrt of D.T

	emitter	base	collector	units
doping	medium	high	low	cm-3
Minority carrier mobility	medium	low	high	cm2/s
Minority carrier diffusion coefficient	medium	high	low
Minority carrier lifetime	medium	short	high	µs
Minority carrier diffusion length	medium	short	high	µm